Effects of auditory stimulation upon non-nutritive sucking by premature infants.

Changes in non-nutritive sucking contingent upon presentation of an auditory stimulus previously found capable of eliciting heart-rate acceleration was investigated in a sample of 24 premature infants. Across 30 10-sec. presentations of the stimulus, only transient changes in sucking rate during the first 6 trials were observed, and these effects obtained primarily for those infants showing few abnormalities in their non-nutritive sucking behavior. These results were discussed as reflecting possible differences in infants' attention associated with sucking pathology and the dependence of psychological assessment upon the specific response index used.     

Central and peripheral vision in early infancy

The size of the effective visual field during the first weeks of life is found to depend on two factors: It increases with age, but it contracts in the face of competition from ongoing activity such as fixation of a central stimulus or non-nutritive sucking.     

Discrimination of color and pattern novelty in one-month human infants

Visual discrimination of novel colors and patterns by one-month infants was studied in two experiments where visual reinforcers were presented contingent upon infants' rate of nonnutritive, high-amplitude sucking. Discrimination was measured by recovery of sucking to the presentation of novel visual reinforcing stimuli following decrements in sucking to familiar visual stimuli. In Expt 1, following decrement to familiar stimuli, independent groups received either a change in color, pattern, both color and pattern, or no stimulus change. Reliable recovery was demonstrated for the three stimulus novelty groups relative to the no-change control. Experiment 2, employing achromatic visual reinforcers also showed reliable recovery to pattern change relative to no-change controls. These findings with one-month infants indicate discrimination between familiar and novel visual reinforcers on the basis of color and pattern differences and an increase due to novelty in the reinforcing effectiveness of visual stimuli. Individual subject differences in response decrement magnitude during familiarization were positively correlated with amount of response recovery to novelty.     

Is Dutch native English? Linguistic analysis by 2-month-olds

A variant of the non-nutritive habituation/dishabituation sucking method was used to test 2-month-old English infants’ perception of languages. This method tests for the spontaneous interest of the baby to a change in the stimulus. English and Japanese were clearly discriminated. The difference between French and Japanese was equally clearly not of interest to babies using this procedure, the babies behaving as though both languages were classified simply as ‘foreign’. In order to further specify babies’ representation of native and foreign language, we used Dutch, which shares a number of suprasegmental features with English. The results from our last 2 experiments indicate that a portion of our 6–12 week-old babies consider Dutch as native, suggesting that we tapped in a transition period where the babies are still refining the suprasegmental specification of their native language.     

Influence of auditory tempo on the endogenous rhythm of non-nutritive sucking

The aim of this study was to examine the perception of time in the first months of life. Does the perception of contextual temporal information (an auditory tempo) induce modifications in spontaneous motor behavior (in the present case, non-nutritive sucking behavior) at birth and at 2 months? Two auditory tempos were successively tested. The first was the same as the previously recorded spontaneous motor tempo (SMT); the second was 15% faster or 15% slower than the infant's SMT according to the group. Results showed that modification of the sucking tempo depended on age and contextual temporal information. Two-month-old infants were able to adapt their endogenous sucking rhythm to an external tempo if it was faster than their spontaneous rhythm. Results also confirmed that slowing down the sucking rate was difficult for both groups of infants. In sum, the results suggest that, to a certain extent, very young infants are sensitive to contextual modifications (which indicates that they perceive them). This study has thus identified certain features of the internal time base rate from birth which could help define a developmental internal clock model of contextual temporal processing.     

Effects of nutritive and non-nutritive sucking on infant heart rate variability during the first 6 months of life

The effects of eating on heart rate variability (HRV) differ between adults and newborns. This may reflect the impact of suckling on the overall psychophysiological and autonomic nervous system maturation. The purpose of the present study was to explore whether the reactions of HRV during feeding change towards the adult pattern during the first 6 months of life. In addition, the effects of non-nutritive and nutritive sucking on heart rate (HR) and HRV were compared. The participants were 23 infants on whom recordings were performed as newborns and at 6, 12 and 24 weeks old. Nutritive sucking caused an increase in HR and a decline in HRV. The results were consistent with previous reports of a decrease in high frequency components of HRV during feeding in newborns, reflecting a decrease in parasympathetic activity. This response was apparent in all four ages studied, and remained similar throughout the 6-month period. However, age as an independent factor seemed to influence both HR and HRV. Pacifier sucking had no significant effects on HRV at any age. The results demonstrate the physical strain that sucking imposes on the baby, with a specific autonomic nervous system response involved. We consider this response an essential part of the overall psychophysiological maturation of infants.     

The quality of sucking in infants with colic

Feeding problems have been reported in infants with colic. The purpose of this study was to examine the nutritive sucking pattern of infants identified as having colic. Twenty-nine infants (16 with colic and 13 controls) between the ages of 1 to 3 months, being bottle-fed by their mothers, were observed by a blind examiner. We hypothesized that infants with colic would show greater disorganization in nutritive sucking and show greater variability in sucking rate than infants without colic, as assessed by the revised Neonatal Oral Motor Assessment Scale (NOMAS). Infants with colic were found to present a disorganized sucking pattern; namely, a lack of rhythmical movement and a difference in amount of sucks per burst than infants without colic. Methods of intervention are suggested.     

Binocular disparity as a discriminable stimulus parameter for young infants

The ability of 8-week-old infants to discriminate between projected stereograms with and without retinal disparity was tested with an habituation-dishabituation paradigm. Infants in two experimental groups received six trials with either the disparity or the nondisparity stimulus and then were given two trials with the other display. Infants in two control groups viewed the same stimulus, either disparity or nondisparity, on all eight trials. There was a suggestion of some response decrement over time in both cardiac deceleration and sucking suppression, although this effect was not significant. However, significant increment was obtained on the dishabituation trials for heart rate in the group that was shifted from the nondisparity to the disparity stimulus. These results were interpreted as indicating that the infants could discriminate between stimuli when the only difference between them was binocular disparity.     

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.     

Reinforcement from the sucking environment and subsequent modification of sucking behavior in the human neonate

The reinforcing aspects of sucking behavior in 36 human newborns was examined in a limited instrumental conditioning paradigm where sucking was both operant and reinforcer. During training, response density (rate based on sucking opportunity time) and latency were measures of two components of nonnutritive sucking, contingent negative pressure suction, and incidental jaw movement. The strategy for determining the reinforcing aspects of sucking involved comparisons of three types of sucking stimuli as reinforcers. The nature of modified operant sucking was investigated during extinction by examining number of sucks per burst, number of bursts emitted, and interburst interval time. The feedback from sucking which acted as reinforcement was concluded to be response density. Sucking was modified by changes in pausing behavior, including response latency and pauses between bursts of sucks. The number of sucks per burst also showed a significant change under certain conditioning arrangements.     

Preference for infant-directed speech in preterm infants

The current study explores the effects of exposure to maternal voice on infant sucking in preterm infants. Twenty-four preterm infants averaging 35 weeks gestational age were divided randomly into two groups. A contingency between high-amplitude sucking and presentation of maternal voice was instituted for one group while the other group served as a yoked control. No significant differences were observed in sucking of the two groups, but the degree of pitch modulation of the maternal voice predicted an increase in the rate of infant sucking.     

Emerging self-exploration by 2-month-old infants

Two-month-olds and newborns were tested in a situation where they had the opportunity to experience different auditory consequences of their own oral activity on a dummy pacifier. Modulation of oral activity was scored and analyzed relative to two types of contingent auditory feedback, either analog or non-analog to the effort exerted by the infant on the pacifier. The dummy pacifier was connected to an air pressure transducer for recording of oral action. In two different experimental conditions, each time the infant sucked above a certain pressure threshold they heard a perfectly contingent sound of varying pitch. In one condition, the pitch variation was analog to the pressure applied by the infant on the pacifier (analog condition). In another, the pitch variation was random (non-analog condition). As rationale, a differential modulation of oral activity in these two conditions was construed as indexing some voluntary control and the sense of a causal link between sucking and its auditory consequences, beyond mere temporal contingency detection and response–stimulus association. Results indicated that 2-month-olds showed clear signs of modulation of their oral activity on the pacifier as a function of analog versus non-analog condition. In contrast, newborns did not show any signs of such modulation either between experimental conditions (analog versus non-analog contingent sounds) or between baseline (no contingent sounds condition) and experimental conditions. These observations are interpreted as evidence of self-exploration and the emergence of a sense of self-agency by 2 months of age.     

Contextual determinants of anger and other negative expressions in young infants

Two experiments examined how different frustration contexts affect the instrumental and emotional responses of 4- to 5-month-old infants. Three different frustrating contexts were investigated: loss of stimulation (extinction), reduction in contingent stimulation (partial reinforcement), and loss of stimulus control (noncontingency). In both experiments, changes in arm activity and facial expressions of anger and sadness coded according to the Maximally Discriminative Facial Movement Coding System (MAX) were the measures of frustration. Both experiments showed that (a) arm responses increased when the contingent stimulus was lost or reduced but decreased when control of the stimulus was lost under noncontingency, (b) MAX-coded anger, but not MAX-coded sad or blends of anger and sad, was associated with frustration, and (c) the pattern of anger and arm responses varied with the frustration context. When contingent stimulation was lost or reduced, both anger and arm responses increased, but when expected control was lost under noncontingency, arm responses decreased while anger increased.     

Unfamiliar voice discrimination for short stimuli in newborns

In order to determine the minimal information required for newborns to discriminate unfamiliar voices two experiments were performed using the presentation of single disyllabic words uttered by male and female speakers. In the first experiment, utilizing the standard high‐amplitude‐sucking procedure, no significant discrimination was obtained. Hypothesizing that this failure in discrimination could be due to a deficient attention at the unique moment of stimulus change, a second experiment was performed in which the same to‐be‐discriminated stimuli alternated every minute and in which multiple tokens of the same word were presented to increase stimulus variability. Evidence for voice discrimination was obtained, suggesting that newborns are able to characterize unfamiliar voices on the basis of restrained vocal‐tract related information and minor prosodic information. Remarks addressing the consequences of stimulus organization upon attentional demands in experimental procedures in young infants are also presented.     

The association between maternal interaction and infant cortisol stress reactivity among preterm and full term infants at 4 months adjusted age

The purpose of this study was to assess the association between maternal interactive behavior and infant cortisol stress reactivity in response to the Still Face paradigm (SF) in a cohort of four-month old infants (adjusted age) born preterm (<32 weeks gestation, N = 22) compared with infants born full term (>37 weeks gestation, N = 28). Infant cortisol reactivity was calculated as area under the curve (AUC) from baseline to the third cortisol sample (30 min post-SF) using the trapezoidal rule, while the percent of time mothers spent using a contingent interaction style was measured (0–100%) during episodes 1 (Play; baseline), 3 (Reunion#1), and 5 (Reunion#2) while mother-infant dyads participated in the SF paradigm. We hypothesized that because infants born preterm are at increased risk for dysregulation, they would show, compared to full-term infants, a blunted stress response, involving under-responsiveness. We found blunted cortisol stress reactivity among the preterm infants. We also found that mothers of preterm infants demonstrated less contingent maternal interaction during Renion#1 of the SF; and that contingent maternal interaction at Reunion#2 of the SF was protective against cortisol stress reactivity in response to the SF. However, we did not find that the influence of maternal interaction on cortisol reactivity was moderated by gestational age group (full term vs preterm): the association between contingent maternal interaction and stress reactivity was similar for both gestational groups across episodes. In order to improve self-regulation and longer term social and cognitive developmental outcomes in medically at-risk infants, future research is warranted to determine how these findings relate to infants’ stress reactions in naturalistic settings, and the directionality and temporal relationship between cortisol stress responses and maternal interactive behavior.     

Dynamics of oralrespiratory coordination in full-term and preterm infants: I. Comparisons at 38-40 weeks postconceptional age

This study compares the coordination of pacifier sucking and breathing between healthy full-term, low risk preterm, and high risk preterm infants at 38–40 weeks postconceptional age. High and low risk preterm infants did not differ in overall score on a neurobehavioral examination (NAPI), but infants in the high risk group differed from the others in breathing frequency and in the coordination of breathing and sucking rhythms. For infants in the high risk group, sucking had less influence on respiratory frequency and patterns of coordination between the frequencies of sucking and breathing were simpler. Oral–respiratory coordination may be a useful marker of infants at risk for later speech problems.     

Infants' discrimination of internal and external pattern elements

Human infants' discrimination of changes in internal and external elements of compound visual patterns was investigated in four experiments employing a familiarization-novelty paradigm in which visual reinforcing patterns were presented contingent upon rate of high-amplitude nonnutritive sucking. In Experiment 1, 4-month infants discriminated changes in the shape of internal, external and both internal and external figures. One-month infants discriminated external changes in both internal and external figures, but failed to show reliable response recovery when only internal figures were changed. Experiments 2 and 3 failed to explain the 1-month results on the basis of poor resolution of internal figures by showing comparable discrimination of small and large singly-presented figures and by failing to find improved internal discrimination with large separation between internal and external figures. In Experiment 4, 1-month infants showed response recovery to figure additions made adjacent to the initial figure, but not to internal additions. The results are interpreted in terms of attentiveness by young infants to external pattern elements and may indicate early processing of figure-ground information. The developmental differences observed suggest an increased breadth of attention to pattern elements.     

Prenatal experience with low-frequency maternal-voice sounds influence neonatal perception of maternal voice samples

By sucking on a nonnutritive nipple in the presence of one discriminative stimulus, newborns were reinforced with a low-pass filtered tape recording of their mothers' voices. Sucking in the presence of a different discriminative stimulus was reinforced with unfiltered maternal-voice recordings. Filtered versions simulated maternal-voice sounds that were available before birth and unfiltered versions simulated maternal-voice sounds available after birth. Newborns in the control group could be reinforced with the same stimuli in the same way, but the voices were unfamiliar to them. Infants hearing their mothers' voices had no preference for either version, but infants hearing the unfamiliar voices preferred the unfiltered version. The difference in the between-groups responsiveness to the low-pass voice samples is consistent with the hypothesis that prenatal experience with low-frequency characteristics of maternal voices influences early postnatal perception of maternal voices.     

Modelling response selection in task switching: Testing the contingent encoding assumption

The contingent encoding assumption is the idea that response selection in task-switching situations does not begin until the cue and the target have both been encoded. The authors tested the assumption by manipulating response congruency, stimulus order, and stimulus onset asynchrony (SOA) in two experiments. They found evidence of response selection prior to cue encoding for congruent targets with target–cue order at a long SOA, indicating that the contingent encoding assumption is invalid. The authors describe how contingent encoding can be removed from an existing task-switching model by introducing baseline evidence—task-neutral evidence that serves as a baseline for response selection prior to stimulus encoding. Simulations revealed that the modified model could reproduce the full pattern of response time data and generate responses prior to cue encoding. The authors conclude by discussing directions for further model development.     

Depressed mothers' newborns show less discrimination of other newborns' cry sounds

Newborns' crying in response to the cry of another newborn has been called an empathetic response. The purpose of this study was to determine whether newborns of depressed mothers showed the same response. Newborns of depressed and non-depressed mothers were presented with cry sounds of themselves or other infants, and their sucking and heart rate were recorded. The newborns of non-depressed mothers responded to the cry sounds of other infants with reduced sucking and decreased heart rate. In contrast, the newborns of depressed mothers did not show a change in their sucking or heart rate to the cry sounds of other infants. This lesser attentiveness/responsiveness to other infants' cry sounds may predict their later lack of empathy.