Seeing the body distorts tactile size perception

Vision of the body modulates somatosensation, even when entirely non-informative about stimulation. For example, seeing the body increases tactile spatial acuity, but reduces acute pain. While previous results demonstrate that vision of the body modulates somatosensory sensitivity, it is unknown whether vision also affects metric properties of touch, and if so how. This study investigated how non-informative vision of the body modulates tactile size perception. We used the mirror box illusion to induce the illusion that participants were directly seeing their stimulated left hand, though they actually saw their reflected right hand. We manipulated whether participants: (a) had the illusion of directly seeing their stimulated left hand, (b) had the illusion of seeing a non-body object at the same location, or (c) looked directly at their non-stimulated right-hand. Participants made verbal estimates of the perceived distance between two tactile stimuli presented simultaneously to the dorsum of the left hand, either 20, 30, or 40 mm apart. Vision of the body significantly reduced the perceived size of touch, compared to vision of the object or of the contralateral hand. In contrast, no apparent changes of perceived hand size were found. These results show that seeing the body distorts tactile size perception.     

An experimental study of the effect of mood on body size perception.

The study presented is an experimental investigation of the effect of mood on body size perception. Female students estimated their body size and indicated their degree of dissatisfaction with their body size before and after the induction of a negative or positive mood state. Compared with women who received the positive induced mood, the induction of low mood led to greater disturbances in body size perception in the form of a tendency to overestimate their body size more and significantly greater dissatisfaction with their body size. Furthermore, among the women who received the negative mood condition, compared with those with little or no concern with their body shape, for those with such concerns the induction of low mood led to greater disturbances in body size perception in the form of overestimating their body size significantly more and a tendency towards greater dissatisfaction with their body size. These findings suggest that depressed mood may play an important role in determining the extent of disturbance in body size perception in clinical populations.     

Visual distortion of body size modulates pain perception

Pain is a complex subjective experience that is shaped by numerous contextual factors. For example, simply viewing the body reduces the reported intensity of acute physical pain. In this study, we investigated whether this visually induced analgesia is modulated by the visual size of the stimulated body part. We measured contact heat-pain thresholds while participants viewed either their own hand or a neutral object in three size conditions: reduced, actual size, or enlarged. Vision of the body was analgesic, increasing heat-pain thresholds by an average of 3.2 °C. We further found that visual enlargement of the viewed hand enhanced analgesia, whereas visual reduction of the hand decreased analgesia. These results demonstrate that pain perception depends on multisensory representations of the body and that visual distortions of body size modulate sensory components of pain.     

Ethnic and racial differences in body size perception and satisfaction

Body dissatisfaction in women in the United States is common. We explored how women from various racial and ethnic groups used figural stimuli by exploring differences in current and preferred silhouette, and their discrepancy. We surveyed 4023 women aged 25–45 in an online investigation. Participants were identified using a national quota-sampling procedure. Asian women chose a smaller silhouette to represent their current body size, which did not remain significant after adjusting for self-reported BMI. After controlling for BMI, African American women selected a smaller silhouette than White women to represent their current size. Both African American and women reporting “Other” race preferred larger silhouettes than White women even after controlling for BMI. The discrepancy score revealed lower body dissatisfaction among African American than White women. Understanding factors that promote body satisfaction differentially across racial and ethnic groups could become a tool in appropriately tailored interventions designed to prevent eating disorders.     

Contest experience and body size affect different types of contest decisions

This study examined the relative importance of contest experience and size differences to behavioral decisions over the course of contests. Using a mangrove rivulus fish, Kryptolebias marmoratus, we showed that although contest experience and size differences jointly determined contest outcomes, they affected contestants’ interactions at different stages of contests. Contest experience affected behavioral decisions at earlier stages of contests, including the tendency and latency to launch attacks, the tendency to escalate contests into mutual attacks and the outcome of non-escalated contests. Once contests were escalated into mutual attacks, the degree of size difference affected the fish’s persistence in escalation and chance of winning, but contest experience did not. These results support the hypothesis that contest experience modifies individuals’ estimation of their fighting ability rather than their actual strength. Furthermore, (1) in contests between two naïve contestants, more than 60 % of fish that were 2–3 mm smaller than their opponent escalated the contest to physical fights, even though their larger opponents eventually won 92 % of escalated fights and (2) fish with a losing experience were very likely to retreat in the face of an opponent 2–3 mm smaller than them without escalating. The result that a 2–3 mm size advantage could not offset the influence of a losing experience on the tendency to escalate suggests that, as well as depending on body size, the fish’s physical strength is influenced by other factors which require further investigation.     

Body size perception and body satisfaction in restrained and unrestrained eaters.

In 21 restrained and 20 unrestrained eaters body size perception was measured using the video distortion technique (VDT), the image marking procedure (IMP) and the kinesthetic size estimating apparatus (KSEA). Body satisfaction was assessed by questionnaires (Body Shape Questionnaire, Dieting scale of the Eating Attitudes Test). Restrained eaters showed no systematic over- or underestimation of the body size but less perceptual accuracy (in VDT and KSEA). Furthermore, they were clearly more dissatisfied with their bodies than unrestrained eaters. Both findings were unrelated to each other. In both groups depressive mood or thoughts seemed to be associated with body dissatisfaction but not with body size misperception. Objective body measures (body mass index, body fat content) were not related to either body size perception or body satisfaction. The findings suggest that a perceptual uncertainty in regard to body size (either for visual or for somatosensory aspects) has already developed in restrained eaters, which may constitute a predisposition for more overt forms of body size misperception as found in eating disorder patients.     

Weber's illusion and body shape: anisotropy of tactile size perception on the hand

The perceived distance between touches on a single skin surface is larger on regions of high tactile sensitivity than those with lower acuity, an effect known as Weber's illusion. This illusion suggests that tactile size perception involves a representation of the perceived size of body parts preserving characteristics of the somatosensory homunculus. Here, we investigated how body shape is coded within this representation by comparing tactile distances presented in different orientations on the hand. Participants judged which of two tactile distances on the dorsum of their left hand felt larger. One distance was aligned with the proximodistal axis (along the hand), the other with the mediolateral axis (across the hand). Across distances were consistently perceived as larger than along ones. A second experiment showed that this effect is specific to the hairy skin of the hand dorsum and does not occur on glabrous skin of the palm. A third experiment demonstrated that this bias reflects orientation on the hand surface, rather than an eye- or torso-centered reference frame. These results mirror known orientational anisotropies of both tactile acuity and of tactile receptive fields (RFs) of cortical neurons. We suggest that the dorsum of the hand is implicitly represented as wider than it actually is and that the shape of tactile RFs may partly explain distortions of mental body representations.     

A multidimensional scaling and semantic differential technique study of the perception of environmental settings

Abstract.— Multidimensional scaling is compared with the semantic differential technique (SDT) as methods for dimensional analysis of the perception of environmental settings. In one experiment employing as stimuli SDT scales used in previous experiments a General Evaluation , a Social Status , a Potency , a Closedness , and an Affection factor were found for both methods. A Unity and a Complexity factor merged into a single factor, an O riginality factor was only found for multidimensional scaling. In a second experiment employing as stimuli perspective drawings of urban and suburban settings, the results differed in that the General Evaluation , the Social Status , the Closedness , and the Unity/Complexity factors were found for the SDT, and only the first two for multidimensional scaling. Further experiments with other stimuli and methods of representation are needed in order to draw firm conclusions regarding the correspondence between SDT and multidimensional scaling results within the area under consideration.     

Wanting a body that's better than average: the effect of manipulated body norms on ideal body size perception

We examined the effect of body norms on ideal and current body size perception. In Study One, female participants were randomly assigned to one of three experimental conditions: (1) a thinner body norm, (2) a heavier body norm, or (3) no body norm. Body norms were manipulated by indicating a bogus "population average," and current and ideal body size perception were subsequently measured using a body silhouettes measure. Women had a thinner ideal body size in the thinner norm condition than in the heavier norm condition. Study Two replicated these results, but in a sample of young men and with regards to muscularity rather than thinness. Men had a more muscular ideal body size in the more muscular norm condition than in the less muscular norm condition. Current body size perception was also influenced by body norms, but only for women and after controlling for BMI.     

The independence of size perception and distance perception

Research on distance perception has focused on environmental sources of information, which have been well documented; in contrast, size perception research has focused on familiarity or has relied on distance information. An analysis of these two parallel bodies of work reveals their lack of equivalence. Furthermore, definitions of familiarity need environmental grounding, specifically concerning the amount of size variation among different tokens of an object. To demonstrate the independence of size and distance perception, subjects in two experiments were asked to estimate the sizes of common objects from memory and then to estimate both the sizes and the distances of a subset of such objects displayed in front of them. The experiments found that token variation was a critical variable in the accuracy of size estimations, whether from memory or with vision, and that distance had no impact at all on size perception. Furthermore, when distance information was good, size had no effect on distance estimation; in contrast, at far distances, the distances to token variable or unknown objects were estimated with less accuracy. The results suggest that size perception has been misconceptualized, so that the relevant research to understand its properties has not been undertaken. The size-distance invariance hypothesis was shown to be inadequate for both areas of research.     

An exploration of perception of body boundary, personal space, and body size in elderly persons.

A study of 108 elderly persons using the Body Distortion Questionnaire and the personal space simulation technique test did not support hypotheses that elderly persons with a large personal space will have a larger distortion of body boundary, a larger perception of large body size, a smaller perception of small body size, a larger distortion of body size, and a larger body distortion than elderly persons with a small personal space. The analyses with one-tail t tests showed elderly persons with a small personal space have a larger perception of large body size and a larger distortion of body size than elderly persons with a large personal space. When the extremes of personal space were used the results were the same. Males have a larger personal space and greater distortion of skin perceptions than females.     

A confusion matrix for the study of taste perception

Taste stimulus identification was studied in order to more thoroughly examine human taste perception. Ten replicates of an array of 10 taste stimuli--NaCl, KCl, Na glutamate, quinine. HCl, citric acid, sucrose, aspartame, and NaCl-sucrose, acid-sucrose, and quinine-sucrose mixtures--were presented to normal subjects for identification from a list of corresponding stimulus names. Because perceptually similar substances are confused in identification tasks, the result was a taste confusion matrix. Consistency of identification for the 10 stimuli (T10) and for each stimulus pair (T2) was quantified with measures derived from information theory. Forty-two untrained subjects made an average of 57.4% correct identifications. An average T10 of 2.25 of the maximum 3.32 bits and an average T2 of 0.84 of a maximum 1.0 bit of information were transmitted. In a second experiment, 40 trained subjects performed better than 20 untrained subjects. The results suggested that the identification procedure may best be used to assess taste function following 1-2 training replicates. The patterns of taste confusion indicate that the 10 stimuli resemble one another to varying extents, yet each can be considered perceptually unique.     

The independence of size perception and distance perception.

Research on distance perception has focused on environmental sources of information, which have been well documented; in contrast, size perception research has focused on familiarity or has relied on distance information. An analysis of these two parallel bodies of work reveals their lack of equivalence. Furthermore, definitions of familiarity need environmental grounding, specifically concerning the amount of size variation among different tokens of an object. To demonstrate the independence of size and distance perception, subjects in two experiments were asked to estimate the sizes of common objects from memory and then to estimate both the sizes and the distances of a subset of such objects displayed in front of them. The experiments found that token variation was a critical variable in the accuracy of size estimations, whether from memory or with vision, and that distance had no impact at all on size perception. Furthermore, when distance information was good, size had no effect on distance estimation; in contrast, at far distances, the distances to token variable or unknown objects were estimated with less accuracy. The results suggest that size perception has been misconceptualized, so that the relevant research to understand its properties has not been undertaken. The size-distance invariance hypothesis was shown to be inadequate for both areas of research.     

EYE LINES: A tool for studying visual perception of size and angle

EYE LINES is a set of programs for preparing and running experiments that measure the perception of the size, position, or angle of orientation of visual stimuli. A drawing program builds images as collections of linked line-segment vectors. The experiments involve the method of adjustment. Subjects use a mouse to adjust the lengths or angles of specified line segments. Designed for use both in research and instructional laboratories, the programs run on the Macintosh.     

Simultaneous time and size perception

Judgments of the apparent duration and size of visually presented circles vary directly with the duration and size of the presented stimuli. When the frequencies of stimulus duration (short vs. long) and stimulus area (small vs. large) are varied, perceived size and duration are directly related to the frequency of the lower attribute value (short or small). These data are compared to the predictions of different information-processing models. The model which accounts for the data best is one in which it is assumed that perceived size and perceived duration grow together over the course of time spent sampling size information, and that attribute frequency affects the rate of sampling and/or the point at which sampling stops.     

Direct and indirect perception of size

Three experiments, using a reaction time paradigm, examine the direct (stimulus bound) and indirect (mediational inference) approaches to size perception. Subjects determine which of two stimuli is the larger when the two can be at different egocentric distances. The effects of two variables on reaction times are examined—distal ratio, the ratio of physical sizes of the stimuli, and proximal ratio, the ratio of the angular projections of the stimuli on the retina. In Experiment 1, both ratios are found to affect reaction times, with the proximal ratios yielding the larger effect, more in line with the predictions of the indirect approach. But the results of Experiments 2 and 3 indicate that distance is taken into greater account, the more similar the distal sizes of the stimuli. In one stimulus condition, distance appears not to affect reaction times. It is suggested that direct size perception occurs for large stimulus differences, indirect size perception for smaller differences. The identical results of the two experiments, one with and one without texture, point to some variable other than texture occlusion or interception as the stimulus for direct size perception. Some aspect of distance from the eye-level plane is suggested as an alternative.