The inversion effect in infancy: the role of internal and external features

Individual Differences in Infants' Temperament Affect Face Processing

Infants show an advantage in processing female and familiar race faces, but the effect sizes are often small, suggesting individual differences in their discrimination abilities. This research assessed whether differences in 6-10-month-olds' temperament (surgency and orienting) predicted how they scanned individual faces varying in race and gender during familiarization and whether and how long it took them to locate the face during a visual search task. This study also examined whether infants viewing faces posing pleasant relative to neutral expressions would facilitate their discrimination of male and unfamiliar race faces. Results showed that infants' surgency on its own or in conjunction with their orienting regularly interacted with facial characteristics to predict their scanning and location of faces. Furthermore, infants' scanning patterns (dwell times and internal-external fixation shifts) correlated with their ability and time to locate a familiarized face. Moreover, infants who viewed faces with pleasant expressions showed better discrimination of unfamiliar race and male faces compared with infants who viewed neutral faces. Including temperament in the analyses consistently demonstrated its significance for understanding infant face processing. Findings suggest that positive interactions with other-race individuals and men might reduce processing disadvantages for those face types. Locating familiar adults in a timely manner is a crucial skill for infants to develop and these data elucidate factors influencing this ability.

Developing the Own-Race Advantage in 4-, 6-, and 9-Month-Old Taiwanese Infants: A Perceptual Learning Perspective

Previous infant studies on the other-race effect have favored the perceptual narrowing view, or declined sensitivities to rarely exposed other-race faces. Here we wish to provide an alternative possibility, perceptual learning, manifested by improved sensitivity for frequently exposed own-race faces in the first year of life. Using the familiarization/visual-paired comparison paradigm, we presented 4-, 6-, and 9-month-old Taiwanese infants with oval-cropped Taiwanese, Caucasian, Filipino faces, and each with three different manipulations of increasing task difficulty (i.e., change identity, change eyes, and widen eye spacing). An adult experiment was first conducted to verify the task difficulty. Our results showed that, with oval-cropped faces, the 4 month-old infants could only discriminate Taiwanese "change identity" condition and not any others, suggesting an early own-race advantage at 4 months. The 6 month-old infants demonstrated novelty preferences in both Taiwanese and Caucasian "change identity" conditions, and proceeded to the Taiwanese "change eyes" condition. The 9-month-old infants demonstrated novelty preferences in the "change identity" condition of all three ethnic faces. They also passed the Taiwanese "change eyes" condition but could not extend this refined ability of detecting a change in the eyes for the Caucasian or Philippine faces. Taken together, we interpret the pattern of results as evidence supporting perceptual learning during the first year: the ability to discriminate own-race faces emerges at 4 months and continues to refine, while the ability to discriminate other-race faces emerges between 6 and 9 months and retains at 9 months. Additionally, the discrepancies in the face stimuli and methods between studies advocating the narrowing view and those supporting the learning view were discussed.

Eye tracking reveals a crucial role for facial motion in recognition of faces by infants

Current knowledge about face processing in infancy comes largely from studies using static face stimuli, but faces that infants see in the real world are mostly moving ones. To bridge this gap, 3-, 6-, and 9-month-old Asian infants (N = 118) were familiarized with either moving or static Asian female faces, and then their face recognition was tested with static face images. Eye-tracking methodology was used to record eye movements during the familiarization and test phases. The results showed a developmental change in eye movement patterns, but only for the moving faces. In addition, the more infants shifted their fixations across facial regions, the better their face recognition was, but only for the moving faces. The results suggest that facial movement influences the way faces are encoded from early in development.

Developmental origins of the face inversion effect

A hallmark of adults' expertise for faces is that they are better at recognizing, discriminating, and processing upright faces compared to inverted faces. We investigate the developmental origins of "the face inversion effect" by reviewing research on infants' perception of upright and inverted faces during the first year of life. We review the effects of inversion on infants' face preference, recognition, processing (holistic and second-order configural), and scanning as well as face-related neural responses. Particular attention is paid to the developmental patterns that emerge within and across these areas of face perception. We conclude that the developmental origins of the inversion effect begin in the first few months of life and grow stronger over the first year, culminating in effects that are commonly thought to indicate adult-like expertise. We posit that by the end of the first year, infants' face-processing system has become specialized to upright faces and a foundation for adults' upright-face expertise has been established. Developmental mechanisms that may facilitate the emergence of this upright-face specialization are discussed, including the roles that physical and social development may play in upright faces' becoming more meaningful to infants during the first year.

Infants' ability to respond to depth from the retinal size of human faces: comparing monocular and binocular preferential-looking

To examine sensitivity to pictorial depth cues in young infants (4 and 5 months-of-age), we compared monocular and binocular preferential looking to a display on which two faces were equidistantly presented and one was larger than the other, depicting depth from the size of human faces. Because human faces vary little in size, the correlation between retinal size and distance can provide depth information. As a result, adults perceive a larger face as closer than a smaller one. Although binocular information for depth provided information that the faces in our display were equidistant, under monocular viewing, no such information was provided. Rather, the size of the faces indicated that one was closer than the other. Infants are known to look longer at apparently closer objects. Therefore, we hypothesized that infants would look longer at a larger face in the monocular than in the binocular condition if they perceived depth from the size of human faces. Because the displays were identical in the two conditions, any difference in looking-behavior between monocular and binocular viewing indicated sensitivity to depth information. Results showed that 5-month-old infants preferred the larger, apparently closer, face in the monocular condition compared to the binocular condition when static displays were presented. In addition, when presented with a dynamic display, 4-month-old infants showed a stronger 'closer' preference in the monocular condition compared to the binocular condition. This was not the case when the faces were inverted. These results suggest that even 4-month-old infants respond to depth information from a depth cue that may require learning, the size of faces.

Female face preference in 4-month-olds: the importance of hairline

At 3-4 months of age, infants respond to gender information in human faces. Specifically, young infants display a visual preference toward female over male faces. In three experiments, using a visual preference task, we investigated the role of hairline information in this bias. In Experiment 1, we presented male and female composite faces with similar hairstyles to 4-month-olds and observed a preference for female faces. In Experiment 2, the faces were presented, but in this instance, without hairline cues, and the preference was eliminated. In Experiment 3, using the same cropping to eliminate hairline cues, but with feminized female faces and masculinized male faces, infants' preference toward female faces was still not in evidence. The findings show that hairline information is important in young infants' preferential orientation toward female faces.

Sex Differences in Facial Scanning: Similarities and Dissimilarities Between Infants and Adults

When face processing studies find sex differences, male infants appear better at face recognition than female infants, whereas female adults appear better at face recognition than male adults. Both female infants and adults, however, discriminate emotional expressions better than males. To investigate if sex and age differences in facial scanning might account for these processing discrepancies, 3-4-month-olds, 9-10-month-olds, and adults viewed faces presented individually while an eye tracker recorded eye movements. Regardless of age, males shifted fixations between internal and external facial features more than females, suggesting more holistic processing. Females shifted fixations between internal facial features more than males, suggesting more second-order relational processing, which may explain females' emotion discrimination advantage. Older male infants made more fixations than older female infants. Female adults made more fixations for shorter fixation durations than male adults. Male infants and female adults' greater encoding of facial information may explain their face recognition advantage.

Infants' Visual Recognition Memory for a Series of Categorically Related Items

We examined the interactions between visual recognition memory, working memory, and categorization by examining 6-month-old infants' (N = 168) memory for individual items in a categorized list (e.g., images of dogs or cats). In Experiments 1 and 2, infants were familiarized with 6 different cats or dogs, presented one at a time on a series of 15-s familiarization trials. When the test occurred immediately after the sixth familiarization trial (Experiment 1), infants showed strong novelty preference for items presented on the fourth or fifth familiarization trial, but not for the items presented on the first three trials or on the sixth trial. When a brief (15-s) retention delay occurred between the end of the sixth trial and the test trials (Experiment 2), memory for the sixth item was enhanced, memory for the fourth item was impaired, and memory for the fifth was unchanged relative to when no retention delay was included. Experiment 3 confirmed that infants can form a memory for the first item presented. These results reveal how factors such as interference and time to consolidate influence infants' visual recognition memory as they categorize a series of items.

An eye-tracking investigation of developmental changes in infants' exploration of upright and inverted human faces

We used eye-tracking to examine 4.5- to 12.5-month-old infants' (N = 92) eye-movements during 3-s presentations of upright and inverted faces. Scanning of inverted faces was statistically indistinguishable at 4.5, 6.5, 8, and 12.5 months of age; at each of these ages infants disproportionately scanned the region containing the eyes. Scanning of upright faces changed over this age range. When viewing upright faces, 4.5-month-old and 6.5-month-old infants focused disproportionately on the region containing the eyes, whereas 12.5-month-old and 8-month-old infants distributed looking more broadly, scanning more of the internal area of the faces. These results are consistent with other observed developmental differences in face processing, and provide insight into how moment-to-moment face processing changes during infancy.

Where and how infants look: the development of scan paths and fixations in face perception

It is well known that infants prefer faces but relatively little is known about how infants look at face. The present work examined the development of face perception by using the scan paths. Infants (aged 6-13.5 months) and adults were presented with images of upright and inverted faces, and looking times and scan paths were compared. Similarity between participants' scan paths demonstrated that infants collect facial information more efficiently from upright faces than from inverted faces, and this ability gradually develops with age. Analyses of looking times also revealed that preferences for upright faces were gradually replaced by preferences for inverted faces by approximately 10 months of age. The results indicate that the processing of configural information gradually develops throughout infancy.

Race-Based Perceptual Asymmetry in Face Processing Is Evident Early in Life

Adults' processing of own-race faces differs from that of other-race faces. The presence of an "other-race" feature (ORF) has been proposed as a mechanism underlying this specialization. We examined whether this mechanism, which was previously identified in adults and in 9-month-olds, is evident at 3.5 months. Caucasian 3.5-month-olds looked longer at a pattern containing a single Asian face among seven Caucasian faces than at a pattern containing a single Caucasian face among seven Asian faces. Homogenous and inverted face control conditions indicated that infants' preference was not driven by the majority of faces in arrays or by low-level features. Thus, 3.5-month-olds found the presence of an other-race face among own-race faces to be more salient than the reverse configuration. This asymmetry suggests sensitivity to an ORF at 3.5 months. Thus, a key mechanism of race-based processing in adults has an early onset, indicating rapid development of specialization early in life.