Perceptual and Motor Skills, 1991, 73, 904-906.
O Perceptual and Motor Skills 199 1
VISUAL DETECTION O F BODY W E I G H T C H A N G E IN YOUNG WOMEN ' THOMAS R. ALLEY Clemson University
Summary.-To assess whether small changes in body weight can be visually detected, college students (58 women and 42 men) were asked to select the less heavy person shown In two photographs for each of 33 young women. All of these women had been photographed twice in a standardized pose and attire, separated by an 8-wk. interval d u r ~ n gwhich most of them lost weight. These pairs were presented in varying orders to control for the order and side of presentation. O n e photograph was reliably selected as the lighter person for 64% of the pairs, but the picture selected was in fact lighter only 57% of the time. The accuracy of selecting the lighter photograph was not correlated with the percent weight change for the person shown in the pain of photographs. The results suggest that small changes in women's weight may not have a significant perceptual effect, particularly for male perceivers.
Women in our society often are very concerned with their body weight. Their concern is reflected in the popularity of dieting and other weight-loss programs and in the prevalence of eating disorders. Most often, their primary motive is to alter their physical appearance (Schlundt & Johnson, 1990; Schwartz, Thompson, & Johnson, 1981). I t appears that women often assume that even small changes in body weight will alter their physical attractiveness (cf. Connor-Greene, 1988), yet no data have been published which indicate whether small changes in body weight can be reliably detected by others. To assess whether small changes in body weight are visually detectable, 100 college students were shown pairs of photographs of young women taken at different body weights.
Materials Weight changes were captured in pairs of photographs of 33 Caucasian women, 18 to 25 years old, taken with an 8-wk. interval separating the two occasions. During this interval, most (91%) of these women participated in a weight-loss program, while the remainder were part of a control group. Three (9%) women gained weight, while the other 30 (91%) lost weight across this interval. The weight differences ranged from .5 to 17.8 Ib. or .3% to 10.2% (M = 4.7%) of their earlier weight. Both photographs of each per-
'I thank Barbara Dickson-Parnell for kindly allowing me to use her photographs, the (anonymous) people whose photographs were used, and Liz Scelzo and Kristin Frey for assistance in collecting the data. Address reprint requests to Thomas R. Alley, Department of Psychology, Clemson University, Clemson, SC 29634-1511.
DETECTION OF WEIGHT CHANGE
905
son depicted the person in a standardized pose wearing shorts and a t-shirt. These 80-mm x 117-mm black-and-white photographs were presented in a photograph album with one pair per page. Subjects and Procedure One hundred college students were recruited from introductory psychology classes. This sample included 58 women and 42 men, ranging in age from 18 to 42 (M = 19.4) years. Most of these men (93%) and women (91%) were Caucasian. To control for the effects of order and side of presentation, each of the students viewed the 33 pairs of photographs in a different random order, and the photograph showing the heavier weight in each pair was presented on the left side for exactly half of the students. All subjects were told that both photographs in each pair depicted the same individual and were asked to select the photograph showing the person at the lighter weight within each pair.
RESULTSAND DISCUSSION Student t tests indicated that one of the photographs was selected as lighter significantly (with p < .01) more often for 21 of the 33 pairs, but the targets that were actually lighter were not consistently selected. The photograph selected as lighter depicted the heavier person in 9 of these 2 1 pairs. In other words, persons reliably selected as lighter were in fact lighter only slightly more than half (57%) of the time. The ability to detect change in stimulation depends on both the amount of change and the initial or "background" level (Falmagne, 1986). Thus, the detectability of changes in body weight should vary with relative weight change. With this in mind, weight differences for each pair of photographs were converted into percent weight change (relative to weight in the earlier photograph) for further analysis. There was no significant correlation between the percent weight change for pairs of photographs and the strength of the tendency to select the correct photograph as lighter (r, = .26, p> .l3). To examine the possibility that gender may heighten sensitivity to weight changes, the data from male and female subjects were analyzed separately. Based on the mean accuracy of each viewer, the over-all accuracy with which men selected the lighter photograph was near chance (t,, = .63, p = .53), whereas women were able to detect accurately relative weight at a rate well above chance (t,,= 3.27, p .07). These results suggest that small changes in a woman's weight, such as those typically produced by a short-term weight-loss program, may not result in a reliable change in perceived weight, particularly for male perceivers. Consequently, women may often have unrealistic expectations about the
906
T. R. ALLEY
perceptual effects of weight loss. This study provides only a preliminary indication of the detectability of weight changes, however, since this study used only young women in frontal photographs as targets. Many factors influence the detectability of weight differences; for instance, weight and differences in weight should be easier to assess in unclothed people or if both lateral and frontal photographs were provided. Likewise, actual moving bodies are likely to provide more information about weight than two-dimensional, static depictions such as frontal photographs. Further research is needed to examine the effects of perceivers' characteristics and various sources of visual information on their ability to detect weight differences. REFERENCES CONNOR-GREENE, P. (1988) Gender differences in body weight perception and weight-loss strategies of college students. Women and Health, 14, 27-42. FALMAGNE, J. C. (1986) Ps chophysical measurement and theory. In K. R. Boff, L. Kaufman, & J. P. Thomas (EL.), Handbook of perception and human performance. Vol. 1. New York: Wiley. Pp. 1-66. SCHLUNDT, D. G., &JOHNSON, W. G. (1990) Eating disorders. Boston, M A : Allyn & Bacon. SCHWARTZ, D. M., THOMPSON,M. G., &JOHNSON,C. L. (1981) Anorexia nervosa and bulimia: their socio-cultural context. InternationaiJournai of Eating Dirorders, 1, 20-36.
Accepted October 28, 1991
O Perceptual and Motor Skills 199 1
VISUAL DETECTION O F BODY W E I G H T C H A N G E IN YOUNG WOMEN ' THOMAS R. ALLEY Clemson University
Summary.-To assess whether small changes in body weight can be visually detected, college students (58 women and 42 men) were asked to select the less heavy person shown In two photographs for each of 33 young women. All of these women had been photographed twice in a standardized pose and attire, separated by an 8-wk. interval d u r ~ n gwhich most of them lost weight. These pairs were presented in varying orders to control for the order and side of presentation. O n e photograph was reliably selected as the lighter person for 64% of the pairs, but the picture selected was in fact lighter only 57% of the time. The accuracy of selecting the lighter photograph was not correlated with the percent weight change for the person shown in the pain of photographs. The results suggest that small changes in women's weight may not have a significant perceptual effect, particularly for male perceivers.
Women in our society often are very concerned with their body weight. Their concern is reflected in the popularity of dieting and other weight-loss programs and in the prevalence of eating disorders. Most often, their primary motive is to alter their physical appearance (Schlundt & Johnson, 1990; Schwartz, Thompson, & Johnson, 1981). I t appears that women often assume that even small changes in body weight will alter their physical attractiveness (cf. Connor-Greene, 1988), yet no data have been published which indicate whether small changes in body weight can be reliably detected by others. To assess whether small changes in body weight are visually detectable, 100 college students were shown pairs of photographs of young women taken at different body weights.
Materials Weight changes were captured in pairs of photographs of 33 Caucasian women, 18 to 25 years old, taken with an 8-wk. interval separating the two occasions. During this interval, most (91%) of these women participated in a weight-loss program, while the remainder were part of a control group. Three (9%) women gained weight, while the other 30 (91%) lost weight across this interval. The weight differences ranged from .5 to 17.8 Ib. or .3% to 10.2% (M = 4.7%) of their earlier weight. Both photographs of each per-
'I thank Barbara Dickson-Parnell for kindly allowing me to use her photographs, the (anonymous) people whose photographs were used, and Liz Scelzo and Kristin Frey for assistance in collecting the data. Address reprint requests to Thomas R. Alley, Department of Psychology, Clemson University, Clemson, SC 29634-1511.
DETECTION OF WEIGHT CHANGE
905
son depicted the person in a standardized pose wearing shorts and a t-shirt. These 80-mm x 117-mm black-and-white photographs were presented in a photograph album with one pair per page. Subjects and Procedure One hundred college students were recruited from introductory psychology classes. This sample included 58 women and 42 men, ranging in age from 18 to 42 (M = 19.4) years. Most of these men (93%) and women (91%) were Caucasian. To control for the effects of order and side of presentation, each of the students viewed the 33 pairs of photographs in a different random order, and the photograph showing the heavier weight in each pair was presented on the left side for exactly half of the students. All subjects were told that both photographs in each pair depicted the same individual and were asked to select the photograph showing the person at the lighter weight within each pair.
RESULTSAND DISCUSSION Student t tests indicated that one of the photographs was selected as lighter significantly (with p < .01) more often for 21 of the 33 pairs, but the targets that were actually lighter were not consistently selected. The photograph selected as lighter depicted the heavier person in 9 of these 2 1 pairs. In other words, persons reliably selected as lighter were in fact lighter only slightly more than half (57%) of the time. The ability to detect change in stimulation depends on both the amount of change and the initial or "background" level (Falmagne, 1986). Thus, the detectability of changes in body weight should vary with relative weight change. With this in mind, weight differences for each pair of photographs were converted into percent weight change (relative to weight in the earlier photograph) for further analysis. There was no significant correlation between the percent weight change for pairs of photographs and the strength of the tendency to select the correct photograph as lighter (r, = .26, p> .l3). To examine the possibility that gender may heighten sensitivity to weight changes, the data from male and female subjects were analyzed separately. Based on the mean accuracy of each viewer, the over-all accuracy with which men selected the lighter photograph was near chance (t,, = .63, p = .53), whereas women were able to detect accurately relative weight at a rate well above chance (t,,= 3.27, p .07). These results suggest that small changes in a woman's weight, such as those typically produced by a short-term weight-loss program, may not result in a reliable change in perceived weight, particularly for male perceivers. Consequently, women may often have unrealistic expectations about the
906
T. R. ALLEY
perceptual effects of weight loss. This study provides only a preliminary indication of the detectability of weight changes, however, since this study used only young women in frontal photographs as targets. Many factors influence the detectability of weight differences; for instance, weight and differences in weight should be easier to assess in unclothed people or if both lateral and frontal photographs were provided. Likewise, actual moving bodies are likely to provide more information about weight than two-dimensional, static depictions such as frontal photographs. Further research is needed to examine the effects of perceivers' characteristics and various sources of visual information on their ability to detect weight differences. REFERENCES CONNOR-GREENE, P. (1988) Gender differences in body weight perception and weight-loss strategies of college students. Women and Health, 14, 27-42. FALMAGNE, J. C. (1986) Ps chophysical measurement and theory. In K. R. Boff, L. Kaufman, & J. P. Thomas (EL.), Handbook of perception and human performance. Vol. 1. New York: Wiley. Pp. 1-66. SCHLUNDT, D. G., &JOHNSON, W. G. (1990) Eating disorders. Boston, M A : Allyn & Bacon. SCHWARTZ, D. M., THOMPSON,M. G., &JOHNSON,C. L. (1981) Anorexia nervosa and bulimia: their socio-cultural context. InternationaiJournai of Eating Dirorders, 1, 20-36.
Accepted October 28, 1991
