Task parameters shape goal-directed movement performance under dual-task conditions

Abstract

Goal-directed movements are an important part of daily life. The conditions under which they are enacted can influence the success of these fine motor movements. Primarily this thesis aims to investigate the impact that changes in visual attention, created by dividing attention, have on pointing movements. All studies used a novel experimental design consisting of a central alphanumeric search presented with a concurrent pointing task. This design required the division of attention between central and peripheral vision. In order to assess the participant’s performance of these tasks, data on several outcome measures were obtained. The pointing endpoint yielded a measure of movement accuracy (or how far the touch was from the target) and how variable the movement endpoint was (precision). Movement time was divided into two sections; the movement latency (ML) or the time between target onset and movement commencement and reach time (RT) the time the hand was in flight. Additionally participant responses to the search task were measured. In study one dual-task performance of a cognitive and motor task was used to assess the effect of the presence or absence of attentional division and therefore the impact of shared resources. While reaching quickly the impact of attentional division was restricted to ML the phase associated with the initial movement plan. Study two built on the findings from the first study to investigate if RT was truly independent of attentional effects by substituting fast reaching times with slow ones. The results of study two showed dual-task interference in both stages of the movement. This suggests resource sharing between the search and at least one factor involved in MT, possibly feedback and updating. The third and final study aimed to assess task parameter influences on movement production. The search task was manipulated by use of high and low difficulty (load) searches combined with either fast or slow movement speeds. When reaching slowly pre-movement planning time was longer, as was MT which reflected the area of experimental manipulation. Slow reaches were also more accurate than fast reaching and more prone to the impact of target eccentricity. The eccentricity of the pointing target only significantly impacted performance while moving slowly coinciding with high accuracy. Fast reaching produces greater variability in performance possibly masking eccentricity effects. The manipulation of cognitive load impacted search performance as expected with high load conditions producing less accurate responses. While cognitive load had some impact upon goal-directed movement performance did not vary in a predictable pattern. Overall attentional effects were evident throughout the reach, not only in ML and pre-movement planning time but also during the reaching stage. The impact of attention on RT was only observable during slow reaching. Although it may be inferred that attentional effects to RT in this experiment were mediated by online updating, this idea needs explicit testing in future studies. We also found that the parameters (and difficulty) of the tasks undertaken did impact goal-directed movement performance. Based on the difference in the patterns of effects when load was modulated via the cognitive (search load) compared to motor task (movement speed), it appears modifications to the motor element displayed more predictable load dependant effects. Overall, the pattern of results in this thesis demonstrate that dividing attention does have systematic effects on reaching performance and the predictable effects dependent on task load appear at this time to be modality specific.