Cardiac deceleration in newborns: habituation, dishabituation, and offset responses.

Twenty healthy, 1–4 day-old infants were selected from a sample of 135 neonates on the basis of alertness during testing. The infants were presented mild intensity colored light with gradual onset and offset while heart rate was monitored. Half the infants received six exposures to blue light followed by two exposures to blue-green light, whereas remaining subjects received colors in reverse order. Stimulus duration was 20 sec and variable periods between stimuli averaged 30 sec. Results of trend analysis of variance of the second-by-second cardiac data indicated that for infants older than the median age, the decelerative responses to both stimulus onset and offset were significant. Further, these subjects' onset decelerations significantly habituated within the six stimulus repetitions and significantly dishabituated with change in the stimulus color. Offset decelerations incremented over habituation trials and decremented with change in stimulus color. Responses of younger subjects were more variable which probably reflects their less complete recovery from the effects of maternal medication and the birth process.     

Infants' responsiveness to the auditory and visual attributes of a sounding/moving stimulus.

Responses to unimodal and multimodal attributes of a compound auditory/visual stimulus were investigated in 4-, 6-, 8-, and 10-month-old infants. First, infants were habituated to a compound stimulus consisting of a visual stimulus that moved up and down on a video monitor and a sound that occurred each time the visual stimulus reversed direction at the bottom. Once each infant met a habituation criterion, a series of test trials was administered to assess responsiveness to the components of the compound stimulus. Response was defined as the total duration of visual fixation in each trial. In the two unimodal test trials, the rate at which the component was presented was changed while the rate of the other component remained the same, whereas in the bimodal test trial the rate of both components was changed simultaneously. Results indicated that infants at each age successfully discriminated the bimodal and the two unimodal changes and that regression to the mean did not account for the results. Results also showed that disruption of the temporal relationship that accompanied the change in rate in the two unimodal test trials was also discriminable, but rate changes appeared to play a greater role in responsiveness than did synchrony changes. Considered together with results from similar prior studies, the current results are consistent with the modality appropriateness hypothesis in showing that discrimination of temporal changes in the auditory and visual modalities is dependent on the specialization of the sensory modalities.     

Infants’ responsiveness to the auditory and visual attributes of a sounding/moving stimulus

Responses to unimodal and multimodal attributes of a compouMauxlitoryMsuat stimulus were investigated in 4-, 6-, 8-, and 10-month-old infants. First, infants were habituated to a compound stimulus consisting of a visual stimulus that moved up anddown on a video monitor and a sound that occurred each time the visual stimulus reversed direction at the bottom. Once each infant met a habituation criterion, a series of test trials was administered to assess responsiveness to the components of the compound stimulus. Response was defined as the total duration of visual fixation in each trial. In the two unimodal test trials, the rate at which the component was presented was changed while the rate of the other component remained the same, whereas in the bimodal test trial the rate of both components was changed simultaneously. Results indicated that infants at each age successfully discriminated the bimodal and the two unimodal changes and that regression to the mean did not account for the results. Results also showed that disruption of the temporal relationship that accompanied the change in rate in the two unimodal test trials was also discriminable, but rate changes appeared to play a greater role in responsiveness than did synchrony changes. Considered together with results from similar prior studies, the current results are consistent with the modality appropriateness hypothesis in showing that discrimination of temporal changes in the auditory and visual modalities is dependent on the specialization of the sensory modalities.     

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.     

Varying temporal placement during CS of an added stimulus correlated with non-delivery of UCS

This experiment extends Pavlov’s method of contrasts for training a stimulus discrimination to the case of the cardiac conditional response in the rhesus monkey. It explores the parameter of temporal placement of an additional stimulus (“CS₂”) within a 10-sec CS (or “CS₁”), with the appearance of the former stimulus on any trial signalling the absence of UCS (electric shock) on that trial. This experimental paradigm is a parallel to that of the “intruded stimulus” studies in operant conditioning. In both cases, several ways of describing the function of the added stimulus are possible, but all seem reducible to the same operational terms. Data were taken in the present study with respect to the form and latency of the cardiac rate changes produced by intrusion of CS₂ (light), across a range of placements varying from simultaneity with CS₁ (a different light) onset to two sec before UCS would have been delivered. The control of CS₂ over the cardiac rate CR was occasionally exhibited with a latency as short as three beats after stimulus onset. The order of CS₂ temporal placements to which a subject was exposed was a factor in determining the form of the conditioned cardiac rate response to CS₁.     

Heart rate and self-report changes accompanying different types of relaxing imagery

Two groups of 10 subjects were instructed, following appropriate training, to evoke different types of relaxing imagery for a total of five 30 s trials. For one group the instruction stressed response elements in the image, for the other stimulus elements. A third, control group of 10 were invited to relax by any means they considered appropriate. No specific imagery instructions were given here. Heart rate was recorded throughout and ratings of sleepiness were made by subjects at the end of each trial. Analogue mood scales were completed pre- and post-experimentally. While the self-report measures intimated an increase in feelings of relaxation and sleepiness over the course of the experiment, no group differences were observed. For heart rate, however, group differences were apparent. Overall, heart rate change during trials took the form of cardiac acceleration. However, while the two imagery groups demonstrated more or less sustained acceleration throughout trial periods, the acceleration observed initially in the control group showed a pronounced linear decline with a net deceleration being recorded toward the end of each trial. The imagining of response or stimulus elements did not differentially affect heart rate. These data imply that the process of imagining constitutes a more important influence on heart rate in these circumstances than image type or affective content.     

Mothers' responses to the cries of normal and premature infants as a function of the birth status of their own child

Mothers of premature and full-term infants viewed and heard videotapes of premature and full-term infants. The onset of crying by both infants elicited physiological arousal (evident in blood pressure, skin conductance, and heart rate increases) in the adults. The mothers of premature infants responded with especially marked arousal to the infants' cries. These mothers also reported that they were more attentive and alert while the infant was crying. The subjects responded similarly to the cries of full-term and premature infants. Mothers who described their own baby as easy exhibited a lower increase in diastolic blood pressure and heart rate, and reported being more alert, attentive, and willing to interact with the stimulus babies than those whose own baby appeared “difficult.”     

Cardiac-somatic integration: An index of visual attention

Eighteen 15-week-old, normal full-term infants were presented with photographic slides of a human facial expression. The infant's heart rate, body movement, and visual attention were recorded simultaneously. The results showed that heart rate and body movement were significantly correlated during visual attention but not during inattention. Both heart rate and body movement decelerated significantly when the infants visually attended to the target stimulus. The results are discussed with reference to cardiac-somatic integration in early infancy and its implication as a possible index of attention.     

Responding time: A response equivalent to inspection time

A response equivalent to ‘inspection time’ (IT) was developed using a reaction time task in which Ss were required to respond as quickly and accurately as possible to whichever one of two lights appeared on each of a number of trials. The appearance of the lights was followed on all trials by a backward mask. IT was estimated for each S as the shortest duration between the onsets of the light and the backward mask at which the S could respond accurately on virtually every trial. An estimate of ‘responding time’ was then made by setting the duration between the stimulus onset and the mask to each S's individual IT and gradually reducing the time between trials so that Ss had less and less time in which to respond correctly. Responding time was taken to be the shortest such interval at which the S could respond accurately on virtually every trial. This measure was found to be reliable although quantitatively different estimates were obtained using two different methods of presenting the stimulus trials. Responding time was longer for a group of lower-intelligence Ss than for a group of higher-intelligence Ss and the measure was also found to correlate with measured intelligence in the former group. However, it did not itself correlate significantly with IT suggesting that responding time and IT may be measuring different underlying processes.     

Simultaneous temporal processing

Seven experiments assessed the ability of rats to process temporal information from two internal clocks simultaneously and independently. In the first six experiments a light stimulus signalled an overall interval between the beginning of a trial and the availability of food reinforcement (e.g., a 50-s fixed interval). During the overall interval a sound stimulus was used to signal shorter intervals that divided the overall interval into equal segments. When there was a fixed temporal relation between the final segment signal and the availability of reinforcement, there was a double-scallop pattern of responding throughout the segmented overall interval; the function relating response rate to time during segment intervals was similar to the function relating response rate to time in unsegmented overall intervals; a change in response rate occurred at the time that a normally presented segment signal was omitted. Taken together, the results indicate that rats timed the overall interval and the segment intervals simultaneously and independently without interference. In Experiment 7 a light stimulus was used on some trials, and a sound stimulus was used on other trials to signal a discrete-trial 50-s peak procedure. When these two signals were presented in compound, there was a leftward shift of the response function, which suggests that rats timed both signals simultaneously. For all of the experiments a scalar timing model with specific stimulus integration rules is used to explain the results. The stimulus integration rule used in the first six experiments, in which there were two signals for the same reinforcement, was to respond if both the segment and the overall interval had exceeded a response threshold. The stimulus integration rule used in Experiment 7, in which there were two signals for different reinforcements, was to respond if the response threshold for either interval had been exceeded.     

The role of attention in children's time perception.

This study tested the role of attention in 7- to 9-year-old children's time estimation. Based on an attentional model of time estimation, it was hypothesized that prospective estimates of short intervals are a function of the degree to which a child is occupied with the passage of time and is focusing his or her attention on estimating the exposure time of a stimulus. Two experiments with two different manipulations on attentional focus were conducted. Eighty children were exposed to two types of light bulbs, one a big bulb kindled with high intensity and the other a small one kindled with low intensity. The light bulbs were kindled for different intervals ranging from 3 to 10 s. In both experiments children estimated the lighting time of the bulbs in each condition by a reproduction method. In the first experiment prospective time estimates were found to be significantly longer than retrospective ones. In the second experiment children gave shorter time estimates when their attention was attracted away from the time estimation task than when it was not. In both experiments the attentional hypothesis was supported. In addition, support for the "more is more" hypothesis was obtained. Implications for understanding children's time perception processes are discussed.     

Recognition memory and cardiac vagal tone in 6-month-old infants

Individual differences in visual recognition memory and cardiac vagal tone were assessed in 14 6-month-old infants. A multi-dimensional problem was presented with the paired-comparison technique to assess recognition memory. Cardiac vagal tone was evaluated by quantifying the amplitude of respiratory sinus arrhythmia. Individual differences in spontaneous baseline cardiac vagal tone were correlated with two measures of visual recognition memory. Infants characterized by high cardiac vagal tone looked for shorter periods at the standard (i.e., familiar) stimulus during familiarization and looked for longer periods at the novel stimulus during the test trials. In response to the visual stimulus during the familiarization and test trials, heart rate decelerated only for the infants who performed well on the visual recognition memory task (i.e., those who looked longer at the novel stimulus than the familiar stimulus).     

Long-term retention in 3.5-month-olds: familiarization time and individual differences in attentional style

Using a paired-comparison procedure, we examined the effect of familiarization variables on 3.5-month-old infants' (n = 120) retention of dynamic visual stimuli after 1-min, 1-day, and 1-month delays. The proportion of total looking time to the novel stimulus revealed novelty, null, and familiarity preferences after 1-min, 1-day, and 1-month delays, respectively, for infants who were permitted 30 s of familiarization time. Twenty seconds of familiarization time was insufficient to produce novelty preferences. These results support models of infant retention in which the direction of attentional preferences (novel, familiar, or null) depends on memory accessibility. To examine the impact of individual differences in familiarization or attentional style on memory, infants were identified as long or short lookers according to their peak-look duration on pretest and familiarization trial measures. Compared to long lookers, short lookers showed better retention over time indicating that much of the variability in the infant group data could be accounted for by these individual differences.     

Infant responses of ocular fixation to moving visual stimuli

Infants of 1, 2, and 3 months of age were presented with two checkerboard patterns, one stationary and the other moving in a horizontal oscillatory motion at one of eight rates. An observer who could see only the infant's head and eyes recorded, for each 30-sec trial, (a) the position of first fixation, (b) position of fixation at the end of each 5-sec interval, and (c) a final forced-choice judgment of the position of the moving stimulus. Results showed reliable differences in ocular behavior as a function of rate of stimulus motion for all three groups of infants.     

Newborn habituation to visual stimuli: a sex difference in novelty detection

Thirty-six newborn human infants were repeatedly exposed to one of two visual stimuli, a four-square or 144-square black and white checkerboard target, until a set criterion of habituation was demonstrated, as measured by a decrement in visual fixation time. When the habituation criterion was reached, independent groups of Ss were either presented with the same target or with a target of either moderate or large discrepancy from the standard habituation stimulus. Results indicated that (1) there was habituation of visual attention, which replicated previous findings, and suggests that some infants soon after birth are capable of storing simple visual information, and (2) following habituation female infants displayed greater recovery of attention than male infants when the moderate stimulus change was introduced.     

Robustness of the rule-learning effect in 7-month-old infants: A close,multicenter replication of Marcus et al. (1999)

We conducted a close replication of the seminal work by Marcus and colleagues from 1999, which showed that after a brief auditory exposure phase, 7-month-old infants were able to learn and generalize a rule to novel syllables not previously present in the exposure phase. This work became the foundation for the theoretical framework by which we assume that infants are able to learn abstract representations and generalize linguistic rules. While some extensions on the original work have shown evidence of rule learning, the outcomes are mixed, and an exact replication of Marcus et al.'s study has thus far not been reported. A recent meta-analysis by Rabagliati and colleagues brings to light that the rule-learning effect depends on stimulus type (e.g., meaningfulness, speech vs. nonspeech) and is not as robust as often assumed. In light of the theoretical importance of the issue at stake, it is appropriate and necessary to assess the replicability and robustness of Marcus et al.'s findings. Here we have undertaken a replication across four labs with a large sample of 7-month-old infants (N = 96), using the same exposure patterns (ABA and ABB), methodology (Headturn Preference Paradigm), and original stimuli. As in the original study, we tested the hypothesis that infants are able to learn abstract “algebraic” rules and apply them to novel input. Our results did not replicate the original findings: infants showed no difference in looking time between test patterns consistent or inconsistent with the familiarization pattern they were exposed to.     

Reaction time as a function of stimulus uncertainty on a single trial

In a discrete choice-reaction-time experiment, reaction times were measured between the onset of a light and the start of S’s pencil toward that light. The reaction time of unpracticed Ss, not aware that their first “practice” trial was being measured, increased as a linear function of stimulus uncertainty. Since this occurred without any prior experience, the effect must have been due to S’s set or expectancy regarding the nature of the future task, formed while the instructions for the task were being given.     

Cardiac activity and information processing: the effects of stimulus significance, and detection and response requirements.

In two experiments, measures of heart rate and electromyographic activity were obtained from 40 male undergraduates while they performed two series of trials involving a sequential information processing task. Each trial consisted of a warning light, three successive tones, and a responded light, separated by 6-sec intervals. In Experiment 1, subjects responded only if the three tones were of different frequencies. Acclerative heart-rate responses to the last tone increased as a function of the significance of that tone. Subsequent cardiac decelerations were only observed if the subject was preparing to make a response. These results were replicated in Experiment 2, in which subjects responded only if two of the preceding tones were of the same frequency. Electromyographic activity was not significantly affected by stimulus significance or response anticipation. The data indicate that cardiac acceleration and deceleration reflect two independent psychological processes, associated with information-processing and decision-making activity on the one hand, and preparatory activity on the other.     

短时距估计中刺激物的动态变化效应

用两个实验考查了时距估计中刺激物的动态变化效应。结果发现,刺激物的运动、速度和旋转角度显著地影响着被试的时间判断,刺激物速度的时距延长效应对于较长时距(18s-24s)来说更加明显;运动刺激与较短、较准确的时距判断相关联;旋转角度的减少使得被试低估时距,而旋转角度的增加使得时距估计呈高估倾向。被试在时间估计过程中表现出长时距低估和短时距高估现象,本研究得到的时间估计转换点是11.4s,此点与先前的有关研究基本一致。     

Comparison of timing and classical conditioning

Four experiments with rats investigated if the timing of a stimulus (sound) correlated with the strength of a conditioned response (CR) to the stimulus. The timing (effective duration) of the stimulus was measured using the peak procedure, similar to a discrete-trials fixed-interval procedure. The rats were trained so that their response rate reached a maximum about 40 s or 60 s after the onset of a light; the time of the maximum measured from the start of the light (peak time) was the measure of timing. On some trials, the light was preceded by a short (5 s) or long (20 s or 30 s) interval of sound. We assumed that the difference in peak time after long and short sounds reflected the timing of the sound--if the sound was timed, the longer sound would produce a lower peak time; if the sound was not timed, the two durations of sound would produce the same peak time. The CR was lever-pressing during the sound. The sound was treated in various ways: presented alone (Experiments 1, 3, and 4), followed by food (Experiments 1, 3, and 4), preceded by food (Experiment 3), and followed by food after 20 s (Experiment 4). Treatments that produced no timing of sound produced no CR, and treatments that increased (or diseased) timing also increased (or decreased) the CR. The results suggest that there is overlap between the mechanisms that produce time discrimination and the mechanisms that produce classical conditioning.