A comparison of two response time models applied to perceptual matching

Two models, a Poisson race model and a diffusion model, are fit to data fro m a perceptual matching task. In each model, information about the similari ty or the difference between two stimuli accumulates toward thresholds for either response. Stimulus variables are assumed to influence the rate at wh ich information accumulates, and response variables are assumed to influenc e the level of the response thresholds. Three experiments were conducted to assess the performance of each model. In Experiment 1, observers performed under different response deadlines; in Experiment 2, response bias was man ipulated by changing the relative frequency of same and different stimuli. Ln Experiment 3, stimulus pairs were presented at three eccentricities: fov eal, parafoveal, and peripheral. We examined whether the race and diffusion models could fit the response time and accuracy data through changes only in response parameters (for Experiments 1 and 2) or stimulus parameters (fo r Experiment 3). Comparisons between the two models suggest that the race m odel, which has not been studied extensively, can account for perceptual ma tching data at least as well as the diffusion model. Furthermore, without t he constraints on the parameters provided by the experimental conditions, t he diffusion and the race models are indistinguishable. This finding emphas izes the importance of fitting models across several conditions and imposin g logical psychological constraints on the parameters of models.