Inhibition in autism: Evidence of excessive inhibition -of -return

Evidence of excessive response inhibition has been reported in autism, despite spared negative priming (NP; Bryson, 1995). These findings were explored systematically in two experiments. First, previous findings were extended to determine whether Bryson's null group effects for NP would hold when location- and object-based NP were examined separately. Second, two competing interpretations (motoric vs. attentional) of the RI finding were explored. Experiment I used a spatial localization task in which targets were selected from nontargets on the basis of colour. Results replicated and extended Bryson's report of intact (location-based) NP: The magnitude of location- and colour-based NP effects did not differ significantly between autistic participants and controls matched on baseline reaction time (RT). A trend toward fewer errors and colour-facilitation in the group with autism, however, suggests that participants with autism may process colour information somewhat more automatically than controls. Experiment 2 used a Go-NoGo spatial localization task, in which stimulus location and identity were systematically manipulated. By comparing responses to stimuli that followed Go versus NoGo primes, evidence for a selective excess of location-based Inhibition-of-Return (IOR) in autism emerged. Results support the distinction, made by others, between location- and object-based inhibition, and are consistent with claims that the former may be stronger and/or more basic than the latter. The finding of excessive IOR in autism is discussed with respect to the putative mechanisms underlying this observed inhibitory deficit. Future research directions and clinical applications are also considered.