Enrico Giora

The DCDC2 Intron 2 Deletion Impairs Illusory Motion Perception Unveiling the Selective Role of Magnocellular-Dorsal Stream in Reading (Dis)ability

Developmental dyslexia (DD) is a heritable neurodevelopmental reading disorder that could arise from auditory, visual, and cross-modal integration deficits. A deletion in intron 2 of the DCDC2 gene (hereafter DCDC2d) increases the risk for DD and related phenotypes. In this study, first we report that illusory visual motion perception-specifically processed by the magnocellular-dorsal (M-D) stream-is impaired in children with DD compared with age-matched and reading-level controls. Second, we test for the specificity of the DCDC2d effects on the M-D stream. Children with DD and DCDC2d need significantly more contrast to process illusory motion relative to their counterpart without DCDC2d and to age-matched and reading-level controls. Irrespective of the genetic variant, children with DD perform normally in the parvocellular-ventral task. Finally, we find that DCDC2d is associated with the illusory motion perception also in adult normal readers, showing that the M-D deficit is a potential neurobiological risk factor of DD rather than a simple effect of reading disorder. Our findings demonstrate, for the first time, that a specific neurocognitive dysfunction tapping the M-D stream is linked with a well-defined genetic susceptibility.

A single "stopwatch" for duration estimation, a single "ruler" for size.

Although observers can discriminate visual targets with long exposures from otherwise-identical targets with shorter exposures, temporally overlapping distracters with an intermediate exposure can produce a striking degradation in performance. This new finding suggests that observers can only estimate one duration at a time. Discrimination on the basis of size, rather than duration, did not degrade as rapidly with the number of distracters but was still worse than predicted by unlimited-capacity models. The critical difference between estimates of temporal length and estimates of spatial length seems to be that the former can only be made at the end of an exposure, while the latter can be made at any time during an exposure. When sizes varied throughout the trial and decisions were based on terminal sizes, the set-size effect was as large as that obtained for duration discrimination. We conclude that when textural filters are not available for segregating a target from distracters, efficient estimates of size or duration require the serial examination of individual display items.

Deeper attentional masking by lateral objects in children with autism

Autism spectrum disorder (ASD) is often associated with a detail-oriented perception and overselective attention in visual tasks, such as visual search and crowding. These results were obtained manipulating exclusively the spatial properties of the stimuli: few is known about the spatio-temporal dynamics of visual processing in ASD. In this study we employed an attentional masking (AM) paradigm comparing children with ASD and IQ-matched typically developing (TD) controls. The AM effect refers to an impaired identification of a target followed by a competitive masking object at different proximities in space and time. We found that ASD and TD groups did not differ in the AM effect provoked by the competitive object displayed in the same position of the target. In contrast, children with ASD showed a deeper and prolonged interference than the TD group when the masking object was displayed in the lateral position. These psychophysical results suggest that the inefficient attentional selection in ASD depends on the spatio-temporal interaction between competitive visual objects. These evidence are discussed in the light of the ASD altered neural connectivity hypothesis and the reentrant theory of perception.

Region- and edge-based configurational effects in texture segmentation.

We have found a new configurational effect in texture segmentation. In addition to collinear facilitation at the edge, this effect results from contextual modulation within the texture-region, i.e. from texels not abutting the segmented edge. The largest facilitation was found when two conditions were fulfilled: (i) elements along the edge were parallel to the edge and collinear, (ii) elements in the texture-region were also collinear but non-parallel to the edge. We show that this facilitation occurs when there are groups of different orientation from the edge in the texture-region. We suggest two possible underlying mechanisms: either a region-based process that links collinear iso-oriented elements and locates the edge when the orientation changes, or else second-order filters tuned to orientation differences rather than orientation per se.

Perceptual compromise between apparent and veridical motion indices: the unchained-dots illusion

A new motion illusion based on dot-trajectory misperception is presented. The illusory effect can not be explained by the aperture problem unlike some previous illusions characterised by misperception of motion direction. We propose an explanation in terms of ‘perceptual compromise’ between an original type of apparent motion and the veridical motion. Several demonstrations are presented in support of that hypothesis.

Behavioural and Cognitive-Behavioural Treatments of Parasomnias.

Parasomnias are unpleasant or undesirable behaviours or experiences that occur predominantly during or within close proximity to sleep. Pharmacological treatments of parasomnias are available, but their efficacy is established only for few disorders. Furthermore, most of these disorders tend spontaneously to remit with development. Nonpharmacological treatments therefore represent valid therapeutic choices. This paper reviews behavioural and cognitive-behavioural managements employed for parasomnias. Referring to the ICSD-3 nosology we consider, respectively, NREM parasomnias, REM parasomnias, and other parasomnias. Although the efficacy of some of these treatments is proved, in other cases their clinical evidence cannot be provided because of the small size of the samples. Due to the rarity of some parasomnias, further multicentric researches are needed in order to offer a more complete account of behavioural and cognitive-behavioural treatments efficacy.

Neurocognitive function in patients with idiopathic Restless Legs Syndrome before and after treatment with dopamine-agonist.

Although a huge amount of clinical evidence for Restless Legs Syndrome (RLS) is present in literature, an exhaustive account of cognitive profile in RLS patients is still lacking. In this study we evaluated the neurocognitive function in RLS patients and the effects of a three-month treatment with a dopamine agonist (pramipexole) at low doses. Clinical and polysomnographic characteristics, cognitive abilities, quality of life and psychological clinical indices were assessed in 20 RLS patients and 15 age-matched controls. The neurocognitive results, obtained by untreated RLS patients (baseline), were firstly compared to those of controls and then to those of the same RLS group after treatment (follow-up). Increased Total Sleep Time, Slow Wave Sleep, Sleep Efficiency and decreased Sleep Latency, Wake After Sleep Onset and periodic leg movement index were found by polysomnographic recording after a three-month treatment. Results showed that cognitive functions, impaired at baseline when compared to control subjects, improved after the pharmacological treatment, reaching the scores of healthy subjects. Decision making, problem solving and categorizing abilities, investigated by the Iowa Gambling Task (IGT) and the Wisconsin Card Sorting Test (WCST), resulted lower in RLS patients at baseline than in controls. All these functions improved after pharmacological treatment, as well as quality of life, depressive and anxiety symptoms, and daytime sleepiness.

Perceptual multistability in figure-ground segregation using motion stimuli

In a series of experiments using ambiguous stimuli, we investigate the effects of displaying ordered, discrete series of images on the dynamics of figure-ground segregation. For low frame presentation speeds, the series were perceived as a sequence of discontinuous, static images, while for high speeds they were perceived as continuous. We conclude that using stimuli varying continuously along one parameter results in stronger hysteresis and reduces spontaneous switching compared to matched static stimuli with discontinuous parameter changes. The additional evidence that the size of the hysteresis effects depended on trial duration is consistent with the stochastic nature of the dynamics governing figure-ground segregation. The results showed that for continuously changing stimuli, alternative figure-ground organizations are resolved via low-level, dynamical competition. A second series of experiments confirmed these results with an ambiguous stimulus based on Petters effect.

Measuring the Breathing Light Illusion by Means of Induced Simultaneous Contrast

By blurring the margins of a surface, both its brightness and the perceived contrast against a superimposed figure with sharp boundaries increase. Also, if one approaches a blurred white spot on a grey background, this spot will appear wider and brighter: this phenomenon is known as the Breathing Light Illusion (BLI) (Gori and Stubbs, 2006 Perception 35 1573–1577). We studied the increment of the achromatic contrast of a grey sharp-boundary disk when it was superimposed on the BLI. This augmentation of the perceived contrast in the dynamic presentation of the BLI was significantly stronger than the effect that Agostini and Galmonte (2002a Psychonomic Bulletin and Review 9 264–269) obtained in static presentation. Our study leads to an indirect quantification of the BLI. Two control experiments showed that the increment of the achromatic contrast depends on the blurred spot and is independent of the dynamic increment in angular size. These results argue for a causal relationship between the increase in brightness due to the BLI and the darkening of the superimposed disk.

How do painters represent motion in garments? Graphic invariants across centuries

Western visual art has radically changed throughout the centuries: different techniques, interest in the representation of reality, and use of graphic signs. Indeed, only a few pictorial cues have retained the same meaning and use. These kinds of graphic invariants may play a key role not only in a comparative study of art history, but also for discovering underlying common perceptual mechanisms. Here the aim is to show that western painters use the same graphic solutions to represent motion in garments, across countries and centuries. A pilot experiment, using 160 paintings representative of all main western European art movements from the thirteenth to the twentieth century, shows that different artists represented the motion of garments with the same orientation, curvature and convergence of lines. Experiment 1 demonstrates, with a smaller sample of paintings (16, i.e. two per century) that the relationship between orientation, curvature and convergence of lines is a good predictor of perceived motion. Experiment 2 shows how the same garments, isolated from the context of the paintings, still give different dynamic impressions according to the same rules. Finally, Experiment 3 confirmed the same results, whilst patterns previously used are simplified to their geometrical structure. These results call for an underlying perceptual mechanism that specifically recognizes orientation, curvature and parallelism levels as cues of motion in a static pattern.