In their first year, infants’ ability to follow eye gaze to allocate attention shifts from being a response to low-level perceptual cues, to a deeper understanding of social intent. By 4 months infants look longer to uncued versus cued targets following a gaze cuing event, suggesting that infants better encode targets cued by shifts in eye gaze compared to targets not cued by eye gaze. From 6 to 9 months of age infants develop biases in face processing such that they show increased differentiation of faces within highly familiar groups (e.g., own-race) and a decreased differentiation of faces within unfamiliar or infrequently experienced groups (e.g., other-race). Although the development of cued object learning and face biases are both important social processes, they have primarily been studied independently. The current study examined whether early face processing biases for familiar compared to unfamiliar groups influences object encoding within the context of a gaze-cuing paradigm. Five- and 10-month-old infants viewed videos of adults, who varied by race and sex, shift their eye gaze towards one of two objects. The two objects were then presented side-by-side and fixation duration for the cued and uncued object was measured. Results revealed 5-month-old infants look significantly longer to uncued versus cued objects when the cuing face was a female. Additionally, 10-month-old infants displayed significantly longer looking to the uncued relative to the cued object when the cuing face was a female and from the infant’s own-race group. These findings are the first to demonstrate that perceptual narrowing based on sex and race shape infants’ use of social cues for allocating visual attention to objects in their environment.

The development of species-typical perceptual preferences has been shown to depend on a variety of socially and ecologically derived sensory stimulation during both the pre- and postnatal periods. The prominent mechanism behind the development of these seemingly innate tendencies in young organisms has been hypothesized to be a domain-general pan-sensory selectivity process referred to as perceptual narrowing, whereby regularly experienced sensory stimuli are honed in upon, while simultaneously losing the ability to effectively discriminate between atypical or unfamiliar sensory stimulation. Previous work with precocial birds has been successful in preventing the development of species-typical perceptual preferences by denying the organism typical levels of social and/or self-produced stimulation. The current series of experiments explored the mechanism of perceptual narrowing to assess the malleability of a species-typical auditory preference in avian embryos. By providing a variety of different unimodal and bimodal presentations of a mixed-species vocalizations at the onset of prenatal auditory function, the following project aimed to 1) keep the perceptual window from narrowing, thereby interfering with the development of a species-typical auditory preference, 2) investigate how long differential prenatal stimulation can keep the perceptual window open postnatally, 3) explore how prenatal auditory enrichment effected preferences for novelty, and 4) assess whether prenatal auditory perceptual narrowing is affected by modality specific or amodal stimulus properties during early development. Results indicated that prenatal auditory enrichment significantly interferes with the emergence of a species-typical auditory preference and increases openness to novelty, at least temporarily. After accruing postnatal experience in an environment rich with species-typical auditory and multisensory cues, the effect of prenatal auditory enrichment rapidly was found to rapidly fade. Prenatal auditory enrichment with extraneous non-synchronous light exposure was shown to both keep the perceptual narrowing window open and impede learning in the postnatal environment, following hatching. Results are discussed in light of the role experience plays in perceptual narrowing during the perinatal period.

In infancy, the ability to tell the difference between two faces within a category (e.g., species, race) that is infrequently experienced declines from 6 to 9 months of age (Kelly et al., 2009, 2007; Pascalis et al., 2005; Pascalis, de Haan, & Nelson, 2002; Scott & Monesson, 2009). This decline in the ability to distinguish faces is known as "perceptual narrowing" and has recently been found to be absent when infants are given experience matching a face with an individual-level proper name between 6 to 9 months of age (Scott & Monesson, 2009). Additionally, individual-level experience between 6 and 9 months of age has led to neural changes at 9 months of age (Scott & Monesson, 2010). It is currently unclear whether brief, early experience between 6 and 9 months leads to sustained behavioral advantages and lasting neural changes. In order to answer these questions, the current study recruited and tested children who previously participated in a face training study when they were infants (Scott & Monesson, 2009, 2010). Findings revealed that individual-level experience with faces during the first year of life: 1) resulted in faster reaction time for faces outside of the trained category, and 2) led to more adult-like neural representations of faces outside of the trained category 3-4 years later. These results suggest that experience with individual-level learning in the first year of life is generalized to visually similar, but environmentally relevant face categories.

During the early stages of infant development the capacity for perceptual (i.e., visual) discrimination is shaped by infants' perceptual experience. Perceptual narrowing is one process hypothesized to account for developmental change. Perceptual narrowing research often demonstrates that infants before 6 months of age are able to discriminate a wide variety of events whereas infants beyond 6 months of age seemingly "lose" some perceptual abilities. Two investigations are proposed to examine the claim that younger, but not older infants can discriminate faces across species. The purpose of Experiment 1 was to determine whether an increase in familiarization and trial times would result in cross-species facial (i.e. faces of macaques) discrimination in 12-month-olds. The hypothesis was supported, adding evidence that perceptual discrimination becomes more constricted, or less efficient with age, but does not decline. Experiment 2 examined whether reducing both the time of familiarization and comparison time by 50% would allow infants sufficient time to discriminate. Results were consistent with the hypothesis and previous studies were corroborated. These findings highlight the important role of perceptual experience in young infants' perceptual discrimination abilities and provide a greater degree of clarity regarding present use of the concept perceptual narrowing.

The theory of perceptual narrowing posits that the ability to make perceptual discriminations is very broad early in development and subsequently becomes more specific with perceptual experience (Scott, Pascalis, & Nelson, 2007). This leads to the formation of biases (Pascalis et al., 2002; 2005; Kelly et al., 2007), including the other-race effect (ORE). Behavioral and electrophysiological measures are used to show that by 9-months-of-age, infants exhibit a decline in ability to distinguish between two faces from another race compared to two faces from within their own race. Significant differences in the P400 component revealed a dampening of response to other-race compared to same-race faces for 9-month-olds only. More negative N290 amplitudes in response to happy compared to sad faces were found for 5-month-olds only. Nine-month-olds did not show different responses based on emotion, indicating that race was interfering with the processing of emotion.

<p>Infants must learn to discriminate between individuals in order to determine who is familiar (and likely to provide their basic needs) from those who are unfamiliar (and possibly a threat to their survival). One cue that humans use to discriminate others is the unique sound of each individual’s voice. Until the present thesis, little research existed on the topic of voice discrimination development during infancy. I conducted the first set of studies to investigate whether voice discrimination develops through a process of perceptual narrowing. Perceptual narrowing is defined as an experience-dependent increase in sensitivity to distinctions important in the native environment and a decrease in sensitivity to distinctions not important (often foreign to) the native environment across the first year. It has been described in previous research for the processing of a number of socially-relevant stimuli in the auditory (e.g., musical rhythms and pitches, linguistic phonemes) and visual (e.g., faces) domains. In Chapter 2, I provide the first evidence that narrowing occurs for voice discrimination, with infants specializing for the discrimination of native (human, English-speaking) over foreign (rhesus monkey) vocalizations between 6 and 12 months. In Chapter 3, I establish that the specialization demonstrated in Chapter 2 resulted primarily from familiarity with the vocalization from the human species, rather than the particular language spoken. In Chapter 4, I show that sensitivity to distinctions between monkey voices can be reinstated at 12 months of age, after narrowing has taken place, with two weeks of exposure to monkey voices. Together, these findings indicate that infants become attuned to individual distinctions between human voices by the end of their first year, but that plasticity remains such that sensitivity to distinctions between voices from rarely-heard species can be reinstated with exposure, at least until the end of the first year.</p> / Doctor of Philosophy (PhD)