Abstract

Categorization and decision making are combined in a task with photorealistic faces. Two different types of face stimuli were assigned probabilistically into one of two fictitious groups; based on the category, faces were further probabilistically assigned to be hostile or friendly. In Part I, participants are asked to categorize a face into one of two categories, and to make a decision concerning interaction. A Markov model of categorization followed by decision making provides reasonable fits to Part I data. A Markov model predicting decision making followed by categorization is rejected. In Part II, a no-parameter model predicts decisions using categorization and decision responses collected in separate trials, suggesting that Part 1 results are not an artifact of the presentation of categorization and decision questions within a single trial. Decisions concerning interaction (defensive/friendly) appear to be based on information from the category decision, and not from the face stimuli alone