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  • Title: PisaVisionLab
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  • Title: David Burr
    Descriptive info: David Burr.. Thursday, 27 January 2011 19:06.. PisaVisionLab.. Professor of Physiological Psychology, University of Florence.. Contacts.. Email: Dave (AT) in.. cnr.. Telephone: +39 050 3153175.. Cell: +39 348 3972 198.. Research laboratories.. CNR Institute of Neuroscience, Pisa.. Department of Psychology, University of Florence.. Stella Maris Foundation, Pisa, Italy.. Current research and interests.. Motion perception.. Numerosity perception.. Visual stability.. Spatiotopicity.. Perception of time.. Multi-sensory perception.. Autism.. 2013.. -.. 2012.. 2011.. 2010.. 2009.. 2008.. 2007.. 2006.. Extended List.. 2013 (.. back to top.. Cicchini, G.. M.. , Binda, P.. , Burr, D.. C.. & Morrone, M.. (2013).. Transient spatiotopic integration across saccadic eye movements mediates visual stability,J Neurophysiol, 4 (109), 1117-1125.. Eye movements pose major problems to the visual system, because each new saccade changes the mapping of external objects on the retina.. It is known that stimuli briefly presented around the time of saccades are systematically mislocalized, whereas continuously visible objects are perceived as spatially stable even when they undergo large transsaccadic displacements.. In this study we investigated the relationship between these two phenomena and measured how human subjects perceive the position of pairs of bars briefly displayed around the time of large horizontal saccades.. We show that they interact strongly, with the perisaccadic bar being drawn toward the other, dramatically altering the pattern of perisaccadic mislocalization.. The interaction field extends over a wide range (200 ms and 20 degrees ) and is oriented along the retinotopic trajectory of the saccade-induced motion, suggesting a mechanism that integrates pre- and postsaccadic stimuli at different retinal locations but similar external positions.. We show how transient changes in spatial integration mechanisms, which are consistent with the present psychophysical results and with the properties of "remapping cells" reported in the literature, can create transient craniotopy by merging the distinct retinal images of the pre- and postsaccadic fixations to signal a single stable object.. Zimmermann, E.. , Morrone, M.. , Fink, G.. R.. & Burr, D.. Spatiotopic neural representations develop slowly across saccades,Curr Biol, 5 (23), R193-194.. One of the long-standing unsolved mysteries of visual neuroscience is how the world remains apparently stable in the face of continuous movements of eyes, head and body.. Many factors seem to contribute to this stability, including rapid updating mechanisms that temporarily remap the visual input to compensate for the impending saccade [1].. However, there is also a growing body of evidence pointing to more long-lasting spatiotopic neural representations, which remain solid in external rather than retinal coordinates [2-6].. In this study, we show that these spatiotopic representations take hundreds of milliseconds to build up robustly.. Burr, D.. Motion Perception: Human Psychophysics.. In J.. S.. Werner & L.. Chalupa (Eds.. ),.. The New Visual Neuroscience.. : MIT Press.. Turi, M.. The "motion silencing" illusion results from global motion and crowding,J Vis, 5 (13),.. Suchow and Alvarez (2011) recently devised a striking illusion, where objects changing in color, luminance, size, or shape appear to stop changing when they move.. They refer to the illusion as "motion silencing of awareness to visual change.. " Here we present evidence that the illusion results from two perceptual processes: global motion and crowding.. We adapted Suchow and Alvarez's stimulus to three concentric rings of dots, a central ring of "target dots" flanked on either side by similarly moving flanker dots.. Subjects had to identify in which of two presentations the target dots were continuously changing (sinusoidally) in size, as distinct from the other interval in which size was constant.. The results show: (a) Motion silencing depends on target speed, with a threshold around 0.. 2 rotations per second (corresponding to about 10 degrees /s linear motion).. (b) Silencing depends on both target-flanker spacing and eccentricity, with critical spacing about half eccentricity, consistent with Bouma's law.. (c) The critical spacing was independent of stimulus size, again consistent with Bouma's law.. (d) Critical spacing depended strongly on contrast polarity.. All results imply that the "motion silencing" illusion may result from crowding.. Lunghi, C.. Long-term effects of monocular deprivation revealed with binocular rivalry gratings modulated in luminance and in color,J Vis, 6 (13),.. During development, within a specific temporal window called the critical period, the mammalian visual cortex is highly plastic and literally shaped by visual experience; to what extent this extraordinary plasticity is retained in the adult brain is still a debated issue.. We tested the residual plastic potential of the adult visual cortex for both achromatic and chromatic vision by measuring binocular rivalry in adult humans following 150 minutes of monocular patching.. Paradoxically, monocular deprivation resulted in lengthening of the mean phase duration of both luminance-modulated and equiluminant stimuli for the deprived eye and complementary shortening of nondeprived phase durations, suggesting an initial homeostatic compensation for the lack of information following monocular deprivation.. When equiluminant gratings were tested, the effect was measurable for at least 180 minutes after reexposure to binocular vision, compared with 90 minutes for achromatic gratings.. Our results suggest that chromatic vision shows a high degree of plasticity, retaining the effect for a duration (180 minutes) longer than that of the deprivation period (150 minutes) and twice as long as that found with achromatic gratings.. The results are in line with evidence showing a higher vulnerability of the P pathway to the effects of visual deprivation during development and a slower development of chromatic vision in humans.. 2012 (.. Anobile, G.. , Cicchini, G.. (2012).. Linear mapping of numbers onto space requires attention,Cognition, 3 (122), 454-459.. Mapping of number onto space is fundamental to mathematics and measurement.. Previous research suggests that while typical adults with mathematical schooling map numbers veridically onto a linear scale, pre-school children and adults without formal mathematics training, as well as individuals with dyscalculia, show strong compressive, logarithmic-like non-linearities when mapping both symbolic and non-symbolic numbers onto the numberline.. Here we show that the use of the linear scale is dependent on attentional resources.. We asked typical adults to position clouds of dots on a numberline of various lengths.. In agreement with previous research, they did so veridically under normal conditions, but when asked to perform a concurrent attentionally-demanding conjunction task, the mapping followed a compressive, non-linear function.. We model the non-linearity both by the commonly assumed logarithmic transform, and also with a Bayesian model of central tendency.. These results suggest that veridical representation numerosity requires attentional mechanisms.. , Arrighi, R.. , Cecchetti, L.. , Giusti M.. Optimal Encoding of Interval Timing in Expert Percussionists,.. J Neurosci, 3 (32), 1056-1060.. We measured temporal reproduction in human subjects with various levels of musical expertise: expert drummers, string musicians, and non-musicians.. While duration reproduction of the non-percussionists showed a characteristic central tendency or regression to the mean, drummers responded veridically.. Furthermore, when the stimuli were auditory tones rather than flashes, all subjects responded veridically.. The behavior of all three groups in both modalities is well explained by a Bayesian model that seeks to minimize reproduction errors by incorporating a central tendency prior, a probability density function centered at the mean duration of the sample.. We measured separately temporal precision thresholds with a bisection task; thresholds were twice as low in drummers as in the other two groups.. These estimates of temporal precision, together with an adaptable Bayesian prior, predict well the reproduction results and the central tendency strategy under all conditions and for all subject groups.. These results highlight the efficiency and flexibility of sensorimotor mechanisms estimating temporal duration.. Pooresmaeili, A.. "Non-retinotopic processing" in Ternus motion displays modeled by spatiotemporal filters,J Vis, 1 (12),.. PDF.. Recently, M.. Boi, H.. Ogmen, J.. Krummenacher, T.. U.. Otto, & M.. H.. Herzog (2009) reported a fascinating visual effect, where the direction of apparent motion was disambiguated by cues along the path of apparent motion, the Ternus-Pikler group motion, even though no actual movement occurs in this stimulus.. They referred to their study as a "litmus test" to distinguish "non-retinotopic" (motion-based) from "retinotopic" (retina-based) image processing.. We adapted the test to one with simple grating stimuli that could be more readily modeled and replicated their psychophysical results quantitatively with this stimulus.. We then modeled our experiments in 3D (x, y, t) Fourier space and demonstrated that the observed perceptual effects are readily accounted for by integration of information within a detector that is oriented in space and time, in a similar way to previous explanations of other motion illusions.. This demonstration brings the study of Boi et al.. into the more general context of perception of moving objects.. Visual motion distorts visual and motor space, J Vis, 2 (12),.. Panichi, M.. & Baldassi, S.. Spatiotemporal dynamics of perisaccadic remapping in humans revealed by classification images,J Vis, 4 (12), 11.. Spatiotopic perceptual maps in humans: evidence from motion adaptation,Proc Biol Sci, 1740 (279), 3091-3097.. One possibility is that our brain actively constructs a spatiotopic representation of the world, which is anchored in external-or at least head-centred-coordinates.. In this study, we show that the positional motion aftereffect (the change in apparent position after adaptation to motion) is spatially selective in external rather than retinal coordinates, whereas the classic motion aftereffect (the illusion of motion after prolonged inspection of a moving source) is selective in retinotopic coordinates.. The results provide clear evidence for a spatiotopic map in humans: one which can be influenced by image motion.. , Turi, M.. The effects of cross-sensory attentional demand on subitizing and on mapping number onto space,Vision Res,.. Various aspects of numerosity judgments, especially subitizing and the mapping of number onto space, depend strongly on attentional resources.. Here we use a dual-task paradigm to investigate the effects of cross-sensory attentional demands on visual subitizing and spatial mapping.. The results show that subitizing is strongly dependent on attentional resources, far more so than is estimation of higher numerosities.. But unlike many other sensory tasks, visual subitizing is equally affected by concurrent attentionally demanding auditory and tactile tasks as it is by visual tasks, suggesting that subitizing may be amodal.. Mapping number onto space was also strongly affected by attention, but only when the dual-task was in the visual modality.. The non-linearities in numberline mapping under attentional load are well explained by a Bayesian model of central tendency.. Gori, M.. , Tinelli, F.. , Sandini, G.. , Cioni, G.. Impaired visual size-discrimination in children with movement disorders,Neuropsychologia, 8 (50), 1838-1843.. Multisensory integration of spatial information occurs late in childhood, at around eight years (Gori, Del Viva, Sandini, & Burr, 2008).. For younger children, the haptic system dominates size discrimination and vision dominates orientation discrimination: the dominance may reflect sensory calibration, and could have direct consequences on children born with specific sensory disabilities.. Here we measure thresholds for visual discrimination of orientation and size in children with movement disorders of upper limbs.. Visual orientation discrimination was very similar to the age-matched typical children, but visual size discrimination thresholds were far worse, in all eight individuals with early-onset movement disorder.. This surprising and counterintuitive result is readily explained by the cross-sensory calibration hypothesis: when the haptic sense is unavailable for manipulation, it cannot be readily used to estimate size, and hence to calibrate the visual experience of size: visual discrimination is subsequently impaired.. This complements a previous study showing that non-sighted children have reduced acuity for haptic orientation, but not haptic size, discriminations (Gori, Sandini, Martinoli, & Burr, 2010).. Together these studies show that when either vision or haptic manipulation is impaired, the impairment also impacts on complementary sensory systems that are calibrated by that one.. 2011 (.. (2011).. Spatiotopic selectivity of adaptation-based compression of event duration, J Vis, 2 (11), 21; author reply 21a.. A.. Bruno, I.. Ayhan, and A.. Johnston (2010) have recently challenged our report of spatiotopic selectivity for adaptation of event time (D.. Burr, A.. Tozzi, & M.. Morrone, 2007) and also our claim that retinotopic adaptation of event time depends on perceived speed.. To assist the reader judge this issue, we present here a mass of data accumulated in our laboratories over the last few years, all confirming our original conclusions.. We also point out that where Bruno et al.. made experimental measurements (rather than relying on theoretical reasoning), they too find clearly significant spatiotopically tuned adaptation-based compression of event time but of lower magnitude to ours.. We speculate on the reasons for the differences in magnitude.. Lunghi C, Burr DC, Morrone C.. Brief periods of monocular deprivation disrupt ocular balance in human adult visual cortex, Curr Biol.. 2011 Jul 26;21(14):R538-9.. Neuroplasticity is a fundamental property of the developing mammalian visual system, with residual potential in adult human cortex [1].. A short period of abnormal visual experience (such as occlusion of one eye) before closure of the critical period has dramatic and permanent neural consequences, reshaping visual cortical organization in favour of the non-deprived eye [2,3].. We used binocular rivalry [4] - a sensitive probe of neural competition - to demonstrate that adult human visual cortex retains a surprisingly high degree of neural plasticity, with important perceptual consequences.. We report that 150 minutes of monocular deprivation strongly affects the dynamics of binocular rivalry, unexpectedly causing the deprived eye to prevail in conscious perception twice as much as the non-deprived eye, with significant effects for up to 90 minutes.. Apparent contrast of stimuli presented to the deprived eye was also increased, suggesting that the deprivation acts by up-regulation of cortical gain-control mechanisms of the deprived eye.. The results suggest that adult visual cortex retains a good deal of plasticity that could be important in reaction to sensory loss.. Visual perception: more than meets the eye,Curr Biol, 4 (21), R159-161.. A recent study shows that objects changing in colour, luminance, size or shape appear to stop changing when they move.. These and other compelling illusions provide tantalizing clues about the mechanisms and limitations of object analysis.. & Thompson, P.. Motion psychophysics: 1985-2010,Vision Res,.. This review traces progress made in the field of visual motion research from 1985 through to 2010.. While it is certainly not exhaustive, it attempts to cover most of the major achievements during that period, and speculate on where the field is heading.. Spatiotopic coding and remapping in humans,Philos Trans R Soc Lond B Biol Sci, 1564 (366), 504-515.. How our perceptual experience of the world remains stable and continuous in the face of continuous rapid eye movements still remains a mystery.. This review discusses some recent progress towards understanding the neural and psychophysical processes that accompany these eye movements.. We firstly report recent evidence from imaging studies in humans showing that many brain regions are tuned in spatiotopic coordinates, but only for items that are actively attended.. We then describe a series of experiments measuring the spatial and temporal phenomena that occur around the time of saccades, and discuss how these could be related to visual stability.. Finally, we introduce the concept of the spatio-temporal receptive field to describe the local spatiotopicity exhibited by many neurons when the eyes move.. Crespi, S.. , Biagi, L.. , d'Avossa, G.. , Tosetti, M.. Spatiotopic Coding of BOLD Signal in Human Visual Cortex Depends on Spatial Attention,PLoS One, 7 (6), e21661.. The neural substrate of the phenomenological experience of a stable visual world remains obscure.. One possible mechanism would be to construct spatiotopic neural maps where the response is selective to the position of the stimulus in external space, rather than to retinal eccentricities, but evidence for these maps has been inconsistent.. Here we show, with fMRI, that when human subjects perform concomitantly a demanding attentive task on stimuli displayed at the fovea, BOLD responses evoked by moving stimuli irrelevant to the task were mostly tuned in retinotopic coordinates.. However, under more unconstrained conditions, where subjects could attend easily to the motion stimuli, BOLD responses were tuned not in retinal but in external coordinates (spatiotopic selectivity) in many visual areas, including MT, MST, LO and V6, agreeing with our previous fMRI study.. These results indicate that spatial attention may play an important role in mediating spatiotopic selectivity.. , Mazzilli, G.. Cross-Sensory Facilitation Reveals Neural Interactions between Visual and Tactile Motion in Humans,Front Psychol, (2), 55.. Many recent studies show that the human brain integrates information across the different senses and that stimuli of one sensory modality can enhance the perception of other modalities.. Here we study the processes that mediate cross-modal facilitation and summation between visual and tactile motion.. We find that while summation produced a generic, non-specific improvement of thresholds, probably reflecting higher-order interaction of decision signals, facilitation reveals a strong, direction-specific interaction, which we believe reflects sensory interactions.. We measured visual and tactile velocity discrimination thresholds over a wide range of base velocities and conditions.. Thresholds for both visual and tactile stimuli showed the characteristic "dipper function," with the minimum thresholds occurring at a given "pedestal speed.. " When visual and tactile coherent stimuli were combined (summation condition) the thresholds for these multisensory stimuli also showed a "dipper function" with the minimum thresholds occurring in a similar range to that for unisensory signals.. However, the improvement of multisensory thresholds was weak and not directionally specific, well predicted by the maximum-likelihood estimation model (agreeing with previous research).. A different technique (facilitation) did, however, reveal direction-specific enhancement.. Adding a non-informative "pedestal" motion stimulus in one sensory modality (vision or touch) selectively lowered thresholds in the other, by the same amount as pedestals in the same modality.. Facilitation did not occur for neutral stimuli like sounds (that would also have reduced temporal uncertainty), nor for motion in opposite direction, even in blocked trials where the subjects knew that the motion was in the opposite direction showing that the facilitation was not under subject control.. Cross-sensory facilitation is strong evidence for functionally relevant cross-sensory integration at early levels of sensory processing.. Binda, P.. , Ross, J.. Underestimation of perceived number at the time of saccades,Vision Res, 1 (51), 34-42.. Saccadic eye movements produce transient distortions in both space and time.. Mounting evidence suggests that space and time perception are linked, and associated with the perception of another important perceptual attribute, numerosity.. Here we investigate the effect of saccades on the perceived numerosity of briefly presented arrays of visual elements.. We report a systematic underestimation of numerosity for stimuli flashed just before or during saccades, of about 35% of the reference numerosity.. The bias is observed only for relatively large arrays of visual elements, in line with the notion that a distinct perceptual mechanism is involved with enumeration of small numerosities in the 'subitizing' range.. This study provides further evidence for the notion that space, time and number share common  ...   Res, 1 (198), 49-57.. The "ventriloquist effect" refers to the fact that vision usually dominates hearing in spatial localization, and this has been shown to be consistent with optimal integration of visual and auditory signals (Alais and Burr in Curr Biol 14(3):257-262, 2004).. For temporal localization, however, auditory stimuli often "capture" visual stimuli, in what has become known as "temporal ventriloquism".. We examined this quantitatively using a bisection task, confirming that sound does tend to dominate the perceived timing of audio-visual stimuli.. The dominance was predicted qualitatively by considering the better temporal localization of audition, but the quantitative fit was less than perfect, with more weight being given to audition than predicted from thresholds.. As predicted by optimal cue combination, the temporal localization of audio-visual stimuli was better than for either sense alone.. Thompson, P.. Visual aftereffects,Curr Biol, 1 (19), R11-14.. , Marini, F.. Meaningful auditory information enhances perception of visual biological motion,J Vis, 4 (9), 25 21-27.. Robust perception requires efficient integration of information from our various senses.. Much recent electrophysiology points to neural areas responsive to multisensory stimulation, particularly audiovisual stimulation.. However, psychophysical evidence for functional integration of audiovisual motion has been ambiguous.. In this study we measure perception of an audiovisual form of biological motion, tap dancing.. The results show that the audio tap information interacts with visual motion information, but only when in synchrony, demonstrating a functional combination of audiovisual information in a natural task.. The advantage of multimodal combination was better than the optimal maximum likelihood prediction.. 2008 (.. & Ross, J.. (2008).. A visual sense of number,Curr Biol, 6 (18), 425-428.. Evidence exists for a nonverbal capacity for the apprehension of number, in humans [1] (including infants [2, 3]) and in other primates [4-6].. Here, we show that perceived numerosity is susceptible to adaptation, like primary visual properties of a scene, such as color, contrast, size, and speed.. Apparent numerosity was decreased by adaptation to large numbers of dots and increased by adaptation to small numbers, the effect depending entirely on the numerosity of the adaptor, not on contrast, size, orientation, or pixel density, and occurring with very low adaptor contrasts.. We suggest that the visual system has the capacity to estimate numerosity and that it is an independent primary visual property, not reducible to others like spatial frequency or density of texture [7].. The knowing visual self,Trends Cogn Sci, 10 (12), 363-364.. Like all information-processing systems, biological visual systems are limited by internal and external noise; but this noise never actually impinges on our conscious perception.. An article recently published in the Journal of Vision suggests that, at least for orientation judgments, the visual system has access to its own noisiness and sets thresholds accordingly.. This could well be a general principle in perception, with important and wide ranging consequences.. , Del Viva, M.. Young children do not integrate visual and haptic form information,Curr Biol, 9 (18), 694-698.. Several studies have shown that adults integrate visual and haptic information (and information from other modalities) in a statistically optimal fashion, weighting each sense according to its reliability [1, 2].. When does this capacity for crossmodal integration develop? Here, we show that prior to 8 years of age, integration of visual and haptic spatial information is far from optimal, with either vision or touch dominating totally, even in conditions in which the dominant sense is far less precise than the other (assessed by discrimination thresholds).. For size discrimination, haptic information dominates in determining both perceived size and discrimination thresholds, whereas for orientation discrimination, vision dominates.. By 8-10 years, the integration becomes statistically optimal, like adults.. We suggest that during development, perceptual systems require constant recalibration, for which cross-sensory comparison is important.. Using one sense to calibrate the other precludes useful combination of the two sources.. 2007 (.. Tozzi, A.. (2007).. The effect of optokinetic nystagmus on the perceived position of briefly flashed targets,Vision Res, 6 (47), 861-868.. Stimuli flashed briefly around the time of an impending saccade are mislocalized in the direction of the saccade and also compressed towards the saccadic target.. Similarly, targets flashed during pursuit eye movements are mislocalized in the direction of pursuit.. Here, we investigate the effects of optokinetic nystagmus (OKN) on visual localization.. Subjects passively viewed a wide-field drifting grating that elicited strong OKN, comprising the characteristic slow-phase tracking movement interspersed with corrected "saccade-like" fast-phase movements.. Subjects reported the apparent position of salient bars flashed briefly at various positions on the screen.. In general, bars were misperceived in the direction of the slow-phase tracking movement.. Bars flashed around the onset of the fast-phase movements were subject to much less mislocalization, pointing to a competing shift in the direction of the fast-phase, as occurs with saccades.. However, as distinct from saccades, there was no evidence for spatial compression around the time of the corrective fast-phase OKN.. The results suggest that OKN cause perceptual mislocalizations similar to those of smooth pursuit and saccades, but there are some differences in the nature of the mislocalizations, pointing to different perceptual mechanisms associated with the different types of eye movements.. Pellicano, E.. , Jeffery, L.. & Rhodes, G.. Abnormal adaptive face-coding mechanisms in children with autism spectrum disorder,Curr Biol, 17 (17), 1508-1512.. In low-level vision, exquisite sensitivity to variation in luminance is achieved by adaptive mechanisms that adjust neural sensitivity to the prevailing luminance level.. In high-level vision, adaptive mechanisms contribute to our remarkable ability to distinguish thousands of similar faces [1].. A clear example of this sort of adaptive coding is the face-identity aftereffect [2, 3, 4, 5], in which adaptation to a particular face biases perception toward the opposite identity.. Here we investigated face adaptation in children with autism spectrum disorder (ASD) by asking them to discriminate between two face identities, with and without prior adaptation to opposite-identity faces.. The ASD group discriminated the identities with the same precision as did the age- and ability-matched control group, showing that face identification per se was unimpaired.. However, children with ASD showed significantly less adaptation than did their typical peers, with the amount of adaptation correlating significantly with current symptomatology, and face aftereffects of children with elevated symptoms only one third those of controls.. These results show that although children with ASD can learn a simple discrimination between two identities, adaptive face-coding mechanisms are severely compromised, offering a new explanation for previously reported face-perception difficulties [6, 7, 8] and possibly for some of the core social deficits in ASD [9, 10].. , Tozzi, A.. Neural mechanisms for timing visual events are spatially selective in real-world coordinates,Nat Neurosci, 4 (10), 423-425.. It is generally assumed that perceptual events are timed by a centralized supramodal clock.. This study challenges this notion in humans by providing clear evidence that visual events of subsecond duration are timed by visual neural mechanisms with spatially circumscribed receptive fields, localized in real-world, rather than retinal, coordinates.. d'Avossa, G.. , Crespi, S.. Spatiotopic selectivity of BOLD responses to visual motion in human area MT,Nat Neurosci, 2 (10), 249-255.. Many neurons in the monkey visual extrastriate cortex have receptive fields that are affected by gaze direction.. In humans, psychophysical studies suggest that motion signals may be encoded in a spatiotopic fashion.. Here we use functional magnetic resonance imaging to study spatial selectivity in the human middle temporal cortex (area MT or V5), an area that is clearly implicated in motion perception.. The results show that the response of MT is modulated by gaze direction, generating a spatial selectivity based on screen rather than retinal coordinates.. This area could be the neurophysiological substrate of the spatiotopic representation of motion signals.. Ciaramelli, E.. , Leo, F.. & Ladavas, E.. The contribution of prefrontal cortex to global perception,Exp Brain Res, 3 (181), 427-434.. Recent research suggests a role of top-down modulatory signals on perceptual processing, particularly for the integration of local elementary information to form a global holistic percept.. In this study we investigated whether prefrontal cortex may be instrumental in this top-down modulation in humans.. We measured detection thresholds for perceiving a circle defined by a closed chain of grating patches in 6 patients with prefrontal lesions, 4 control patients with temporal lesions and 17 healthy control subjects.. Performance of patients with prefrontal lesions was worse than that of patients with temporal lesions and normal controls when the patterns were sparse, requiring integration across relatively extensive regions of space, but similar to the control groups for denser patterns.. The results clearly implicate the prefrontal cortex in the process of integrating elementary features into a holistic global percept, when the elements do not form a "pop-out" display.. Chirimuuta, M.. The role of perceptual learning on modality-specific visual attentional effects,Vision Res, 1 (47), 60-70.. Morrone et al.. [Morrone, M.. , Denti, V.. , & Spinelli, D.. (2002).. Color and luminance contrasts attract independent attention.. Current Biology, 12, 1134-1137] reported that the detrimental effect on contrast discrimination thresholds of performing a concomitant task is modality specific: performing a secondary luminance task has no effect on colour contrast thresholds, and vice versa.. Here we confirm this result with a novel task involving learning of spatial position, and go on to show that it is not specific to the cardinal colour axes: secondary tasks with red-green stimuli impede performance on a blue-yellow task and vice versa.. We further show that the attentional effect can be abolished with continued training over 2-4 training days (2-20 training sessions), and that the effect of learning is transferable to new target positions.. Given the finding of transference, we discuss the possibility that V4 is a site of plasticity for both stimulus types, and that the separation is due to a luminance-colour separation within this cortical area.. , Bruno, A.. Fusion of visual and auditory stimuli during saccades: a Bayesian explanation for perisaccadic distortions,J Neurosci, 32 (27), 8525-8532.. Brief stimuli presented near the onset of saccades are grossly mislocalized in space.. In this study, we investigated whether the Bayesian hypothesis of optimal sensory fusion could account for the mislocalization.. We required subjects to localize visual, auditory, and audiovisual stimuli at the time of saccades (compared with an earlier presented target).. During fixation, vision dominates and spatially "captures" the auditory stimulus (the ventriloquist effect).. But for perisaccadic presentations, auditory localization becomes more important, so the mislocalized visual stimulus is seen closer to its veridical position.. The precision of the bimodal localization (as measured by localization thresholds or just-noticeable difference) was better than either the visual or acoustic stimulus presented in isolation.. Both the perceived position of the bimodal stimuli and the improved precision were well predicted by assuming statistically optimal Bayesian-like combination of visual and auditory signals.. Furthermore, the time course of localization was well predicted by the Bayesian approach.. We present a detailed model that simulates the time-course data, assuming that perceived position is given by the sum of retinal position and a sluggish noisy eye-position signal, obtained by integrating optimally the output of two populations of neural activity: one centered at the current point of gaze, the other centered at the future point of gaze.. 2006 (.. Alais, D.. , Morrone, C.. (2006).. Separate attentional resources for vision and audition,Proc Biol Sci, 1592 (273), 1339-1345.. Current models of attention, typically claim that vision and audition are limited by a common attentional resource which means that visual performance should be adversely affected by a concurrent auditory task and vice versa.. Here, we test this implication by measuring auditory (pitch) and visual (contrast) thresholds in conjunction with cross-modal secondary tasks and find that no such interference occurs.. Visual contrast discrimination thresholds were unaffected by a concurrent chord or pitch discrimination, and pitch-discrimination thresholds were virtually unaffected by a concurrent visual search or contrast discrimination task.. However, if the dual tasks were presented within the same modality, thresholds were raised by a factor of between two (for visual discrimination) and four (for auditory discrimination).. These results suggest that at least for low-level tasks such as discriminations of pitch and contrast, each sensory modality is under separate attentional control, rather than being limited by a supramodal attentional resource.. This has implications for current theories of attention as well as for the use of multi-sensory media for efficient informational transmission.. & Morrone, C.. Perception: transient disruptions to neural space-time,Curr Biol, 19 (16), R847-849.. How vision operates efficiently in the face of continuous shifts of gaze remains poorly understood.. Recent studies show that saccades cause dramatic, but transient, changes in the spatial and also temporal tuning of cells in many visual areas, which may underly the perceptual compression of space and time, and serve to counteract the effects of the saccades and maintain visual stability.. , McKee, S.. Resolution for spatial segregation and spatial localization by motion signals,Vision Res, 6-7 (46), 932-939.. We investigated two types of spatial resolution for perceiving motion-defined contours: grating acuity, the capacity to discriminate alternating stripes of opposed motion from transparent bi-directional motion; and alignment acuity, the capacity to localize the position of motion-defined edges with respect to stationary markers.. For both tasks the stimuli were random noise patterns, low-pass filtered in the spatial dimension parallel to the motion.. Both grating and alignment resolution varied systematically with spatial frequency cutoff and speed.. Best performance for grating resolution was about 10 c/deg (for unfiltered patterns moving at 1-4 deg/s), corresponding to a stripe resolution of about 3'.. Grating resolution corresponds well to estimates of smallest receptive field size of motion units under these conditions, suggesting that opposing signals from units with small receptive fields (probably located in V1) are contrasted efficiently to define edges.. Alignment resolution was about 2' at best, under similar conditions.. Whereas alignment judgment based on luminance-defined edges is typically 3-10 times better than resolution, alignment based on motion-defined edges is only 1.. 1-1.. 5 times better, suggesting motion contours are less effectively encoded than luminance contours.. The effects of opposite-polarity dipoles on the detection of Glass patterns,Vision Res, 6-7 (46), 1139-1144.. Glass patterns--randomly positioned coherently orientated dipoles--create a strong sensation of oriented spatial structure.. On the other hand, coherently oriented dipoles comprising dots of opposite polarity ("anti-Glass" patterns) have no distinct spatial structure and are very hard to distinguish from random noise.. Although anti-Glass patterns have no obvious spatial structure themselves, their presence can destroy the structure created by Glass patterns.. We measured the strength of this effect for both static and dynamic Glass patterns, and showed that anti-Glass patterns can raise thresholds for Glass patterns by a factor of 2-4, increasing with density.. The dependence on density suggests that the interactions occur at a local level.. When the Glass and anti-Glass dipoles were confined to alternate strips (in translational and circular Glass patterns), the detrimental effect occurred for stripe widths less than about 1.. 5 degrees, but had little effect for larger stripe widths, reinforcing the suggestion that the interaction occurred over a limited spatial extent.. The extent of spatial interaction was much less than that for spatial summation of these patterns, at least 30 degrees under matched experimental conditions.. The results suggest two stages of analysis for Glass patterns, an early stage of limited spatial extent where orientation is extracted, and a later stage that sums these orientation signals.. & Alais, D.. Combining visual and auditory information,Prog Brain Res, (155), 243-258.. Robust perception requires that information from by our five different senses be combined at some central level to produce a single unified percept of the world.. Recent theory and evidence from many laboratories suggests that the combination does not occur in a rigid, hardwired fashion, but follows flexible situation-dependent rules that allow information to be combined with maximal efficiency.. In this review we discuss recent evidence from our laboratories investigating how information from auditory and visual modalities is combined.. The results support the notion of Bayesian combination.. We also examine temporal alignment of auditory and visual signals, and show that perceived simultaneity does not depend solely on neural latencies, but involves active processes that compensate, for example, for the physical delay introduced by the relatively slow speed of sound.. Finally, we go on to show that although visual and auditory information is combined to maximize efficiency, attentional resources for the two modalities are largely independent.. Time perception: space-time in the brain,Curr Biol, 5 (16), R171-173.. , Alais, D.. Perceptual synchrony of audiovisual streams for natural and artificial motion sequences,J Vis, 3 (6), 260-268.. We investigated the conditions necessary for perceptual simultaneity of visual and auditory stimuli under natural conditions: video sequences of conga drumming at various rhythms.. Under most conditions, the auditory stream needs to be delayed for sight and sound to be perceived simultaneously.. The size of delay for maximum perceived simultaneity varied inversely with drumming tempo, from about 100 ms at 1 Hz to 30 ms at 4 Hz.. Random drumming motion produced similar results, with higher random tempos requiring less delay.. Video sequences of disk stimuli moving along a motion profile matched to the drummer produced near-identical results.. When the disks oscillated at constant speed rather than following "biological" speed variations, the delays necessary for perceptual synchrony were systematically less.. The results are discussed in terms of real-world constraints for perceptual synchrony and possible neural mechanisms.. Baldassi, S.. , Megna, N.. Visual clutter causes high-magnitude errors,PLoS Biol, 3 (4), e56.. Perceptual decisions are often made in cluttered environments, where a target may be confounded with competing "distractor" stimuli.. Although many studies and theoretical treatments have highlighted the effect of distractors on performance, it remains unclear how they affect the quality of perceptual decisions.. Here we show that perceptual clutter leads not only to an increase in judgment errors, but also to an increase in perceived signal strength and decision confidence on erroneous trials.. Observers reported simultaneously the direction and magnitude of the tilt of a target grating presented either alone, or together with vertical distractor stimuli.. When presented in isolation, observers perceived isolated targets as only slightly tilted on error trials, and had little confidence in their decision.. When the target was embedded in distractors, however, they perceived it to be strongly tilted on error trials, and had high confidence of their (erroneous) decisions.. The results are well explained by assuming that the observers' internal representation of stimulus orientation arises from a nonlinear combination of the outputs of independent noise-perturbed front-end detectors.. The implication that erroneous perceptual decisions in cluttered environments are made with high confidence has many potential practical consequences, and may be extendable to decision-making in general.. Extended Publications List..

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  • Title: Faculty
    Descriptive info: Title Filter.. Display #.. 5.. 10.. 15.. 20.. 25.. 30.. 50.. 100.. All.. #.. Article Title.. Author.. Hits.. 1.. 91.. 2.. David Burr Extended Publications.. 2494.. 3.. Concetta Morrone Extended Publications.. 1932.. 4.. 12998.. 5.. 7951.. 6.. 2432..

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  • Title: PisaVisionLab
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  • Title: Maria Concetta Morrone
    Descriptive info: Maria Concetta Morrone.. Maria Concetta Morron.. e.. Professor of Physiology, Faculty of Medicine, University of Pisa.. Email: concetta (AT) in.. Cell: +39 123 456 789.. Department of Translational Research on New Technologies in Medicine and Surgery, University of Pisa, via San Zeno 31, 56123 Pisa (Italy).. Curriculum Vitae:.. English.. -.. Italian.. Numerosity perception.. Multi-sensory perception.. Infant vision.. Development and plasticity of human visual system.. fMRI of human visual cortex.. Knoll, J.. & Bremmer, F.. Spatio-temporal topography of saccadic overestimation of time,Vision Res, (83C), 56-65.. Rapid eye movements (saccades) induce visual misperceptions.. A number of studies in recent years have investigated the spatio-temporal profiles of effects like saccadic suppression or perisaccadic mislocalization and revealed substantial functional similarities.. Saccade induced chronostasis describes the subjective overestimation of stimulus duration when the stimulus onset falls within a saccade.. In this study we aimed to functionally characterize saccade induced chronostasis in greater detail.. Specifically we tested if chronostasis is influenced by or functionally related to saccadic suppression.. In a first set of experiments, we measured the perceived duration of visual stimuli presented at different spatial positions as a function of presentation time relative to the saccade.. We further compared perceived duration during saccades for isoluminant and luminant stimuli.. Finally, we investigated whether or not saccade induced chronostasis is dependent on the execution of a saccade itself.. We show that chronostasis occurs across the visual field with a clear spatio-temporal tuning.. Furthermore, we report chronostasis during simulated saccades, indicating that spurious retinal motion induced by the saccade is a prime origin of the phenomenon.. Saccadic compression of symbolic numerical magnitude,PLoS One, 11 (7), e49587.. Stimuli flashed briefly around the time of saccadic eye movements are subject to complex distortions: compression of space and time; underestimate of numerosity.. Here we show that saccadic distortions extend to abstract quantities, affecting the representation of symbolic numerical magnitude.. Subjects consistently underestimated the results of rapidly computed mental additions and subtractions, when the operands were briefly displayed before a saccade.. However, the recognition of the number symbols was unimpaired.. These results are consistent with the hypothesis of a common, abstract metric encoding magnitude along multiple dimensions.. They suggest that a surprising link exists between the preparation of action and the representation of abstract quantities.. Tinelli, T.. M.. , Morrone M.. Blindsight in children with congenital and acquired cerebral lesions, Cortex (published online 10 August 2012).. It has been shown that unconscious visual function can survive lesions to optical radiations and/or primary visual cortex (V1), a phenomenon termed “blindsight”.. Studies on animal models (cat and monkey) show that the age when the lesion occurs determines the extent of residual visual capacities.. Much less is known about the functional and underlying neuronal repercussions of early cortical damage in humans.. We measured sensitivity to several visual tasks in four children with congenital unilateral brain lesions that severely affected optic radiations, and in another group of three children with similar lesions, acquired in childhood.. In two of the congenital patients, we measured blood oxygenation level dependent (BOLD) activity in response to stimulation of each visual field quadrants.. Results show clear evidence of residual unconscious processing of position, orientation and motion of visual stimuli displayed in the scotoma of congenitally lesioned children, but not in the children with acquired lesions.. The calcarine cortical BOLD responses were abnormally elicited by stimulation of the ipsilateral visual field and in the scotoma region, demonstrating a profound neuronal reorganization.. In conclusion, our data suggest that congenital lesions can trigger massive reorganization of the visual system to alleviate functional effects of early brain insults.. Tomassini, A.. , Gori, M.. Active movement restores veridical event-timing after tactile adaptation,J Neurophysiol, 8 (108), 2092-2100.. Growing evidence suggests that time in the subsecond range is tightly linked to sensory processing.. Event-time can be distorted by sensory adaptation, and many temporal illusions can accompany action execution.. In this study, we show that adaptation to tactile motion causes a strong contraction of the apparent duration of tactile stimuli.. However, when subjects make a voluntary motor act before judging the duration, it annuls the adaptation-induced temporal distortion, reestablishing veridical event-time.. The movement needs to be performed actively by the subject: passive movement of similar magnitude and dynamics has no effect on adaptation, showing that it is the motor commands themselves, rather than reafferent signals from body movement, which reset the adaptation for tactile duration.. No other concomitant perceptual changes were reported (such as apparent speed or enhanced temporal discrimination), ruling out a generalized effect of body movement on somatosensory processing.. We suggest that active movement resets timing mechanisms in preparation for the new scenario that the movement will cause, eliminating inappropriate biases in perceived time.. Our brain seems to utilize the intention-to-move signals to retune its perceptual machinery appropriately, to prepare to extract new temporal information.. Plasticità ed adattabilità della visione,Giornale Italiano di Psicologia, (3), 517-522.. Spatiotemporal profile of peri-saccadic contrast sensitivity,J Vis, 14 (11),.. Sensitivity to luminance contrast is reduced just before and during saccades (saccadic suppression), whereas sensitivity to color contrast is unimpaired peri-saccadically and enhanced post-saccadically.. The exact spatiotemporal map of these perceptual effects is as yet unknown.. Here, we measured detection thresholds for briefly flashed Gaussian blobs modulated in either luminance or chromatic contrast, displayed at a range of eccentricities.. Sensitivity to luminance contrast was reduced peri-saccadically by a scaling factor, which was almost constant across retinal space.. Saccadic suppression followed a similar time course across all tested eccentricities and was maximal shortly after the saccade onset.. Sensitivity to chromatic contrast was enhanced post-saccadically at all tested locations.. The enhancement was not specifically linked to the execution of saccades, as it was also observed following a displacement of retinal images comparable to that caused by a saccade.. We conclude that luminance and chromatic contrast sensitivities are subject to distinct modulations at the time of saccades, resulting from independent neural processes.. Brain development: critical periods for cross-sensory plasticity,Curr Biol, 21 (20), R934-936.. Recent work has shown that visual deprivation of humans during a critical period leads to motion area MT+ responding to auditory motion.. This cross-sensory plasticity, an important form of brain reorganization, may be mediated by top-down brain circuits from pre-frontal cortex.. Schutz, A.. Compression of time during smooth pursuit eye movements,Vision Res, 24 (50), 2702-2713.. Humans have a clear sense for the passage of time, but while implicit motor timing is quite accurate, explicit timing is prone to distortions particularly during action (Wenke & Haggard, 2009) and saccadic eye movements (Morrone, Ross, & Burr, 2005).. Here, we investigated whether perceived duration is also affected by the execution of smooth pursuit eye movements, showing a compression of apparent duration similar to that observed during saccades.. To this end, we presented two brief bars that marked intervals between 100 and 300 ms and asked subjects to judge their duration during fixation and pursuit.. We found a compression of perceived duration for bars modulated in luminance  ...   independent cortical processing for translational, and circular or radial flow motion, and further suggest that the two systems have different vulnerability and plasticity to prenatal damage.. They also highlight the complexity of visual motion perception, and how the delicate balance of neural activity can lead to paradoxical effects such as consistent misperception of the direction of motion.. We advance a possible explanation of a reduced spatial sampling of the motion stimuli and report a simple model that simulates well the experimental results.. Perna, A.. BOLD response to spatial phase congruency in human brain,J Vis, 10 (8), 15 11-15.. Human psychophysical observations, computational models, and the selectivity of neurons in primary visual cortex all suggest that an early step in visual processing is the detection of features such as lines and edges.. However, previous fMRI experiments investigating the responses of early visual areas to phase coherence have led to apparently discordant results.. We studied the human brain BOLD responses to structured periodic band-pass images of matched amplitude spectrum but of different phase spectra, arranged to create three distinct types of stimuli: pure edges; pure lines (matched global and local energy to the edges, but different phase); and random noise (random phase spectrum, hence no salient features, and a different spatial distribution of local energy from the lines and edges stimuli).. Alternation of lines against edges did not activate primary visual cortex, but did activate two higher order visual areas.. Alternation of these lines or edges against the random stimulus produced a strong activity in many visual areas, including primary visual cortex.. Interestingly, the BOLD activity was higher for the edges and lines than for the random stimuli for a wide range of stimulus contrasts, indicating the presence of non-linear gain modulation in the cell response.. These results show that phase congruency is coded at the level of primary visual cortex.. We show that a stage of response gain modulation can explain our present and previous fMRI discordant results.. Bruno, A.. Influence of saccadic adaptation on spatial localization: comparison of verbal and pointing reports,J Vis, 5 (7), 16 11-13.. Under conditions of short-term saccadic adaptation, stimuli presented long before saccadic onset are perceptually mislocalized in space.. Here we study whether saccadic adaptation can also affect localization of objects by pointing.. We measured localization performance during fixation and after normal saccades and adapted saccades, for a bar presented well before a saccadic eye movement, for both pointing and verbal localization, under open-loop conditions generated by a transient dark period about 300 ms after the presentation of the bar.. During fixation and normal saccade, localization performance for verbal report was veridical, while for pointing there was an overestimation of the target eccentricity respect to gaze, in agreement with the idea of separate representations of space for action and perception.. During saccadic adaptation, there was a significant shift of both pointing and verbal report localization in the direction of adaptation with similar spatial selectivity for both tasks.. These results indicate that saccadic adaptation induces a similar re-calibration of the action map as well as of the perceptual map, suggesting a common site of operation in the transformation from eye-centered to gaze-centered coordinates.. The lowest spatial frequency channel determines brightness perception,Vision Res, 10 (47), 1282-1291.. This study investigates the role played by individual spatial scales in determining the apparent brightness of greyscale patterns.. We measured the perceived difference in brightness across an edge in the presence of notch filtering and high-pass filtering for two stimulus configurations, one that elicits the perception of transparency and one that appears opaque.. For both stimulus configurations, the apparent brightness of the surfaces delimited by the border decreased monotonically with progressive (ideal) high-pass filtering, with a critical cut-off at 1 c/deg.. Using two octave ideal notch filtering, the maximum detrimental effect on apparent brightness was observed at about 1c/deg.. Critical frequencies for apparent brightness did not vary with contrast, viewing distance, or surface size, suggesting that apparent brightness is determined by the channel tuned at 1 c/deg.. Modelling the data with the local energy model [Morrone, M.. , & Burr, D.. (1988).. Feature detection in human vision: a phase dependent energy model.. Proceedings of the Royal Society (London), B235, 221-245] at 1c/deg confirmed the suggestion that this channel mediates apparent brightness for both opaque and transparent borders, with no need for pooling or integration across spatial channels.. Del Viva, M.. A feature-tracking model simulates the motion direction bias induced by phase congruency,J Vis, 3 (6), 179-195.. Here we report a new motion illusion where the prevailing motion direction is strongly influenced by the relative phase of the harmonic components of the stimulus.. The basic stimulus is the sum of three sinusoidal contrast-reversing gratings: the first, the third, and the fifth harmonic of two square wave gratings that drift in opposite direction.. The phase of one of the fifth components was kept constant at 180 deg, whereas the phase of the other fifth harmonic was varied over the range 0-150 deg.. For each phase value of the fifth harmonic, the motion was strongly biased toward its direction, corresponding to the direction with stronger phase congruency between the three harmonics.. The strength of the prevailing motion was assessed by measuring motion direction discrimination thresholds, by varying the contrast of the third and the fifth harmonics plaid pattern.. Results show that the contrast of high harmonics had to be increased by more than a factor of 10, to achieve a balance of motion for phase differences greater than 60 deg between the 2 fifth harmonics.. We also measured the dependence on the absolute phase of harmonic components and found that it is not an important parameter, excluding the possibility that local luminance cues could be mediating the effect.. A feature-tracking model based on previous work is proposed to simulate the data.. The model computes local energy function from a pair of space-time separable front stage filters and applies a battery of directional second stage mechanisms.. It is able to simulate quantitatively the phase congruency dependence illusion and the insensitivity to overall phase.. Other energy models based on directional filters fail to simulate the phase congruency dependency effect.. , Brambati, S.. , Perani, D.. Development of saccadic suppression in children,J Neurophysiol, 3 (96), 1011-1017.. We measured saccadic suppression in adolescent children and young adults using spatially curtailed low spatial frequency stimuli.. For both groups, sensitivity for color-modulated stimuli was unchanged during saccades.. Sensitivity for luminance-modulated stimuli was greatly reduced during saccades in both groups but far more for adolescents than for young adults.. Adults' suppression was on average a factor of about 3, whereas that for the adolescent group was closer to a factor of 10.. The specificity of the suppression to luminance-modulated stimuli excludes generic explanations such as task difficulty and attention.. We suggest that the enhanced suppression in adolescents results from the immaturity of the ocular-motor system at that age.. Extended Publication List..

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  • Title: PisaVisionLab
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  • Title: Stefano Baldassi
    Descriptive info: Stefano Baldassi.. Research Scientist, University of Florence.. Email: stefano.. baldassi (AT) unifi.. currently @ Stanford University, Dep.. of Psychology, Stanford, CA, USA.. Attention.. Visual search.. Perceptual decisions.. Attention and reward.. Visual integration.. Autism.. Perceptual processes in sport.. Recent Publications.. Pascucci, D.. , Panichi, M.. Acoustic cues to visual detection: a classification image study,J Vis, 6 (11),.. A non-informative sound is known to improve contrast detection thresholds for a synchronous visual target (M.. Lippert, N.. K.. Logothetis, & C.. Kayser, 2007).. We investigated the spatio-temporal characteristics of the mechanisms underlying this crossmodal effect by using a classification image paradigm specifically suited to investigate perceptual templates across both space and time (P.. Neri & D.. J.. Heeger, 2002).. A bright bar was embedded in 2D (space-time) dynamic noise and observers were asked to detect its presence in both unimodal (only visual) and bimodal (audio-visual) conditions.. Classification image analysis was performed and the 1st and 2nd order kernels were derived.. Our results show that the cross-modal facilitation of detection consists in a reduction of activity of the early mechanisms elicited by the onset of the stimulation and not directly involved in the identification of the target.. In fact, the sound sharpens the 2nd order kernels (involved in target detection) by suppressing the activation preceding the target, whereas it does not influence the 1st order kernels.. These data suggest that the sound affects some non-linear process involved with the detection of a visual stimulus by, decreasing the activity of contrast energy filters temporally uncorrelated with the target, hence reducing temporal uncertainty.. & Simoncini, C.. Reward sharpens orientation coding independently of attention,Front Neurosci, (5), 13.. It has long been known that rewarding improves performance.. However it is unclear whether this is due to high level modulations in the output modules of associated neural systems or due to low level mechanisms favoring more "generous" inputs? Some recent studies suggest that primary sensory areas, including V1 and A1, may form part of the circuitry of reward-based modulations, but there is no data indicating whether reward can be dissociated from attention or cross-trial forms of perceptual learning.. Here we address this issue with a psychophysical dual task, to control attention, while perceptual performance on oriented targets associated with different levels of reward is assessed by measuring both orientation discrimination thresholds and behavioral tuning functions for tilt values near threshold.. We found that reward, at any rate, improved performance.. However, higher reward rates showed an improvement of orientation discrimination thresholds by about 50% across conditions and sharpened behavioral tuning functions.. Data were unaffected by changing the attentional load and by dissociating the feature of the reward cue from the task-relevant feature.. These results suggest that reward may act within the span of a single trial independently of attention by modulating the activity of early sensory stages through a improvement of the signal-to-noise ratio of task-relevant channels.. Toscani, M.. , Marzi, T.. , Righi, S.. , Viggiano, M.. P.. Alpha waves: a neural signature of visual suppression,Exp Brain Res, 3-4 (207), 213-219.. Alpha waves are traditionally considered a passive consequence of the lack of stimulation of sensory areas.. However, recent results have challenged this view by showing a modulation of alpha activity in cortical areas representing unattended information during active tasks.. These data have led us to think that alpha waves would support a 'gating function' on sensorial stimulation that actively inhibits unattended information in attentional tasks.. Visual suppression occurring during a saccade and blink entails an inhibition of incoming visual information, and it seems to occur at an early processing stage.. In this study, we hypothesized that the neural mechanism through which the visual system exerts this inhibition is the active imposition of alpha oscillations in the occipital cortex, which in turn predicts an increment of alpha amplitude during a visual suppression phenomena.. We measured visual suppression occurring during short closures of the eyelids, a situation well suited for EEG recordings and stimulated the retinae with an intra-oral light administered through the palate.. In the behavioral experiment, detection thresholds were measured with eyes steady open and steady closed, showing a reduction of sensitivity in the latter case.. In the EEG recordings performed under identical conditions we found stronger alpha activity with closed eyes.. Since the stimulation does not depend on whether the eyes were open or closed, we reasoned  ...   group, while in the experimental group only the 1st harmonic was present.. In the Contour condition the 1st harmonic was not present for both groups while the 3rd harmonic was significantly present in the control group but absent in the group with autism.. Moreover, the amount of organization required to elicit significant 1st harmonic response in the texture condition was higher in the clinical group.. The present results bring additional support to the idea that texture and contour processing are supported by independent mechanisms in normal vision.. Autistic vision would thus be characterized by a preserved, perhaps weaker texture mechanism, possibly mediated by feedback interactions between visual areas, and by a disfunction of the mechanism supporting contour processing, possibly mediated by long-range intra-cortical connections.. Within this framework, the residual ability to detect contours shown in psychophysical studies could be due to the contribution of the texture mechanism to contour processing.. , Pei, F.. , Recupero, G.. , Viespoli, M.. Search superiority in autism within, but not outside the crowding regime,Vision Res, 16 (49), 2151-2156.. Visual cognition of observers with autism spectrum disorder (ASD) seems to show an unbalance between the complementary functions of integration and segregation.. This study uses visual search and crowding paradigms to probe the relative ability of children with autism, compared to normal developments children, to extract individual targets from cluttered backgrounds both within and outside the crowding regime.. The data show that standard search follows the same pattern in the ASD and control groups with a strong effect of the set size that is substantially weakened by cueing the target location with a synchronous spatial cue.. On the other hand, the crowding effect of eight flankers surrounding a small peripheral target is virtually absent in the clinical sample, indicating a superior ability to segregate cluttered visual items.. This data, along with evidence of an impairment to the neural system for binding contours in ASD, bring additional support to the general idea of a shift of the trade-off between integration and segregation toward the latter.. More specifically, they show that when discriminability is balanced across conditions, an advantage in odd-man out tasks is evident in ASD observers only within the crowding regime, when binding mechanism might get compulsorily triggered in normal observers.. Tinelli, F.. , Bancale, A.. , Mazzotti, S.. The assessment of visual acuity in children with periventricular damage: a comparison of behavioural and electrophysiological techniques,Vision Res, 10 (48), 1233-1241.. It has been controversial whether electrophysiology offers better precision than behavioural techniques in measuring visual acuity in children with brain damage.. We investigated the concordance between sweep VEPs and Acuity Cards (AC) in 29 children with periventricular leukomalacia (PVL), the most common type of brain damage in preterm infants.. An overall good correlation was shown but with relatively better behavioural acuity values.. VEP/AC ratio was significantly correlated to corpus callosum posterior thinning.. We propose that this result reflects the efficacy of the compensatory mechanisms following early brain damage which may differentially affect the two methods.. Gheri, C.. Non-linear integration of crowded orientation signals,Vision Res, 22 (48), 2352-2358.. Crowding of oriented signals has been explained as linear, compulsory averaging of the signals from target and flankers [Parkes, L.. , Lund, J.. , Angelucci, A.. , Solomon, J.. , & Morgan, M.. (2001).. Compulsory averaging of crowded orientation signals in human vision.. Nature Neuroscience, 4(7), 739-744].. On the other hand, a comparable search task with sparse stimuli is well modeled by a 'Signed-Max' rule that integrates non-linearly local tilt estimates [Baldassi, S.. , & Verghese, P.. Comparing integration rules in visual search.. Journal of Vision, 2(8), 559-570], as reflected by the bimodality of the distributions of reported tilts in a magnitude matching task [Baldassi, S.. Visual clutter causes high-magnitude errors.. PLoS Biology, 4(3), e56].. This study compares the two models in the context of crowding by using a magnitude matching task, to measure distributions of perceived target angles and a localization task, to probe the degree of access to local information.. Response distributions were bimodal, implying uncertainty, only in the presence of abutting flankers.. Localization of the target is relatively preserved but it quantitatively falls in between the predictions of the two models, possibly suggesting local averaging followed by a max operation.. This challenges the notion of global averaging and suggests some conscious access to local orientation estimates..

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  • Title: PisaVisionLab
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  • Title: Roberto Arrighi
    Descriptive info: Roberto Arrighi.. Post-Doc in Cognitive Science, University of Florence.. Email: roberto.. arrighi (AT) gmail.. com.. Telephone: +39 050 3153185.. Biological Motion.. Clinical Psychology.. Temporal Perception.. Giacomelli, G.. , Volpe, R.. , Virgili, G.. , Farini, A.. , Tarli-Barbieri, C.. Contrast reduction and reading: assessment and reliability with the Reading Explorer test,Eur J Ophthalmol, 2 (20), 389-396.. PURPOSE: To investigate the reliability of the Reading Explorer (REX) charts and to assess the impact of text contrast reduction (1.. 5 cycle/degree) on reading speed in subjects with normal and low vision.. METHODS: Standard visual acuity (ETDRS charts), reading speed (MNread charts), and contrast sensitivity (Pelli-Robson charts) measurements were obtained in 3 groups of subjects stratified by visual acuity level in the better eye from 0.. 0 to 1.. 0 logMAR, with intermediate cutoffs at 0.. 3 and 0.. 6 logMAR.. Measurements of reading speed for decreasing levels of text contrast were obtained with the REX charts using a 1.. 5 cycle/degree text.. RESULTS: Since in many patients with lower vision a plateau of maximum reading speed across different levels of text contrast was not found, reliability indexes were computed for average reading speed and reading contrast threshold.. In the group with lower visual acuity, 95% limits of agreement were +/-0.. 134 log word/minute and +/-0.. 175 log contrast sensitivity, suggesting good reliability.. The proportion of subjects with a 20% loss of reading speed from 90% to 45% text contrast was estimated to be 1/3 at 0.. 6 logMAR visual acuity level and 2/3 at 1.. 0 logMAR.. CONCLUSIONS: The adverse effect of decreased text contrast, which may be found in ordinary reading material, on the reading performance of subjects with advanced and initial low vision is probably underestimated.. The REX test proved to be a reliable investigation tool for this phenomenon.. Guzzetta, A.. , Pascale, R.. Motion perception in preterm children: role of prematurity and brain damage,Neuroreport, 15 (20), 1339-1343.. We tested 26 school-aged children born preterm at a gestational age below 34 weeks, 13 with and 13 without periventricular brain damage, with four different visual stimuli assessing perception of pure global motion (optic flow), with some form information (segregated translational  ...   the cube depth in two different ways.. We manipulated the cube ambiguity by darkening one of the cube faces (cue) to provide a clear cube interpretation due to the occlusion depth index.. When the position of the cue is stationary the cube perceived perspective is steady and driven by the cue position.. However, when we alternated in time the cue position (i.. e.. we changed the position of the darkened cube face) two different perceptual phenomena occurred: for low frequencies the cube perspective alternated in line with the position of the cue; however for high frequencies the cue was no longer able to bias the perception but it appears as a floating feature traveling across the solid with the cube whole perspective that returns to be bistable as in the conventional, bias-free, case.. , Lorenceau, J.. & Cass, J.. Contour interactions between pairs of Gabors engaged in binocular rivalry reveal a map of the association field,Vision Res, 8-9 (46), 1473-1487.. A psychophysical study was conducted to investigate contour interactions (the 'association field').. Two Gabor patches were presented to one eye, with random-dot patches in corresponding locations of the other eye so as to produce binocular rivalry.. Perceptual alternations of the two rivalry processes were monitored continuously by observers and the two time series were cross-correlated.. The Gabors were oriented collinearly, obliquely, or orthogonally, and spatial separation was varied.. A parallel condition was also included.. Correlation between the rivalry processes strongly depended on separation and relative orientation.. Correlations between adjacent collinear Gabors was near-perfect and reduced with spatial separation and as relative orientation departed from collinear.. Importantly, variations in cross-correlation did not alter the rivalry processes (average dominance duration, and therefore alternation rate, was constant across conditions).. Instead, synchronisation of rivalry oscillations accounts for the correlation variations: rivalry alternations were highly synchronised when contour interactions were strong and were poorly synchronised when contour interactions were weak.. The level of synchrony between these two stochastic processes, in depending on separation and relative orientation, effectively reveals a map of the association field.. These association fields are not greatly affected by contrast, and can be demonstrated between contours that are presented to separate hemispheres..

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  • Title: PostDocs
    Descriptive info: 204.. 2303.. 2457.. 2024.. 2142.. 2971.. 7.. 2651.. 8.. Francesca Tinelli.. 2715.. 9.. 1483.. 10.. 294..

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