We deseribe a model to account for the redundant-largets effect which combines the idea of superposed channel activity under redundant-target trials with the concept of stochastic accumulation of information over time. The model assumes that the accumulation of information over time in each channel can be described as a Wiener process and that the overt response is initiated as soon as a threshold is reached. In redundant-target trials, the activation from both stimulated channels is assumed to be superposed in order to form the overall accumulation process. Formally, the joint activation in redundant-target trials is described as a two-dimensional Wiener process which admits an arbitrary channel correlation. We derive the predictions of this model on the level of the means and variances of the reaction times for simultaneous, as well as for non-simulaneous, target presentations. The results show that the channel correlation does not influence the predictions on the level of the mean reaction times at all. The application of the model is illustrated using data from Miller's ( 1986 , Perception & Psychophysics, 40, 331-343), study on bimodal detection. 2) 1994 Academic Press, Inc.