Future research might elucidate whether alterations in early cortical areas directly affect processing in upstream areas within the dorsal processing stream. In addition to studying visual cortical mapping, the current study also aimed to assess differences in low-level visual processing in individuals with an ASD. The goal was to use an established, sensitive and objective probe of magnocellular processing, and in this way to resolve the question of whether differences in magnocellular function might account for some of the visual processing differences that are so commonly observed in this group. The resulting data strongly
favor a model of visual function selleck kinase inhibitor in ASD in which magnocellular function is intact. Magnocellular-biased visual responses (as measured using learn more the Magno VESPA) were highly similar to, and did not differ significantly from, those recorded in a typically developing control group for centrally presented stimuli. Examination of scalp topographies and source localization data supported successful biasing of the
dorsal visual stream, indicating that our measure should be sensitive to magnocellular processing differences were they present. A caveat should be made about the VESPA technique used here to examine visual processing. The VESPA estimates the brain’s impulse response function assuming a linear relationship between brain activity and stimulus contrast. Glutamate dehydrogenase Non-linear aspects of cortical processing and processing of stimulus features other than contrast are therefore not captured by this version of the technique. This is a limiting factor for inferences drawn from our results. For example, it is known that the firing rate of neurons in early visual cortex increases in a sigmoidal fashion with increasing contrast (Reich et al., 2001). Therefore, for both the Magno (~70% of the contrast values ranging between 3 and 7%) as well as the Full-Range VESPA (~70%
of the contrast values between 30 and 70%), the contrast response in early visual cortex can be approximated by a linear function (Albrecht & Hamilton, 1982). While less accurate eye movement control has commonly been described in autism, at least one study has reported no differences in a visually guided saccade task (Minshew et al., 1999). Therefore, it is possible that not all participants with ASD exhibit less accurate saccadic eye movements. We did not perform a separate saccadic eye movement task and therefore could not correlate saccadic eye movement accuracy with electrophysiological responses, an obvious avenue for future study. A number of clinical case reports suggest that the fovea in ASD might be especially hyper-sensitive (Bogdashina, 2003; Gerrard & Rugg, 2009). That is, ASD individuals sometimes report averting direct gaze to alleviate discomfort caused by a sense of over-stimulation from complex or moving stimuli, thereby favoring the use of parafoveal retinal areas.