The Development of Sustained Visual Attention in Infants from 14 to 26 Weeks of Age

The development of sustained visual attention was examined in infants cross-sectionally at 14, 20, and 26 weeks of age. Heart rate, heart rate variability, and respiratory sinus arrhythmia were measured in a 5-min baseline period. Two methods for measuring visual attention were used. The “infant control” method consisted of checkerboard presentations which were terminated when the infant looked away from them. The “interrupted stimulus” method consisted of a blinking panel in addition to the checkerboard patterns in order to attempt to actively terminate the fixation. The visual and cardiac responses during the interrupted stimulus method were more highly correlated with baseline respiratory sinus arrhythmia than were the responses during the infant control trials. The long latency heart rate responses during the interrupted stimulus trials showed a developmental change toward more mature response patterns from 14 to 26 weeks of age. It may be concluded that: 1) sustained attention, measured with the interrupted stimulus method, increases from 14 to 26 weeks of age; and 2) baseline respiratory sinus arrhythmia is correlated with sustained attention responses and their development.     

Respiratory Sinus Arrhythmia Predicts Heart Rate and Visual Responses during Visual Attention in 14 and 20 Week Old Infants

The prediction of cardiac attentional responses by respiratory sinus arrhythmia was tested in infants at 14 and at 20 weeks of age. Heart rate, heart rate variability, and respiratory sinus arrhythmia were measured in a 5-min baseline period. Respiration and heart rate responses were recorded during the habituation of infant visual attention. The level of respiratory sinus arrhythmia in the baseline was significantly correlated with the cardiac deceleration, especially in the 20-week-old infants. The relationship between cardiac and respiratory responses during attention was stronger in the 20-week-olds, paralleling the increase in respiratory sinus arrhythmia at this age. Visual fixation durations were also significantly correlated with measures of heart rate variability from the baseline. These results imply that cardiac variability not only predicts the level of cardiac attentional responsivity, but may be useful in the indexing of individual differences in the responsivity of more general attentional systems.     

Baseline respiratory sinus arrhythmia and heart rate responses during sustained visual attention in preterm infants from 3 to 6 months of age

Three groups of preterm infants were studied longitudinally at 14, 20, and 26 weeks of age (corrected for gestational age). The groups included infants with no perinatal medical complications, those with mild respiratory problems requiring ventilatory assistance, and those with respiratory distress syndrome. Baseline heart rate and respiratory sinus arrhythmia (RSA) were recorded for 5 min, and heart rate was also recorded while the infants engaged in sustained visual attention to stimuli presented on video monitors. The heart rate response during stimulus orienting and sustained attention was smaller in those infants with respiratory distress syndrome than in the other preterm infants and in comparison with the response seen in full-term infants in previous research. Magnitude of RSA was positively correlated with the attention responses irrespective of the preterm group assignment. There was greater stability in baseline heart rate and RSA for the preterm infants than has been found with full-term infants. These data suggest that the cardiorespiratory functioning of the preterm infant indexes a stable individual difference characteristic that is correlated with heart responses during sustained attention, and heart rate attention systems may be damaged in the high-risk preterm infant.     

Heart Rate Offset Responses to Visual Stimuli in Infants from 14 to 26 Weeks of Age

Heart rate offset responses to visual stimuli were studied in infants tested cross-sectionally at 14, 20, and 26 weeks of age. In Experiments 1 and 2, offset responses were measured in each infant following visual stimuli presented with three procedures. The fixed interval method consisted of stimulus presentations of 7 s in duration. The infant control method consisted of stimulus presentations which were terminated when the infant looked away from them. The interrupted stimulus method consisted of stimulus presentations which were terminated when the infant looked away toward an interrupting, secondary stimulus. In Experiment 3 these procedures were compared with two procedures in which stimulus termination occurred at the point of heart rate deceleration or the return of heart rate toward prestimulus level. The stimuli in Experiment 1 were checkerboard patterns, in Experiment 2 were complex and varying stimuli, and in Experiment 3 were either TV stimuli or an overhead light. The offset responses were similar for the fixed interval and infant control methods, and consisted of brief heart rate decelerations. The magnitude of the heart rate response was generally small (1.5 to 2 bpm), with the largest heart rate response being 4 bpm. The pre-offset heart rate response was similar for the infant control and interrupted stimulus and heart rate acceleration trials, with heart rate showing a return to prestimulus levels immediately preceding subject-controlled fixation termination. Infants with high levels of respiratory sinus arrhythmia (RSA) measured during a 5-min baseline showed larger heart rate offset responses than did low RSA infants. These results call into question the interpretation of heart rate offset responses in the context of Sokolov's model of the orienting response. However, the offset paradigm is useful in the study of subject-controlled attention processes.     

Individual differences in the autonomic origins of heart rate reactivity: the psychometrics of respiratory sinus arrhythmia and preejection period

Heart rate reactivity has been conceptualized, at least implicitly, as a unidimensional construct ranging from low to high, reflecting individual differences in adrenergic reactivity to daily stressors. However, an individual's classification as high in heart rate reactivity ignores possible individual differences in the autonomic origins of this reactivity. Sixty-eight women were exposed to orthostatic and speech stressors to determine the psychometric properties (postural stability, convergent and discriminant validity) of heart rate, preejection period, and respiratory sinus arrhythmia. Results revealed that (a) basal, stress, simple reactivity (stress - baseline), and residualized change indices of heart rate, preejection period, and respiratory sinus arrhythmia were stable across postures and (b) heart rate reactivity was significantly related to preejection period and respiratory sinus arrhythmia reactivity, whereas the latter two measures were unrelated. Reactivity classifications may therefore be significantly improved by attention to concurrent estimates of the activity of both autonomic branches.     

Infant regulation of the vagal “brake” predicts child behavior problems: A psychobiological model of social behavior

Cardiac vagal tone is a construct that describes the functional relationship between the brainstem and the heart. Cardiac vagal tone is measured by quantifying the amplitude of respiratory sinus arrhythmia, a component of heart rate variability reflecting the functional output of vagal pathways on the heart. Although there is an extensive literature evaluating baseline vagal tone and its relation to behavior, the relation between individual differences in the ability to regulate cardiac vagal tone and behavior has been theoretically vague. This article introduces a theoretical model to explain the relation between vagal tone during steady states and vagal reactivity (i.e., the vagal brake) in response to environmental challenges. Based upon the proposed model, it was hypothesized that infants who had difficulties in regulating the vagal brake (i.e., decreasing cardiac vagal tone) during social/attention tasks would have difficulties developing appropriate social interactions requiring reciprocal engagement and disengagement strategies. Data from 24 infants are presented. The findings support the model and demonstrate that infants with difficulties in decreasing vagal tone during a social/attention task at 9 months of age had significantly more behavioral problems at 3 years of age. © 1996 John Wiley & Sons, Inc.     

Physiological responses of 5-month-old infants to smiling and blank faces.

Physiological responses (i.e., EEG, heart period, respiratory sinus arrhythmia (RSA)) were monitored in 5-month-old infants during the replacement of an adult's smiling (SF) with a blank face (BF) in a face-to-face setting. Affect, while the infant looked at and away from the adult's face during both conditions, was analyzed. Infants displayed neutral and some positive affect while looking at both SF and BF. RSA was quantified continuously during both conditions. RSA increased during BF relative to SF. EEG was quantified only while the infants were looking at the adult's face during both conditions. An increase in theta over multiple scalp areas (AF3,4; F7,8; FC3; T6) was observed during BF relative to SF. The data suggest that infant attention to BF and SF reflect different psychophysiological processes that can be indexed by RSA and scalp-recorded theta.     

Effects of interstimulus intervals on behavioral,heart rate,and event‐related potential indices of infant engagement and sustained attention

Maximizing infant attention to stimulus presentation during an EEG or ERP experiment is important for making valid inferences about the neural correlates of infant cognition. The present study examined the effects of stimulus presentation interstimulus interval (ISI) on behavioral and physiological indices of infant attention including infants' fixation to visual presentation, the amount of heart rate (HR) change during sustained attention, and ERP components. This study compared an ISI that is typically used in infant EEG/ERP studies (e.g., 1,500–2,000 ms) with two shorter durations (400–600 ms and 600–1,000 ms). Thirty‐six infants were tested cross‐sectionally at 3, 4.5, and 6 months. It was found that using the short (400–600 ms) and medium (600–1,000 ms) ISIs resulted in more visually fixated trials and reduced frequency of fixation disengagement per experimental block. We also found larger HR changes during sustained attention to both of the shorter ISIs compared with the long ISI, and larger ERP responses when using the medium ISI compared to using the short and long ISIs. These data suggest that utilizing an optimal ISI (e.g., 600–1,000 ms), which increases the presentation complexity and provides sufficient time for information processing, can promote infant engagement and sustained attention during stimulus presentation.     

Cardiac Response to Speech Sounds in Preterm Infants: Effects of Postnatal Illness at Three Months

The effect of postnatal illness, specifically respiratory distress syndrome (RDS), on preterm infants’ attention to auditory stimuli at 3 months of age was examined in three groups of infants; healthy preterm, preterms who had RDS, and a sample of normal term infants. Infants were presented 2 sessions of 9 trials of synthesized consonant-vowel sounds. The first 7 trials consisted of a binaural presentation in which the CV stimulus /ba/ or /pa/ was presented simultaneously to both left and right ears. The eighth and ninth trials consisted of a dichotic presentation in which the speech stimuli /ba/ and /pa/ were presented, one sound to the left ear and one sound to the right ear. EKG was recorded throughout the presentation. Analyses of covariance with prestimulus heart period as the covariate and heart period during stimulus presentation as the dependent measure were computed to investigate cardiac orienting, habituation and recovery. Results reveal significant cardiac orienting by healthy term and preterm infants on trial 1, habituation across trials 1–7, and recovery of cardiac orienting to stimulus change on the second novel presentation by healthy term and preterm. RDS preterm infants exhibited cardiac orienting to the first stimulus presentation but they did not evidence a change in cardiac level across redundant trials or a response recovery to the novel stimulus. RDS preterms throughout exhibited shorter heart period levels (faster heart rates) than either healthy term or healthy preterm infants. Results are discussed in relation to the effect of RDS on autonomic reactivity.     

Atypical autonomic regulation,auditory processing,and affect recognition in women with HIV

This study examined the effect of HIV on visceromotor (i.e., heart rate and heart rate variability) and somatomotor (i.e., auditory processing and affect recognition) components of a Social Engagement System defined by the Polyvagal Theory (Porges, 1995) that links vagal regulation of the heart with brainstem regulation of the striated muscles of the face and head. Relative to at risk HIV-seronegative women, HIV-seropositive women had less heart rate variability (i.e., respiratory sinus arrhythmia) and had poorer performance on auditory processing and affect recognition tasks. CD4 was negatively correlated with the accuracy to detect specific emotions. The observed indices of atypical autonomic and behavioral regulation may contribute to greater difficulties in social behavior and social communication between HIV-infected women and other individuals in their social network.     

Development of multimodal attention in young infants: modification of the startle reflex by attention

This study examined the effect of attention engagement to compound auditory-visual stimuli on the modification of the startle blink reflex in infants. Infants at 8, 14, 20, or 26 weeks of age were presented with interesting audiovisual stimuli. After stimulus onset, at delays defined by heart rate changes known to be associated with sustained attention or attention disengagement, blink reflexes were elicited by visual or auditory stimuli. Blink amplitude to either visual or auditory stimuli was enhanced when the infants were engaged in attention to the foreground auditory-visual stimuli relative to control trials with no foreground patterns. This enhancement of the blink amplitude increased from 8 to 26 weeks of age. In contrast to selective modality enhancement for single-modality foreground stimuli, these results show that these multimodal stimuli engage both visual and auditory attention systems in this age range.     

Cardiorespiratory Reactivity During the Brazelton Scale in Term and Preterm Infants

Determined the relationship between behavior measured with theBrazelton Scale and simultaneously recorded cardiorespiratoryactivity. The Brazelton Scale was administered and videotapedin a sample of 22 term and 22 preterm infants at term conceptionalage. The videotapes were coded off line with a computer interfaceto time lock behavior and physiological activity for the durationof four alert, non-crying conditions. Term infants showed increasesin heart rate and breathing rate when unswaddled and cuddledfollowing cry and increases in respiratory sinus arrhythmia(RSA) during orientation and swaddling. Preterm infants showedthe same general trend as term infants in heart rate and breathingrate. However, RSA decreased during orientation in preterm infants.On behavioral scores, preterm infants showed lower scores onself-regulation and a higher cost of attention. Correlationsbetween behavior and physiological activity showed lower RSAassociated with enhanced behavioral scores for the preterm infants.Results of this study are consistent with the hypothesis thatattentional responsivity in the preterm infant may be at theexpense of physiological stability.     

Prediction of Tonic Parasympathetic Cardiac Control Using Respiratory Sinus Arrhythmia: The Need for Respiratory Control

Respiratory sinus arrhythmia (RSA) has received much attention in recent years due to the large body of evidence indicating that variations in this phenomenon represent alterations in parasympathetic cardiac control. Although it appears that respiratory sinus arrhythmia is mediated by vagal mechanisms, the extent to which the well-known respiratory influences (i.e., rate and tidal volume) on respiratory sinus arrhythmia (in altering its magnitude) may moderate the relationship between RSA and cardiac vagal tone has never been systematically studied. We addressed this issue by examining intraindividual relationships among RSA magnitude, respiration (rate and tidal volume), and heart period among six healthy male adults after intravenous administration of 10 mg propranolol, a beta-adrenergic blocker. Subjects were exposed to various behavioral tasks which altered all physiological variables measured. Variations in heart period after beta blockade were assumed to be predominantly vagally mediated. Within-subject regression analyses consistently showed that respiratory parameters influenced RSA magnitude, but not tonic variations in beta-blocked heart period, suggesting that respiratory-mediated RSA alterations are not associated with changes in cardiac vagal tone. Only when respiratory variables were statistically controlled was there evidence of a reasonable correspondence between beta-blocked heart period and RSA amplitude, providing support for the idea that respiratory parameters need to be controlled when using RSA amplitude as an index of cardiac vagal tone. Repeated-measures analyses of variance of mean levels of heart period and respiratory sinus arrhythmia across subjects supplemented and supported the intraindividual results. These findings point to the importance of controlling for respiratory parameters when using respiratory sinus arrhythmia as a cardiac vagal index.     

Sigh rate and respiratory variability during mental load and sustained attention

Spontaneous breathing consists of substantial correlated variability: Parameters characterizing a breath are correlated with parameters characterizing previous and future breaths. On the basis of dynamic system theory, negative emotion states are predicted to reduce correlated variability whereas sustained attention is expected to reduce total respiratory variability. Both are predicted to evoke sighing. To test this, respiratory variability and sighing were assessed during a baseline, stressful mental arithmetic task, nonstressful sustained attention task, and recovery in between tasks. For respiration rate (excluding sighs), reduced total variability was found during the attention task, whereas correlated variation was reduced during mental load. Sigh rate increased during mental load and during recovery from the attention task. It is concluded that mental load and task‐related attention show specific patterns in respiratory variability and sigh rate.     

Data-dependent filter characteristics of peak-valley respiratory sinus arrhythmia estimation: A cautionary note

Filter characteristics of the peak-valley respiratory sinus arrhythmia estimation method are described. To identify filter characteristics of this method, models were generated that combined signals of different frequencies with trends of varying slopes. These models simulate the influence of trend and changing respiratory frequency on the accuracy of peak-valley estimates. The transfer function of the peak-valley method, unlike that of other time domain filters, is not solely dependent upon signal frequency. Two factors interact to determine the relative accuracy of the peak-valley method: (a) slope of the signal component and (b) slope of the underlying trend. Combinations of these factors may result in significant distortion to the input signal. The direction of error is a function of the direction of the trend (i.e., overestimation with deceleration and underestimation with acceleration). In many situations when respiratory sinus arrhythmia amplitude is low in special populations (e.g., cardiovascular disorders, high-risk infants, or human fetuses) or under conditions that greatly reduce respiratory sinus arrhythmia amplitude (e.g., exercise, drugs, pharmacological manipulations), use of the peak-valley method may result in significant measurement error. The use of this method to evaluate respiratory sinus arrhythmia over short epochs (i.e., less than 2 min) or to quantify changes in respiratory sinus arrhythmia due to discrete stimulation (e.g., breath by breath) may result in inconsistent measurement error. Recommendations are made for detrending heart rate data prior to application of the peak-valley method.     

Assessment of autonomic function by the spectral analysis of heart rate variability: an examination in a mirror drawing task]

The effect of an experimental task on autonomic function was investigated by spectral analysis of heart rate variability in 13 male college students. Power spectral density of heart rate variability has been said to contain two significant components: respiratory sinus arrhythmia (RSA) as an index of cardiac vagal activity, and Mayer wave related sinus arrhythmia (MWSA) as an index of sympathetic activity with vagal modulation. Those two components were examined during a task of mirror drawing on the CRT. In order to eliminate the effect of respiratory rate on RSA, the respiratory rate was controlled at 15 breaths/min. Furthermore, the coefficient of variance of R-R interval (CV-RR) and the fluctuation of plethysmograph (PTG) were calculated simultaneously. Results indicated that, while RSA decreased significantly, MWSA did not change during the task. On the other hand, neither CV-RR nor PTG showed any significant differences during the task. These findings indicated that cardiac parasympathetic activity was diminished in the mirror drawing task. The significance of spectral analysis of heart rate variability were discussed.     

Cardiovascular Responses to the Combination of Caffeine and Mental Arithmetic, Cold Pressor, and Static Exercise Stressors

The present study examined cardiovascular responses to the combination of caffeine (250mg) and mental arithmetic, cold pressor, and static exercise stressors in 48 healthy males. Subjects were tested in a within-subject, placebo-controlled, double-blind design. Repeated measurements of heart rate, finger temperature, respiratory sinus arrhythmia, forearm blood flow, and blood pressure were obtained during a pre-drug resting baseline, a post-drug resting baseline, the three stressor tasks, and a recovery baseline. The primary analyses were 2(Drug) x 5(Period) x 6(Stress Order) MANCOVAs using pre-drug baseline values as covariates. Significant period main effects were observed for all measures. Significant drug main effects were observed for blood pressure, finger temperature, respiratory sinus arrhythmia, and forearm blood flow. The significant changes in blood pressure and finger temperature produced by caffeine combined in an additive fashion with the effects produced by the stressors. Significantly greater increases in forearm blood flow and heart rate during mental arithmetic on the caffeine day suggested a potentiation of sympathetic, beta-adrenergic activity. Questionnaires administered during baseline periods to assess psychological responses to stress and caffeine revealed a potentiation of anxiety and anger responses to stress on the caffeine day.     

Autonomic cardiac control. II. Noninvasive indices and basal response as revealed by autonomic blockades

Heart period, systolic time intervals, low and high frequency heart period variability, blood pressure, and respiration were measured in female subjects under three drug conditions (saline, atropine sulfate, metoprolol) while sitting and standing on three consecutive days. Following preinfusion baseline recordings, saline, metoprolol (14 mg), or atropine sulfate (2 mg) was infused for 15 min (by using a double-blind procedure). Recordings were taken during a postinfusion baseline and in response to an orthostatic stressor (standing versus sitting postures). At the end of the metoprolol session, atropine sulfate was infused and responses were monitored during the post-infusion (i.e., double blockade) baseline and during orthostatic stressor. Analyses of the blockade data revealed that the preejection period (PEP) reflected sympathetic but not vagal influences on the heart, and high frequency (HF, 0.12–0.40 Hz) heart rate variability (respiratory sinus arrhythmia) reflected vagal but not sympathetic influences on the heart. No other measure provided a specific index of the tonic sympathetic or vagal activation of the heart. Postinfusion PEP under saline predicted individual differences in postinfusion cardiac sympathetic activation, whereas postinfusion heart period (but not HF variability) under saline predicted individual differences in postinfusion cardiac vagal activation.     

The properties of V in newborns across repeated measures

It has been argued that a recently developed measure, vagal tone (V), is a significant advancement over other existing methods of assessing the periodic variation in heart rate associated with respiration (respiratory sinus arrhythmia). It has been further suggested that, as a noninvasive measure of vagal nerve efferent activity, V may facilitate the early identification of infants at risk for developmental disabilities. This study addressed the relationship between V and other measures of cardiac activity and behavioral state and the stability of V across repeated measures. Twelve samples of cardiac activity were collected from each of 20 full term infants, 6 samples on each of two consecutive days. V values were derived using a spectral analysis program comparable to Porges' patented MXedit process. Measures of behavioral states were collected by continuous observation. Heart period and heart period variability were highly correlated with V. Variation in V between behavioral states was also detected. Repeated assessments revealed that average V values collected in the same state were not significantly correlated across successive days. This short-term variability both between and within individuals does not support the notion that a single assessment of V can, by itself, be used to identify at-risk infants or predict developmental outcome.     

Development of sinus arrhythmia during sleeping and waking states in normal infants.

The development of variability in heart rate (HR) due to respiration (sinus arrhythmia; SA) has been examined in normal infants from birth through the first 6 months of life. Two aspects of HR variation were examined: the absolute variation at the median respiratory frequency, or extent of sinus arrhythmia (XSA), and the degree to which HR follows respiration regardless of the absolute amount of variation, or coherence of sinus arrhythmia (CSA). Extent of sinus arrhythmia tended to be highest in quiet sleep (QS), lower in active or REM sleep (AS), and lowest in waking (AW), especially after 2 months of age. Extent declined at 1 month of age in QS, but rose over the first 6-month period in all states. During this same period, CSA was also highest in QS, lower in AS, and lowest in AW. Coherence in QS also declined at 1 month and rose between 1 and 6 months; however, no age effects were found in other states. Heart rate was negatively correlated with XSA, but less so with CSA. Sleep state appears to have a significant effect on cardiorespiratory coupling, and this coupling undergoes dramatic changes at 1 month in QS.