The compression of perceived time in a hot environment depends on physiological and psychological factors

The Effects of Physical and Mental Fatigue on Time Perception

The perception of time holds a foundational significance regarding how we elucidate the chronological progression of events. While some studies have examined exercise effects on time perception during exercise periods, there are no studies investigating the effects of exercise fatigue on time perception after an exercise intervention. This study investigated the effects of physical and mental fatigue on time estimates over 30 s immediately post-exercise and 6 min post-test. Seventeen volunteers were subjected to three conditions: physical fatigue, mental fatigue, and control. All participants completed a familiarization session and were subjected to three 30 min experimental conditions (control, physical fatigue (cycling at 65% peak power output), and mental fatigue (Stroop task)) on separate days. Time perception, heart rate, and body temperature were recorded pre-test; at the start of the test; 5, 10, 20, 30 seconds into the interventions; post-test; and at the 6 min follow-up. Rating of perceived exertion (RPE) was recorded four times during the intervention. Physical fatigue resulted in a significant (p = 0.001) underestimation of time compared to mental fatigue and control conditions at the post-test and follow-up, with no significant differences between mental fatigue and control conditions. Heart rate, body temperature, and RPE were significantly (all p = 0.001) higher with physical fatigue compared to mental fatigue and control conditions during the intervention and post-test. This study demonstrated that cycling-induced fatigue led to time underestimation compared to mental fatigue and control conditions. It is crucial to consider that physical fatigue has the potential to lengthen an individual's perception of time estimates in sports or work environments.

Frequency matters: how changes in hippocampal theta frequency can influence temporal coding, anxiety-reduction, and memory

Hippocampal theta frequency is a somewhat neglected topic relative to theta power, phase, coherence, and cross-frequency coupling. Accordingly, here we review and present new data on variation in hippocampal theta frequency, focusing on functional associations (temporal coding, anxiety reduction, learning, and memory). Taking the rodent hippocampal theta frequency to running-speed relationship as a model, we identify two doubly-dissociable frequency components: (a) the slope component of the theta frequency-to-stimulus-rate relationship ("theta slope"); and (b) its y-intercept frequency ("theta intercept"). We identify three tonic determinants of hippocampal theta frequency. (1) Hotter temperatures increase theta frequency, potentially consistent with time intervals being judged as shorter when hot. Initial evidence suggests this occurs via the "theta slope" component. (2) Anxiolytic drugs with widely-different post-synaptic and pre-synaptic primary targets share the effect of reducing the "theta intercept" component, supporting notions of a final common pathway in anxiety reduction involving the hippocampus. (3) Novelty reliably decreases, and familiarity increases, theta frequency, acting upon the "theta slope" component. The reliability of this latter finding, and the special status of novelty for learning, prompts us to propose a Novelty Elicits Slowing of Theta frequency (NEST) hypothesis, involving the following elements: (1) Theta frequency slowing in the hippocampal formation is a generalised response to novelty of different types and modalities; (2) Novelty-elicited theta slowing is a hippocampal-formation-wide adaptive response functioning to accommodate the additional need for learning entailed by novelty; (3) Lengthening the theta cycle enhances associativity; (4) Even part-cycle lengthening may boost associativity; and (5) Artificial theta stimulation aimed at enhancing learning should employ low-end theta frequencies.

How physical activity and passion color the passage of time: A response with ultra-trail runners

The aim of this study was to replicate the results of a lengthening effect caused by physical activity already observed in duration length judgment, using the time passage judgment measure, while exploring the effects of passion types (obsessive vs. harmonious) on time perception. A total of 378 ultra-trail runners responded to an online questionnaire in which the type of passion and the passage of time (PoT) judgments associated with both an ultra-trail context and a non-trail daily context were collected. The results showed that participants systematically judged the time as being dilated in a situation of sports practice, thus extending the results obtained in interval duration judgment studies. This study also showed an influence of the type of passion: higher levels of harmonious passion were related to greater feelings of time dilation, while higher levels of obsessive passion were related to greater feelings of both time contraction and time dilation. Results are discussed in light of the two major factors that influence the PoT referenced in the literature, namely, attention and happiness level.

Workers’ Perception Heat Stress: Results from a Pilot Study Conducted in Italy during the COVID-19 Pandemic in 2020

Many workers are exposed to the effects of heat and often to extreme temperatures. Heat stress has been further aggravated during the COVID-19 pandemic by the use of personal protective equipment to prevent SARS-CoV-2 infection. However, workers’ risk perception of heat stress is often low, with negative effects on their health and productivity. The study aims to identify workers’ needs and gaps in knowledge, suggesting the adaptation of measures that best comply with the needs of both workers and employers. A cross-sectional online questionnaire survey was conducted in Italy in the hottest months of 2020 (June–October) through different multimedia channels. The data collected were analyzed using descriptive statistics; analytical tests and analysis of variance were used to evaluate differences between groups of workers. In total, 345 questionnaires were collected and analyzed. The whole sample of respondents declared that heat is an important contributor to productivity loss and 83% of workers did not receive heat warnings from their employer. In this context, the internet is considered as the main source of information about heat-related illness in the workplace. Results highlight the need to increase workers’ perception of heat stress in the workplace to safeguard their health and productivity. About two-thirds of the sample stated that working in the sun without access to shaded areas, working indoors without adequate ventilation, and nearby fire, steam, and hot surfaces, represent the main injuries’ risk factors.

Effects of Acute Exposure to Thermal Stress on Cardiorespiratory Function, Skeletal Muscle Oxygenation, and Exercise Performance in Healthy Males

We investigated the effects of acute thermal stress (30 °C and 40 °C) and ordinary temperature (20 °C) on cardiorespiratory function, skeletal muscle oxygenation, and exercise performance in healthy men. Eleven healthy males (21.5 ± 2.3 years) performed a graded exercise test (GXT) using a cycle ergometer in each environmental condition (20 °C, 30 °C, and 40 °C) in a random order with an interval of 1 week between each test. Before the test, they were allowed to rest for 30 min in a given environmental condition. All dependent variables (body temperature, cardiorespiratory function parameters, skeletal muscle oxygenation profiles, and exercise performance) were measured at rest and during GXT. GXT was started at 50 W and increased by 25 W every 2 min until subjects were exhausted. Body temperature increased proportionally at rest and at the end of exercise as thermal stress increased. There were no differences in the rating of perceived exertion, oxygen uptake, respiratory exchange ratio, and carbon dioxide excretion between environmental conditions. Heart rate (HR), minute ventilation (VE), and blood lactate levels were significantly higher at 30 °C and 40 °C than at 20 °C, and oxygen pulse was significantly lower at 40 °C than at 20 °C at various exercise loads. None of the skeletal muscle oxygenation profiles showed significant changes at rest or during exercise. Maximal oxygen uptake, peak power, and exercise time significantly decreased proportionally as thermal stress increased, and this decrease was most pronounced at 40 °C. Acute thermal stress induces a decrease in exercise performance via increased body temperature, HR, VE, and blood lactate levels and decreased oxygen pulse during load-homogenized exercise. This phenomenon was more prominent at 40 °C than at 30 °C and 20 °C.

Effect of Exercise-Related Factors on the Perception of Time

The concept of time whether considered through the lenses of physics or physiology is a relative measure. Alterations in time perception can have serious implications in sport, fitness and work. Accurate perception of time is an important skill with many time constrained sports (i.e., basketball, North American football, tennis, gymnastics, figure skating, ice hockey, and others), and work environments (i.e., workers who need to synchronize their actions such as police and military). In addition, time distortions may play a role in exercise adherence. Individuals may be disinclined to continue with healthy, exercise activities that seem protracted (time dilation). Two predominant theories (scalar expectancy theory and striatal beat frequency model) emphasize the perception of the number of events in a period and the role of neurotransmitters in activating and coordinating cortical structures, respectively. A number of factors including age, sex, body temperature, state of health and fitness, mental concentration and exercise intensity level have been examined for their effect on time perception. However, with the importance of time perception for work, sport and exercise, there is limited research on this area. Since work, sports, and exercise can involve an integration of many of these aforementioned factors, they are interventions that need further investigations. The multiplicity of variables involved with work, sport, and exercise offer an underdeveloped but fruitful field for future research. Thus, the objective of this review was to examine physiological and psychological factors affecting human perception of time and the mechanisms underlying time perception and distortion with activity.

Time perception and timed decision task performance during passive heat stress

This study investigates the hypotheses that during passive heat stress, the change in perception of time and change in accuracy of a timed decision task relate to changes in thermophysiological variables gastrointestinal temperature and heart rate (HR), as well as subjective measures of cognitive load and thermal perception. Young adult males (N = 29) participated in two 60-min head-out water immersion conditions (36.5°C-neutral and 38.0°C-warm). Cognitive task measurements included accuracy (judgment task), response time (judgment ask), and time estimation (interval timing task). Physiological measurements included gastrointestinal temperature and heart rate. Subjective measurements included cognitive task load (NASA-TLX), rate of perceived exertion, thermal sensation, and thermal comfort. Gastrointestinal temperature and HR were significantly higher in warm versus neutral condition (gastrointestinal temperature: 38.4 ± 0.2°C vs. 37.2 ± 0.2°C, p < 0.01; HR: 105 ± 8 BPM vs. 83 ± 9 BPM, p < 0.01). The change in accuracy was significantly associated with the change in gastrointestinal temperature, and attenuated by change in thermal sensation and change in HR (r2=0.40, p< 0.01). Change in response time was significantly associated with the change in gastrointestinal temperature (r2=0.26, p< 0.002), and change in time estimation was best explained by a change in thermal discomfort (r2=0.18, p< 0.01). Changes in cognitive performance during passive thermal stress are significantly associated with changes in thermophysiological variables and thermal perception. Although explained variance is low (<50%), decreased accuracy is attributed to increased gastrointestinal temperature, yet is attenuated by increased arousal (expressed as increased HR and warmth thermal sensation).

Productivity and physiological responses during exposure to varying air temperatures and clothing conditions

This study assessed the effects of clothing and air temperature combinations on workplace productivity and physiological response. Ten male Japanese subjects were exposed to six combinations of clothing (0.3 clo and 0.9 clo) and air temperature (16°C, 26°C, and 36°C) during which cognitive performance (Bourdon and calculation tests), manual motor performance (finger-tapping test), and physiological responses (heart rate, blood pressure, and skin and oral temperatures) were measured. Both cold exposure and lower clothing levels likely increased the Bourdon test performance. Calculation test performance tended to be affected by exposure to cold or neutral temperatures at the beginning of the test. Cold exposure undermined manual motor performance (especially when combined with fewer clothing items) while heat exposure significantly increased heart rate. Both cold exposure and higher clothing level during heat exposure increased blood pressure. Body temperature, particularly mean skin temperature, increased with higher air temperature and was significantly influenced by clothing insulation during cold exposure. These results provide novel evidence for the effects of clothing and air temperature (particularly cold) on human productivity and physiological responses in humans.

Workplace heat exposure, health protection, and economic impacts: A case study in Canada

BACKGROUND

Occupational heat exposure is a serious concern for worker health, productivity, and the economy. Few studies in North America assess how on-site wet bulb globe temperature (WBGT) levels and guidelines are applied in practice.

METHODS

We assessed the use of a WBGT sensor for localized summertime heat exposures experienced by outdoor laborers at an industrial worksite in Ontario, Canada during the warm season (May-October) from 2012 to 2018 inclusive. We further examined informed decision making, approximated workers' predicted heat strain (sweat loss, core temperature), and estimated potential financial loss (via hourly wages) due to decreased work allowance in the heat.

RESULTS

Significantly higher worksite WBGT levels occured compared with regional levels estimated at the airport, with an upward trend in heat warnings over the 7 years and expansion of warnings into the fall season. The maximum WBGT during warnings related strongly to predicted hourly sweat loss. On average, 22 hours per worker were lost each summer (~1% of annual work hours) as a result of taking breaks or stopping due to heat. This amount of time corresponded to an average individual loss of C$1100 Canadian dollars (~C$220,000 combined for ~200 workers) to workers or the company. The additional losses for an enterprise due to reduced product output were not estimated.

CONCLUSIONS

Worksite observations and actions at the microscale are essential for improving the estimates of health and economic costs of extreme heat to enterprises and society. Providing worksite heat metrics to the employees aids in appropriate decision making and health protection.

Heat acclimation attenuates the increased sensations of fatigue reported during acute exercise-heat stress

Athletes exercising in heat stress experience increased perceived fatigue acutely, however it is unknown whether heat acclimation (HA) reduces the magnitude of this perceptual response and whether different HA protocols influence the response. This study investigated sensations of fatigue following; acute exercise-heat stress; short- (5-sessions) and medium-term (10-sessions) HA; and between once- (ODHA) and twice-daily HA (TDHA) protocols. Twenty male participants (peak oxygen uptake: 3.75 ± 0.47 L·min-1) completed 10 sessions (60-min cycling at ~2 W·kg-1, 45°C/20% relative humidity) of ODHA (n = 10) or non-consecutive TDHA (n = 10). Sensations of fatigue (General, Physical, Emotional, Mental, Vigor and Total Fatigue) were assessed using the multi-dimensional fatigue scale inventory-short form pre and post session 1, 5 and 10. Heat adaptation was induced following ODHA and TDHA, with reductions in resting rectal temperature and heart rate, and increased plasma volume and sweat rate (P < 0.05). General, Physical and Total Fatigue increased from pre-to-post for session 1 within both groups (P < 0.05). Increases in General, Physical and Total Fatigue were attenuated in session 5 and 10 vs. session 1 of ODHA (P < 0.05). This change only occurred at session 10 of TDHA (P < 0.05). Whilst comparative heat adaptations followed ODHA and TDHA, perceived fatigue is prolonged within TDHA.

ABBREVIATIONS

∆: Change; ANOVA: Analysis of variance; HA: Heat acclimation; HR: Heart rate; IL-6: Interleukin-6; MFS-SF: Multi-dimensional fatigue symptom inventory-short form (MFSI-SF); MTHA: Medium-term heat acclimation; Na+: Sodium; ODHA: Once daily heat acclimation; PV: Plasma volume; RH: Relative humidity; RPE: Rating of perceived exertion; SD: Standard deviation; SE: Standard error of the slope coefficient or intercept; SEE : Standard error of the estimate for the regression equation; STHA: Short-term heat acclimation; TDHA: Twice daily heat acclimation; TC: Thermal Comfort; Tre: Rectal temperature; TSS: Thermal sensation; V̇O2peak: Peak oxygen uptake; WBSL: whole-body sweat loss.

Core body temperature speeds up temporal processing and choice behavior under deadlines

Evidence suggests that human timing ability is compromised by heat. In particular, some studies suggest that increasing body temperature speeds up an internal clock, resulting in faster time perception. However, the consequences of this speed-up for other cognitive processes remain unknown. In the current study, we rigorously tested the speed-up hypothesis by inducing passive hyperthermia through immersion of participants in warm water. In addition, we tested how a change in time perception affects performance in decision making under deadline stress. We found that participants underestimate a prelearned temporal interval when body temperature increases, and that their performance in a two-alternative forced-choice task displays signatures of increased time pressure. These results show not only that timing plays an important role in decision-making, but also that this relationship is mediated by temperature. The consequences for decision-making in job environments that are demanding due to changes in body temperature may be considerable.

It's about Time: Effects of Physical Exertion on Duration Estimates

BACKGROUND

Task duration is a fundamental aspect of exercise, but little is known about how completed bouts of physical activity are perceived. Consequently, the purpose of the five experiments conducted for this investigation was to examine the effects of engaging in physical tasks on retrospective duration estimates with college student participants.

METHODS

Across the five experiments, participants were 113 college students (82 women, 31 men). In Experiments 1 and 2, participants provided duration estimates of a period spent engaging in physical activity or rest. In Experiments 3, 4, and 5, participants provided duration estimates of periods spent engaged in physical tasks of high intensity and low intensity.

RESULTS

In Experiments 1, 2, and 3, participants engaged in physical activity tended to perceive durations as shorter than participants at rest. When completing less familiar tasks (Experiments 4 and 5), however, participants recalled a high intensity bout of physical activity as lasting longer than a low intensity bout of physical activity of comparable duration. Cohen's d values for physical activity effects on duration estimates ranged from 0.40 to 1.60.

CONCLUSION

The findings, which partially support a contextual-change interpretation, suggest that factors, such as perceived exertion and task familiarity, affect retrospective duration estimates.

Exploring Heat Stress Relief Measures among the Australian Labour Force

Australia experiences frequent heat waves and generally high average temperatures throughout the continent with substantial impacts on human health and the economy. People adapt to heat by adopting various relief measures in their daily lives including changing their behaviour. Many labour intensive outdoor industries implement standards for heat stress management for their workforce. However, little is known about how people cope with heat at their workplaces apart from studies targeting some specific industries where labourers are exposed to extreme heat. Here, we analysed responses from 1719 people in the Australian labour force to self-reported heat stress and associated coping mechanisms. Three quarters of respondents experienced heat stress at their workplace with fatigue and headache being the two most frequently stated symptoms. Almost all of those who were affected by heat would hydrate (88%), 67% would cool, and 44% would rest as a strategy for coping with heat. About 10% intended to change their jobs because of heat stress in the workplace. We found differences in heat relief measures across gender, education, health, level of physical intensity of job, and time spent working outside. People working in jobs that were not very demanding physically were more likely to choose cooling down as a relief measure, while those in labour intensive jobs and jobs that required considerable time outside were more likely to rest. This has potential consequences for their productivity and work schedules. Heat affects work in Australia in many types of industry with impact dependent on workforce acclimatisation, yet public awareness and work relief plans are often limited to outdoor and labour intensive industries. Industries and various levels of government in all sectors need to implement standards for heat management specific to climate zones to help people cope better with high temperatures as well as plan strategies in anticipation of projected temperature increases.

Time Flies When You're at RPE13: How Exercise Intensity Influences Perception of Time

Hanson, NJ and Lee, TL. Time flies when you're at RPE13: How exercise intensity influences perception of time. J Strength Cond Res 34(12): 3546-3553, 2020-Previous studies have shown that there are some changes in our perception of time during exercise, but the relationship between intensity level and these perceptions is unclear. Therefore, the purpose of this study was to determine the effect of exercise intensity on prospective time estimations. Twenty-two trained runners (10 male, 12 female; age 25 ± 6 years) participated in three 30-minute treadmill runs that were perceptually regulated at rating of perceived exertion (RPE) levels of 13 ("somewhat hard"), 15 ("hard"), and 17 ("very hard"). Prospective time assessments, in which subjects estimated durations of 1, 3, 7, and 20 seconds, were obtained immediately before exercise, during (at 10 and 20 minutes), and after exercise. A 3 (RPE) × 4 (timepoint) × 4 (estimated duration) repeated-measures analysis of variance was completed. There was a significant main effect of RPE level (p = 0.013). Post hoc tests revealed that time estimations at RPE17 were significantly lower than those at RPE13 (p = 0.021). The main effects of timepoint and estimated duration were not significant (both p ≥ 0.05), and no interactions were present. However, there was a trend for time estimations to decrease in all conditions as exercise progressed, with a rebound after cessation of exercise. This study showed a clear effect of exercise intensity on time perception. Specifically, the subjects perceived time to pass by more slowly as intensity increased.

Drivers of self-reported heat stress in the Australian labour force

Heat stress causes reductions in well-being and health. As average annual temperatures increase, heat stress is expected to affect more people. While most research on heat stress has explored how exposure to heat affects functioning of the human organism, stress from heat can be manifest long before clinical symptoms are evident, with profound effects on behavior. Here we add to the little research conducted on these subclinical effects of environmental heat using results from an Australian-wide cross-sectional study of nearly 2000 respondents on their self-reported level of heat stress. Slightly less than half (47%) of the respondents perceived themselves as at least sometimes, often or very often stressed by heat during the previous 12 months. Health status and smoking behavior had the expected impact on self-reported perceived heat stress. There were also regional differences with people living in South Australia, Victoria and New South Wales most likely to have reported to have felt heat stressed. People generally worried about climate change, who had been influenced by recent heat waves and who thought there was a relationship between climate change and health were also more likely to have been heat stressed. Surprisingly average maximum temperatures did not significantly explain heat stress but stress was greater among people who perceived the day of the survey as hotter than usual. Currently heat stress indices are largely based on monitoring the environment and physical limitations to people coping with heat. Our results suggest that psychological perceptions of heat need to be considered when predicting how people will be affected by heat under climate change and when developing heat relief and climate change adaptation plans, at work, at home or in public spaces. We further conclude that the perception of temperature and heat stress complements measures that assess heat exposure and heat strain.

Stronger cortisol response to acute psychosocial stress is correlated with larger decrease in temporal sensitivity

As a fundamental dimension of cognition and behavior, time perception has been found to be sensitive to stress. However, how one’s time perception changes with responses to stress is still unclear. The present study aimed to investigate the relationship between stress-induced cortisol response and time perception. A group of 40 healthy young male adults performed a temporal bisection task before and after the Trier Social Stress Test for a stress condition. A control group of 27 male participants completed the same time perception task without stress induction. In the temporal bisection task, participants were first presented with short (400 ms) and long (1,600 ms) visual signals serving as anchor durations and then required to judge whether the intermediate probe durations were more similar to the short or the long anchor. The bisection point and Weber ratio were calculated and indicated the subjective duration and the temporal sensitivity, respectively. Data showed that participants in the stress group had significantly increased salivary cortisol levels, heart rates, and negative affects compared with those in the control group. The results did not show significant group differences for the subjective duration or the temporal sensitivity. However, the results showed a significant positive correlation between stress-induced cortisol responses and decreases in temporal sensitivity indexed by increases in the Weber ratio. This correlation was not observed for the control group. Changes in subjective duration indexed by temporal bisection points were not correlated with cortisol reactivity in both the groups. In conclusion, the present study found that although no significant change was observed in time perception after an acute stressor on the group-level comparison (i.e., stress vs. nonstress group), individuals with stronger cortisol responses to stress showed a larger decrease in temporal sensitivity. This finding may provide insight into the understanding of the relationship between stress and temporal sensitivity.

Higher chronic stress is associated with a decrease in temporal sensitivity but not in subjective duration in healthy young men

Maintaining accurate and precise temporal perception under conditions of stress is important. Studies in animal models and clinic patients have suggested that time perception can change under chronic stress. Little is known, however, about the relationship between chronic stress and time perception in healthy individuals. Here, a sample of 62 healthy young men completed Cohen’s Perceived Stress Scale (PSS) as a measure of chronic stress levels, while time perception was measured using a temporal bisection task. This task used short (400 ms) and long (1600 ms) visual signals as anchor durations. Participants were presented with a range of intermediate probe durations and were required to judge whether the durations were more similar to the short or the long anchor. Results showed that chronic stress was negatively related to temporal sensitivity indexed by the Weber ratio. However, there was no significant correlation between chronic stress and subjective duration indexed by the bisection point. These results demonstrate that higher chronic stress is associated with lower temporal sensitivity and thus provide evidence for a link between chronic stress and time perception in healthy adults.

Emotional modulation of attention affects time perception: evidence from event-related potentials

Emotional effects on human time perception are generally attributed to arousal speeding up or slowing down the internal clock. The aim of the present study is to investigate the less frequently considered role of attention as an alternative mediator of these effects with the help of event-related potentials (ERPs). Participants produced short intervals (0.9, 1.5, 2.7, and 3.3s) while viewing high arousal images with pleasant and unpleasant contents in comparison to neutral images. Behavioral results revealed that durations were overproduced for the 0.9s interval whereas, for 2.7 and 3.3s intervals, underproduction was observed. The effect of affective valence was present for the shorter durations and decreased as the target intervals became longer. More specifically, the durations for unpleasant images were less overproduced in the 0.9s intervals, and for the 1.5s trials, durations for unpleasant images were slightly underproduced, compared to pleasant images, which were overproduced. The analysis of different ERP components suggests possible attention processes related to the timing of affective images in addition to changes in pacemaker speed. Early Posterior Negativity (EPN) was larger for positive than for negative images, indicating valence-specific differences in activation of early attention mechanisms. Within the early P1 and the Late Positive Potential (LPP) components, both pleasant and unpleasant stimuli exhibited equal affective modulation. Contingent Negative Variation (CNV) remained independent of both timing performance and affective modulation. This pattern suggests that both pleasant and unpleasant stimuli enhanced arousal and captured attention, but the latter effect was more pronounced for pleasant stimuli. The valence-specificity of affective attention revealed by ERPs combined with behavioral timing results suggests that attention processes indeed contribute to emotion-induced temporal distortions, especially for longer target intervals.