Feedback and stimulus-offset timing effects in perceptual category learning

Abstract

We examined how feedback delay and stimulus offset timing affected declarative, rule-based and procedural, information-integration category-learning. We predicted that small feedback delays of several hundred milliseconds would lead to the best information-integration learning based on a highly regarded neurobiological model of learning in the striatum. In Experiment 1 information-integration learning was best with feedback delays of 500ms compared to delays of 0 and 1000ms. This effect was only obtained if the stimulus offset following the response. Rule-based learning was unaffected by the length of feedback delay, but was better when the stimulus was present throughout feedback than when it offset following the response. In Experiment 2 we found that a large variance (SD=150ms) in feedback delay times around a mean delay of 500ms attenuated information-integration learning, but a small variance (SD=75ms) did not. In Experiment 3 we found that the delay between stimulus offset and feedback is more critical to information-integration learning than the delay between the response and feedback. These results demonstrate the importance of feedback timing in category-learning situations where a declarative, verbalizable rule cannot easily be used as a heuristic to classify members into their correct category.

Figure 1

Two category structures used in the Experiment along with sample stimuli from each category. (a) A unidimensional rule-based structure, and (b) a two-dimensional information integration structure. Actual stimulus size was 200 × 200 pixels presented on a screen with resolution set at 1024 × 768. Participants sat approximately two feet from the screen.

Figure 2

Response patterns of participants who are best fit by models assuming rule-based or information-integration strategies in the information-integration task. Stimuli that were classified into Category 1are represented by black diamonds and stimuli that were classified into Category 2 are represented by white squares. (a) Responses for a participant whose data were best fit by a frequency rule model. (b) Responses for a participant whose data were best fit by a conjunctive rule model. (c) Responses for a participant whose data were fit by a different type of conjunctive rule model. (d) Responses for participants whose data were best fit by an information-integration model.

Figure 3

Proportion of correct responses for participants in each condition in Experiment 1 during the final block of trials. (a) Accuracy for participants performing a rule-based task. (b) Accuracy for participants performing an information-integration task.

Figure 4

Proportion of correct responses during the final block of trials.

Figure 5

Final block accuracy for participants in each condition in Experiment 3. The numbers for each condition listed along the x-axis indicate the stimulus offset delay followed by the corrective feedback delay.