A Mackworth-clock monitoring task was introduced into a standard compensatory tracking task located at different lateral positions in S's visual field, while the tracking task was located in the center of the visual field. The variables tracking frequency and monitor position were hypothesized to produce mutual interference in the dual-task arrangement, and the spatial separation of the two tasks was assumed to adversely affect peripheral signal detection. As the tracking frequency increased, peripheral monitoring performance remained high, while tracking accuracy was reduced. The position of the monitor task did not affect monitoring performance, but did influence tracking accuracy at the low tracking frequency. A divided-attention effect was found with respect to the monitoring task when both tasks were located directly in S's field of view. Eye-movement data provided some support for the notion of a functional visual field.