Visual complexity accentuates picture description deficit in amnesia

Abstract

Objective: A recent study indicates that amnesic patients have difficulties not only in describing past and imagined scenarios, but also in describing pictures that are in full view. This finding suggests that impaired memory hampers descriptions of scenarios more broadly. However, no such impairment in picture description in amnesic patients was observed in a related study. One key methodological difference between these studies was the complexity of the pictures to be described, hinting that picture description differences between amnesic patients and controls might be marked only if pictures are sufficiently complex to tax aspects of memory. Methods: To test this complexity hypothesis, we examined whether differences in picture description between amnesic patients and controls increase with increasing picture complexity (4 levels). As in previous studies, we also assessed our participants’ ability to describe imagined scenarios. Results: Amnesic patients reported significantly fewer elements than did controls when describing pictures and imagined scenarios. The group difference in picture description was significantly larger for complex than simple pictures. Conclusions: although variations in lesion sites might account for the aforementioned cross-study differences in picture description in amnesic patients, our results suggest that, at least in amnesic patients with extra-medial temporal lobe lesions, the complexity of pictures can determine whether or not a (substantial) picture description deficit is observed. We interpret these findings in terms of a narrative construction deficit. We hypothesise that whereas brief narrative can be constructed via non-memory cognitive processes, the construction of more detailed narrative depends upon intact functioning of a temporary memory system such as the episodic buffer. However, future research in patients with confirmed isolated amnesia is required to test this hypothesis further.