The time course of explicit and implicit categorization

Abstract

Contemporary theory in cognitive neuroscience distinguishes, among the processes and utilities that serve categorization, explicit and implicit systems of category learning that learn, respectively, category rules by active hypothesis testing or adaptive behaviors by association and reinforcement. Little is known about the time course of categorization within these systems. Accordingly, the present experiments contrasted tasks that fostered explicit categorization (because they had a one-dimensional, rule-based solution) or implicit categorization (because they had a two-dimensional, information-integration solution). In Experiment 1, participants learned categories under unspeeded or speeded conditions. In Experiment 2, they applied previously trained category knowledge under unspeeded or speeded conditions. Speeded conditions selectively impaired implicit category learning and implicit mature categorization. These results illuminate the processing dynamics of explicit/implicit categorization.

Keywords: Category learning; Cognitive neuroscience; Explicit cognition; Implicit cognition; Response deadlines.

Figure 1

Illustrative tasks. Two categorization tasks, showing the position in XY space of Category A exemplars (gray symbols) and Category B exemplars (black symbols).

Figure 2

Illustrative stimuli. The stimuli were unframed rectangles containing green illuminated pixels. Box Size (Dimension X) and Box Density (Dimension Y) had 101 levels (Levels 0 to 100) that were concretized into stimuli using formulae specified in the text. Shown are: Stimulus 0 0 (small-sparse), Stimulus 100 0 (big-sparse), Stimulus 0 100 (small-dense), and Stimulus 100 100 (big-dense).

Figure 3

A,B. Backward learning curves for RB-unspeeded and II-unspeeded participants in Experiment 1, constructed as described in the text.

Figure 4

Average proportion correct over the first 13 20-trial blocks for RB-unspeeded, RB-deadline, II-unspeeded, and II-deadline conditions in Experiment 1. The averages include the data from 117 out of 124 participants who completed at least 260 trials.

Figure 5

The decision bounds that provided the best fits to the last 100 category responses of participants in the RB-unspeeded, RB-deadline, II-unspeeded, and II-deadline conditions in Experiment 1.

Figure 6

Training and testing performance in Experiment 2. A. Average proportion correct over the 20-trial training blocks for participants in the RB and II tasks. B. Average proportion correct over the 20-trial testing blocks for unspeeded and deadline phases in the RB and II tasks.

Figure 7

A,B. The decision bounds that provided the best fits for the last 60 trials of training for RB and II tasks in Experiment 2.

Figure 8

The decision bounds that fit best categorization responses in the testing trials of the RB-unspeeded, RB-deadline, II-unspeeded, and II-deadline conditions in Experiment 2.