Our study investigated fixation frequency and duration during an EFT in ASD and TD children. Consistent with prior EFT research, we found accelerated RT in individuals with ASD. Similar to Manjaly et al. (2007)
, we observed interaction between group and condition. However, whereas Manjaly et al. found equivalent RT in the EFT and slower RT in the baseline condition for ASD as compared to TD individuals, our ASD group was significantly faster at the EFT and equivalent in the baseline condition, compared to TD children. This pattern of superior performance in ASD on tasks in which processing of global features impedes performance (test trials), and equivalent performance in tasks for which a local processing strategy is no longer advantageous (baseline trials), is consistent with a model of enhanced perceptual processing, as proposed by Mottron et al. (2006)
Analysis of eye-movements revealed that while ASD and TD groups did not differ in fixation frequency during either test or baseline trials, or in the frequency with which they fixated on the target or figure, fixation durations were significantly shorter in children with ASD across all trial types. To further elucidate differences, fixation durations were analyzed based on location. Only fixations on the complex figure, not those located on the target shape, were significantly shorter in ASD compared to the TD group, suggesting that any perceptual advantage that may be reflected in shorter fixation durations occurred while ASD children attended to the complex figure.
Fixations were further grouped into first and final fixations. First fixations were significantly shorter for ASD compared to TD children, suggesting that the ASD group was faster at initially encoding stimulus features and planning initial saccades. In addition, first fixation durations were significantly longer in test compared to baseline conditions for TD children, but not for children with ASD, suggesting that children with ASD perceived the target in both test and baseline condition as equally salient. This result is congruent with the WCC theory. If children with ASD perceive the local features of the complex figure, as opposed to the global whole, latency to initiate first saccade should be similar in both test and baseline trials. Similarly, Jarrold et al. (2005)
showed that while RT for an EFT was correlated with conjunctive search slopes in TD individuals, EFT RT was correlated with feature search slopes in individuals with ASD, indicating that targets may ‘pop out’ for individuals with ASD.
While similar initial fixation durations for test and baseline conditions in the ASD group may be indicative of a local processing bias associated with the WCC theory, shorter durations for all fixations, including first and final fixations, suggests that individuals with ASD are quicker at discriminating the stimulus at each fixation. These results indicate that enhanced lower-level perceptual processes may also play a role in ASD EFT advantage.
In summary, our findings suggest that the EFT advantage in children with ASD arises from both local perception of global figures and enhanced discrimination. Previous fMRI studies have demonstrated decreased involvement of frontal cortices during EFT in ASD (Lee, Foss-Feig, Henderson, Kenworthy, Gilotty, Gaillard, et al., 2007
; Ring, Baron-Cohen, Wheelwright, Williams, Brammer, Andrew, et al., 1999
), indicative of reduced need to suppress global perception, and increased right occipital involvement in ASD (Manjaly et al., 2007
; Ring et al., 1999
), which may represent enhanced processing of local features. Our findings are consistent, providing partial support for both WCC and EPF models.