RESPONSE-TIME DISTRIBUTIONS IN MULTIDIMENSIONAL PERCEPTUAL CATEGORIZATION

Three speeded categorization experiments were conducted using separabl e dimension stimuli. The form of the category boundary was manipulated across experiments, and the distance from category exemplars to the c ategory boundary was manipulated within each experiment. Observers com pleted several sessions in each experiment, yielding 300-400 repetitio ns of each stimulus. The large sample sizes permitted accurate estimat es of the response time (RT) distributions and RT hazard functions. An alyses of these data indicated: (1) RT was faster for stimuli farther from the category boundary, and this stochastic dominance held at the level of the RT distributions; (2) RT was invariant for all stimuli th e same distance from the category boundary; (3) when task difficulty w as high, errors were slower than correct responses, whereas this diffe rence disappeared when difficulty was low; (4) small, consistent respo nse biases appeared to have a large effect on the relation between cor rect and error RT; (5) the shape of the RT hazard function was qualita tively affected by distance to the category boundary. These data estab lish a rich set of empirical constraints for testing developing models of categorization RT.