NAVAL HEALTH RESEARCH CENTER EYE MOVEMENTS DURING VISUAL AND AUDITORY TASK PERFORMANCE

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. 1. Objective and Background In optimization of the design of new systems and adaptation of existing technologies, the accurate measure and prediction of human operator workload can be critical. Within the context of a complex human-machine system, there is the environment, task, and operator state. It is the latter, operator state, which is the focus of this study. Visual attention has increased in importance as the systems into which humans are being integrated become more visually complex. The ability of humans to attend to a variety of stimuli in these complex systems is often the limiting factor in overall system performance. Eye movement behaviour can now be detected by stand-off video cameras. Thus a system that could reliably detect eye movement behaviour patterns related to operator states such as fatigue, loss of attention or workload would be then able to alter the task presentation to optimize operator-system performance. In this pilot study we sought to extend the process of understanding, quantifying and modelling eye movement behaviours that are indicative of physiological and cognitive states. Human eye tracking technology has experienced significant improvement in recent years in such critical areas as sampling. Further, reduced costs and improved reliability of systems makes it feasible to monitor both eyes and thus provide additional parameters to measure, a second eye and its correlation with the first eye. To date, many eye activity behaviours have been correlated with visual and cognitive demands of various tasks. What is lacking in the current body of literature are a variety of real time models of human operator state that can be integrated into system functions. In the present study we wished to examine measures of operator workload as indicated by oculomotor activity. We chose to combine a visual task (tracking an object) with an auditory task. A priori, the auditory task should have no direct requirement for change of oculomotor behaviour while it is being performed. Thus any changes in behaviour may potentially be ascribed to the increase in workload when going from visual alone to visual and auditory. The participants were 8 volunteers who, while wearing the headmounted eye tracker, performed a visual tracking task and a combination of the visual tracking task and auditory task. A simulated screen shot of the visual tracking task is shown in Figure 1. The subject uses a joystick to center in two dimensions a visual target that is being constantly perturbed. This task is a reasonable proxy for simultaneous lane keeping and speed maintenance during driving. The second task is an auditory task – a version of the Paced Auditory Serial Addition Test (PASAT). In this task the subject hears a series of numbers and must then add each number to the previous number and state the sum. Task difficulty is a function of number presentation speed. It can demand total attention from the subject at moderately fast speeds for successful performance. We recorded eye movements through high-bandwidth, binocular tracking. The eye tracking system utilized in this study was the EyeLink II, from SR Research Ltd, Mississauga, Canada. Videobased eye tracking systems have long been acknowledged as the simplest to set up and operate. EyeLink II has a high resolution (noise-limited at <0.01°) and fast data rate (500 samples per second). This exceptional data quality results in very low velocity noise, making the EyeLink II ideal for saccade analysis and smooth pursuit studies. On-line gaze position data is available with delays as low as 3 milliseconds, making the system ideal for gaze-contingent display applications. In addition, on-line data parsing occurs, making eye events such as saccade, fixation, and blink available within 25 ms to the display computer. We tested subjects performing each task independently and both tasks simultaneously. Our initial analysis shows it may be possible to discriminate between a visual and an auditory focus based on eye movements for independent task performance. Subjects anecdotally reported that they felt they were doing the visual tracking task automatically and without attention. However, we found differences in eye movement behaviour when performing the visual tracking task alone and performing both tasks together. In particular, depth of field changes indicated that