Olfactory context and memory retrieval in 3-month-old infants

Three experiments examineed whether olfactory stimuli can produce context-dependent effects in infant memory. In eash, 3-month-old infants learned to kick to control the movement of an overhead modile in the presence of an ambient odor. Retention was assessed 1, 3, or 5 days later. During the retention test, the olfactory context was either the same odor, a different odor, or “no odor.” At 1 day, infants exhibited retention when tested in the presence of the same odor. Infants in the no odor condition exhibited partial retention, whereas memory retrieval was completely disrupted for infants tested in the presence of the different odor. After the 3- and 5-day intervals, all groups showed forgetting. These results were not consistent with recent studies of 3-month-old infants trained and tested in the presence of a distinctive visual and auditory context. The findings suggest that olfactory stimuli are a silent feature of the environment for 3-month-old infants, but that they function as context cues in a way that differs from other sensory modalities.     

Object individuation and labelling in 6-month-old infants

The ability to determine how many objects are involved in physical events is fundamental for reasoning about the world that surrounds us. Previous studies suggest that infants can fail to individuate objects in ambiguous occlusion events until their first birthday and that learning words for the objects may play a crucial role in the development of this ability. The present eye-tracking study tested whether the classical object individuation experiments underestimate young infants’ ability to individuate objects and the role word learning plays in this process. Three groups of 6-month-old infants (N = 72) saw two opaque boxes side by side on the eye-tracker screen so that the content of the boxes was not visible. During a familiarization phase, two visually identical objects emerged sequentially from one box and two visually different objects from the other box. For one group of infants the familiarization was silent (Visual Only condition). For a second group of infants the objects were accompanied with nonsense words so that objects’ shape and linguistic labels indicated the same number of objects in the two boxes (Visual & Language condition). For the third group of infants, objects’ shape and linguistic labels were in conflict (Visual vs. Language condition). Following the familiarization, it was revealed that both boxes contained the same number of objects (e.g. one or two). In the Visual Only condition, infants looked longer to the box with incorrect number of objects at test, showing that they could individuate objects using visual cues alone. In the Visual & Language condition infants showed the same looking pattern. However, in the Visual vs Language condition infants looked longer to the box with incorrect number of objects according to linguistic labels. The results show that infants can individuate objects in a complex object individuation paradigm considerably earlier than previously thought and that linguistic cues enforce their own preference in object individuation. The results are consistent with the idea that when language and visual information are in conflict, language can exert an influence on how young infants reason about the visual world.     

Large number discrimination in 6-month-old infants

Two experiments with the Stroop paradigm were conducted to investigate the role of phonological codes in access to the meaning of Chinese characters. Subjects named the ink color of viewed characters or color patches. Key items were color characters, their homophones with the same tone, homophones with different tones, and semantic associates. Apart from finding the usual Stroop interference effect, homophones produced significant interference in the incongruent condition, provided that they had the same tone as the color characters. The interference effect from homophones, however, was significantly smaller than that from color characters. Semantic associates generated an interference effect in the incongruent condition, an effect of the same magnitude as the effect from the same-tone homophones. Finally, in the congruent conditions, all the key items yielded facilitations compared to neutral controls, though the facilitation from color characters was larger than the facilitations from other types of characters. These findings suggest that phonological codes in Chinese are activated obligatorily and provide early sources of constraint in access to meaning.     

Ratio abstraction by 6-month-old infants

Human infants appear to be capable of the rudimentary mathematical operations of addition, subtraction, and ordering. To determine whether infants are capable of extracting ratios, we presented 6-month-old infants with multiple examples of a single ratio. After repeated presentations of this ratio, the infants were presented with new examples of a new ratio, as well as new examples of the previously habituated ratio. Infants were able to successfully discriminate two ratios that differed by a factor of 2, but failed to detect the difference between two numerical ratios that differed by a factor of 1.5. We conclude that infants can extract a common ratio across test scenes and use this information while examining new displays. The results support an approximate magnitude-estimation system, which has also been found in animals and human adults.     

Recognition of color-form compounds by 4-month-old infants

In two studies, a paired-comparison procedure was used to investigate whether 4-month-old infants can perceive and remember correlations of color and form. In Study 1, infants were shown simultaneous presentations of two different colored shapes until two criteria for familiarization had been met. They were then offered a simultaneous choice between a colored form that they had already seen and one that was a new combination of a familiar color and a familiar shape. The infants looked significantly longer at the new combination than at the familiar combination on the test trial. In Study 2, the same procedure was used, except that the familiarization criteria were less stringent and additional analyses of the infants' test trial behavior were conducted. Infants again exhibited a significant preference for the new combination, both when looking time accumulated during the entire test-trial was analyzed and when looking just up to the “first look away” was considered. These findings that 4-months-olds can perceive and remember compounds of visual attributes conflict with the results of several studies in which the habituation and test stimuli were presented sequentially rather than simultaneously. Differences in the nature of the information processing that may be evoked by the two methods are discussed.     

Facial expressions and vagal tone of infants of depressed and non-depressed mothers

Mothers classified as ‘depressed’, ‘non-depressed’ or ‘low scoring’ on the Beck Depression Inventory and their 3-month-old infants were videotaped during 3-minute face-to-face play interactions. Infants' facial expressions were coded using the AFFEX facial expression coding system and their EKG was recorded during the interactions to assess the relationship between cardiac measures and facial expressivity. Infants of both ‘depressed’ and ‘low scoring’ mothers showed significantly more sad and anger expressions and fewer interest expressions than infants of nondepressed mothers. Cardiac vagal tone, (quantified from the amplitude of respiratory sinus arrhythmia) was correlated with infants' joy and interest expressions and with self-comfort behaviours in the non-depressed and low scoring groups, but not in the depressed group. The results suggest that matermal depression affects infants' affective state and appearance as well as their biobehavioural emotional regulation systems.     

Coregulation in mother-infant dyads: links to infants' cardiac vagal tone

This investigation explored links between mother-infant coregulated communication patterns and infants' emerging parasympathetic regulatory processes (cardiac vagal tone). Participants included 56 first-time mothers and their 6-mo.-old infants (31 girls, 25 boys). A 4-min. baseline EKG was gathered from the infant and an ensuing 15-min. mother-infant dyadic free-play episode was videotaped and coded using Fogel's 1994 Regional Coding System. This system was developed to describe variations in coregulated features of communication among dyads, ranging from symmetrical patterns to disruptive patterns of coregulation. Analysis suggests a positive link between infants' cardiac vagal tone and more symmetrical features of coregulated communication patterns in mother-infant dyads. Cardiac vagal tone was also negatively correlated with unilateral features of coregulation communication systems. These findings point toward the potential relation between emerging physiological regulatory abilities of infants and the more relational regulatory processes in mother-infant dyads.     

Resilience and vagal tone predict cardiac recovery from acute social stress

Previous studies showed that heart period decreases during and recovers after an acute stress. We investigated if individual predispositions and emotional priming influence heart period recovery after a speech stress task. Psychometric scales and resting cardiac vagal tone were used to measure individual traits. The presentation of a sequence of either pleasant or unpleasant pictures, as emotional primers, preceded the speech stress. Heart period was measured throughout the experiment. Stress induced tachycardia irrespective of emotional priming or traits. In the recovery period, participants with higher resting cardiac vagal tone or presenting higher resilience significantly reduced the heart acceleration. Furthermore, these traits interacted synergistically in the promotion of the recovery of heart period. Pleasant priming also improved recovery for participants with lower negative affect. In conclusion, the stress recovery measured through heart period seemed dependent upon individual predispositions and emotional priming. These findings further strengthen previous observations on the association between greater cardiac vagal tone and the ability to regulate emotion.     

Neural markers of categorization in 6-month-old infants

Little is known of the neural processes that underlie concept-formation abilities in human infants. We investigated category-learning processes in infants both by using a common behavioral measure and by recording the brain's electrical activity (event-related potentials, or ERPs). ERPs were recorded while 6-month-olds viewed cat images during training, followed by novel cat images interspersed with novel dog images during test. The data indicate that distinct neural signals correspond with learning of a category presented during familiarization, preferential responding to a novel category, and representation of category exemplars at multiple levels of inclusiveness. The results suggest that fundamental components of the neural architecture supporting object categorization are functional within the first half-year of postnatal life, before infants acquire language and young children engage in formal learning of semantic categories. The findings are discussed in terms of their implications for models of category learning and development.     

Night waking in 6-month-old infants and maternal depressive symptoms

Relations between night waking in infants and depressive symptoms in their mothers at 6 months postpartum were examined using the data from the National Institute for Child Health and Human Development Study of Early Child Care. Although more depressive symptoms were only weakly correlated with a higher frequency of infant waking, longer wake times, and more total time awake, the rate of clinically significant depression scores was about double in mothers of chronically waking infants in comparison with mothers whose infants did not awaken during the night. The value of comparing subgroups to elucidate relations identified through correlations is discussed.     

Long-term memory,forgetting, and deferred imitation in 12-month-old infants

Long-term recall memory, as indexed by deferred imitation, was assessed in 12-month-old infants. Independent groups of infants were tested after retention intervals of 3 min, 1 week and 4 weeks. Deferred imitation was assessed using the ‘observation-only’ procedure in which infants were not allowed motor practice on the tasks before the delay was imposed. Thus, the memory could not have been based on re-accessing a motor habit, because none was formed in the first place. After the delay, memory was assessed either in the same or a different environmental context from the one in which the adult had originally demonstrated the acts. In Experiments 1 and 3, infants observed the target acts while in an unusual environment (an orange and white polka-dot tent), and recall memory was tested in an ordinary room. In Experiment 2, infants observed the target acts in their homes and were tested for memory in a university room. The results showed recall memory after all retention intervals, including the 4 week delay, with no effect of context change. Interestingly, the forgetting function showed that the bulk of the forgetting occurred during the first week. The findings of recall memory without motor practice support the view that infants as young as 12 months old use a declarative (nonprocedural) memory system to span delay intervals as long as 4 weeks.     

Recognition,discrimination and categorization of smiling by 5-month-old infants

Perceiving emotions correctly is foundational to the development of interpersonal skills. Five-month-old infants’ abilities to recognize, discriminate and categorize facial expressions of smiling were tested in three coordinated experiments. Infants were habituated to four degrees of smiling modeled by the same or different people; following habituation, infants were presented with a new degree of smile worn by the same and by a new person (Experiment 1), a new degree of smile and a fearful expression worn by the same person (Experiment 2) or a new degree of smile and a fearful expression worn by new people (Experiment 3). Infants showed significant novelty preferences for the new person smiling and for the fearful expressions over the new degree of smiling. These findings indicate that infants at 5 months can categorize the facial expression of smiling in static faces, and yet recognize the same person despite changes in facial expression; this is the youngest age at which these abilities have been demonstrated. The findings are discussed in light of the significance of emotion expression face processing in social interaction and infants’ categorization of faces.     

Auditory-visual intermodal matching of small numerosities in 6-month-old infants

Recent studies have reported that preverbal infants are able to discriminate between numerosities of sets presented within a particular modality. There is still debate, however, over whether they are able to perform intermodal numerosity matching, i.e. to relate numerosities of sets presented with different sensory modalities. The present study investigated auditory-visual intermodal matching of small numerosities in infancy by using a violation-of-expectation paradigm. After being familiarized with events of a few objects impacting a surface successively, 6-month-old infants were alternatively presented with two and three tones while the movement of each object remained hidden behind an opaque screen. The screen was then removed to reveal either two or three objects. Results showed that the infants looked significantly longer at the numerically nonequivalent events (the three-tone/two-object and the two-tone/three-object events) than at the numerically equivalent events (the two-tone/two-object and the three-tone/three-object events) irrespective of the rate or duration of auditory tones presented. These findings suggest that infants are capable of performing intermodal matching of small numerosities and that they might possess abstract representations of numerosity beyond sensory modalities.     

Patterns of brain-electrical activity during declarative memory performance in 10-month-old infants

This study of infant declarative memory concurrently examined brain-electrical activity and deferred imitation performance in 10-month-old infants. Continuous electroencephalogram (EEG) measures were collected throughout the activity-matched baseline, encoding (modeling) and retrieval (delayed test) phases of a within-subjects deferred imitation task. Infants were divided into two memory performance groups based on the exhibition of ordered-recall after a 24-h delay. Whereas no group differences were found in EEG collected during encoding, performance-group differences in EEG were present during retrieval. Infants who successfully displayed ordered-recall showed a pattern of increasing EEG from baseline to task at anterior temporal scalp locations, whereas infants showing no ordered-recall displayed no changes in EEG from baseline to task. These findings are discussed with respect to the biobehavioral developments underlying declarative memory abilities.     

Visual speech contributes to phonetic learning in 6-month-old infants

Previous research has shown that infants match vowel sounds to facial displays of vowel articulation [Kuhl, P. K., & Meltzoff, A. N. (1982). The bimodal perception of speech in infancy. Science, 218, 1138–1141; Patterson, M. L., & Werker, J. F. (1999). Matching phonetic information in lips and voice is robust in 4.5-month-old infants. Infant Behaviour & Development, 22, 237–247], and integrate seen and heard speech sounds [Rosenblum, L. D., Schmuckler, M. A., & Johnson, J. A. (1997). The McGurk effect in infants. Perception & Psychophysics, 59, 347–357; Burnham, D., & Dodd, B. (2004). Auditory-visual speech integration by prelinguistic infants: Perception of an emergent consonant in the McGurk effect. Developmental Psychobiology, 45, 204–220]. However, the role of visual speech in language development remains unknown. Our aim was to determine whether seen articulations enhance phoneme discrimination, thereby playing a role in phonetic category learning. We exposed 6-month-old infants to speech sounds from a restricted range of a continuum between /ba/ and /da/, following a unimodal frequency distribution. Synchronously with these speech sounds, one group of infants (the two-category group) saw a visual articulation of a canonical /ba/ or /da/, with the two alternative visual articulations, /ba/ and /da/, being presented according to whether the auditory token was on the /ba/ or /da/ side of the midpoint of the continuum. Infants in a second (one-category) group were presented with the same unimodal distribution of speech sounds, but every token for any particular infant was always paired with the same syllable, either a visual /ba/ or a visual /da/. A stimulus-alternation preference procedure following the exposure revealed that infants in the former, and not in the latter, group discriminated the /ba/–/da/ contrast. These results not only show that visual information about speech articulation enhances phoneme discrimination, but also that it may contribute to the learning of phoneme boundaries in infancy.     

Patterns of brain-electrical activity during declarative memory performance in 10-month-old infants

This study of infant declarative memory concurrently examined brain-electrical activity and deferred imitation performance in 10-month-old infants. Continuous electroencephalogram (EEG) measures were collected throughout the activity-matched baseline, encoding (modeling) and retrieval (delayed test) phases of a within-subjects deferred imitation task. Infants were divided into two memory performance groups based on the exhibition of ordered-recall after a 24-h delay. Whereas no group differences were found in EEG collected during encoding, performance-group differences in EEG were present during retrieval. Infants who successfully displayed ordered-recall showed a pattern of increasing EEG from baseline to task at anterior temporal scalp locations, whereas infants showing no ordered-recall displayed no changes in EEG from baseline to task. These findings are discussed with respect to the biobehavioral developments underlying declarative memory abilities.     

Stressing the feedback: attention and cardiac vagal tone during a cognitive stress task

Objectives: The present study examined relationships among gaze behaviour and cardiac vagal tone using a novel stress-inducing task.

Methods: Participants’ (N?=?40) eye movements and heart rate variability (HRV) were measured during an unsolvable computer-based task randomly presenting feedback of “Right” and “Wrong” answers distinctly onscreen after each trial. Subgroups were created on the basis of more frequent eye movements to the right (“Correct”-Attenders; n?=?23) or wrong (“Incorrect”-Attenders; n?=?17) areas onscreen.

Results: Correct-Attenders maintained HRV from baseline to the stress task. In contrast, Incorrect-Attenders spent significantly more time viewing “Wrong” feedback, exhibited a reduction in HRV during the stress condition (p?Conclusions: Results demonstrate that pervasive attention to negative feedback (“Wrong”) elicits perseverative stress and negative self-evaluations among university students. This study highlights the potential for studying attentional biases and emotional distress through combined measures of gaze behaviour and cardiac vagal tone.     

Perceptual sensitivity and motoric competence in 5- and 6-month-old infants

The authors explored whether 5- to 6-month-old infants were sensitive to perceptual information and how they used perception as a recognition cue to search for a hidden object. In addition, the authors categorized and examined infant grasp by developmental effectiveness to determine any impact on infant search behaviors. In a within-participants design, 20 infants were presented with a toy in 2 occluder conditions. The toy was hidden under either a thick, camouflaging cloth or a thin, semitransparent cloth. The data revealed significant effects of perceptual sensitivity, age, and motor sophistication on search tasks. The results suggest that motor competence might be a limiting factor in infants' abilities to link motoric responses to notions about an object.