Testing evidence accrual models by manipulating stimulus onset

Many models of response time assume that subjects accrue stimulus "evidence " samples in time (e.g.. random walk models, counter models). In this paper , the concept of one stimulus dominating another is used to construct a tes t of the whole class of evidence accrual models. For an example of dominanc e, consider stimuli that are presented either virtually instantaneously (st epped) or in a gradually increasing manner (ramped). Ramped stimuli are pre sented such that the ramped portion precedes the stepped onset of stepped s timuli. In this case ramped stimuli dominate stepped stimuli, in this paper the class of evidence accrual models is formalized. It is shown that under appropriate assumptions evidence accrual models do predict more accurate r esponses to dominating stimuli. However, this result does not hold for resp onse latencies. There are anomalous cases where an evidence accrual model ( the accumulator model of Vickers (1970, Ergonomics 13, 37-58)) 13, 37-58)) predicts slower mean correct response latencies to dominating stimuli. It i s shown through extensive computer simulation that these anomalous cases oc cur only when response criteria are so asymmetric that there are exceedingl y extreme response biases. For experiments where response biases are not ex ceedingly extreme, random walk and accumulator models predict more accurate and quicker correct responses to dominating stimuli. In sum, manipulating the time course of stimuli in accordance with the concept of dominance can provide empirical tests of the class of evidence accrual models. (C) 2001 A cademic Press.