Electrophysiological Signals of Familiarity and Recency in the Infant Brain

Dynamic effects of habituation and novelty detection on newborn event-related potentials

Newborns habituate to repeated auditory stimuli, and discriminate syllables, generating opportunities for early language learning. This study investigated trial-by-trial changes in newborn electrophysiological responses to auditory speech syllables as an index of habituation and novelty detection. Auditory event-related potentials (ERPs) were recorded from 16 term newborn infants, aged 1-3 days, in response to monosyllabic speech syllables presented during habituation and novelty detection tasks. Multilevel models demonstrated that newborns habituated to repeated auditory syllables, as ERP amplitude attenuated for a late-latency component over successive trials. Subsequently, during the novelty detection task, early- and late-latency component amplitudes decreased over successive trials for novel syllables only, indicating encoding of the novel speech syllable. We conclude that newborns dynamically encoded novel syllables over relatively short time periods, as indicated by a systematic change in response patterns with increased exposure. These results have important implications for understanding early precursors of learning and memory in newborns.

Nine-month-old infants update their predictive models of a changing environment

Humans generate internal models of their environment to predict events in the world. As the environments change, our brains adjust to these changes by updating their internal models. Here, we investigated whether and how 9-month-old infants differentially update their models to represent a dynamic environment. Infants observed a predictable sequence of stimuli, which were interrupted by two types of cues. Following the update cue, the pattern was altered, thus, infants were expected to update their predictions for the upcoming stimuli. Because the pattern remained the same after the no-update cue, no subsequent updating was required. Infants showed an amplified negative central (Nc) response when the predictable sequence was interrupted. Late components such as the PSW were also evoked in response to unexpected stimuli; however, we found no evidence for a differential response to the informational value of surprising cues at later stages of processing. Infants rather learned that surprising cues always signal a change in the environment that requires updating. Interestingly, infants responded with an amplified neural response to the absence of an expected change, suggesting a top-down modulation of early sensory processing in infants. Our findings corroborate emerging evidence showing that infants build predictive models early in life.

Infant Visual Attention and Stimulus Repetition Effects on Object Recognition

This study examined behavioral, heart rate (HR), and event-related potential (ERP) correlates of attention and recognition memory for 4.5-, 6-, and 7.5-month-old infants (N = 45) during stimulus encoding. Attention was utilized as an independent variable using HR measures. The Nc ERP component associated with attention and the late slow wave (LSW) associated with recognition memory were analyzed. The 7.5-month-olds demonstrated a significant reduction in Nc amplitude with stimulus repetition. This reduction in Nc was not found for younger infants. Additionally, infants only demonstrated differential LSW amplitude based on stimulus type on attentive trials as defined by HR changes. These findings indicate that from 4.5 to 7.5 months, infants' attentional engagement is influenced by an increasingly broader range of stimulus characteristics.

Increased cortical reactivity to repeated tones at 8 months in infants with later ASD

Dysregulation of cortical excitation/inhibition (E/I) has been proposed as a neuropathological mechanism underlying core symptoms of autism spectrum disorder (ASD). Determining whether dysregulated E/I could contribute to the emergence of behavioural symptoms of ASD requires evidence from human infants prior to diagnosis. In this prospective longitudinal study, we examine differences in neural responses to auditory repetition in infants later diagnosed with ASD. Eight-month-old infants with (high-risk: n = 116) and without (low-risk: n = 27) an older sibling with ASD were tested in a non-linguistic auditory oddball paradigm. Relative to high-risk infants with typical development (n = 44), infants with later ASD (n = 14) showed reduced repetition suppression of 40-60 Hz evoked gamma and significantly greater 10-20 Hz inter-trial coherence (ITC) for repeated tones. Reduced repetition suppression of cortical gamma and increased phase-locking to repeated tones are consistent with cortical hyper-reactivity, which could in turn reflect disturbed E/I balance. Across the whole high-risk sample, a combined index of cortical reactivity (cortical gamma amplitude and ITC) was dimensionally associated with reduced growth in language skills between 8 months and 3 years, as well as elevated levels of parent-rated social communication symptoms at 3 years. Our data show that cortical 'hyper-reactivity' may precede the onset of behavioural traits of ASD in development, potentially affecting experience-dependent specialisation of the developing brain.

The Development of Attentional Biases for Faces in Infancy: A Developmental Systems Perspective

We present an integrative review of research and theory on major factors involved in the early development of attentional biases to faces. Research utilizing behavioral, eye-tracking, and neuroscience measures with infant participants as well as comparative research with animal subjects are reviewed. We begin with coverage of research demonstrating the presence of an attentional bias for faces shortly after birth, such as newborn infants' visual preference for face-like over non-face stimuli. The role of experience and the process of perceptual narrowing in face processing are examined as infants begin to demonstrate enhanced behavioral and neural responsiveness to mother over stranger, female over male, own- over other-race, and native over non-native faces. Next, we cover research on developmental change in infants' neural responsiveness to faces in multimodal contexts, such as audiovisual speech. We also explore the potential influence of arousal and attention on early perceptual preferences for faces. Lastly, the potential influence of the development of attention systems in the brain on social-cognitive processing is discussed. In conclusion, we interpret the findings under the framework of Developmental Systems Theory, emphasizing the combined and distributed influence of several factors, both internal (e.g., arousal, neural development) and external (e.g., early social experience) to the developing child, in the emergence of attentional biases that lead to enhanced responsiveness and processing of faces commonly encountered in the native environment.

The effects of stimulus symmetry on hierarchical processing in infancy

The current study investigated the effects of stimulus symmetry on the processing of global and local stimulus properties by 6-month-old short- and long-looking infants through the use of event-related potentials (ERPs). Previous research has shown that individual differences in infant visual attention are related to hierarchical stimulus processing, such that short lookers show a global processing bias, while long lookers demonstrate a local processing bias (Guy, Reynolds, & Zhang, 2013). Additional research has shown that in comparison with asymmetry, symmetry is associated with more efficient stimulus processing and more accurate memory for stimulus configuration (Attneave, 1955; Perkins, 1932). In the current study, we utilized symmetric and asymmetric hierarchical stimuli and predicted that the presence of asymmetry would direct infant attention to the local features of stimuli, leading short lookers to regress to a local processing strategy. Results of the ERP analysis showed that infants familiarized with a symmetric stimulus showed evidence of global processing, while infants familiarized with an asymmetric stimulus did not demonstrate evidence of processing at the global or local level. These findings indicate that short- and long-looking infants, who might otherwise fail to process global stimulus properties due to limited visual scanning, may succeed at global processing when exposed to symmetric stimuli. Furthermore, stimulus symmetry may recruit selective attention toward global properties of visual stimuli, facilitating higher-level cognitive processing in infancy.

Infant visual attention and object recognition

This paper explores the role visual attention plays in the recognition of objects in infancy. Research and theory on the development of infant attention and recognition memory are reviewed in three major sections. The first section reviews some of the major findings and theory emerging from a rich tradition of behavioral research utilizing preferential looking tasks to examine visual attention and recognition memory in infancy. The second section examines research utilizing neural measures of attention and object recognition in infancy as well as research on brain-behavior relations in the early development of attention and recognition memory. The third section addresses potential areas of the brain involved in infant object recognition and visual attention. An integrated synthesis of some of the existing models of the development of visual attention is presented which may account for the observed changes in behavioral and neural measures of visual attention and object recognition that occur across infancy.

The relationship between deferred imitation, associative memory, and communication in 14-months-old children. Behavioral and electrophysiological indices

The present study combines behavioral observations of memory (deferred imitation, DI, after a brief delay of 30 min and after a long delay of 2-3 weeks) and electrophysiological (event-related potentials, ERPs) measures of associative memory, as well as parental reports of non-verbal and verbal communication in sixteen 14-months-old children. Results show that for DI, the children remembered the stimulus after the brief but not after the long delay. There was a clear electrophysiological response indicating associative memory. Furthermore, a correlation between DI and ERP suggests that both measures of memory (DI and associative memory) tap into similar mechanisms in 14-months-old children. There was also a statistically significant relation between parental report of receptive (verbal) language and the ERP, showing an association between receptive language skills and associative memory.

Neural correlates of intersensory processing in 5-month-old infants

Two experiments assessing event-related potentials in 5-month-old infants were conducted to examine neural correlates of attentional salience and efficiency of processing of a visual event (woman speaking) paired with redundant (synchronous) speech, nonredundant (asynchronous) speech, or no speech. In Experiment 1, the Nc component associated with attentional salience was greater in amplitude following synchronous audiovisual as compared with asynchronous audiovisual and unimodal visual presentations. A block design was utilized in Experiment 2 to examine efficiency of processing of a visual event. Only infants exposed to synchronous audiovisual speech demonstrated a significant reduction in amplitude of the late slow wave associated with successful stimulus processing and recognition memory from early to late blocks of trials. These findings indicate that events that provide intersensory redundancy are associated with enhanced neural responsiveness indicative of greater attentional salience and more efficient stimulus processing as compared with the same events when they provide no intersensory redundancy in 5-month-old infants.

The comparator model of infant visual habituation and dishabituation: recent insights

Current knowledge of the perceptual and cognitive abilities in infancy is largely based on the visual habituation-dishabituation method. According to the comparator model [e.g., Sokolov (1963a) Perception and the conditioned reflex. Oxford: Pergamon Press], habituation refers to stimulus encoding and dishabituation refers to discriminatory memory performance. The review also describes the dual-process theory and the attention disengagement approach. The dual-process theory points to the impact of natural stimulus preferences on habituation-dishabituation processes. The attention disengagement approach emphasizes the contribution of the ability to shift the attention away from a stimulus. Moreover, arguments for the cognitive interpretation of visual habituation and dishabituations are discussed. These arguments are provided by physiological studies and by research on interindividual differences. Overall, the review shows that current research supports the comparator model. It emphasizes that the investigation of habituation and dishabituation expands our understanding of visual attention processes in infants.

A meta-analysis investigating factors underlying attrition rates in infant ERP studies

In this meta-analysis, we examined interrelationships between characteristics of infant event-related potential (ERP) studies and their attrition rates. One-hundred and forty-nine published studies provided information on 314 experimental groups of which 181 provided data on attrition. A random effects meta-analysis revealed a high average attrition rate of 49.2%. Additionally, we used meta-regression for 178 groups with attrition data to analyze which variables best explained attrition variance. Our main findings were that the nature of the stimuli-visual, auditory, or combined as well as if stimuli were animated-influenced exclusion rates from the final analysis and that infant age did not alter attrition rates.

Neural Correlates of Individual Differences in Infant Visual Attention and Recognition Memory

Past studies have identified individual differences in infant visual attention based upon peak look duration during initial exposure to a stimulus. Colombo and colleagues (e.g., Colombo & Mitchell, 1990) found that infants that demonstrate brief visual fixations (i.e., short lookers) during familiarization are more likely to demonstrate evidence of recognition memory during subsequent stimulus exposure than infants that demonstrate long visual fixations (i.e., long lookers). The current study utilized event-related potentials to examine possible neural mechanisms associated with individual differences in visual attention and recognition memory for 6- and 7.5-month-old infants. Short- and long-looking infants viewed images of familiar and novel objects during ERP testing. There was a stimulus type by looker type interaction at temporal and frontal electrodes on the late slow wave (LSW). Short lookers demonstrated a LSW that was significantly greater in amplitude in response to novel stimulus presentations. No significant differences in LSW amplitude were found based on stimulus type for long lookers. These results indicate deeper processing and recognition memory of the familiar stimulus for short lookers.