Timecourse of coactivation in bimodal divided attention

Abstract

Reaction time distributions were obtained from practiced subjects in a go/no-go detection task with attention divided across the visual and auditory modalities. Redundant signals were sometimes presented asynchronously on the two modalities, with the time between signals varying from 0 to 167 msec. An extension of the inequality derived by Miller (1982) was used to test between separate-decisions models, in which the response is initiated solely by whichever signal is detected first, and coactivation models, in which both signals contribute to the activation of a single response. As in previous studies with bimodal detection tasks, the results contradicted separate-decisions models and favored coactivation models. The largest violations of separate-decisions models were observed when the visual signal was presented 67–100 msec before the auditory signal. A new inequality was also derived to discriminate between two classes of coactivation models that differ about whether responses are generated by processes combining activation across time as well as across signals. Violations of this inequality ruled out exponential coactivation models, in which activation processes are sensitive only to the instantaneous properties of the signal(s). Instead, the results require an accumulation model of coactivation, in which both signals provide input to a process that accumulates activation over a considerable period of time, even if signal conditions change during that time.