Rhythmic organization of heart rate in breast-fed and bottle-fed newborn infants

Heart rates and behavioural states of 14 breast-fed and 14 bottlefed newborn infants were assessed every 30 seconds for 2 continuous hours. The 240 observations of heart rate were treated as time-series data and spectrum-analysed for behavioural rhythmicities. Of the 28 infants, 25 showed reliable cycles in heart rate; 22 of the 25 infants showed a dominant frequency with a 30–60 min periodicity, one that approximates the basic-rest activity cycle (BRAC). In addition to this basic cycle, additional higher frequency cycles in long-term heart rate variability were evident in the spectra of many infants. Breast-fed newborns had greater numbers of reliable cycles in heart rate than bottle-fed newborns. Further, breast-fed newborns had lower overall mean heart rates and lower mean heart rates in Quiet and Active Sleep states than bottle-fed newborns. Bottle-fed newborns were observed more often in Quiet Sleep than breast-fed newborns. Without knowledge of the specific mechanisms causing these behavioural differences, the results of this study suggest that the context in which breast-feeding occurs results in a more complex and energy-efficient pattern of behavioural organization than the context of bottle-feeding.     

Representing within-session response rates proportionally and entirely.

In this technical article, methods for collecting and representing response rates maintained by schedules of reinforcement are presented. First, the time in a session that each important event (e.g., responses, reinforcers) occurs is collected and stored by a computer. Another computer program is used, then, to convert each response to a percentage of the total responses in a session and to plot these percentages cumulatively as a function of the time in the session that they occurred. In this manner, response rates may be expressed proportionally (i.e., using the same y-axis scale regardless of absolute response rate) without requiring the arbitrary selection of an interval over which responses are aggregated and expressed relative to the entire-session rate. A property of these records is that deviations in the slope of the obtained record from the diagonal, which connects (x, y) = (start of session, 0%) to (x, y) = (end of session, 100%), occurring at any point and for any duration, represent changes in the local response rate from the entire-session rate. This method of representing ongoing responding is illustrated by several records of key pecking of a pigeon on a variable-interval 60-s schedule of food reinforcement. Relative local response rates were also computed from these data at several levels of resolution (i.e., the time over which responses were aggregated), including the level typically employed by those interested in within-session changes in response rates.     

Concurrent choice: Effects of overall reinforcer rate and the temporal distribution of reinforcers

Six pigeons responded on a series of concurrent exponential variable-interval schedules, offering a within-subject comparison with previously published data from concurrent arithmetic variable-interval schedules. Both relative and overall reinforcer rates were varied between conditions. The generalized matching law described the data well, with undermatching much more frequent than strict matching. Time-allocation sensitivity consistently exceeded response-allocation sensitivity for both schedule types, and exponential-schedule sensitivity exceeded arithmetic-schedule sensitivity for both measures of choice. A further set of conditions using variable-interval schedules whose shortest interval was correlated with the mean interval, like arithmetic schedules, but that provided a constant conditional probability of reinforcement, like exponential schedules, produced sensitivities between those produced by conventional arithmetic and exponential schedules. Unlike previous arithmetic-schedule results, exponential sensitivity changed nonmonotonically with changes in overall reinforcer rate. The results clarify our knowledge of the effects of arithmetic and exponential schedules but confuse our understanding of the effects of overall reinforcer rate on concurrent choice.     

Psychophysiological responding as a function of age: The importance of matching

Few studies in the past which have employed psychophysiological measures have controlled for age. We have studied the effects of age on the heart rate, hand surface temperature, cephalic vasomotor response, and frontal electromyographic activity (EMG) of 73 normal individuals who varied in age from 18 to 68 years and were evenly divided into younger, middle, and older age groups. Comparisons were made between groups across eight conditions — baseline, relax body, warm hand, relax facial muscles, mental arithmetic, positive imagery, negative imagery, and cold pressor. Results indicated a direct linear relationship between age and electromyographic activity during relax facial muscles and mental arithmetic conditions. There was also a linear relationship between age and hand surface temperature during stressor conditions. Most important, significant interactions were found for both frontal EMG and heart rate measures with age. Post hoc analyses revealed differences on the frontal EMG levels between younger and older age groups during negative imagery, warm hand, and cold pressor conditions. Heart rate differences were found during positive imagery between the younger age group and the medium age group and during cold pressor between the younger age group and both the medium and the older groups. The implications of these findings are discussed.This research was supported in part by NINCDS Grant NS-15235.     

The role of verbal behavior in human learning: infant performance on fixed-interval schedules

The performances of two infants less than one year old were investigated on fixed-interval schedules. When the infants touched a cylinder either music or food was presented according to fixed-interval schedules ranging in value from 10 to 50 seconds. With respect to two principal criteria, namely, pattern of responding and sensitivity to the schedule parameter, the subjects' behavior closely resembled that of animals but differed markedly from that of older children and adults. Negatively accelerated responding in the course of the fixed interval in the early sessions gave way to a scalloped pattern, consisting of a pause after reinforcement followed by an accelerated response rate. This scalloped pattern was the final form of responding on all schedule values. Analysis of data after performance had stabilized showed that postreinforcement pause was a negatively accelerated increasing function, and running rate (calculated after excluding the postreinforcement pause) was a declining function, of schedule value. On each schedule, the durations of mean successive interresponse times declined in the course of the fixed interval and were directly related to schedule value. The results supported Lowe's (1979) suggestion that verbal behavior may be responsible for major differences in the schedule performance of older humans and animals.     

Choice for aperiodic versus periodic ratio schedules: A comparison of concurrent and concurrent-chain procedures

Choice between mixed-ratio schedules, consisting of equiprobable ratios of 1 and 99 responses per reinforcement, and fixed-ratio schedules of food reinforcement was assessed by two commonly used procedures: concurrent schedules and concurrent-chains schedules. Rats were trained under concurrent fixed-ratio mixed-ratio schedules, in which both ratio schedules were simultaneously available, and under a concurrent-chains schedule, in which access to one of the mutually exclusive ratio schedules comprising the terminal links was contingent on a single “choice” response. The distribution of responses between the two ratio schedules was taken as the choice proportion under the concurrent procedure, and the distribution of “choice” responses was taken as the choice proportion under the concurrent-chains procedure. Seven of eight rats displayed systematic choice; of those, each displayed nearly exclusive choice for fixed-ratio 35 to the mixed-ratio schedule under the concurrent procedure, but each displayed nearly exclusive choice for the mixed-ratio schedule to fixed-ratio 35 under the concurrent-chains procedure. Thus, preference for a fixed or a mixed schedule of reinforcement depended on the procedure used to assess preference.     

Effects of ethanol on multiple fixed-interval fixed-ratio schedule performances: dynamic interactions at different fixed-ratio values.

Key pecking by three pigeons was maintained under a multiple fixed-interval fixed-ratio schedule of food presentation. The fixed-interval value remained at 3 minutes, while the fixed-ratio size was increased systematically in 30-response increments from 30 to either 120 (two pigeons) or 150 (one pigeon). At least two lower fixed-ratio values were also redetermined. The effects of ethanol (5 to 2.5 g/kg) were assessed at each of the different schedule parameters. Both overall and running response rates under the fixed-ratio schedule decreased with increases in the size of the fixed-ratio schedule; pause duration under the fixed-ratio schedule was directly related to increases in fixed-ratio size. Overall and running rates of responding under the fixed-interval schedule changed little with increases in the size of the fixed-ratio schedule. Despite the relative invariance of fixed-interval responding across the different fixed-ratio values, the effects of ethanol on responding under the fixed-interval schedule differed depending on the size of the fixed-ratio schedule. Greater increases occurred in both overall and in lower local rates of responding under the fixed-interval schedule when the fixed-ratio value was 120 or 150. The effects of ethanol on responding under the fixed-ratio schedule also depended on the size of the fixed ratio. Increases in responding under the fixed-ratio schedule were typically greater at the higher fixed-ratio values where response rates were lower. When the effects of ethanol were redetermined at the lower fixed-ratio parameter values, rates and patterns of responding were comparable to those obtained initially. However, the dose-effect curves for responding under both fixed-ratio and fixed-interval schedules were shifted up and to the right of those determined during the ascending series. The effects of ethanol can depend on rate or responding, behavioral history, and the context in which behavior occurs.     

Relationship between response rate and reinforcement frequency in variable-interval schedules: the effect of the concentration of sucrose reinforcement

Four rats were exposed to variable-interval schedules specifying a range of different reinforcement frequencies, using sucrose of two different concentrations and distilled water as the reinforcer. With sucrose, the rates of responding of all four rats were increasing negatively accelerated functions of reinforcement frequency, the data conforming closely to Herrnstein's equation; this was also true of the data from three of the four rats when distilled water was used as the reinforcer. The values of both constants in Herrnstein's equation were related to the sucrose concentration: the asymptotic response rate decreased, and the reinforcement frequency corresponding to the half-maximal response rate increased, with decreasing sucrose concentration.     

Fixed-interval matching-to-sample: intermatching time and intermatching error runs

Four pigeons were trained on a matching-to-sample task in which reinforcers followed either the first matching response (fixed interval) or the fifth matching response (tandem fixed-interval fixed-ratio) that occurred 80 seconds or longer after the last reinforcement. Relative frequency distributions of the matching-to-sample responses that concluded intermatching times and runs of mismatches (intermatching error runs) were computed for the final matching responses directly followed by grain access and also for the three matching responses immediately preceding the final match. Comparison of these two distributions showed that the fixed-interval schedule arranged for the preferential reinforcement of matches concluding relatively extended intermatching times and runs of mismatches. Differences in matching accuracy and rate during the fixed interval, compared to the tandem fixed-interval fixed-ratio, suggested that reinforcers following matches concluding various intermatching times and runs of mismatches influenced the rate and accuracy of the last few matches before grain access, but did not control rate and accuracy throughout the entire fixed-interval period.