Inattentional Blindness and Perceptual Capacity In Children with An Autism Spectrum Condition

Background:  

Our research examines selective attention in individuals with an Autism Spectrum Condition (ASC) using the Load Theory of Selective Attention and Cognitive Control (Lavie et al 2004). Perceptual load theory suggests that the perception of irrelevant stimuli depends on the perceptual load of task-relevant processing.  At low levels of load, when finite perceptual capacity is not reached, remaining resources ‘spill over’ and irrelevant stimuli are automatically processed; when perceptual load exhausts capacity, irrelevant stimuli are no longer processed. Our previous results showed that as perceptual load (e.g. number of items in a search task) increases, distractor stimuli continue to be processed in adults with ASC but not in controls, suggesting a higher perceptual capacity in adults with ASC (Remington et al 2009).  

The effect of perceptual load on selective attention in typical adults has also been studied using the ‘inattentional blindness’ paradigm. Cartwright-Finch and Lavie (2007) have shown that the awareness of an unexpected task-irrelevant stimulus is significantly reduced by higher perceptual load (e.g. harder discrimination vs. detection). 

Objectives:

This study tested the effects of perceptual load on conscious perception in children with ASC using the ‘inattentional blindness’ paradigm. Previous data suggesting an increased perceptual capacity in ASC has only been reported for adults.

Methods:  

24 children with ASC (mean age 10y 6m) and 38 typically developing children (TD) (mean age 10y, 9m), matched for chronological age and non-verbal ability (Ravens) took part.  The procedure was an adaptation of Cartwright-Finch and Lavie (2007). On each of 7 trials participants observed a brief presentation (100ms) of a cross on a computer screen and were asked to judge which line was longest (vertical or horizontal).  Half the participants in each group were randomly assigned to a high load condition (difficult discrimination – lines similar in length) and half to a low load condition (easier discrimination). On the 7^th trial an unexpected and irrelevant critical stimulus (CS) (a small square) was simultaneously presented, and following the line length judgement participants were asked if they had seen anything else. On a final 8^th trial participants were again shown the cross and the CS together, but instructed only to look for the CS.

Results:  

All children passed the inclusion criteria (detection of CS on 8^th trial and at least 5/7 correct line judgements). TD children showed significantly higher levels of CS detection on the low load vs. the high load condition (X² (1) = 8.105, p=.001) as predicted by load theory, in contrast children with ASC showed equally high CS detection for high and low load conditions (X² (1) = 0.087, p=.768) and a higher detection rate than the TD group overall (X² (1) = 9.851, p=.002)

Conclusions:  

Our data demonstrate that conscious awareness of a task-irrelevant stimulus is reduced by increasing perceptual load in TD children but not in children with ASC.  The results support the hypothesis that individuals with ASC have a higher perceptual capacity than neurotypical controls. We show this effect for the first time in children with ASC.