Ocular kinematics and eye-hand coordination

Visually guided tracking on a handheld device: can it be used to measure visuomotor skill in shift workers?

OBJECTIVE

We introduced a new visually controlled tracking task that can be assessed on a handheld device in shift workers to evaluate time-of-day dependent modulations in visuomotor performance.

BACKGROUND

Tracking tasks have been used to predict performance fluctuations depending on time of day mainly under laboratory conditions. One challenge to an extended use at the actual working site is the complex and fixed test setup consisting of a test unit, a monitor, and a manipulation object, such as a joystick.

METHOD

Participants followed an unpredictably moving target on the screen of a handheld device with an attachable stylus. A total of 11 shift workers (age range: 20-59, mean: 33.64, standard deviation: 10.56) were tested in the morning, the evening, and the night shift in 2-hr intervals with the tracking task and indicated their fatigue levels on visual analogue scales. We evaluated tracking precision by calculating the mean spatial deviation from the target for each session.

RESULTS

Tracking precision was significantly influenced by the interaction between shift and session, suggesting a clear time-of-day effect of visuomotor performance under real-life conditions. Tracking performance declined during early-morning hours whereas fatigue ratings increased.

CONCLUSION

These findings suggest that our setup is suitable to detect time-of-day dependent performance changes in visually guided tracking.

APPLICATION

Our task could be used to evaluate fluctuations in visuomotor coordination, a skill that is decisive in various production steps at the actual working place to assess productivity.

Behavioral investigation on the frames of reference involved in visuomotor transformations during peripheral arm reaching

BACKGROUND

Several psychophysical experiments found evidence for the involvement of gaze-centered and/or body-centered coordinates in arm-movement planning and execution. Here we aimed at investigating the frames of reference involved in the visuomotor transformations for reaching towards visual targets in space by taking target eccentricity and performing hand into account.

METHODOLOGY/PRINCIPAL FINDINGS

We examined several performance measures while subjects reached, in complete darkness, memorized targets situated at different locations relative to the gaze and/or to the body, thus distinguishing between an eye-centered and a body-centered frame of reference involved in the computation of the movement vector. The errors seem to be mainly affected by the visual hemifield of the target, independently from its location relative to the body, with an overestimation error in the horizontal reaching dimension (retinal exaggeration effect). The use of several target locations within the perifoveal visual field allowed us to reveal a novel finding, that is, a positive linear correlation between horizontal overestimation errors and target retinal eccentricity. In addition, we found an independent influence of the performing hand on the visuomotor transformation process, with each hand misreaching towards the ipsilateral side.

CONCLUSIONS

While supporting the existence of an internal mechanism of target-effector integration in multiple frames of reference, the present data, especially the linear overshoot at small target eccentricities, clearly indicate the primary role of gaze-centered coding of target location in the visuomotor transformation for reaching.

Gambling in the visual periphery: a conjoint-measurement analysis of human ability to judge visual uncertainty

Recent work in motor control demonstrates that humans take their own motor uncertainty into account, adjusting the timing and goals of movement so as to maximize expected gain. Visual sensitivity varies dramatically with retinal location and target, and models of optimal visual search typically assume that the visual system takes retinal inhomogeneity into account in planning eye movements. Such models can then use the entire retina rather than just the fovea to speed search. Using a simple decision task, we evaluated human ability to compensate for retinal inhomogeneity. We first measured observers' sensitivity for targets, varying contrast and eccentricity. Observers then repeatedly chose between targets differing in eccentricity and contrast, selecting the one they would prefer to attempt: e.g., a low contrast target at 2° versus a high contrast target at 10°. Observers knew they would later attempt some of their chosen targets and receive rewards for correct classifications. We evaluated performance in three ways. Equivalence: Do observers' judgments agree with their actual performance? Do they correctly trade off eccentricity and contrast and select the more discriminable target in each pair? Transitivity: Are observers' choices self-consistent? Dominance: Do observers understand that increased contrast improves performance? Decreased eccentricity? All observers exhibited patterned failures of equivalence, and seven out of eight observers failed transitivity. There were significant but small failures of dominance. All these failures together reduced their winnings by 10%–18%.

Human ability to discriminate drops dramatically with increasing distance from the center of vision. If you fixate a word on a page, you likely can not read words a short distance away. Because of this retinal inhomogeneity, we need to move our eyes to search a scene. The efficiency of search depends on how well the visual system compensates for inhomogeneity in planning eye movements. We used a simple decision task to find out what the observer “knows” about his or her own retina. We first measured observers' sensitivity for targets, varying contrast and eccentricity. Observers then repeatedly chose between targets differing in eccentricity and contrast, selecting the one they would prefer to attempt: e.g., a low contrast target at 2° versus a high contrast target at 10°. Could observers correctly trade off contrast and eccentricity and pick the more discriminable of the two targets? We found that observers exhibited large, patterned errors in their choices, making choices that were not even self-consistent.

The impact of sustained wakefulness and time-of-day on OSPAT performance

Fatigue associated with shiftwork is a key contributor to human error in the workplace. One way to prevent fatigue-related errors from occurring is to identify fatigue in employees using fitness-for-duty measures. The Occupational Safety Performance Assessment Test (OSPAT), an unpredictable tracking task that measures hand-eye coordination, is currently being used as a fitness-for-duty measure in a variety of industries, but has not yet been validated as a test sensitive to the effects of fatigue. Consequently, the aim of this study was to systematically examine the impact of sustained wakefulness and time-of-day on OSPAT performance. Twenty individuals (10 male, 10 female), aged between 18-25 yr (M=20.90, SD=2.29) participated in the study, which was conducted in Australia. The study had a repeated measures design, whereby participants completed the OSPAT and measures of sustained attention (i.e., the psychomotor vigilance task: PVT), and subjective alertness (i.e., the Visual Analog Scale: VAS) every 2 h during 24 h of sustained wakefulness, beginning at 07:00 h. Results revealed that VAS ratings of alertness, PVT performance, and OSPAT performance declined significantly as hours of wakefulness increased during the night-time (all p<.01). Furthermore, a positive correlation between OSPAT and PVT performance was observed (r=0.40, p<.01). Overall, these findings suggest that OSPAT is sensitive to sustained wakefulness during the night-time, and builds the case for OSPAT being a suitable measure for determining fitness-for-duty in workplace environments.