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Despite the vast amount of behavioral data showing a pronounced tendency in individuals with autism spectrum disorder (ASD) to process fine visual details, much less is known about the neurophysiological characteristics of spatial vision in ASD. Here, we address this issue by assessing the contrast sensitivity response properties of the early visual-evoked potentials (VEPs) to sine-wave gratings of low, medium and high spatial frequencies in adults with ASD and in an age- and IQ-matched control group. Our results show that while VEP contrast responses to low and high spatial frequency gratings did not differ between ASD and controls, early VEPs to mid spatial frequency gratings exhibited similar response characteristics as those to high spatial frequency gratings in ASD. Our findings show evidence for an altered functional segregation of early visual channels, especially those responsible for processing mid- and high-frequency spatial scales.

This is the accepted version of the paper.This version of the publication may differ from the final published version. (Bowler, Gardiner and Gaigg, 2007), but it is still unknown whether memory in ASD relies on qualitatively similar or different neurophysiology. We sought to explore the neural activity underlying recognition by employing the old/new word repetition event-related potential (ERP) effect. Behavioural recognition performance was comparable across both groups, and demonstrated superior recognition for low frequency over high frequency words. However, the ASD group showed a parietal rather than anterior onset (300-500 ms), and diminished right frontal old/new effects (800-1500 ms) relative to TD individuals. This study shows that undiminished recognition performance results from a pattern of differing functional neurophysiology in ASD. Permanent repository linkKeywords: Memory, Autism Spectrum Disorder, Event-Related Potential, Recognition, Old/New effect Corresponding author: Esha.Massand.1@city.ac.ukRecognition Old-New effect in ASD 1One of the intriguing features of ASD is the profile of memory abilities often observed in this population. In general, HFA individuals show comparable immediate memory, cued recall (Boucher and Lewis, 1989) and recognition (Bowler, Gardiner & Gaigg, 2007) but impairments on measures of free recall. Some individuals with autism present exceptional memory performance in their domain of expertise (eg. Mottron et al., 1998). They characteristically fail to use semantic relations amongst studied items to aid free recall (Bowler, Matthews and Gardiner, 1997; see Tager-Flusberg, 1991, for similar findings in LFA individuals). Although first noted by Boucher and Warrington (1976), this pattern of spared and impaired memory performance has been developed by Bowler and Gardiner into the Task-Support Hypothesis (TSH), (Bowler et al., 1997;, which states that the performance of individuals with ASD will be closer to that of TD individuals if support is provided at test. Support is defined as any information relevant to the resolution of the task being present in the test materials. Supported test procedures include cued recall and recognition, where participants are presented with a clue (the studied word) and are asked whether or not it figured in the study list. In contrast, tasks such as free recall do not offer this kind of support, and often show diminished performance in individuals with ASD. This is especially the case when the task involves multiple trials (Bowler, Gaigg & Gardiner, 2008b;Bowler, Mottron & Limoges, 2009) or the use of semantic relations among studied items to enhance recall (Bowler, Matthews & Gardiner, 1997).Confirming evidence for the TSH and for difficulties in processing inter-item relations has been provided by numerous subsequent studies. In one example, Bowler, Gaigg and Gardiner (2008a) tested the effects of item versus context relatedness on recall and recognition in adults with ASD by asking individuals to study a series of words presented on a ...

In grapheme-color synesthesia, letters and numbers evoke abnormal colored perceptions. Although the underlying mechanisms are not known, it is largely thought that the synesthetic brain is characterized by atypical connectivity throughout various brain regions, including the visual areas. To study the putative impact of synesthesia on the visual brain, we assessed lateral interactions (i.e., local functional connectivity between neighboring neurons in the visual cortex) by recording steady-state visual evoked potentials (ssVEPs) over the occipital region in color-grapheme synesthetes (n = 6) and controls (n = 21) using the windmill/dartboard paradigm. Discrete Fourier Transform analysis was conducted to extract the fundamental frequency and the second harmonics of ssVEP responses from contrast-reversing stimuli presented at 4.27 Hz. Lateral interactions were assessed using two amplitude-based indices: Short-range and long-range lateral interactions. Results indicated that synesthetes had a statistically weaker signal coherence of the fundamental frequency component compared to the controls, but no group differences were observed on lateral interaction indices. However, a significant correlation was found between long-range lateral interactions and the type of synesthesia experience (projector versus associator). We conclude that the occipital activity related to lateral interactions in synesthetes does not substantially differ from that observed in controls. Further investigation is needed to understand the impact of synesthesia on visual processing, specifically in relation to subjective experiences of synesthete individuals.