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A hybrid sustained attention task was developed in order to examine the relationships between manual response times and the timing and morphology of horizontal saccades involved in shifting gaze to a source of task relevant visual information. Twelve subjects performed this task for 60 min with no breaks. Performance and gaze control measures were aggregated across 20 min intervals comprising early, middle and late segments of the task. Response time variability was significantly increased during later task segments (p<0.05). These segments were also associated with increased variability in the amplitude of saccades (p<0.05). Saccade durations during the late task segments were also longer and more variable (p<0.05). Correlations between response times and measure of saccadic activity were also computed across consecutive 5 min intervals for each individual subject. The obtained correlations between saccade latency and response times exceeded 0.70 for six of the twelve subjects. Additional analyses examined the relationship between trials characterized by extreme values on either the performance or the gaze control measures. Trials characterized by extremely long response times were also associated with increased saccade amplitudes, durations and latencies (p<0.01). Conversely, response times were abnormally long on trials categorized as extreme on the basis of the saccade morphology and timing measures (p<0.01). These results confirm the utility of the sustained attention task as a laboratory platform for the development of real-time systems for alertness monitoring. The data also support the contention that measures of gaze control behavior can reflect aspects of cognitive activity and, therefore, should be seriously considered for inclusion in any physiologically-based alertness assessment battery.
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