Recognition memory in non intellectually disabled individuals with ASD tends to be undiminished compared to TD individuals (Bowler et al., 2000), however the question remains of whether the processes underlying recognition in ASD result from similar or different mechanisms than in TD. Behavioural studies have used the Remember/Know paradigm to assess the contributions of the episodic and semantic memory systems to recognition. Compared to TD individuals, people with ASD show diminished episodic Remember experiences but undiminished semantic Know responses (Bowler et al., 2000a; 2000b and Bowler and Gaigg, 2007).
Event-related potentials (ERPs) were used to record the brain activity during item recognition and Remember/Know judgements in a sample of ASD and age and IQ-matched TD adults. ERP studies in TD individuals have shown that that correctly recognised words show enhanced positive potentials relative to new words - the ‘Old-New ERP effect’ (Rugg and Curran, 2007). The effect is thought to reflect the contribution of both the episodic Remember responses and semantic Know responses (parietal positivity 400-800ms for remember responses and earlier frontal positivity 300-500ms for know responses, Curran et al., 2006).
The early Old-New effect (300-800ms), the late Old-New effect (800-950ms) for Remember and Know judgements were compared across groups to assess the qualitative similarity of Remember responses in the ASD group to those of the TD group.
Fourteen ASD (mean age and VIQ; 36.2years, 113) and 19 TD (36.5 years, 111) individuals participated in a Remember/Know recognition memory task. ERPs were recorded from 32 scalp sites and averaged according to correctly recognised words judged as Remember or Know versus correctly rejected new words.
Behavioural data revealed no significant difference in overall recognition between the two groups, F(1,31)=1.67, n.s. There was a trend towards less Remembering and more Knowing in the ASD group compared to the TD group (in line with existing findings).
Early Old-New effects (300-800ms) did not differ between groups, F(1,31)=0.95, n.s., however the late Old-New effect for overall recognition was significantly attenuated from 800-950ms in the ASD group, F(1,31)= 9.29, p<.01. Remember-New differences in this time window were significantly diminished in the ASD group compared to the TD group (F(1,31)=6.89, p<.05). There were no differences in the Know-New ERPs from 800-950ms across groups (F(1,31)=1.61 n.s.). Both ASD and TD individuals’ Remember responses were characterised by a positive Remember-New effect from 400-800ms (F(1,31)=0.01, n.s.). The results demonstrated that TD individuals had a residual Remember positivity from 800-950ms, which was absent in the ASD group.
The findings suggest that the Remember component of overall recognition in ASD is in large-part qualitatively similar to that of TD individuals, reflecting existing behavioural work. However the late (800-950ms) group difference for Remember responses may reflect processes that contribute to a quantitative diminution in overall rates of remembering in the ASD group. This has implications for our understanding of the operation of the episodic memory system of individuals with ASD.