Age-related impairments in active learning and strategic visual exploration

Abstract

Old age could impair memory by disrupting learning strategies used by younger individuals. We tested this possibility by manipulating the ability to use visual-exploration strategies during learning. Subjects controlled visual exploration during active learning, thus permitting the use of strategies, whereas strategies were limited during passive learning via predetermined exploration patterns. Performance on tests of object recognition and object-location recall was matched for younger and older subjects for objects studied passively, when learning strategies were restricted. Active learning improved object recognition similarly for younger and older subjects. However, active learning improved object-location recall for younger subjects, but not older subjects. Exploration patterns were used to identify a learning strategy involving repeat viewing. Older subjects used this strategy less frequently and it provided less memory benefit compared to younger subjects. In previous experiments, we linked hippocampal-prefrontal co-activation to improvements in object-location recall from active learning and to the exploration strategy. Collectively, these findings suggest that age-related memory problems result partly from impaired strategies during learning, potentially due to reduced hippocampal-prefrontal co-engagement.

Keywords: active learning; age-related memory impairment; aging; hippocampus; memory; prefrontal cortex; revisitation; vicarious trial-and-error behavior.

FIGURE 1

Overview of the behavioral paradigm for Experiments 1 and 2. (A) In both experiments, subjects studied objects arranged in a 5 × 5 grid. Objects were viewed through a window that permitted clear viewing of only one object at a time. The figure depicts the window moving across the top row of objects, to reveal an insect, and ring, a bicycle, and a bird. Window movements were controlled by the subject in the active learning condition, and were prerecorded from the previous subject and merely watched in the passive learning condition, as described in the text. (B) In Experiment 1, passive window movements were yoked to active window movements within younger subjects, and the passive window movements from younger subjects were also delivered to older subjects. Older and younger subjects controlled window movements in the active condition. (C) In Experiment 2, active and passive window movements were yoked within older subjects only.

FIGURE 2

Effects of age on object-location recall but not object recognition in Experiment 1. (A) Mean placement error for object-location recall in Experiment 1. (B) Mean performance (discrimination sensitivity) for object recognition in Experiment 1. Note that lower bars indicate better performance for object-location recall (less placement error), whereas higher bars indicate better performance for object recognition (higher discrimination sensitivity). Error bars depict standard error.

FIGURE 3

Effects of age on spontaneous revisitation strategy in Experiment 1. (A) The overall proportion of transitions categorized as involving spontaneous revisitation is shown for older and younger adults. (B) The overall proportion of transitions are broken down as a function of the number of objects within each revisitation event (two to six objects) on the right. This shows the distribution of revisitation “path lengths” in each age group, irrespective of overall differences in the amount of revisitation (i.e., the overall amount is given in Panel A, and Panel B shows the proportion of the total involved in each path length separately for each age group). Back-and-forth transitions are shown as arrows on the grid. Error bars depict standard error.

FIGURE 4

Object-location recall and object recognition in Experiment 2. (A) Mean placement error for object-location recall in Experiment 2. (B) Mean performance (discrimination sensitivity) for object recognition in Experiment 1. Data from younger subjects from Experiment 1 are shown to facilitate comparison with Figure 2. Note that lower bars indicate better performance for object-location recall (less placement error), whereas higher bars indicate better performance for object recognition (higher discrimination sensitivity). Error bars indicate standard error.

FIGURE 5

Spontaneous revisitation strategy in Experiment 2. (A) The overall proportion of transitions categorized as involving spontaneous revisitation. (B) The overall proportion of transitions are broken down as a function of the number of objects within each revisitation event (two to six objects), as in Figure 3B. Back-and-forth transitions are shown as arrows on the grid. Data from younger subjects from Experiment 1 are shown to facilitate comparison with Figure 3. Error bars depict standard error.