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PubMed2003

Manual size estimation: a neuropsychological measure of perception?

Manual size estimation (participants indicate the size of an object with index finger and thumb) is often interpreted as a measure of perceptual size information in the visual system, in contrast to size information used by the motor system in visually guided grasping. Because manual estimation is a relatively new measure, I compared it to a more traditional perceptual measure (method of adjustment). Manual estimation showed larger effects of the Ebbinghaus (or Titchener) illusion than the traditional perceptual measure. This inconsistency can be resolved by taking into account that manual estimation is also unusually responsive to a physical variation of size. If we correct for the effect of physical size, manual estimation and the traditional perceptual measure show similar illusion effects. Most interestingly, the corrected illusion effects are also similar to the illusion effects found in grasping. This suggests that the same neuronal signals which generate the illusion in the traditional perceptual measure are also responsible for the effects of the illusion on manual estimation and on grasping.

Adolescent↗
PubMed1990

Perception of size and lightness of human observers: two criteria for holistic and analytic processing show no correlation in individuals.

Results of a triad-classification task and a multidimensional-scaling (MDS) experiment are compared for individual observers. Both paradigms are designed to reveal whether stimuli are perceived in a holistic or analytic manner (Garner 1974). Subjects differed substantially and consistently in their triad classification pattern. The majority of subjects selected stimuli according to dimensional criteria; this classification type is thought to indicate an analytic stimulus processing. Approximately one third of subjects, however, used a classification according to overall similarity (indicating holistic processing). Except for the very first session, virtually no intermediate classification occurred. This clear separation into two classification types suggests that there actually exist two strongly preferred processing modes. Intraindividual variability between sessions in general was small. In one case, however, a spontaneous switching from a purely dimensional classification to a purely similarity classification occurred. This indicates that the observers have different processing options at their disposal, and are not forced to use a particular processing mode by the stimulus type--as has been supposed in the original concept of integrality/separability of stimuli (Garner 1974). In the MDS experiment also substantial interindividual differences in the "best-fitting" Minkowski metric were found, indicating different processing types. However, for individuals participating in both experiments, there was no correlation between the results of the two experimental paradigms. This is interpreted as a result of the subject's ability to choose between a few perceptual-processing options.

Central Nervous System↗
PubMed2000

Jean Théophile Desaguliers (1683-1744) and eighteenth century vision research.

The emergence of psychology as an empirical discipline was influenced to a great extent by experimental investigations of visual phenomena, particularly in the nineteenth century. Less attention has been paid to experimental enquiries conducted in the eighteenth century, especially those of Jean Théophile Desagliers (1683-1744). He was an ardent advocate of Newtonian optics, on which he lectured and gave demonstrations. His research on colour and binocularity is outlined, together with those of other students of vision in that century. Experiments on visual vertigo conducted at the end of the century are also described. In 1716 Desaguliers reported a method of binocular combination that became widely employed in other studies of binocular vision, namely, placing an aperture in such a position that two more distant, adjacent objects were in the optical axes of each eye. Under these circumstances red and green patches of silk did not mix after the manner of combining prismatic lights, but engaged in rivalry. Desaguliers also investigated size perception and showed that apparent size was determined by apparent distance rather than physical distance. Moreover, he did not base his conclusions on his own observation but on those of 'any unprejudic'd Person'. Thus, both stimulus control and the use of the unbiased observer were employed in eighteenth century experimental studies of vision.

England↗
PubMed2004

Maternal perception of body size as a determinant of infant adiposity in an African-American community.

For 10 weeks, a sample of 105 postpartum African-American clients of three inner-city clinics, were recruited for this nine-month prospective study. Data from 54 mother-infant dyads were used to explore the associations between maternal perceptions of infant body size and the development of adiposity at six- to seven months of age. Correlations, chi-square, paired t-test, ANOVA, and logistic regression analyses were performed. Quantitative assessments of BMI using weight and length measures and qualitative assessments of body size perceptions using questionnaires, silhouette, and ranking scales were conducted. At six- to seven months of age, 40% of the infants were above the 85th percentile and 31% were above the 95th percentile of the NCHS standards for weight for height. Maternal perception of infant body size was positively correlated with early introduction of nonmilk foods. Significantly, more infants perceived as small were introduced to nonmilk foods earlier, compared to infants perceived as average, p=0.03. Additionally, it was observed that the earlier the introduction of nonmilk foods, the greater the infant's BMI at six- to seven months of age (r=0.59, p=0.02). Finally, one-third of mothers were obese with BMI's exceeding 30, and 31.1% were overweight with BMI's between 25 and 30.

Adult↗
PubMed1995

Does perceived size depend on perceived distance? An argument from extended haptic perception.

Two experiments were directed at the comparison between two perspectives on the perception of size achieved by probing the gap between two occluded distal surfaces by means of a hand-held rod. One perspective was the classical size-distance invariance hypothesis developed for the problem of visual size perception with a central role for perceived distance; the other was the hypothesis that the extended haptic perception of gap size is specific to a physical invariant lambda of the dynamics of probing. Experiment 1 examined the relation between hepatically perceived gap size and haptically perceived gap distance. No causal connection between the two was found, and all the variance in perceived size was accounted for by lambda. Experiment 2 manipulated the rotational inertia of the probe. Its effect was different for the two perceptions of size and distance, underscoring their independence. The indifference of perceived size to perceived distance was discussed in reference to identifying invariants for both the haptic and the visual perception of size at a distance.

Adult↗
PubMed1985

Apparent spatial frequency and contrast of gratings: separate effects of contrast and duration.

Variations in apparent spatial frequency of sinusoidal gratings were assessed using a matching method. Perceived spatial frequency increased as contrast decreased and as duration of presentation decreased (from 320 to 20 msec). The effect of duration was not produced via changes in apparent contrast (a) because the changes in perceived spatial frequency were much the same when subjective contrasts were matched as when physical contrasts were matched and (b) because reducing duration to 20 msec produced very little change in perceived contrast, despite a factor of four reduction in threshold contrast sensitivity. The effects of duration and contrast on apparent spatial frequency are therefore dissociable, but both might exert their effects via changes in the balance of centre-surround antagonism within receptive fields; the "selectivity shift" theory of these size perception phenomena is discussed.

Form Perception↗
PubMed1992

The role of instructions and familiar size in absolute judgments of size and distance.

The effects of familiar size and instructions (apparent, objective) on direct reports of size and distance were evaluated. Subjects estimated the size and distance of two different-sized playing cards or two unfamiliar stimuli under either apparent or objective instructions. The stimuli were presented successively at a distance of 5.48 m under reduced-cue conditions. The form of the instructions selectively influenced the effect of familiar size on absolute judgments of size and distance, with apparent instructions minimizing, and objective instructions promoting, familiar-size effects. The ratio of the distance judgments of the first to the second presented stimuli approximated the relative retinal sizes of the two objects under both apparent and objective instructions, while the ratio of size judgments tended to be either influenced by or independent of the object's relative retinal sizes under apparent and objective instructions, respectively. These results are consistent with Gogel's theory of off-size perception and, in particular, with the claim that, in comparison with apparent instructions, objective instructions are more likely to direct observers to base their judgments on cognitive, as opposed to perceptual, sources of spatial information.

Adult↗
PubMed2002

Two visual systems and two theories of perception: An attempt to reconcile the constructivist and ecological approaches.

The two contrasting theoretical approaches to visual perception, the constructivist and the ecological, are briefly presented and illustrated through their analyses of space and size perception. Earlier calls for their reconciliation and unification are reviewed. Neurophysiological, neuropsychological, and psychophysical evidence for the existence of two quite distinct visual systems, the ventral and the dorsal, is presented. These two perceptual systems differ in their functions; the ventral system's central function is that of identification, while the dorsal system is mainly engaged in the visual control of motor behavior. The strong parallels between the ecological approach and the functioning of the dorsal system, and between the constructivist approach and the functioning of the ventral system are noted. It is also shown that the experimental paradigms used by the proponents of these two approaches match the functions of the respective visual systems. A dual-process approach to visual perception emerges from this analysis, with the ecological-dorsal process transpiring mainly without conscious awareness, while the constructivist-ventral process is normally conscious. Some implications of this dual-process approach to visual-perceptual phenomena are presented, with emphasis on space perception.

Animals↗
PubMed1982

The construction of a plane from pictorial information.

Experiments are described which support the theory that the perception of a plane receding in depth is based on a process of construction. Displays were created which eliminated direct or higher-order stimulus information concerning the orientation of a plane, such as texture gradients or perspective. Instead, objects and the shadows they cast sufficed to suggest and support a depth interpretation. The perceived location of objects on this constructed plane affects size perception thereby providing evidence for a computational rather than a direct theory of constancy.

Cues↗
PubMedDate not supplied

Perceptions of body size and obesity: a selected review of the literature.

In this article, the literature on body image and related obesity perceptions is discussed. Research findings which span a 20 year period are summarized. Initially, Cheryl Rittenbaugh's concept of obesity as 'a culture bound syndrome' serves as a rationale for understanding sociocultural dimensions of body size perceptions. In this regard, the premise that perceptions of obesity and overweight have cultural determinants is substantiated in the reviewed literature. Societal preferences for body build and size and attitudes about weight are examined as a framework for understanding the impact that social perceptions have on individuals who are either overweight or obese. As a result of negative attitudes toward fatness, stigmatization of overweight people has been consistently documented. In related studies, investigators have centered on self-perceptions of obese and overweight individuals. According to the data, the existence of body image disturbance among extremely overweight individuals is a common phenomenon. However, evidence is also presented that suggests that normal weight individuals (especially women) may also have difficulty in accurately assessing their body size. The final focus of this paper is the relationship between body image and weight change behavior. As indicated in the discussion, this area of research has received the least amount of attention in the literature, and the present findings are contradictory. The paper concludes with recommendations for future research directions.

Body Image↗
PubMed1989

Mirror feedback and judgments of body size.

Body size perception was measured in 44 obese and normal weight subjects using a video TV methodology. Subjects performed a task whereby they manipulated the size of their body image on a TV screen. Subjects viewed their images in the presence and absence of a full length mirror. Subjects were more accurate judging body size with the mirror present. Subjects also responded more slowly and made more adjustments of their body image when the mirror was present. No differences between obese and normal weight subjects were found. Ramifications of the findings for individuals who diet are discussed.

Body Constitution↗
PubMed1996

Performance of 3-D digitizing in stereoscopic images.

Experiments were conducted to understand the basic characteristics of pointing to three-dimensional images generated by stereoscopic images. The experimental examination found that it was difficult to point to the correct position of the image and that the depth of the image was underestimated so that the object perceived by the subject was distorted. Subjects who were familiar with viewing 3-D images made less error in position and size perception than did subjects having little experience in viewing 3-D images. These results imply that the performance of 3-D pointing in stereoscopic 3-D images will improve with experience although it is difficult to perform a 3-D pointing precisely.

Adult↗