Abstract
In neurotypical observers, it is widely believed that the visual system samples the world in a coarse-to-fine fashion. Past studies on Autism Spectrum Disorder (ASD) have identified atypical responses to fine visual information but did not investigate the time course of the sampling of information at different levels of granularity (i.e. Spatial Frequencies, SF). Here, we examined this question during an object recognition task in ASD and neurotypical observers using a novel experimental paradigm. Our results confirm and characterize with unprecedented precision a coarse-to-fine sampling of SF information in neurotypical observers. In ASD observers, we discovered a different pattern of SF sampling across time: in the first 80 ms, high SFs lead ASD observers to a higher accuracy than neurotypical observers, and these SFs are sampled differently across time in the two subject groups. Our results might be related to the absence of a mandatory precedence of global information, and to top-down processing abnormalities in ASD.
Highlights
SFs are not sampled all at once during recognition in neurotypicals: they are extracted in a coarse-to-fine manner[15,16]
To uncover which spatial frequencies in which time frames led to accurate object recognition, we performed multiple least-square linear regressions between accuracies and the SF x time sampling matrices of the corresponding trials, for each subject
Results show that while Autism Spectrum Disorder (ASD) subjects seem to use each SF in an approximately constant manner across time, neurotypical subjects use SFs around 25 cpi increasingly across time (p < 0.05, FWER-corrected; peak d = 0.57). These same SFs are used more in an increasing manner across time in neurotypical subjects than in ASD subjects (p < 0.05, FWER-corrected; peak d = 1.08; Fig. 1). This confirms an interaction between group and time course of sampling of SFs around 25 cpi and shows that this time course differed between the groups for these SFs
Summary
SFs are not sampled all at once during recognition in neurotypicals: they are extracted in a coarse-to-fine manner[15,16]. Most studies demonstrating a coarse-to-fine sampling of SF information in neurotypicals compared a single low SF condition to a single high SF condition, which is unhelpful to uncover the exact SFs at play in this process. Subjects had to recognize an object from a brief video sampling random SFs on random frames; we reverse correlated the revealed SFs with response accuracy. This technique allows us to reveal the difference between the groups for each SF in each time frame, and to settle major issues such as whether ASD subjects exhibit a deficit in sampling low SFs, an enhanced sampling of high SFs, or a difference in the time course of SF sampling
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