Note on Decision Time/Movement Time Relationships in Normal and Depressed Subjects

The decision time/movement time (DT/MT) measures which are obtained when using reaction-time apparatus incorporating a home key are being used to investigate a wide range of group differences. It is usually assumed that the time from stimulus onset to release of the home key is a good measure of central processin speed. It is on or just after detecting rather than fully identifying the stimulus, thus giving an invalidly short DT and long MT. Two experiments are described which show subjects do use such a detection strategy when they can. An alternative procedure which masks out stimulus information when the home key is released is shown to make subjects use a full decision strategy and release the home key only after processing sufficient information to respond correctly, thus giving a better measure of cognitive time.argued that it is not always the case since a possible strategy IS to release t i e home key Choice reaction time has commonly been studied with two types of apparatus; one with a "home key," the other without. In the latter, the subjects place their fingers directly on a set of response keys throughout the task and use the appropriate finger to press the key specified by the stimulus. The reaction time (RT) is the time between the stimulus onset and the press of a response key. I n contrast, a typical task with home key requires the subject to hold down the home key with one finger at the start of a trial. A stimulus is presented specifying to which of a set of response keys the subject should move to and press with the finger. Two durations can be measured with this apparatus (Miles, 1942): the time from stimulus onset to release of the home key which has been called "decision time" (DT). and the time taken moving from the home key to press the response key, called the "movement time" (MT). The sum of these two durations can be called the total response time (TRT). Some writers refer to the decision time as the reaction time, but this is not done here for two reasons. First, RT is used here only for the non-home key tasks to keep separate the measures from the two types of apparatus. Second, using the name decision time makes explicit the assumption by most researchers that DT is a good measure of the central processing or decision making time on a trial. In this view, MT reflects simply the time to execute the movement. This assumption was clearly stated by Landauer, Armstrong, and Digwood ( 1980): "Decision time, according to this model, can therefore be thought to consist of (a) receptor and afferent transmission, (b) a perceptual, and (c) a cognitive component."Requests for reprints should be sent to Glen A. Smith.

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Note on Decision Time/Movement Time Relationships in Normal and Depressed Subjects

Cited by 10 publications

References 11 publications

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