Preparing to react in the absence of uncertainty: II. Stimulus uncertainty and response compatibility in tactile reaction time

Abstract

Stimulus uncertainty and stimulus response compatibility were manipulated in three reaction time (RT) experiments. Key‐release responses were summoned either by direct tactile or visual cuing of the response finger or by oblique cuing of the contralateral finger. Comparisons of standard simple reaction time (SRT) with 2: 1 convergent RT (CoRT), in which participants were required to execute the same response to either of two stimuli, invariably revealed a stimulus uncertainty effect. Extended practice and high compatibility diminished, but did not eliminate, this effect. The effect was not confined to trials in which the stimulus differed from the previous one, trials following an error, or to a longer tail on participants' CoRT distribution. CoRT remained longer than SRT when tactile imperative stimuli were replaced by visual ones, establishing that the stimulus uncertainty effect was not a peculiarity of the bimanual tactile RT set‐up. The latencies of CoRT were invariably shorter than for binary Go/No‐Go RT or standard choice RT (CRT), indicating a role for factors other than stimulus uncertainty. A remarkable feature of the tactile paradigm was the varying impact of compatibility on different tasks: for example, CRT was actually shorter than Go/No‐Go RT when participants responded with the finger stimulated but considerably longer when responding with the contralateral finger.