Infant information processing and family history of specific language impairment: converging evidence for RAP deficits from two paradigms

An infant's ability to process auditory signals presented in rapid succession (i.e. rapid auditory processing abilities [RAP]) has been shown to predict differences in language outcomes in toddlers and preschool children. Early deficits in RAP abilities may serve as a behavioral marker for language-based learning disabilities. The purpose of this study is to determine if performance on infant information processing measures designed to tap RAP and global processing skills differ as a function of family history of specific language impairment (SLI) and/or the particular demand characteristics of the paradigm used. Seventeen 6- to 9-month-old infants from families with a history of specific language impairment (FH+) and 29 control infants (FH-) participated in this study. Infants' performance on two different RAP paradigms (head-turn procedure [HT] and auditory-visual habituation/recognition memory [AVH/RM]) and on a global processing task (visual habituation/recognition memory [VH/RM]) was assessed at 6 and 9 months. Toddler language and cognitive skills were evaluated at 12 and 16 months. A number of significant group differences were seen: FH+ infants showed significantly poorer discrimination of fast rate stimuli on both RAP tasks, took longer to habituate on both habituation/recognition memory measures, and had lower novelty preference scores on the visual habituation/recognition memory task. Infants' performance on the two RAP measures provided independent but converging contributions to outcome. Thus, different mechanisms appear to underlie performance on operantly conditioned tasks as compared to habituation/recognition memory paradigms. Further, infant RAP processing abilities predicted to 12- and 16-month language scores above and beyond family history of SLI. The results of this study provide additional support for the validity of infant RAP abilities as a behavioral marker for later language outcome. Finally, this is the first study to use a battery of infant tasks to demonstrate multi-modal processing deficits in infants at risk for SLI.     

Habituation to repeated stress: get used to it

Habituation, as described in the landmark paper by Thompson et al. [Thompson, R. F., & Spencer, W. A. (1966). Habituation: A model phenomenon for the study of neuronal substrates of behavior. Psychological Review, 73(1), 16–43], is a form of simple, nonassociative learning in which the magnitude of the response to a specific stimulus decreases with repeated exposure to that stimulus. A variety of neuronal and behavioral responses have been shown to be subject to habituation based on the criteria presented in that paper. It has been known for several decades that the magnitude of hypothalamic–pituitary–adrenal (HPA) activation occurring in response to a stressor declines with repeated exposure to that same stressor. For some time this decline has been referred to as “habituation” in the stress neurobiology literature. However, how this usage compares to the definition proposed by Thompson and Spencer has not been systematically addressed. For this special issue, we review the stress neurobiology literature and examine the support available for considering declines in HPA response to repeated stress to be response habituation in the sense defined by Thompson and Spencer. We conclude that habituation of HPA activity meets many, but not all, important criteria for response habituation, supporting the use of this term within the context of repeated stress. However, we also propose that response habituation can, at best, only partially explain the phenomenon of HPA habituation, which also involves well-known negative feedback mechanisms, activation of broad stress-related neural circuitry and potentially more complex associative learning mechanisms.     

Attentional focus moderates habituation–language relationships: slow habituation may be a good thing

An interesting paradox in the developmental literature has emerged in which fast‐habituating babies tend to be temperamentally difficult and fast language learners, even though temperamentally difficult babies tend to be slow language learners. The purpose of the present investigation was to examine whether the paradoxical relationships among habituation, temperamental difficulty, and language acquisition could be mediated partly or wholly by infant attentional focus, because the latter also tends to correlate with temperamental difficulty and vocabulary size. Forty mother–infant dyads were followed from child age 5–20‐months. Results replicated those of Tamis‐LeMonda and Bornstein (Child Develop 1989, 60, 738–751): measures of visual habituation at 5 months were related to 13‐month vocabulary. However, relationships between 5‐month habituation and 20‐month vocabulary were moderated by temperamental attentional focus. For children low in attentional focus, 5‐month habituation was related negatively to 20‐month productive vocabulary; whereas for children high in attentional focus, early habituation was positively related to later vocabulary. Results are consistent with a model of habituation in which volitional attentional focus overrides basic attentional mechanisms that occur during habituation. Copyright © 2008 John Wiley & Sons, Ltd.     

Infant visual habituation and parental psychological distress

Research is equivocal concerning the relationship between parental psychological distress and infant cognitive functioning. Four potential limitations of the literature are addressed: reliance on mothers' but not fathers' psychological distress, use of categorical measures of psychological distress, use of standardized measures of infant cognitive functioning, and failure to take into account potential gender differences. Ninety‐nine twin pairs and both their mothers and fathers were assessed. Infants cognitive functioning was assessed using an infant‐controlled habituation–recovery–dishabituation task. Maternal and paternal psychological distress was assessed using the Symptom Check List‐90‐Revised. No gender differences were obtained for infant visual information‐processing abilities or parental psychological distress. Maternal and paternal psychological distress was related to female visual encoding abilities only. It was concluded that parental psychological distress might degrade parent–infant interactions. Characteristics of girls when faced with parents exhibiting psychiatric difficulties may exacerbate difficulties of parent–infant interactions, thereby hindering the full development of cognitive abilities involved in the process of habituation. A need exists to examine the relationship between parental psychological distress and infant visual attention separately for girls and boys. ©2001 Michigan Association for Infant Mental Health.     

Behavioral and neuronal attributes of short- and long-term habituation in the crab Chasmagnathus

Investigations using invertebrate species have led to a considerable progress in our understanding of the mechanisms underlying learning and memory. In this review we describe the main behavioral and neuronal findings obtained by studying the habituation of the escape response to a visual danger stimulus in the crab Chasmagnathus granulatus. Massed training with brief intertrial intervals lead to a rapid reduction of the escape response that recovers after a short term. Conversely, few trials of spaced training renders a slower escape reduction that endures for many days. As predicted by Wagner’s associative theory of habituation, long-term habituation in the crab proved to be determined by an association between the contextual environment of the training and the unconditioned stimulus. By performing intracellular recordings in the brain of the intact animal at the same time it was learning, we identified a group of neurons that remarkably reflects the short- and long-term behavioral changes. Thus, the visual memory abilities of crabs, their relatively simple and accessible nervous system, and the recording stability that can be achieved with their neurons provide an opportunity for uncovering neurophysiological and molecular events that occur in identifiable neurons during learning.     

Only the right noise? Effects of phonetic and visual input variability on 14‐month‐olds' minimal pair word learning

Seminal work by Werker and colleagues (Stager & Werker [1997] Nature, 388, 381–382) has found that 14‐month‐old infants do not show evidence for learning minimal pairs in the habituation‐switch paradigm. However, when multiple speakers produce the minimal pair in acoustically variable ways, infants' performance improves in comparison to a single speaker condition (Rost & McMurray [2009] Developmental Science, 12, 339–349). The current study further extends these results and assesses how different kinds of input variability affect 14‐month‐olds' minimal pair learning in the habituation‐switch paradigm testing German learning infants. The first two experiments investigated word learning when the labels were spoken by a single speaker versus when the labels were spoken by multiple speakers. In the third experiment we studied whether non‐acoustic variability, implemented by visual variability of the objects presented together with the labels, would also affect minimal pair learning. We found enhanced learning in the multiple speakers compared to the single speaker condition, confirming previous findings with English‐learning infants. In contrast, visual variability of the presented objects did not support learning. These findings both confirm and better delimit the beneficial role of speech‐specific variability in minimal pair learning. Finally, we review different proposals on the mechanisms via which variability confers benefits to learning and outline what may be likely principles that underlie this benefit. We highlight among these the multiplicity of acoustic cues signalling phonemic contrasts and the presence of relations among these cues. It is in these relations where we trace part of the source for the apparent paradoxical benefit of variability in learning.     

Neurogenetic approaches to habituation and dishabituation in Drosophila

We review work in the major model systems for habituation in Drosophila melanogaster, encompassing several sensory modalities and behavioral contexts: visual (giant fiber escape response, landing response); chemical (proboscis extension reflex, olfactory jump response, locomotory startle response, odor-induced leg response, experience-dependent courtship modification); electric (shock avoidance); and mechanical (leg resistance reflex, cleaning reflex). Each model system shows several of Thompson and Spencer’s [Thompson, R. F., & Spencer, W. A. (1966). Habituation: A model phenomenon for the study of neuronal substrates of behavior. Psychological Review, 73, 16–43] parametric criteria for habituation: spontaneous recovery and dishabituation have been described in almost all of them and dependence of habituation upon stimulus frequency and stimulus intensity in the majority. Stimulus generalization (and conversely, the delineation of stimulus specificity) has given insights into the localization of habituation or the neural architecture underlying sensory processing.The strength of Drosophila for studying habituation is the range of genetic approaches available. Mutations have been used to modify specific neuroanatomical structures, ion channels, elements of synaptic transmission, and second-messenger pathways. rutabaga and dunce, genes of the cAMP signal pathway that have been studied most often in the reviewed experiments, have also been implicated in synaptic plasticity and associative conditioning in Drosophila and other species including mammals. The use of the Gal4/UAS system for targeting gene expression has enabled genetic perturbation of defined sets of neurons. One clear lesson is that a gene may affect habituation differently in different behaviors, depending on the expression, processing, and localization of the gene product in specific circuits. Mutations of specific genes not only provide links between physiology and behavior in the same circuit, but also reveal common mechanisms in different paradigms of behavioral plasticity. The rich repertoire of models for habituation in the fly is an asset for combining a genetic approach with behavioral, anatomical and physiological methods with the promise of a more complete understanding.     

Visual habituation in human infants: development and rearing circumstances

Summary Habituation is a type of learning that reflects changing responsiveness to repeated information. In two longitudinal studies, we examined individual differences, stability, and developmental change in the ontogeny of visual habituation in human infants across the middle of the first year of life. To study this phenomenon in breadth, we tested infants from two social classes within the same culture and infants from two different cultures. Infants demonstrated significant, but comparable, individual differences in habituation across socioeconomic and cultural variations in rearing circumstances; they showed significant, if moderate, stability in habituation; and they habituated significantly more quickly with age. These results are interpreted in terms of developing human beings' increasing efficiency in processing visual information near the beginning of extrauterine life.     

Using dynamic field theory to rethink infant habituation

Much of what psychologists know about infant perception and cognition is based on habituation, but the process itself is still poorly understood. Here the authors offer a dynamic field model of infant visual habituation, which simulates the known features of habituation, including familiarity and novelty effects, stimulus intensity effects, and age and individual differences. The model is based on a general class of dynamic (time-based) models that integrate environmental input in varying metric dimensions to reach a single decision. Here the authors provide simulated visual input of varying strengths, distances, and durations to 2 coupled and interacting fields. The 1st represents the activation that drives "looking," and the 2nd, the inhibition that leads to "looking away," or habituation. By varying the parameters of the field, the authors simulate the time course of habituation trials and show how these dynamics can lead to different depths of habituation, which then determine how the system dishabituates. The authors use the model to simulate a set of influential experiments by R. Baillargeon (1986, 1987a, 1987b) using the well-known "drawbridge" paradigm. The dynamic field model provides a coherent explanation without invoking infant object knowledge. The authors show that small changes in model parameters can lead to qualitatively different outcomes. Because in typical infant cognition experiments, critical parameters are unknown, effects attributed to conceptual knowledge may be explained by the dynamics of habituation.     

Influences of information processing and disengagement in infants' looking behaviour

The present study considers the joint influences of information processing and disengagement in looking behaviour within a habituation paradigm. Six‐month‐old infants were habituated, during which their heart rate (HR) was measured. A parametric model of habituation yielded for each infant parameter estimates of their habituation performance. These parameters were interpreted as assessing information processing and disengagement. Corresponding measures were obtained from the HR data. The HR measures and habituation model parameter estimates were significantly correlated, as predicted. In addition, an attention getter, presented prior to each habituation trial, influenced indicators of information processing, but not of disengagement. Results confirmed the advantages of a modelling approach. In addition, and more importantly, findings led to the conclusion that both information processing as well as disengagement are involved in infants' looking behaviour in visual habituation. Copyright © 2009 John Wiley & Sons, Ltd.     

Analyses of habituation in Caenorhabditis elegans

Although the nonassociative form of learning, habituation, is often described as the simplest form of learning, remarkably little is known about the cellular processes underlying its behavioral expression. Here, we review research on habituation in the nematode Caenorhabditis elegans that addresses habituation at behavioral, neural circuit, and genetic levels. This work highlights the need to understand the dynamics of a behavior before attempting to determine its underlying mechanism. In many cases knowing the characteristics of a behavior can direct or guide a search for underlying cellular mechanisms. We have highlighted the importance of interstimulus interval (ISI) in both short- and long-term habituation and suggested that different cellular mechanisms might underlie habituation at different ISIs. Like other organisms, C. elegans shows both accumulation of habituation with repeated training blocks and long-term retention of spaced or distributed training, but not for massed training. Exposure to heat shock during the interblock intervals eliminates the long-term memory for habituation but not the accumulation of short-term habituation over blocks of training. Analyses using laser ablation of identified neurons, and of identified mutants have shown that there are multiple sites of plasticity for the response and that glutamate plays a role in long-term retention of habituation training.     

Visual variability affects early verb learning

Research demonstrates that within‐category visual variability facilitates noun learning; however, the effect of visual variability on verb learning is unknown. We habituated 24‐month‐old children to a novel verb paired with an animated star‐shaped actor. Across multiple trials, children saw either a single action from an action category (identical actions condition, for example, travelling while repeatedly changing into a circle shape) or multiple actions from that action category (variable actions condition, for example, travelling while changing into a circle shape, then a square shape, then a triangle shape). Four test trials followed habituation. One paired the habituated verb with a new action from the habituated category (e.g., ‘dacking’ + pentagon shape) and one with a completely novel action (e.g., ‘dacking’ + leg movement). The others paired a new verb with a new same‐category action (e.g., ‘keefing’ + pentagon shape), or a completely novel category action (e.g., ‘keefing’ + leg movement). Although all children discriminated novel verb/action pairs, children in the identical actions condition discriminated trials that included the completely novel verb, while children in the variable actions condition discriminated the out‐of‐category action. These data suggest that – as in noun learning – visual variability affects verb learning and children's ability to form action categories.     

Early learning as ontogenetic adaptation for ingestion by rats

Ontogenetic adaptation is an “ecological” concept in which mammalian maturation is seen as a coordinated sequence of specializations (stages) that enables the infant to survive within a sequence of distinct niches created by the parent(s) and the rest of the environment. Natural selection is presumed to operate at each point in development. The development of ingestive behavior in the rat pup as a series of ontogenetic adaptations enabling the infant while in the nursing niche to obtain and utilize mother's milk and progress gradually into the feeding niche in which a variety of solid foods must either be obtained or avoided is discussed. Data to show that learning is an integral part of these ontogenetic adaptations for ingestion are reviewed and interpreted. Preweanling rats that are capable of learning and remembering toxiphobic food aversions do not display an aversion to a flavor conditioned stimulus (CS) paired with illness if the CS is presented during suckling. In contrast, 20-day-old pups (weanlings) trained identically do show conditioned taste aversions under these conditions. A perspective of ontogenetic adaptations to this phenomenon of “blockade of toxiphobia by suckling” and its dissolution at weaning is applied. The generality of the blockade phenomenon and its mechanisms are explored, and it is shown that feeding experience regulates the stage-appropriate learning strategies used by the pups.     

Intermodal perception at birth: Intersensory redundancy guides newborn infants’ learning of arbitrary auditory−visual pairings

In this study the ability of newborn infants to learn arbitrary auditory–visual associations in the absence versus presence of amodal (redundant) and contingent information was investigated. In the auditory-noncontingent condition 2-day-old infants were familiarized to two alternating visual stimuli (differing in colour and orientation), each accompanied by its ‘own’ sound: when the visual stimulus was presented the sound was continuously presented, independently of whether the infant looked at the visual stimulus. In the auditory-contingent condition the auditory stimulus was presented only when the infant looked at the visual stimulus: thus, presentation of the sound was contingent upon infant looking. On the post-familiarization test trials attention recovered strongly to a novel auditory–visual combination in the auditory-contingent condition, but remained low, and indistinguishable from attention to the familiar combination, in the auditory-noncontingent condition. These findings are a clear demonstration that newborn infants’ learning of arbitrary auditory–visual associations is constrained and guided by the presence of redundant (amodal) contingent information. The findings give strong support to Bahrick’s theory of early intermodal perception.     

Habituation, response to novelty, and dishabituation in human infants: tests of a dual-process theory of visual attention

Two experiments were conducted to test a dual-process theory of infants' performance on visual habituation-dishabituation tasks. The findings demonstrate that (a) infant habituation functions are often nonmonotonic, with fixation increasing before the eventual response waning; (b) this initial increment in responding is related to stimulus "complexity"; (c) response to novelty is enhanced by increasing the "complexity" of the novelty-test stimulus; and (d) dishabituation, followed by decay, occurs for familiarized patterns when retested after the introduction of a "complex" stimulus, but not after introduction of a "simple" stimulus. Following P. Groves and R. Thompson (1970, Psychological Review, 77, 419-450) we propose that infant visual attention to repeated presentations of a stimulus involves two processes, habituation and sensitization.     

Distinguishing novelty and familiarity effects in infant preference procedures

This paper considers possible problems researchers might face when interpreting the results of studies that employ variants of the preference procedure. Infants show a tendency to shift their preference from familiar to novel stimuli with increasing exposure to the familiar stimulus, a behaviour that is exploited by the habituation paradigm. This change in attentional preference with exposure leads us to suggest that researchers interested in infants' pre‐experimental or spontaneous preferences should beware of the potentially confounding effects of exposing infants to familiarization trials prior to employing the preference procedure. The notion that infant attentional preference is dynamic also calls into question the use of the direction of post‐familiarization preference per se when interpreting the knowledge or strategies available to infants. We look into the results of a cross‐modal word learning study to show how the interpretation of results may be difficult when infants exhibit a significant preference in an unexpected direction. As a possible solution to this problem we propose that significant preferences in both directions should be sought at multiple intervals over time. Copyright © 2004 John Wiley & Sons, Ltd.     

Perception of internal elements of compound figures by one-month-old infants

Previous research has shown that infants younger than 2 months frequently concentrate their attention on peripheral or external features of visual stimuli and that they do not appear to process the internal elements of a compound visual stimulus composed of a simple geometric figure enclosed in a larger figure. A visual habituation-dishabituation paradigm was used to determine whether 1-month-old infants would process internal information if the internal elements of the stimulus were patterns often found to be preferred by young infants. Four groups of eight infants each were habituated to a compound stimulus consisting of a square or triangle surrounding a checkerboard or bull's-eye. Following habituation each group was presented with one of four types of stimulus: the identical stimulus (control group), a stimulus differing only in the internal component, a stimulus differing only in the external component, or a stimulus differing in both components. The results of the present study suggest that when the internal element of a compound stimulus is a highly preferred or salient stimulus, the young infant will process information about its characteristics.     

Sensory substitution: an approach to the experimental study of perception / Sustitución sensorial: un abordaje para el estudio experimental de la percepción

Abstract

Sensory substitution refers to the phenomenon where object and environment information normally acquired through one sense can be obtained by another sense. For example, visual input being provided by hearing or touching. Sensory substitution devices are technological designs that transform the characteristics of one sensory modality into stimuli of another sensory modality. These devices were developed with two purposes: (1) to assist people with sensory disabilities in daily tasks; and (2) to study the involved mechanisms of brain plasticity. This article reviews studies in which sensory substitution phenomenon is employed as a methodological strategy to study visual perception. Furthermore, its use is discussed as an experimental platform to contrast new perceptual theories and underlying neurophysiological mechanisms that are currently under review.