The experiment was designed to divide the attention demands of a total motor response time into two components, the initiation of a response and the execution of a movement. The purpose was to determine the effects of movement complexity on the relative degree of attention required during these component processes. Six male right handed S's were tested in a situation involving two discrete reactions to two stimuli separated by a short time interval. The first stimulus was associated with the

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... formance of a primary motor task that was varied in complexity and that was performed with the S's right hand. The second or probe stimulus was associated with a simple reaction time performed with the left hand. The probe stimulus was presented during the S's performance of the primary task and the reaction to this stimulus was used as an index of the attentional demands of the primary task. The results of the primary task indicate that the reaction time (RT) component of the response was not a function of movement complexity, although there was an apparent difference between the simplest response and responses of greater complexity. Movement complexity affected the movement time (MT) component of the response in that MT increased as complexity increased. The second or probe reaction time (PRT) was delayed when the probe occurred during the initiation of the response and during the execution of the response. When the probe was presented during the initiation of the response, the PRT was related directly to the RT, and when presented during the execution of the response, the PRT related directly to MT. PRT was also seen to vary throughout the range of movement with the longest PRTs occurring at the beginning and end of a movement terminated at a target. These results provide evidence for a model of human performance that suggests component processes of limited capacity in that the attention demands of initiating and executing a motor task tend to vary with task complexity and position of the responding limb in moving t [...]