SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Visual illusions tell us that size perception depends heavily upon complex contextual cues, often thought to be extracted by brain areas high in the visual hierarchy. Now, a new study shows that perceived size is reflected in activity as early as the primary visual cortex.
When a horizontally elongated surface is occluded in the middle by a larger surface, it appears narrower than its true width (Kanizsa's compression illusion). We report that a similar compression effect occurs for closed-loop visuomotor matches of size, but not for otherwise comparable open-loop "mimed" reaching or size-matching visuomotor responses. Our study is the first in which a comparison of size perception in personal space with bilateral actions performed with both hands (instead of precision grips employing the thumb and the index finger) is used to investigate motor responses to Kanizsa's compression illusion. Implications for the current debate on the existence of dissociations between spatial perception and visually controlled actions in personal space are discussed.
BACKGROUND: Dysmetropsia or distorted image size perception (smaller: micropsia; larger: macropsia) is known to occur after successful surgical re-attachment for macula-off rhegmatogenous retinal detachment. However, the vertical and horizontal components of size distortion have not been previously quantified separately. The purpose of this article is to describe horizontal and vertical dysmetropsia occurring in patients following pars plana vitrectomy and gas treatment (octafluoropropane, C(3)F(8) or sulfur hexafluoride, SF(6)) for macula-off rhegmatogenous retinal detachment. MATERIAL AND METHODS: Four patients (mean+/-SD, 59+/-8 years; three women and one man) who had had pars plana vitrectomy and gas treatment for macula-off rhegmatogenous retinal detachment 6-7 months earlier underwent ocular examination, best corrected visual acuity test, threshold horizontal and vertical dysmetropsia measurement using a computerised version of the New Aniseikonia Test, slit-lamp examination and optical coherence tomography of the macula. RESULTS: All patients had binocular visual complaints including difficulty judging distances or reading, rivalry or asthenopia. The logMAR visual acuity (mean+/-SD) in the operated eye was 0.52+/-0.199 and 0.02+/-0.171 in the unaffected eye. All patients perceived the image as smaller (micropsia) with the affected eye, with differences ranging from -9 to 0%. Four patients showed 3% or more size difference between horizontal and vertical meridians. CONCLUSIONS: Dysmetropsia does occur in symptomatic patients following successful surgical repair of macula-off rhegmatogenous retinal detachment by pars plana vitrectomy and gas treatment. The effect on image size is heterogenous across the retinal area affected.
The relationship between distance and size perception is unclear because of conflicting results of tests investigating the size-distance invariance hypothesis (SDIH), according to which perceived size is proportional to perceived distance. We propose that response bias with regard to measures of perceived distance is at the root of the conflict. Rather than employ the usual method of magnitude estimation, the bias-free two-alternative forced choice (2AFC) method was used to determine the precision (1/sigma) of discriminating depth at different distances. The results led us to define perceptual distance as a bias free power function of physical distance, with an exponent of approximately 0.5. Similar measures involving size differences among stimuli of equal angular size yield the same power function of distance. In addition, size discrimination is noisier than depth discrimination, suggesting that distance information is processed prior to angular size. Size constancy implies that the perceived size is proportional to perceptual distance. Moreover, given a constant relative disparity, depth constancy implies that perceived depth is proportional to the square of perceptual distance. However, the function relating the uncertainties of depth and of size discrimination to distance is the same. Hence, depth and size constancy may be accounted for by the same underlying law.
Information displays commonly use 2-D and 3-D objects even though the numbers represented are 1-D. This practice may be problematic because the psychophysical relation between perceived and physical magnitudes is generally nonlinear for areas and volumes. Nonetheless, this research shows that apparent 2-D and 3-D objects can produce linear psychophysical functions if only one dimension shows variation. Processing time increases with the number of dimensions in the objects that show variation, not with the apparent dimensionality. Indeed, when only one dimension showed variation, apparent 3-D objects were judged more quickly than were apparent 2-D or 1-D objects. These results present a challenge for computational models of size perception and have implications for the design of information displays. Actual or potential applications of this research include the design and use of statistical graphs and information displays; objects that display variation in more than one dimension should not be used to represent single (1-D) numerical variables if they are to be judged accurately and rapidly.
The hypothesis that visual size is determined from the low-frequency Fourier spectrum of the image has been tested in a variety of ways. The fact that size discrimination of vertical bars is unimpaired when high spatial frequencies are filtered out of the image by blurring, and the fact that spatial-frequency adaptation alters perceived size, argue in favor of such hypothesis. However, the hypothesis is weakened by the observation that discrimination is also unimpaired by filtering low frequencies out of the image and by the observation that some manipulations which alter the Fourier transform produce no corresponding perceptual change. No current theory of size perception appears to fit all of these data.
Despite much recent interest in the objective measurement of body image in anorexia nervosa, many questions remain regarding basic mechanisms responsible for the findings as well as their meaning in the disorder. It is unclear if "whole body" measures assess the same underlying phenomena as the "body part" method, and it is unclear if body image disturbances are etiologic or a byproduct of anorexia nervosa. The possible association between self-esteem and body satisfaction and the relationship of the latter variable to actual size estimation supports the hypothesis that size perception may be closely tied to satisfaction with non-physical aspects of self. Finally it must be determined if overestimation is a function of a general psychological disturbance or of a deficit of specific interest in this disorder. Despite these questions, the way in which anorexic patients see themselves as well as the cognitive and affective responses to this perception remains an interesting and potentially fruitful area of study with this disorder.
It has been suggested that perceived size depends upon the distribution of responses among a localized population of different size-tuned mechanisms. If so, then spatial frequency masking, which alters the distribution of responses, should produce shifts in a test pattern's perceived size. We have found this to be the case. The magnitude and direction of the shifts depend only on the frequency difference in octaves (delta omega) between mask and standard. The results are not antisymmetric about the point delta omega = 0, however, as they would be if perceived size were based purely on local size-tuning properties. Our results suggest that size perception depends both on these local properties and on the spatial distribution of mechanism responses.
OBJECTIVE: To evaluate the contributions of weight status, skin tone, peer teasing, and parental appraisals of child's size to self-esteem and psychosocial adjustment in overweight African American children. METHOD: Overweight to very obese 5- to 10-year-old African American children (N = 117) completed measures of self-esteem, skin tone satisfaction, peer teasing, and body size perception. Caregivers completed the Child Behavior Checklist and rated their child's body size. RESULTS: Overweight was associated with low appearance self-esteem, and body size dissatisfaction with low global self-worth and low appearance self-esteem in children 8 and older. Appearance self-esteem but not global self-worth was lower in girls than boys. Parental perception of child's size as heavier than average was associated with low child appearance self-esteem. Heavier children also had more parental report of behavior and psychosocial problems, but their scores were in the nonclinical range. Child skin tone dissatisfaction was associated with low global self-worth. Weight-related peer teasing was associated with low self-esteem. CONCLUSIONS: The relationship between obesity and self-esteem in African American children depends upon age, gender, and children's experiences with teasing and parental evaluation of their size. Other factors, like skin tone satisfaction, contribute to a child's sense of self-worth.
Length judgments were compared for Müller-Lyer stimuli and figures which had line junctions at only one end of the central shaft. A length illusion occurred for fractional figures, only slightly reduced in magnitude from the usual illusion, and the largest reduction occurred for fractional figures with fork junctions. These results are consistent with an hypothesis (drawn from artificial intelligence algorithms for interpreting line drawings) that isolated line junctions are treated as boundary junctions with constrained interpretations of convex and concave edges for the shafts of arrow and fork junctions, respectively. Information about relative position of edges may be used to constrain computation of metric properties and consequential differences in size scaling would be responsible for the illusion. Illusions can arise when information well suited for one kind of task (eg object recognition) is employed in tasks for which it is not well suited (eg size perception).
Body size perception was measured in 41 children aged 6-10 who had been either sexually or physically abused, or had no history of abuse. Two psychophysical methods were used, including the staircase method and a signal detection method. In the staircase methodology, children adjusted the direction of distortion of their continuously changing body size. In the signal detection method, children made judgments about the presence or absence of size distortion in presented images. Results using the staircase method indicated children overestimated their body sizes, with no differences between abuse conditions, gender, or age. For the signal detection methodology, no difference in ability to detect the presence/absence of size distortion (d') was found between abuse conditions, although females were less accurate than males. All groups were better able to detect distortion when the image was distorted too wide. Measures of response bias (Ln beta) indicated that sexually abused children had a greater bias to report size distortion as present, as compared with the physically abused children.
The experiment reported here examined the kinaesthetic reproduction of two-dimensional patterns from three different modes of presentation: kinaesthetic only, visual only and visual plus kinaesthetic. The patterns were open and consisted of three linear segments of different lengths. All reproductions tended to underestimate pattern size. Subjects who had received visual experience of the pattern with or without simultaneous kinaesthetic experience produced significantly greater underestimates than subjects who had not seen the patterns. This is discussed in terms of the dominance of vision over kinaesthesis, and differences in size perception in the two modalities. Least distortion of the pattern shape was found in the reproduction of subjects who had received both kinaesthetic and visual experience of the criterion.
Explore the source record for details and available documents.
In this study, we mainly investigated the visual selectivity of hand-manipulation-related neurons in the anterior intraparietal area (area AIP) while the animal was grasping or fixating on three-dimensional (3D) objects of different geometric shapes, sizes, and orientations. We studied the activity of 132 task-related neurons during the hand-manipulation tasks in the light and in the dark, as well as during object fixation. Seventy-seven percent (101/132) of the hand-manipulation-related neurons were visually responsive, showing either lesser activity during manipulation in the dark than during that in the light (visual-motor neurons) or no activation in the dark (visual-dominant neurons). Of these visually responsive neurons, more than half (n = 66) responded during the object-fixation task (object-type). Among these, 55 were tested for their shape selectivity during the object-fixation task, and many (n = 25) were highly selective, preferring one particular shape of the six different shapes presented (ring, cube, cylinder, cone, sphere, and square plate). For 28 moderately selective object-type neurons, we performed multidimensional scaling (MDS) to examine how the neurons encode the similarity of objects. The results suggest that some moderately selective neurons responded preferentially to common geometric features shared by similar objects (flat, round, elongated, etc.). Moderately selective nonobject-type visually responsive neurons, which did not respond during object fixation, were found by MDS to be more closely related to the handgrip than to the object shape. We found a similar selectivity for handgrip in motor-dominant neurons that did not show any visual response. With regard to the size of the objects, 16 of 26 object-type neurons tested were selective for both size and shape, whereas 9 object-type neurons were selective for shape but not for size. Seven of 12 nonobject-type and all (8/8) of the motor-dominant neurons examined were selective for size, and almost all of them were also selective for objects. Many hand-manipulation-related neurons that preferred the plate and/or ring were selective for the orientation of the objects (17/20). These results suggest that the visual responses of object-type neurons represent the shape, size, and/or orientation of 3D objects, whereas those of the nonobject-type neurons probably represent the shape of the handgrip, grip size, or hand-orientation. The activity of motor-dominant neurons was also, in part, likely to represent these parameters of hand movement. This suggests that the dorsal visual pathway is concerned with the aspect of form, orientation, and/or size perception that is relevant for the visual control of movements.
Macular dysfunction was studied in 7 patients recovering after surgery for a retinal detachment involving the macula. The degree of disturbed size perception (dysmetropsia) and metamorphopsia was measured in parallel with letter and grating acuity in patients during the recovery process for time periods up to 47 months following successful re-attachment. The demonstration of dysmetropsia, quantitatively assessed by a matching technique, in several patients indicate that the spatial density of the macular photoreceptors changes following detachment. In 3 patients out of 7 a longstanding micropsia was present. The degree of micropsia was not related to the degree of metamorphopsia. Subclinical/clinical macular oedema is considered to be the most probable cause for the increased separation of the macular photoreceptors. The study indicates that quantitative measurement of dysmetropsia gives valid information about receptor displacement and of unilateral subclinical macular oedema. The relations between letter acuity, grating acuity and micropsia gives certain information about the role of changed receptor separation as a cause of impaired central vision, and we found that incomplete recovery of acuity partly can be due to long-standing separation of foveal receptors.
Patients with visual neglect show deficits in horizontal size perception in their neglected hemispace, as previously reported. The present study examined whether this size distortion can be modulated by visual background motion to the left or right while the patient performs a visual size judgment task. Six neglect patients and six normal subjects were investigated with a psychophysical size judgment task. All neglect patients showed a significant perceptual underestimation of horizontal bars in their left hemispace expressed as an overestimation of horizontal object size in the baseline (no motion) condition. Slow visual motion of background stimuli towards the right, ipsilesional side aggravated the deficit slightly, but not significantly, whereas leftward background motion completely normalized the size distortion (in four cases) or even led to an overcompensation (in two cases). This facilitatory effect was specific as it was obvious for the constant errors in the size judgments, but not in their accuracy as reflected by unchanged difference thresholds. These results suggest that coherent background motion restores temporarily the disturbed perception and representation of horizontal object size in spatial neglect.
Explore the source record for details and available documents.
Explore the source record for details and available documents.