The ERP Old-New Word Repetition Effect in Autism Spectrum Disorder: Abnormal Neural Functioning Underlying Typical Recognition Memory Performance

Background:

Although recognition memory in ASD (Autism Spectrum Disorder) tends to be undiminished compared to typically developing individuals (Bowler et al., 2000), it is still unknown whether memory processes in ASD rely on similar or qualitatively different mechanisms than those underlying recognition memory in typical development. One way to investigate this is to record online brain electrical activity during item recognition at test in ASD individuals and age- and IQ-matched typically developing individuals. Previous event-related potential (ERP) studies have shown that recognition of previously studied words is indexed by enhanced positive potentials of words that are correctly identified as ‘old’ from an earlier study phase, compared to words correctly identified as ‘new’ (known as old-new ERP effect). This effect is argued to reflect cognitive strategies engaged during recognition of an item and the recall of its contextual information.

Objectives:

The objective of the study was to investigate the ERP old-new recognition effect in adults with autism spectrum disorder.

Methods:

Data are currently available for 8 adults with ASD (mean age of 25.5 years and mean VIQ of 101) and 6 typical adults (mean age of 25.4 years and mean VIQ of 99). Expected group sizes are 15 participants in each group. Participants engaged in a yes/no recognition task, in which they studied 6 blocks of 50 words. After each block they were tested on the 50 study words and 25 lures. Study and test words comprised 450 French nouns (300 targets and 150 lures) extracted from the Baudot (1992) French dictionary. Matching was done on frequency, imagability rating and number of syllables. Starting letters were equated for every 1 in 4 words between target and lure. ERPs were collected from 64 scalp sites and averaged according to correctly recognized old words and correctly rejected new words.

Results:

Behavioural data revealed no overall differences in recognition between the ASD group and comparison group (corrected hit-rate proportions of 0.54 and 0.60 and standard deviations of 0.19 and 0.27 respectively. F (1, 12) = 0.124). ERP data revealed diminished Old-New ERP effects in the ASD group when compared to the typically developing group, mainly at the central and fronto-central scalp sites. In addition, the old-new effects were shorter-lasting in ASD than in typical participants. Indeed, the onset of the old-new ERP differences was approximately 300ms for both groups, ending approximately 700ms in the ASD group and lasting well on into 1700ms for the comparison group.

Conclusions:

The enhanced ERP positivity for old words in typical individuals is assumed to reflect the engagement of cognitive strategies to aid the recognition of an old word (Cycowicz et al., 2001). The short lasting and diminished old-new ERP effect in ASD found here, indicates that ASD individuals do not utilise cognitive strategies in a similar manner to typically developing individuals. This study is the first to demonstrate abnormal old-new ERP repetition effects in ASD.