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Results for “Size Perception”

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PubMed1994

Selective deficit of visual size perception: two cases of hemimicropsia.

Hemimicropsia is a rare disorder of visual perception characterized by an apparent reduction of the size of objects when presented in one hemifield. We report two cases of hemimicropsia resulting from focal brain lesions. The first patient was an art teacher and could accurately depict his abnormal visual perception. He subsequently died and his brain was examined post mortem. In the second patient, micropsia was assessed by a quantified size comparison task. The size of a given object is normally perceived as constant across any spatial position. Hemimicropsia may thus be considered a limited violation of the size constancy principle. Behavioural and anatomical data are discussed in relation to the neural basis of visual object perception in humans.

Autopsy↗
PubMed1999

Non-veridical size perception of expanding and contracting objects.

Observers were presented with various types of stimulus expansion and contraction which resulted in marked misperceptions of size. Firstly, the perceived size of an object which is changing in size is shown to be biased in the direction of the size change. Secondly, expansion or contraction of the internal texture of objects is found to influence their perceived size. Finally, an illusory texture manipulation in the form of a movement after-effect is shown to produce the same type of size misperception as a real expansion or contraction of internal texture. The spatio-temporal characteristics of these illusory size changes are investigated.

Humans↗
PubMed1994

Evidence for separate, task dependent noise processes in orientation and size perception.

Spatial acuity was estimated as the minimum difference in target spatial frequency which could act as a cue in a double concurrent, single interval orientation discrimination task. Experiments were conducted with vertical and oblique (45 deg) targets at three different spatial frequencies covering a range of two octaves. Frequency thresholds were found to be lower than those estimated by conventional methods by a factor of nearly 50%. They followed Weber's law for target frequency and were independent of target orientation. The orientation thresholds exhibited a normal oblique effect, and were not affected by the simultaneous judgements of target frequency. The data support the contention that the neural codes for image size and image orientation are segregated at an early stage of processing, and that the main source of noise that limits the precision of coding in these domains exists beyond the level of early mechanisms.

Differential Threshold↗
PubMed2003

Viewing geometry determines how vision and haptics combine in size perception.

Vision and haptics have different limitations and advantages because they obtain information by different methods. If the brain combined information from the two senses optimally, it would rely more on the one providing more precise information for the current task. In this study, human observers judged the distance between two parallel surfaces in two within-modality experiments (vision-alone and haptics-alone) and in an intermodality experiment (vision and haptics together). In the within-modality experiments, the precision of visual estimates varied with surface orientation, as expected from geometric considerations; the precision of haptic estimates did not. An ideal observer that combines visual and haptic information weights them differently as a function of orientation. In the intermodality experiment, humans adjusted visual and haptic weights in a fashion quite similar to that of the ideal observer. As a result, combined size estimates are finer than is possible with either vision or haptics alone; indeed, they approach statistical optimality.

Adult↗
PubMed1995

Body size perception and dissatisfaction in female subjects of different ages.

The relationships between age and both body size estimation and body dissatisfaction were assessed by Distorting Television Image Method (DTIM) and Body Cathexis Scale (BCS) in a sample of 96 female subjects of ages ranging from 7 to 65 years. We found that there were no significant body distortion differences between different age ranges, although the most accurate perception seemed to occur during adolescence. As far as DTIM assessment of body dissatisfaction was concerned, adolescents showed no significantly greater aesthetic preoccupation than subjects of other age groups. On the other hand, using BCS, body dissatisfaction appeared to increase proportionally with age. The low, although significant, correlations between these two techniques of measuring body dissatisfaction suggest that, in addition to evaluating aesthetic features, BCS also assesses the degree of satisfaction with functional body aspects which are exposed to unavoidable decline with ageing.

Adolescent↗
PubMed1999

Body size perception in anorexia nervosa: a signal detection approach.

This study investigated whether individuals with anorexia nervosa (AN) visualize themselves as fatter than they are because they perceive themselves as fatter. Females with AN who overestimated their own body size judged size differences between pictures of their own body, and then again of someone else's body. Signal detection analysis of the results showed no differences in perceptual sensitivity between the AN and normal and thin control groups. No significant correlations were found between body size estimates and perceptual sensitivity. The anorexic group did, however, show a bias to report seeing "thin" differences, which was opposite to that of thin controls. Because bias differences between the groups were significant while sensitivity differences were not, it was concluded that abnormalities of body image most probably arise during reconstruction of the visual body image, rather than during perception of the body.

Adult↗
PubMed2003

Garment sizes in perception of body size.

This paper reports an experimental investigation of the effect of garment size on perceived body size. The perceived body sizes of three Chinese men (thin, medium, and obese build) wearing different sizes of white T-shirts were assessed using Thompson and Gray's 1995 Nine-figural Scale in 1 (thinnest) to 9 (obese) grade and a newly-proposed method. Within the limit of commercially available T-shirt sizes, for thin and medium persons, perceived body sizes are bigger when wearing T-shirts of larger sizes. For an obese person, however, wearing a large size T-shirt tends to make him look thinner. The study also showed that the newly proposed comparative method is more reliable in comparing body size perception but without measuring the magnitude of the change in body-size grade. The figural scale and the comparative method can be complementary.

Adult↗
PubMed1996

Perception of stimulus size in patients with burning mouth syndrome.

Twenty subjects with burning mouth syndrome (BMS) and 20 control subjects were tested for oral size perception. Blindfolded subjects assessed the size of holes (2.38-12.70 mm diameter) presented to the tongue, using their fingers to select a matching hole from a comparator series of 31 holes (0.76-15.87 mm diameter) using first static then phasic touch. Both groups overestimated the size of the holes less than 10 mm in diameter but no systematic disparity was evident with holes greater than 10 mm in diameter. The relationship between the stimulus size and the illusion (expressed as the ratio of apparent size to real size) was hyperbolic, with the illusion tending towards unity for holes greater than 10 mm. No differences were found in object size perception amongst patients with BMS or control subjects. It is therefore unlikely that altered oral size perception is a precipitating factor or accompanying feature in patients with BMS.

Adult↗
PubMed2005

The processing and perception of size information in speech sounds.

There is information in speech sounds about the length of the vocal tract; specifically, as a child grows, the resonators in the vocal tract grow and the formant frequencies of the vowels decrease. It has been hypothesized that the auditory system applies a scale transform to all sounds to segregate size information from resonator shape information, and thereby enhance both size perception and speech recognition [Irino and Patterson, Speech Commun. 36, 181-203 (2002)]. This paper describes size discrimination experiments and vowel recognition experiments designed to provide evidence for an auditory scaling mechanism. Vowels were scaled to represent people with vocal tracts much longer and shorter than normal, and with pitches much higher and lower than normal. The results of the discrimination experiments show that listeners can make fine judgments about the relative size of speakers, and they can do so for vowels scaled well beyond the normal range. Similarly, the recognition experiments show good performance for vowels in the normal range, and for vowels scaled well beyond the normal range of experience. Together, the experiments support the hypothesis that the auditory system automatically normalizes for the size information in communication sounds.

Humans↗
PubMed2002

The influence of density and material on oral perception of ball size with and without palatal coverage.

The size of a bolus determines how it will be manipulated in the mouth and swallowed. Ten healthy individuals assessed the size of ball bearings of five sizes (4-11 mm diameter) and four materials with different densities in order to investigate the effect of weight on oral size perception. To study the role of the tongue and palate, the experiment was performed with and without a custom-made plastic palate. The results revealed that size itself determines size perception, and that material and weight are negligible factors. An illusional effect in the direction of under-estimation was found for the ball bearings, especially for the small sizes up to 8 mm diameter. While wearing a plastic palate a significant improvement (P<0.05) occurred; the participants performed better and there was less under-estimation. An explanation for this could be that only a minor part of the total area of the ball bearing touches the palate and is hence detected, while the tongue alone is more compliant and thereby able to sense the ball's whole size.

Humans↗
PubMed1999

Perception of body size in the Tongan community: differences from and similarities to an Australian sample.

OBJECTIVE: The prevalence of obesity in Tonga is high and increasing. Attempts to address this major health issue would be assisted by a realistic concept of current and preferred body sizes. In this study, body size perception in Tongans was compared with that of Australians. DESIGN: Cross-sectional comparative study. SUBJECTS: 542 Tongans, 89 of whom were enrolled in a weight-loss programme (WLP); 481 Australians. MEASUREMENTS: Subjects were weighed and measured. Two series of photographs (one female, one male), representing specific body mass indexes (BMIs) were used to assess body perception. RESULTS: The BMIs of the Tongans were higher than those of the Australians (Tongans: female 32.6+/-0.35 (mean +/- s.e.m); male, 30.4+/-0.33; Australians: female, 25.6+/-0.33; male 26.3+/-0.26 kg/m2). Tongan women underestimated their body size; Tongan men and Australians overestimated. WLP and younger Tongan women preferred smaller body sizes for themselves and for men and women in general. There were gender differences in preferred healthy and attractive female sizes (men: 27 kg/m2; non-WLP women: 25 kg/m2; WLP women: 23 kg/m2) and male sizes (men: 29-30 kg/m2; women: 26-27 kg/m2 chosen by Tongans. Preferred, attractive and healthy body sizes chosen by Australian men and women were similar; about 24 kg/m2 for males and 21-22 kg/m2 for females. CONCLUSION: Tongans preferred larger body sizes than did Australians, particularly the men, but WLP women's preferences were similar to those of Australians. There is evidence that preferences are changing in Tonga with time, and probably with increasing Western influence.

Adult↗