Time and space order effetcs in timed brightness discrimination of paired visual stimuli

Despite the considerable import of both response probability and response time for testing models of choice there is a dearth of chronometric studies of time- and space-order effects in discrimination of paired visual stimuli. In this study, systematic asymmetries in discriminating the brightness of paired visual stimuli are examined by way of binary response probability scaled in terms of log-odds ratios, as well as by signed response speed (i.e., the inverse of response time with the sign of the judged difference). For two stimuli separated by a time interval, psychometric and chronometric results revealed equivalent time-order effects, and when presented simultaneously, separated by a spatial interval, no effects of space order were found. Implications of these findings for random walk and diffusion models of sensory discrimination are discussed.