Memory functioning in Autism Spectrum Disorder (ASD) follows a characteristic pattern, including good rote memory (Kanner, 1943) and cued recall (Bowler, Matthews & Gardiner (1997). Impairments have been demonstrated in the free recall of semantically related items (Tager-Flusberg, 1991), and the recognition of combinations of features (Bowler, Gardiner & Gaigg, 2008). This suggests a difficulty with relational binding - the ability to encode items and events, and the relationships between them, to allow for adaptive use of the information, which is thought to be mediated by the hippocampus (Eichenbaum, 2000).
Hippocampal function can be assessed using a novelty preference paradigm. When presented with a single item (familiarisation phase) then after a short interval, that item is presented alongside a new item (recognition phase), hippocampally-damaged participants will tend to show a novelty preference only if the background on which the items are presented stays the same between familiarisation and recognition (Pascalis et al., 2009). This indicates that when the background changes, the familiar stimulus is perceived as new, due to impaired relational binding. The current study hypothesises that, since the patterning of memory in ASD is consistent with impaired hippocampal function, the same pattern of results will be demonstrated here.
20 participants with a diagnosis of ASD and 17 typically developed (TD) individuals were matched on age and full scale IQ. Replicating Pascalis et al.’s paradigm, a single item was presented on a patterned background (familiarisation phase), after which two items were presented together, one of which was the familiar stimulus, and one new item, either on the same or different background (recognition phase). Eye movements were measured using a head-mounted eye tracker.
No significant difference was found between the groups in the total length of looking time during the recognition phase (same: t(35) = .17, p > .05; different: t(35) = .48, p > .05), indicating that any differential looking behaviour relating to novelty preference cannot be explained by differences in the amount of time spent exploring the stimuli. Analysis of novelty preference showed no significant main effects of either context (F(1,35) = 3.86, p > .05) or group (F(1,35) = 0.00, p > .05), as well as no significant interaction between the two factors (F(1,35) = .71, p > .05). In addition to these findings, novelty preferences exhibited by each group were found to be significantly above chance in both conditions (TD group, same: t(16) = 4.25, p < .001; different: t(16) = 3.30, p < .005. ASD group, same: t(19) = 4.20, p < .001; different: t(19) = 2.54, p < .05).
The findings indicate that, despite a similar patterning of memory to patients with hippocampal damage, individuals with ASD have intact hippocampal function on this task. Alternatively, the findings may support the idea of Chalfonte & Johnson (1996), that relational binding should be viewed in terms of combinations of features of an episodically-defined event, rather than item-context associations.
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