Localizing practice effects in dual-task performance

Abstract

Practice effects on dual-task processing are of interest in current research because they may reveal the scope and limits of parallel task processing. Here we used onsets of the lateralized readiness potential (LRP), a time marker for the termination of response selection, to assess processing changes after five consecutive dual-task sessions with three stimulus onset asynchronies (SOAs) and priority on Task 1. Practice reduced reaction times in both tasks and the interference between tasks. As indicated by the LRP, the reduction of dual-task costs can be explained most parsimoniously by a shortening of the temporal demands of central bottleneck stages, without assuming parallel processing. However, the LRP also revealed a hitherto unreported early activation over the parietal scalp after practice in the short SOA condition, possibly indicating the isolation of stimulus–response translation from other central processing stages. In addition, further evidence was obtained from the LRP for a late motoric bottleneck, which is robust against practice.

This study was made possible by the project Group Interaction in High Risk Environments, which was supported by the Daimler-Benz-Foundation.

Notes

¹Ruling out some methodological issues such as the type of baseline performance to be used.

²There is not much agreement on how to interpret LRP amplitudes. The late effects shown here might reflect changes in the processing of reafferent information, which is beyond the scope of the current study.

³This was also true when, as Sangals et al. (2004) did, 30% thresholds were used, F(2, 18) = 15.4, p < .01, ϵ = .62.

⁴If all participants had always grouped their responses, RT1 should have increased across SOA with slope 1.

⁵To further test for possible changes in grouping tendency, we analysed interresponse intervals. As to be expected, they were affected by SOA but did not change across sessions.