Titis Wijayanto

Cutaneous Warm and Cool Sensation Thresholds and the Inter-threshold Zone in Malaysian and Japanese Males

The purpose of this study was to investigate ethnic differences in cutaneous thermal sensation thresholds and the inter-threshold sensory zone between tropical (Malaysians) and temperate natives (Japanese). The results showed that (1) Malaysian males perceived warmth on the forehead at a higher skin temperature (Tsk) than Japanese males (p<0.05), whereas cool sensations on the hand and foot were perceived at a lower Tsk in Malaysians (p<0.05); (2) Overall, the sensitivity to detect warmth was greater in Japanese than in Malaysian males; (3) The most thermally sensitive body region of Japanese was the forehead for both warming and cooling, while the regional thermal sensitivity of Malaysians had a smaller differential than that of Japanese; (4) The ethnic difference in the inter-threshold sensory zone was particularly noticeable on the forehead (1.9±1.2C for Japanese, 3.2±1.6°C for Malaysians, p<0.05). In conclusion, tropical natives had a tendency to perceive warmth at a higher Tsk and slower at an identical speed of warming, and had a wider range of the inter-threshold sensory zone than temperate natives.

Effects of duration of stay in temperate area on thermoregulatory responses to passive heat exposure in tropical south-east Asian males residing in Japan

BackgroundIn this study, we investigated the effects of duration of stay in a temperate area on the thermoregulatory responses to passive heat exposure of residents from tropical areas, particularly to clarify whether they would lose their heat tolerance during passive heat exposure through residence in a temperate country, Japan.MethodsWe enrolled 12 males (mean ± SE age 25.7 ± 1.3 years) from south-east Asian countries who had resided in Japan for a mean of 24.5 ± 5.04 months, and 12 Japanese males (age 24.1 ± 0.9 years). Passive heat exposure was induced through leg immersion in hot water (42°C) for 60 minutes under conditions of 28°C air temperature and 50% relative humidity.ResultsCompared with the Japanese group, the tropical group displayed a higher pre-exposure rectal temperature (P < 0.01) and a smaller increase in rectal temperature during 60 minutes of leg immersion (P = 0.03). Additionally, the tropical group showed a tendency towards a lower total sweat rate (P = 0.06) and lower local sweat rate on the forehead (P = 0.07). The tropical group also had a significantly longer sweating onset time on the upper back (P = 0.04) compared with the Japanese groups. The tropical group who stayed in Japan for > 23 months sweated earlier on the forehead and upper back than those who stayed in Japan < 11 months (P < 0.01 and P = 0.03 for the forehead and upper back, respectively). There was a positive correlation between duration of stay in Japan and total sweat rate (r = 0.58, P <0.05), and negative correlations between duration of stay and sweating onset time on the forehead (r = −0.73, P = 0.01) and on the upper back (r = −0.66, P = 0.02). Other physiological indices measured in this study did not show any difference between the subjects in the tropical group who had lived in Japan for a shorter time and those who had lived there for a longer time.ConclusionsWe conclude that the nature of heat acclimatization of the sweating responses to passive heat exposure that are acquired from long-term heat acclimatization is decayed by a stay in a temperate area, as shown by the subjects in our tropical group. We did not find any evidence of a decay in the other physiological indices, indicating that heat tolerance acquired from long-term heat acclimatization is not completely diminished through residence in a temperate area for less than 4 years, although some aspects of this heat tolerance may be decayed.

Ethnic differences in thermoregulatory responses during resting, passive and active heating: application of Werner’s adaptation model

For the coherent understanding of heat acclimatization in tropical natives, we compared ethnic differences between tropical and temperate natives during resting, passive and active heating conditions. Experimental protocols included: (1) a resting condition (an air temperature of 28°C with 50% RH), (2) a passive heating condition (28°C with 50% RH; leg immersion in a hot tub at a water temperature of 42°C), and (3) an active heating condition (32°C with 70% RH; a bicycle exercise). Morphologically and physically matched tropical natives (ten Malaysian males, MY) and temperate natives (ten Japanese males, JP) participated in all three trials. The results saw that: tropical natives had a higher resting rectal temperature and lower hand and foot temperatures at rest, smaller rise of rectal temperature and greater temperature rise in bodily extremities, and a lower sensation of thirst during passive and active heating than the matched temperate natives. It is suggested that tropical natives’ homeostasis during heating is effectively controlled with the improved stability in internal body temperature and the increased capability of vascular circulation in extremities, with a lower thirst sensation. The enhanced stability of internal body temperature and the extended thermoregulatory capability of vascular circulation in the extremities of tropical natives can be interpreted as an interactive change to accomplish a thermal dynamic equilibrium in hot environments. These heat adaptive traits were explained by Wilder’s law of initial value and Werner’s process and controller adaptation model.

The use of language to express thermal sensation suggests heat acclimatization by Indonesian people

The purpose of this study was to explore whether there is evidence of heat acclimatization in the words used to express thermal sensation. A total of 458 urban Japanese and 601 Indonesians participated in a questionnaire. In addition, in a preliminary survey, 39 native English speakers in the UK participated. Our results showed that (1) for Indonesians, the closest thermal descriptor of a feeling of thermal comfort was ‘cool’ (75%) followed by ‘slightly cool’ (7%), ‘slightly cold’ (5%) and ‘cold’ (5%), while Japanese responses were distributed uniformly among descriptors ‘cool’, ‘slightly cool’, ‘neither’, ‘slightly warm’, and ‘warm’; (2) the closest thermal descriptors of a feeling of discomfort for Indonesians were less affected by individual thermal susceptibility (vulnerability) than those for Japanese; (3) in the cases where ‘cool’ and ‘slightly cold’ were imagined in the mind, the descriptors were cognized as a thermal comfortable feeling by 97% and 57% of Indonesians, respectively; (4) the most frequently voted choice endorsing hot weather was ‘higher than 32°C’ for Indonesians and ‘higher than 29°C’ for Japanese respondents; for cold weather, ‘lower than 15°C’ for Japanese and ‘lower than 20°C’ for Indonesians. In summary, the descriptor ‘cool’ in Indonesians connotes a thermally comfortable feeling, but the inter-zone between hot and cold weather that was judged in the mind showed a upward shift when compared to that of Japanese. It is suggested that linguistic heat acclimatization exists on a cognitive level for Indonesians and is preserved in the words of thermal descriptors.

Quantifying visual attention and visually induced motion sickness during day-night driving and sleep deprivation

Investigation of drivers physical fitness is an important research topic in accident prevention and intelligent driver monitoring system. Visual attention is one of physical fitness indicators that can be measured quantitatively. Driving simulator can be used to support observation of visual attention and behavior of the driver. On the other side, biomedical effect of driving simulator namely visually induced motion sickness (VIMS) is actively investigated to encourage appropriate usage of the simulator. However, there is no information on how sleep deprivation and day-night difference provoke VIMS and affect visual attention during simulation. In this paper, we present a novel investigation on effect of sleep deprivation and day-night difference on VIMS and visual attention using simulator sickness questionnaire (SSQ) and eye tracking. Statistical analysis on SSQ data shows that day-night difference and sleep deprivation induce symptoms of nausea (F(2,22)=5.825, p<;0.05), oculomotor (F(2,22)=12.657, p<;0.05), and disorientation (F(2,22)=8.270, p<;0.05) significantly. Results of eye tracking analysis show that sleep deprivation and day-night difference affect visual attention significantly (F(2,22)=3.904, p<;0.05). Experimental results suggest that driving simulation is better used in day-time to minimize VIMS. Furthermore, proper night rest beforehand and good room illumination are important to support physical fitness during day-time driving.

Investigation of visual attention in day-night driving simulator during cybersickness occurrence

Studies involving simulator are often used to support scientific research, such as research on post-traumatic stress disorder (PTSD) and fear of flying. However, the use of driving simulator may produce biomedical side effect, namely cybersickness. Although the research of simulator sickness has been done before, there is no study that focuses on how cybersickness affects visual attention during day and night driving condition. This study aims to investigate the effect of cybersickness on visual attention during day-night driving condition by observing SSQ score and user eye movements. SSQ analysis showed a significant difference of nausea score (F (2,18) = 5,434, p<0,05), oculomotor score (F (2,18) = 11,277, p<0,05), disorientation score (F (2,18) = 7,822, p<0,05), and total score (F (2,18) = 9,511, p<0,05). Correlation analysis of various eye movements and SSQ shows a significant relationship between the score of SSQ and the number of fixation. Experimental results imply that this research may be used as an alternative recommendation to avoid stress when using driving simulator.

Effects of morning-night differences and sleep deprivation on situation awareness and driving performance

The purpose of this study was to investigate the effect of morning-night differences and sleep deprivation on situation awareness and driving performance. Twelve male students (mean of age 21.0±0.7 years old) participated in this study. They drove in following driving scenarios under three conditions: night condition, morning condition with and without sleep deprivation, on a driving simulator. Statistical analysis on situation awareness (SA) data shows that morning-night differences and sleep deprived condition during driving significantly affect Level 1 SA (F(2,22)=18.54, P<;0.01), Level 2 SA (F(2,22)=14.47, P<;0.01), and Level 3 SA (F(2,22)=4.54, P=0.03). There are also significantly higher risky driving behavior score when driving in the morning with sleep deprived condition, as compared to driving in the Morning with proper sleep (P<;0.01). The results of this study suggested that sleep deprivation or driving at night produced a degradation of situation awareness and a higher risky driving behavior.

Authors’ response to A. Flouris’s correspondence ‘The advantage of using differential data in thermal biology’

We are grateful for the correspondence from Dr. Flouris (Flouris 2010) suggesting “differential data analysis” for a comparison of time course data of body temperature during 60 min of submaximal exercise between Japanese and Malaysians, in our recent original paper (Wakabayashi et al. 2010). Following the suggestion, we additionally conducted data analysis for time course of a relative change of rectal (ΔTre) and hand skin temperature (ΔThand) from their resting baseline, instead of actual level data. As a result, a significant difference was observed in both ΔTre and ΔThand between groups from 10 min after onset of exercise to the end of the experiment (P<0.05, Fig. 1); ΔTre was greater in Japanese and ΔThand was greater in Malaysians. The greater increase of Thand in Malaysian participants suggested a greater hand blood flow as a heat dissipation response during exercise in humid heat stress, which partly explained the smaller increase of Tre in Malaysians. This differential data analysis is pertinent to the discussion in our manuscript (Wakabayashi et al. 2010). As Dr. Flouris suggests, the differential data analysis has the advantage of focusing on the magnitude of change in thermoregulatory response to thermal stress, while minimizing variation of data due to individual differences in the resting baseline. However, in some cases, the actual level data have a significant meaning for the thermoregulation. In our series of studies, tropical indigene Malaysians showed a significantly higher resting Tre than Japanese (Lee