Bradley Chase

A study of computer-based task performance under thermal stress.

A visual-visual dual computer task was designed to test the effect of the thermal environment on dual task performance. The temperatures selected for testing were 20 and 35 °C Wet Bulb Globe Temperature (WBGT). 34 volunteers were randomly assigned to 1 of the 2 temperature conditions. Individual differences in single task performance were controlled by equating the baselines of single task performance. Once individual differences in single task capacity were controlled, statistically significant differences in performance were demonstrated. Mean accuracy was computed over a 1-hr testing period in each temperature condition. Participants’ mean accuracy in the 35° condition (38.18%) was substantially lower than in the 20° condition (50.88%).

61.2: Eye Movements During Visual and Auditory Task Performance

Abstract : The primary focus of this research effort was the tracking of eye movements during complex cognitive tasks. 8 volunteers performed a visual tracking task alone and a combination of the visual task and the auditory Paced Serial Addition Task (PASAT). Results showed a reduction in range on the order of 50% for eye movements and an increase in variability of vergence eye movements during the dual task. This change can be characterized as visual tunneling.

From Explicit to Implicit Speech Recognition

We consider the problem of determining the word or concept that a subject holds in their mind prior to the act of speech using only a scalp-recorded electroencephalogram (EEG). Such speech acts are called covert, silent, or implicit speech acts in the literature. We consider a binary-tree classifier that uses one of a number of candidate feature types, including temporal correlation coefficients, spectral correlation, and time-gated raw voltages. The particular features and binary-tree parameters are blindly determined using the local discriminant basis (LDB) technique. The experiments involve sequential presentation of words and numbers on a computer screen. The subject wears an EEG scalp cap and is instructed to first consider the stimulus, then speak it. Later, the subject is instructed to perform the same task without the actual utterance, resulting in implicit speech. We present performance results for the various obtained classifiers, which show that the approach has significant merit.

A methodology to control for individual differences in dual-task performance

A study was designed to test the effect of a secondary visual task on a primary visual task. In one condition, participants performed the dual-task, while assigning no weight to the secondary task. In the second condition, the primary task was performed simultaneously with the secondary task. The effect of the added workload was measured via the effect on primary task performance. In the baseline portion of the task, participants had their baseline (90% accuracy) of performance collected by adjusting the stimulus duration. The individual participant stimulus duration was then used as the experimental stimulus duration and the effect of secondary task performance on primary task performance was measured. In a third condition, practice was used as a method of controlling for individual differences. Participants performed the task as in the control condition, however they were given twice as much exposure to the task. Participants ran the study for the full duration twice. Only the performance from the second exposure was collected.

Cognitive performance baseline measurement and eye movement performance measures

Personnel are often required to perform multiple simultaneous tasks at the limits of their cognitive capacity. In research surrounding cognitive performance resources for tasks during stress and high cognitive workload, one area of deficiency is measurement of individual differences. To determine the amount of attentional demand a stressor places on a subject, one must first know that all subjects are performing at the same level with the same amount of available capacity in the control condition. By equating the baselines of performance across all subjects (“baselining”) we can control for differing amounts of performance capacity or attentional resources in each individual. For example, a given level of task performance without a time restriction may be equated across subjects to account for attentional resources. Training to a fixed level of proficiency with time limits might obliterate individual differences in mental resources. Eye movement parameters may serve as a real-time measure of attentional demand. In implementing a baselining technique to control for individual differences, eye movement behaviors will be associated with the true cognitive demands of task loading or other stressors. Using eye movement data as a proxy for attentional state, it may be possible to “close the loop” on the human-machine system, providing a means by which the system can adapt to the attentional state of the human operator. In our presentation, eye movement data will be shown with and without the benefit of the baselining technique. Experimental results will be discussed within the context of this theoretical framework.

Eye Movement Measures of Performance on Visual Search Tasks: Equating the Baselines of Task Performance

Previous research suggests that eye measures can indicate decrements in performance on a visual tracking task due to increased difficulty in task execution from fatigue-induced conditions (Van Orden, 2000). In order to examine the sensitivity of eye movement to increased cognitive workload as indicated by difficulty of task, we chose a visual search paradigm. Using a basic visual search task, we studied the effects of increased task difficulty on subject performance and their corresponding eye measures. Results show a decrease in performance as the number of objects on the screen increase. What results could be expected if differences in individual abilities to perform visual search were controlled? This experiment looks at one method that can be used to control for individual differences in visual search abilities.

Controlling for Individual Differences in a Dual-Task Setting: Equating the Baselines of Single Task Performance

Individual differences in human performance is an issue that confounds many studies and has not been properly controlled in the ergonomics/human factors literature. This paper examines the concept of individual differences in performance primarily from the perspective of cognitive performance. A study was designed to test the effect of a secondary visual task on a primary visual task. In one condition, participants performed the dual task, while assigning no weight to the secondary task. In the second condition, the primary task was performed simultaneously with the secondary task. The effect of the added workload was measured via the effect on primary task performance. In the baseline portion of the task participants had their baseline (80–90% accuracy) of performance collected by adjusting the stimulus duration. The individual participant stimulus duration was then used as the experimental stimulus duration and the effect of secondary task performance on primary task performance was measured.

Attention Allocation under Thermal Stress

A visual-visual dual task was designed to test the effect of the thermal environment on dual task performance. The temperatures selected for testing were 77, 86 and 95 °F Wet Bulb Globe Temperature (WBGT). Forty-two volunteers were randomly assigned to one of the three temperature conditions. During the hour session, the emphasis was switched every 12 minutes between the two tasks (i.e., 100/0, 75/25, 50/50, 25/75, 0/100). POC analysis could then be conducted using data from these 5 emphasis conditions. Individual differences in single task performance were controlled by equating the baselines of single task performance. Once individual differences in single task capacity were controlled, statistically significant differences were demonstrated in terms of functional performance region (FPR) and in divided attention cost.