Search

It is nearly impossible to concurrently initiate and execute two motor actions with independent timing. For example, it is difficult to tap one rhythm with the right hand while tapping a different rhythm with the left hand, even after these rhythms have been practiced individually. However, if this task is restructured so that it is represented internally as one action done by two hands rather than as two actions, one with each hand, these same rhythms can be produced easily. These findings, which indicate that motor action is limited to a single time base, are in marked contrast with the fact that it is easy to mechanically generate two independent rhythms simply by using mechanisms that are not linked to each other. After an in-depth review of the extensive research on this topic we propose a new theoretical interpretation. This attributes the difficulty to a fundamental constraint that prevents initiation of any motor action until after completion of programming the internal code that controls timing. The timing code is volatile in the sense that it must be generated immediately prior to the action to be controlled and then it must be implemented without delay. This constraint, which has been studied as it applies to single motor actions, can be extended to concurrent motor actions where it can account for the difficulty in doing two differently timed actions at once. Additional phenomena which may be attributed to this constraint are described in a concluding section. [ABSTRACT FROM AUTHOR]

We investigated the processes underlying stimulus-response compatibility by using a lateralized auditory stimulus in a simple and choice reaction time (RT) paradigm. Participants were asked to make either a left or right key lift in response to either a control (80dB) or startling (124dB) stimulus presented to either the left ear, right ear, or both ears. In the simple RT paradigm, we did not find a compatibility effect for either control or startle trials but did find a right-ear advantage which we attribute to anatomical asymmetry of auditory pathways. In the choice RT paradigm, we found compatibility effects for both startle and control trials as well a high incidence of error for contralateral stimulus-response mapping. We attribute these results to automatic activation of the ipsilateral response, which must then be inhibited prior to initiation of the correct response. The presence of compatibility effects for startle trials also suggest that similar pathways are being used to initiate movements in a choice RT situation, as opposed to involuntary triggering that is thought to occur in a simple RT situation. (Contains 2 tables and 3 figures.)

ABSTRACT. The authors tested specificity and the guidance hypothesis by examining the effects of continuous or discrete concurrent feedback during acquisition, retention, and transfer of a 90[degrees] phase offset bimanual [...]

ABSTRACT. Anchoring has been defined as synchronizing a point in a movement cycle with an external stimulus (W. D. Byblow, R. G. Carson, & D. Goodman, 1994). Previously, investigators have [...]