Behavioral effects of low-level exposure to Hg0 among dental professionals: a cross-study evaluation of psychomotor effects.

A Across-study design was used to evaluate the sensitivities of five psychomotor tasks previously used to assess preclinical effects of low-level Hg0 (urinary < or =55 microg/l). Pooling dental professional subject populations from six studies conducted over the last 6 years, a larger study population was obtained with a high degree of uniformity (N = 230). The five psychomotor tests were: Intentional Hand Steadiness Test (IHST); Finger Tapping: The One-Hole Test: NES Simple Reaction Time (SRT); and Hand Tremor. Multivariate analyses were conducted following the hierarchical analysis of multiple responses (HAMR) approach. First, multiple scores of each test were combined into a single-factor (or related summary) variable and its reliability was estimated. Second. multiple regression analyses were conducted including log-transformed [Hg0]U levels, age, gender, and alcohol consumption in each model. Computed were both B and bu, the magnitudes of the log-Hg0 standardized coefficient. respectively uncorrected and corrected for dependent variable attenuation due to unreliability. Results indicated remarkable differences in the effects of relative level of Hg0 on psychomotor performance. Significant associations were found for the IHST factor (B = 0.415, p < 10(-6)), followed by finger tapping, which was relatively meager and insignificant (B 0.141, p = 0.17). The IHST results hold the greatest occupational relevance for dental professionals who rely on manual dexterity in restorative dentistry. Further, this statistical approach is recommended in future studies for condensation of multiple scores into summary scores with enhanced reliabilities useful in correcting for attenuation relationships (B(u)s) with exposure levels.

Neurobehavioral effects from exposure to dental amalgam Hg(o): new distinctions between recent exposure and Hg body burden.

Potential toxicity from exposure to mercury vapor (Hg(o)) from dental amalgam fillings is the subject of current public health debate in many countries. We evaluated potential central nervous system (CNS) toxicity associated with handling Hg-containing amalgam materials among dental personnel with very low levels of Hg(o) exposure (i.e., urinary Hg <4 microg/l), applying a neurobehavioral test battery to evaluate CNS functions in relation to both recent exposure and Hg body burden. New distinctions between subtle preclinical effects on symptoms, mood, motor function, and cognition were found associated with Hg body burden as compared with those associated with recent exposure. The pattern of results, comparable to findings previously reported among subjects with urinary Hg >50 microg/l, presents convincing new evidence of adverse behavioral effects associated with low Hg(o) exposures within the range of that received by the general population.

Analyzing multivariate neurobehavioral outcomes in occupational studies: a comparison of approaches.

Neurobehavioral studies often employ test batteries and confront issues of multiple testing and comparability between batteries. We have organized our battery of 12 tests into areas of neurobehavioral function to reduce the number of reported results, provide greater statistical power, and improve interpretability of the results. We explored several different organizational and statistical methods of creating summary scores including a priori groupings based upon clinical experience and factor analysis. We compared the sensitivity of these summary scores to performance changes associated with exposure to styrene in the manufacture of reinforced plastics. Our results demonstrated dramatic increases in power to detect exposure related changes compared to using individual test scores. Furthermore, the various methods provided generally compatible and comparable results. We encourage other neurobehavioral investigators to pursue and refine this approach.

Behavioral effects of low-level exposure to elemental Hg among dentists.

Exposure thresholds for health effects associated with elemental mercury (Hg degree) exposure were examined by comparing behavioral test scores of 19 exposed (mean urinary Hg = 36 micrograms/l) with those of 20 unexposed dentists. Thirty-six micrograms Hg/l is 7 times greater than the 5 micrograms Hg/l mean level measured in a national sample of dentists. To improve the distinction between recent and cumulative effects, the study also evaluated porphyrin concentrations in urine, which are correlated with renal Hg content (a measure of cumulative body burden). Subjects provided an on-site spot urine sample, were administered a 1-h assessment consisting of a consent form, the Profile of Mood Scales, a symptom and medical questionnaire, and 6 behavioral tests: digit-span, symbol-digit substitution, simple reaction time, the ability to switch between tasks, vocabulary, and the One Hole Test. Multivariate regression techniques were used to evaluate dose-effects controlling for the effects of age, race, gender and alcohol consumption. A dose-effect was considered statistically significant below a p value of 0.05. Significant urinary Hg dose-effects were found for poor mental concentration, emotional lability, somatosensory irritation, and mood scores. Individual tests evaluating cognitive and motor function changed in the expected directions but were not significantly associated with urinary Hg. However, the pooled sum of rank scores for combinations of tests within domains were significantly associated with urinary Hg, providing evidence of subtle preclinical changes in behavior associated with Hg exposure. Coproporphyrin, one of three urinary porphyrins altered by mercury exposure, was significantly associated with deficits in digit span and simple reaction time.(ABSTRACT TRUNCATED AT 250 WORDS)

Performance Evaluation Tests for Environmental Research (PETER): evaluation of 114 measures.

The goal of the Performance Evaluation Tests for Environmental Research (PETER) Program was to identify a set of measures of human capabilities for use in the study of environmental and other time-course effects. 114 measures studied in the PETER Program were evaluated and categorized into four groups based upon task stability and task definition. The Recommended category contained 30 measures that clearly obtained total stabilization and had an acceptable level of reliability efficiency. The Acceptable-But-Redundant category contained 15 measures. The 37 measures in the Marginal category, which included an inordinate number of slope and other derived measures, usually had desirable features which were outweighed by faults. The 32 measures in the Unacceptable category had either differential instability or weak reliability efficiency. It is our opinion that the 30 measures in the Recommended category should be given first consideration for environmental research applications. Further, it is recommended that information pertaining to preexperimental practice requirements and stabilized reliabilities should be utilized in repeated-measures environmental studies.

Performance evaluation tests for environmental research (PETER): code substitution test.

The effects of repeated testing on code substitution performance were studied in three experiments to determine reliability and stability of task performance under laboratory and at-sea conditions. In Exp. 1, a single 2-min. testing trial per day was administered to a group of 19 subjects for 15 consecutive weekdays. In the second experiment a 4-min. per-day test was administered to 12 of the 19 original subjects for an additional 15 consecutive weekdays. In Exp. 3, six US Coast Guardsmen were tested hourly for four consecutive days, two days at dockside and two days at sea. In Exps. 1 and 2, means, variances, and cross-session correlations became stable after Day 8. Stabilized reliabilities were .75 for Exp. 1 and .80 for Exp. 2. The results of Exp. 3 were comparable to those obtained in the first two experiments with the exception that decrements in performance corresponding to high frequencies of motion sickness symptoms occurred during the at-sea trials. The Code Substitution Test is recommended for inclusion in the PETER battery.

Automated Portable Test (APT) System: overview and prospects.

The Automated Portable Test (APT) System is a notebook-sized, computer-based, human-performance and subjective-status assessment system. It is now being used in a wide range of environmental studies (e.g., simulator aftereffects, flight tests, drug effects, and hypoxia). Three questionnaires and 15 performance tests have been implemented, and the adaptation of 30 more tests is underway or is planned. The APT System is easily transportable, is inexpensive, and has the breadth of expansion options required for field and laboratory applications. The APT System is a powerful and expandable tool for human assessment in remote and unusual environments.

Performance Evaluation Tests for Environmental Research (PETER): critical tracking test.

A critical tracking test was considered for inclusion in the Performance Evaluation Tests for Environmental Research (PETER) Battery which was designed for use in unusual environments. Baseline measures were obtained by testing 18 subjects for 14 consecutive days. Mean performances increased but standard deviations were constant over the 14 days. Test-retest reliabilities improved over the first 8 days after which differential stability was seen. The implications for the use of this test in exotic environments are discussed. The critical tracking test is recommended as a good candidate for environmental research when practiced to total stability.

Performance Evaluation Tests for Environmental Research (PETER): Moran and computer batteries.

This investigation was directed at evaluating nine cognitive ability tasks for repeated measures applications and inclusion in the Performance Evaluation Tests for Environmental Research (PETER) battery. In the first study, five tasks from the Moran Battery, which were adapted from the French kit of factor-referenced tests, were administered to 18 subjects daily for 13 workdays. In the second study, four tasks from the Carter and Sbisa Computer Generated Battery were administered daily to 17 subjects (12 in common with first study) for 15 workdays. Examination of the means, variances, and interday reliabilities, together with factor analysis of the cross-task correlations, led to the recommendation of four tasks. Tasks recommended for repeated measures applications were Vertical Addition, Perceptual Speed, Grammatical Reasoning, and Flexibility of Closure.

Television computer games: a 'new look' in performance testing.

Work at the Naval Biodynamics Laboratory aims at developing a battery of performance evaluation tests for environmental research (PETER). Because repeated-measures designs are virtually universal in environmental studies, the paradigm focuses on stabilisation with practice; thus far, over 50 tasks have been studied. The present report describes how five computerized video games fare as performance tests. The tasks were performed for 3 weeks each, in the same order, by the same subjects. The results show that four out of the five games meet all criteria satisfactorily and one does not, a favorable showing for the video games in comparison with conventional tests of either the paper-and-pencil or apparatus types. In terms of availability, equipment reliability, expense, and other practical considerations, the video games have many advantages. It is concluded that video games have considerable promise for performance testing and other applied contexts.

Development of performance evaluation tests for environmental research (PETER): time estimation.

A time-estimation task was considered for inclusion in the Performance Evaluation Tests for Environmental Research (PETER) battery. As part of this consideration, the effects of repeated testing on the reliability of time judgments were studied. The method of production was used to estimate eight time intervals. Five trials per day at each interval were administered individually to each of 19 subjects for 15 consecutive workdays. Two scores, constant error and variable error, were reported. The effect of days was not significant for constant error and was moderate for variable error (p < .04). The standard deviations were relatively stable across trials. A pronounced decline in reliability over repeated days of testing was found for both errors. It was concluded that this time-estimation test would be a poor candidate for inclusion in PETER, but further research is warranted because of the potential unique contribution of a time-estimation task in a performance test battery.

Development of performance evaluation tests for environmental research (PETER): complex counting test.

This study is the first in a program to develop a battery of Performance Evaluation Tests for Environmental Research (PETER). Nineteen volunteer subjects were tested daily for 3 weeks on a complex task requiring the operator to keep simultaneous track of several things with changing states. Average daily performances are reported as well as reliabilities of three main types: 1) internal consistency of the test; 2) sensitivity--the ability to differentiate subjects, and 3) stability--consistency of measurement over repeated sessions. The results showed that, on this task, learning was accomplished quickly, and performance stayed level for 3 weeks. The cross-tidal reliability for this test was found relatively stable after 3 d of practice, with a decline of only r=.94 to r=.79 over 11 d. This task is further noted as having several characteristics which make it particularly suitable for use in environmental research. It is concluded that the complex counting test can be recommended for use in environmental and other time-course research.