Visual Control of Discrete Aiming Movements

Abstract

An experiment is reported which investigated the visual control of discrete rapid arm movements. Subjects were required to move as rapidly as possible to several target width-movement distance combinations under both visual and non-visual conditions. The movement time (MT) data were supportive of Fitts' Law in that MT was linearly related and highly correlated to the Index of Difficulty (ID). MT was also similar for different target width-distance combinations sharing the same ID value. The error rate analysis, which compared visual to non-visual Performance, indicated that vision was only used, and to varying degrees, when MT exceeded 200 ms (3.58 ID level). There was some evidence that vision was differentially used within target width-distance combinations sharing the same ID. Estimates of endpoint variability generally reflected the results of the error rate analysis. These results do not support the discrete correction model of Fitts' Law proposed by Keele (1968).

Consequences of increased neuromotor noise for reaching movements in persons with stroke

“…In the more affected arm, both increased skewness (conservative planning strategy) and segmentation (trajectory corrections) were related to the intercept, while reduced directness (path accuracy and execution) was related to increased transmission capacity (i.e., slope −1 ). Wallace and Newell (1983) found that in healthy subjects, there is an increased reliance on sensory feedback for increasing accuracy requirement suggesting that there is a gradual shift from a feedforward to a feedback model of control depending upon the difficulty of the task (Siegel, 1977). The steeper slope in the Fitts' relation, together with the increased skewness and segmentation of profiles for the more affected arm of subjects with stroke, suggests that this shift from feedforward to feedback loop control occurs at reduced levels of accuracy for movement of the more affected arm.…”

Quantifying online visuomotor feedback utilization in the frequency domain

“…Three target amplitudes were employed in an attempt to reduce the predictability of the specifics of an upcoming trial and, thus, in turn to reduce the degree to which movements could be influenced by offline processing. The task itself-namely a simple discrete reaching movement-was chosen to provide a straightforward context from which to infer changes in performance due to online feedback utilization, while also being consistent with the literature that has investigated online control mechanisms (e.g., Plamondon & Alimi, 1997;Wallace & Newell, 1983).…”

“…Such an effect can theoretically be attributed in part to the temporal costs associated with the use of feedback (see Fitts, 1954). Indeed, when utilizing targets with relatively high indices of difficulty (i.e., indices of difficulty above 3.58 bits; see Wallace & Newell, 1983), FV-versus-NV performance differences may be more confidently associated with visual feedback utilization. As such, in the present study we employed targets approximately 1 cm in width at distances ranging from 27 to 33 cm, yielding indices of difficulty from 5.75 to 6.04 bits.…”

Low vision, stimulus encoding and information processing: a characterization of performance of partially sighted users on computer-based tasks

“…However, Wallace and Newell (1983) condition, resulting in initial saturation of most cone and some rod photopigments. As these photopigments regenerate, sensitivity to light progressively improves.…”

“…Distorting the perception of the stimuli is an alternative approach to altering the stimuli directly (illuminated vs. dark conditions). One method to test Wallace and Newell's (1983) hypothesis is to use participants who are partially sighted. This could provide evidence that as the ID increases the need for vision increases.…”