Analysis of Paradoxical Phenomenon in Thermal Sensation Keisuke Arai arai@rm.is.ritsumei.ac.jp Satoshi Hashiguchi hasiguti@rm.is.ritsumei.ac.jp Fumihisa Shibata fshibata@is.ritsumei.ac.jp Asako Kimura asa@rm.is.ritsumei.ac.jp Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for thirdparty components of this work must be honored. For all other uses, contact the Owner/Author. Copyright is held by the owner/author(s). CHI'17 Extended Abstracts, May 06-11, 2017, Denver, CO, USA ACM 978-1-4503-4656-6/17/05. http://dx.doi.org/10.1145/3027063.3052959 Abstract Thermal Referral (TR) and Thermal Grill Illusion (TGI) are known as illusions of thermal sensation, have been well studied. In a previous study, the experiment using two thermal-tactile stimulations to the forearm revealed that those illusions simultaneously occurred. On the other hand, in the experiment result, a few subjects perceived a hot stimulation as a cold sensation or a cold stimulation as a hot sensation. This paradoxical phenomenon of thermal sensation which is not discussed specifically in the previous study could be a fatal problem in the case presenting a thermal stimulation on multiple spots intentionally. Therefore, we decided to analyze this paradoxical phenomenon. In this paper, we confirmed that this phenomenon occurs when we present thermal stimulation on two spots and three spots. And in Comparison between the results of two spots and three spots, the occurred probability increased on three spots than on two spots. Author Keywords Thermal sensation; Thermal Referral; Thermal Grill Illusion;
Figure 1: Device for presenting thermal sensation ACM Classification Keywords H.5.2. Information interfaces and presentation (e.g.,hci): User Interfaces. Introduction Thermal Referral (TR) and Thermal Grill Illusion (TGI) are known as illusions of thermal sensation. The TR is a phenomenon in which thermal sensation is changing when thermal stimulation is presented on one location and tactile stimulation is presented to another [1]. The TGI refers to paradoxical sensations of heat and pain resulting from simultaneous application of interlaced hot and cold stimuli [2]. THERMAL STIMULATIONS In our experiments, hot and cold stimulations were presented by using Peltier devices (size: 40 40mm) and the temperature controller sets (VPE20-5-20SS, Ltd. VICS, Fig. 1). Considering the stability of the temperature stimulation, we set the devices on a table and ask subjects to put their inside of the forearm on them. Three devices were set on the table in a row keeping 100 mm between each other. Each device had contact with the wrist, the center, and the elbow spot of the forearm (Fig. 2). Also, two pillows were prepared for subject s wrist and elbow to hold and stabilize his/her forearm. Figure 2: Experimental situation In a previous study, an experiment using two thermaltactile stimulations to the forearm revealed these illusions simultaneously occurred [3]. From the result of this study, we noticed that a few subjects perceived a hot stimulation as a cold sensation and/or a cold stimulation as a hot sensation. This paradoxical phenomenon of thermal sensation which is not discussed specifically in the previous study could be a fatal problem in the case presenting a thermal stimulation on multiple spots intentionally. Therefore, we decided to analyze this paradoxical phenomenon of thermal sensation. As a first step (experiment 1), we re-evaluated that this phenomenon really occurs when we present thermal stimulation on two spots similarly to the previous study. Next step (experiment 2), we investigated whether this phenomenon occurs in the case expanding the stimulation from two spots to three spots. Also, we compared with result of experiments in cases of the thermal stimulation on two spots and three spots. Thermal stimulation becomes painful when the temperature is too low or too high (the cold stimulation: 10 C, the hot stimulation: 45 C) [4]. We selected 11 C and 44 C as the cold and hot stimulation to avoid pain. The experiments were conducted in a room with a constant temperature of 25 C. EXPERIMENT 1: Presenting thermal stimulations on two spots Objective In the previous study, a few subject perceived a hot stimulation as a cold sensation and/or a cold stimulation as a hot sensation when a hot stimulation and a cold stimulation were presented simultaneously on two spots on the forearm. In the experiment 1, we re-evaluated this phenomenon. Condition In the experiment 1, the hot and the cold stimulations were presented to two of the three spots and an null stimulation which was neither hot nor cold was
Table 1: The answer rate of temperature and pain sensation in each pattern when thermal stimulation is presented on two spots (Subjects: 10) presented on the remaining spot of the forearm. This null-stimulation was set to 32 C, because indifferent temperature (do not feel hot or cold sensation) of the human is known between 30-36 C. In our preliminary experiment presenting this null stimulation to each three spots (the wrist, the center, and the elbow), we confirmed that none of ten subjects feel hot and/or cold. The center of subject right forearm was placed on the center Peltier devices as shown in Fig. 2. At the same time, remaining two devices had contact with the wrist and the elbow of the forearm. After an interval of twenty seconds placing his/her forearm on the devices, the subject was asked to answer their sensations finally perceived (Hot, Null, or Cold) on each spot. We also asked whether he/she felt pain on each spot. A series of the twelve combinations (Table 1) was presented in random order. The number of subjects was ten males from twenties to thirties. Procedure The experimental procedures are as follows; (1) Measure the center position of the forearm (2) Set the temperature and wait until the temperature is stabilized (3) Put the subject s forearm on those devices and wait for twenty seconds (4) Determine the subject s sensation on each of the three spots (5) Provide sufficient interval (over two minutes) to eliminate the effect of temperature changes on the skin (6) Steps (2) to (5) are repeated twelve times If subjects wish to redo in the procedure (4), we provide sufficient interval and redo the same trial. Result and Discussion The results are shown in Table 1. "H", "N", and "C" in the table indicate the presented hot, null, and cold stimulation, respectively. The characters are described in the order of the wrist, the center, and the elbow. The values in Table 1 show the answer rate of the temperature and pain sensations perceived on each spot. The dotted values are of the correct answers and the double underlined values indicate of the opposite answers. (i) When only the hot or the cold stimulation was presented, the subjects correctly answered the presented stimulation In the patterns (HHN, HNH, NHH, CCN, CNC, NCC) that present the same thermal stimulations (e.g. hot and hot / cold and cold), the subjects generally perceived the presented thermal stimulation accurately. However, the null stimulations were substantially affected by the neighboring thermal stimulation (TR phenomenon). (ii) When both of the hot and the cold stimulation were presented, a few subjects gave opposite answers In the patterns (HCN, HNC, NHC, CHN, CNH, NCH) that present the opposite thermal stimulation, especially in the patterns (HCN, NHC, CHN, NCH), the answer rate which correctly perceived the presented thermal stimulation became lower than the result of (i). A few subjects commented that I could not feel some of the hot/cold spots, Perceived the temperature reversely to the presented stimulation. Particularly in the center
Table 2: The answer rate of temperature and pain sensation in each pattern when thermal stimulation is presented on three spots (Subject: 10) of HCN and NHC, the occurrence of the paradoxical phenomenon of thermal sensation was 30%. Most of the null stimulations were under the influence of the neighboring stimulation (TR phenomenon). (iii) A few subjects perceived pain sensation at the center spot. From the results of this experiment, we confirmed that the significant influence of the TR phenomenon made the null stimulation inaccurate. Furthermore, the thermal stimulation was not necessarily perceived accurately, and even paradoxical results could occur. EXPERIMENT 2: Presenting thermal stimulations on three spots Objective In the experiment 2, we evaluate the incidence of paradoxical phenomenon of thermal sensation when thermal stimulation is presented on three spots on the forearm. Condition and Procedure In the experiment 2, the hot or cold thermal stimulation is presented on three spots. The null stimulation is not used. Eight combinations of hot and cold stimulation on the three spots (Table 2) were presented to the subjects in random order. Other experimental conditions and procedures are the same with those in experiment 1. Result and Discussion The results are shown in Table 2. (i) When only the hot or the cold stimulation was presented, the subjects correctly answered the presented stimulation Similar to the result of experiment 1 (i), in the patterns (HHH, CCC) that present the same thermal stimulations, the subjects perceived the presented thermal stimulation accurately. (ii) When identical two thermal stimulations were aligned side by side, a few subjects perceived the presented stimulation reversely Similar with the result of experiment 1 (ii), in the patterns (HHC, CHH, HCC, CCH) that present two same thermal stimulations side by side, the answer rate which correctly perceived the presented thermal stimulation became lower than the result of (i). (iii) When the hot and the cold stimulation were aligned alternately, half of subjects reversely perceived the presented stimulation In the patterns (HCH, CHC) that present the thermal stimulations alternately, the incidence of paradoxical phenomenon of thermal sensation increased more than the result of experiment 1(ii) and the result of experiment 2 (i) and (ii); 40% in the center of HCH and CHC, and 50% in the wrist side of CHC. (iv) Some subjects perceived pain sensation at the center spot. Particularly, in the patterns CHH, HCC, and HCH that aligned the hot and the cold stimulation side by side, more subjects perceived pain sensation than the result of experiment 1 (iii). From the results, we found that the paradoxical phenomenon of thermal sensation also occurred in the experiment 2. Additionally, we found that increasing
the number of spots of the thermal stimulation increased the incidence of paradoxical phenomenon of thermal sensation and TGI. synaptic transmission and nerve conduction, Pain Research, Vol. 26, No. 4, pp. 197-214, 2011. Conclusions and Future Work In experiment 1, we confirmed that this phenomenon really occurs when we present thermal stimulation on two spots. In experiment 2, we evaluated the incidence of paradoxical phenomenon of thermal sensation when thermal stimulation is presented on three spots on the forearm. As the result, this phenomenon occurred in the patterns that alternately present thermal stimulation with a probability of 50%. In Comparison between the results of two spots and three spots, the incidence increased on three spots than on two spots. In the future, we would like to investigate why this paradoxical phenomenon of thermal sensation is occurs by changing some parameter such as presentation temperature and positions, and how we can avoid this. References [1] B. G. Green: Localization of thermal sensation: An illusion and synthetic heat, Perception & Psychophysics, Vol. 22, No. 4, pp. 331-337, 1977. [2] P. Bach, S. Becker, D. Kleinböhl, and R. Hölzl: The thermal grill illusion and what is painful about it, Neuroscience letter, Vol. 505, No. 1, pp. 31-35, 2011. [3] R. Watanabe, R. Okazaki, H. Kajimoto: Mutual Referral of Thermal Sensation between Two Thermal-tactile Stimuli, IEEE Haptics Symposium, pp. 299-302, 2014. [4] E. Kumamoto, and T. Fujita: Regulation of nociceptive information transmitting to the spinal dorsal horn from periphery: the modulation of