Mental Time Travel in ASD: Assessing Episodic Memory and Episodic Future Thinking

Background: Recent research has revealed that episodic memory (remembering past experiences) and episodic future thinking (imagining future experiences) rely on the same underlying neuro-cognitive system (Spreng et al., 2009, J Cognitive Neurosci, 21, 489-510).  Numerous studies have demonstrated that individuals with ASD show impaired episodic memory (see Lind, 2010, Autism, 14, 430-456) but Lind and Bowler (2010, J Abnorm Psychol, 119, 896-905) were the first researchers to establish that individuals with ASD show impairments in both episodic memory and episodic future thinking.

Objectives: The current study was designed to further explore the nature of ASD-specific impairments in episodic memory and episodic future thinking.  

Methods: Eighteen intellectually high-functioning adults with ASD (diagnoses confirmed using ADOS) and 18 age- and IQ-matched comparison participants undertook two sentence-completion tasks designed to assess memory and future thinking, respectively (Anderson & Dewhurst, 2009, Memory, 17, 367-373).  In the Past Events Task, participants completed 11 past-oriented sentence stems such as “When I think back to…”  In the Future Events Task, participants completed 11 future-oriented sentence stems such as “Next year…”  Each sentence was scored on a scale from 0 to 4 according to degree of specificity (0 = omissions; 1 = semantic associates; 2 = extended events; 3 = categoric [reoccurring] events; 4 = specific events). Scores across the 11 sentences were then summed to produce a “total” score for each task (total score range: 0 to 44).  It was predicted that the sentences produced by individuals with ASD would be significantly less specific (more overgeneral) in both the Past Events and Future Events Tasks, reflecting impaired episodic memory and episodic future thinking, respectively. 

Results: The ASD group obtained slightly lower scores than the comparison group in both the Past Events Task (ASD: M = 28.22, SD = 8.58; comparison: M = 29.06, SD = 2.90) and the Future Events Task (ASD: M = 22.83, SD = 7.83; comparison: M = 24.61, SD = 5.53).  A 2 (Group: ASD/comparison) x 2 (Task: Past Events/Future Events) mixed ANOVA revealed no significant main effect of Group, F(1,34) = 0.42, p = .52; a significant main effect of Task, F(1,34) = 31.12, p < .001; and no significant interaction effect, F(1,34) = 0.29, p = .60. 

Conclusions: In contrast with previous research and contrary to predictions, results indicated that participants with ASD and comparison participants showed similar levels of episodic memory and episodic future thinking.  While it is possible that these results are an accurate reflection of the habitual levels of episodic memory and episodic future thinking in these groups, an alternative explanation is feasible.  Whereas previous studies have explicitly asked participants to try to recall/imagine specific events, the current study imposed no such constraints.  This aspect of the method may have elevated the proportion of general (i.e., non-episodic) memories and simulations in the comparison group, thereby masking difficulties in episodic memory and episodic future thinking in the ASD group.  Therefore, this study has important implications for how we assess episodic memory and episodic future thinking in ASD.