In recent years, there has been increasing concern over the neurotoxic effects of workplace exposure to solvents and other noxious substances. Studies carried out within the field of neurobehavioral toxicology have shown that it is possible to measure decrements in cognitive performance in exposed workers using psychometric tests. However, positive results reported in these studies can be difficult to interpret. Many of the neuropsychological and neurobehavioral tests that have been employed require a variety of subskills, and decrements in overall test performance can reflect reduced capacity in any one or a subgroup of these. This causes particular problems for professionals making judgements about the health and safety consequences of these exposure-related decrements. This difficulty in interpretation is further compounded by the fact that observed effects are frequently at subclinical level. A better understanding of the underlying functionality of neurobehavioral tests, therefore, would be helpful in interpreting decrements reported in the numerous neurobehavioral studies carried out to date [2].

We describe an ongoing project that is investigating the potential of eye-movement methodology to provide information about the mental functions underlying neurobehavioral tests. Eye movements are thought to reflect ongoing cognitive processes and thus provide a "window" on the stages of information processing that underlie task performance. Tasks that involve processing and responding to an array of visual information are typically composed of a sequence of distinct subcomponents. Eye-movement analysis provides information about the time spent looking at particular items in a test, and the order in which they are fixated. This information can then be identified with previously identified subcomponents of the task, providing additional performance data.

Initial investigations have concentrated upon the digit-symbol substitution task; variants of this are found in several well-known test batteries. A group of healthy adult participants completed the task wearing a head mounted eyetracker (Applied Science Laboratories, Model 4000SU). Eye-gaze latencies associated with each specified subtask were used to derive three performance measures. Correlations were then carried out to determine the relative contributions of each subskill to the overall test score. Interestingly, work showed that motor response speed was not the most significant correlate of task performance. Instead, factors such as perceptual search speed and sustained attention made the most important contribution to the overall score [1].

The goal of current work is to establish the applicability of this methodology to other types of neurobehavioral tests. Further studies will seek to determine the specific effects of alcohol and demographic factors upon these measures. It is intended that this information can be applied retrospectively to appraise the nature of measured decrements in any previous study featuring the tests examined.

References

1. Stephens, R. (1997). The feasibility of using eye movement data in the analysis of performance of neurobehavioural tests. Paper 6th International Symposium on Neurobehavioural Methods and Effects in Occupational and Environmental Health (Shanghai, China).
2. Stephens, R.; Barker, P. (1998). The role of human neurobehavioural tests in regulatory activity on chemicals. Occupational and Environ--mental Medicine, 55, 210-214.

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