Tactual perception: a review of experimental variables and procedures <s> Sex differences <s> The literature on gender differences in touch is divided into the categories of observational studies of touch frequency, people's beliefs about frequency and meaning, data on qualitative differences in touch, and studies of response to touch. The observational studies reveal: (a) no overall tendency for males to touch females more than vice versa, though two studies of specifically intentional touch with the hand did find such asymmetry; (b) a tendency for females to initiate touch more than males; (c) a questionable tendency for females to receive touch more than males; (d) a tendency for more female same-gender touch than male same-gender touch (at least for white samples); and (e) a tendency for same-gender dyads to touch more than opposite-gender dyads, especially when the dyads are unlikely to be intimate. Some of these conclusions are debatable, owing to methodologica l problems.1 Data dealing with qualitative aspects of touch are found to be too sparse and inconsistent to yield much information about gender differences in the uses or meanings of particular types of touch. The literature shows a tendency for women to respond more positively to touch than men. Henley's power hypothesis, the primary hypothesis concerning gender differences in touch, is given special scrutiny as a possible explanatory framework. Despite the psychological significance of touch as a means of communication , not a great deal is known about when and why touching occurs and what meaning it may have in same-gender and opposite-gender interaction. Studies on the topic of gender and touch have focused on observed occurrences of touch, self-reports of touch frequency, people's beliefs about the meanings of touch, observers' perceptions of interactions that involved touch, and empirically assessed response to touch. Relevant questions and methods are many and the literature smaller than we would wish, considering this variety. But the literature is actually much larger than most psychologists alluding to the topic seem to be aware of; a handful of studies at best, and usually the same ones, are generally cited. There has been only one substantial review of gender and touch, that of Major (1981), whose review differs from <s> BIB001 </s> Tactual perception: a review of experimental variables and procedures <s> Sex differences <s> In this study, we are interested in the following two questions: (1) how does perceived roughness ::: correlate with physical roughness, and (2) how do visually and haptically perceived roughness compare? ::: We used 96 samples of everyday materials, such as wood, paper, glass, sandpaper, ceramics, ::: foams, textiles, etc. The samples were characterized by various different physical roughness measures, ::: all determined from accurately measured roughness profiles. These measures consisted of spectral ::: densities measured at different spatial scales and industrial roughness standards (Ra, Rq and Rz). ::: In separate haptic and visual conditions, 12 nai¨ve subjects were instructed to order the 96 samples ::: according to perceived roughness. The rank orders of both conditions were correlated with the various ::: physical roughness measures. With most physical roughness measures, haptic and visual correspondence ::: with the physical ordering was about equal. With others, haptic correspondence was ::: slightly better. It turned out that different subjects ordered the samples using different criteria; for ::: some subjects the correlation was better with roughness measures that were based on higher spatial ::: frequencies, while others seemed to be paying more attention to the lower spatial frequencies. Also, ::: physical roughness was not found to be the same as perceived roughness. <s> BIB002 </s> Tactual perception: a review of experimental variables and procedures <s> Sex differences <s> Abstract Surprisingly little scientific research has been conducted on the topic of interpersonal touch over the years, despite the importance of touch in our everyday social interactions from birth through to adulthood and old age. In this review, we critically evaluate the results of the research on this topic that have emerged from disciplines, such as cognitive and social psychology, neuroscience, and cultural anthropology. We highlight some of the most important advances to have been made in our understanding of this topic: For example, research has shown that interpersonal tactile stimulation provides an effective means of influencing people's social behaviors (such as modulating their tendency to comply with requests, in affecting people's attitudes toward specific services, in creating bonds between couples or groups, and in strengthening romantic relationships), regardless of whether or not the tactile contact itself can be remembered explicitly. What is more, interpersonal touch can be used to communicate emotion in a manner similar to that demonstrated previously in vision and audition. The recent growth of studies investigating the potential introduction of tactile sensations to long-distance communication technologies (by means of mediated or ‘virtual’ touch) are also reviewed briefly. Finally, we highlight the synergistic effort that will be needed by researchers in different disciplines if we are to develop a more complete understanding of interpersonal touch in the years to come. <s> BIB003
Literature on touch and sex differences appears mainly in social and interpersonal research, analysing touch as a form of communication (e.g., BIB003  BIB001  . However, other studies have explored sex differences in touch within experimental tasks. BIB002 presented a review of studies about tactile perception in females and concludes that the evidence for sex differences was scarce and incongruent, and for that reason argued in favour of assuming no differences in performance. Researchers have discarded sex differences analysis from their works, and research on haptic perception has focused in establishing general rules of processing, regardless of the participants' sex. However, some studies can be identified in which sex differences are reported.  explored differences between women and men in a study in which participants had to detected changes of position in raised line drawings presented in a matrix. Results revealed that female participants presented better results than male participants, but these differences disappeared in more difficult tasks. Overall, the reported sex difference was small and congruent with the differences found in vision for a similar task. Analysing the perception of tactile simultaneity of pairs of stimuli did not result in consistent sex differences between participants, reporting that male performance was faster, but not in all conditions (Geffen et al. 2000a, b) . Using positron emission topography,  described differences between men and women in the activation of the dorsal premotor cortex, which was asymmetrical in men but symmetrical in women. The authors concluded that this might suggest differences between the groups in tasks such as discrimination through active touch, where inter-hemispheric connection would be stronger in women, facilitating performance. In haptic orientation perception, differences were found between male and female participants . In this study, participants were distributed through three experiments, in which they were asked to touch a fixed plastic bar with one hand and orient a movable plastic bar with the other hand in a way that both bars were parallel (Experiment 1); use one hand and, considering the bar as a pointer in a clock, provide a verbal answer identifying the represented minutes for each orientation (Experiment 2); orient a bar as a clock pointer according to the verbal indication of the experimenter (Experiment 3). Results showed that males were more accurate in parallel setting and haptic orientation perception. Although there are some studies reporting differences between male and female participants in some specific haptic tasks, this variable has not been part of most systematic studies on touch. In addition, experimental results of sex differences manipulations are not very clear, usually presenting small or inconsistent effects. The study of touch according to the participants' group can add relevant knowledge. Studies with blind participants allow the evaluation of touch performance in individuals with a high degree of specialisation and experience in tactual interaction of stimuli, and a clear analysis of tactual performance without visual mediation that is not available in blindfolded sighted participants. Experiments with children and infants can bring an interesting development perspective to how we touch and how we perceived touched stimuli and can even allow the evaluation of tactual perception independently of verbal mediation (with preverbal infants). Finally, the summary of research directly addressing sex differences in touch revealed that this dimension is still unexplored and that the few studies that address it do not seem to imply a systematic effect of sex in tactual perception.