Further evidence for episodic memory difficulties in individuals with ASD

Background: Individuals with ASD experience difficulties with episodic memory and memory for temporal order but not with semantic memory. Healy et al. (2000) demonstrated episodic/semantic memory differences by asking typical individuals to re-order alphabetical lists of the names of US presidents either in their historical order (semantic task) or in the pseudo-random order in which they had just studied them (episodic task). Enhanced pre-recency effects were found for the semantic but not the episodic task.  We predicted no difference between ASD and typical groups on the semantic memory task and diminished serial order reconstruction on the episodic task.

Objectives: To compare serial reconstruction memory for episodically and semantically ordered lists of items high-functioning adults with ASD and typical comparison participants.

Methods: 23 individuals with ASD and 24 verbal ability matched typical individuals took part. For the episodic task, participants were asked to try to remember seven lists of seven historical figures presented in random order (e.g. Archimedes, Churchill, Columbus, Napoleon…). There was no study phase for the semantic task. Participants were then given the names in alphabetical order and asked to put them in the order in which they had studied them, or, in the semantic task, to place them in their correct historical order.

Results: Both groups showed similar serial position curves for the semantic task, but the ASD group showed diminished reconstruction accuracy on the episodic task, which was confirmed by a significant Task x Group x Serial Position quadratic trend (F (1,45) = 4.25, p < .05).

Conclusions: The diminished performance on the episodic but not the semantic task for the individuals with ASD confirms their particular difficulty memory for the order of occurrence of personally-experienced events.