Tickle Torture

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/282534829 Laterality of Tickle Sensation Produced by Self-Stimulation Article · September 2015 DOI: 10.2466/27.CP.4.17 CITATIONS READS 0 1,631 2 authors, including: Hikari Yamashita Ehime University 73 PUBLICATIONS   1,644 CITATIONS    SEE PROFILE All content following this page was uploaded by Hikari Yamashita on 25 October 2015. The user has requested enhancement of the downloaded file.

COMPREHENSIVE Laterality of tickle sensation produced PSYCHOLOGY by self-stimulation1, 2 2015, Volume 4, Article 17 Mayo Suzuki and Hikari Yamashita ISSN 2165-2228 DOI: 10.2466/27.CP.4.17 Faculty of Education, Ehime University, Matsuyama-city, Japan © M. Suzuki & H. Yamashita 2015 Attribution-NonCommercial- Abstract NoDerivs CC-BY-NC-ND Received October 4, 2014 Numerous authors have reported that people cannot create a tickling reaction in Accepted September 1, 2015 themselves. However, Provine (2000) claimed that ticklishness was felt even if Published September 16, 2015 he stimulated his own leg with his fingers. Ticklishness was stronger when the hand and leg were on opposite sides of the body. Provine's findings were rep- CITATION licated with 30 university students. Two types of stimulus presentation meth- Suzuki, M. & Yamashita H. ods were adopted: a participant's fingers and a paintbrush. Ticklishness was assessed by self-rating and evaluation by observers. Provine's claim was sup- (2015) Laterality of tickle ported only by the self-rating of stimulation with the fingers. sensation produced by self- stimulation. Comprehensive Although ticklishness is a sensation in humans, its physiological basis and mechanism Psychology, 4, 17. still remain obscure. Many authors have emphasized that people cannot tickle them- selves (e.g., Darwin, 1872; Harris, 1999; Weiskrantz, Elliot, & Darlington, 1971), which is Ammons Scientific presumed to be evidence for the hypothesis that ticklishness is not merely a physiolog- ical response but is also a social phenomenon. Blakemore and colleagues (Blakemore, www.AmSci.com Wolpert, & Frith, 1998; Blakemore, Frith, & Wolpert, 1999; Blakemore, Smith, Steel, John- stone, & Frith, 2000) investigated how the brain distinguishes between self-produced and externally produced sensations. Functional MRI data suggest that two brain regions are involved in processing the sensation of tickling: the somatosensory cortex processes touch sensations, and the anterior cingulate cortex processes pleasant information. The researchers found that both regions are less active during self-tickling than during tick- ling by another. Further studies using robots showed that a short delay between the participants’ own movement and the resulting tickle can make a sensation feel ticklish (Blakemore, Frith, & Wolpert, 2001). The longer the delay, the more ticklish it feels. They presumed that the cerebellum might be implicated in distinguishing between self-gen- erated and externally generated sensations based on cerebral blood flow data. The cere- bellum functions in motor control by coordinating, so it might be involved in predicting what effect movement of one part of the body has on other body parts. However, it is possible that one can actually tickle oneself, as argued by Provine (2000). In anecdotal studies, Provine claimed he experienced ticklishness while soap- ing the sole of his foot with his fingers in the shower. Furthermore, the ticklishness was stronger when he tickled his left foot with his right hand or his right foot with his left hand, and was weaker when he tickled his left foot with his left hand or his right foot with his right hand. He tested these findings in a semi-formal experiment with his stu- dents. Participants stroked the naked soles of their feet with their five fingers, first with one hand and then with the other. Participants rated contralateral stimulation as more ticklish than ipsilateral stimulation, with the most intense self-tickle occurring when the left foot was stimulated by the right hand. Provine (2000) interpreted the results as fol- lows: relative to ipsilateral stimulation, the human brain is less likely to recognize con- tralateral stimulation as self-produced; therefore, this generates a more potent tickling sensation. In sum, Provine's predictions were that a stronger tickle sensation will be re- lated to the difference in arrival time of the sensory signal to the two halves of the brain, and resulting in greater otherness/lower selfness. In the current study, we added a condition to test Provine's suggestion about the im- portance of “otherness” in creating the tickle response. Because he assumed that tick- 1Address correspondence to Hikari Yamashita, Faculty of Education, Ehime University, Bunkyo-cho 3, Mat- suyama 790-8577, Japan or e-mail ([email protected]). 2This research was supported by a Grant-in-Aid for Scientific Research (C) from JPSP (No. 15K04130). There are no known potential conflicts of interest. We would like to thank Ayumi Sechi and Ayako Kaneyama for their technical assistance.

Tickle Sensation / M. Suzuki & H. Yamashita ling done contralaterally creates a greater sense of “oth- lish; 1: Slightly ticklish; and 0: Hardly ticklish. For objec- erness,” and this underlies the increased sensation of tive evaluation of ticklishness, two raters (including the tickling, conditions that increase the “otherness” (i.e., first author) evaluated video images using a five-point that somebody else is doing the tickling, and not the rating scale to quantify the behavior to progressively person him or herself) might be expected to increase the greater tickling response, also modified from Hoshikawa tickling sensation as well. Thus, when tickling is done (1991): 4: Pulling back one's foot or laughing; 3: Twisting using tools the sense of otherness is increased, and the the body without pulling back the foot; 2: Suppressing a tickle sensation should increase. laugh; 1: Voiceless smiling; and 0: No response. Hypothesis. The tickle sensation will be stronger when Procedure tickling with an object compared to tickling with one's own fingers. The experiment was carried out individually, in a quiet room. Each participant sat in a chair with the ankle Although some questionnaire surveys have report- of one leg resting on the knee of the other, the posi- ed quantitative and qualitative differences between men tion adopted in Provine's (2000) study. They stroked and women in response to tickling (e.g., Provine, 2000; the naked sole of their own foot with five fingers or a Juárez-Ramos, Salazar-López, Artacho, Chmielowiec, paintbrush. There were eight conditions, each involv- Riquelme, Fernández-Gómez, et al., 2014), there are no ing 10 sec. of stimulation: four combinations of foot and experimental studies in which the sex difference was hand × two types of stimulation. Specifically, the par- significant (e.g., Claxton, 1975; Pridmore, Garry, Karst, ticipants were asked in a random sequence, according Rahe-Meyer & Rybak (2006). For example, Harris and to the one-time instruction of the experimenter (first Alvarado (2005) reported that 70% of men and 75% of author) to (1) tickle the left foot with the fingers of the women laughed in response to a tickle manipulation in left hand, (2) tickle the left foot with the fingers of the their experiment. right hand, (3) tickle the right foot with the fingers of the left hand, (4) tickle the right foot with the fingers Research goal. Sex differences in the tickle response of the right hand, (5) tickle the left foot with the paint- by self-stimulation was examined. brush held in the left hand, (6) tickle the left foot with the paintbrush held in the right hand, (7) tickle the right Method foot with the paintbrush held in the left hand, and (8) tickle the right foot with the paintbrush held in the right Participants hand. Immediately after each stimulus presentation, the participants were asked to estimate the magnitude of Thirty right-handed university students (15 women, 15 the tickle sensation on a 5-point scale, which they had men; M age = 20.6 yr., SD = 1.7) volunteered for the study. to write down on a standard answer form. The experi- Right-handedness of all participants was assured using menter told participants which stimulation to use and the Hatta-Nakatsuka Handedness Inventory (HNI). The so guided them through the conditions and stimuli, and HNI, which has been widely used in Japanese handed- indicated the beginning and ending of the stimulation. ness-related studies, consists of 10 items regarding hand The stimulation order was random, one at a time. The preference for daily activities. One point is counted experiment was recorded with a digital video camera. when the right hand is used for an activity, and one point is subtracted when the left hand is used; 0 points Data Analysis are counted when either hand is used in equally. The handedness score of HNI can range from -10 to+10. Right- The self-rated ticklishness of participants in the four handedness is operationally defined as a score≥+8 (Hatta foot–hand combinations (left foot–left hand, LF/LH; & Nakatsuka, 1975). left foot–right hand, LF/RH; right foot–left hand, RF/ LH; and right foot–right hand RF/LH) was analyzed All participants gave written informed consent. All by a two-way analysis of variance (ANOVA; 2 sex × 4 the procedures in this study conformed to the code of combination) for the use of their own fingers or the ethics and conduct of the Japanese Psychological Asso- paintbrush. A similar analysis was also conducted with ciation. respect to the objective evaluation of ticklishness as determined from scoring the video record. Inter-scorer Materials reliability of the two raters was evaluated by intra-class correlation (ICC) of all reactions by all participants. Two types of stimulus presentation methods were adopted: (1) the participant's five fingers lightly stroking up and Results down the foot in a tickling manner and (2) a paintbrush with a 1-cm wide tip moving in the same manner. The means and standard deviations for self-rated tick- lishness of each condition, by fingers or paintbrush, For the participants’ self-evaluation of ticklishness, we used a five-point rating scale, modified from Ho- shikawa (1991): 4: Very ticklish; 3: Rather ticklish; 2: Tick- Comprehensive Psychology 2 2015, Volume 4, Article 17

Tickle Sensation / M. Suzuki & H. Yamashita TABLE 1 Means and Standards Deviations of Self-rated Tickle Sensation in Four Foot/Hand Combinations Fingers Paintbrush Foot/Hand Women (n = 15) Men (n = 15) All (n = 30) Women (n = 15) Men (n = 15) All (n = 30) M SD M SD M SD M SD M SD M SD LF/LH 1.13 0.92 0.60 0.99 0.87 0.97 1.07 0.70 0.60 0.83 0.83 0.79 LF/RH 1.93 1.03 1.00 1.00 1.47 1.11 1.07 0.70 0.67 0.72 0.87 0.73 RF/LH 1.80 1.26 0.87 0.64 1.33 1.09 1.13 0.83 0.93 0.88 1.03 0.85 RF/RH 1.27 1.03 0.73 0.80 1.00 0.95 0.73 0.46 0.87 0.92 0.80 0.71 Note LF/LH: Left Foot/Left Hand; LF/RH: Left Foot/Right Hand; RF/LH: Right Foot/Left Hand; RF/RH: Right Foot/Right Hand. are displayed in Table 1. For finger stimulation, a Discussion two-way ANOVA indicated significant effects of sex (F1,28 = 6.36, p = .02, η2p = 0.19) and foot/hand combina- Provine's (2000) findings were supported only by self- tions (F3,84 = 5.62, p = .001, η2p = 0.17). The interaction ratings when participants tickled themselves with their of sex × foot/hand combinations was non-significant fingers; i.e., participants rated contralateral stimulation (F3,84 = 0.95, p = .42, η2p = .05). Pairwise comparison with as more ticklish than ipsilateral stimulation, with the a Bonferroni correction among four combinations iden- most intense self-tickle occurring when the left foot was tified significant differences between LF/RH vs RF/RH stimulated by the right hand. Provine claimed that rel- (p < .05), between LF/RH vs LF/LH (p < .05), between ative to ipsilateral stimulation, the human brain is less RF/LH vs LF/LH (p < .05), and between RF/LH vs RF/ likely to recognize contralateral stimulation as self-pro- RH (p < .05). For paintbrush stimulation, there was a duced, and therefore generates a more intense feeling non-significant effect of sex (F1,28 = 1.49, p = .23, η2p = 0.05) of ticklishness. The ability to extend one arm across the and foot/hand combinations (F3,84 =0.77, p=.52, η2p =0.03). midline to reach for laterally positioned objects emerges The interaction of sex × 4 foot/hand combinations was at approximately 18 weeks, and all infants older than also non-significant (F3,84 = 1.29, p = .28, η2p = 0.04). 20 weeks of age managed to reach for and touch single objects placed in the contralateral space (Provine & Wes- Means and standard deviations of objectively eval- terman, 1979). Based on these findings, Provine (2000) uated ticklishness for each condition, by self-fingers or insisted that even in adulthood the two sides of the paintbrush, are shown in Table 2. Although the ICC us- brain may have harmonious but not perfectly synchro- ing a two-way random effects model for all reactions of nous communication. The differences from expected all participants was sufficiently high (ICC = .93), proto- arrival time of afferent signals in contralateral stimula- cols rated by the first author were used in the following tion may be associated with greater tickle sensation. data analysis. Furthermore, according to Provine (2000), using tools For stimulation with fingers, there was no significant to tickle should increase the “otherness” and hence increase effect of sex (F1,28 = 0.10, p = 0.76, η2p = 0.003) and foot/ the tickle sensation. In particular, the sensation should be hand combinations (F3,84 = 0.15, p = .93, η2p= 0.005). The greater for the tool (paintbrush) than if tickling with one's interaction of sex × foot/hand combinations was also own fingers. Contrary to this hypothesis, stimulation with non-significant (F3,84=0.84, p=.48, η2p=0.03). For paint- a paintbrush did not produce ticklishness as strong when brush stimulation, there was no significant sex differ- tickling was done with the fingers, either as measured ence (F1,28 = 0.58, p = .45, η2p = 0.02) or difference for foot/ by self-ratings or as measured by the videoed respons- hand combinations (F3,84 = 2.03, p = .12, η2p = 0.07). The es of facial expressions or bodily action. In our prelimi- interaction of sex × foot/hand combinations was also nary experiments, unlike other parts of the body (e.g., non-significant (F3,84 = 2.14, p = .10, η2p= 0.07). cheek, neck, or palm), the feet showed particularly TABLE 2 Means and Standards Deviations of Objectively Evaluated Ticklishness in Four Foot/Hand Combinations Fingers Paintbrush Foot/Hand Women (n = 15) Men (n = 15) All (n = 30) Women (n = 15) Men (n = 15) All (n = 30) M SD M SD M SD M SD M SD M SD LF/LH 0.27 0.46 0.60 0.74 0.43 0.63 0.47 0.52 0.20 0.41 0.33 0.48 LF/RH 0.53 0.74 0.47 0.83 0.50 0.78 0.00 0.00 0.27 0.59 0.13 0.43 RF/LH 0.60 1.06 0.40 0.51 0.50 0.82 0.20 0.41 0.67 1.18 0.43 0.90 RF/RH 0.33 0.62 0.47 0.83 0.40 0.72 0.53 0.64 0.47 0.74 0.50 0.68 Note LF/LH: Left Foot/Left Hand; LF/RH: Left Foot/Right Hand; RF/LH: Right Foot/Left Hand; RF/RH: Right Foot/Right Hand. Comprehensive Psychology 3 2015, Volume 4, Article 17

Tickle Sensation / M. Suzuki & H. Yamashita strong reaction when feet were tickled by another per- Blakemore, S. J., Smith, J., Steel, R., Johnstone, E., & Frith, C. son, rather than with a paintbrush or cotton swab. For (2000) The perception of self-produced sensory stimuli in pa- the hypothesis of Provine (2000), it is necessary to per- tients with auditory hallucinations and passivity experiences: form more detailed studies. evidence for a breakdown in self monitoring. Psychological Medicine, 30, 1131-1139. Sex differences were observed only in the self-rat- ed tickle sensation stimulated by the participant's own Blakemore, S. J., Wolpert, D., & Frith, C. (1998) Central cancelation fingers. This was the first experimental study, to our of self-produced tickle sensation. Nature Neuroscience, 1, 635- knowledge, to find evidence of sex differences in tick- 640. le responses. However, the present study did not have a male experimenter, the sexes of the experimenter and Claxton, G. (1975) Why can't we tickle ourselves? Perception & participants may have affected the results. Whether the Motor Skills, 41, 335-338. observer is the same sex or the opposite sex of the par- ticipants could affect the embarrassment and social de- Darwin, C. (1872) Expression of the emotions in man and animals. sirability behavior of the participants. To study the sex London, UK: John Murray. differences in detail, it is necessary to have more partici- pants and both experimenters of both sexes. Harris, C. R. (1999) The mystery of ticklish laughter. American Sci- entist, 87, 344-351. Despite the limitations, the present study contributes to a better understanding of the physiological and psy- Harris, C. R., & Alvarado, N. (2005) Facial expressions, smile chological mechanism of tickling and laughter. Recently, types, and self-report during humour, tickle, and pain. Cogni- many researchers have suspected whether schizophren- tion and Emotion, 19, 655-669. ic patients with auditory hallucinations or the feeling of being controlled by an external agent, have the ca- Hatta, T., & Nakatsuka, Z. (1975) H. N. Handedness Inventory. pacity to tickle themselves (e.g., Blakemore, et al., 2000; In S. Ohno (Ed.), Papers for the celebration of the 63rd birthday of Provine, 2000; Pridmore, et al., 2006). Our findings can Prof. Ohnishi. Osaka, Japan: Osaka City Univer.. Pp. 224-247. also be useful as reference data for such studies identi- fying markers for various disorders. Hoshikawa, T. (1991) Effects of attention and expectation on tickle sensation. Perceptual & Motor Skills, 72, 27-33. References Juárez-Ramos, V., Salazar-López, E., Artacho, M., Chmielowiec, Blakemore, S. J., Frith, C., & Wolpert, D. (1999) Spatio-temporal K., Riquelme, A., Fernández-Gómez, J., Fernández-Ramirez, prediction modulates the perception of self-produced stimuli. A. I., Vicente de Haro, A., Miranda, A., Caballero, M., Mach- Journal of Cognitive Neuroscience, 11, 551-559. ado, B., A. G. Hernández, A., & Milán, E. (2014) The laughter of ticklishness is a Darwinian feature related to empathy in Blakemore, S. J., Frith, C., & Wolpert, D. (2001) The cerebellum both genders: self-esteem in men and sexism in women. Open is involved in predicting the sensory consequences of action. Journal of Medical Psychology, 3, 18-23. NeuroReport, 12, 1879-1884. Pridmore, S., Garry, M., Karst, M., Rahe-Meyer, N., & Rybak, M. (2006) Tickling healthy subjects. German Journal of Psychiatry, 9, 107-110. Provine, R. R. (2000) Laughter: a scientific investigation. New York: Penguin Books. Provine, R. R., & Westerman, J. A. (1979) Crossing the midline: lim- its of early eye-hand behavior. Child Development, 50, 437-441. Weiskrantz, L., Elliot, J., & Darlington, C. (1971) Preliminary ob- servations of tickling oneself. Nature, 230, 598-599. Comprehensive Psychology 4 2015, Volume 4, Article 17 View publication stats