حساسیت به متن حالت چهره در 3، 6 و 9 ماهگی

Abstract Thirty-eight 3-, 6-, and 9-month-old infants interacted in a face to face situation with a female stranger who disrupted the on-going interaction with 30 s Happy and Neutral still face episodes. Three- and 6-month-olds manifested a robust still face response for gazing and smiling. For smiling, 9-month-olds manifested a floor effect such that no still face effect could be shown. For gazing, 9-month-olds’ still face response was modulated by the context of interaction such that it was less pronounced if a happy still face was presented first. The findings point to a developmental transition by the end of the first year, whereby infants’ still face response becomes increasingly influenced by the context of social interaction.

. Introduction The still face paradigm has been widely used to assess human infants’ early social expectations (Adamson & Frick, 2003; Tronick, Als, Adamson, Wise, & Brazelton, 1978). As young as 2-months of age, infants avert their gaze, smile less, and self-comfort when they encounter a suddenly still faced partner who had been communicating with them (Cohn & Tronick, 1987; Field, Vega-Lahr, Goldstein, & Scafidi, 1986; Toda & Fogel, 1993). Such findings index infants’ rudimentary expectations about the nature of face to face interactions with people (see also Gusella, Muir, & Tronick, 1988; Muir & Hains, 1993; Rochat & Striano, 1999). Modifications of the still face paradigm reveal that the still face response is robust but also selective. Based on a variety of careful manipulations to rule out alternative explanations, it has been shown that the still face situation is not due simply to a general loss of stimulation or fatigue over time (e.g., Gusella et al., 1988; see also Muir & Hains, 1993). The still face effect is reserved for people and not objects (i.e., Ellsworth, Muir, & Hains, 1993), and shows that infants are attuned to more than the presence or absence of stimulation. While the still face paradigm has been systematically used with infants in the first half of the first year, it has not been commonly used to investigate the social competencies of older infants. Once infants start to systematically coordinate attention between people and objects by 9–12 months of age (i.e., Tomasello, 1999), researchers have turned to triadic paradigms which involve the integration of people and objects (e.g., Bakeman & Adamson, 1984; Carpenter, Nagell, & Tomasello, 1998). However, the still face effect may be used to track the development of social competencies over the course of the first year (see also Striano & Rochat, 1999). The current study assessed infants’ still face responses at 3, 6, and 9 months of age. The procedure was based on prior research that assessed infants’ response to “emotional” still faces. In a study with 5-month-old infants, D’Entremont and Muir (1997) found that infants manifested a small but significant effect for smiling when their mother presented a happy still face compared to a neutral and sad still face. Taking a developmental approach, Rochat, Striano, and Blatt (2002) compared 2-, 4-, and 6-month-olds’ responses to 30 s Happy, Neutral, and Sad still face episodes presented by a stranger. Two-month-olds did not show a reduction in gazing for the Happy still face. The authors suggest that between 4 and 6 months of age, infants become more sensitive to the timing and structure of face to face interactions (see also Rochat, Querido, & Striano, 1999), whereas younger infants are focused on the presence or absence of positive facial expressions. In the current study, we extended the research of D’Entremont and Muir (1997) and Rochat et al. (2002) by presenting different emotional still faces to 3-, 6-, and 9-month-old infants. Developmental transitions that happen by the end of the first year, such as the capacity for joint attention (Carpenter et al., 1998) and social re-engagement efforts (Cohn & Tronick, 1987; Striano & Rochat, 1999) are thought to reflect, in part, the infants’ developing capacity to understand the underlying motives and goals of others. Considering prior actions assists in understanding the meaning of others’ behaviors (i.e., Carpenter, Call, & Tomasello, 2002). Similarly, a sensitivity to others’ facial expressions is a necessary precursor to recognizing the meaning behind others’ emotions and predicting how people will behave in the future (Walker-Andrews, 1997). Interestingly, by the end of the first year, infants categorize various static expressions based on their underlying meaning rather than perceptual similarity (i.e., Ludemann, 1991 and Nelson, 1987), and to use these expressions to interpret others’ future actions (Phillips, Wellman, & Spelke, 2002; Poulin-Dubois, 1999) and to guide their own behavior (Campos & Sternberg, 1981; Moses, Baldwin, Rosicky, & Tidball, 2001; Sorce, Emde, Campos, & Klinnert, 1985). In the current study, infants were presented between normal interaction periods with a happy still face and a neutral still face episode, with the order counterbalanced. We expected that infants at all ages would discriminate facial expressions (see Nelson, 1987; Serrano, Iglesias, & Loeches, 1992; Striano, Brennan, & Vanman, 2002; Walker-Andrews, 1997), but that the context of these expressions which were presented after a normal interaction period and during a sudden still-face period would modulate infants’ behavioral response. In particular, we expected that by 3 months of age infants would show sensitivity to the static facial expression posed during the still face episode. In particular, following Rochat et al.'s interpretation that young infants before 4 months of age show selective attunement to positive affect mirroring and expressions, we expected that this age group would show a reduced still face effect when a happy expression was posed. We predicted that they would not be influenced by the order of the still face expressions. Following prior research (i.e., Rochat et al., 2002; see also Rochat & Striano, 1999) we expected that infants at 6 months of age would not respond differentially to the emotional still faces. At this age, research suggests that infants are primarily attuned to the presence or absence of interpersonal contact, and not to the underlying reason behind a loss of social contingencies (Delgado, Messinger, & Yale, 2002), or emotional expressions posed during the break of contact. We expected a different pattern for the 9-month-olds, such that they would be influenced by the emotion posed during the still face episode, and also by the order of the emotion presentation. By the end of the first year, categorize emotional expressions based on their meaning rather than perceptual characteristics (i.e., Ludemann, 1991; however see also Bornstein & Arterberry, 2003), and begin to interpret others’ behavior as intentional (Tomasello, 1995). Thus, we expected that the context of the still face expression would influence infants’ responses at this age. We expected a reduced still face effect when the happy expression was presented first, given that it fell in the context of a preceding positive and reciprocal interaction. When the happy expression was presented second (i.e., following experience with a Neutral still face episode), we expected 9-month-olds to show a more robust still face effect given the prior ambiguous emotional context.

. Results Analyses were carried out separately for gazing and smiling. Following D’Entremont and Muir (1997), we performed a four (episode: Normal 1, Still face 1, Normal 2, Still face 2) × two (order: Happy still face first, Neutral still face first) × three (age: 3, 6, and 9 months) ANOVA. To test a main effect of episode we performed two planned contrasts. First, we compared the two normal episodes to the two still face episodes (the still face effect). Second, to check for behavioral changes over time we compared the first normal episode to the second normal episode. To investigate the effect of the different emotional expressions, we conducted a two (emotion: Happy still face, Neutral still face) × 2 (order: Happy still face first, Neutral still face first) × 3 (age: 3-, 6-, 9-months) ANOVA. Preliminary analyses with a four (episode) × 2 (sex) ANOVA on effects of gender did not yield significant differences, so this variable was collapsed for further analyses. Table 1 provides the means and standard errors of means of each episode and age group for gazing and smiling. As indicated in Table 1, there was an overall episode effect for gazing and smiling response (respectively, F (3, 96) = 31.6; p < 0.001; F (3, 96) = 16.2; p < 0.001). Planned contrasts confirmed a still face effect with a reduction in gazing and smiling during the still face episodes relative to the normal interactions (respectively, F (1, 32) = 65.6, p < 0.001; F (1, 32) = 35.8, p < 0.001), and showed that there were no significant difference between the normal episodes (p's > 0.1), thus ruling out fatigue. There were age effects, such that 3-month-olds gazed and smiled significantly more than 6- and 9-month-olds (Tukey post hoc, p's < 0.02). Table 1. Mean statistics for gazing and smiling by age and episode Age group Measure Normal interaction 1a Still face 1a Normal interaction 2a Still face 2a 3-month-oldsb Gazing 92.66 (4.80)c 56.78 (8.89)d 94.33 (2.48)c 53.55 (7.82)d Smiling 33.29 (6.7)c 9.46 (2.64)d 27.19 (6.98)c 4.64 (2.13)d 6-month-olds Gazing 53.86 (7.42)c 33.77 (9.05)d 44.63 (7.52)c 31.35 (6.77)d Smiling 17.89 (5.26)c 2.38 (1.33)d 8.32 (4.80)c 2.11 (1.16)d 9-month-olds Gazing 53.13 (7.39)c 34.19 (5.79)d 59.20 (5.32)c 26.96 (6.11)d Smilinge 3.83 (1.54) 3.16 (1.58) 3.53 (1.54) 1.58 (1.58) Superscripts indicate significant differences (p < 0.05) according to the analyses reported. a Significant main effect. b Significantly different from 6- to 9-month-olds. c Not significantly different. d Significantly different from normal interactions. e No statistics are computed because less than half of the infants smiled. Table options For gazing there was an age × episode interaction (F (6, 96) = 2.3, p = 0.038). Analyzing each age group separately confirmed a significant still face effect in each age group (p's < 0.01). As indicated in Table 1, the interaction likely rests on a more pronounced still face effect for the group of 3-month-olds. There was also an age × episode effect for smiling (F (6, 96) = 4.6, p < 0.001). The interaction was due to a significant reduction in smiling during the still face for both 3- and 6-month-old infants, and no reduction for 9-month-old infants. However, it is important to note that less than half of the 9-month-olds smiled at E in any of the four episodes (number of smiling infants per episode: Normal 1 = 5; SF1 = 4; Normal 2 = 3; SF2 = 1) such that no still face effect could be confirmed for this age group. Comparison of the emotional expressions for gazing revealed a significant order × age interaction (F (2, 32) = 3.7, p = 0.036). Fig. 1 shows infants’ gazing as a function of both orders. As shown by comparing the right and left panels of Fig. 1, 9-month-olds gazed reliably more in the Happy still face episode when the Happy still face was presented first (F (1, 10) = 11.50, p = 0.007). Normal and Still face episodes for gazing. Left and right panel present, ... Fig. 1. Normal and Still face episodes for gazing. Left and right panel present, respectively, the order with the Happy or Neutral still face first. Figure options For smiling, there was a significant order × emotion interaction (F (2, 32) = 4.1, p = 0.049) suggesting that infants smiled significantly more to the Happy than Neutral still face in the Happy Order (F (1, 17) = 9.4, p = 0.008). However, given the floor effect in the 9-month-olds and a marginal age effect (F (2, 32) = 3, p = 0.064), the order effect for smiling was analyzed for each age group separately. Fig. 2 shows that 3- but not 6-month-olds displayed an order × emotion interaction (F (1, 11) = 6.13, p = 0.031). At 3 months, infants smiled significantly more to the first still face regardless of the order of expression. Normal and Still face episodes for smiling. Left and right panel present, ... Fig. 2. Normal and Still face episodes for smiling. Left and right panel present, respectively, the order with the Happy or Neutral still face first. Figure options 3.1. Summary of main results Three- and 6-month-olds showed a significant still face effect for both expressions for gazing and smiling. Three-month-olds smiled more at the experimenter in the first still face episode, regardless of which expression was presented. For smiling, 9-month-olds showed a floor effect. For gazing, there was an order by age interaction such that 9-month-olds gazed reliably more to the still faces when the Happy expression was presented first.