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. Author manuscript; available in PMC: 2020 Nov 16.
Published in final edited form as: Infancy. 2010 Jan 19;15(5):534–544. doi: 10.1111/j.1532-7078.2009.00026.x

Body Representation in the First Year of Life

Nicole Zieber 1, Ramesh S Bhatt 1, Angela Hayden 1, Ashley Kangas 1, Rebecca Collins 1, Henrietta Bada 1
PMCID: PMC7668307  NIHMSID: NIHMS1644643  PMID: 32693509

Abstract

Like faces, bodies are significant sources of social information. However, research suggests that infants do not develop body representation (i.e., knowledge about typical human bodies) until the second year of life, although they are sensitive to facial information much earlier. Yet, previous research only examined whether infants are sensitive to the typical arrangement of body parts. We examined whether younger infants have body knowledge of a different kind, namely the relative size of body parts. Five- and 9-month-old infants were tested for their preference between a normal versus a proportionally distorted body. Nine-month-olds exhibited a preference for the normal body when images were presented upright but not when they were inverted. Five-month-olds failed to exhibit a preference in either condition. These results indicate that infants have knowledge about human bodies by the second half of the first year of life. Moreover, given that better performance on upright than on inverted stimuli has been tied to expertise, the fact that older infants exhibited an inversion effect with body images indicates that at least some level of expertise in body processing develops by 9 months of age.

Humans’ perception of faces is thought of as a specialized process, which profits both from a bias to attend to faces early in life as well as repeated exposure to faces (Diamond & Carey, 1986; Gauthier & Tarr, 1997; Johnson, Dziurawiec, Ellis, & Morton, 1991; Leder & Bruce, 2000; Mondloch, Le Grand, & Maurer, 2002). Adults’ perception of bodies may benefit from a similar specialized type of processing (Reed, Stone, Bozova, & Tanaka, 2003; Reed, Stone, & McGoldrick, 2006). However, while there is rapid development of face processing expertise during the first year of life (e.g., Bhatt, Bertin, Hayden, & Reed, 2005; de Haan, Pascalis, & Johnson, 2002; Morton & Johnson, 1991; Simion, Leo, Turati, Valenza, & Dalla Barba, 2007), research suggests that body processing abilities develop significantly later (Heron & Slaughter, 2008; Slaughter & Heron, 2004; Slaughter, Heron, & Sim, 2002; Slaughter, Stone, & Reed, 2004).

Slaughter and Heron (2004) sought to document the development of body representation by testing whether infants have knowledge of the canonical arrangement of human body parts. In Experiment 1, infants were habituated to a series of line drawings of typical body postures and then tested on scrambled bodies, which were created by moving body parts to novel locations (e.g., arms attached to the head). Fifteen- and 18-month-olds showed a significant recovery of interest to scrambled bodies, whereas 12-month-olds failed to detect the violations to the bodies. Using more complex categorization tasks, Slaughter and Heron and Heron and Slaughter (2008) found that it takes up to 24–30 months of age for infants to exhibit evidence of a relatively mature body representation. Slaughter and Heron concluded that, compared with face processing, body representation is slow to develop in infancy.

The type of change in bodies that Slaughter and Heron’s studies investigated involved the reorganization of body parts. However, bodies are flexible, such that it is possible for the arms to be stretched above the head, or twisted to reach behind the back, etc. Many of these postures may be similar in appearance to a scrambled body; this may, at least in part, account for infants’ failure to discriminate between the typical versus scrambled bodies. In essence, to make this discrimination, it is necessary to know the origin of parts. The Slaughter and Heron studies suggest that infants do not have this high level of knowledge during the first year of life.

However, it is possible that infants are sensitive to other aspects of bodies. Body proportions are significant sources of information that adults utilize to differentiate between human bodies (e.g., Johnson & Tassinary, 2005, 2007; Tassinary & Hansen, 1998). For instance, adults use body proportions to identify people’s gender (Johnson & Tassinary, 2005). In addition, adults’ perception of attractiveness is influenced by body proportions (Johnson & Tassinary, 2007). Given these significant roles of body proportions, it is possible that infants are sensitive to this information during the first year of life.

To examine this issue, we tested whether infants differentiate between a typical versus a proportionally distorted body. Infants saw two body images, side by side, one normally proportioned, while the other was distorted by lengthening the neck and torso and shortening the legs (Figure 1). If infants exhibit a preference between the bodies, then it would suggest that infants are sensitive to the relative proportion of body parts. We also included a control condition in which we tested infants on inverted bodies (Figure 1). It is possible that infants differentiate between the bodies in the upright condition not because of differences in proportions but because of some low-level feature, such as the amount of blackness (Figure 1). However, the same differences in amount of blackness will be present if the stimuli are inverted. Therefore, if amount of blackness or other such feature is the reason for infants’ preference, then they should exhibit a preference in the inverted condition also. If, however, infants exhibit discrimination in the upright condition but not in the inverted condition, then one can conclude that performance was on the basis of body proportions rather than due to a low-level feature.

Figure 1.

Figure 1

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Examples of the normal (a) and distorted (b) proportion bodies in the upright condition, and the normal (c) and distorted (d) proportion bodies in the inverted condition.

We included the inverted condition also because the inversion effect (superior discrimination between upright than between inverted images) is a hallmark of expert face processing (e.g., Bhatt et al., 2005; Carey & Diamond, 1994; Leder & Bruce, 2000; Maurer, LeGrand, & Mondloch, 2002; Yin, 1969). In addition, adults exhibit inversion effects when processing bodies (e.g., Reed et al., 2003, 2006). We are aware of only one previous study that has found an inversion effect with static human bodies in infancy (Quinn, Lee, Pascalis, & Slater, 2007). However, that study was not intended to directly address infants’ knowledge about human body structure. An inversion effect with the type of body images used in the current study would indicate that infants’ body knowledge, specifically knowledge about the relative proportion of body parts, is associated with canonically orientated bodies, thereby indicating a commonality between expertise in face and body processing.

Research indicates that face processing skills are highly developed by 9 months of age. For instance, by this age, infants have specialized on own-race and own-species faces (e.g., Hayden, Bhatt, Zieber, & Kangas, 2009; Pascalis, de Haan, & Nelson, 2002). Given this level of expertise on faces, it is possible that 9-month-olds have developed at least a certain level of expertise on bodies. Thus, as an initial starting point for the investigation of body knowledge during the first year of life, we studied 9-month-olds in the current study. We also tested a younger age group from the first half year of life (5-month-olds) as a comparison point to document the development of body knowledge early in life.

METHOD

Participants

The participants were 24 nine-month-olds (M age = 270.67 days, SD = 9.55; 12 girls) and 32 five-month-olds (M age = 155.69 days, SD = 3.94; 9 girls), who were recruited through birth announcements and from a local hospital. They were predominately Caucasians from middle-class families. Data from an additional infant were excluded due to sibling interference.

Stimuli

We used three pairs of photographs of young women, with each pair including an image of a woman’s body as well as the same woman’s body distorted such that the torso and the neck were disproportionately long as shown in Figure 1. Distorted bodies were created from normal bodies by elongating the torso and neck as well as by shortening the legs, yet maintaining the same body height as the normal body. Changes in proportions of the distorted body in relation to the normal body and the body sizes (22.86° × 20.48°) were approximately the same across the three pairs.

Procedure

We used a spontaneous preference procedure that is commonly employed (e.g., Hayden et al., 2009; Kelly et al., 2005). Infants were seated on their parent’s lap in a darkened chamber, approximately 45 cm in front of a 45-cm computer monitor. They were tested on two 20-sec preference trials. At the beginning of each trial, the infant’s attention was directed to the center of the screen by rapidly alternating colorful shapes. Once attention was focused on the monitor, the image pair was presented, one image on the left and the other on the right. Infants were randomly assigned to either an upright or inverted condition in which they saw one of the body pairs. The initial left–right position of the normal and distorted bodies was counterbalanced across infants in each condition. In addition, the left–right position of the images was switched across test trials in order to avoid side bias.

A video camera, located on top of the monitor, recorded the session. Offline coding was completed by a coder blinded to experiment condition and the left–right location of stimuli, with the video slowed to 25% of normal speed. Data from 20% of the infants were coded by a second coder to document reliability. The Pearson correlation between the two observers was .97.

The dependent measure was the percent preference for the normal body, calculated by dividing the total duration of looking at the normal body across the two trials by the total duration of looking at both the novel and distorted images across the two trials, and multiplying this ratio by 100.

RESULTS

Nine-month-old infants exhibited a preference for the normal bodies in the upright but not in the inverted condition, whereas 5-month-olds failed to exhibit a preference in either condition (Table 1). An age group (5 months, 9 months) × condition (upright, inverted) ANOVA revealed a significant interaction, F(1, 52) = 5.27, p < .03, ηp2=.09.

TABLE 1.

Preference for the Normal Body Across the Two Spontaneous Test Trials

Condition Normal preference (%) M (SE) N t (versus chance) p (two-tailed)
Nine-month-olds
 Upright 56.70 (2.05) 12 3.27 <.007
 Inverted 50.73 (2.10) 12 .34 >.737
Five-month-olds
 Upright 49.40 (2.22) 16 −.268 >.792
 Inverted 53.40(2.08) 16 1.63 >.124
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Preplanned tests revealed that the preference score was significantly greater in the upright condition than in the inverted condition at 9 months of age, t(22) = 2.04, p < .05, d = .83, but not at 5 months, t(30) = 1.31, p > .15. In addition, the 9-month-olds’ score in the upright condition was significantly greater than the chance level of 50%, but their score in the inverted condition was not; at 5 months of age, neither group’s score was significantly different from 50% (Table 1).

Although significantly different from the chance level of 50%, 9-month-olds’ average of 56.70% preference for the normal bodies was not strong. However, it is in line with performance by infants in spontaneous preference studies in which scores range anywhere from 55 to 65% (e.g., Hayden et al., 2009; Kelly et al., 2005). Moreover, the t-test comparing 9-month-olds’ performance in the upright versus inverted conditions indicated a robust effect with Cohen’s d = .83. Thus, although 9-month-olds’ look durations did not indicate a strong preference for normal over distorted bodies, this preference was highly reliable.

Moreover, nonparametric tests confirmed our conclusions about infants’ preferences. Nine of 12 nine-month-olds in the upright condition preferred the normal body, whereas only 5 of the 12 infants in the inverted condition exhibited this preference, χ2(1, N = 24) = 2.74, p < .05. In contrast, in the case of 5-month-olds, 7 of 16 infants in the upright condition and 11 of 16 infants in the inverted condition preferred the normal body, a difference that was not statistically significant, χ2(1, N = 32) = 2.03, p > .05. Thus, nonparametric tests were consistent with parametric tests in indicating that 9-month-olds exhibited a preference for normal over proportionally distorted bodies in the upright but not inverted condition, whereas 5-month-olds failed to exhibit a preference in either condition.

DISCUSSION

The current study indicates that 9-month-olds are sensitive to the relative proportions of human body parts, whereas 5-month-olds are not. Nine-month-olds exhibited a preference for normally proportioned over distorted bodies when they were presented upright but not when they were inverted. By contrast, 5-month-olds did not exhibit discrimination with either orientation. These results indicate that, contrary to the conclusions from several prior studies (Heron & Slaughter, 2008; Slaughter & Heron, 2004; Slaughter et al., 2002), infants have knowledge about human bodies during the first year of life, although this knowledge is apparent only during the latter half of the first year of life.

The discrimination in the upright condition by the older infants suggests that by 9 months of age, infants’ representation of the human body includes information about the relative proportions of body parts. The lack of discrimination in the inverted condition signifies the disruption of the processing of relative proportions of body parts by a noncanonical orientation, which is an indication of expert processing. These findings suggest that, by 9 months of age, infants have developed an expertise with bodies that is analogous to the specialization that occurs with face processing.

The current study indicates that body representation at 9 months is more detailed than predicted by Slaughter and Heron’s (2004) model. One reason for this might be the fact that the Slaughter studies examined infants’ knowledge about the locations of body parts, whereas the current study examined the relative proportions of body parts. As noted previously, infants may be exposed to various body postures, such as hands reaching above the head. Consequently, body part arrangements may not appear to be stable to infants. In contrast, the relative proportions of body parts are not altered with changes in posture, and thus might be a stronger component of infants’ representation.

Another difference is that, while most of the Slaughter studies used male body images, the current study used female bodies. Research suggests that infants prefer female faces to male faces and also processes female faces at a more specific level than male faces (e.g., Quinn, Yahr, Kuhn, Slater, & Pascalis, 2002; Ramsey-Rennels & Langlois, 2007). It is possible, therefore, that infants exhibited greater knowledge about human bodies with our female stimuli than did infants in the Slaughter studies with male stimuli.

The Slaughter and Heron (2004) studies examined infants’ sensitivity to the arrangement of body parts. In the Diamond and Carey (1986) (also see Carey & Diamond, 1994) model of face processing, the arrangement of features is considered to be first-order relations; thus, the Slaughter and Heron studies could be characterized as the study of first-order relations among body features. Specific spacing relations among features in faces (e.g., the distance between eyes) are considered to be second-order relations. One question that arises is whether the changes in body proportions that we examined in the current study can be characterized as second-order relations in bodies. We consider this issue next.

Infants are sensitive to second-order relations in faces (e.g., Bhatt et al., 2005; Hayden, Bhatt, Reed, Corbly, & Joseph, 2007; Thompson, Madrid, Westbrook, & Johnston, 2001). In addition, 9-month-olds’ preference for the normal over proportionally distorted bodies in the current study is analogous to the finding of Thompson et al. (2001) that infants prefer normal faces to second-order distorted faces. Moreover, the inversion effect that 9-month-olds exhibited in the current study with bodies parallels the inversion effect that adults and infants exhibit when processing second-order information in faces (e.g., Bhatt et al., 2005; Carey & Diamond, 1994; Hayden et al., 2007; Leder & Bruce, 2000; Maurer et al., 2002). These parallels could be taken to indicate that 9-month-olds in the current study processed second-order relational information in bodies.

However, we believe that caution should be exercised in drawing this conclusion. The notion of second-order information in faces is based on the assumption that foreground features (like eyes) are located on a background (face surface) and the space between the features constitute relational information rather than featural information (e.g., Carey & Diamond, 1994; Diamond & Carey, 1977; Leder & Bruce, 2000). Thus, the space between features is assumed to be qualitatively different from the features themselves. It is not clear that the body part proportions that we altered in the current experiment constitute such changes in background spacing information. More generally, it is uncertain whether body parts and their relations are analogous to facial features and the space between them. Given this uncertainty, we think that it is premature to characterize body proportion changes as being analogous to changes in second-order information in faces.

While 9 months of age is significantly younger than the age at which visuo-spatial body representation has currently been documented in infancy,1 it is consistent with other research on body processing, including infants’ sensitivity to body movement in point-light displays (e.g., Bertenthal, Proffitt, & Cutting, 1984; Fox & McDaniel, 1982; Hirai & Hiraki, 2005; Reid, Hoehl, & Striano, 2005). However, Slaughter and Heron (2004) account for the findings of infants’ sensitivity to body motion by categorizing this type of body knowledge as sensorimotor knowledge. They contrast sensorimotor knowledge from visuo-spatial knowledge, which refers to detailed structural descriptions and relations between body parts (Slaughter & Heron, 2004). Slaughter and Heron state that while infants may have sensorimotor knowledge relatively early in life, their visuo-spatial knowledge is not developed during the first year of life. Yet, there is some uncertainty about this distinction because Gliga and Dehaene-Lambertz (2005) found that event-related potential responses of infants as young as 3 months of age differ between intact versus part-reorganized static body images (i.e., in the absence of sensorimotor information).

In the current study, 5-month-olds failed to demonstrate body knowledge, thereby indicating a developmental change between 5 and 9 months. One possibility is that the relatively slow development of body expertise compared with face expertise is because infants have different types of experience with bodies than with faces. Interactions with caregivers typically involve face-to-face contact, while the typical supine positions of infants early in life may shield the caregiver’s body. Additionally, faces are more directly associated with verbal communication, which is a strong medium of interaction between the infant and the caregiver, and the relationship between faces and verbal communication may further increase the salience of faces compared with bodies.

Another possibility is that infants of 5 months of age do have knowledge about body proportions, but the spontaneous preference procedure used in the current study may have been unable to assess this ability. Although 5-month-olds may be able to discriminate between these two categories, they may not have a preference between them, which is required by the spontaneous preference procedure. Future studies utilizing a habituation procedure may clarify whether 5-month-olds’ failure is based upon a lack of preference for normal versus distorted bodies or a lack of body knowledge at this age.

In summary, the current research suggests the presence of visuo-spatial body knowledge during the second half of the first year of life. To our knowledge, the current study is the first to indicate that 9-month-olds are sensitive to the relative proportions of body parts. Moreover, the current research found that infants exhibit inversion effects with bodies that parallel those with faces, thereby indicating that 9 months of experience is enough for infants to develop enough expertise with bodies to engender orientation-specific processing. The presence of a developmental change between 5 and 9 months of age implies that body knowledge is rapidly developing throughout the first year of life, and one goal of future research should be to specify the type of body information that is available to infants prior to 9 months of age.

ACKNOWLEDGMENTS

This research was supported by grants from the National Institute of Child Health and Human Development (HD042451, HD052724). We thank the infants and the parents who participated in this study.

Footnotes

1

After this work was completed, we learned that Heron and Slaughter (in press) have recently found evidence that even infants as young as 9 months of age are sensitive to part organization in human bodies, provided they are tested with actual humans rather than pictures. These results show at least tentative knowledge about body part organization by 9 months of age, which is consistent with and complementary to our finding that infants of this age are sensitive to the proportion of body parts.

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