![]() In the block-design task (BDT), the individual is shown a two-dimensional red and white geometric design. Superior performance has also been demonstrated in tasks relying on low-level perceptual processing like pattern ( Plaisted et al., 1998 b) or grating ( Bertone et al., 2005) discrimination tasks, in discrimination of elementary stimuli differing at the featural level ( Plaisted et al., 2003) and in featural and conjunctive visual search tasks ( Plaisted et al., 1998 a O'Riordan et al., 2001 O'Riordan, 2004 Jarrold et al., 2005).Īmong the large number of visual tasks in which autistic individuals display superior performance, one of the most replicated is the ‘block design’ (this terminology is unrelated to fMRI terminology, where there can be block or event-related designs) subtest of the Wechsler Intelligence Scales (WISC, WAIS: Wechsler, 1981, 1994). This is the case in the embedded figures task ( Shah and Frith, 1983 Jolliffe et al., 1997), the impossible figures task ( Mottron et al., 1999) and the maze-map task ( Caron et al., 2004). ![]() Within the visual modality, the performance of persons with autism on tasks necessitating the detection of visual elements embedded in larger fields has been found to be either more locally oriented ( Shah and Frith, 1983 Jolliffe et al., 1997 Mottron et al., 2003 Lahaie et al., 2006 see Happé, 1999 and Happé and Frith, 2006, for reviews) or enhanced ( Plaisted et al., 1999 O'Riordan et al., 2001 Caron et al., 2004 Pellicano et al., 2005 see Mottron et al., 2006 for a review) when compared with typically developing individuals. ![]() There is accumulating evidence that atypical perception plays a prominent role in the autistic behavioural and cognitive phenotype. ![]() In contrast, superior or typical performance of autistics in tasks requiring global processing is inconsistent with the global-deficit-driven Weak Central Coherence hypothesis and its neurobiological magnocellular deficit counterpart. Locally oriented processing, enhanced performance in multiple tasks relying on detection of simple visual material and enhanced discrimination of first-order gratings converge towards an enhanced functioning and role of the primary visual cortex (V1) in autism. Diminished detrimental influence of perceptual coherence on BDT performance is both sensitive and specific to autism, and superior low-level processing interacts with locally oriented bias to produce outstanding BDT performance in a subgroup of autistic individuals. The HFA-P group showed no differences in performance level or profile in comparison with the gifted BDT-matched group, apart from locally oriented perception. ![]() Neither autistic group displayed a deficit in construction of global representations. Both HFA-P and HFA-NP groups presented with diminished detrimental influence of increasing perceptual coherence compared with their BDT-matched comparison groups. Their performance was compared with that of 8 autistics without a visuospatial peak (HFA-NP), 10 typically developing individuals (TD) and 8 gifted comparison participants with a visuospatial peak (TD-P). In order to explain the cognitive and cerebral mechanisms responsible for the visuospatial peak in autism, and to document its specificity to this condition, a group of eight high-functioning individuals with autism and a visuospatial peak (HFA-P) performed a modified block-design task (BDT subtest from Wechsler scales) at various levels of perceptual cohesiveness, as well as tasks tapping visuomotor speed, global perception, visual memory, visual search and speed of visual encoding. ![]()
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