The effects of grouping on speed discrimination thresholds in adults, typically developing children, and children with autism

Abstract

Adult observers show elevated speed discrimination thresholds when comparing the speeds of objects moving across a boundary compared to those moving parallel to a boundary (Verghese & McKee, 2006)-an effect that has been attributed to grouping processes in conjunction with a prior for smooth motion. Here, we extended Verghese and McKee's (2006) paradigm to typically developing children (n = 35) and children with autism (n = 26) and compared their performance with that of typical adults (n = 19). Speed discrimination thresholds were measured in three conditions: (a) with dots moving parallel to a boundary, (b) with dots moving perpendicular to a boundary, and (c) with dots in each stimulus half moving in orthogonal, oblique directions. As expected, participants had higher speed discrimination thresholds when dots appeared to cross a boundary compared to when dots moved parallel to the boundary. However, participants had even higher thresholds when dots moved in oblique, orthogonal directions, where grouping should be minimal. All groups of participants showed a similar pattern of performance across conditions although children had higher thresholds than adult participants overall. We consider various explanations for the pattern of performance obtained, including enhanced sensitivity for shearing motions and reduced sensitivity for discriminating different directions. Our results demonstrate that the speed discrimination judgments of typically developing children and children with autism are similarly affected by spatial configuration as those of typical adults and provide further evidence that speed discrimination is unimpaired in children with autism.

Can speed be judged independent of direction?

“…We propose, therefore, that the considerable individual differences in psychophysical estimates reflect more than just measurement error. Such individual differences could also help explain previous discrepant results, including those between Verghese and McKee ( 2006 ) and Manning et al ( 2015 ). Generally, studies of speed discrimination may require larger participant samples than the common practice in visual psychophysics.…”

“…Verghese and McKee reported discrimination thresholds that were equally low in the two cases. Manning, Neil, Karaminis, and Pellicano ( 2015 ) used a similar display with adults, typical and autistic children, but did not replicate Verghese and McKee's result; for all three groups, thresholds for the split oblique motions were substantially higher than for the parallel (vertical or horizontal) motions. The interpretation of the results from both these studies is complicated by the fact that as well as difference in the relation between the directions of the motions being compared, the conditions also differed in the axis of motion, which was one of the cardinal axes in the parallel case, but oblique in the “split” case.…”

“…Most of the studies cited above have been based on data from a small number of highly practiced observers. However, there are substantial individual variations in motion discrimination performance (Halpern, Andrews, & Purves, 1999 ; Bosten et al, 2017 ), which may account for discrepancies such as those between the 2–3 observers in each of Verghese and McKee's ( 2006 ) experiments and the larger group in Manning et al ( 2015 ). In the present study we chose to represent such variations, and minimize their effect, by testing a relatively large group of young adult participants who were psychophysically naïve, but were well familiarized with the discrimination task before data was collected for the analysis.…”

The Use of Prior Knowledge for Perceptual Inference Is Preserved in ASD

“…Most illusions also rely on structural priors, and show that such priors are often not very malleable. Despite findings of reduced susceptibility to (some) illusions (Mitchell, Mottron, Soulieres, & Ropar, 2010), several recent studies suggest that structural priors are actually intact in ASD (Croydon, Karaminis, Neil, Burr, & Pellicano, 2017; Manning, Neil, Karaminis, & Pellicano, 2015; Spanò, Peterson, Nadel, Rhoads, & Edgin, 2015).…”

Visual Perception and Reading: New Clues to Patterns of Dysfunction Across Multiple Visual Channels in Developmental Dyslexia

“…68,69 On the contrary, speed discrimination impairments seem to be preserved in, at least, some of these disorders. 70,71 Thus, it seems that speed discrimination deficits may represent more specific motion deficits in dyslexia than coherent motion deficits. Additionally, recent genetic studies showed that some motion deficits, including coherent motion but not speed discrimination, are particularly strong in dyslexic individuals with a deletion in intron 2 of the DCDC2 gene rather than in the whole dyslexic population.…”