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Perceptual closure (Pc) refers to the neural processes responsible for filling-in of missing information that enable object-recognition under partial viewing conditions. Event-related potential (ERPs) studies showed that Pc is not an all-or-none phenomenon but is achieved gradually with progressively less fragmented images until enough visual attributes are present. Given that autism is typically associated with a detail-oriented visual processing style, one could argue that object recognition might rely on different perceptual mechanisms in this condition.
Objectives:
Track the neuronal mechanisms underlying Pc during object identification in High Functioning Autism (HFA) and Asperger Syndrome (AS).
Methods:
11 Adults with HFA, 11 with AS and 11 matched control subjects were shown line-drawing objects and non-objects (scrambled objects) presented according to the ascending method of limits; each picture was gradually revealed in a sequence of seven fragmentation levels, from the most to the least fragmented, up to complete version. EEG was recorded while participants indicated at each fragmentation level if they recognized or not the object. ERPs were averaged at object identification level, at 1-prior and 2-prior identification levels.
Results:
Controls identified objects at a more fragmented level than HFA and AS did. Spatio-temporal analysis of ERPs revealed differential electrical brain activity associated to Pc in the three groups of subjects. In controls, occipito-temporal P2 and frontal/centroparietal late ERPs gradually increased in amplitude with levels of object identification. However, in HFA and AS, early visual P1 showed amplitude differences between levels of identification. Later ERPs showed different patterns of identification level effects suggesting that Pc in autistic participants was achieved in an all-or-none fashion.
Conclusions:
Behavioral data suggest that Pc in autism relies more on the amount of local visual information than in typical subjects. ERP data indicate that object recognition in autism is mainly stimulus-driven and that Pc does not operate in a gradual manner.