Age-related changes in visual encoding strategy preferences during a spatial memory task

Abstract

Ageing is associated with declines in spatial memory, however, the source of these deficits remains unclear. Here we used eye-tracking to investigate age-related differences in spatial encoding strategies and the cognitive processes underlying the age-related deficits in spatial memory tasks. To do so we asked young and older participants to encode the locations of objects in a virtual room shown as a picture on a computer screen. The availability and utility of room-based landmarks were manipulated by removing landmarks, presenting identical landmarks rendering them uninformative, or by presenting unique landmarks that could be used to encode object locations. In the test phase, participants viewed a second picture of the same room taken from the same (0°) or a different perspective (30°) and judged whether the objects occupied the same or different locations in the room. We found that the introduction of a perspective shift and swapping of objects between encoding and testing impaired performance in both age groups. Furthermore, our results revealed that although older adults performed the task as well as younger participants, they relied on different visual encoding strategies to solve the task. Specifically, gaze analysis revealed that older adults showed a greater preference towards a more categorical encoding strategy in which they formed relationships between objects and landmarks.

Fig. 1

a Experimental protocol; b, c and d Virtual environment and stimuli for the experimental task, Blue and Green cameras represent the possible virtual cameras positions for the Learning and Test phase, respectively. Examples of possible object cluster layouts are shown in b (No Landmarks), c (Uninformative Landmarks) and d (Informative Landmarks). The left panel shows a survey perspective of the example trials, indicating the rotation of the camera (Orange arrow) and swapping of the two object clusters (Black arrow) in Swap trials (b, c). The middle and right panels show the two corresponding snapshots for the learning and test phases, respectively. In b and d there is a 30° perspective shift, to the left and right respectively. In c there is no perspective shift. The black arrows in the right panel (b, c) indicate which clusters were swapped on the test stimuli

Fig. 2

Bar plots of accuracy values for a significant main effect of a Perspective Shift, b Manipulation, and significant interactions c between Manipulation and Perspective Shift and d Interaction between Age Group, Manipulation and Perspective Shift with a mean (solid line) and 95% CIs (grey shaded area) with individual data points and violin plots behind

Fig. 3

Bar plots of Response Times values for significant main effects of A: Age Group B: Perspective Shift C: Landmark Type (significant only for the Informative Landmark Type) D: Manipulation and interactions between E: Age Group and Manipulation F: Perspective Shift and Manipulation G: Landmark Type and Condition (significant only for Landmark Type (Informative): Manipulation (Swap)) H: Age Group, Manipulation and Perspective Shift with mean (solid line) and 95% CIs (grey shaded area) with individual data points and violin plots behind

Fig. 4

Bar plots for Response Bias as a function of Age Group, Landmark Type and Perspective Shift with mean (solid line) and 95% CIs (grey shaded area) with individual data points and violin plots behind. Stars indicate response bias significantly different from 0 (1 star [p < 0.05], 2 stars [p < 0.01] and 3 stars [p < 0.001])

Fig. 5

Heatmaps representing number of fixations as a function of age group and landmark type

Fig. 6

Scatter Plot between Dwell Time on the top IA and Accuracy as a function of Landmark Type with regression line and CI (shaded area)