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Children's judgments of body size and distortion
Cognitive
Development,
5, 38.5-394
(1990)
Children’s
judgments
of Body Size and Distortion Rick M. Gardner Russell Urrutia James Morrell Deborah Watson Susan Sandoval University
of Southern
Colorado
Body size estimates of 69 children aged 5-13 years were obtained using a TV video methodology. Tasks included an adjustment procedure where children manipulated the width of their body image on a TV, and a discrete task, where they judged the accuracy of their TV image which was presented as either normal or distorted, that is, too wide or too thin. On the continuous task, judgments were more accurate on ascending trials where children had to increase the width of the image. On the discrete task, a signal detection analysis revealed older children were better in detecting size distortion in their images and that the differences were due to differences in the biological sensory system and not due to a bias to report that they were too fat or too thin. However, there were response bias differences between genders. Females were more likely to report size distortion with increasing age while males were less likely.
Shontz (1969) and Fisher (1970) have reviewed the literature on the developmental changes that occur in the perception of one’s own body size. Studies have generally shown that children’s body size estimates are reasonably accurate, even as early as ages 6 and 7 (Koff & Kiekhofer, 1978; Shontz, 1969). As children grow older they become more accurate in their body size estimates, although the trend is a weak one (Gellert & Stem, 1964). Children display a tendency to underestimate body height, although no clear pattern of differences were found when estimating the sizes of body parts (Koff and Kiekhofer, 1978). Boys have been found to be slightly more accurate than girls in body size judgments (Gellert & Stem, 1964; Stiles & Smith, 1977) although the small size of the differences found requires further evaluation. This
research
was supported
by Grant
08 197-06
and the National Institute of Mental Health. Correspondence and requests for reprints Psychology, University of Southern Colorado, Manuscript
received
December
6, 1989;
funded
by the Division
should be sent to Rick Pueblo, CO 81001. manuscript
accepted
M.
January
of Research Gardner,
Resources
Department
10, 1990
of
385
386
Gardner,
Urrutia,
Morrell,
Watson
and Sandoval
In many respects, these findings parallel the findings with adult judgments of body size. This has led Koff and Kiekhofer (1978) to conclude that errors in judgment of body size are established at an early age and are apparently relatively stable and enduring cognitive predispositions. Studies of body size have used a variety of techniques, including the Draw A Person and Rod und Frame tests, distortion of photographs, adjustable mirrors, adjustable light bars, and other similar estimation methods (Fisher, 1986). Each of these techniques has disadvantages, including lack of convergent data from other laboratories (Garner & Garfinkel, 198 1). In addition, it has been difftcult to obtain a uniform deviation scale and accurate measurements with many of these methods (Garner & Garfinkel, 1981). Allebeck, Hallberg, and Espmark (1976) devised a better technique for measuring body size, using a video TV methodology. With this method, subjects adjust their image on a TV monitor and precise readings of distortion are made. Brodie, Slade, & Rose (1989) investigated the reliability of this technique as compared to the distorting mirror technique. Their findings show that the reliability of such a technologically advanced technique should benefit our studies of body-image distortion. Our laboratory research has employed a modified TV video methodology in conjunction with a signal detection methodology and analysis to evaluate separately the role of the biological sensory system, and psychological, nonsensory factors in body size judgments. A detailed description of signal detection theory is available elsewhere (Gescheider, 1976) and is beyond the scope of this article. Briefly, signal detection theory states that several factors determine whether people will be able to perceive sensory stimuli (signals) or a difference between two sensory stimuli. Factors include the sensory stimuli themselves (i.e., the biological sensory system of the person) as well as psychological factors. Factors involving the sensory stimuli include how intense the sensory stimuli are, whether they can be distinguished from background stimuli, and how sharp or acute the individual’s sensory system is. Psychological factors include motivation, expectation, and learning. For example, how motivated is the individual to try and perceive the stimulus? Does the individual know what to expect? Thus, it is a combination of physical, biological, and psychological factors which determine whether “signals” will be perceived. Signal detection theory is a psychophysical methodology that allows for a separate quantification of sensory factors from the psychological (nonsensory or response bias) factors. In studies in our laboratory a TV camera is modified so that subjects may adjust the width of their image (i.e., fatter or thinner) on a TV monitor by manipulating a hand-held control device. By employing the signal detection methodology and analysis, we have determined the separate roles that both the sensory and psychological factors play in judgments of body size under a variety of conditions. A brief review of these studies can be found in Gardner, Martinez, Espinoza and Gallegos (1988). In one of the techniques used in our previous studies, the individual sees a television picture of themselves which is the correct size on some trials, and too
Children’s
Perception
of Body
Size
387
or too thin on other trials. On each trial the subject must report whether their image is distorted in size or not. Responses can be categorized as “hits” (body size was distorted and individual reported that distortion was present), “misses” (body size was distorted but individual did not report distortion), “false alarms” (body size was not distorted but individual reported that distortion was present), and “correct rejections” (individual correctly reported that no distortion was present). Signal detection theory utilizes these values to determine separately the individual’s biological sensory sensitivity to detect body size distortion as distinct from psychological factors which influence their tendency to report their body size as distorted. Our findings (Gardner et al., 1988; Gardner & Moncrieff, 1988) indicated that the ability to detect body size distortion is not necessarily related to the ability to accurately reproduce one’s body size using the TV video methodology. Individuals who can accurately adjust the size of their image on a TV screen are not necessarily able to detect the presence of size distortion on their projected image. In this study we again employed the video TV methodology and a signal detection methodology and analysis to examine separately the sensory and psychological factors in children’s body size judgments. When a child views his or her body and reports that it is distorted in size, is it because of factors related to the biological sensory systems, or is it because of psychological factors (e.g., their beliefs or expectations about their body size) that influence their judgment? This is important because of the role that body image plays in many psychological disorders, particularly eating disorders (Bruch, 1973) where distorted body images in young adolescents are often a precursor to anorexia nervosa. Distorted body images have also been implicated in schizophrenia, obesity, mental retardation, various neuroses, brain damage, and socially deviant behaviors (see review in Fisher, 1986). Almost all of this research has been conducted on adults who had little knowledge of how the perception of body size changes during the developmental process. This is of particular importance because many disorders, including schizophrenia and eating disorders, often begin during adolescence and may have antecedent causes in childhood. Many of these disorders have been associated with distortions of body size, as mentioned earlier. A clearer understanding of the developmental changes that occur in body perception is needed. In the present study we were specifically interested in both the ability of the children to accurately reproduce their body size as well as to detect the presence or absence of body size distortion. We examined the developmental differences between the ages of 5 and 13 and made gender comparisons as well.
wide
METHOD Subjects. Subjects were 69 children aged 5 to 13 attending two day-care centers in the local community. There were 32 females and 37 males. All subject participation was voluntary with parental consent. Table 1 illustrates the age and
388
Gardner,
Urrutia,
Morrell,
Table 1. Age and Gender Classifications 69 Children in Body Size Experiment he
n
5
6 I 8 9 IO II-13 Total
Watson
and
Sandoval
of
Male
Female
8 19 10 13 9 6 4
4 8 5 4 I 6 3
4 I1 5 9 2 0 I
69
3-l
32
gender characteristics of the children. The average age of males was 7.95 years, while females averaged 6.94 years, with a range of 8 years for both groups. Procedure. Data collection occurred at the day-care centers during the summer months when school was not in progress. The child was positioned 48 in in front of a TV camera. A high resolution 16-in black and white monitor was positioned 68 in in front of the child. The TV camera was modified so that the horizontal dimensions of the TV image could be altered, causing the resulting body image to appear wider or thinner without affecting the height of the image. An Apple II+ computer controlled the distortion of the televised body image. A separate continuous and discrete task was used for body perception. In the continuous task the subject was presented an image on the TV monitor of his or her body that was initially distorted as either too wide or too thin. The amount of distortion possible with this apparatus ranged between 162% too wide to 104% too narrow. A value of + 100% reflects a distortion of twice the actual body size, while - 100% reflects a distortion of one half the actual body size. The subject held a control device mounted in a small box. By pressing one of the two buttons, the subject could vary the width of the body image, making it either wider or thinner. Pressing the buttons caused the image to shrink or expand at a constant rate, determined electronically. During the first half of the trials, the child was presented an initial body image which was too thin and was asked to adjust the image upward (larger) until the image reflected an accurate representation of the child’s body (ascending trials). During the second half of the trials, the initial image presentation was too wide and the child was asked to adjust the image downward (thinner) until the image was perceived as being an accurate one (descending trials). The child pressed another button on the hand-held control device when the perceived accurate image had been produced. The initial amount of distortion presented varied randomly from trial to trial so that the subject had to use differing amounts of adjustments to arrive at the perceived correct image size. Instructions were read to each child after which he or she was
Children’s
Perception
of Body
389
Size
asked to explain the instructions back to the experimenter, to ensure that each one understood what the procedure was. In addition, 10 practice trials were given to each child, allowing the subject to become familiar with the procedure and to further check that the child understood the instructions. Following the practice trials, subjects completed 20 data trials. The order of ascending and descending trials was randomized. Subjects were allowed as much time and as many adjustments as needed to adjust the image in either direction (wider and thinner) in order to arrive at an accurate image. An Apple II+ computer recorded the amount of distortion present in terms of percentage of overestimation or underestimation, the number of seconds required to make the judgment, and the number of adjustments (wider/thinner) made in arriving at the final image. In the discrete phase of the experiment, the “yes/no” signal detection procedure (Gescheider, 1976, pp. 73-76) was used, whereby a signal (in this case, a too wide or too thin body image) was either present or absent on the TV monitor and the child was required to report whether it was present or absent. The distortion consisted of the presentation of an image which was either 9% too wide or 9% too thin. The 9% level was based on pilot studies which indicated it to be that level of distortion that most children could correctly detect about 75% of the time, and thus was appropriate for generating relevant signal detection parameters. Subjects responded by pressing a button on the hand-held controller which signified whether the image was judged to be accurate or distorted. All children received verbal feedback from a voice synthesizer after each trial regarding the correctness of their response. Subjects were informed that a distorted image would be presented randomly on 50% of the trials. This procedure, including the use of feedback, follows standard signal detection methodology and gives the subject information necessary to freely adjust their response criterion in a fashion which will maximize hits while minimizing false alarms. For the discrete task, each child completed a total of 40 data trials, including 20 trials with too wide and too thin distortion. The sequence of over/under distortion was randomized across subjects. Ten practice trials preceded each task.
RESULTS In the continuous task, subjects were asked to adjust an image that was initially presented as either too wide or too thin compared to the perceived actual size. A three-way ANOVA compared gender, age groups, and ascending/descending trials on the children’s final judgment of their body size. This ANOVA revealed a main effect only for ascending/descending trials, F( 1, 59) = 136.96, p < .OOl, as illustrated in Figure 1. Subjects were much more accurate during the ascending trials, where they increased the width of their body, underestimating body size by an average of 8.60% on final estimation. During descending trials subjects overestimated body size by an average of 32.67%. Averaging across ascending/descending trials, Figure 1 shows that children at differing ages con-
Gardner,
50 45 40
Watson
and Sandoval
A-
i
-J 5
6
7
Age Groups Figure 1. descending
Morrell,
o-o hcending Trials l -m Descending Trialr t. A Avemgs
35 30 25 20 15 10 5
-25
Urrutia,
Average percent over/underestimation trials on continuous task.
a
9-13
(yrs.) of body size on ascending
and
sistently overestimated body size by a relatively constant magnitude. These findings are consistent with previous studies using adult subjects. There were no main effects for gender or age, nor were any interaction terms indicated. In addition, no differences were found in time to make judgments, or in the number of adjustments made (wider/thinner) to reach the final image. For the discrete part of the experiment subjects were asked if the image presented on the TV monitor was their actual body size or one that was a distorted image (either too large or too small). Use of the signal detection analysis involves the separate determination of values reflecting the sensitivity of the biological sensory system of the person as well as a measure of psychological factors reflecting the response bias of the person. Response bias within the context of this experiment would be reflected in any tendencies for a child to report that his or her body either was or was not distorted in size. Sensitivity of the biological sensory system is reflected in the signal detection value d’ wherein the larger the d’ value, the more sensitive the child’s sensory systems were in detecting distortion of body size. A three-way ANOVA ford’ values comparing gender, age, and direction of distortion revealed a main effect for age, F(4,59) = 3.82, p < .008. Figure 2 reveals that as the subjects’ age increased, the d’ values increased, indicating that the subjects’ ability to distinguish between the distorted image and the actual image improved as the subjects’ age increased. No other main effects or interaction terms were significant. A similar analysis was conducted for the signal detection measure, reflecting the psychological factors affecting the children’s response bias to report that
Children’s Perception of Body Size
391
l.OOO0.900 -0.800 -0.700-0.600-&
0.400-0.300--
71 P : Q
0.500 0.200-- -O.lOO-0.000 -O.lOO--0.200--0.300--0.400--0.500 -I
.
/.P
.
.
5
6
7
Age Groups Figure 2. distortion.
8
I 9-13
I
(yrs.)
Sensory sensitivity (d’) values of children at differing ages to body size A d’ = 0 reflects an inability to detect body size distortion.
distortion was present or absent. A particular child may have a bias (i.e., a tendency) to report that his or her body is not distorted in size, while another child may have a tendency to report that his or her body is nearly always distorted in size. In signal detection theory, this response bias is reflected by the value Ln /?. If a child has a bias to report size distortion being present, then he or she will have an Ln I3 value less than zero. Conversely, if a child has a bias to report no size distortion, then he or she will have an Ln I3 value greater than zero. Moreover, if a child has no bias to report size distortion either present or absent, then he or she will have an Ln I3 value of zero. Ln I3 values were calculated using a recently developed computer program (Boice & Gardner, 1988). A three-way ANOVA for Ln I3 scores revealed a main effect for gender, F( 1, 59) = 6.54, p = .012. Males had Ln I3 values slightly greater than zero (M = + .03) whereas females had values less than zero (M = - .08). This indicates that females had a greater tendency to report that a given image of their body was distorted too large or too small as compared to male reports. In other words, females have a stronger “response bias” to report size distortion being present in their televised body image. In addition, there was an interaction between age group and gender, F(4, 59) = 2.80, p = .033, as illustrated in Figure 3. With increasing age, females developed a progressively increased tendency to report size distortion being present whereas the opposite trend is noted for males. As males become older, there is an increasing tendency to report no distortion present in their body size. Finally, a significant difference in Ln I3 values was obtained between discrimi-
392
Gardner,
0.200 0.150
o--o 0-m
Urrutia,
Morrell,
Watson
and Sandoval
Males Females
T
5
6
7
Age Groups
6
9-13
(yrs.)
Figure 3. Response bias (Ln /3) for male and female children ages 5-13 on body size distortion task. A Ln j3 > 0 reflects a response bias to report size distortion is absent while a Ln /3 < 0 reflect a bias to report size distortion is present.
nation trials on which the image was either normal or too wide versus normal or too thin, F( 1,59) = 7.71, p = .007. Children had a bias to report size distortion as absent on the wide/normal discriminations (M = + .04) and a bias to report size distortion as present on the thin/normal discriminations (M = - .07). Thus, children have a greater tendency to report size distortion as being present when seeing themselves as either normal size or too thin as compared to normal size or too wide. DISCUSSION The present data suggest that estimating body size by adjusting the width of a projected TV image and detecting the presence or absence of distortion in one’s projected image are two very different perceptual and perhaps cognitive tasks for children. Significant changes with age occur on the size distortion task, but not on the continuous adjustment task. Like previous researchers, we found no difference across ages in the ability to accurately estimate body size. Just as Koff and Kiekhofer (1978) found that children overestimate the size of individual body parts, we similarly found that they overestimate when reproducing overall body width. After averaging across ascending and descending trials, the magnitude of overestimation is relatively constant across ages, except for an unexplained (and statistically insignificant) drop at age 8. A very large effect occurs between trials where the children increase or decrease the size of their televised image. We have consistently obtained similar differences with adults in several
Children’s
Perception
of Body
Size
393
previous studies. Shontz (1969) has also noted that the starting position of the size judgment continuum greatly effects body size estimates. Shontz believed this reflected a relatively large range of uncertainty about the size aspects of one’s body. The present data would suggest that this uncertainty is a longstanding one, extending back to at least 5 years of age. Furthermore, the uncertainty would appear to remain relatively constant through the developmental process into adulthood. Some previous researchers, including Koff and Kiekhofer’s (1978) study with children, have only used ascending trials in body size judgments. The present data clearly indicate the need for counterbalancing ascending and descending trials in judgments of body size. The data from the discrete task is of particular interest because the signal detection analysis allows for a separate evaluation of the role of sensory and psychological response factors in detecting the presence of size distortion in one’s body image. Unlike the continuous task in which children adjusted the size of their image, we now find significant differences across ages, with older children being significantly better at detecting the presence of size distortion in their projected body image. At age 5, children are unable to detect size distortion, as indicated by the negative d’ value illustrated in Figure 2. Between ages 6 and 13 a significant increase in discriminability is noted. The signal detection analysis allows one to conclude that these differences are due to the biological sensory sensitivity systems, and are not due just to psychological factors. There is some question within the literature regarding whether children younger than 7 can conceptually understand the process of continuous scales. If this is the case, it may account for some of the findings obtained with the younger subjects. The separate analysis of the psychological bias (Ln p) factor is particularly revealing. While no overall significant main effect between age groups was found, a powerful interaction effect between age and gender was revealed. As male children become older, they adopt a decreasing tendency to report the presence of size distortion in their body. The exact opposite trend is found with females, who, as they become older, adopt an increasing tendency to report the presence of size distortion. This finding may be relevant to the topic of anorexia nervosa, a condition found most often in young females, although it is being observed with increasing frequency in males. The present data suggest that part of the developmental process for young females is an increasing response bias to report that their body size is somehow distorted. A previous study in our laboratory (Gardner & Moncrieff, 1988) with female anorexics indicated that they too have a bias to report size distortion as present. These findings are suggestive and indicate a need for additional exploration in this area. A variety of techniques have been developed to adjust the response bias of an observer, including giving appropriate feedback immediately following judgments. Such techniques could aid in adjusting appropriately the response bias of individuals who have an eating disorder or who are otherwise at risk for such a condition.
394
Gardner,
Urrutia,
Morrell,
Watson
and Sandoval
The present study indicates further the viability of the TV video methodology for studying body size perception in children. There is an ongoing need for the development of empirically based assessment techniques in psychology of which this technique is one example. The value of a signal detection methodology and analysis in examining separately the role of biological sensory systems and psychological factors in detecting body size distortion is also indicated. REFERENCES Allebeck.
P.. Hallberg. D.. & Espmark, S. (1976). Body image: An apparatus for disturbances in estimation of size and shape. Jownal of Psvrhosomaric Research,
measuring 20. 583-
589.
Boice,
R., & Gardner, R.M. (1988). A computer program to generate parametric and nonparametric signal-detection parameters. Bulletin of the Psyhonomic Sociey. 26. 365-367. Brodie, D.A., Slade, P.D., & Rose, H. (1989). Reliabiliy measures in distorting body-image. SubmQted for publication. Bruch. H. (1973). Earing disorders. New York: Basic Books. Fisher, S. (1970). Body experience in fanrosy and behavior. New York: Appleton-Century-Crofts. Fisher, S. (1986). Developmenf and srructure of the body image. Hillsdale, NJ: Erlbaum. Gardner, R.M., Martinez, R.. Espinoza, T., & Gallegos, V. (1988). Distortion of body image in the obese: A sensory phenomena. Psychological Medicine, 18. 633-64 I. Gardner, R.M.. & Moncrieff, C. (1988). Body image distortion in anorexics as a non-sensory phenomena: A signal detection approach. Journal of Clinical Psychology. 44, 101-107. Garner, D.M., & Garfinkel, P.E. (1981). Body image in anorexia nervosa: Measurement, theory, and clinical implications. Infernarional Journal of Psychiarry in Medicine, I I, 263-284. Gellert, E.. & Stem, J.B. (1964, August). Age and sex dtrerences in children’s judgmenfs of rheir heighr and bodyproporfions. Paper presented at Annual Meeting of the American Psychological Association, Los Angeles. Gescheider. G.A. (1976). Psychophysics: Method and theory. Hillsdale. NJ: Erlbaum. Koff. E., & Kiekhofer, M. (1978). Body-part size estimation in children. Perceptual and Motor Ski//s, 47, 1047-1050. Shontz. F.C. (1969). Perceptual and cognitive aspects of body experience. New York: Academic. Stiles, D.B.. & Smith, H.M. (1977). A film technique for assessing children’s self-estimation of body size under static and dynamic conditions. Perceprual andMoror Skills. 45, 1275-1282.
Development,
5, 38.5-394
(1990)
Children’s
judgments
of Body Size and Distortion Rick M. Gardner Russell Urrutia James Morrell Deborah Watson Susan Sandoval University
of Southern
Colorado
Body size estimates of 69 children aged 5-13 years were obtained using a TV video methodology. Tasks included an adjustment procedure where children manipulated the width of their body image on a TV, and a discrete task, where they judged the accuracy of their TV image which was presented as either normal or distorted, that is, too wide or too thin. On the continuous task, judgments were more accurate on ascending trials where children had to increase the width of the image. On the discrete task, a signal detection analysis revealed older children were better in detecting size distortion in their images and that the differences were due to differences in the biological sensory system and not due to a bias to report that they were too fat or too thin. However, there were response bias differences between genders. Females were more likely to report size distortion with increasing age while males were less likely.
Shontz (1969) and Fisher (1970) have reviewed the literature on the developmental changes that occur in the perception of one’s own body size. Studies have generally shown that children’s body size estimates are reasonably accurate, even as early as ages 6 and 7 (Koff & Kiekhofer, 1978; Shontz, 1969). As children grow older they become more accurate in their body size estimates, although the trend is a weak one (Gellert & Stem, 1964). Children display a tendency to underestimate body height, although no clear pattern of differences were found when estimating the sizes of body parts (Koff and Kiekhofer, 1978). Boys have been found to be slightly more accurate than girls in body size judgments (Gellert & Stem, 1964; Stiles & Smith, 1977) although the small size of the differences found requires further evaluation. This
research
was supported
by Grant
08 197-06
and the National Institute of Mental Health. Correspondence and requests for reprints Psychology, University of Southern Colorado, Manuscript
received
December
6, 1989;
funded
by the Division
should be sent to Rick Pueblo, CO 81001. manuscript
accepted
M.
January
of Research Gardner,
Resources
Department
10, 1990
of
385
386
Gardner,
Urrutia,
Morrell,
Watson
and Sandoval
In many respects, these findings parallel the findings with adult judgments of body size. This has led Koff and Kiekhofer (1978) to conclude that errors in judgment of body size are established at an early age and are apparently relatively stable and enduring cognitive predispositions. Studies of body size have used a variety of techniques, including the Draw A Person and Rod und Frame tests, distortion of photographs, adjustable mirrors, adjustable light bars, and other similar estimation methods (Fisher, 1986). Each of these techniques has disadvantages, including lack of convergent data from other laboratories (Garner & Garfinkel, 198 1). In addition, it has been difftcult to obtain a uniform deviation scale and accurate measurements with many of these methods (Garner & Garfinkel, 1981). Allebeck, Hallberg, and Espmark (1976) devised a better technique for measuring body size, using a video TV methodology. With this method, subjects adjust their image on a TV monitor and precise readings of distortion are made. Brodie, Slade, & Rose (1989) investigated the reliability of this technique as compared to the distorting mirror technique. Their findings show that the reliability of such a technologically advanced technique should benefit our studies of body-image distortion. Our laboratory research has employed a modified TV video methodology in conjunction with a signal detection methodology and analysis to evaluate separately the role of the biological sensory system, and psychological, nonsensory factors in body size judgments. A detailed description of signal detection theory is available elsewhere (Gescheider, 1976) and is beyond the scope of this article. Briefly, signal detection theory states that several factors determine whether people will be able to perceive sensory stimuli (signals) or a difference between two sensory stimuli. Factors include the sensory stimuli themselves (i.e., the biological sensory system of the person) as well as psychological factors. Factors involving the sensory stimuli include how intense the sensory stimuli are, whether they can be distinguished from background stimuli, and how sharp or acute the individual’s sensory system is. Psychological factors include motivation, expectation, and learning. For example, how motivated is the individual to try and perceive the stimulus? Does the individual know what to expect? Thus, it is a combination of physical, biological, and psychological factors which determine whether “signals” will be perceived. Signal detection theory is a psychophysical methodology that allows for a separate quantification of sensory factors from the psychological (nonsensory or response bias) factors. In studies in our laboratory a TV camera is modified so that subjects may adjust the width of their image (i.e., fatter or thinner) on a TV monitor by manipulating a hand-held control device. By employing the signal detection methodology and analysis, we have determined the separate roles that both the sensory and psychological factors play in judgments of body size under a variety of conditions. A brief review of these studies can be found in Gardner, Martinez, Espinoza and Gallegos (1988). In one of the techniques used in our previous studies, the individual sees a television picture of themselves which is the correct size on some trials, and too
Children’s
Perception
of Body
Size
387
or too thin on other trials. On each trial the subject must report whether their image is distorted in size or not. Responses can be categorized as “hits” (body size was distorted and individual reported that distortion was present), “misses” (body size was distorted but individual did not report distortion), “false alarms” (body size was not distorted but individual reported that distortion was present), and “correct rejections” (individual correctly reported that no distortion was present). Signal detection theory utilizes these values to determine separately the individual’s biological sensory sensitivity to detect body size distortion as distinct from psychological factors which influence their tendency to report their body size as distorted. Our findings (Gardner et al., 1988; Gardner & Moncrieff, 1988) indicated that the ability to detect body size distortion is not necessarily related to the ability to accurately reproduce one’s body size using the TV video methodology. Individuals who can accurately adjust the size of their image on a TV screen are not necessarily able to detect the presence of size distortion on their projected image. In this study we again employed the video TV methodology and a signal detection methodology and analysis to examine separately the sensory and psychological factors in children’s body size judgments. When a child views his or her body and reports that it is distorted in size, is it because of factors related to the biological sensory systems, or is it because of psychological factors (e.g., their beliefs or expectations about their body size) that influence their judgment? This is important because of the role that body image plays in many psychological disorders, particularly eating disorders (Bruch, 1973) where distorted body images in young adolescents are often a precursor to anorexia nervosa. Distorted body images have also been implicated in schizophrenia, obesity, mental retardation, various neuroses, brain damage, and socially deviant behaviors (see review in Fisher, 1986). Almost all of this research has been conducted on adults who had little knowledge of how the perception of body size changes during the developmental process. This is of particular importance because many disorders, including schizophrenia and eating disorders, often begin during adolescence and may have antecedent causes in childhood. Many of these disorders have been associated with distortions of body size, as mentioned earlier. A clearer understanding of the developmental changes that occur in body perception is needed. In the present study we were specifically interested in both the ability of the children to accurately reproduce their body size as well as to detect the presence or absence of body size distortion. We examined the developmental differences between the ages of 5 and 13 and made gender comparisons as well.
wide
METHOD Subjects. Subjects were 69 children aged 5 to 13 attending two day-care centers in the local community. There were 32 females and 37 males. All subject participation was voluntary with parental consent. Table 1 illustrates the age and
388
Gardner,
Urrutia,
Morrell,
Table 1. Age and Gender Classifications 69 Children in Body Size Experiment he
n
5
6 I 8 9 IO II-13 Total
Watson
and
Sandoval
of
Male
Female
8 19 10 13 9 6 4
4 8 5 4 I 6 3
4 I1 5 9 2 0 I
69
3-l
32
gender characteristics of the children. The average age of males was 7.95 years, while females averaged 6.94 years, with a range of 8 years for both groups. Procedure. Data collection occurred at the day-care centers during the summer months when school was not in progress. The child was positioned 48 in in front of a TV camera. A high resolution 16-in black and white monitor was positioned 68 in in front of the child. The TV camera was modified so that the horizontal dimensions of the TV image could be altered, causing the resulting body image to appear wider or thinner without affecting the height of the image. An Apple II+ computer controlled the distortion of the televised body image. A separate continuous and discrete task was used for body perception. In the continuous task the subject was presented an image on the TV monitor of his or her body that was initially distorted as either too wide or too thin. The amount of distortion possible with this apparatus ranged between 162% too wide to 104% too narrow. A value of + 100% reflects a distortion of twice the actual body size, while - 100% reflects a distortion of one half the actual body size. The subject held a control device mounted in a small box. By pressing one of the two buttons, the subject could vary the width of the body image, making it either wider or thinner. Pressing the buttons caused the image to shrink or expand at a constant rate, determined electronically. During the first half of the trials, the child was presented an initial body image which was too thin and was asked to adjust the image upward (larger) until the image reflected an accurate representation of the child’s body (ascending trials). During the second half of the trials, the initial image presentation was too wide and the child was asked to adjust the image downward (thinner) until the image was perceived as being an accurate one (descending trials). The child pressed another button on the hand-held control device when the perceived accurate image had been produced. The initial amount of distortion presented varied randomly from trial to trial so that the subject had to use differing amounts of adjustments to arrive at the perceived correct image size. Instructions were read to each child after which he or she was
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Size
asked to explain the instructions back to the experimenter, to ensure that each one understood what the procedure was. In addition, 10 practice trials were given to each child, allowing the subject to become familiar with the procedure and to further check that the child understood the instructions. Following the practice trials, subjects completed 20 data trials. The order of ascending and descending trials was randomized. Subjects were allowed as much time and as many adjustments as needed to adjust the image in either direction (wider and thinner) in order to arrive at an accurate image. An Apple II+ computer recorded the amount of distortion present in terms of percentage of overestimation or underestimation, the number of seconds required to make the judgment, and the number of adjustments (wider/thinner) made in arriving at the final image. In the discrete phase of the experiment, the “yes/no” signal detection procedure (Gescheider, 1976, pp. 73-76) was used, whereby a signal (in this case, a too wide or too thin body image) was either present or absent on the TV monitor and the child was required to report whether it was present or absent. The distortion consisted of the presentation of an image which was either 9% too wide or 9% too thin. The 9% level was based on pilot studies which indicated it to be that level of distortion that most children could correctly detect about 75% of the time, and thus was appropriate for generating relevant signal detection parameters. Subjects responded by pressing a button on the hand-held controller which signified whether the image was judged to be accurate or distorted. All children received verbal feedback from a voice synthesizer after each trial regarding the correctness of their response. Subjects were informed that a distorted image would be presented randomly on 50% of the trials. This procedure, including the use of feedback, follows standard signal detection methodology and gives the subject information necessary to freely adjust their response criterion in a fashion which will maximize hits while minimizing false alarms. For the discrete task, each child completed a total of 40 data trials, including 20 trials with too wide and too thin distortion. The sequence of over/under distortion was randomized across subjects. Ten practice trials preceded each task.
RESULTS In the continuous task, subjects were asked to adjust an image that was initially presented as either too wide or too thin compared to the perceived actual size. A three-way ANOVA compared gender, age groups, and ascending/descending trials on the children’s final judgment of their body size. This ANOVA revealed a main effect only for ascending/descending trials, F( 1, 59) = 136.96, p < .OOl, as illustrated in Figure 1. Subjects were much more accurate during the ascending trials, where they increased the width of their body, underestimating body size by an average of 8.60% on final estimation. During descending trials subjects overestimated body size by an average of 32.67%. Averaging across ascending/descending trials, Figure 1 shows that children at differing ages con-
Gardner,
50 45 40
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and Sandoval
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i
-J 5
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Age Groups Figure 1. descending
Morrell,
o-o hcending Trials l -m Descending Trialr t. A Avemgs
35 30 25 20 15 10 5
-25
Urrutia,
Average percent over/underestimation trials on continuous task.
a
9-13
(yrs.) of body size on ascending
and
sistently overestimated body size by a relatively constant magnitude. These findings are consistent with previous studies using adult subjects. There were no main effects for gender or age, nor were any interaction terms indicated. In addition, no differences were found in time to make judgments, or in the number of adjustments made (wider/thinner) to reach the final image. For the discrete part of the experiment subjects were asked if the image presented on the TV monitor was their actual body size or one that was a distorted image (either too large or too small). Use of the signal detection analysis involves the separate determination of values reflecting the sensitivity of the biological sensory system of the person as well as a measure of psychological factors reflecting the response bias of the person. Response bias within the context of this experiment would be reflected in any tendencies for a child to report that his or her body either was or was not distorted in size. Sensitivity of the biological sensory system is reflected in the signal detection value d’ wherein the larger the d’ value, the more sensitive the child’s sensory systems were in detecting distortion of body size. A three-way ANOVA ford’ values comparing gender, age, and direction of distortion revealed a main effect for age, F(4,59) = 3.82, p < .008. Figure 2 reveals that as the subjects’ age increased, the d’ values increased, indicating that the subjects’ ability to distinguish between the distorted image and the actual image improved as the subjects’ age increased. No other main effects or interaction terms were significant. A similar analysis was conducted for the signal detection measure, reflecting the psychological factors affecting the children’s response bias to report that
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.
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.
.
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Age Groups Figure 2. distortion.
8
I 9-13
I
(yrs.)
Sensory sensitivity (d’) values of children at differing ages to body size A d’ = 0 reflects an inability to detect body size distortion.
distortion was present or absent. A particular child may have a bias (i.e., a tendency) to report that his or her body is not distorted in size, while another child may have a tendency to report that his or her body is nearly always distorted in size. In signal detection theory, this response bias is reflected by the value Ln /?. If a child has a bias to report size distortion being present, then he or she will have an Ln I3 value less than zero. Conversely, if a child has a bias to report no size distortion, then he or she will have an Ln I3 value greater than zero. Moreover, if a child has no bias to report size distortion either present or absent, then he or she will have an Ln I3 value of zero. Ln I3 values were calculated using a recently developed computer program (Boice & Gardner, 1988). A three-way ANOVA for Ln I3 scores revealed a main effect for gender, F( 1, 59) = 6.54, p = .012. Males had Ln I3 values slightly greater than zero (M = + .03) whereas females had values less than zero (M = - .08). This indicates that females had a greater tendency to report that a given image of their body was distorted too large or too small as compared to male reports. In other words, females have a stronger “response bias” to report size distortion being present in their televised body image. In addition, there was an interaction between age group and gender, F(4, 59) = 2.80, p = .033, as illustrated in Figure 3. With increasing age, females developed a progressively increased tendency to report size distortion being present whereas the opposite trend is noted for males. As males become older, there is an increasing tendency to report no distortion present in their body size. Finally, a significant difference in Ln I3 values was obtained between discrimi-
392
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0.200 0.150
o--o 0-m
Urrutia,
Morrell,
Watson
and Sandoval
Males Females
T
5
6
7
Age Groups
6
9-13
(yrs.)
Figure 3. Response bias (Ln /3) for male and female children ages 5-13 on body size distortion task. A Ln j3 > 0 reflects a response bias to report size distortion is absent while a Ln /3 < 0 reflect a bias to report size distortion is present.
nation trials on which the image was either normal or too wide versus normal or too thin, F( 1,59) = 7.71, p = .007. Children had a bias to report size distortion as absent on the wide/normal discriminations (M = + .04) and a bias to report size distortion as present on the thin/normal discriminations (M = - .07). Thus, children have a greater tendency to report size distortion as being present when seeing themselves as either normal size or too thin as compared to normal size or too wide. DISCUSSION The present data suggest that estimating body size by adjusting the width of a projected TV image and detecting the presence or absence of distortion in one’s projected image are two very different perceptual and perhaps cognitive tasks for children. Significant changes with age occur on the size distortion task, but not on the continuous adjustment task. Like previous researchers, we found no difference across ages in the ability to accurately estimate body size. Just as Koff and Kiekhofer (1978) found that children overestimate the size of individual body parts, we similarly found that they overestimate when reproducing overall body width. After averaging across ascending and descending trials, the magnitude of overestimation is relatively constant across ages, except for an unexplained (and statistically insignificant) drop at age 8. A very large effect occurs between trials where the children increase or decrease the size of their televised image. We have consistently obtained similar differences with adults in several
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previous studies. Shontz (1969) has also noted that the starting position of the size judgment continuum greatly effects body size estimates. Shontz believed this reflected a relatively large range of uncertainty about the size aspects of one’s body. The present data would suggest that this uncertainty is a longstanding one, extending back to at least 5 years of age. Furthermore, the uncertainty would appear to remain relatively constant through the developmental process into adulthood. Some previous researchers, including Koff and Kiekhofer’s (1978) study with children, have only used ascending trials in body size judgments. The present data clearly indicate the need for counterbalancing ascending and descending trials in judgments of body size. The data from the discrete task is of particular interest because the signal detection analysis allows for a separate evaluation of the role of sensory and psychological response factors in detecting the presence of size distortion in one’s body image. Unlike the continuous task in which children adjusted the size of their image, we now find significant differences across ages, with older children being significantly better at detecting the presence of size distortion in their projected body image. At age 5, children are unable to detect size distortion, as indicated by the negative d’ value illustrated in Figure 2. Between ages 6 and 13 a significant increase in discriminability is noted. The signal detection analysis allows one to conclude that these differences are due to the biological sensory sensitivity systems, and are not due just to psychological factors. There is some question within the literature regarding whether children younger than 7 can conceptually understand the process of continuous scales. If this is the case, it may account for some of the findings obtained with the younger subjects. The separate analysis of the psychological bias (Ln p) factor is particularly revealing. While no overall significant main effect between age groups was found, a powerful interaction effect between age and gender was revealed. As male children become older, they adopt a decreasing tendency to report the presence of size distortion in their body. The exact opposite trend is found with females, who, as they become older, adopt an increasing tendency to report the presence of size distortion. This finding may be relevant to the topic of anorexia nervosa, a condition found most often in young females, although it is being observed with increasing frequency in males. The present data suggest that part of the developmental process for young females is an increasing response bias to report that their body size is somehow distorted. A previous study in our laboratory (Gardner & Moncrieff, 1988) with female anorexics indicated that they too have a bias to report size distortion as present. These findings are suggestive and indicate a need for additional exploration in this area. A variety of techniques have been developed to adjust the response bias of an observer, including giving appropriate feedback immediately following judgments. Such techniques could aid in adjusting appropriately the response bias of individuals who have an eating disorder or who are otherwise at risk for such a condition.
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The present study indicates further the viability of the TV video methodology for studying body size perception in children. There is an ongoing need for the development of empirically based assessment techniques in psychology of which this technique is one example. The value of a signal detection methodology and analysis in examining separately the role of biological sensory systems and psychological factors in detecting body size distortion is also indicated. REFERENCES Allebeck.
P.. Hallberg. D.. & Espmark, S. (1976). Body image: An apparatus for disturbances in estimation of size and shape. Jownal of Psvrhosomaric Research,
measuring 20. 583-
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Boice,
R., & Gardner, R.M. (1988). A computer program to generate parametric and nonparametric signal-detection parameters. Bulletin of the Psyhonomic Sociey. 26. 365-367. Brodie, D.A., Slade, P.D., & Rose, H. (1989). Reliabiliy measures in distorting body-image. SubmQted for publication. Bruch. H. (1973). Earing disorders. New York: Basic Books. Fisher, S. (1970). Body experience in fanrosy and behavior. New York: Appleton-Century-Crofts. Fisher, S. (1986). Developmenf and srructure of the body image. Hillsdale, NJ: Erlbaum. Gardner, R.M., Martinez, R.. Espinoza, T., & Gallegos, V. (1988). Distortion of body image in the obese: A sensory phenomena. Psychological Medicine, 18. 633-64 I. Gardner, R.M.. & Moncrieff, C. (1988). Body image distortion in anorexics as a non-sensory phenomena: A signal detection approach. Journal of Clinical Psychology. 44, 101-107. Garner, D.M., & Garfinkel, P.E. (1981). Body image in anorexia nervosa: Measurement, theory, and clinical implications. Infernarional Journal of Psychiarry in Medicine, I I, 263-284. Gellert, E.. & Stem, J.B. (1964, August). Age and sex dtrerences in children’s judgmenfs of rheir heighr and bodyproporfions. Paper presented at Annual Meeting of the American Psychological Association, Los Angeles. Gescheider. G.A. (1976). Psychophysics: Method and theory. Hillsdale. NJ: Erlbaum. Koff. E., & Kiekhofer, M. (1978). Body-part size estimation in children. Perceptual and Motor Ski//s, 47, 1047-1050. Shontz. F.C. (1969). Perceptual and cognitive aspects of body experience. New York: Academic. Stiles, D.B.. & Smith, H.M. (1977). A film technique for assessing children’s self-estimation of body size under static and dynamic conditions. Perceprual andMoror Skills. 45, 1275-1282.