Three experiments examined interference effects in concurrent temporal and nontemporal tasks. The timing task in each experiment required subjects to generate a series of 2-or 5-sec temporal productions. The nontemporal tasks were pursuit rotor tracking (Experiment 1), visual search (Experiment 2), and mental arithmetic (Experiment 3). Each nontemporal task had two levels of difficulty. All tasks were performed under both single-and dual-task conditions. A simple attentional allocation model predicts bidirectional interference between concurrent tasks. The main results showed the classic interference effect in timing. That is, the concurrent nontemporal tasks caused temporal productions to become longer (longer productions represent a shortening of perceived time) and/or more variable than did timing-onlyconditions. In general, the difficult version of each nontemporal task disrupted timing more than the easier version. The timing data also exhibited a serial lengthening effect, in which temporal productions became longer across trials. Nontemporal task performance showed a mixed pattern. Tracking and visual search were essentially unaffected by the addition of a timing task, whereas mental arithmetic was disrupted by concurrent timing. These results call for a modification of the attentional allocation model to incorporate the idea of specialized processing resources. Two major theoretical frameworks-multiple resource theory and the working memory model-are critically evaluated with respect to the resource demands of timing and temporal/nontemporal dual-task performance.The interference effect is one of the most consistent findings in the time perception literature. The effect refers to a disruption in timing that occurs when subjects are required to perform some demanding nontemporal task during the interval. The usual result is that perceived time becomes shortened. Because of differences between time judgment methods (see below), this effect is manifested as either shorter verbal estimations and reproductions or longer temporal productions. Time judgments also may display more error and variability under nontemporal task conditions than under control (no-task) conditions. This paper explores the nature of this effect, with special reference to the role ofattentional processes in timing. First, a review of the empirical and theoretical work in the area is presented, and issues involving mutual interference between temporal and nontemporal processing are raised. Three experiments designed to address these issues are reported. The paper concludes with a discussion centering on the relationship between timing and current models of attentional resources.

The effects of stimulus motion on time perception were examined in five experiments. Subjects judged the durations (6-18 sec) of a series of computer-generated visual displays comprised of varying numbers of simple geometrical forms. In Experiment 1, subjects reproduced the duration of displays consisting of stationary or moving (at 20 em/sec) stimulus figures. In Experiment 2, subjects reproduced the durations of stimuli that were either stationary, moving slowly (at 10 em/sec), or moving fast (at 30 em/sec). In Experiment 3, subjects used the production method to generate specified durations for stationary, slow, and fast displays. In Experiments 4 and 6, subjects reproduced the duration of stimuli that moved at speeds ranging from 0 to 46 em/sec. Each experiment showed that stimulus motion lengthened perceived time. In general, faster speeds lengthened perceived time to a greater degree than slower speeds. Varying the number of stimuli appearing in the displays had only limited effects on time judgments. Other findings indicated that shorter intervals tended to be overestimated and longer intervals underestimated (Vierordt's law), an effect which applied to both stationary and moving stimuli. The results support a change model of perceived time, which maintains that intervals associated with more changes are perceived to be longer than intervals with fewer changes.

This study has identified unique glenohumeral joint rotational patterning in unilaterally dominant upper extremity athletes that has ramifications for rehabilitation after injury and for both injury prevention and performance enhancement.