Int J Biometeorol DOI 10.1007/s00484-015-0956-3
ORIGINAL PAPER
Nonthermal sensory input and altered human thermoregulation: effects of visual information depicting hot or cold environments Jun’ya Takakura & Takayuki Nishimura & Damee Choi & Yuka Egashira & Shigeki Watanuki
Received: 9 August 2014 / Revised: 3 January 2015 / Accepted: 4 January 2015 # ISB 2015
Abstract A recent study showed that thermoregulatory-like cardiovascular responses can be invoked simply by exposure to visual information, even though the thermal environments are neutral and unchanged. However, it was not clear how such responses affect actual human body temperature regulation. We investigated whether such visually invoked physiological responses can substantively affect human core body temperature in a thermally challenging cold environment. Participants comprised 13 graduate or undergraduate students viewing different video images containing hot, cold, or no scenery, while room temperature was gradually lowered from 28 to 16 °C over 80 min. Rectal temperature, mean skin temperature, core to skin temperature gradient, and oxygen consumption were measured during the experiment. Rectal temperature was significantly lower when hot video images were presented compared to when control video images were presented. Oxygen consumption was comparable among all video images, but core to skin temperature gradient was significantly lower when hot video images were presented. This result suggests that visual information, even in the absence of thermal energy, can affect human thermodynamics and core body temperature. Keywords Visual information . Visual-thermal interaction . Thermoregulation . Artificial media environment J. Takakura (*) : D. Choi : Y. Egashira Graduate School of Integrated Frontier Science, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka, Japan e-mail: [email protected] T. Nishimura Department of Public Health, Nagasaki University Graduate School of Biomedical Sciences, 1-12-4 Sakamoto, Nagasaki, Japan S. Watanuki Faculty of Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka, Japan
Introduction Maintaining core body temperature at a quasi-constant level is pivotal for hominids, including humans (Tattersall et al. 2012). An elaborate thermoregulatory system plays an important role in maintaining human core body temperature. Temperature (thermal energy) is sensed by central and peripheral sensory receptors that show sensitivity to thermal energy (Patapoutian et al. 2003). Afferent thermal sensory information is integrated in the preoptic area (POA) of the hypothalamus (Boulant 1998) and used to control effectors regulating heat production, vasocontraction, and cardiac functions (Kanosue et al. 2010; Romanovsky 2007). The system mentioned above seems to allow quite reasonable control of core body temperature. One important feature facilitating such successful regulation is that the thermoregulatory system shows specific sensitivity to thermal energy (Fraden 2010). Sensitivity to inputs lacking thermal energy would mean that the regulatory system would be vulnerable to disturbance. For example, sensitivity of the thermoregulatory system to visual inputs does not appear rational, because visible light has little thermal energy. However, many researchers have focused on effects of visual information, particularly in terms of perceptual or cognitive perspectives. For example, the hue-heat hypothesis is one of the most famous concepts in this field, with red color related to warmness and blue color related to coldness. However, substantial effects of color have generally not been demonstrated (Bennett and Rey 1972; Berry 1961; Candas and Dufour 2005), while other reports have suggested the existence of a small effect under extreme conditions (Fanger et al. 1977) or a relatively large effect under moderate conditions (Winzen et al. 2014). Such contradictory results may be attributable to differences in experimental context and the ambiguity of the meanings of colors. Perceptual visual-thermal interactions have been reported to exist depending on the
Int J Biometeorol
context and by using an ice cube, which is not ambiguous in terms of thermal meaning, as a visual stimulus (Kanaya et al. 2012). Moreover, physiological effects have also been suggested to exist, in addition to perceptual interactions. Our previous study demonstrated that thermoregulatory-like cardiovascular responses can be invoked simply by viewing video images containing depictions of hot or cold scenery, even when the actual thermal condition remains constant (Takakura et al. 2013). In the previous study, when participants were exposed to video images containing cold images, cardiac output and heart rate tended to be small and total peripheral resistance tended to be large. In contrast, when participants were exposed to video images containing hot images, cardiac output and heart rate tended to be large and total peripheral resistance tended to be small. Such antagonistic cardiac and vascular responses are known to be observed in actual thermoregulatory responses (Walther et al. 1970). In other words, the human thermoregulatory system may respond inappropriately to visual information, which lacks thermal energy. However, whether this trait can actually affect human thermoregulation in a substantive way remains unclear, because the experiment was conducted under thermally neutral conditions and the exposure time was not long enough. In addition, direct measurement of body temperature was not conducted. As long as the visual information and actual thermal environment are consistent, such traits will not disturb human homeostasis. In natural environments, when humans were exposed to cold visual information (for example, scenery of snow), the actual thermal environment would most often also have been cold. However, considering the rapid increase in media technology (Marshall et al. 2006; Sechrist 2014), discrepancies between visual inputs and the actual thermal environment can now occur much more easily. Investigation of such human traits is thus important in order to design adequate artificial and media environments. Our previous study focused on internal hemodynamics but did not measure body temperature (actual thermal regulation). The purpose of this study was to confirm whether visual information without thermal energy can affect human thermal regulations in a substantive way. To clarify this issue, participants were exposed to visually cold, hot, or neutral information in thermally challenging cold environments, because exposing thermally challenging environment is an effective way to examine the difference in the ability of thermoregulation (Wagner et al. 1974; Wakabayashi et al. 2011; Nishimura et al. 2011). We investigated this issue with a particular focus on body temperature rather than cardiovascular responses. If thermoregulatory systems are affected by visual information in a substantive manner, core body temperature would differ depending on the visual information.
Materials and methods Thirteen male undergraduate or graduate Japanese students (age range, 20–23 years) participated in the experiment. Mean (±standard deviation) characteristics were as follows: height, 172.4±7.5 cm; weight, 61.2±13.2 kg; and body mass index, 20.0±2.65 kg/m2. Temperature in the experiment room was initially set and kept at 28 °C for 20 min, then gradually lowered to 16 °C over the course of >80 min (Fig. 1). Relative humidity was set at 50 %, and wind speed was
ORIGINAL PAPER
Nonthermal sensory input and altered human thermoregulation: effects of visual information depicting hot or cold environments Jun’ya Takakura & Takayuki Nishimura & Damee Choi & Yuka Egashira & Shigeki Watanuki
Received: 9 August 2014 / Revised: 3 January 2015 / Accepted: 4 January 2015 # ISB 2015
Abstract A recent study showed that thermoregulatory-like cardiovascular responses can be invoked simply by exposure to visual information, even though the thermal environments are neutral and unchanged. However, it was not clear how such responses affect actual human body temperature regulation. We investigated whether such visually invoked physiological responses can substantively affect human core body temperature in a thermally challenging cold environment. Participants comprised 13 graduate or undergraduate students viewing different video images containing hot, cold, or no scenery, while room temperature was gradually lowered from 28 to 16 °C over 80 min. Rectal temperature, mean skin temperature, core to skin temperature gradient, and oxygen consumption were measured during the experiment. Rectal temperature was significantly lower when hot video images were presented compared to when control video images were presented. Oxygen consumption was comparable among all video images, but core to skin temperature gradient was significantly lower when hot video images were presented. This result suggests that visual information, even in the absence of thermal energy, can affect human thermodynamics and core body temperature. Keywords Visual information . Visual-thermal interaction . Thermoregulation . Artificial media environment J. Takakura (*) : D. Choi : Y. Egashira Graduate School of Integrated Frontier Science, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka, Japan e-mail: [email protected] T. Nishimura Department of Public Health, Nagasaki University Graduate School of Biomedical Sciences, 1-12-4 Sakamoto, Nagasaki, Japan S. Watanuki Faculty of Design, Kyushu University, 4-9-1 Shiobaru, Minami-ku, Fukuoka, Japan
Introduction Maintaining core body temperature at a quasi-constant level is pivotal for hominids, including humans (Tattersall et al. 2012). An elaborate thermoregulatory system plays an important role in maintaining human core body temperature. Temperature (thermal energy) is sensed by central and peripheral sensory receptors that show sensitivity to thermal energy (Patapoutian et al. 2003). Afferent thermal sensory information is integrated in the preoptic area (POA) of the hypothalamus (Boulant 1998) and used to control effectors regulating heat production, vasocontraction, and cardiac functions (Kanosue et al. 2010; Romanovsky 2007). The system mentioned above seems to allow quite reasonable control of core body temperature. One important feature facilitating such successful regulation is that the thermoregulatory system shows specific sensitivity to thermal energy (Fraden 2010). Sensitivity to inputs lacking thermal energy would mean that the regulatory system would be vulnerable to disturbance. For example, sensitivity of the thermoregulatory system to visual inputs does not appear rational, because visible light has little thermal energy. However, many researchers have focused on effects of visual information, particularly in terms of perceptual or cognitive perspectives. For example, the hue-heat hypothesis is one of the most famous concepts in this field, with red color related to warmness and blue color related to coldness. However, substantial effects of color have generally not been demonstrated (Bennett and Rey 1972; Berry 1961; Candas and Dufour 2005), while other reports have suggested the existence of a small effect under extreme conditions (Fanger et al. 1977) or a relatively large effect under moderate conditions (Winzen et al. 2014). Such contradictory results may be attributable to differences in experimental context and the ambiguity of the meanings of colors. Perceptual visual-thermal interactions have been reported to exist depending on the
Int J Biometeorol
context and by using an ice cube, which is not ambiguous in terms of thermal meaning, as a visual stimulus (Kanaya et al. 2012). Moreover, physiological effects have also been suggested to exist, in addition to perceptual interactions. Our previous study demonstrated that thermoregulatory-like cardiovascular responses can be invoked simply by viewing video images containing depictions of hot or cold scenery, even when the actual thermal condition remains constant (Takakura et al. 2013). In the previous study, when participants were exposed to video images containing cold images, cardiac output and heart rate tended to be small and total peripheral resistance tended to be large. In contrast, when participants were exposed to video images containing hot images, cardiac output and heart rate tended to be large and total peripheral resistance tended to be small. Such antagonistic cardiac and vascular responses are known to be observed in actual thermoregulatory responses (Walther et al. 1970). In other words, the human thermoregulatory system may respond inappropriately to visual information, which lacks thermal energy. However, whether this trait can actually affect human thermoregulation in a substantive way remains unclear, because the experiment was conducted under thermally neutral conditions and the exposure time was not long enough. In addition, direct measurement of body temperature was not conducted. As long as the visual information and actual thermal environment are consistent, such traits will not disturb human homeostasis. In natural environments, when humans were exposed to cold visual information (for example, scenery of snow), the actual thermal environment would most often also have been cold. However, considering the rapid increase in media technology (Marshall et al. 2006; Sechrist 2014), discrepancies between visual inputs and the actual thermal environment can now occur much more easily. Investigation of such human traits is thus important in order to design adequate artificial and media environments. Our previous study focused on internal hemodynamics but did not measure body temperature (actual thermal regulation). The purpose of this study was to confirm whether visual information without thermal energy can affect human thermal regulations in a substantive way. To clarify this issue, participants were exposed to visually cold, hot, or neutral information in thermally challenging cold environments, because exposing thermally challenging environment is an effective way to examine the difference in the ability of thermoregulation (Wagner et al. 1974; Wakabayashi et al. 2011; Nishimura et al. 2011). We investigated this issue with a particular focus on body temperature rather than cardiovascular responses. If thermoregulatory systems are affected by visual information in a substantive manner, core body temperature would differ depending on the visual information.
Materials and methods Thirteen male undergraduate or graduate Japanese students (age range, 20–23 years) participated in the experiment. Mean (±standard deviation) characteristics were as follows: height, 172.4±7.5 cm; weight, 61.2±13.2 kg; and body mass index, 20.0±2.65 kg/m2. Temperature in the experiment room was initially set and kept at 28 °C for 20 min, then gradually lowered to 16 °C over the course of >80 min (Fig. 1). Relative humidity was set at 50 %, and wind speed was
