Max Vercruyssen

Work tolerance and subjective responses to wearing protective clothing and respirators during physical work

This study examined work tolerance and subjective responses while performing two levels of work and wearing four types of protective ensembles. Nine males (mean age = 24.8 years, weight = 75.3 kg, VO2 max = 44.6 ml/kg min) each performed a series of eight experimental tests in random order, each lasting up to 180 min in duration. Work was performed on a motor-driven treadmill at a set walking speed and elevation which produced work intensities of either 30% or 60% of each subjects maximum aerobic capacity. Work/rest intervals were established based on anticipated SCBA refill requirements. Environmental temperature averaged 22.6 degrees C and average relative humidity was 55%. The four protective ensembles were: a control ensemble consisting of light work clothing (CONTROL); light work clothing with an open circuit self-contained breathing apparatus (SCBA); firefighters turnout gear with SCBA (FF); and chemical protective clothing with SCBA (CHEM). Test duration (tolerance time) was determined by physiological responses reaching a predetermined indicator of high stress or by a 180-min limit. Physiological and subjective measurements obtained every 2.5 min included: heart rate, skin temperature, rectal temperature, and subjective ratings of perceived exertion, thermal sensation, and perspiration. The mean tolerance times were 155, 130, 26, and 73 min, respectively, for the CONTROL, SCBA, FF, and CHEM conditions during low intensity work; and 91, 23, 4, and 13 min, respectively, during high intensity work. Differences between ensemble and work intensity were significant. FF and CHEM heart rate responses did not reach a steady state, and rose rapidly compared to CONTROL and SCBA values. SCBA heart rates remained approximately 15 beats higher than the CONTROL ensemble during the tests. At the low work intensity, mean skin temperatures at the end of the test were 32.7, 33.1, 36.7, and 36.3 degrees C, while mean core temperatures were 37.6, 37.9, 37.9, and 38.5 degrees C, respectively. The subjective data indicated that, in general, subjects were able to perceive relative degrees of physiologic strain under laboratory conditions. Wearing protective clothing and respirators results in significant and potentially dangerous thermoregulatory and cardiovascular stress to the wearer even at low work intensities in a neutral environment. Physiologically and subjectively, firefighters turnout gear (the heaviest ensemble) produced the most stress, followed by the CHEM, SCBA, and CONTROL protective ensembles.

The effect of gender and time-of-day on time perception and mental workload

Two experiments are reported which investigated how subject gender and time-of-day influenced the estimation of duration and the perception of task-related mental workload. In the first experiment, 24 subjects performed a filled time-estimation task in a constant blacked-out, noise-reduced environment at 0800h, 1200h, 1600h, and 2000h, respectively. In the second experiment, 12 different subjects performed an unfilled time estimation task in similar conditions at 0900h, 1400h, and 1900h. At the termination of all experimental sessions, participants completed the NASA Task Load Index workload assessment questionnaire as a measure of perceived mental workload. Results indicated that physiological response, reflected in body temperature change, followed an expected pattern of sequential increase with time-of-day. However, estimates of duration and the perception of mental workload showed no significant effects for time-of-day. In each of the experiments there were significant differences in time estimation and mental workload response contingent on the gender of the participant. These results are interpreted in light of the previous positive findings for circadian fluctuation in performance efficiency and the equivocal findings of a gender difference in time estimation. A unifying account of these collective results is given based on gender by time-of-day interactional effects.

Limits of behavioral efficiency for workers in heat stress

This paper describes three zones which differentiate the limits of human behavioral efficiency in heat stress. They are: (1) a zone of thermal intolerance, (2) a zone which identifies the upper thermal tolerances for unimpaired cognitive and neuromuscular performance, and (3) a zone of thermal equilibration. Description of the boundaries to these zones through concurrent identification of time/intensity specifications and physiological criteria allows their broad application across both traditional industrial industrial conditions and activity in unusual occupational environments (e.g., those requiring enclosed garment useage), where contemporary indices based on physical values of the ambient surround are of restricted applicability. It is suggested that these criteria, based upon performance change, can be used to augment current heat stress standards which are founded upon physiological evidence of impairment.

Effects of carbon dioxide inhalation on psychomotor and mental performance during exercise and recovery.

On separate days, 6 highly trained participants performed psychomotor tests while breathing for 60 mm 3 carbon dioxide (CO2) mixtures (room air, 3% CO2, or 4% CO2) prior to, between, and following two 15-mm treadmill exercise bouts (70% VO2max). Each individual was extensively practiced (at least 4 days) before testing began, and both gas conditions and order of tasks were counterbalanced. Results showed physiological reactions and work-related psychomotor effects, but no effects of gas concentration on addition, multiplication, grammatical reasoning, or dynamic postural balance. These findings help define behavioral toxicity levels and support a re-evaluation of existing standards for the maximum allowable concentrations (also emergency and continuous exposure guidance levels) of CO2. This research explored the selection of psychometric instruments of sufficient sensitivity and reliability to detect subtle changes in performance caused by exposure to low levels of environmental stress, in this case differential levels of CO2 in the inspired air.

Estimation of duration and mental workload at differing times of day by males and females

Two experiments are reported which investigated whether male and female operator duration estimation and subjective workload followed conventional circadian fluctuation. In the first experiment, twenty-four subjects performed a filled time-estimation task in a constant blacked-out, noise-reduced environment at 0800, 1200, 1600, and 2000h. In the second experiment, twelve subjects performed an unfilled time estimation task in similar conditions at 0900, 1400, and 1900h. At the termination of all experimental sessions, participants completed the NASA TLX workload assessment questionnaire as a measure of perceived mental workload. Results indicated that while physiological response followed an expected pattern, estimations of duration and subjective perception of workload showed no significant effects for time-of-day. In each of the experiments, however, there were significant differences in durational estimates and mental workload response depending upon the gender of the participant. Results are taken to support the assertion that subjective workload is responsive largely to task-related factors and indicates the important differences that may be expected due to operator gender.

Longitudinal Analysis of Age-Related Slowing: BLSA Reaction Time Data

Reported are preliminary findings from analyses of cross-sectional and longitudinal reaction time data collected on 865 male and 453 female volunteers who ranged in age from 20 to 96 years. Evident in both simple and disjunctive reaction time measures was a consistent slowing with age. In nearly all cases, males were faster than females but gender differences were negligible for the simple reaction time (SRT) compared to disjunctive reaction time (DRT). Repeated testing within subjects over 2–8 years also showed age-related slowing across decades. Cross-sectional studies have been criticized for overestimating the actual age-related slowing found in longitudinal analysis. However, this was not the case in the present research. Similar effects were observed in analyses of data from all subjects on their first visit (n = 1318 subjects) compared to data from all subjects over all of their visits (n = 3855 subject visits) compared to data from only those subjects across decades who were tested repeatedly over at least 8 years (n = 314 subjects X 5 visits = 1570 subject visits). Findings from this research have human factors implications for task design, personnel selection, performance prediction, accident analysis, human tests and measurements, and demographic norms, to mention a few.

Experimental Evaluations of a Model of Mental Workload

The present experiments were designed to test predictions from a model of mental workload. The model predicts non-linear increases in mental workload as perceived distance from a task goal grows and effective time for action is reduced. Diminution of mental workload is achieved by application of effort which brings the task goal into the region of acceptable time/distance constraints for successful resolution. Two experiments are reported which tested these assertions using the timepools performance task. Timepools is unique as a performance task in that it generates a spatial representation of a shrinking temporal target. The independent effects of path length, i.e., the number of sequential targets to be acquired, and shrink rate, i.e., the collapse time during which the circle is halved in area, may be assessed using performance variables such as reaction time (RT), movement time (MT), error rate (E), and the subjective perception of workload. Data from Experiment 1, indicate systematic effects for task related factors across performance and workload measures, although such a pattern was not isomorphically mapped to the a priori assumed difficulty of the task. In Experiment 2, shrink rate and path length had independent effect on RT and MT respectively, which were reflected in components of the individual workload scales. The ramifications with respect to the model are elaborated.

Age-Related Slowing, S-R Compatibility, and Stages of Information Processing

Previous work in this laboratory (Vercruyssen, Carlton & Diggles-Buckles, 1989) has found that older individuals are at a disproportional disadvantage when stimulus-response (S-R) compatibility relationships are made more difficult. When stimulus quality and S-R compatibility were manipulated, age interacted with the S-R manipulation, suggesting in an additive factors framework that the locus of age-related slowing was the response selection stage. In that study S-R compatibility was manipulated by changing the S-R spatial map as well as changing the environment (subjects were required to cross their arms). The present study attempted to tease apart factors that might be contributing to that age x S-R compatibility relationship by using S-R maps of simple, moderate, and high difficulty as one factor and the arm position (crossed or uncrossed, a test of the Simon effect, Simon, Sly & Vilapakkam, 1981) as a different factor. In addition, stimulus quality was manipulated as a factor in this 4 factor design: age x stimulus quality x S-R map x arm position. Results revealed that both factors, S-R compatibility and arm position interacted with age. The conclusion from an additive factors perspective is that the stages of decision making (S-R compatibility) and response preparation (arm position) show age-dependent slowing whereas the stimulus encoding stage (stimulus quality) does not.

Gender Differences in Posture Effects on Cognition

To investigate the effects of and body posture on reaction time, 28 healthy university students (14 male and 14 female) served as subjects performing four-choice visual reaction tasks while sitting and standing, with intersession practice and a complete duplication of the study on a second day. Intratask manipulations were stimulus degradation, stimulus-response compatibility, and the response-stimulus interval (foreperiod uncertainty). Results showed main effects for all intratask variables and practice with interactions related to gender, posture, and degradation. Significant gender differences in the effects of posture and degradation were such that females had a slight advantage over males on tasks which emphasize early stages of processing. In general, it is concluded that the large disparity of findings within the gender-related psychomotor literature may be largely a function of methodological differences between studies. This investigation showed that experimental findings may vary according to the particular task used and the circumstances under which it was performed.

Aging, Reaction Time, and Stages of Information Processing

Using Sternbergs (1969) Additive Factors Method (AFM), previous investigations in search of the locus of age-related slowing in reactive capacity have found conflicting results possibly due to inconsistencies in research methodologies. This experiment was conducted to examine age differences in the performance of AFM intratask manipulations of a reaction time task using both fixed and variable foreperiod conditions with subject testing at both naive and practiced skill levels. Twenty male subjects, ten young and ten old, performed a visual four-choice RT task with intratask manipulations of stimulus-degradation, stimulus-response compatibility, and response-stimulus intervals (RSIs were fixed at 0, 2, and 5 sec and variable with random presentations at 0, 2, and 5 sec), once when subjects were naive and again when practiced. The results varied by level of practice and RSI, but clearly the older subjects had difficulty with the intratask manipulations. The older subjects took twice as long, on the average, to respond. Interactions of age by compatibility suggest that, according to the AFM, with age comes inordinately long delays in the response selection stage of information processing. Conclusions are made with caution since this research points to limitations and methodological confounds which serve to explain many of the equivocal findings in previous studies.