One of the overarching questions in the field of infant perceptual and cognitive development concerns how selective attention is organized during early development to facilitate learning. The following study examined how infants’ selective attention to properties of social events (i.e., prosody of speech and facial identity) changes in real time as a function of intersensory redundancy (redundant audiovisual, nonredundant unimodal visual) and exploratory time. Intersensory redundancy refers to the spatially coordinated and temporally synchronous occurrence of information across multiple senses. Real time macro- and micro-structural change in infants’ scanning patterns of dynamic faces was also examined. According to the Intersensory Redundancy Hypothesis, information presented redundantly and in temporal synchrony across two or more senses recruits infants’ selective attention and facilitates perceptual learning of highly salient amodal properties (properties that can be perceived across several sensory modalities such as the prosody of speech) at the expense of less salient modality specific properties. Conversely, information presented to only one sense facilitates infants’ learning of modality specific properties (properties that are specific to a particular sensory modality such as facial features) at the expense of amodal properties (Bahrick & Lickliter, 2000, 2002). Infants’ selective attention and discrimination of prosody of speech and facial configuration was assessed in a modified visual paired comparison paradigm. In redundant audiovisual stimulation, it was predicted infants would show discrimination of prosody of speech in the early phases of exploration and facial configuration in the later phases of exploration. Conversely, in nonredundant unimodal visual stimulation, it was predicted infants would show discrimination of facial identity in the early phases of exploration and prosody of speech in the later phases of exploration. Results provided support for the first prediction and indicated that following redundant audiovisual exposure, infants showed discrimination of prosody of speech earlier in processing time than discrimination of facial identity. Data from the nonredundant unimodal visual condition provided partial support for the second prediction and indicated that infants showed discrimination of facial identity, but not prosody of speech. The dissertation study contributes to the understanding of the nature of infants’ selective attention and processing of social events across exploratory time.

The development of perceptual-cognitive processes during infancy has been traditionally studied using visual habituation and paired-comparison techniques. There has been extensive work within the field of infant attention that has focused on the development of visual attention. Within this field, it has been well established that there are two distinct classifications of infants' visual behavior; infants with short visual fixations who perform well in a recognition task following familiarization and infants with long visual fixation with impaired performance. There are two hypotheses for the differences underlying these groups. First, that visual fixation duration is reflective of the speed of information processing such that long-looking infants process information more slowly than short-looking infants. The second hypothesis is that infants who are long-looking have difficulty disengaging and shifting their attention to another location. There has not been any work exploring how these differences manifest themselves in other modalities. Thus, this project has three purposes: (1) to explore whether group differences emerge in an auditory recognition task similar to those found in the visual recognition phase of the paired-comparison task, (2) to better understand how performance differences in the visual task correspond to any observed differences in an auditory task, and (3) to identify any potential mechanisms which may account for the observed differences in group performance on an auditory task. / Ph. D.

Social engagement has been clearly associated with socio-developmental outcomes in clinical and at-risk populations of infants, who show deficits in gaze following, face processing, and joint attention. Importantly, these are all skills related to language learning. This is most prominently illustrated by individuals with autism, for whom social engagement and language are markedly dysfunctional. In contrast, for typically developing infants the parameters of social engagement and language learning have only been generally defined. The present study was designed to relate infants' social attention to later language outcomes. In this longitudinal study, 11-month-old infants participated in social attention tasks (distracter, gaze following and face scanning tasks); at 14 months, infants returned to participate in language (word/object association) and joint attention (Early Social Communication Scales) tasks; at 18-20 months, caregivers reported on language (vocabulary size) and autistic symptomatology (developmental screening measures). Overall, the results indicated that measures of social attention predict later language outcomes. In particular, joint attention accounted for 13% of the variance in infants' word/object association performance at 14-months. More frequent response to the joint attention bids of an adult female tester (e.g., looking in the direction of her pointing) was associated with better word/object association learning. With regard to vocabulary size, two tasks emerged as significant predictors, the distracter and joint attention tasks, which together accounted for 38% of the variance in language at 18-months. Specifically, longer latencies (i.e., less distractibility) to look away from the face when an adult female was speaking (distracter task) and more frequently responding to the attention bids of the tester were associated with a larger productive vocabulary size. / Ph. D.

Research shows the way adults communicate with children can be classified into two main categories: Adult Directed Speech (ADS) and Infant Directed speech (IDS) (Schachner & Hannon, 2011). Past research focused on the maternal use of IDS; however, the current study investigated differences in maternal and paternal use of IDS. We hypothesize that 1) there will be a difference in the amount of paternal caregiving depending on mothers’ work status, 2) the acoustic properties of IDS will be influenced by the amount of parental involvement in caregiving activities, and 3) infants will pay more attention to parents who use more exaggerated IDS. No changes were found for paternal involvement when mothers were employed compared to when mothers were not employed. No relationships were found between IDS, parental involvement, or infants’ attention. These findings provide a better understanding of fathers’ contributions in caregiving and their influences on infants’ cognitive development.

Infants of various ages across the first postnatal year have shown behavioral preferences (i.e., more attention) to visual displays when looking resulted in the presentation of Infant-Directed Speech (IDS) compared to Adult-Directed Speech (ADS). Although IDS differs from ADS on a variety of measures, most research has focused on various pitch characteristics (i.e., IDS is higher in absolute pitch and more variable in pitch across utterance length). Work from our lab has found that when the pitch characteristics of IDS were held constant, but the temporal features were manipulated, younger (but not older) infants attended more to slower rates of IDS, even though it was unlikely that they had heard such speech (when speech is spoken at this slow rate, the fundamental frequency cannot be maintained). The purpose of this study was to expand our investigation of how speaking rate affects infant attention by adding the physiological measure of heart rate to our protocol. Of specific interest was whether infants would show differential amounts of heart-rate (HR) decelerations as a function of rate (i.e. greater decelerations to slowed speech). 4-month-old infants were tested with normal IDS (unaltered rate) and slow IDS (rate was twice as slow as normal). Behaviorally, infants did not differentially attend to a display as a function of speech type. Psychophysiologically, infants showed more pronounced HR decelerations to slow than to normal IDS. The discrepancy between measures of attention is discussed, especially with regard to the organization of attention in infants of this age. / Master of Science

Infant speech perception develops within the context of specific language experience. While there is a corpus of empirical evidence concerning infants' perception of linguistic and prosodic information in speech, few studies have explored the interaction of the two. The present investigation was designed to combine what is known about infants' perception of nonnative phonemes (linguistic information) with what is known about infant preferences for ID speech (prosodic information). In particular, the purpose of this series of studies was to examine infant preferences for ID speech within the timeline of the phonemic perceptual reorganization that occurs at the end of the first postnatal year. In Experiment 1, 20 Native-English 10- to 11-month-old infants were tested in an infant-controlled preference procedure for attention to ID speech in their native language versus ID speech in a foreign language. The results showed that infants significantly preferred the ID-native speech. In Experiment 2, the preferred prosodic information (ID speech) was separated from the preferred linguistic information (native speech), as a means of discerning the relative perceptual draw of these types of speech characteristics. Specifically, a second group of 20 10- to 11-month-old infants was tested for a preference between ID speech in a foreign language and AD speech in their native language. In this case the infants exhibited a significant preference for ID-foreign speech, suggesting that prosodic information in speech has more perceptual weight than linguistic information. This pattern of results suggests that infants attend to linguistic-level information by 10- to 11-months of age, and that ID speech may play a role in the native-language tuning process by directing infants' attention to linguistic specifics in speech. / Master of Science

Much research has examined how rate affects visual preferences in human infants and auditory preferences in avian infants. In the visual domain, it seems that human infants prefer stimuli (e.g., flashing displays) presented at faster relative rates. Research using avian species has shown that ducklings, for example, prefer their species- specific maternal call only when it is presented at values close to the species-typical mean. These studies have shown that experience affects ducklings'­ preferences for rate in auditory events. Researchers in the areas of human infant preferences for visual rate and avian infant preferences for auditory rate have suggested that an effective window of frequencies exists for which infants show maximal attention. Unlike these two areas, little research has addressed how rate affects human infants' preferences for auditory events. A study by Cooper and Cooper (1997) was the first to find that infants attend to rates of speaking infant directed (ID) speech. Specifically, infants preferred ID speech at its normal rate to ID speech at a faster rate. The present study was intended to further investigate how rate of speaking affected infants' preferences for ID speech. More specifically, this study sought to determine whether a window of effective rates also exists for infant preferences for rate in ID speech. Using an infant-controlled preference procedure, 20 six- to eight-week old infants were presented with ID-normal speech (ID speech as its normal rate) and ID- slow speech (ID speech slowed to half the normal rate). It was found that infants looked longer to a visual display when it was paired with ID-slow speech than when it was paired with ID-normal speech. How these results relate to research and theory on visual rate preferences in human infants and auditory rate in avian species is discussed, as well as future directions for this line of research. / Master of Science

A recent study by Polka, Rvachew, and Molnar (2008) found that 6- to 8-month-old infants do not discriminate a simple native consonant-vowel contrast when familiarized to it in the presence of distraction noise (i.e., recordings of crickets and birds chirping), even when testing was conducted in quiet. Because the distraction noise did not overlap with the phonemes' frequencies, failure to encode the familiarization phoneme could be due more to a disruption in infant attention than to direct masking effects. Given that infants learn speech under natural conditions involving noise and distraction, it is important to identify factors that may 'protect' their speech perception under non-ideal listening conditions. The current study investigated three possible factors: speech register, face information, and speaker gender. Six-month-old infants watched a video of a female speaker producing a native phoneme in either an adult-directed or infant-directed manner accompanied by the same background noise as in Polka et al. (2008). After habituation, infants were tested with alternating trials of the familiar phoneme and a novel phoneme in quiet. Phoneme discrimination was measured by recording infants' heart rate and looking times during familiar and novel trials. Discrimination was poor in infants who viewed a female speaker using adult-directed speech but was significantly improved (as seen in both dependent measures of attention) when the female speaker used infant-directed speech. Results indicate that common factors in the typical environment of infants can promote speech perception abilities in noise. / Master of Science

Infant visual attention develops rapidly over the first year of life, significantly altering the way infants respond to peripheral visual events. Here we present data from 5-, 7- and 10-month-old infants using the Infant Orienting With Attention (IOWA) task, designed to capture developmental changes in visual spatial attention and saccade planning. Results indicate rapid development of spatial attention and visual response competition between 5 and 10 months. We use a dynamic neural field (DNF) model to link behavioral findings to neural population activity, providing a possible mechanistic explanation for observed developmental changes. Together, the behavioral and model simulation results provide new insights into the specific mechanisms that underlie spatial cueing effects, visual competition, and visual interference in infancy.