ERP Correlates of Episodic and Semantic Memory Judgements In ASD

Background:  

Recognition memory in Autism Spectrum Disorder (ASD) tends to be undiminished, but is characterised by fewer episodic ‘remember’ judgements and more semantic ‘know’ judgements relative to typically developing (TD) individuals (Bowler et al., 2000a, b, 2007). In addition to this, semantic know old-new event related potentials (ERPs) thought to reflect cognitive strategies engaged during recognition, show altered topography in ASD (Massand and Bowler, in prep). However to date, these studies have exclusively used word stimuli and little is known about old-new effects for other types of stimuli in ASD.

Objectives:  

This study investigated the nature of the previously reported differences in the semantic know old-new word repetition effect using nameable line drawings and the Inclusion/Exclusion paradigm.

Methods:  

Fifteen ASD (mean age and FIQ; 38.9 years, 114) and 18 TD (37.2 years, 111) individuals took part in the study. Study stimuli were coloured nameable line drawings (Cycowicz et al., 2001) and were presented in either red or blue. At test studied stimuli and new stimuli were presented in black. Item memory (memory for the line drawing alone), and Source memory (Target/Other judgement; memory for the line drawing and its presentation colour) was tested. ERPs were recorded from 32 scalp sites and averaged according to (correctly) recognised, Items and Targets versus correctly rejected New stimuli.

Results:  

The behavioural data revealed that Item recognition was better than Target recognition in both groups (F(2,30)=39.47, p<.01). The ASD group demonstrated marginally diminished recognition performance (F(1,31)=3.64, p=.07).

Early old-new effects associated with item recognition in the TD group were diminished in the ASD group.

ERPs for Target and Non-target recognition showed significantly enhanced late posterior negativity in the TD group, associated with episodic recollection of contextual information (Cycowicz et al., 2001). ASD individuals demonstrated late posterior negativity for Item, Target and Non-target recognition suggesting that this effect was not specific to Episodic recollection of contextual information.

TD individuals demonstrated an enhanced late anterior positivity associated with episodic recollection (Squire and Knowlton, 2000; Cycowicz et al., 2001; Wolk et al., 2009). ASD individuals demonstrated anterior positivity during recognition, however this ERP was not modulated by latency (was not enhanced in the later time window).

Conclusions:  

Episodic memory, although quantitatively diminished in ASD is in large part qualitatively preserved. This suggests that the phenomenological experience of (residual) Remember judgements is preserved in ASD. These findings provide further evidence for differing functional neurophysiology underlying semantic memory judgements in ASD.