A Forthcoming Key Press Can Be Selected While Earlier Ones Are Executed.

The possibility that a key press can be selected during execution of earlier key presses and the resulting pattern of interferences were investigated in this study. Subjects (N equals 26) were required to press a series of keys, determined in advance, before they pressed a stimulus-dependent key. Response selection demands were manipulated by using spatially compatible and incompatible SndashR mappings because S-R compatibility is well known to not disappear with practice. The longer time needed to select an incompatible key vanished when the choice key was preceded by two or four predetermined key presses. Only early in practice did the time to press the first and the choice key in a three-key sequence exhibit part of the compatibility effect. With limited practice, concurrent preparation in the three-key sequence was relatively slow and took longer than the time required for executing the fixed keys. These findings suggest that processes involved in execution are not affected by concurrent response selection and that one of the effects of practicing movement sequences is that later movements can be selected while earlier ones are being executed. This need not affect execution rate. Therefore, different degrees of concurrent processing are not always reflected in reduced execution rates.