Rick M. Gardner

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.

Obesity and body image: an evaluation of sensory and non-sensory components.

Body image in 38 obese and normal weight subjects was measured using a video TV monitor. Tasks included a continuous task where subjects manipulated the size of their body image on a TV screen, and a discrete task, where they judged the accuracy of their TV image which was presented as either too heavy or too thin. Subjects viewed their images in both regular street clothes and with minimal clothing. Results from the continuous task revealed that obese subjects overestimated body size. All subjects were more accurate on trials in which the initial image was adjusted in the heavier direction. On the discrete task, a signal detection analysis revealed sensory sensitivity differences between obese and normal weight subjects. Obese subjects were better at detecting distortion caused by a too thin image, but were inferior in detecting a too heavy distortion. No significant differences were obtained in response criteria or between clothing conditions.

A computer program to generate parametric and nonparametric signal-detection parameters

A computer program is described that calculates parametric and nonparametric signal-detection parameters for sensory sensitivity and response bias. Advantages of this program over previously published programs are discussed.

THE PRISONER'S DILEMMA GAME AND COOPERATION IN THE RAT

Cooperation in pairs of rats playing the prisoners dilemma game was investigated. Six pairs of animals were taught to make either cooperative or uncooperative responses by running to one or the other end of a T-maze. Two T-mazes were joined together such that animals could respond simultaneously. Animals were run under conditions in which visual communication was present and absent. Mutually uncooperative responses were the most common and mutually cooperative behaviors the least preferred. Introduction of a barrier between the mazes, which removed visual communication between pairs, sharply accentuated uncooperative behavior. Similarities of the present findings to results with human subjects and the implications of using game theory for studying cooperative behavior in animals are discussed.

PUPILLARY CHANGES DURING ENCODING, STORAGE, AND RETRIEVAL OF INFORMATION

6 subjects were each auditorily presented six lists of 7-digit numbers for retention intervals of 0, 5, and 10 sec. Pupil size was recorded during stimulus presentation, retention interval, and recall of items. Results indicated that pupil dilation occurred during encoding and retrieval of stimulus items. Pupillary constriction was found during the retention interval when rehearsal was presumed to occur.

Distortion of body image in the obese: a sensory phenomenon.

Body weight in 42 obese and normal weight subjects was measured using a video TV monitor. Tasks included a continuous task where subjects manipulated the width of their body image on TV, and a discrete task, where they judged the accuracy of their TV image which was presented as either normal, too heavy, or too thin. Subjects rated their full body, body regions which included face, waist, and thighs, and two inanimate control objects. Results from the continuous task revealed that obese subjects overestimated body size more than normals. There was also a significant difference in the ratings of the four body regions, with all regions overestimated. Judgements were more accurate for body regions and control objects on ascending trials where the subjects had to increase the width of the image. No differences were obtained between obese and normals on judgements of the control objects. On the discrete discrimination task, a signal detection analysis revealed sensory sensitivity differences between obese and normal weight subjects. Obese subjects were poorer at detecting size distortions of the body regions. The thin/normal discrimination was more difficult than the heavy/normal discrimination. No response criterion differences were found between obese and control subjects, although subjects adopted a more strict criterion with the thin/normal discriminations. Implications of these findings for clinical intervention in eating disorders are discussed.

Subjective equality and just noticeable differences in body-size judgments by obese persons.

Body-size estimates by obese and normal-weight subjects were compared using two different procedures with a TV-video methodology. In the continuous method subjects adjusted an image larger or smaller until they judged a correct TV-image had been achieved. In the second procedure the method of constant stimuli was used wherein values corresponding to the point of subjective equality (PSE) and difference threshold (DL) were determined. No differences between obese and normal-weight subjects were obtained with these procedures. On the continuous task subjects slightly underestimated body size and were more accurate on descending trials where they adjusted the size of the image downwards. With the second procedure, an average PSE of −.62% was obtained, with an average DL = 7.27%. Different PSE values were obtained when subjects were judging whether their image was distorted too wide or too thin. Data from the two procedures are compared and ramifications for the study of body size are discussed.

Table of criterion values (β) used in signal detection theory

A table of criterion values for use with the theory of signal detection (TSD) is presented. Criterion values (β) are presented for varying proportions of hits and false alarms. A brief explanation of signal detection theory is given, and the measures for sensory sensitivity (d′) and response criterion (β) are described.

SOMATIZATION TENDENCIES AND ABILITY TO DETECT INTERNAL BODY CUES

39 subjects performed a task in which they were required to detect the presence of a resistive load during the inhalation phase of breathing. Subjects were also measured on somatization tendencies, using the SCL-90—R test. A signal-detection analysis indicated an inverse relationship between ability to detect the resistive load during breathing and somatization score. Results are discussed relative to possible ramifications for somatoform disorders.

Sensitivity to proprioceptive feedback in obese subjects

40 subjects, 20 obese and 20 normal, were run on a weight-discrimination task requiring judgments dependent on proprioceptive feedback. A signal-detection analysis was used to separate sensory factors from non-sensory, response-bias factors in the analysis of the discriminations. Obese subjects were inferior to normals in ability to make sensory discriminations; the largest differences occurred between obese and normal males. Obese subjects also adopted a more strict criterion (β); the largest differences again occurred for male subjects. Obese subjects showed more variability in their sensory judgments, although there was a significant difference on only one of the 5 discrimination tasks. Results are discussed in terms of the internal-external explanation of obesity.