Francesca Pei

Attentional skills during the first 6 months of age in autism spectrum disorder.

OBJECTIVE To study the quality of early attention in autism spectrum disorder (ASD) through home movies. METHOD Fifteen home movies from the first 6 months of life of children who later received a diagnosis of ASD were compared with home movies of 15 normal children. The diagnosis was performed after the third year of life of children by two senior child and adolescent psychiatrists using a checklist of symptoms according to the. The films of the two groups were mixed and rated by blind observers through a Grid for the Assessment of Attentional Skills in Infants, composed of 13 items grouped into three developmental areas. RESULTS Using multivariate analysis of variance, the authors found significant differences between the two groups for the items in the social attention and the social behavior areas; on the contrary, there were no differences in nonsocial attention. CONCLUSIONS The authors pose some hypotheses about a specific early-appearing impairment of attention in ASD in which children shift their spontaneous attention mainly toward nonsocial stimuli rather than toward social stimuli. The importance of this finding for early diagnosis and treatment is underlined.

Search superiority in autism within, but not outside the crowding regime

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.

Development of Sensitivity to Texture and Contour Information in the Human Infant

Texture discrimination and bounding contour extraction are essential parts of the object segmentation and shape discrimination process. As such, successful texture and contour processing are key components underlying the development of the perception of both objects and surfaces. By recording visual-evoked potentials, we investigate whether young infants can detect orientation-defined textures and contours. We measured responses to an organized texture comprised of many Gabor patches of the same orientation, alternated with images containing the same number of patches, but all of random orientation. These responses were compared with a control condition consisting of the alternation between two independently random configurations. Significant difference potentials were found as early as 25 months, as were significant odd harmonics in the test conditions. Responses were also measured to Gabor patches organized either as circles (all patches tangent to an imaginary circular path) alternated with pinwheels (all patches having a fixed orientation offset from the path). Infants between 6 and 13 months also showed sensitivity to the global organization of the elements along contours. Differential responses to our texture and contour stimuli and their controls could only have been generated by mechanisms that are capable of comparing the relative orientation of 2 or more patches, as no local information at a single patch distinguished the random and organized textures or the circle and pinwheel configurations.

Event-related potentials show configural specificity of global form processing

Glass patterns are a type of moiré created when a random-dot field is overlaid with a rotated, translated or dilated copy. The overall form of the moiré cannot be detected using local processing mechanisms, and because of this, Glass patterns are useful probes of global form processing. Here, we use event-related potentials to show that certain global organizations (concentric structure created by rotation and radial structure produced by dilation) produce much larger brain responses than others (linear structure created by translation). The results are consistent with the existence of specialized form processing mechanisms in the extrastriate cortex.

Electrophysiological measures of low-level vision reveal spatial processing deficits and hemispheric asymmetry in autism spectrum disorder

There is accumulating evidence from electrophysiological studies that low-level visual processing is atypical in individuals with autism spectrum disorders (ASDs). Abnormalities in early stages of sensory processing are of interest because they could lead to downstream functional deficits in social or cognitive domains. Using steady-state visual evoked potentials (SSVEPs), we studied how well spatial information is transmitted over a wide range of spatial frequencies (2-30 cycles/deg), including those at the limit of visibility (visual acuity). SSVEPs were recorded over 128 channels in 16 ASD participants between 5 and 17 years old and 17 age-matched, neurotypical (NT) participants. We observed a selective reduction of the amplitude of the SSVEP second harmonic pattern reversal response between 5 and 17 cycles/deg. Responses measured at the fourth harmonic were normal at all spatial frequencies tested, as were responses at the lowest and highest spatial frequencies at the second harmonic. The reduction of second harmonic responses occurred preferentially over right occipital electrodes. Because response abnormalities are restricted to a specific response harmonic and to specific ranges of spatial frequency, we can rule out nonspecific differences between the ASD participants and the NT controls. This particular pattern of loss, combined with the observed exaggeration of the loss over the right hemisphere, suggests that a highly specific neural substrate early in the visual pathway is compromised in ASD.

Neural correlates of texture and contour integration in children with autism spectrum disorders.

In this study, we have used an electrophysiological paradigm to investigate the neural correlates of the visual integration of local signals across space to generate global percepts in a group of low functioning autistic kids. We have analyzed the amplitude of key harmonics of the Visual Evoked Potentials (VEPs) recorded while participants observed orientation-based texture and contour stimuli, forming coherent global patterns, alternating with visual patterns in which the same number of local elements were randomly oriented in order to loose any globally organized feature. Comparing the results of the clinical sample with those obtained in an age-matched control group, we have observed that in the texture conditions the 1st and 3rd harmonics, containing signature of global form processing (Norcia, Pei, Bonneh, Hou, Sampath, & Pettet, 2005), were present in the control 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.

Sensitivity and configuration-specificity of orientation-defined texture processing in infants and adults

Here we use textures made up of widely spaced Gabor patches to compare infant and adult sensitivity to the global organization of the elements comprising the textures. Visual Evoked Potentials (VEPs) were recorded to alterations between random images and images containing varying proportions of patches that were of the same orientation. The patches were placed on rectangular, hexagonal or random lattices. Texture-specific responses were robust in adults and their VEP threshold was reached when 1-17% of the patches had the same orientation in the structured image. Infant thresholds were approximately 20-60%. While infants are capable of detecting the global structure of our textures, their sensitivity is low. In adults we found, unexpectedly, that sensitivity and response gain were higher for horizontal compared to vertical global orientations. Infant sensitivity was the same for the two orientations. Comparable orientation anisotropies have not been previously reported for gratings, suggesting that the Gabor-defined textures are tapping different mechanisms. There were small, but measurable effects of the lattice type in adults, with the rectangular lattice producing the largest responses.

Development of contrast normalization mechanisms during childhood and adolescence

ABSTRACT Contrast sensitivity is regulated by neural mechanisms that flexibly adjust responsiveness to optimize stimulus encoding across different environments. Here we studied the developmental status of gain control mechanisms in school‐age children (5–17 years) and adults using a visual masking paradigm. A variable contrast, spatially random 2‐D noise test pattern was masked by the presence of a superimposed independent noise pattern presented at 0, 12 and 40% contrast. Frequency‐tagged steady state visual evoked potentials were used to separately record responses to the test (5.14 Hz) and the mask (7.2 Hz). By incrementally increasing the test contrast we measured contrast response functions for each mask contrast. The unmasked contrast response functions were largely similar in shape across age, but peak amplitude was higher in the children. Masking shifted the contrast response function rightward on the contrast axis in both the adults and older children, elevating contrast thresholds by a similar factor across age. However, in younger children, masking resulted in a change in the slope of the contrast response function. These findings suggest that immaturity in the contrast normalization process persists until approximately 11 years of age.

Evidence for long-range spatiotemporal interactions in infant and adult visual cortex

The development of spatiotemporal interactions giving rise to classical receptive field properties has been well studied in animal models, but little is known about the development of putative nonclassical mechanisms in any species. Here we used visual evoked potentials to study the developmental status of spatiotemporal interactions for stimuli that were biased to engage long-range spatiotemporal integration mechanisms. We compared responses to widely spaced stimuli presented either in temporal succession or at the same time. The former configuration elicits a percept of apparent motion in adults but the latter does not. Component flash responses were summed to make a linear prediction (no spatiotemporal interaction) for comparison with the measured evoked responses to sequential or simultaneous flash conditions. In adults, linear summation of the separate flash responses measured with 40% contrast stimuli predicted sequential flash responses twice as large as those measured, indicating that the response measured under apparent motion conditions is subadditive. Simultaneous-flash responses at the same spatial separation were also subadditive, but substantially less so. The subadditivity in both cases could be modeled as a simple multiplicative gain term across all electrodes and time points. In infants aged 3–8 months, responses to the stimuli used in adults were similar to their linear predictions at 40%, but the responses measured at 80% contrast resembled the subadditive responses of the adults for both sequential and simultaneous flash conditions. We interpret the developmental data as indicating that adult-like long-range spatiotemporal interactions can be demonstrated by 3–8 months, once stimulus contrast is high enough.

Autism sensory dysfunction in an evolutionarily conserved system

Individuals with Autism Spectrum Disorder (ASD) report a host of sensory symptoms, which suggests a fundamental, genetic (Miles, 2011) neural signaling deficit in autistic brains (Rubenstein & Merzenich, 2003). However, neither animal models nor previous theories explaining sensory symptoms have been able to predict neurophysiological data in autistic humans. Here we show a strikingly similar trajectory of visual development in a genetic Drosophila Nhe3 model of autism and in autistic human participants. We report a dissociation between first- and second-order electrophysiological visual responses to steady-state stimulation in adults with ASD as well as a large sample of neurotypical individuals with high numbers of autistic traits. We also report a strikingly similar impairment in the adult fruit fly model of ASD. We explain this as a selective signaling abnormality in the transient response mechanisms in the visual system. In contrast to adults, autistic children show decreases in both first- and second-order responses, which are closely matched by the fruit fly model, suggesting a compensatory change in processing occurs over the course of development. Our results provide the first animal model of autism comprising a developmental sensory pathway phenotype. Significance statement Autism Spectrum Disorder exhibits strong and widespread sensory symptoms that have not yet been explained by previous research. Here we have developed a novel Drosophila model of sensory deficits in autism that is highly predictive of electrophysiological visual data in both autistic adults and children. Both the animal model, and human data from three samples (total N=154), point towards a deficit of a fundamental signaling mechanism in early parts of the sensory system. This deficit shows signs of change during development indicating a possible partial rescue of function at later stages of life. Our findings can explain previous inconsistencies in research into visual perception in autism. The Drosophila model can be used in future biomarker and treatment development.