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Guido Marco Cicchini

Post-Doc in Cognitive Science, Institute of Neuroscience - CNR

Contacts

  • Email: cicchini (AT) in.cnr.it
  • Telephone:  +39 050 3153185

Research laboratories

  • CNR Institute of Neuroscience, Pisa
  • Department of Psychology, University of Florence
  • Stella Maris Foundation, Pisa, Italy

Current research and interests

  • Temporal Perception
  • Eye Movements
  • Clinical Psychology
  • Optimal Behaviour

2016

Bruno, A. & Cicchini, G. M. (2016). Multiple channels of visual time perception, Current Opinion in Behavioral Sciences, (8), 131-139. PDF

The proposal that the processing of visual time might rely on a network of distributed mechanisms that are vision-specific and timescale-specific stands in contrast to the classical view of time perception as the product of a single supramodal clock. Evidence showing that some of these mechanisms have a sensory component that can be locally adapted is at odds with another traditional assumption, namely that time is completely divorced from space. Recent evidence suggests that multiple timing mechanisms exist across and within sensory modalities and that they operate in various neural regions. The current review summarizes this evidence and frames it into the broader scope of models for time perception in the visual domain.

Fornaciai, M., Cicchini, G. M. & Burr, D. C. (2016). Adaptation to number operates on perceived rather than physical numerosity, Cognition, (151), 63-67.PDF

Humans share with many animals a number sense, the ability to estimate rapidly the approximate number of items in a scene. Recent work has shown that like many other perceptual attributes, numerosity is susceptible to adaptation. It is not clear, however, whether adaptation works directly on mechanisms selective to numerosity, or via related mechanisms, such as those tuned to texture density. To disentangle this issue we measured adaptation of numerosity of 10 pairs of connected dots, as connecting dots makes them appear to be less numerous than unconnected dots. Adaptation to a 20-dot pattern (same number of dots as the test) caused robust reduction in apparent numerosity of the connected-dot pattern, but not of the unconnected dot-pattern. This suggests that adaptation to numerosity, at least for relatively sparse dot-pattern, occurs at neural levels encoding perceived numerosity, rather than at lower levels responding to the number of elements in the scene.

Karaminis, T., Cicchini, G. M., Neil, L., Cappagli, G., Aagten-Murphy, D., Burr, D., et al. (2016). Central tendency effects in time interval reproduction in autism, Sci Rep, (6), 28570. PDF

Central tendency, the tendency of judgements of quantities (lengths, durations etc.) to gravitate towards their mean, is one of the most robust perceptual effects. A Bayesian account has recently suggested that central tendency reflects the integration of noisy sensory estimates with prior knowledge representations of a mean stimulus, serving to improve performance. The process is flexible, so prior knowledge is weighted more heavily when sensory estimates are imprecise, requiring more integration to reduce noise. In this study we measure central tendency in autism to evaluate a recent theoretical hypothesis suggesting that autistic perception relies less on prior knowledge representations than typical perception. If true, autistic children should show reduced central tendency than theoretically predicted from their temporal resolution. We tested autistic and age- and ability-matched typical children in two child-friendly tasks: (1) a time interval reproduction task, measuring central tendency in the temporal domain; and (2) a time discrimination task, assessing temporal resolution. Central tendency reduced with age in typical development, while temporal resolution improved. Autistic children performed far worse in temporal discrimination than the matched controls. Computational simulations suggested that central tendency was much less in autistic children than predicted by theoretical modelling, given their poor temporal resolution.

Cicchini, G. M., Anobile, G. & Burr, D. C. (2016). Spontaneous perception of numerosity in humans, Nat Commun, (7), 12536. PDF

Humans, including infants, and many other species have a capacity for rapid, nonverbal estimation of numerosity. However, the mechanisms for number perception are still not clear; some maintain that the system calculates numerosity via density estimates-similar to those involved in texture-while others maintain that more direct, dedicated mechanisms are involved. Here we show that provided that items are not packed too densely, human subjects are far more sensitive to numerosity than to either density or area. In a two-dimensional space spanning density, area and numerosity, subjects spontaneously react with far greater sensitivity to changes in numerosity, than either area or density. Even in tasks where they were explicitly instructed to make density or area judgments, they responded spontaneously to number. We conclude, that humans extract number information, directly and spontaneously, via dedicated mechanisms.

Castaldi, E., Cicchini, G. M., Cinelli, L., Biagi, L., Rizzo, S. & Morrone, M. C. (2016). Visual BOLD Response in Late Blind Subjects with Argus II Retinal Prosthesis, PLoS Biol, 10 (14), e1002569. PDF

Retinal prosthesis technologies require that the visual system downstream of the retinal circuitry be capable of transmitting and elaborating visual signals. We studied the capability of plastic remodeling in late blind subjects implanted with the Argus II Retinal Prosthesis with psychophysics and functional MRI (fMRI). After surgery, six out of seven retinitis pigmentosa (RP) blind subjects were able to detect high-contrast stimuli using the prosthetic implant. However, direction discrimination to contrast modulated stimuli remained at chance level in all of them. No subject showed any improvement of contrast sensitivity in either eye when not using the Argus II. Before the implant, the Blood Oxygenation Level Dependent (BOLD) activity in V1 and the lateral geniculate nucleus (LGN) was very weak or absent. Surprisingly, after prolonged use of Argus II, BOLD responses to visual input were enhanced. This is, to our knowledge, the first study tracking the neural changes of visual areas in patients after retinal implant, revealing a capacity to respond to restored visual input even after years of deprivation.


2015

Cicchini, G. M. & Kristjànsson, A. (2015). On the Possibility of a Unifying Framework for Serial Dependencies, i-Perception, 6(6) 1–16. PDF

Serial effects in perception have been studied since the dawn of psychophysics. Color aftereffects greatly advanced the understanding of color vision in the 19th century, and motion aftereffects have intrigued perceptual scientists for centuries. Recent discoveries in visual attention and psychophysics have intensifed interest in such effects. The current consensus is that they are not curiosities but serve an important function and can be critical for understanding perception.
The current article summarizes the contributions to a recent conference (SFX 2014, Pisa, Italy) and underscores the idea that the brain has learned how to exploit temporal regularities in the environment.

Anobile, G., Turi, M., Cicchini, G. M. & Burr, D. (2015). Mechanisms for perception of numerosity or texture-density are governed by crowding-like effects,Journal of Vision, 15(5), 1-12. PDF

We have recently provided evidence that the perception of number and texture density is mediated by two independent mechanisms: numerosity mechanisms at relatively low numbers, obeying Weber’s law, and texture-density mechanisms at higher numerosities, following a square root law. In this study we investigated whether the switch between the two mechanisms depends on the capacity to segregate individual dots, and therefore follows similar laws to those governing visual crowding. We measured numerosity discrimination for a wide range of numerosities at three eccentricities. We found that the point where the numerosity regime (Weber’s law) gave way to the density regime (square root law) depended on eccentricity. In central vision, the regime changed at 2.3 dots/82, while at 158 eccentricity, it changed at 0.5 dots/82, three times less dense. As a consequence, thresholds for low numerosities increased with eccentricity, while at higher numerosities thresholds remained constant. We further showed that like crowding, the regime change was independent of dot size, depending on distance between dot centers, not distance between dot edges or ink coverage. Performance was not affected by stimulus contrast or blur, indicating that the transition does not depend on low-level stimulus properties. Our results reinforce the notion that numerosity and texture are mediated by two distinct processes, depending on whether the individual elements are perceptually segregable. Which mechanism is engaged follows laws that determine crowding.

Arrighi, R., Binda, P. & Cicchini, G. M. (2015). Introduction to the Special Issue on Multimodality of Early Sensory Processing: Early Visual Maps Flexibly Encode Multimodal Space, Multisensory Research, 3-4 (28), 249-252. PDF

As living organisms, we have the capability to explore our environments through different senses, each making use of specialized organs and return ing unique information. This is relayed to a set of cortical areas, each of which appears to be specialized for processing information from a single sense — hence the definition of ‘unisensory’ areas. Many models assume that primary unisensory cortices passively reproduce information from each sensory organ; these then project to associative areas, which actively combine multisensory signals with each other and with cognitive stances. By the same token, the textbook view holds that sensory cortices undergo plastic changes only within a limited ‘critical period’; their function and architecture should remain stable and unchangeable thereafter. This model has led to many fundamental discoveries on the architecture of the sensory systems (e.g., oriented receptive fields, binocularity, topographic maps, to name just the best known). However, a growing body of evidence calls for a review of this conceptual scheme. Based on single-cell recordings from non-human primates, fMRI in humans, psychophysics, and sensory deprivation studies, early sensory areas are losing their status of fixed readouts of receptor activity; they are turning into functional nodes in a network of brain areas that flexibly adapts to the statistics of the input and the behavioral goals. This special issue in Multisensory Research aims to cover three such lines of evidence: suggesting that (1) the flexibility of spatial representations, (2) adult plasticity and (3) multimodality, are not properties of associative areas alone, but may depend on the primary visual cortex V1.

Cicchini, G. M., Marino, C., Mascheretti, S., Perani, D. & Morrone, M. C. (2015). Strong Motion Deficits in Dyslexia Associated with DCDC2 Gene Alteration,J Neurosci, 21 (35), 8059-8064. PDF

Dyslexia is a specific impairment in reading that affects 1 in 10 people. Previous studies have failed to isolate a single cause of the disorder, but several candidate genes have been reported. We measured motion perception in two groups of dyslexics, with and without a deletion within the DCDC2 gene, a risk gene for dyslexia. We found impairment for motion particularly strong at high spatial frequencies in the population carrying the deletion. The data suggest that deficits in motion processing occur in a specific genotype, rather than the entire dyslexia population, contributing to the large variability in impairment of motion thresholds in dyslexia reported in the literature.

Mikellidou, K., Cicchini, G. M., Thompson, P. G. & Burr, D. C. (2015). The oblique effect is both allocentric and egocentric,Journal of Vision, 8 (15), 24-24. PDF

Despite continuous movements of the head, humans maintain a stable representation of the visual world, which seems to remain always upright. The mechanisms behind this stability are largely unknown. To gain some insight on how head tilt affects visual perception, we investigate whether a well-known orientation-dependent visual phenomenon, the oblique effect—superior performance for stimuli at cardinal orientations (0° and 90°) compared with oblique orientations (45°)—is anchored in egocentric or allocentric coordinates. To this aim, we measured orientation discrimination thresholds at various orientations for different head positions both in body upright and in supine positions. We report that, in the body upright position, the oblique effect remains anchored in allocentric coordinates irrespective of head position. When lying supine, gravitational effects in the plane orthogonal to gravity are discounted. Under these conditions, the oblique effect was less marked than when upright, and anchored in egocentric coordinates. The results are well explained by a simple “compulsory fusion” model in which the head-based and the gravity-based signals are combined with different weightings (30% and 70%, respectively), even when this leads to reduced sensitivity in orientation discrimination.

Anobile, G., Cicchini, G. M. & Burr, D. C. (2015). Number as a primary perceptual attribute: a review, Perception 1-27 DOI: 10.1177/0301006615602599. PDF

Although humans are the only species to possess language-driven abstract mathematical capacities, we share with many other animals a nonverbal capacity for estimating quantities or numerosity. For some time, researchers have clearly differentiated between small numbers of items—less than about four—referred to as the subitizing  range, and larger numbers, where counting or estimation is required. In this review, we examine more recent evidence suggesting a further division, between sets of items greater than the subitizing range, but sparse enough to be individuated as single items; and densely packed stimuli, where they crowd each other into what is betterconsidered as a texture. These two different regimes are psychophysically discriminable in that they follow distinct psychophysical laws and show different dependencies on eccentricity and on luminance levels. But provided the elements are not too crowded (less than about two items per square degree in central vision, less in the periphery), there is little evidence that estimation of numerosity depends on mechanisms responsive to texture. The distinction is important, as the ability to discriminate numerosity, but not texture, correlates with formal maths skills.

Cicchini, G. M. & Kristjànsson, A. (2015). On the Possibility of a Unifying Framework for Serial Dependencies, i-Perception, 6(6) 1–16. PDF

erial effects in perception have been studied since the dawn of psychophysics. Color aftereffects greatly advanced the understanding of color vision in the 19th century, and motion aftereffects have intrigued perceptual scientists for centuries. Recent discoveries in visual attention and psychophysics have intensifed interest in such effects. The current consensus is that they are not curiosities but serve an important function and can be critical for understanding perception.
The current article summarizes the contributions to a recent conference (SFX 2014, Pisa, Italy) and underscores the idea that the brain has learned how to exploit temporal regularities in the environment.


2014

Cicchini, G. M., Anobile, G. & Burr, D. C. (2014). Compressive mapping of number to space reflects dynamic encoding mechanisms, not static logarithmic transform,Proc Natl Acad Sci U S A, 21 (111), 7867-7872. PDF

The mapping of number onto space is fundamental to measurement and mathematics. However, the mapping of young children, unschooled adults, and adults under attentional load shows strong compressive nonlinearities, thought to reflect intrinsic logarithmic encoding mechanisms, which are later "linearized" by education. Here we advance and test an alternative explanation: that the nonlinearity results from adaptive mechanisms incorporating the statistics of recent stimuli. This theory predicts that the response to the current trial should depend on the magnitude of the previous trial, whereas a static logarithmic nonlinearity predicts trialwise independence. We found a strong and highly significant relationship between numberline mapping of the current trial and the magnitude of the previous trial, in both adults and school children, with the current response influenced by up to 15% of the previous trial value. The dependency is sufficient to account for the shape of the numberline, without requiring logarithmic transform. We show that this dynamic strategy results in a reduction of reproduction error, and hence improvement in accuracy.

Anobile, G., Cicchini, G. M. & Burr, D. C. (2014). Separate mechanisms for perception of numerosity and density,Psychol Sci, 1 (25), 265-270. PDF

Despite the existence of much evidence for a number sense in humans, several researchers have questioned whether number is sensed directly or derived indirectly from texture density. Here, we provide clear evidence that numerosity and density judgments are subserved by distinct mechanisms with different psychophysical characteristics. We measured sensitivity for numerosity discrimination over a wide range of numerosities: For low densities (less than 0.25 dots/deg(2)), thresholds increased directly with numerosity, following Weber's law; for higher densities, thresholds increased with the square root of texture density, a steady decrease in the Weber fraction. The existence of two different psychophysical systems is inconsistent with a model in which number is derived indirectly from noisy estimates of density and area; rather, it points to the existence of separate mechanisms for estimating density and number. These results provide strong confirmation for the existence of neural mechanisms that sense number directly, rather than indirectly from texture density.

Burr, D. & Cicchini, G. M. (2014). Vision: efficient adaptive coding,Curr Biol, 22 (24), R1096-1098. PDF

Recent studies show that perception is driven not only by the stimuli currently impinging on our senses, but also by the immediate past history. The influence of recent perceptual history on the present reflects the action of efficient mechanisms that exploit temporal redundancies in natural scenes.

2013

Cicchini, G. M., Binda, P., Burr, D. C. & Morrone, M. C. (2013). Transient spatiotopic integration across saccadic eye movements mediates visual stability,J Neurophysiol, 4 (109), 1117-1125. PDF

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.

Scocchia, L. , Cicchini, G.M. & Triesch, J. (2013). What's "up"? Working memory contents can bias orientation processing, Vision Res, (76), 46-55. PDF

We explored the interaction between the processing of a low-level visual feature such as orientation and the contents of working memory (WM). In a first experiment, participants memorized the orientation of a Gabor patch and performed two subsequent orientation discriminations during the retention interval. The WM stimulus exerted a consistent repulsive effect on the discrimination judgments: participants were more likely to report that the discrimination stimulus was rotated clockwise compared to the oblique after being presented with a stimulus that was tilted anti-clockwise from the oblique. A control condition where participants attended to the Gabor patch but did not memorize it, showed a much reduced effect. The repulsive effect was stable across the two discriminations in the memory condition, but not in the control condition, where it decayed at the second discrimination. In a second experiment, we showed that the greater interference observed in the WM condition cannot be explained by a difference in cognitive demands between the WM and the control condition. We conclude that WM contents can bias perception: the effect of WM interference is of a visual nature, can last over delays of several seconds and is not disrupted by the processing of intervening visual stimuli during the retention period.

Cicchini, G.M. and Spillmann, L. (2013). Neon color spreading in dynamic displays: Temporal factors, Journal of Vision (13):12,2. PDF

When a red star is placed in the middle of an Ehrenstein figure so as to be collinear with the surrounding black rays, a reddish veil is perceived to fill the white center. This is called neon color spreading. To better understand the processes that give rise to this phenomenon, we studied the temporal properties of the effect. Specifically, we presented a “sustained” black Ehrenstein figure (rays) for 600 ms and a “transient” red star for 48 ms, or the converse pattern, at various stimulus onset asynchronies (?100–700 ms) and asked subjects to compare the strength of the neon color in the test stimulus to that of a reference pattern in which the transient star had an onset asynchrony of 300 ms. Additional exposure durations of 24 and 96 ms were used for each transient stimulus in order to study the effect of temporal integration. Simultaneity of the on- and off-transients of the star and the Ehrenstein rays were found to optimize neon color spreading, especially when both stimuli terminated together. Longer exposure durations of the transient stimulus up to 96 ms further improved the effect. Neon color spreading was much reduced when the transient stimulus was presented soon after the beginning of the sustained stimulus, with a gradual build-up towards the end. These results emphasize the importance of stimulus onset asynchrony (SOA) and stimulus termination asynchrony (STA) for the perception of neon color spreading.

Pooresmaeili, A., Cicchini, G.M., Morrone, M. C. & Burr, D.C. (2013). Spatiotemporal filtering and motion illusions, Journal of Vision, (13)10-21. PDF

Our group has long championed the idea that perceptual processing of information can be anchored in a dynamic coordinate system that need not correspond to the instantaneous retinal representation that need not correspond to the istantaneus retinal representation...


2012

Anobile, G., Cicchini, G. M. & Burr, D. C. (2012). Linear mapping of numbers onto space requires attention,Cognition, 3 (122), 454-459. PDF

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.

Cicchini, G. M., Arrighi, R., Cecchetti, L., Giusti M. & Burr, D. C. (2012). Optimal Encoding of Interval Timing in Expert Percussionists, J Neurosci, 3 (32), 1056-1060. PDF

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., Cicchini, G. M., Morrone, M. C. & Burr, D. (2012). "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.

Cicchini, G. M. (2012). Perception of duration in the parvocellular system, Front Integr Neurosci 6:14 PDF

Both theoretical and experimental evidence suggests that duration perception is mediated preferentially by the color-blind but high temporally sensitive luminance pathway. In this experiment we tested whether color modulated stimuli and high spatial frequency luminance modulated stimuli, which are known to be relayed mostly by the slow parvocellular system, are able to elicit reliable sense of duration. We show that ramped color modulated stimuli seem to last less than luminance modulated stimuli matched for visibility. The effect is large, about 200 ms and is constant at all durations tested (range 500–1100 ms). However, high spatial frequency luminance stimuli obtain duration matches similar to those of low spatial frequency luminance modulated stimuli. The results at various levels of contrast and temporal smoothing indicate that equiluminant stimuli have higher contrast thresholds to activate the mechanisms which time visual stimuli. Overall the results imply that both the magnocellular and the parvocellular systems access reliably the timing mechanisms with a difference only in the way these are engaged

Anobile, G., Turi, M., Cicchini, G. M. & Burr, D. C. (2012). The effects of cross-sensory attentional demand on subitizing and on mapping number onto space,Vision Res, PDF

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.

Tinelli, T., Cicchini, G.M., Arrighi, R., Tosetti, M., Cioni, G.,  Morrone M. C. (2012). Blindsight in children with congenital and acquired cerebral lesions, Cortex (published online 10 August 2012) PDF

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.

2011

Burr, D. C., Cicchini, G. M., Arrighi, R. & Morrone, M. C. (2011). Spatiotopic selectivity of adaptation-based compression of event duration, J Vis, 2 (11), 21; author reply 21a. PDF

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. C. 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.

2010

Morrone, M. C., Cicchini, M. & Burr, D. C. (2010). Spatial maps for time and motion,Exp Brain Res, 2 (206), 121-128. PDF

In this article, we review recent research studying the mechanisms for transforming coordinate systems to encode space, time and motion. A range of studies using functional imaging and psychophysical techniques reveals mechanisms in the human brain for encoding information in external rather than retinal coordinates. This reinforces the idea of a tight relationship between space and time, in the parietal cortex of primates.

2009

Cicchini, G. M. & Morrone, M. C. (2009). Shifts in spatial attention affect the perceived duration of events,J Vis, 1 (9), 9 1-13. PDF

We investigated the relationship between attention and perceived duration of visual events with a double-task paradigm. The primary task was to discriminate the size change of a 2 degree circle presented 10 degrees left, right, above, or below fixation; the secondary task was to judge the temporal separation (from 133 ms to 633 ms) of two equiluminant horizontal bars (10 deg x 2 deg) briefly flashed 12 degrees above or below fixation. The stimulus onset asynchrony (SOA) between primary and secondary task ranged from -1300 ms to +1000 ms. Temporal intervals in proximity of the onset of the primary task stimuli were perceived strongly compressed by up to 40%. The effect was proportional to the size of the interval with a maximum effect at 100 ms SOA. Control experiments show that neither primary-task difficulty, nor the type of primary task discrimination (form or motion, or equiluminant or luminance contrast) nor spatial congruence between primary and secondary task alter the effect. Interestingly, the compression occurred only when the intervals are marked by bars presented in separated spatial locations: when the interval is marked by two bars flashed in the same spatial position no temporal distortion was found. These data indicate that attention can alter perceived duration when the brain has to compare the passage of time at two different spatial positions, corroborating earlier findings that mechanisms of time perception may monitor separately the various spatial locations possibly at high level of analysis.

Burr, D., Silva, O., Cicchini, G. M., Banks, M. S. & Morrone, M. C. (2009). Temporal mechanisms of multimodal binding,Proc Biol Sci, 1663 (276), 1761-1769. PDF

The simultaneity of signals from different senses-such as vision and audition-is a useful cue for determining whether those signals arose from one environmental source or from more than one. To understand better the sensory mechanisms for assessing simultaneity, we measured the discrimination thresholds for time intervals marked by auditory, visual or auditory-visual stimuli, as a function of the base interval. For all conditions, both unimodal and cross-modal, the thresholds followed a characteristic 'dipper function' in which the lowest thresholds occurred when discriminating against a non-zero interval. The base interval yielding the lowest threshold was roughly equal to the threshold for discriminating asynchronous from synchronous presentations. Those lowest thresholds occurred at approximately 5, 15 and 75 ms for auditory, visual and auditory-visual stimuli, respectively. Thus, the mechanisms mediating performance with cross-modal stimuli are considerably slower than the mechanisms mediating performance within a particular sense. We developed a simple model with temporal filters of different time constants and showed that the model produces discrimination functions similar to the ones we observed in humans. Both for processing within a single sense, and for processing across senses, temporal perception is affected by the properties of temporal filters, the outputs of which are used to estimate time offsets, correlations between signals, and more.

Binda, P., Cicchini, G. M., Burr, D. C. & Morrone, M. C. (2009). Spatiotemporal distortions of visual perception at the time of saccades,J Neurosci, 42 (29), 13147-13157. PDF

Both space and time are grossly distorted during saccades. Here we show that the two distortions are strongly linked, and that both could be a consequence of the transient remapping mechanisms that affect visual neurons perisaccadically. We measured perisaccadic spatial and temporal distortions simultaneously by asking subjects to report both the perceived spatial location of a perisaccadic vertical bar (relative to a remembered ruler), and its perceived timing (relative to two sounds straddling the bar). During fixation and well before or after saccades, bars were localized veridically in space and in time. In different epochs of the perisaccadic interval, temporal perception was subject to different biases. At about the time of the saccadic onset, bars were temporally mislocalized 50-100 ms later than their actual presentation and spatially mislocalized toward the saccadic target. Importantly, the magnitude of the temporal distortions co-varied with the spatial localization bias and the two phenomena had similar dynamics. Within a brief period about 50 ms before saccadic onset, stimuli were perceived with shorter latencies than at other delays relative to saccadic onset, suggesting that the perceived passage of time transiently inverted its direction. Based on this result we could predict the inversion of perceived temporal order for two briefly flashed visual stimuli. We developed a model that simulates the perisaccadic transient change of neuronal receptive fields predicting well the reported temporal distortions. The key aspects of the model are the dynamics of the "remapped" activity and the use of decoder operators that are optimal during fixation, but are not updated perisaccadically.

2008

Cicchini, G. M., Valsecchi, M. & De'Sperati, C. (2008). Head movements modulate visual responsiveness in the absence of gaze shifts,Neuroreport, 8 (19), 831-834. PDF

Visuospatial attention is strongly associated with saccades. Given that gaze shifts are often accomplished by combined eye-head movements, attention may also be coupled to head movements. We showed that simply turning the head without shifting the gaze is sufficient to cause a transient unbalance in responding to a visual stimulus. Manual responses to a stimulus flashed shortly before the onset of a horizontal head movement were faster in congruent trials, when the head moved towards the stimulus, than in incongruent trials, when the head moved away from the stimulus. These effects are similar to those observed for saccades. We take this as evidence for a tight link between visuospatial attention and head movements, even when the gaze does not shift.

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