Fair Flom Jones and Martin 2012 - BYU Infant Lab

Child Development, November/December 2012, Volume 83, Number 6, Pages 1996–2006

Perceptual Learning: 12-Month-Olds’ Discrimination of Monkey Faces Joseph Fair, Ross Flom, Jacob Jones, and Justin Martin Brigham Young University

Six-month-olds reliably discriminate different monkey and human faces whereas 9-month-olds only discriminate different human faces. It is often falsely assumed that perceptual narrowing reflects a permanent change in perceptual abilities. In 3 experiments, ninety-six 12-month-olds’ discrimination of unfamiliar monkey faces was examined. Following 20 s of familiarization, and two 5-s visual-paired comparison test trials, 12-montholds failed to show discrimination. However, following 40 s of familiarization and two 10-s test trials, 12-month-olds showed reliable discrimination of novel monkey faces. A final experiment was performed demonstrating 12-month-olds’ discrimination of the monkey face was due to the increased familiarization rather than increased time of visual comparison. Results are discussed in the context of perceptual narrowing, in particular the flexible nature of perceptual narrowing.

Ever since Robert Fantz (1961) first placed infants in his ‘‘looking chamber’’ and observed that 1- to 5-month-olds show a visual preference for schematic faces compared to geometric patterns and scrambled faces, a large body of empirical and theoretical work has accrued examining the developmental course of face perception. Moreover, the development of face perception is pertinent to our understanding of cognitive, linguistic, and social development and vice versa. Infants’ discrimination and recognition of faces is also relevant to our broader knowledge of early development and has become one of the most widely studied areas of infant development (see Barrera & Maurer, 1981; Farah, Wilson, Drain, & Tanaka, 1998; Johnson, Dziurawiec, Ellis, & Morton, 1991; Nelson, 2001; Pascallis & Kelly, 2009; Slater et al., 2010, for reviews). One facet of perception and early development that has garnered a great deal of attention in recent years is perceptual narrowing. Perceptual narrowing typically occurs during the first 9–12 months of an infant’s life where their perceptual systems become attuned to those properties or features that are frequently encountered or experienced. Likewise, their perceptual systems become attenuated to those This research was supported by the Brigham Young University (BYU) Family Studies Center and a BYU undergraduate mentoring grant awarded to the second author. A portion of these data were presented at the International Conference on Perception and Action, Minneapolis, MN, July 2009, and the International Conference for Infant Studies, Baltimore, MD, March 2010. Correspondence concerning this article should be addressed to Ross Flom, Department of Psychology, Brigham Young University, Provo, UT 84602. Electronic mail may be sent to flom@ byu.edu.

properties or features of objects and events that are not frequently encountered or experienced (Nelson, 2001; Scott, Pascalis, & Nelson, 2007). Evidence of perceptual narrowing has been found in infants’ auditory discrimination of phonemes (e.g., Werker & Tees, 1984), their perceptual discrimination of faces of another species (e.g., Pascalis, de Haan, & Nelson, 2002; Simpson, Varga, Frick, & Fragaszy, 2011), as well as their discrimination of faces of other races (e.g., Kelly et al., 2007). Finally, evidence of perceptual narrowing in human infants has also been shown in the area of cross-species intersensory (auditory–visual) matching (e.g., Lewkowicz & Ghazanfar, 2006; Lewkowicz, Sowinski, & Place, 2008; cf. Flom, Whipple, & Hyde, 2009). One of the first, and perhaps most well-known examples of perceptual narrowing, is infants’ discrimination of speech phonemes. Werker and colleagues (Werker, Gilbert, Humphrey, & Tees, 1981; Werker & Tees, 1984) have shown that 7-month-old infants discriminate native and nonnative phonemes; however, by 12 months of age, infants only discriminate native phonemes. Specifically, Werker et al. (1981) examined whether Hindispeaking adults, English-speaking adults, and 7-month-olds born to English-speaking adults could discriminate Hindi retroflex and dental stops ( ⁄ Ta ⁄ & ⁄ ta ⁄ ) as well as Hindi voiced and voiceless dental stops ( ⁄ th ⁄ & ⁄ dh ⁄ ). Their results revealed that

2012 The Authors Child Development 2012 Society for Research in Child Development, Inc. All rights reserved. 0009-3920/2012/8306-0012 DOI: 10.1111/j.1467-8624.2012.01814.x

Perceptual Learning

7-month-old infants and Hindi-speaking adults were able to discriminate the Hindi retroflex and dental stops as well as voiced and voiceless stops whereas the English-speaking adults did not show discrimination for either contrast (Werker et al., 1981). Interestingly, however, they did find limited evidence that the English-speaking adults (who had minimal exposure to Hindi during their first 2 years of life) discriminated the Hindi voiced and voiceless contrast if they were given additional training. Thus, the results of Werker and colleagues (Werker & Tees, 1984; Werker et al., 1981) and others (e.g., Oh, Jun, Knightly, & Au, 2003) are important as they highlight the experience-dependent and somewhat flexible nature of perceptual narrowing using speech phonemes (see Werker & Tees, 2005, for a review). Just as infants’ auditory discrimination of speech phonemes is affected by their social and cultural experiences, infants’ visual discrimination of faces is also affected by similar experiences. One of the clearest examples of this phenomenon is known as the ‘‘other race effect’’ (ORE). The ORE is defined as discriminating or recognizing faces within one’s own ethnicity but not showing this perceptual discrimination or recognition for faces of a different or unfamiliar ethnicity (see Meissner & Brigham, 2001, for a review). Early experiments with children found evidence of the ORE in 6- to 8-year-olds (Chance, Turner, & Goldstein, 1982; Feinman & Entwhistle, 1976). More recently, however, there is evidence of the ORE emerging sometime between 3 and 6 months of age (Bar-Haim, Ziv, Lamy, & Hodes, 2006; Kelly et al., 2005; Kelly et al., 2007). Like infants’ discrimination of native and nonnative phonemes, infants’ discrimination of faces of other races is also somewhat flexible. For example Sangrigoli and de Schonen (2004) demonstrated, using a visual paired comparison (VPC) procedure, that 3month-olds are able to discriminate faces within their own ethnicity but not faces of a different and unfamiliar ethnicity. These same infants, however, did show reliable discrimination of faces of an unfamiliar ethnicity using a different procedure (i.e., infant-controlled habituation). In addition, Sangrigoli, Pallier, Argenti, Ventureyra, and de Schonen (2005) found that Korean adults who were adopted into Caucasian families in Europe (i.e., primarily French families) between 3 and 9 years of age showed discrimination of Caucasian faces. Moreover, the facial discrimination of the adoptees did not differ from the native French adults but did differ from native Koreans who moved to France as adults (Sangrigoli et al., 2005). Thus, it seems that

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the ORE, although robust, is not a permanent decline. Instead, it seems that the discrimination of faces of another race is largely affected by one’s social and cultural experiences throughout childhood (see Bar-Haim et al., 2006, for additional evidence of this flexibility, but see de Heering, de Liedekerke, Deboni, & Rossion, 2010, for evidence showing less flexibility). Just as infants’ discrimination of speech phonemes and faces of other races are subject to perceptual narrowing, infants’ discrimination of faces of another species is also subject to perceptual narrowing. For example, Pascalis et al. (2002) provided 6- and 9-month-olds, as well as adults, with 20 s of familiarization (adults only received 5 s of familiarization) to either an unfamiliar human face or unfamiliar monkey face and following familiarization participants received two 5-s VPC test trials. Results revealed that 6- and 9-month-olds, as well as the adults, showed reliable discrimination of the human faces but only the 6-month-olds showed reliable discrimination of the monkey faces. The results of Pascalis et al. (2002) suggest that infants’ discrimination of faces, like speech perception and the ORE, is initially fairly broad and over time becomes more specific to those types of faces frequently encountered (Scott et al., 2007). In a follow-up experiment Pascalis et al. (2005) examined the plasticity of infants’ discrimination of monkey faces by providing 6-month-olds with folders containing pictures of six unfamiliar monkey faces where parents were asked to show these pictures to their infant for 1–2 min each day (see Pascalis et al., 2005, p. 5298). Results revealed that 6-month-olds showed reliable discrimination of the monkey faces, thus replicating their prior experiment (Pascalis et al., 2002). Importantly, the results of Pascalis et al. (2005) also revealed that the now 9month-olds (i.e., those infants who received additional exposure to the monkey faces) still showed reliable discrimination of monkey faces whereas a second group of 9-month-olds who did not receive the 3 months of training failed to show reliable discrimination. Although Pascalis et al. (2005) showed exposure can maintain infants’ discrimination of monkey faces, more recent research has examined what type of exposure promotes infants continued discrimination of monkey faces. Scott and Monesson (2009) found that 6-month-olds who were trained for 3 months with individually named monkey faces (i.e., Boris, Dario, etc.) continued to show discrimination of these same faces at 9 months of age. In contrast, 6-month-olds who received additional

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Fair, Flom, Jones, and Martin

exposure but no labeling, or 6-month-olds who received a categorical label (i.e., monkey), failed to show reliable discrimination of unfamiliar monkey faces at 9 months of age. Specifically, the authors state that this individualization of faces may lead infants to ‘‘attend to the unique features of . . . monkey faces’’ whereas category-level naming or mere exposure training led them to ‘‘focus on what the monkey faces have in common’’ (p. 678). The results of Pascalis et al. (2005) and Scott and Monesson (2009) are important as they demonstrate that perceptual narrowing of unfamiliar monkey faces can be delayed when provided additional exposure or when infants learn to individuate unfamiliar monkey faces. In general, infants’ visual discrimination of monkey faces (like the ORE) and infants’ discrimination of speech phonemes follow a similar trajectory where the infants’ perceptual system is initially quite broad and over time become attuned to the experiences of the infant. It has also been shown that infants can maintain the ability to discriminate speech phonemes as well as faces of other races and faces of other species if they continue to receive either exposure early in development (Bar-Haim et al., 2006; Oh et al., 2003; Pascalis et al., 2005; Sangrigoli et al., 2005; Werker & Tees, 1984; Werker et al., 1981) or are taught to individuate faces (Scott & Monesson, 2009). This area of research is important as it highlights the somewhat flexible nature of face and speech perception. Specifically, continued exposure and experience maintain infants’ discrimination of various speech sounds and faces—or delay the onset of perceptual narrowing. However, it is not known whether, and under what conditions, infants’ discrimination of faces of another species (i.e., unfamiliar monkey faces) remains possible once they have reached an age where discrimination is typically not evident. That is, experience can maintain an existing ability (Pascalis et al., 2005), but research is needed that examines whether, and under what conditions, experience leads to the ‘‘re-emergence’’ of perceptual discrimination of previously unfamiliar faces of another species once perceptual narrowing has occurred. One purpose of this study (Experiment 1) was to examine whether we could replicate the general pattern of results found by Pascalis and colleagues (Pascalis et al., 2002; Pascalis et al., 2005), specifically whether perceptual narrowing has occurred for 12-month-olds’ discrimination of faces of an unfamiliar species. A second purpose (Experiment 2) was to examine whether 12-month-olds would discriminate unfamiliar monkey faces when pro-

vided (a) increased familiarization time and (b) increased time to visually compare the two unfamiliar faces. We also examined (Experiment 3) whether 12-month-olds’ discrimination in Experiment 2 was a result of increased familiarization time, increased time to visually compare the two faces, or whether both were necessary. Twelvemonth-olds were chosen for as participants in all three experiments because they represent an age where perceptual narrowing of faces of other species is hypothesized to have occurred. Finally, the significance of examining whether, and under what conditions, 12-month-olds show reliable discrimination of unfamiliar monkey faces is that it allows us to examine the degree of openness or flexibility of the perceptual system and it may provide insights into the changing nature of children’s early face representations (Valentine, 1991). Experiment 1 The purpose of Experiment 1 was to examine whether we could replicate the general pattern of results found by Pascalis and colleagues (Pascalis et al., 2002; Pascalis et al., 2005). In Experiment 1, twenty-four 12-month-olds were familiarized to an image of one unfamiliar Barbary macaque for 20 s and following familiarization each infant received two 5-s VPC test trials. During the VPC test trials, infants’ preference for the novel or familiar face was assessed. Following the two test trials (i.e., Block 1) infants were familiarized to a second face (i.e., Block 2) and then received two additional 5-s VPC test trials. Based on the results of Pascalis and colleagues (Pascalis et al., 2002; Pascalis et al., 2005), it was predicted that 12-month-olds would fail to reliably discriminate the face of familiarization and a novel face of another unfamiliar Barbary macaque. Method Participants. Twenty-four 12-month-olds (12 females, M = 359 days, SD = 15 days) and one of the infant’s parents, primarily mothers, participated. Four additional infants (16%) participated; however, their data were excluded from the final analyses due to fussiness during familiarization (2) and experimenter error (2). Twenty-two of the 24 participants were White of non-Hispanic origin (92%), 1 participant was Hispanic (4%), and 1 participant was Pacific Islander (4%). Socioeconomic status for the participants was not collected. All participants were healthy, normal, full-term infants weighing at

Perceptual Learning

least 5 pounds at birth, with 5-min Apgar scores of 7 or higher. Infants were recruited from a database maintained at the university. Parents were contacted and recruited by telephone. Stimuli. The same 24 color pictures of Barbary macaques used in Pascalis et al. (2005) were used in this experiment to create 12 pairings (6 easy and 6 hard pairings). Sample pairings used in the current experiment are shown in Figure 1. See Pascalis et al. (2005) for details regarding image properties and editing. As in Pascalis et al., the pairing of each of the faces was completed by the authors and was done such that each pairing was similar but distinguishable. The 12 pairs of photos were labeled by the authors and three undergraduates as being a hard or easy to discriminate. Ratings of easy or hard were made by having each rater rank order the pairings in terms of the degree of discriminability and the six pairs that received the highest ranking were labeled as hard, the six pairs that received the lowest ranking were labeled as easy. Infants were randomly assigned to view one hard and one easy pairing. Half of the infants viewed a hard pairing during Block 1 (i.e., Trials 1–2) and half viewed an easy pairing during Block 1. Apparatus. The experiment took place in a quiet testing room. Infants were seated in an infant chair Hard Pairing

Easy Pairing

Figure 1. One hard and one easy pairing of the Barbary macaques (Macaca sylvanus) used in Experiments 1–3.

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on a table facing a three-panel display. The panels were covered with dark gray cloth. All stimulus events were viewed on two 25-in. (63.5 cm) color video monitors (Sony KV-20M10; Sony Electronics, San Diego, CA) 70 cm from the seated infant. Two experimenters, unaware of the hypotheses of the experiment and unable to view the visual events, monitored infants’ visual fixations by depressing a button while the infant fixated on the event and released it while the infant looked away. The button box was connected to a computer programmed to record visual fixations online. The signal was transmitted to a third experimenter through a small headphone. The observations of the first experimenter were used as the dependent variable (infants’ looking time) and the observations of a second experimenter (present on 50% of the participants) were used in the calculation of interobserver reliability. The third experimenter controlled the presentation of the faces. Procedure. Upon arrival at the laboratory, the purpose and the procedure of the experiment were explained to the parent and informed consent was obtained. The infant was seated in front of the video monitors and the parent was seated behind their infant. Parents were asked to sit as still as possible and asked not to say anything to their infant during the experiment. Once the infant was looking forward and their gaze was between the two monitors, two warm-up trials were presented. On each warmup trial, the infant was presented with a static and silent human face on one monitor for 4 s and then on the second monitor for 4 s. Warm-up trials were included to highlight to the infant that two monitors were being used and to make sure that the infant could turn and look toward each monitor. No infant was excluded for failing the warm-up trials. Following the two warm-up trials, infants were presented with one monkey face presented simultaneously on both monitors. Like Pascalis et al. (2005), infants were familiarized to the monkey face until each infant reached 20 s of cumulative looking. The mean time to reach 20 s of cumulative looking was 26 s (SD = 4 s). Following familiarization and a brief 2-s interstimulus interval where both monitors were blank, infants were presented with two 5-s VPC test trials. During each VPC test trial, the infant viewed the monkey face of familiarization and a novel monkey face. During the second test trial, the lateral position of the familiar and novel faces was reversed. Following the two 5-s VPC test trials, infants were given a 2-min break. Following this break, the procedure was repeated with each infant using a different pairing of monkey faces.

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Results and Discussion Two criteria were set for the data of the participants to be included in the analyses. Infants were required to complete all four VPC test trials. An attention criterion was also included and required infants look at least 5% of the time to the least preferred face. All participants met these two criteria. Interoberserver reliability was calculated by correlating the visual fixation scores of the primary and secondary observers across the VPC test trials for each infant and it averaged 0.93 (SD = 0.11). An analysis of variance (ANOVA) was first performed with gender of the infant as a main factor and revealed no significant effect of gender in terms of the time required to reach familiarization, F(1, 22) = 0.022, p > .1, or overall looking during the test trials, F(1, 22) = 0.03, p > .1. We also examined whether infants’ discrimination differed based on whether the pairing was rated as hard or easy. The results of this analysis also failed to reach significance F(1, 22) = 1.6, p > .1. Thus, all further analyses were collapsed across participant gender and pairing of faces. The primary dependent variable in Experiment 1 was infants’ looking toward the novel face. Results are expressed in terms of the proportion of total looking time (PTLT) to the novel face. Proportions were derived for each trial separately by dividing the time spent looking to the novel face by the time spent looking at both faces. A separate PTLT was computed for the second face (i.e., second set of test trials or Block 2). Finally, we averaged each infant’s PTLT across both Blocks 1 and 2 and then averaged across all infants. Proportions above 0.50 reflect novelty preferences and proportions below 0.50 reflect familiarity preferences. To assess infants’ preference for novel face, we compared the mean PTLT against the chance value of 0.50 (an equivalent proportion of time spent looking toward each face). Proportions of looking to the novel and familiar face are presented in Table 1. Across both blocks, infants’ looking to the novel face (M = 0.524, SD = 0.06) failed to reach significance t(23) = 1.92, p > .05. Likewise, infants’ looking behavior in Block 1 (M = 0.524, SD = 0.07) and Block 2 (M = 0.525, SD = 0.09) also failed to exceed chance (both ps > .10). Thus, in Experiment 1, when provided 20 s of familiarization and two 5-s VPC test trials, 12-month-olds failed to show reliable evidence of discrimination, replicating Pascalis and colleagues (Pascalis et al., 2002; Pascalis et al., 2005). In addition, infants’ average duration

Table 1 Infants’ Proportion of Total Looking Time (PTLT) to the Novel Face Combined (Blocks 1 and 2)

Block 1 (Trials 1 and 2)


Experiment 1: 20-s familiarization and 4- to 5-s test trials PTLT to the novel face M 0.524 0.524 0.525 Range 0.39–0.62 0.41–0.70 0.36–0.72 SD 0.06 0.07 0.09 Number of infants who showed a preference for the novel face N = 24 16 14 13 Time (s) to reach familiarization M 26.31 26.22 26.4 Range 21.56–34.71 20.0–35.69 20.0–43.88 SD 3.61 3.29 5.49 Experiment 2: 40-s familiarization and 4- to 10-s test trials PTLT to the novel face M 0.574** 0.575** 0.572** Range 0.45–0.73 0.34–0.80 0.34–0.71 SD 0.07 0.11 0.09 Number of infants who showed a preference for the novel face N = 24 22** 19** 20** Time (s) to reach familiarization M 57.23 55.77 55.75 Range 45.37–82.94 41.00–89.12 42.39–94.00 SD 10.54 10.69 12.65 **p < .01.

of time required to reach the 20 s of accumulated looking to the face of familiarization did not differ across Blocks 1 and 2 (p > .10) nor did infants’ looking during the test trials for Block 1 or Block 2 (p > .1). Because infants did not take longer, across Blocks 1 and 2, in terms of the time to reach 20 s of cumulative looking and familiarization, or the time spent looking to the faces during the test trials, it is concluded that infants did not become bored or overly fatigued with the experiment. Finally, from an individual subjects perspective, across Blocks 1 and 2, 16 of 24 infants preferred the novel face and this did not differ from chance, v2(1, n = 24) = 0.67, p = .41. The results of the 12-month-olds in Experiment 1 are consistent with the results of Pascalis and colleagues (Pascalis et al., 2002; Pascalis et al., 2005) as they demonstrated that by 9-months of age, infants no longer discriminate unfamiliar monkey faces. The purpose of Experiment 2 was to examine 12month-olds’ flexibility in discriminating unfamiliar monkey faces. Specifically, if 12-month-olds are given more time to become familiarized to each face, and are given more time to visually compare the two faces, will they show reliable discrimination?

Perceptual Learning

Experiment 2 The purpose of Experiment 2 was to examine whether increasing the amount of time of familiarization from 20 to 40 s and increasing the VPC test trials from 5 to 10 s affect 12-month-olds’ discrimination of unfamiliar monkey faces. All stimuli, apparatus, and procedures were identical to Experiment 1 with the exceptions of (a) doubling the amount of time for familiarization (40 vs. 20 s) and (b) doubling the length of each VPC test trial (10 vs. 5 s). Method Twenty-four 12-month-olds (18 females, M = 359 days, SD = 14 days) and one of the infant’s parents, primarily mothers, participated. Six additional infants (25%) participated; however, their data were excluded from the final analyses. Three infants were excluded for fussiness during familiarization and one for fussiness during the test trials. One infant was excluded for equipment failure and one infant was excluded for experimenter error. Twenty-three of the 24 participants were White of non-Hispanic origin (96%) and 1 participant was Hispanic (4%). Socioeconomic status for the participants was not collected. All participants were healthy, normal, full-term infants weighing at least 5 pounds at birth, with 5-min Apgar scores of 7 or higher. Infants were recruited in a manner identical to Experiment 1. Results and Discussion As in Experiment 1, two criteria were set for the data of the participants to be included in the analyses. Infants were required to complete all four VPC test trials and infants were required to look at least 5% of the time to the least preferred face. All participants met these two criteria. Interoberserver reliability was again calculated by correlating the visual fixation scores of the primary and secondary observers across the VPC test trials for nine infants (37.5%) and it averaged 0.91 (SD = 0.14). An ANOVA was performed with gender of the infant as a main factor and revealed no significant effects of participant gender for time to reach familiarization, F(1, 22) = 0.193, p > .1, or looking during the test trials, F(1, 22) = 0.913, p > .1. As in Experiment 1, infants’ discrimination did not differ based on whether the pairing was rated as hard or easy, F(1, 22) = 0.054, p > .1. Thus, all analyses were again collapsed across participant gender and pairing of faces.

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The primary dependent variable in Experiment 2 was infants’ looking toward the novel face and was computed in a manner identical to Experiment 1. Infants’ proportions of looking to the novel and familiar face in Experiment 2 are presented in Table 1. Overall, infants’ looking to the novel face (M = 0.574, SD = 0.07) significantly differed from chance, t(23) = 4.91, p < .01. Infants’ looking behavior in Block 1 (M = 0.575, SD = 0.11) and Block 2 (M = 0.572, SD = 0.09) also exceeded chance, t(23) = 3.29, p < .01; t(23) = 3.77, p < .01. Thus, 12month-olds in Experiment 2, when provided 40 s of familiarization and two 10-s VPC test trials showed reliable evidence of discrimination. From an individual subjects perspective, across Blocks 1 and 2, 22 of 24 infants preferred the novel face and this differed from chance, v2(1, n = 24) = 16.7, p < .01. Nineteen infants in Block 1 and 20 infants in Block 2 showed a preference for the novel face, and this too differed from chance, v2(1, n = 24) = 8.2, p < .01; v2(1, n = 24) = 10.7, p < .01 for Blocks 1 and 2, respectively. Finally, infants’ average duration of time required to reach the 40 s of accumulated looking to the face of familiarization did not differ across Blocks 1 and 2 (p > .10) nor did infants’ looking during the test trials for Block 1 or Block 2 (p > .1). Because Experiments 1 and 2 only differed in terms of the length of familiarization and the length of the VPC test trials, we compared infants’ visual preference to the novel face in Experiment 2 with infants’ visual preference to the novel face in Experiment 1. Results of this analysis revealed that infants’ overall novelty preference in Experiment 2 (M = 0.574, SD = 0.07) reliably differed from Experiment 1 (M = 0.524, SD = 0.06), t(46) = 2.45, p < .05. The results of Experiment 2 are important as they indicate that 12-month-olds visually discriminate previously unfamiliar monkey faces when the time of familiarization and the time to visually compare the faces are doubled. In addition, the results of Experiment 2 are not due to a few infants showing relatively large or strong preferences as 80% or more of the infants in each block showed a preference for the novel face. In Experiment 2, the decision to increase the time of familiarization, as well as the test trial (i.e., visual-paired comparison) time, was done a priori; thus, in Experiment 2, we could not directly examine whether infants’ discrimination was due to the increase in familiarization time or was a result of the increased test trial time. The purpose of Experiment 3 was to examine whether 12-month-olds’ discrimination in Experiment 2 was a result of the

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increase in familiarization time, an increase in test trials, or whether both were necessary. Experiment 3 One purpose of Experiment 3 was to examine whether we could replicate the results of Experiment 2. We also examined in Experiment 3 whether 12-month-olds’ discrimination in Experiment 2 was the result of increased familiarization time or possibly increased length of the test trials. All stimuli and apparatus were identical to Experiment 2. Method Participants. Forty-eight 12-month-olds (24 females, M = 366 days, SD = 4 days) and one of the infant’s parents, primarily mothers, participated. Ten additional infants (21%) participated; however, their data were excluded from the final analyses. Six infants were excluded for fussiness during familiarization and two infants were excluded for fussiness during the test trials. One infant was excluded for equipment failure and one infant was excluded for experimenter error. Forty-three (90%) of the participants were White of non-Hispanic origin, 4 (8%) were Hispanic, and 1 (2%) participant was Asian. Socioeconomic status for the participants was not collected. All participants were healthy, normal, full-term infants weighing at least 5 pounds at birth, with 5-min Apgar scores of 9 or higher. Infants were recruited in a manner identical to Experiments 1 and 2. Procedure. In Experiment 3, participants were randomly assigned to the long familiarization (40 s) and short test trial (5 s) condition (n = 24) or the short familiarization (20 s) and long test trial (10 s) condition (n = 24). All other procedures were identical to Experiments 1 and 2. Results and Discussion As in previous experiments, infants were required to complete all four VPC test trials and infants were to notice that there were two faces side by side. All participants met these two criteria. Interoberserver reliability was again calculated by correlating the visual fixation scores of the primary and secondary observers across the VPC test trials for 20 infants (42%) and it averaged .90 (SD = 0.23). The primary dependent variable in Experiment 3 was infants’ proportion of time spent looking

toward the novel face and was computed in a manner identical to Experiments 1 and 2. An ANOVA was performed with gender of the infant as a main factor and revealed no significant effects of participant gender for time to reach familiarization, F(1, 46) = 1.3, p > .1, or looking during the test trials, F(1, 46) = 2.0, p > .1. As in Experiments 1 and 2, infants’ discrimination did not differ based on whether the pairing was rated as hard or easy, F(1, 46) = 0.78, p > .1. Thus, all analyses were collapsed across participant gender and pairing of faces. The proportion of time 12-month-olds looked to the novel face with the long familiarization (40 s) and short test trials (5 s) is presented in Table 2. In both Blocks 1 and 2 combined, infants’ looking to the novel face (M = 0.56, SD = 0.10) significantly differed from chance t(23) = 2.87, p < .01. Likewise, infants’ looking behavior in Block 1 (M = 0.55, SD = 0.10) and Block 2 (M = 0.57, SD = 0.15) also exceeded chance, t(23) = 2.35, p < .05; t(23) = 2.34, p < .05. Because this condition of Experiment 3 and Experiment 2 differed only in the length of the test

Table 2 Infants’ Proportion of Total Looking Time (PTLT) to the Novel Face Combined (Blocks 1 and 2)



Experiment 3: 40-s familiarization and 4- to 5-s test trials (long familiarization and short test trials) PTLT to the novel face M 0.561** 0.549* 0.573* Range 0.39–0.78 0.38–0.75 0.31–0.79 SD 0.10 0.10 0.15 Number of infants who showed a preference for the novel face N = 24 18* 16 17 Time (s) to reach familiarization M 52.7 51.1 54.2 Range 41.5–73.2 41.1–65.0 41.8–90.0 SD 8.57 6.8 12.3 Experiment 3: 20-s familiarization and 4- to 10-s test trials (short familiarization long test trials) PTLT to the novel face M 0.516 0.513 0.519 Range 0.40–0.73 0.33–0.82 0.20–0.70 SD 0.08 0.08 0.14 Number of infants who showed a preference for the novel face N = 24 15 14 12 Time (s) to reach familiarization M 25.7 25.5 25.9 Range 21.9–36.0 21.3–32.5 21.5–39.6 SD 2.9 3.0 4.2 *p < .05. **p < .01.

Perceptual Learning

trials (5 vs. 10 s), but not in the length of familiarization (40 s), we examined infants’ looking behavior across these two groups. Using an independent samples t test, infants’ looking behavior in Block 1, Block 2, and Blocks 1 and 2 combined did not reliably differ (all ps > .1). From an individual subjects perspective, across Blocks 1 and 2 combined, when 12-month-olds were provided longer familiarization and shorter test trials, 18 of 24 infants preferred the novel face and this differed from chance, v2(1, n = 24) = 4.2, p < .05. Sixteen infants in Block 1 and 17 infants in Block 2 showed a preference for the novel face and this failed to differ from chance (both ps > .1). The proportion of time 12-month-olds looked to the novel face with the short familiarization (20 s) and long test trials (10 s) is also presented in Table 2. In both blocks combined, infants’ looking to the novel face (M = 0.52, SD = 0.08) failed to differ from chance, t(23) = 1.13, p > .1. Likewise infants’ looking behavior in Block 1 (M = 0.51, SD = 0.08) and Block 2 (M = 0.52, SD = 0.14) also failed to exceed chance (both ps > .1). From an individual subjects perspective, across Blocks 1 and 2 combined, Block 1, and Block 2, the number of infants who showed a preference for the novel face failed to differ from chance (all ps > .1). Again, using an independent samples t test, we compared infants’ novelty preference from this condition of Experiment 3 and Experiment 2 where these two groups differed in the amount of familiarization (20 vs. 40 s) but not in the length of the test trials (10 s). Results revealed that infants’ novelty preference was greater in Experiment 2 in Block 1, t(46) = 2.14, p < .05; and Blocks 1 and 2 combined, t(46) = 2.63, p < .05; but not Block 2, t(46) = 1.51, p > .05. Thus, it appears 12-month-olds’ novelty preference in Experiments 2 and 3 is due to the increased familiarization time rather than increased test trial or comparison time. In the long familiarization condition, infants’ average duration of time required to reach the 40 s of accumulated looking to the face of familiarization did not differ across Blocks 1 and 2 (p > .10) nor did infants’ looking during the test trials for Block 1 or Block 2 (p > .1). Similarly, no difference in time to reach familiarization was observed in the short familiarization condition across Blocks 1 and 2. In both conditions, the looking behavior of males and females did not differ in the time to reach familiarization or their visual preference for the novel face. The results of Experiment 3 demonstrate that 12month-olds’ discrimination (i.e., preference) for the novel face is based on the increased exposure dur-

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ing familiarization rather than the increased time to compare the faces during the test trials. The results of Experiment 2 and the results of the long familiarization condition of Experiment 3 also demonstrate that infants’ preference for the novel face is not a result of a few infants with strong visual preferences. General Discussion In Experiment 1, using the stimuli from Pascalis et al. (2005) and the same duration of familiarization and test trials used in Pascalis and colleagues (Pascalis et al., 2002; Pascalis et al., 2005), we demonstrated that 12-month-olds fail to reliably discriminate unfamiliar monkey faces. In Experiment 2, by increasing the time of familiarization and the duration of the test trials, 12-month-olds discriminated unfamiliar monkey faces. The results of Experiment 3 replicate and extend the results of Experiment 2. The results of Experiment 3 demonstrate that 12-month-olds’ discrimination of monkey faces occurred when provided an increased familiarization phase but not when provided increased test trials. As articulated and demonstrated by others (e.g., Pascalis, & Kelly, 2009; Pascalis et al., 2005; Scott et al., 2007), infants’ perception of faces becomes attuned to those faces frequently encountered. However, as shown in Experiments 2 and 3, infants’ discrimination of faces of an unfamiliar species remains more flexible than previously demonstrated. From a theoretical and empirical perspective, the results of these experiments extend our understanding of what has been described as perceptual narrowing. Within the framework of perceptual narrowing, it has been consistently shown that infants’ discrimination of speech phonemes, faces of other races, faces of other species, and infants’ intersensory perception becomes attuned or ‘‘tuned in’’ to certain properties or features that are frequently encountered. According to Werker and Tees (2005), one possible reason that infants become more sensitive to phonological contrasts within their native language, and less sensitive to phonological contrasts outside their nonnative language, is to promote infants’ discrimination of meaningful phonological distinctions as well as their differentiation of higher order phonological structures. From our perspective, learning to discriminate faces or features of faces within a particular species or race, however, does not mean that in many cases infants cannot learn to discriminate between features or faces of

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another race or species. Thus, what is often neglected in this literature is whether and under what conditions infants discriminate a particular property or feature after perceptual narrowing of that property has occurred (see Werker & Tees, 2005, for examples with speech). The fact that we were able to demonstrate that 12-month-olds’ discriminate unfamiliar monkey faces raises the issue as to whether perceptual narrowing requires a decline or loss of some related perceptual ability. The results of these experiments demonstrate that a permanent loss of some ability is not an accurate characterization of this perceptual narrowing (cf. Sugita, 2008). Still, we often read ‘‘we observed a specialization of the face-processing system, as shown by the loss of ability to discriminate between faces from other species’’ (see Pascalis et al., 2005, p. 5300; emphasis added). Other examples include ‘‘. . . only 6-month olds can also discriminate two monkey faces’’ (Pascalis et al., 2005, p. 5298; emphasis added); ‘‘. . . 10- to 12-month-olds can only discriminate the phonetic variations used in their native language . . . [and] 9-month-old infants and adults show a marked advantage for recognizing only human faces’’ (Pascalis et al., 2002, p. 1321; emphasis added); ‘‘. . . the ability to individuate monkey faces is absent in 9month-old infants and in adults’’ (Kelly et al., 2005, p. 1085; emphasis added). Using words such as only, absent, or loss to describe perceptual narrowing, although convenient and somewhat commonplace in this literature, is misleading. Critically however, it is unlikely that the authors cited earlier would conclude that various perceptual discriminations do not happen beyond an optimal period. For example, Scott et al. (2007) point out that 9-month-olds continue to exhibit neural but not behavioral discrimination of monkey faces stating, ‘‘thus, perceptual narrowing may not reflect the complete erasure of neural connections, making these systems flexible and ready to be reactivated at a later period in time’’ (p. 201). Therefore, the belief or assumption that perceptual narrowing leads to a loss or absence of some ability is likely perpetuated, somewhat ironically, by narrow descriptions or explanations of this perceptual phenomenon. From our perspective, it seems the current results, along with those of Pascalis and others (Pascalis et al., 2002; Pascalis et al., 2005), are equally consistent within a framework of perceptual learning. More specifically, and as defined by Gibson and Pick (2000, p. 10), ‘‘perceptual learning is a change toward a closer correspondence with

the environment and this has implications for development as children in the normal course of growing up distinguish among more and more features of the world that they encounter.’’ The current results, along with several other studies (e.g., Kelly et al., 2007; Pascalis et al., 2002; Pascalis et al., 2005; Werker & Tees, 1984; Werker et al., 1981), demonstrate that human infants’ perceptual systems do become attuned to their environment. Given the somewhat flexible nature of this perceptual process, we may be better suited using terms such as perceptual attunement and attenuation rather than perceptual narrowing. That is, perceptual attunement and attenuation, like perceptual narrowing, captures the experience-dependent processes but does not imply the same degree of permanency. The fact that others have shown that continued experience or exposure can modify when perceptual narrowing (or perceptual attenuation) occurs (Pascalis et al., 2005; Scott & Monesson, 2009), and the current results that perceptual discrimination is possible after narrowing has occurred, demonstrate substantial flexibility within the process of perceptual development. However, it is worth noting that Sugita (2008) showed that there might be less flexibility within the perceptual system. Sugita examined monkeys’ discrimination of human faces and monkey faces, when, from birth, they were deprived of seeing faces for a period ranging from 6 to 24 months. Prior to their subsequent exposure to faces, but following their period of facial deprivation, monkeys preferred human and monkey faces equally over other nonface stimuli, and could distinguish between novel and familiar faces, whereas age-matched controls could only discriminate between monkey faces. In addition, 1 month following the deprivation period, half of the monkeys were exposed to either human faces or monkey faces. At the end of this initial exposure period, the monkeys were placed in a normal environment that enabled them to interact with humans and monkeys daily. Even after a year of exposure to both human and monkey faces, those monkeys who were first exposed to human faces significantly preferred human faces, whereas those first exposed to monkey faces significantly preferred monkey faces. The results of Sugita demonstrate that facial processing may become less flexible over time and further illustrates the active debate within this area of perceptual development and the need for additional research examining the flexibility of the perceptual system. One possibility for future research includes examining infants’ discrimination of human faces

Perceptual Learning

concurrently with their discrimination of faces of another species. The current results show that extending the period of familiarization promotes infants’ discrimination of unfamiliar monkey faces after perceptual narrowing has occurred. It is quite likely, however, that infants’ discrimination of monkey faces remains impaired, or attenuated, relative to their discrimination of human faces. Another possibility, based on Hunter and Ames’s (1988) exploratory looking model and Bahrick and Pickens’s (1995) four-phase model of visual attention, where infants initially show a familiarity preference and with increasing amounts of exposure or familiarization infants’ familiarity preference shifts to a null preference and then shifts to a novelty preference, one would predict that for human faces infants would transition through these phases, or visual preferences, earlier than for faces of another species. Thus, additional research is needed that examines infants’ discrimination of faces for familiar and unfamiliar species and that systematically varies the amount or degree of familiarization and, of course, the age of the infant or child (Simpson, Varga, Frick, & Fragaszy, 2011). Finally, nearly all of the research within the domain of perceptual development has focused on whether and when infants’ perceptual discrimination of various properties or features emerges—or more recently, declines (see Lewkowicz & Ghazanfar, 2009; for a review). The results of the current study bring to light the need for research that examines the specific conditions and circumstances whereby infants and young children are able to discriminate various objects and events. It is clear that infants’ experiences affect the ease (or difficulty) with which they are able to make certain perceptual discriminations. Based on these results, as well as the results of others (e.g., Oh et al., 2003; Sangrigoli et al., 2005; Werker & Tees, 1984; Werker et al., 1981), there is flexibility, or openness, of the perceptual system in making various perceptual discriminations. What is less clear, however, is the degree of flexibility within the perceptual systems, as well as the nature and timing of various experiences necessary in promoting and maintaining infants’ discrimination of various properties or features. The results of this study provide another step in examining the flexibility of this perceptual process. References Bahrick, L. E., & Pickens, J. N. (1995). Infant memory for object motion across a period of three-months: Implica-

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tions for a four-phase attention function. Journal of Experimental Child Psychology, 59, 343–371. Bar-Haim, Y., Ziv, T., Lamy, D., & Hodes, R. M. (2006). Nature and nurture in own-race face processing. Psychological Science, 17, 159–163. Barrera, M. E., & Maurer, D. (1981). The perception of facial expressions by the three-month-old. Child Development, 52, 203–206. Chance, J. E., Turner, A.L., & Goldstein, A. G. (1982). Development of differential recognition for own- and other-race faces. Journal of Psychology, 112, 29–37. de Heering, A., de Liedekerke, C., Deboni, M., & Rossion, B. (2010). The role of experience during childhood in shaping the other-race effect. Developmental Science, 13, 181–187. Fantz, R. (1961). The origin of form perception. Scientific American, 204, 66–72. Farah, M. J., Wilson, K. D., Drain, M., & Tanaka, J. N. (1998). What is ‘‘special’’ about face perception? Psychological Review, 105, 482–498. Feinman, S., & Entwhistle, D. R. (1976). Children’s ability to recognize other children’s faces. Child Development, 47, 506–510. Flom, R., Whipple, H., & Hyde, D. (2009). Infants’ intermodal perception of canine (Canis familairis) faces and vocalizations. Developmental Psychology, 45, 1143–1151. Gibson, M. J., & Pick, A. (2000). An ecological approach to perceptual learning and development. New York: Oxford University Press. Hunter, M. A., & Ames, E. W. (1988). A multifactor model of infant preferences for novel and familiar stimuli. Advances in Infancy Research, 5, 69–95. Johnson, M. H., Dziurawiec, S., Ellis, H., & Morton, J. (1991). Newborns’ preferential tracking of face-like stimuli and its subsequent decline. Cognition, 40, 1–19. Kelly, D. J., Quinn, P. C., Slater, A. M., Lee, K., Ge, L., & Pascalis, O. (2007). The other-race effect develops during infancy: Evidence of perceptual narrowing. Psychological Science, 18, 1084–1089. Kelly, D. J., Quinn, P. C., Slater, A. M., Lee, K., Gibson, A., Smith, M., et al. (2005). Three-month-olds, but not newborns, prefer own-race faces. Developmental Science, 8, 31–36. Lewkowicz, D. J., & Ghazanfar, A. A. (2006). The decline of cross-species intersensory perception in human infants. Proceedings of the National Academy of Sciences of the United States of America, 103, 6771–6774. Lewkowicz, D. J., & Ghazanfar, A. A. (2009). The emergence of multisensory systems through perceptual narrowing. Trends in Cognitive Science, 13, 470–478. Lewkowicz, D. J., Sowinski, R., & Place, S. (2008). The decline of cross-species intersensory perception in human infants: Underlying mechanisms and its developmental persistence. Brain Research, 1242, 291–302. Meissner, C. A., & Brigham, J. C. (2001). Thirty years of investigating the own-race bias memory for faces: A meta-analytic review. Psychology, Public Policy, & Law, 7, 3–35.

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Nelson, C. A. (2001). The development and neural bases of face recognition. Infant and Child Development, 10, 3– 18. Oh, J. S., Jun, S.-A., Knightly, L. M., & Au, T. K. (2003). Holding on to childhood language memory. Cognition, 86, 53–64. Pascalis, O., de Haan, M., & Nelson, C. A. (2002). Is face processing species-specific during the first year of life? Science, 296, 1321. Pascalis, O., & Kelly, D. J. (2009). On the development of face processing Perspective in Psychological Science, 4, 200–209. Pascalis, O., Scott, L. S., Kelly, D. J., Shannon, R. W., Nicholson, E., Coleman, M., et al. (2005). Plasticity of face processing in infancy. Proceedings of the National Academy of Sciences of the United States of America, 102, 5297–5300. Pascallis, O., & Kelly, D. J. (2009). The origins of face processing in humans: Phylogeny and ontogeny. Perspectives on Psychological Science, 4, 200–209. Sangrigoli, S., & de Schonen, S. (2004). Effect of visual experience on face processing: A developmental study of inversion and non-native effects. Developmental Science, 7, 74–87. Sangrigoli, S., Pallier, C., Argenti, A. M., Ventureyra, V. A. G., & de Schonen, S. (2005). Reversibility of the other-race effect in face recognition during childhood. Psychological Science, 16, 440–444. Scott, L. S., & Monesson, A. (2009). The origin of biases in face perception. Psychological Science, 20, 676–680. Scott, L. S., Pascalis, O., & Nelson, C. A. (2007). A domain-general theory of the development of percep-

tual discrimination. Current Directions in Psychological Science, 16, 197–201. Simpson, E., Varga, K., Frick, J., & Fragaszy, D. (2011). Infants experience perceptual narrowing for nonprimate faces. Infancy, 16, 318–328. Simpson, E., Varga, K., Frick, J., & Fragaszy, D. (2011, April). Developmental changes in animal face discrimination. Poster presented at the biennial meeting for Society for Research in Child Development, Montreal, Quebec. Slater, A., Quinn, P. C., Kelly, D. J., Lee, K., Longmore, C. A., McDonald, P. R., et al. (2010). The shaping of the face space in early infancy: Becoming a native face processor. Child Development Perspectives, 4, 205–211. Sugita, Y. (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, 394–398. Valentine, T. (1991). A unified account of the effects of distinctiveness, inversion, and race in face recognition. Quarterly Journal of Experimental Psychology, 43, 161–204. Werker, J. F., Gilbert, J. H., Humphrey, K., & Tees, R. C. (1981). Developmental aspects of cross-language speech perception. Child Development, 52, 349–355. Werker, J. F., & Tees, R. C. (1984). Cross-language speech perception: Evidence for perceptual reorganization during the first year of life. Infant Behavior and Development, 7, 49–63. Werker, J. F., & Tees, R. C. (2005). Speech perception as a window for understanding plasticity and commitment in language systems of the brain. Developmental Psychobiology, 46, 233–234.