Age effects on category learning, categorical perception, and generalization

Abstract

Age deficits in memory for individual episodes are well established. Less is known about how age affects another key memory function: the ability to form new conceptual knowledge. Here we studied age differences in concept formation in a category-learning paradigm with face-blend stimuli, using several metrics: direct learning of category members presented during training, generalisation of category labels to new examples, and shifts in perceived similarity between category members that often follow category learning. We found that older adults were impaired in direct learning of training examples, but that there was no significant age deficit in generalisation once we accounted for the deficit in direct learning. We also found that category learning affected the perceived similarity between members of the same versus opposing categories, and age did not significantly moderate this effect. Lastly, we compared traditional category learning to categorisation after a learning task in which a category label (shared last name) was presented alongside stimulus-specific information (unique first names that individuated category members). We found that simultaneously learning stimulus-specific and category information resulted in decreased category learning, and that this decrement was apparent in both age groups.

Keywords: Aging; associative memory; categorical perception; category learning; generalisation.

Figure 1.

Example face-blend stimuli. Parent faces on the leftmost side are designated “category relevant parents” as these parents determined family membership—Miller, Wilson, or Davis—during training and generalization. Parent faces across the top are designated “category irrelevant parents” as these parents introduced physical similarity among faces but did not determine categories. Three irrelevant parents were used for training. An additional 14 irrelevant parents were used for the creating new faces used for generalization. Parent faces were never viewed by participants, only the resulting blended faces. The face blending procedure produced pairs of faces that shared a category-relevant parent and belonged to the same family (shared parent and family; example indicated with solid dark grey box), pairs of faces that shared a category-irrelevant parent and belonged to different families (shared parent only; example indicated with dashed dark grey box). Non-adjacent pairs did not share a parent or a family name (example indicated with light grey boxes).

Figure 2.

Task procedure. Participants in all groups first passively viewed all nine training stimuli once prior to any experimental task. All participants also rated the similarity of all possible pairs of faces before and after the training phase. Participants were randomly assigned to complete either feedback-based or paired-associate training. In feedback-based training, participants were presented with a face, responded which family they thought the face belonged to, were told whether they were correct or wrong, and told the correct family label. In paired-associate training, participants were shown a face along with its full name and made a prospective memory judgment (PMJ). Following training and post-learning similarity ratings, all participants completed a cued-recall phase. Those in the paired-associate condition were shown a face and were first asked to recall that person’s first name followed by their family name. Those in the feedback-based condition were only asked to recall the family name, as they were not provided with first name information at any point in the task. Next, all participants completed an old/new recognition task (results not reported here). Lastly, participants completed a surprise categorization task using all faces from the recognition phase and categorized them into the three families.

Figure 3.

Training and cued-recall results. A. Mean categorization accuracy by training block for learning family names in the feedback-based training condition. B. Mean rating of prospective memory by training block for learning full names in the paired-associate training condition. In A and B, young adult means are represented with a solid line. Older adult means are depicted with a dashed line. C. Proportion of family names, first names, and full names recalled in the cued-recall test. Dark grey bars depict means for the feedback-based training group, and light grey bars depict means for the paired-associate training group. Solid bars depict means from young adults, and striped bars depict means from older adults. For A-C, errors bars depict the standard error of the mean across subjects.

Figure 4.

Categorization accuracy. Mean accuracy for training items (dark grey bars) and new items (light grey bars) during the categorization phase. Results are presented separately for each age and training group. Dashed line represents chance performance (33% for three categories). Error bars depict standard error of the mean.

Figure 5.

Pre- and post-training similarity ratings. A. Mean similarity ratings from the pre-training phase. B. Mean similarity ratings from the post-training phase. C. Mean change in similarity rating from the pre- to post-training phases (post-ratings minus pre-ratings). Ratings of pairs of faces sharing a parent and a family name are indicated in dark grey bars, those of pairs sharing a parent only are in medium grey, and those not sharing a parent are in light grey. D. Pre-training (darker grey) and post-training (lighter grey) category bias in similarity ratings. The category bias is computed as the difference in ratings between pairs of faces sharing both a parent and a family name compared to those sharing a parent but not a family name. In the case of the pre-training ratings, the family names are not yet known to participants. Ratings are presented separately for each age and training group. Error bars depict the standard error of the mean.