Refutation of Poffenberger's inference: An existence proof and a countermodel

Interhemispheric relay time (IHRT) is inferred from simple (visual) reactio n time (SRT) by subtracting SRTs in ipsilateral hand-field conditions from SRTs in contralateral hand-field conditions. This index, the "crossed-uncro ssed differential" (CUD) is a synonym of IHRT in the current literature. Th e CUD has been shown to be significantly moderated by experimental variable s, including attentional. One reason the CUD = IHRT hypostasy persists toda y is that no experimental manipulation has yet been able to generate a sign ificantly negative CUD in a subject manifesting a significant positive CUD in classical conditions. We implemented an experimental manipulation, in SR T. consisting of increasing complexity of the response after the initial ke y press required at detection. In a very large scale single-case experiment , we found that the CUD thus went from significantly positive in classical SRT to significantly negative in the increased response load condition. (C) 2001 Academic Press.