Verbal recall in amnesia: Does scene construction matter?

Abstract

The hippocampus plays a critical role in episodic memory and imagination. One theoretical model posits that the hippocampus is important for scene construction, namely, the ability to conjure and maintain a scene-based representation in one's mind. To test one idea put forth by this view, we examined whether amnesia is associated with more severe impairment in memory when the to-be-remembered content places high demands on scene construction. To do so, we examined free recall performance for abstract (i.e., low scene imagery) and concrete, high scene-imagery single words in seven amnesic patients with hippocampal lesions and concomitant scene-construction deficits, and compared their performance to demographically matched healthy controls. As expected, amnesic patients were severely impaired in their free recall performance; however, their impairment did not differ as a function of word type. That is, their impairment was equally severe for words that evoke high versus low scene imagery. These findings suggest that the role of the hippocampus in verbal memory extends to content that does not place high demands on scene construction. Theoretical implications of these findings are discussed.

Keywords: Amnesia; Episodic memory; Hippocampus; Imagery; Medial temporal lobes; Scenes.

Figure 1. Patient Scans.

Note. Structural MRI or CT scans depicting medial temporal lobe (MTL) lesions for 6 of the 7 amnesic participants. The left side of the brain is shown on the right side of the image. CT slices show lesion location for P1 in the axial plane. T1-weighted MRI images depict lesions for P2, P3, P5, and P7 in the coronal and axial plane. T2-flair MRI images depict lesion locations for P6 in the axial plane.

Figure 2. Free recall task.

Note. Overview of the task design, including counterbalancing and performance matching. A distractor task was used to separate sets of lists to provide a break to participants.

Figure 3. Free recall performance in amnesic patients and healthy controls.

Note. Raincloud plots depicting performance in amnesic participants and healthy controls. Black dots and vertical lines represent the mean and standard error of the mean (SEM), respectively. Plots were made using the R tool provided in Allen et al. (2021). Non-transformed data are shown in the figure.