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Recognition of familiar individuals by touch
Physiology&Behavior,Vol. 52, pp. 565-567, 1992
0031-9384/92 $5.00 + .00 Copyright © 1992 Pergamon Press Ltd.
Printed in the USA.
Recognition of Familiar Individuals by Touch MARSHA
KAITZ
Department of Psychology, Hebrew University, Jerusalem, Israel R e c e i v e d 3 J a n u a r y 1992 KAITZ, M. Recognition offamiliar individuals by touch. PHYSIOL BEHAV 52(3) 565-567, 1992.--I have examined whether adults can recognize their boyfriends/husbands or girlfriends/wives by stroking either their partner's hand or face. On both trials, subjects were asked to chose their mate from amongst two unfamiliar age- and gender-matched adult foils. During testing, the subject's eyes and nose were covered and auditory cues were masked by ambient noise. The results show that a significant proportion of the total sample succeeded on one or both of the touch-recognition tasks. However, while both women and men were successful at the face-touch-recognition task, only the women were successful at the hand-recognition task. I conclude that tactile cues afforded by stroking skin are sufficiently salient to allow for individual recognition. As for the gender-related difference, women may have an advantage at hand recognition because men's hands are more discriminable than women's hands. Tactile
Touch recognition
Person recognition
Couples
METHOD
T O U C H I N G is an integral component of social interactions between familiar individuals. It communicates caring, reassurance, compliance, and comfort [for review see (7)]. Perhaps for these reasons, being touched, even fleetingly, can enhance feelings of well-being and promote a positive attitude about the surroundings in which the touch occurred (2). If, however, touch is inappropriate, too intimate, intense, frequent, or confining, it can be stressful and result in overarousal, anxiety, or fear (6). These data, amongst others, show that we are highly sensitive to the tactile stimulation afforded by either touching someone or by being touched ourselves. This led to the hypothesis that adults are sensitive to the tactile features of familiar individuals and that they can use them as cues for individual recognition. In the first experiment on touch recognition, we tested w o m e n after childbirth and used their newborn infant as the individual to be recognized (3,4). The women's task in the experiment was to discriminate their own newborn from two unfamiliar newborns by stroking either the infants' hand (dorsal surface) or their face (cheek). Design features of the experiment prevented access to extraneous nontactile cues, and control experiments confirm that the discrimination was tactile. The results show that the w o m e n succeeded at the task using either of the two target areas and that they required approximately 6.5 h of exposure to do so. In this first attempt to show touch recognition of familiar individuals, we chose the mother-infant pairing because mothers touch their infant frequently during the parturient period, and they are usually highly motivated to get to know their newborn (5). We, therefore, considered the experimental design a likely one to show positive touch recognition. Now, I ask whether or not touch recognition is possible under other conditions, namely between adults who live together as boyfriend and girlfriend or as husband and wife. Positive results would support the contention that human adults learn the tactile cues of individuals with whom they engage in social touching. They would also show touch recognition to be a more general talent than previously realized.
Subjects Couples were included in the sample if they had considered themselves a couple for at least 6 months at the time of the experiment. Most of the subjects (n = 72, 36 couples) were undergraduates or graduate students at Hebrew University of Jerusalem. The m e n were, on average, 25.3 _+ 2.5 years of age, the w o m e n 23.0 _+ 2.5 years of age. At the time of testing, the couples had been together, on average, for 24.6 + 13.5 months. Sixty-nine percent were living together, and of these, 44% (16/36) were married. N o n e bad children. The subjects had no extraordinary tactile features on their hands or face, such as warts or scars. They did not know of our previous touch-recognition experiments and were not aware of the purpose of the present experiment until the time of testing.
Procedure All of the experiments were carried out in a testing r o o m at the university. There were two reciprocal phases to each testing session. In one, the male partner was asked to select his partner from amongst three women (models), two of w h o m were unfamiliar to him. In the second phase, the female was asked to identify her partner from among three male models, two of w h o m were unfamiliar to her. The unfamiliar models were similar to the target model in age, height, and weight ( m a x i m u m difference 4 years, 10 cm, 8 kg). In half of the experiments, the female was tested first and in half of the experiments the male partner was tested first, the order being randomized across the 36 couples. Each of the subjects was tested twice, once for touch recog: nition using the models' hand (dorsal surface of the right hand) as the target area and once using the models' forehead as the target area. The hand was chosen as a target area because hand holding and hand touching are frequent responses between in-
565
566 timate persons and, therefore, I assume that the subjects of this experiment had extensive tactile experience with their partner's hands. The forehead was chosen as the target area on the face because it is another easily accessible body part that is usually without hair or other distinctive tactile features. At the onset of the experimental session, the individual who would be first to attempt touch recognition (partner 1) was escorted to the testing room and seated at a table. He/she was told the purpose and procedure of the study and instructed on the correct mode of stroking (see below). Then, partner l's eyes and nose were covered completely with a scarf (four layers of cotton). This was done to prevent access to visual and olfactory cues that could be used for recognition (see control experiment 1). Partner l's forehead was also covered with the scarf so that partner 2 did not have the opportunity to search out discriminative cues once he/she knew the forehead would serve as one of the target stroking areas. For the same reason, the hands of partner 1 were placed under the table top, out of view, at all times during the experiment in which partner 2 was not blindfolded. I add here that 30 dB of ambient white noise masked subtle auditory signals that could serve as recognizable cues. The models, including partner 2, were briefed on the procedure of the experiment in a separate room and when signalled, filed into the testing room and sat on one of the three chairs facing the subject. The seating arrangement was randomized across subjects and trials. Once seated, the models were blindfolded. For the hand-recognition task, the models' right hand was positioned palm down on the table. Partner 1 was required to stroke each of the three hands in turn and was not allowed to return to a model a second time. The target area to be stroked was defined as the surface area extending from the base of the digits to the wrist (approximately 7 × 3 cm). Partner l's fingertips were initially positioned on the model's hand by the experimenter. If the subject stroked outside the limits of the target area (fingers or contour of the hand), his/her hand was repositioned by the experimenter. Stroking was accomplished using the tips of the middle and index finger of the dominant hand with repeated movements made in the direction from fingers to wrist. Subjects were allowed to stroke each model's hand for as long as they felt necessary. However, in most trials, stroking time per model did not exceed 5 s. For the face-recognition task, the models' forehead served as the target area. Stroking was in a horizontal direction over a distance of approximately 8 cm. Movements were consistently from right to left. Before the forehead of each model was stroked, the experimenter laid her hand over the models' hairline to prevent the subjects from touching the models' hair. All other aspects of the face-recognition task were similar to those of the handrecognition task described above. Between the two recognition tasks, the models removed their blindfolds and changed their seating position. The experimenter issued instructions on the new seating arrangement nonverbally, by pointing. Once the models were seated, the models were again blindfolded and the second phase of the experiment was initiated. When partner 1 had completed both recognition tasks, the experiment was repeated with partner 2 as subject. The order of the hand- and face-recognition tasks were varied among subjects. The experimenter could not be kept blind as to the identities of the target models because one of the partners serves as subject before acting as a model. Instead, indirect measures were taken that should prevent the experimenter from inadvertently biasing the subject's guess. First, she was told that some of the couples that she would test would not be true couples, but rather students
KAITZ who had met for the first time just prior to the experiment. In fact, there were no such sessions; however, this information should have prevented her from having any expectations as to the outcome of the experiment. Second, the experimenter spoke only to call out the ordinal position of each model and to ask the subject for his/her guess. The purpose of the experiment was not kept from the subjects because after the first trial the purpose of the study was obvious. The unfamiliar adults who acted as models were used in only one experimental session, with the exception of one adult who served as a foil in three experiments. All of the subjects stated prior to the experiment that they were unaware of its purpose. They were told not to discuss the experiment until they were notified that the experiment had been completed. Interview. In the final stage of the experiment, subjects were asked for personal data including age, weight, height, time living together as a couple, and related details on the history of their romance. Control experiment. Two control experiments were run in order to ascertain whether nontactile cues were available to the subjects during the touch-recognition test. In the first, I tested the efficacy of the nose- and eye-cover in preventing access to visual and olfactory cues. Ten subjects (mean age 22.4 years) participated in the experiment. For the visual test, they were blindfolded with the eye-cover used in the primary experiment. Then they were asked to identify 10 pictures of common objects. For the smell test, the subjects were first familiarized (10 trials, at least 90% success) with two common household odors (lemon and vanilla extract). Their eyes and nose were then covered, and they were again asked to identify the smells. Smell order was randomized in both the covered and uncovered trials, and the interstimulus interval was 30 s. The second control experiment was a direct test of whether identification of individuals, as tested by our touch-recognition task, could be based on nontactile cues. For this study, we tested an additional 10 couples for hand-touch recognition using the same procedures as in the primary experiment. However, in this experiment we placed a cloth over each of the models' hands so that the subject made no tactile contact with the surface of their skin. RESULTS Taking the sample as a whole, 57% of the 72 subjects succeeded at the hand-recognition and 58% succeeded at the face recognition test (Table 1). For both tasks, the success-rate expected by chance was 33%. An analysis by gender shows that both men and women (50%, 67%) successfully identified their partner by stroking their partner's face. Further, there was no difference between their success rates on the face-recognition test (X2, p > 0.05). However, only the women successfully recognized their partner by stroking his hand (69% success, Table 1). The men's success rate on the hand-recognition test did not exceed chance probability (44% success vs. 33%) and was significantly inferior to that of their partners, X2(1) = 4.6, p < 0.05. Successful recognition by one partner did not predict success by his/her mate (X2, p > 0.05). Performance on neither test was related to marital status, whether or not the couples were cohabitating, nor to the duration of the couple's relationship (range 6-49 months, x 2, p > 0.05).
Control Experiments The results of the control experiments support the conclusion that proficiency at touch recognition, as tested in this study, was
TOUCH RECOGNITION
567
TABLE 1 PERFORMANCE ON THE HAND- AND FACE-TOUCH RECOGNITION TEST
Hand test n n success Success (%) *p Face test n n success Success (%) *p Total n n success Success (%) *p
Men
Women
Total
36 16 44 =0.21
36 25 69 <0.0001
72 41 57 ~0.0001
36 18 50 -0.05
36 24 67 -<0.0001
72 42 58 ~<0.0001
72 34 47 =0.02
72 49 68 -<0.0001
144 83 58 _<0.0001
* Binomial probability, two-tailed.
based on tactile cues. In the first control experiment, none of the 10 subjects recognized any of the visual shapes, and all of them said that they had no perception of light. They could also not identify the test odors when their nose was covered with the scarf (average performance 25%, p > 0.05). In the second control experiment, only 20% of the subjects correctly identified their partner's hand. This is as would be expected by chance (33%). DISCUSSION The results of this experiment show that a significant proportion of adults in established couples can recognize their partner by cutaneous touch. Although it is assumed that the subjects had had extensive tactile contact with their partner prior to testing, they were unaware that they would be tested for tactile recognition. Their successful overall performance indicates, therefore, that the discriminative tactile cues are learned unintentionally in the course of social interactions. Men and w o m e n were equally proficient at the face-recognition test. Only the women, however, succeeded at the handrecognition test. The most likely reason for the performance difference is that men's hands vary more than w o m e n ' s hands
in hair density and therefore are more discriminable. In effect, then, the hand-recognition test is probably objectively easier for the w o m e n than for the men. The success of men on one test but not the other serves as adjuvant support for our claim that successful recognition was not based on extraneous nontactile cues. If that had been the case then the men should have shown equal proficiency on both tests, since only the tactile cues differed between trials. The most direct evidence that the discrimination was a tactile one, however, comes from the results of Control Experiment 2. The results of that experiment show that, without access to tactile cues of the models' skin, individual recognition was not successful. I cannot specify, based on the present data, which of the available tactile cues were used for recognition. Temperature, texture (i.e., hair density, skin ridges), flaccidity, m o v e m e n t of the skin during stroking, and felt size of the stroking area are all prime candidates. It is most probable that touch recognition depends on a combination or the sum total of the available cues, as is the case for both recognition by sight and by sound (1,8). However, whether or not recognition depends on one or many of these cues and whatever their nature, recognition as tested in this study should still be considered tactile since it was based on cutaneous cues afforded by stroking the surface of the skin. This study confirms and extends our previous results on touch recognition. We now know that touch recognition is not the exclusive talent of mothers and that individuals besides babies can be recognized by tactile cues. This confirms that h u m a n adults are sensitive to subtle aspects of social touching. It also shows touch recognition to be a more general h u m a n skill than previously realized, and puts it amongst the other sensory modalities as an effective channel by which an individual can be recognized. In everyday terms, the results suggest that when we touch a person with whom we have had a great deal of tactile contact, they feel differently to us than does a person with w h o m we have had little or no tactile experience. Put another way, the data suggests that there is be a sense of familiarity evoked by touching a familiar individual that is not evoked by touching an individual with w h o m we are less familiar. This feeling of familiarity is probably an important c o m p o n e n t of the sensory background against which social behaviors are played out. As such, the tactile cues may have subtle, but significant influences on social behavior. ACKNOWLEDGMENTS This research was supported by the Levine Center, the Sturman Center, and the Israel Basic Science Foundation for Science and Humanities.
REFERENCES 1. Courtois, M. R.; Mueller, J. H. Processing multiple physical features in facial recognition. Bull. Psychon. Soc. 14:74-76; 1979. 2. Fisher, J. D.; Rytting, M.; Heslin, R. Hands touching hands: Affective and evaluative effects of an interpersonal touch. Sociometry 39:416421; 1976. 3. Kaitz, M.; Lapidot, P.; Bronner, R.; Eidelman, A. Parturient women can recognize their infants by touch. Dev. Psychol. 28:35-39; 1992. 4. Kaitz, M.; Meirov, H.; Landsman, I.; Eidelman, A. I. Infant-recognition by tactile cues. Infant Behav. Dev. (in press).
5. Millot, J. C.; Filiatre, J. C.; Montagner, H. Les comportements de toucher de la mere a l'egard du noveau-ne. C. R. Acad. Sci. [III] 20: 499-502; 1987. 6. Nicosia, G. L.; Aiello, J. R. Effects of bodily contact on reactions to crowding. Paper presented at the American Psychological Association, Washington, DC, September, 1976. 7. Thayer, S. Social touching. In: Schiff, W.; Foulke, E., eds. Tactual-perception--a source book. Cambridge: University Press; 1982:363-304. 8. Voiers, W. D. Perceptual bases of speaker identity. J. Acoust. Soc. Am. 36:1065-1073; 1986.
0031-9384/92 $5.00 + .00 Copyright © 1992 Pergamon Press Ltd.
Printed in the USA.
Recognition of Familiar Individuals by Touch MARSHA
KAITZ
Department of Psychology, Hebrew University, Jerusalem, Israel R e c e i v e d 3 J a n u a r y 1992 KAITZ, M. Recognition offamiliar individuals by touch. PHYSIOL BEHAV 52(3) 565-567, 1992.--I have examined whether adults can recognize their boyfriends/husbands or girlfriends/wives by stroking either their partner's hand or face. On both trials, subjects were asked to chose their mate from amongst two unfamiliar age- and gender-matched adult foils. During testing, the subject's eyes and nose were covered and auditory cues were masked by ambient noise. The results show that a significant proportion of the total sample succeeded on one or both of the touch-recognition tasks. However, while both women and men were successful at the face-touch-recognition task, only the women were successful at the hand-recognition task. I conclude that tactile cues afforded by stroking skin are sufficiently salient to allow for individual recognition. As for the gender-related difference, women may have an advantage at hand recognition because men's hands are more discriminable than women's hands. Tactile
Touch recognition
Person recognition
Couples
METHOD
T O U C H I N G is an integral component of social interactions between familiar individuals. It communicates caring, reassurance, compliance, and comfort [for review see (7)]. Perhaps for these reasons, being touched, even fleetingly, can enhance feelings of well-being and promote a positive attitude about the surroundings in which the touch occurred (2). If, however, touch is inappropriate, too intimate, intense, frequent, or confining, it can be stressful and result in overarousal, anxiety, or fear (6). These data, amongst others, show that we are highly sensitive to the tactile stimulation afforded by either touching someone or by being touched ourselves. This led to the hypothesis that adults are sensitive to the tactile features of familiar individuals and that they can use them as cues for individual recognition. In the first experiment on touch recognition, we tested w o m e n after childbirth and used their newborn infant as the individual to be recognized (3,4). The women's task in the experiment was to discriminate their own newborn from two unfamiliar newborns by stroking either the infants' hand (dorsal surface) or their face (cheek). Design features of the experiment prevented access to extraneous nontactile cues, and control experiments confirm that the discrimination was tactile. The results show that the w o m e n succeeded at the task using either of the two target areas and that they required approximately 6.5 h of exposure to do so. In this first attempt to show touch recognition of familiar individuals, we chose the mother-infant pairing because mothers touch their infant frequently during the parturient period, and they are usually highly motivated to get to know their newborn (5). We, therefore, considered the experimental design a likely one to show positive touch recognition. Now, I ask whether or not touch recognition is possible under other conditions, namely between adults who live together as boyfriend and girlfriend or as husband and wife. Positive results would support the contention that human adults learn the tactile cues of individuals with whom they engage in social touching. They would also show touch recognition to be a more general talent than previously realized.
Subjects Couples were included in the sample if they had considered themselves a couple for at least 6 months at the time of the experiment. Most of the subjects (n = 72, 36 couples) were undergraduates or graduate students at Hebrew University of Jerusalem. The m e n were, on average, 25.3 _+ 2.5 years of age, the w o m e n 23.0 _+ 2.5 years of age. At the time of testing, the couples had been together, on average, for 24.6 + 13.5 months. Sixty-nine percent were living together, and of these, 44% (16/36) were married. N o n e bad children. The subjects had no extraordinary tactile features on their hands or face, such as warts or scars. They did not know of our previous touch-recognition experiments and were not aware of the purpose of the present experiment until the time of testing.
Procedure All of the experiments were carried out in a testing r o o m at the university. There were two reciprocal phases to each testing session. In one, the male partner was asked to select his partner from amongst three women (models), two of w h o m were unfamiliar to him. In the second phase, the female was asked to identify her partner from among three male models, two of w h o m were unfamiliar to her. The unfamiliar models were similar to the target model in age, height, and weight ( m a x i m u m difference 4 years, 10 cm, 8 kg). In half of the experiments, the female was tested first and in half of the experiments the male partner was tested first, the order being randomized across the 36 couples. Each of the subjects was tested twice, once for touch recog: nition using the models' hand (dorsal surface of the right hand) as the target area and once using the models' forehead as the target area. The hand was chosen as a target area because hand holding and hand touching are frequent responses between in-
565
566 timate persons and, therefore, I assume that the subjects of this experiment had extensive tactile experience with their partner's hands. The forehead was chosen as the target area on the face because it is another easily accessible body part that is usually without hair or other distinctive tactile features. At the onset of the experimental session, the individual who would be first to attempt touch recognition (partner 1) was escorted to the testing room and seated at a table. He/she was told the purpose and procedure of the study and instructed on the correct mode of stroking (see below). Then, partner l's eyes and nose were covered completely with a scarf (four layers of cotton). This was done to prevent access to visual and olfactory cues that could be used for recognition (see control experiment 1). Partner l's forehead was also covered with the scarf so that partner 2 did not have the opportunity to search out discriminative cues once he/she knew the forehead would serve as one of the target stroking areas. For the same reason, the hands of partner 1 were placed under the table top, out of view, at all times during the experiment in which partner 2 was not blindfolded. I add here that 30 dB of ambient white noise masked subtle auditory signals that could serve as recognizable cues. The models, including partner 2, were briefed on the procedure of the experiment in a separate room and when signalled, filed into the testing room and sat on one of the three chairs facing the subject. The seating arrangement was randomized across subjects and trials. Once seated, the models were blindfolded. For the hand-recognition task, the models' right hand was positioned palm down on the table. Partner 1 was required to stroke each of the three hands in turn and was not allowed to return to a model a second time. The target area to be stroked was defined as the surface area extending from the base of the digits to the wrist (approximately 7 × 3 cm). Partner l's fingertips were initially positioned on the model's hand by the experimenter. If the subject stroked outside the limits of the target area (fingers or contour of the hand), his/her hand was repositioned by the experimenter. Stroking was accomplished using the tips of the middle and index finger of the dominant hand with repeated movements made in the direction from fingers to wrist. Subjects were allowed to stroke each model's hand for as long as they felt necessary. However, in most trials, stroking time per model did not exceed 5 s. For the face-recognition task, the models' forehead served as the target area. Stroking was in a horizontal direction over a distance of approximately 8 cm. Movements were consistently from right to left. Before the forehead of each model was stroked, the experimenter laid her hand over the models' hairline to prevent the subjects from touching the models' hair. All other aspects of the face-recognition task were similar to those of the handrecognition task described above. Between the two recognition tasks, the models removed their blindfolds and changed their seating position. The experimenter issued instructions on the new seating arrangement nonverbally, by pointing. Once the models were seated, the models were again blindfolded and the second phase of the experiment was initiated. When partner 1 had completed both recognition tasks, the experiment was repeated with partner 2 as subject. The order of the hand- and face-recognition tasks were varied among subjects. The experimenter could not be kept blind as to the identities of the target models because one of the partners serves as subject before acting as a model. Instead, indirect measures were taken that should prevent the experimenter from inadvertently biasing the subject's guess. First, she was told that some of the couples that she would test would not be true couples, but rather students
KAITZ who had met for the first time just prior to the experiment. In fact, there were no such sessions; however, this information should have prevented her from having any expectations as to the outcome of the experiment. Second, the experimenter spoke only to call out the ordinal position of each model and to ask the subject for his/her guess. The purpose of the experiment was not kept from the subjects because after the first trial the purpose of the study was obvious. The unfamiliar adults who acted as models were used in only one experimental session, with the exception of one adult who served as a foil in three experiments. All of the subjects stated prior to the experiment that they were unaware of its purpose. They were told not to discuss the experiment until they were notified that the experiment had been completed. Interview. In the final stage of the experiment, subjects were asked for personal data including age, weight, height, time living together as a couple, and related details on the history of their romance. Control experiment. Two control experiments were run in order to ascertain whether nontactile cues were available to the subjects during the touch-recognition test. In the first, I tested the efficacy of the nose- and eye-cover in preventing access to visual and olfactory cues. Ten subjects (mean age 22.4 years) participated in the experiment. For the visual test, they were blindfolded with the eye-cover used in the primary experiment. Then they were asked to identify 10 pictures of common objects. For the smell test, the subjects were first familiarized (10 trials, at least 90% success) with two common household odors (lemon and vanilla extract). Their eyes and nose were then covered, and they were again asked to identify the smells. Smell order was randomized in both the covered and uncovered trials, and the interstimulus interval was 30 s. The second control experiment was a direct test of whether identification of individuals, as tested by our touch-recognition task, could be based on nontactile cues. For this study, we tested an additional 10 couples for hand-touch recognition using the same procedures as in the primary experiment. However, in this experiment we placed a cloth over each of the models' hands so that the subject made no tactile contact with the surface of their skin. RESULTS Taking the sample as a whole, 57% of the 72 subjects succeeded at the hand-recognition and 58% succeeded at the face recognition test (Table 1). For both tasks, the success-rate expected by chance was 33%. An analysis by gender shows that both men and women (50%, 67%) successfully identified their partner by stroking their partner's face. Further, there was no difference between their success rates on the face-recognition test (X2, p > 0.05). However, only the women successfully recognized their partner by stroking his hand (69% success, Table 1). The men's success rate on the hand-recognition test did not exceed chance probability (44% success vs. 33%) and was significantly inferior to that of their partners, X2(1) = 4.6, p < 0.05. Successful recognition by one partner did not predict success by his/her mate (X2, p > 0.05). Performance on neither test was related to marital status, whether or not the couples were cohabitating, nor to the duration of the couple's relationship (range 6-49 months, x 2, p > 0.05).
Control Experiments The results of the control experiments support the conclusion that proficiency at touch recognition, as tested in this study, was
TOUCH RECOGNITION
567
TABLE 1 PERFORMANCE ON THE HAND- AND FACE-TOUCH RECOGNITION TEST
Hand test n n success Success (%) *p Face test n n success Success (%) *p Total n n success Success (%) *p
Men
Women
Total
36 16 44 =0.21
36 25 69 <0.0001
72 41 57 ~0.0001
36 18 50 -0.05
36 24 67 -<0.0001
72 42 58 ~<0.0001
72 34 47 =0.02
72 49 68 -<0.0001
144 83 58 _<0.0001
* Binomial probability, two-tailed.
based on tactile cues. In the first control experiment, none of the 10 subjects recognized any of the visual shapes, and all of them said that they had no perception of light. They could also not identify the test odors when their nose was covered with the scarf (average performance 25%, p > 0.05). In the second control experiment, only 20% of the subjects correctly identified their partner's hand. This is as would be expected by chance (33%). DISCUSSION The results of this experiment show that a significant proportion of adults in established couples can recognize their partner by cutaneous touch. Although it is assumed that the subjects had had extensive tactile contact with their partner prior to testing, they were unaware that they would be tested for tactile recognition. Their successful overall performance indicates, therefore, that the discriminative tactile cues are learned unintentionally in the course of social interactions. Men and w o m e n were equally proficient at the face-recognition test. Only the women, however, succeeded at the handrecognition test. The most likely reason for the performance difference is that men's hands vary more than w o m e n ' s hands
in hair density and therefore are more discriminable. In effect, then, the hand-recognition test is probably objectively easier for the w o m e n than for the men. The success of men on one test but not the other serves as adjuvant support for our claim that successful recognition was not based on extraneous nontactile cues. If that had been the case then the men should have shown equal proficiency on both tests, since only the tactile cues differed between trials. The most direct evidence that the discrimination was a tactile one, however, comes from the results of Control Experiment 2. The results of that experiment show that, without access to tactile cues of the models' skin, individual recognition was not successful. I cannot specify, based on the present data, which of the available tactile cues were used for recognition. Temperature, texture (i.e., hair density, skin ridges), flaccidity, m o v e m e n t of the skin during stroking, and felt size of the stroking area are all prime candidates. It is most probable that touch recognition depends on a combination or the sum total of the available cues, as is the case for both recognition by sight and by sound (1,8). However, whether or not recognition depends on one or many of these cues and whatever their nature, recognition as tested in this study should still be considered tactile since it was based on cutaneous cues afforded by stroking the surface of the skin. This study confirms and extends our previous results on touch recognition. We now know that touch recognition is not the exclusive talent of mothers and that individuals besides babies can be recognized by tactile cues. This confirms that h u m a n adults are sensitive to subtle aspects of social touching. It also shows touch recognition to be a more general h u m a n skill than previously realized, and puts it amongst the other sensory modalities as an effective channel by which an individual can be recognized. In everyday terms, the results suggest that when we touch a person with whom we have had a great deal of tactile contact, they feel differently to us than does a person with w h o m we have had little or no tactile experience. Put another way, the data suggests that there is be a sense of familiarity evoked by touching a familiar individual that is not evoked by touching an individual with w h o m we are less familiar. This feeling of familiarity is probably an important c o m p o n e n t of the sensory background against which social behaviors are played out. As such, the tactile cues may have subtle, but significant influences on social behavior. ACKNOWLEDGMENTS This research was supported by the Levine Center, the Sturman Center, and the Israel Basic Science Foundation for Science and Humanities.
REFERENCES 1. Courtois, M. R.; Mueller, J. H. Processing multiple physical features in facial recognition. Bull. Psychon. Soc. 14:74-76; 1979. 2. Fisher, J. D.; Rytting, M.; Heslin, R. Hands touching hands: Affective and evaluative effects of an interpersonal touch. Sociometry 39:416421; 1976. 3. Kaitz, M.; Lapidot, P.; Bronner, R.; Eidelman, A. Parturient women can recognize their infants by touch. Dev. Psychol. 28:35-39; 1992. 4. Kaitz, M.; Meirov, H.; Landsman, I.; Eidelman, A. I. Infant-recognition by tactile cues. Infant Behav. Dev. (in press).
5. Millot, J. C.; Filiatre, J. C.; Montagner, H. Les comportements de toucher de la mere a l'egard du noveau-ne. C. R. Acad. Sci. [III] 20: 499-502; 1987. 6. Nicosia, G. L.; Aiello, J. R. Effects of bodily contact on reactions to crowding. Paper presented at the American Psychological Association, Washington, DC, September, 1976. 7. Thayer, S. Social touching. In: Schiff, W.; Foulke, E., eds. Tactual-perception--a source book. Cambridge: University Press; 1982:363-304. 8. Voiers, W. D. Perceptual bases of speaker identity. J. Acoust. Soc. Am. 36:1065-1073; 1986.