Face preference in infancy and its relation to motor activity

Abstract

Infants’ preference for faces was investigated in a cross-sectional sample of 75 children, aged 3 to 11 months, and 23 adults. A visual preference paradigm was used where pairs of faces and toys were presented side-by-side while eye gaze was recorded. In addition, motor activity was assessed via parent report and the relation between motor activity and face preference was examined. Face preference scores followed an inverted U-shaped developmental trajectory with no face preference in 3-month-olds, a strong face preference in 5- and 9-month-olds, and a weaker face preference in 11-month-olds. Adults showed no reliable face preference. Motor activity was a significant predictor of face preference in 3-month-old infants, supporting the presence of motor-social connections in early infancy.

Keywords

eye tracking face processing infancy motor development

Faces provide important information about another persons’ identity, interests, mood, and possibly also intentions. Learning to use the information provided in a face is important for social development and attending to faces early in life is thought to play an important role in social learning and in shaping the brain circuits involved in the “social brain” (Johnson, 2005). Therefore, establishing when infants show a reliable preference for faces, and what factors influence their attention towards faces, can inform our understanding of infants’ social-cognitive development.

Face preference at birth

Using simple visual-orienting paradigms, a preference for faces has been observed already in newborns (Goren, Sarty, & Wu, 1975; Johnson, Dziurawiec, Ellis, & Morton, 1991; Kleiner, 1987; Valenza, Simion, Cassia, & Umilta, 1996). A neonatal face preference is not limited to humans and can also be found in chicks and infant monkeys—even those reared without exposure to faces for 6 months or more (Rosa-Salva, Farroni, Regolin, Vallortigara, & Johnson, 2011; Rosa-Salva, Regolin, & Vallortigara, 2010; Sugita, 2008). These findings suggest that newborns’ face preference is independent of experiences with faces and may be explained by a face-specific representational bias or by general constrains of the visual system (e.g., de Schonen & Mathivet, 1989; Johnson & Morton, 1991; Simion, Leo, Turati, Valenza, & Barba, 2007). For example, it has been suggested that perceptual features, such as up-down asymmetry (i.e., more elements in the upper part of display), may account for newborns’ preference for faces (Macchi Cassia, Turati, & Simion, 2004; Simion, Valenza, Macchi Cassia, Turati, & Umilta, 2002; Turati, Simion, Milani, & Umilta, 2002). However, experiences quickly begin to shape face preferences and after only 4 days, newborns begin to show a preference for their mother’s face over a stranger’s face, and this preference varies as a function of infants’ exposure to their mother (I. W. R. Bushnell, 2001; I. W. R. Bushnell, Sai, & Mullin, 1989; Field, Cohen, Garcia, & Greenberg, 1984; Pascalis, de Schonen, Morton, Deruelle, & Fabre-Grenet, 1995).

Face preference following the newborn period

While infants seem more interested in faces than in other visual stimuli, a preference for faces over other salient visual stimuli has not been reported consistently in the 2 months following the newborn period. On the one hand, there is evidence for a face preference in 3-month-old infants when comparing photographic images of faces to scrambled faces, or in the presence of face-like movements (Ichikawa, Tsuruhara, Kanazawa, & Yamaguchi, 2013; Macchi Cassia, Kuefner, Westerlund, & Nelson, 2006; Simion et al., 2007; Turati, Valenza, Leo, & Simion, 2005). On the other hand, Johnson, Ellis, and Morton (1991) reported a decline in preferential face tracking in 2-month-old infants, and a number of other studies observed no clear preference for face over competing images in 1–3-month-olds (e.g., Chien, 2011; Dannemiller & Stephens, 1988; Keller & Boigs, 1991; Maurer & Barrera, 1981; Wilcox, 1969).

An extensive review of some early studies on infants’ face preference suggests that no face preference is evident in infants younger than 4 months of age when static faces alongside competing visual stimuli are presented side-by-side for less than 30 seconds (Maurer, 1985). It is possible that 3-month-old infants require more time to process faces and therefore do not show a spontaneous face preference when images are presented for less than 30 seconds. Supporting this view, faces have been shown to automatically capture attention in 6-month-old but not 3-month-old infants (Di Giorgio, Turati, Altoe, & Simion, 2012; Gliga, Elsabbagh, Andravizou, & Johnson, 2009). Further, it has been shown that 3–4-month-old infants require 90 seconds of familiarization to successfully recognize a previously encountered face (Otsuka et al., 2009).

Starting at around 4–5 months of age, infants again start to show a preference for faces over other, highly salient, images such as toys or cars (Durand, Baudouin, Lewkowicz, Goubet, & Schaal, 2013; Libertus & Needham, 2011). A face preference has also been confirmed in 6- and 9-month-old infants using animated video clips (Frank, Vul, & Johnson, 2009). In particular, this study reported an increase in face preference from 3 to 9 months of age, with the strongest face preference being evident in adults. Such changes in face preference over the first year are likely influenced by infants’ own experiences. For example, infants’ face discrimination skills have been shown to become increasingly specialized to human faces over the first 9 months in a process called “perceptual narrowing” that is dependent on the kinds of faces infants are exposed to (Pascalis, de Haan, & Nelson, 2002; Pascalis et al., 2005).

Learning through motor experiences

Experiences such as exposure to different types of visual stimuli play a critical role throughout development and can strongly impact infants’ face processing skills. However, the infant is not a passive observer, but actively moving around while exploring the world. Consequently, the kinds of experiences infants are able to provide for themselves are limited by their own motor abilities. For this reason, motor skills have been called a “rate limiting” factor in infant development (E. W. Bushnell & Boudreau, 1993).

It has long been recognized that motor experiences offer a foundation for learning (Piaget, 1952) and several studies have investigated how motor skills affect development across domains. To describe how infants’ own motor abilities influence their perception of the potential for actions offered by objects, Gibson (1988) introduced the concept of “affordance.” Infants’ object exploration skills have also been shown to affect their perception of 3D objects (Soska, Adolph, & Johnson, 2010). Similarly, a growing literature has found associations between infants’ crawling skills and their spatial abilities such as mental rotation or spatial search (Bai & Bertenthal, 1992; Campos et al., 2000; Clearfield, 2004; Schwarzer, Freitag, Buckel, & Lofruthe, 2012). Together, these findings highlight the important role played by motor skills for infants’ cognitive and perceptual development.

Motor skills and social development

Going beyond cognitive and perceptual domains, a number of recent studies have identified connections between infants’ motor skills and their social development. For example, studies of infants at high familial risk for Autism Spectrum Disorders (ASD) have found associations between fine and gross motor skills during the first year of life and subsequent social and language development (Bhat, Galloway, & Landa, 2012; Bhat, Landa, & Galloway, 2011; LeBarton & Iverson, 2013). Flanagan, Landa, Bhat, and Bauman (2012) have even reported that head lag during a pull-to-sit task administered at 6 months of age is predictive of ASD outcomes at 3 years of age.

In typically developing infants, motor experiences have been shown to affect elementary aspects of infants’ social development. For example, facilitating independent reaching in 3-month-old infants (via “sticky mittens”) has been found to encourage a preference for face (Libertus & Needham, 2011), and facilitate infants’ perception and understanding of observed actions (Gerson & Woodward, 2013; Skerry, Carey, & Spelke, 2013; Sommerville, Woodward, & Needham, 2005). In slightly older infants, the transition from crawling to walking has been found to alter infants’ social exchanges with their mothers (Karasik, Tamis-LeMonda, & Adolph, 2011, 2014). These findings suggest that new motor skills providing infants with different ways to interact with others (such as grasping and walking) alter their attention to and engagement with social interaction partners. One could argue that experiencing a new motor skill changes the “affordances for interaction” that infants perceive in others.

The relation between infants’ grasping experiences and their preference for faces is of particular interest, as grasping is an early emerging motor milestone and early attention to faces is, as reviewed above, critical for the development of the “social brain” (Johnson, 2005). Two previous studies have reported a relation between grasping experiences and face preference, but only in the context of training paradigms where infants’ motor experiences were actively manipulated (Libertus & Needham, 2011, 2014). It remains unclear, whether a similar relation exists in naïve, untrained infants.

The current study

The first goal of this research was to investigate the developmental trajectory of face preference across infancy and in adults. Libertus and Needham (2011, 2014) reported no face preference in three separate groups of 3-month-old infants, a result that contrasts with other studies reporting a face preference at this age (Ichikawa et al., 2013; Macchi Cassia et al., 2006; Turati et al., 2005). Therefore, it seemed important to re-investigate face preference in 3-month-olds using the same stimuli as Libertus and Needham (2011). We hypothesized that 3-month-olds would not show a face preference using static face-toy pairs (Maurer, 1985), that a face preference would be evident by age 5 months, and that this preference would strengthen into adulthood (Frank et al., 2009).

Our second goal was to examine the relation between face preference and motor development. Libertus and Needham (2011) reported that scaffolded reaching experiences (“sticky mittens”) increased infants’ face preference. In a more recent study, the same authors report that experiences of actively moving an object attached to the infant’s hand also encouraged their preference for faces (Libertus & Needham, 2014). However, it is possible that the interactive exchanges during these training procedures, rather than the motor experiences themselves, encouraged a preference for faces in their study. The current study addresses this issue by examining the relation between face preference and a parent-report measure of motor activity in naïve, untrained infants. Activity level is inversely related to infants’ ability to control and focus their own limb movements, which in turn predicts the onset of successful grasping (Thelen et al., 1993). If face preference were indeed related to aspects of infants’ grasping skills (as suggested by the findings of Libertus & Needham, 2011), one would expect to observe a similar relation between infants’ motor activity level and their preference for faces. Such a motor-social relation could be driven by changes in what opportunities for social interactions infants perceive in others depending on their own ability to control their limb movements. For example, once infants engage in independent grasping, opportunities for sharing games and triadic exchanges with others open up (Striano & Reid, 2006).

Methods

Participants

A total of 75 full-term infants and 23 adults participated in this experiment. Infants were divided into five groups based on their age: 20 children aged 3 months, 19 children aged 5 months, 18 children aged 9 months, and 18 children aged 11 months. All participants came from a middle- to upper-class background, full participant details can be found in Table 1. Eleven additional participants were recruited (2 adults, 9 infants) but excluded from the final sample due to technical difficulties (1 adult), calibration failure resulting inaccurate tracking and data loss (1 adult, 7 infants), and due to prematurity (2 infants).

Table 1.

Participant demographic information

Group	n	#F	Race	Age (days)	Parent education	Birth weight
3-month-olds	20	10	16C, 2B, 2A	100.35 (8.03)	8.95 (2.39)	3490 (504)
5-month-olds	19	10	15C, 3B, 1M	144.11 (16.81)	9.06 (2.53)	3445 (393)
9-month-olds	18	7	15C, 3A	257.53 (18.48)	9.93 (1.94)	3354 (492)
11-month-olds	18	9	16C, 2B	334.08 (12.42)	8.88 (2.12)	3335 (444)
Adults	23	14	–	20.83 (1.17) years	–	–

Note. The total number of participants in each group (n) and the number of female participants per group (#F) are group totals. All other values are group averages with standard deviations given in parentheses. Age is reported in days except for the adult group where age is reported in years. Education level of the parents was assessed on a scale from 0–6 for each parent separately and added (max 12). Parent education, race and birth weight data were not obtained from adult participants. Race abbreviations: C = Caucasian, B = Black or African American, A = Asian, M = More than one race.

Infant participants were recruited from public birth records. Parents received $5 travel reimbursement and an infant-sized t-shirt as gift for their participation. Adult participants were undergraduate students at a major research university and received course credit for their participation. The university Institutional Review Board approved the research protocol and informed consent was obtained (from a parent or legal guardian for infants) prior to testing. Although all infants were born after 37 weeks of gestation, age was recorded as post-menstrual age (PMA) based on parent report (van der Fits, Klip, van Eykern, & Hadders-Algra, 1999).

Procedure

Testing was completed in a small, dimly lit room. Adults were seated in a stable chair; infants were seated in a reclined bouncy chair, a stable high chair, or on a caregiver’s lap at a distance of about 60 cm from a Tobii 1750 remote cornea-reflection eye-tracker with a 50 Hz sampling rate. At the beginning of the experiment, a 9-point calibration procedure was performed. Tracking quality and drift was monitored throughout the experiment using a recurring central fixation stimulus.

Stimuli

All stimuli were presented sequentially on a 17″ screen (33.4 × 25.4 degrees of visual angle) at a resolution of 1024 × 786 pixels. Sample stimuli are shown in Figure 1. To facilitate comparisons of our results with previous studies that only used the Face-Preference Task (Libertus & Needham, 2011), infants first completed the Face-Preference Task and then the Visual Acuity Task.

Figure 1.

Example of the stimuli used during the face-preference task (a) and High-Spatial Frequency (HSF) preference task (b)

Face-preference task

Stimuli used in the face-preference task consisted of colored photographs of faces and infant toys displayed side-by-side for a fixed trial-duration of 10 seconds on a white background (Figure 1) followed by a 1-second central fixation stimulus. Two male and two female faces showing neutral expressions were selected from the NimStim database (Tottenham et al., 2009) and were each paired with a different toy to create four unique face-toy pairs. The same stimuli were used by Libertus and Needham (2011, 2014) and by DeNicola, Holt, Lambert, and Cashon (2013). Side of face presentation was counterbalanced. Faces or toys were not equated for visual saliency but were of similar luminance (DeNicola et al., 2013).

Visual acuity

Maturity of the visual system, in particular the ability to perceive high-spatial frequency content, is likely to influence infants’ face preferences. To account for differences in visual acuity across the large age-range tested here, a High-Spatial Frequency (HSF) preference task was included. This task estimates preferences for high- vs. low-spatial frequency information in faces using a preferential looking paradigm identical to the face-preference task. Gray scale photographs of one male and one female face selected from the NimStim database (Tottenham et al., 2009) were modified using low-pass, and high-pass filters in Adobe Photoshop^®. For each face, the Low-Spatial Frequency (LSF) and the High-Spatial Frequency (HSF) version were then presented side-by-side for fixed trial-duration of 10 seconds on a white background (Figure 1) followed by a 1-second central fixation stimulus. Each face identity was presented twice, counterbalancing for the side of the HSF image (total of 4 presentations).

Activity level

Parents of all infants were asked to complete the Infant Behavior Questionnaire (IBQ, Rothbart, 1981). From the IBQ, the activity level temperament dimension was used to provide an estimate of the child’s overall motor activity level (e.g., general limb movements, locomotion) and their ability to control and focus these movements. IBQ data is missing for two 11-month-old infants.

Analyses

Due to the large age range of the participants tested here (ranging from 3 months to 21 years of age), an assumption free approach to analyze eye gaze was used. Instead of defining fixations using an arbitrary filter algorithm, raw eye-gaze was used as a time-varying signal recorded at 50 Hz. Blinks were treated as missing data. Previous findings suggest that fixation and raw gaze results yield similar results (Tichacek, 2004). To be included in the final analyses, infants had to look at the screen for at least 25% of cumulative time for each task (face preference or HSF preference). On the face-preference task, all infants met this criterion. Two infants were excluded from analyses for the HSF-preference task because they failed to reach this minimum criterion (one 9-month-old and one 11-month-old infant).

Face preference was assessed by calculating the proportion of looking time to the face or the toy using two rectangular Areas of Interests (AOIs) centered over the face and toy stimulus. Looks outside of these AOIs were removed from analysis (%face + %toy = 100%). A single face-preference score was then derived (%face − %toy), with positive values indicating a face preference, negative values a toy preference, and 0 indicating no preference (Libertus & Needham, 2011). Face-preference scores where compared to 0 using separate single-sample t tests (two-tailed) within each age group and Cohen’s d is provided as measure of effect size for these comparisons. This analytic approach is equivalent to using paired t test comparing between %face vs. %toy or %HSF vs. %LSF. Between-group differences were explored using Analysis of Variance (ANOVA) with Group (5) as between-subjects factor, followed by Tukey’s HSD corrected post-hoc comparisons. For the HSF-preference task, the same AOIs and statistical analyses were used. In addition to reporting difference scores for face preference and HSF preference in Figure 2, proportions of looking duration towards each stimulus are shown in Table 2. Preliminary analyses revealed no effects of Gender (all ps > .13) and this factor was removed from all further analyses.

Figure 2.

Mean face preference and HSF preference scores by age group. Error bars represent SEM. * p < .05, one-sample t test (2-tailed).

Table 2.

Proportion of looking time by stimulus type

Group	Face (SD)	Toy (SD)	HSF (SD)	LSF (SD)
3-month-olds	52.20 (22.65)	47.90 (22.65)	48.26 (18.23)	51.74 (18.23)
5-month-olds	68.88 (18.43)	31.12 (18.43)	49.91 (17.58)	50.09 (17.58)
9-month-olds	72.03 (19.65)	27.97 (19.65)	60.13 (17.29)	39.87 (17.29)
11-month-olds	62.33 (11.81)	37.67 (11.81)	60.83 (12.22)	39.17 (12.22)
Adults	54.45 (17.68)	45.55 (17.68)	68.25 (15.69)	31.75 (15.69)

Note. Face + toy = 100% and HSF + LSF = 100%. All values are group averages with standard deviations given in parentheses.

Results

Face preference

Within-group analyses indicate no face preference in three-month-olds (M = 4.20, SD = 45.30; t(19) = 4.12, p = .68, 95% CI [−17.00, 25.40], Cohen’s d = .19). A stable face preference is present around age 5 months (M = 37.76, SD = 36.87; t(18) = 4.47, p < .01, [19.99, 55.53], d = 2.05), seems to peak around age nine months (M = 44.07, SD = 39.30; t(17) = 4.76, p < .01, [24.52, 63.61], d = 2.24), and weakens somewhat by age 11 months (M = 24.66, SD = 23.61; t(17) = 4.43, p < .01, [12.91, 36.4], d = 2.09). These results are summarized in Figure 2. In adults, no significant face preference was observed (M = 8.90, SD = 35.36; t(22) = 1.21, p = .24, [−6.39, 24.20], d = .50). However, visual inspection of the horizontal eye-gaze position over time (Figure 3) indicates that adults show a rapid face preference during the first 500 ms following stimulus onset.

Figure 3.

Horizontal eye-gaze position during face-preference task by time. Starting at 5 months, all infant groups show a preference for faces over toys. Adults show no overall face preference but rapid orienting to faces in the first 500 ms. Gray shaded area represents SEM.

A between-subject ANOVA revealed significant differences in face preference between the 5 age groups, F(4, 93) = 4.37, p < .01, η² = .16. Post-hoc comparisons indicated a stronger face preference in 5-month-olds compared to 3-month-olds (p = .04, [0.66, 66.46], Cohen’s d = .83), in 9-month-olds compared to 3-month-olds (p = .01, [6.50, 73.23], d = .96), and in 9-month-olds compared to adults (p = .03, [2.85, 67.48], d = .97). No other comparisons were significant.

HSF preference

Within-group analyses revealed no HSF preference in 3-month-old (M = −3.47, SD = 36.45; t(19) = −0.43, p = .68, 95% CI [−20.53, 13.59], Cohen’s d = −.19), or 5-month-old infants (M = −0.17, SD = 35.16; t(18) = −0.02, p = .98, [−17.12, 16.78], d = .01). A significant HSF preference was observed in 9-month-olds (M = 20.27, SD = 34.57; t(16) = 2.42, p = .03, [2.5, 38.05], d = 1.17), 11-month-olds (M = 21.65, SD = 24.43; t(16) = 3.65, p < .01, [9.09, 34.22], d = 1.77), and in adults (M = 36.49, SD = 31.37; t(22) = 5.58, p < .01, [22.91, 50.06], d = 2.33). These results are summarized in Figure 2.

A between-subject ANOVA revealed significant main effect of Group, F(4, 91) = 5.36, p < .01, η² = .19. Post-hoc comparisons indicate a stronger HSF preference in adults compared to 3-month-olds (p < .01, [12.06, 67.87], Cohen’s d = .1.21), and in adults compared to 5-month-olds (p < .01, [8.37, 64.96], d = .1.13). No other group comparisons were significant (all ps > .14).

Activity level

Infants’ motor activity level was assessed via parent report using the IBQ (Rothbart, 1981). A between-subject ANOVA revealed a significant main effect of Group, F(3, 69) = 7.73, p < .01, η² = .25. Post-hoc comparisons indicated that 3-month-olds (M = 3.71, SD = 0.98) showed lower activity-level scores than both 9-month-old (M = 4.61, SD = 0.71; p < .01, 95% CI [−1.52, −0.27], Cohen’s d = −1.06) and 11-month-old infants (M = 4.75, SD = 0.44; p < .01, [-1.69, −0.40], d = −1.36). No other comparisons were significant.

Relation between motor activity and face preference

The relation between motor activity level and face preference was assessed separately in 3-month-old infants (as in Libertus & Needham, 2011) and in the older infants combined using a regression model with face-preference as dependent variable and activity level as predictor while simultaneously controlling for demographic variables (age, birth weight, parent education, and gender), and HSF preference (as estimate for visual acuity).

Together, activity level, demographic factors, and HSF preference explained a significant proportion of variation in 3-month-olds’ preference for faces, F(6, 13) = 4.25, p = .01, R ² _Adj = .51. Activity level was a significant predictor for face preference above and beyond all other predictors in the model and uniquely accounted for 27% of the variance in 3-month-old infants’ face preference, t(13) = −3.23, p < .01, β = −.61, ▵ R² = .27 (Figure 4). Other significant predictors in this model were Age, t(13) = 2.57, p = .02, and HSF preference, t(13) = −2.57, p = .02. That HSF preference is a significant predictor of infants’ face preference indicates that visual acuity affects face preference in early infancy. Together, these findings confirm and extend previous results suggesting a relation between motor and social development in 3-month-old infants (Libertus & Needham, 2011).

Figure 4.

Relation between activity level (IBQ) and face preference in 3-month-old infants. Unstandardized residuals of face-preference scores are shown to control for influences of age, gender, parent education, and HSF preference. Face preference shows a negative relation with activity level.

The same regression model was used to examine the relation between face preference and activity level in the remaining infant groups combined. In these older infants, the model failed to reach significance despite the larger sample size, F(6, 43) = 1.31, p = .27, R ² _Adj = .04, and activity level was not a significant predictor of face preference t(43) = −1.20, p = .24, β = −.19.

In summary, our results suggest a relation between motor activity and face preference in 3-month-old infants. Changes in infants’ motor activation have been found to predict the onset of independent grasping skills (Thelen et al., 1993) and may therefore increase infants’ awareness of others as social interaction partners. No such relation was observed in older infants, possibly due to reduced variability in infants’ face preference scores and motor activity scores (i.e., most older infants show a strong face preference, see Figure 2).

Discussion

The present study reports three main findings. First, we demonstrate that 3-month-old infants do not show a reliable preference for faces when photographic images of faces and toys are presented briefly (10 seconds). This finding confirms previous studies using similar paradigms and suggests a dip in spontaneous face preference around the third month (Johnson et al., 1991; Keller & Boigs, 1991; Maurer, 1985). Second, our results show a significant preference for faces over highly salient toys by 5 months of age, with a peak around 9 months. This pattern agrees with other reports on infants’ face preference and suggests that a strong face bias exists in mid infancy (DeNicola et al., 2013; Frank et al., 2009). And third, we report a relation between 3-month-olds’ motor activity and their emerging preference for faces. The observed negative relation between motor activity and face preference seems to contradict Libertus and Needham (2011, 2014), who reported a positive relation between successful grasping and face preference. However, these findings are compatible as high levels of motor activity are likely inversely related to successful reaching, which requires slower and controlled arm movements (Thelen et al., 1993). One possible explanation for this motor-social connection is a change in infants’ perception of people as potential interaction partners following the onset of independent grasping.

Face preference at age 3 months and beyond

Our results show a dip in infants’ spontaneous face preference around the third month, followed by an increase in face preference. This finding is surprising, as others reliably reported a face preference in 3-month-old infants (e.g., Chien, 2011; Ichikawa et al., 2013; Macchi Cassia et al., 2006). However, our negative findings of a preference for faces in 3-month-old infants do not undermine the fact that 3-month-old infants are able to process faces. In fact, several studies show that 3-month-old infants’ face processing skills are highly sophisticated. For example, by 3 months of age infants show evidence for holistic face processing (Turati, Di Giorgio, Bardi, & Simion, 2010), face specific representations (de Haan, Johnson, Maurer, & Perrett, 2001; Macchi Cassia et al., 2006; Turati et al., 2005), preferences for faces of their own or primarily exposed ethnic group (Kelly et al., 2007, 2005), a preference for human faces over monkey faces (Di Giorgio, Leo, Pascalis, & Simion, 2012; Heron-Delaney, Wirth, & Pascalis, 2011), and a preference for faces of the gender of their primary caregiver (Quinn et al., 2008). Further, brain-imaging studies suggest that a cortical specialization for faces is already present around this age (Halit, de Haan, & Johnson, 2003; Tzourio-Mazoyer et al., 2002). Consequently, our negative findings with 3-month-old infants may have been influenced by other factors such as the duration of stimulus presentation or the relative saliency of the competing visual stimuli. In particular, it has been reported that infants prefer “attractive” (e.g., symmetric) faces (Hoss & Langlois, 2003; Slater et al., 1998) and it is possible that the objects used in the current study were perceived as “attractive” by 3-month-old infants because most of the objects were symmetrical. Further, Maurer (1985) has identified stimulus duration as a critical factor influencing face preference and notes that face preference is absent at this age when short stimulus durations (< 30 seconds) are used. Libertus and Needham (2011, 2014) reported no face preference in three independent groups of 3-month-old infants (mean ages 88.27 days, 90.51 days, and 92.61 days, respectively) using short trial durations (10 seconds) and photorealistic images of faces and toys. Our results confirm this pattern in slightly older infants (mean age 100.35 days). It is possible that 3-month-old infants would require more time to process the information provided in a face to show a reliable preference (Otsuka et al., 2009).

Going beyond the third month, our results suggest an initial increase in face preference followed by a decline after 9 months of age. We did not observe evidence for an overall face preference in adults – although adults did show a strong bias to look more at faces at the beginning of each trial. This pattern differs from the findings reported by Frank and colleagues (2009) who used animated videos as stimuli. It is possible that older infants and adults require less time to process static faces and consequently disengage attention faster. Indeed, the face preference time course shown in Figure 3 reveals that adults show a reliable face preference during the first second of stimulus presentation. Faces in animated videos require more processing and therefore elicit a prolonged face preference in adults.

Connections between motor and social development

The current study suggests that infants’ motor activity predicts their preference for faces, at least in the context used here. This relation may seem surprising, but is in agreement with a number of other studies that have identified connections between motor and social development. For example, following the onset of locomotion infants showed more emotional expressions and engaged in more interactive social exchanges with their caregivers (Biringen, Emde, Campos, & Appelbaum, 1995; Clearfield, 2011). Similarly, being able to carry and share objects during upright locomotion has been reported to change infants’ social interaction bids and parents’ responses to these bids (Karasik et al., 2011, 2013). Collectively, these findings demonstrate that dynamic social exchanges require certain motor skills and that the child’s own motor skills influence social engagement from others.

With regard to grasping experiences, training studies using “sticky mittens” have been shown to change infants’ action perception and action understanding (Gerson & Woodward, 2013; Skerry et al., 2013; Sommerville et al., 2005). More relevant to the current study, Libertus and Needham (2011, 2014) reported that 3-month-olds’ own grasping skills (directly observed) predicted their preference for faces. Our findings support this result by showing that infants’ motor activity level—which has been associated with the onset of successful grasping (Thelen et al., 1993)—predicts face preference in three-month-old infants.

Interaction affordances

It remains unclear why grasping experiences would affect infants’ attention towards faces as suggested by our results. As infants acquire new motor skills, their perception of the potential for actions offered by objects changes. To describe this phenomenon, Gibson (1988) introduced the concept of “affordance.” Affordances reflect the fit between a child’s abilities and the opportunities provided by the environment to utilize these skills (Gibson & Pick, 2000). For example, 4–5-month-old infants who already engage in independent reaching have been found to attempt reaching only when they perceive an object to be close enough to succeed with their reach (Rochat & Goubet, 1995; Yonas & Hartman, 1993). Similarly, it has been shown that reaching attempts in 4–6-month-old infants are guided by object size in infants with more independent reaching experiences, while less-experienced infants mainly attempt to touch the most visually salient object (Libertus et al., 2013). These two examples show that experiences with independent reaching facilitate infants’ perception of an object’s affordances for reaching (that is, distance) and grasping (that is, size).

Here, we like to make a similar argument regarding infants’ perception of the potential for interactions offered by other people: Depending on their own motor abilities, infants may perceive different “interaction affordances” in faces. In the context used here, faces and toys were both presented beyond reach on a computer screen. This may have reduced infants’ interest in the toy, as it was not perceived as reachable. At the same time, once infants engage in independent grasping, opportunities for sharing and triadic exchanges emerge (Striano & Reid, 2006). Consequently, infants may start to perceive an affordance for social interactions in faces that they have not perceived before and this may heighten their interest in faces. In fact, it is likely that parents actively encourage perceiving interaction affordances in infants who independently grasp a toy, but not in infants who are handed a toy by the parent. For example, mothers’ who observe a child picking up a toy may respond with request statements like “What do you have there?” or “Can you show me?” whereas mothers may produce more descriptive statements when they hand a toy to the child (such as “Look, it’s a block”). Support for this notion comes from a recent study by Karasik and colleagues (2014) who showed that crawling and walking infants elicit different verbal responses from their mothers. Future research should investigate mothers’ verbal responses towards their 4–6-month-old infants as they make the transition into independent grasping.

Face preference and visual acuity

The current study introduced a novel task to estimate visual acuity development in infancy and observed a transition away from a preference for low spatial frequency to a preference for high spatial frequency information. This developmental progression is consistent with the literature on visual acuity development in infancy (Braddick & Atkinson, 2011; Catford & Oliver, 1973; Lenassi, Likar, Stirn-Kranjc, & Brecelj, 2008). However, until a direct comparison between the HSF preference task and an established acuity measure has been performed, it remains unclear whether the HSF preference task truly estimates visual acuity. Nonetheless, our results do suggest that infants’ face preference depends upon their ability to detect the detailed features present in faces. This stands in contrast to findings with newborns, who seem to rely on LSF information when learning and recognizing faces and show a LSF advantage (de Heering et al., 2008). The information provided in an LSF image provides only coarse, global information about the face, whereas a HSF image offers fine local details. With increasing visual acuity, these fine details become accessible to the infants and may attract attention because of the increased local complexity of the HSF stimulus (which may also require additional processing time).

Interestingly, both the HSF preference and the face preference task used here utilized a nearly identical preferential looking paradigm with a fixed trial duration of 10 s. However, the developmental patterns we observed in the two tasks were vastly different. This suggests that the results of the face preference task do not just reflect the development of visual orienting in a two-choice context. By controlling for HSF preference in our regression analysis, we demonstrate that the relation between face preference and motor activity is not merely an artifact of the development of visual orienting in general.

Limitations

The current study used a parent-report questionnaire to estimate infants’ motor activity level and a preferential looking paradigm to estimate infants’ preference for photographic images of faces over toys. While researchers have used both measures widely and successfully in the past, the limitations of these measures need to be considered. First of all, concerns regarding the validity of parent report measures have been raised, and it is possible that parents under- or overestimate their child’s true ability (Bartlett & Piper, 1994; Long, 1992; Seifer, 2008). A recent study compared infants’ motor performance on professionally administered standardized assessments to parent report and showed that parents provided quite reliable estimates of their child’s motor skills (Libertus & Landa, 2013). Second, looking time is an indirect measure and a variety of factors can affect infants’ visual preferences. For example, infants in our study may show a preference for the face stimulus because it shows a “face” or because it shows a “non-graspable” object. With the measures used here, we cannot discriminate between these two possibilities. Future studies should investigate this possibility more closely to determine how motor experiences shape infants visual preferences.

Conclusion

The results reported here indicate that face preference follows a non-linear, inverted U-shaped developmental pattern over the first year of life with an initial increase from 3 to 9 months of age, followed by a relative decline. Further, regression analyses suggest a relation between motor development and face preference in 3-month-old infants and add to a growing body of evidence on the importance of motor development for social-cognitive development (e.g., Bhat et al., 2012; Iverson, 2010; Libertus & Needham, 2011).

Footnotes

*This article accepted during Marcel van Aken’s term as Editor-in-Chief.

Funding

Financial support was provided by NIH grant R01 HD057120 to AN.

Acknowledgments

The work reported in this article was completed in partial fulfillment of a Doctor of Philosophy degree to the first author. We would like to thank Jennifer Gibson, Katherine Rief, and Addie Price for help with data collection, and the parents and infants who generously spent their time participating in our studies.

References

Bai

D. L.

Bertenthal

B. I.

(1992). Locomotor status and the development of spatial search skills. Child Development, 63(1), 215–226.

Bartlett

Piper

M. C.

(1994). Mothers’ difficulty in assessing the motor development of their infants born preterm: Implications for intervention. Pediatric Physical Therapy, 6(2), 55–60.

Bhat

A. N.

Galloway

J. C.

Landa

(2012). Relation between early motor delay and later communication delay in infants at risk for autism. Infant Behavior & Development, 35, 838–846. doi: https://dx-doi-org.web.bisu.edu.cn/10.1016/j.infbeh.2012.07.019

Bhat

A. N.

Landa

R. J.

Galloway

J. C

. (2011). Current perspectives on motor functioning in infants, children, and adults with autism spectrum disorders. Physical Therapy, 91(7), 1116–1129. doi: https://dx-doi-org.web.bisu.edu.cn/10.2522/ptj.20100294

Biringen

Emde

R. N.

Campos

J. J.

Appelbaum

M. I.

(1995). Affective reorganization in the infant, the mother, and the dyad: The role of upright locomotion and its timing. Child Development, 66(2), 499–514.

Braddick

Atkinson

(2011). Development of human visual function. Vision Research, 51(13), 1588–1609. doi:10.1016/j.visres.2011.02.018

Bushnell

E. W.

Boudreau

J. P.

(1993). Motor development and the mind: The potential role of motor abilities as a determinant of aspects of perceptual development. Child Development, 64(4), 1005–1021. doi: https://dx-doi-org.web.bisu.edu.cn/10.1111/J.1467-8624.1993.Tb04184.X

Bushnell

I. W. R.

(2001). Mother’s face recognition in newborn infants: Learning and memory. Infant and Child Development, 10 (1–2), 67–74. doi:10.1002/icd.248

Bushnell

I. W. R.

Sai

Mullin

J. T.

(1989). Neonatal recognition of the mother’s face. British Journal of Developmental Psychology, 7(1), 3–15. doi:10.1111/j.2044-835X.1989.tb00784.x

10.

Campos

J. J.

Anderson

D. I.

Barbu-Roth

M. A.

Hubbard

E. M.

Hertenstein

M. J.

Witherington

(2000). Travel broadens the mind. Infancy, 1(2), 149–219.

11.

Catford

G. V.

Oliver

(1973). Development of visual acuity. Archives of Disease in Childhood, 48(47), 47–50.

12.

Chien

S. H.-L.

(2011). No more top-heavy bias: Infants and adults prefer upright faces but not top-heavy geometric or face-like patterns. Journal of Vision, 11(6), 13. doi:10.1167/11.6.13

13.

Clearfield

M. W.

(2004). The role of crawling and walking experience in infant spatial memory. Journal of Experimental Child Psychology, 89(3), 214–241. doi:10.1016/j.jecp.2004.07.003

14.

Clearfield

M. W.

(2011). Learning to walk changes infants’ social interactions. Infant Behavior & Development, 34(1), 15–25. doi: https://dx-doi-org.web.bisu.edu.cn/10.1016/j.infbeh.2010.04.008

15.

Dannemiller

J. L.

Stephens

B. R.

(1988). A critical test of infant pattern preference models. Child Development, 59(1), 210–216.

16.

de Haan

Johnson

M. H.

Maurer

Perrett

D. I.

(2001). Recognition of individual faces and average face prototypes by 1- and 3-month-old infants. Cognitive Development, 16(2), 659–678. doi: https://dx-doi-org.web.bisu.edu.cn/10.1016/S0885-2014(01)00051-X

17.

de Heering

Turati

Rossion

Bulf

Goffaux

Simion

(2008). Newborns’ face recognition is based on spatial frequencies below 0.5 cycles per degree. Cognition, 106(1), 444–454.

18.

de Schonen

Mathivet

(1989). First come, first served: A scenario about the development of hemispheric specialization in face recognition during infancy. Cahiers de Psychologie Cognitive/Current Psychology of Cognition, 9(1), 3–44.

19.

DeNicola

Holt

N. A.

Lambert

A. J.

Cashon

C. H.

(2013). Attention-orienting and attention-holding effects of faces on 4- to 8-month-old infants. International Journal of Behavioral Development, 37(2), 143–147. doi:10.1177/0165025412474751

20.

Di Giorgio

Leo

Pascalis

Simion

(2012). Is the face-perception system human-specific at birth? Developmental Psychology, 48(4), 1083–1090. doi:10.1037/a0026521

21.

Di Giorgio

Turati

Altoe

Simion

(2012). Face detection in complex visual displays: an eye-tracking study with 3- and 6-month-old infants and adults. Journal of Experimental Child Psychology, 113(1), 66–77. doi:10.1016/j.jecp.2012.04.012

22.

Durand

Baudouin

J. Y.

Lewkowicz

D. J.

Goubet

Schaal

(2013). Eye-catching odors: Olfaction elicits sustained gazing to faces and eyes in 4-month-old infants. PLoS ONE, 8(8), e70677. doi:10.1371/journal.pone.0070677

23.

Field

T. M.

Cohen

Garcia

Greenberg

(1984). Mother-stranger face discrimination by the newborn. Infant Behavior and Development, 7(1), 19–25. doi:10.1016/s0163-6383(84)80019-3

24.

Flanagan

J. E.

Landa

Bhat

Bauman

(2012). Head lag in infants at risk for autism: A preliminary study. The American Journal of Occupational Therapy, 66(5), 577–585. doi: https://dx-doi-org.web.bisu.edu.cn/10.5014/Ajot.2012.004192

25.

Frank

M. C.

Vul

Johnson

S. P.

(2009). Development of infants’ attention to faces during the first year. Cognition, 110(2), 160–170. doi:10.1016/j.cognition.2008.11.010

26.

Gerson

S. A.

Woodward

A. L

. (2013). Learning from their own actions: The unique effect of producing actions on infants’ action understanding. Child Development, 85(1), 264–277. doi: https://dx-doi-org.web.bisu.edu.cn/10.1111/cdev.12115

27.

Gibson

E. J.

(1988). Exploratory behavior in the development of perceiving, acting and acquiring of knowledge. Annual Review of Psychology, 39, 1–41. doi: https://dx-doi-org.web.bisu.edu.cn/10.1146/Annurev.Ps.39.020188.000245

28.

Gibson

E. J.

Pick

A. D.

(2000). An ecological approach to perceptual learning and development. New York, NY: Oxford University Press.

29.

Gliga

Elsabbagh

Andravizou

Johnson

(2009). Faces attract infants’ attention in complex displays. Infancy, 14(5), 550–562. doi:10.1080/15250000903144199

30.

Goren

C. C.

Sarty

P. Y. K.

(1975). Visual following and pattern-discrimination of face-like stimuli by newborn infants. Pediatrics, 56(4), 544–549.

31.

Halit

de Haan

Johnson

M. H.

(2003). Cortical specialisation for face processing: Face-sensitive event-related potential components in 3-and 12-month-old infants. Neuroimage, 19(3), 1180–1193. doi:10.1016/s1053-8119(03)00076-4

32.

Heron-Delaney

Wirth

Pascalis

(2011). Infants’ knowledge of their own species. Philosophical Transactions of the Royal Society B: Biological Sciences, 366(1571), 1753–1763. doi:10.1098/rstb.2010.0371

33.

Hoss

R. A.

Langlois

J. H.

(2003). Infants prefer attractive faces. In Pascalis

Slater

(Eds.), The development of face processing in infancy and early childhood: Current perspectives (pp. 27–38). New York, NY: Nova Science Publishers, Inc.

34.

Ichikawa

Tsuruhara

Kanazawa

Yamaguchi

M. K.

(2013). Two- to three-month-old infants prefer moving face patterns to moving top-heavy patterns. Japanese Psychological Research, 55(3), 254–263. doi:10.1111/j.1468-5884.2012.00540.x

35.

Iverson

J. M

. (2010). Developing language in a developing body: The relationship between motor development and language development. Journal of Child Language, 37(2), 229–261. doi: https://dx-doi-org.web.bisu.edu.cn/10.1017/S0305000909990432

36.

Johnson

M. H.

(2005). Subcortical face processing. Nature Reviews Neuroscience, 6(10), 766–774. doi:10.1038/nrn1766

37.

Johnson

M. H.

Dziurawiec

Ellis

Morton

(1991). Newborns preferential tracking of face-like stimuli and its subsequent decline. Cognition, 40 (1–2), 1–19.

38.

Johnson

M. H.

Morton

(1991). Biology and cognitive development: The case of face recognition. Oxford, UK: Blackwell.

39.

Karasik

L. B.

Tamis-LeMonda

C. S.

Adolph

K. E.

(2011). Transition from crawling to walking and infants’ actions with objects and people. Child Development, 82(4), 1199–1209. doi: https://dx-doi-org.web.bisu.edu.cn/10.1111/j.1467-8624.2011.01595.x

40.

Karasik

L. B.

Tamis-LeMonda

C. S.

Adolph

K. E.

(2014). Crawling and walking infants elicit different verbal responses from mothers. Developmental Science, 17(3), 388–395. doi: 10.1111/desc.12129

41.

Keller

Boigs

(1991). The development of exploratory behavior. In Lamb

M. E.

Keller

(Eds.), Infant development: Perspectives from German-speaking countries (pp. 275–297). Hillsdale, NJ: Lawrence Erlbaum Associates.

42.

Kelly

D. J.

Quinn

P. C.

Slater

A. M.

Lee

L. Z.

Pascalis

(2007). The other-race effect develops during infancy: Evidence of perceptual narrowing. Psychological Science, 18(12), 1084–1089.

43.

Kelly

D. J.

Quinn

P. C.

Slater

A. M.

Lee

Gibson

Smith

Pascalis

. (2005). Three-month-olds, but not newborns, prefer own-race faces. Developmental Science, 8(6), F31–F36. doi:10.1111/j.1467-7687.2005.0434a.x

44.

Kleiner

K. A.

(1987). Amplitude and phase spectra as indexes of infants pattern preferences. Infant Behavior & Development, 10(1), 49–59.

45.

LeBarton

E. S.

Iverson

J. M

. (2013). Fine motor skill predicts expressive language in infant siblings of children with autism. Developmental Science, 16(6), 815–827. doi: https://dx-doi-org.web.bisu.edu.cn/10.1111/desc.12069

46.

Lenassi

Likar

Stirn-Kranjc

Brecelj

(2008). VEP maturation and visual acuity in infants and preschool children. Documenta Ophthalmologica, 117(2), 111–120. doi:10.1007/s10633-007-9111-8

47.

Libertus

Gibson

Hidayatallah

N. Z.

Hirtle

Adcock

R. A.

Needham

(2013). Size matters: How age and reaching experiences shape infants’ preferences for different sized objects. Infant Behavior and Development, 36(2), 189–198. doi: https://dx-doi-org.web.bisu.edu.cn/10.1016/j.infbeh.2013.01.006

48.

Libertus

Landa

R. J.

(2013). The Early Motor Questionnaire (EMQ): A parental report measure of early motor development. Infant Behavior and Development, 36(4), 833–842. doi: https://dx-doi-org.web.bisu.edu.cn/10.1016/j.infbeh.2013.09.007

49.

Libertus

Needham

. (2011). Reaching experience increases face preference in 3-month-old infants. Developmental Science, 14(6), 1355–1364. doi: https://dx-doi-org.web.bisu.edu.cn/10.1111/j.1467-7687.2011.01084.x

50.

Libertus

Needham

(2014). Encouragement is nothing without control: Factors influencing the development of reaching and face preference. Journal of Motor Development & Learning, 2(1), 16–27. doi: 10.1123/jmld.2013-0019

51.

Long

T. M.

(1992). The use of parent report measures to assess infant development. Pediatric Physical Therapy, 4(2), 74–77.

52.

Macchi Cassia

Kuefner

Westerlund

Nelson

C. A.

(2006). A behavioural and ERP investigation of 3-month-olds’ face preferences. Neuropsychologia, 44, 2113–2125. doi:10.1016/j.neuropsychologia.2005.11.014

53.

Macchi Cassia

Turati

Simion

(2004). Can a nonspecific bias toward top-heavy patterns explain newborns’ face preference? Psychological Science, 15(6), 379–383.

54.

Maurer

(1985). Infants’ perception of facedness. In Field

T. M.

Fox

N. A.

(Eds.), Social Perception in Infants (pp. 73–100). Norwood, NJ: Ablex Publishing Corporation.

55.

Maurer

Barrera

(1981). Infants perception of natural and distorted arrangements of a schematic face. Child Development, 52(1), 196–202.

56.

Otsuka

Konishi

Kanazawa

Yamaguchi

M. K.

Abdi

O’Toole

A. J.

(2009). Recognition of moving and static faces by young infants. Child Development, 80(4), 1259–1271. doi:10.1111/j.1467-8624.2009.01330.x

57.

Pascalis

de Haan

Nelson

C. A.

(2002). Is face processing species-specific during the first year of life? Science, 296(5571), 1321–1323.

58.

Pascalis

de Schonen

Morton

Deruelle

Fabre-Grenet

. (1995). Mother’s face recognition by neonates: A replication and an extension. Infant Behavior and Development, 18(1), 79–85. doi: https://dx-doi-org.web.bisu.edu.cn/10.1016/0163-6383(95)90009-8

59.

Pascalis

Scott

L. S.

Kelly

D. J.

Shannon

R. W.

Nicholson

Coleman

Nelson

C. A.

(2005). Plasticity of face processing in infancy. Proceedings of the National Academy of Sciences of the United States of America, 102(14), 5297–5300.

60.

Piaget

(1952). The origins of intelligence in children. New York, NY: International Universities Press.

61.

Quinn

P. C.

Uttley

Lee

Gibson

Smith

Slater

A. M.

Pascalis

(2008). Infant preference for female faces occurs for same- but not other-race faces. Journal of Neuropsychology, 2(1), 15–26. doi:10.1348/174866407X231029

62.

Rochat

Goubet

(1995). Development of sitting and reaching in 5-month-old to 6-month-old infants. Infant Behavior & Development, 18(1), 53–68.

63.

Rosa-Salva

Farroni

Regolin

Vallortigara

Johnson

M. H.

(2011). The evolution of social orienting: Evidence from chicks (Gallus gallus) and human newborns. PLoS ONE, 6(4), e18802. doi:10.1371/journal.pone.0018802

64.

Rosa-Salva

Regolin

Vallortigara

(2010). Faces are special for newly hatched chicks: Evidence for inborn domain-specific mechanisms underlying spontaneous preferences for face-like stimuli. Developmental Science, 13(4), 565–577.

65.

Rothbart

M. K.

(1981). Measurement of temperament in infancy. Child Development, 52(2), 569–578.

66.

Schwarzer

Freitag

Buckel

Lofruthe

(2012). Crawling is associated with mental rotation ability by 9-month-old infants. Infancy, 18(3), 432–441. doi: https://dx-doi-org.web.bisu.edu.cn/10.1111/j.1532-7078.2012.00132.x

67.

Seifer

(2008). Who should collect our data: Parents or trained observers? In Teti

D. M.

(Ed.), Handbook of Research Methods in Developmental Science (pp. 15–137). Oxford, UK: Blackwell. doi: 10.1002/9780470756676.ch7

68.

Simion

Leo

Turati

Valenza

Barba

B. D.

(2007). How face specialization emerges in the first months of life. From Action to Cognition, 164, 169–185.

69.

Simion

Valenza

Macchi Cassia

Turati

Umilta

(2002). Newborns’ preference for up-down asymmetrical configurations. Developmental Science, 5(4), 427–434.

70.

Skerry

A. E.

Carey

S. E.

Spelke

E. S

. (2013). First-person action experience reveals sensitivity to action efficiency in prereaching infants. Proceedings of the National Academy of Sciences of the United States of America, 110(46), 18728–18733. doi: https://dx-doi-org.web.bisu.edu.cn/10.1073/pnas.1312322110

71.

Slater

Von der Schulenburg

Brown

Badenoch

Butterworth

Parsons

Samuels

(1998). Newborn infants prefer attractive faces. Infant Behavior and Development, 21(2), 345–354. doi: https://dx-doi-org.web.bisu.edu.cn/10.1016/S0163-6383(98)90011-X

72.

Sommerville

J. A.

Woodward

A. L.

Needham

(2005). Action experience alters 3-month-old infants’ perception of others’ actions. Cognition, 96(1), B1–B11. doi: https://dx-doi-org.web.bisu.edu.cn/10.1016/j.cognition.2004.07.004

73.

Soska

K. C.

Adolph

K. E.

Johnson

S. P

. (2010). Systems in development: Motor skill acquisition facilitates three-dimensional object completion. Developmental Psychology, 46(1), 129–138. doi: https://dx-doi-org.web.bisu.edu.cn/10.1037/a0014618

74.

Striano

Reid

V. M.

(2006). Social cognition in the first year. Trends in Cognitive Sciences, 10(10), 471–476. doi: https://dx-doi-org.web.bisu.edu.cn/10.1016/j.tics.2006.08.006

75.

Sugita

(2008). Face perception in monkeys reared with no exposure to faces. Proceedings of the National Academy of Sciences of the United States of America, 105(1), 394–398.

76.

Thelen

Corbetta

Kamm

Spencer

J. P.

Schneider

Zernicke

R. F.

(1993). The transition to reaching: Mapping intention and intrinsic dynamics. Child Development, 64(4), 1058–1098.

77.

Tichacek

(2004). Cross-modal integration of natural visual and auditory stimuli. (Unpublished bachelor thesis). University of Osnabrück, Osnabrück, Germany.

78.

Tottenham

Tanaka

Leon

A. C.

McCarry

Nurse

Hare

T. A.

Nelson

C. A

. (2009). The NimStim set of facial expressions: Judgments from untrained research participants. Psychiatry Research, 168(3), 242–249. doi:10.1016/j.psychres.2008.05.006

79.

Turati

Di Giorgio

Bardi

Simion

(2010). Holistic face processing in newborns, 3-month-old infants, and adults: Evidence from the composite face effect. Child Development, 81(6), 1894–1905. doi:10.1111/j.1467-8624.2010.01520.x

80.

Turati

Simion

Milani

Umilta

(2002). Newborns’ preference for faces: What is crucial? Developmental Psychology, 38(6), 875–882.

81.

Turati

Valenza

Leo

Simion

(2005). Three-month-olds’ visual preference for faces and its underlying visual processing mechanisms. Journal of Experimental Child Psychology, 90(3), 255–273. doi:10.1016/j.jecp.2004.11.001

82.

Tzourio-Mazoyer

De Schonen

Crivello

Reutter

Aujard

Mazoyer

(2002). Neural correlates of woman face processing by 2-month-old infants. Neuroimage, 15(2), 454–461. doi:10.1006/nimg.2001.0979

83.

Valenza

Simion

Cassia

V. M.

Umilta

(1996). Face preference at birth. Journal of Experimental Psychology-Human Perception and Performance, 22(4), 892–903.

84.

van der Fits

I. B. M.

Klip

A. W. J.

van Eykern

L. A.

Hadders-Algra

(1999). Postural adjustments during spontaneous and goal-directed arm movements in the first half year of life. Behavioural Brain Research, 106 (1–2), 75–90.

85.

Wilcox

B. M.

(1969). Visual preferences of human infants for representations of human face. Journal of Experimental Child Psychology, 7(1), 10–20.

86.

Yonas

Hartman

(1993). Perceiving the affordance of contact in four- and five-month-old infants. Child Development, 64(1), 298–308.