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Biomedical subjects

R J Somsen

Publications and source records attributed to R J Somsen.

At least 19 recordsLinked to original sources
PubMed2000

Wisconsin Card Sorting in adolescents: analysis of performance, response times and heart rate.

Forty-nine adolescents performed the Wisconsin Card Sorting Test (WCST). A main PCA component of WCST performance was identified as 'efficiency of reasoning'. This factor was related to feedback processing. From the WCST, a perseveration score can be derived. Perseveration is the continued application of a rule, after it has been disconfirmed. We compared more and less perseverating subjects in relation to stimulus-response (SR) time, feedback inspection time and cardiac acceleration and deceleration. Less perseverating subjects responded faster, and had longer and more adaptive inspection times of error feedback. We examined the switch from rule application to rule search, and the difference between correct and error responses. A transient cardiac deceleration at the initiation of rule search was interpreted as a change in supervisory attention. An error-related deceleration to negative feedback was interpreted as a disturbance of higher control processing. Previous trial feedback influenced current processing time, feedback inspection time, and the cardiac acceleration and deceleration responses.

Adolescent↗
PubMed2000

Developmental change in auditory selective attention as reflected by phasic heart rate changes.

Heart rate was recorded from five different groups of children (ages 7, 10, 12, 14, and 20 years) while they were performing an auditory selective attention task. The participants were instructed to count rare tone pips embedded in a series of standard tone pips presented at one (attended) ear while ignoring rare and standard stimuli presented at the other (unattended) ear. A pattern of anticipatory heart rate deceleration followed by acceleration was associated with rare tone pips at the attended ear but not with rare tone pips that should be ignored. The absence of differential sensitivity of heart rate responses to rare tone pips presented at the unattended ear was observed for all age groups. These findings were interpreted to suggest that the ability to ignore irrelevant target stimuli has reached mature levels during middle childhood. The depth of anticipatory deceleration increased until age 14, suggesting that the ability to maintain attentional set continues to develop beyond childhood.

Acoustic Stimulation↗
PubMed1998

Changes in heart beat timing: reactivity, resetting, or perturbation?

A widely held hypothesis within behavioral medicine is that cardiovascular reactivity is a risk factor for cardiovascular disease. The measurement model for this cardiovascular reactivity is rather simple. A basal level of function is seen to increase while the organism is stressed and then return to basal function. We argue that this model is incomplete and that other forms of 'reactivity' may be relevant to pathophysiology. A pathophysiological hypothesis is discussed which assumes a cyclic heart beat generation mechanism that is sensitive to stimulation only at certain phases of its cycle. Implications of this hypothesis for measurement are developed to illustrate the point that models of normal function can determine the measures most relevant to pathophysiology.

Arousal↗
PubMed1998

Ocular artifacts in children's EEG: selection is better than correction.

The electroencephalogram (EEG) during middle childhood may be highly distorted by the occurrence of eye and head movement artifacts. Between 5 and 12 years children display a great number of such artifacts. In the present study we studied different methods to assess EEG artifacts in children. Three artifact treatments were compared with the uncorrected EEG: one widely used method which corrected the EEG for electrooculogram (EOG) EEG transfer and two methods which selected artifact-free EEG segments. The most effective method should selectively reduce the spectral power in the lower frequency bands and at the frontal regions which are most susceptible to eye artifacts. The results demonstrated that the selection procedure, which combined two criteria for the selection of artifact-free EEG segments, was superior. The procedure that corrected the EEG for EOG-EEG transfer unselectively removed spectral power across the whole scalp and across all frequency bands. Furthermore, part of the maturational change in frontal Alpha power was filtered out by the correction procedure. It was concluded that for the background EEG in children, it is better to carefully select artifact-free EEG segments than to correct for EOG-EEG transfer.

Age Factors↗
PubMed1997

Growth spurts in brain maturation during middle childhood as indexed by EEG power spectra.

Developmental changes in background EEG power spectra were examined in 5-12-year-old children. The results confirmed older and more recent studies that reported continuous maturation and more sudden growth spurts in power spectral amplitude. EEG power in the Delta and Theta frequency bands decreased gradually with age, while power in the Alpha and Beta bands changed very little. Changes in spectral power were relatively increased between 6 and 7 years and between 9, 10 and 11 years. Some methodological problems concerning the assessment of cross-sectional age changes in EEG power spectra were addressed. Peak frequency increased with age; between 5 and 12 years the peak in the power spectrum shifted from fast Theta via slow Alpha to fast Alpha. Transformation of absolute power into relative power produced a high degree of interdependency between the broad bands. This interdependency affected the change with age of relative Alpha. Absolute power Alpha only changed in the eldest children, but because of a substantial decrease in Delta and Theta with increasing age, the proportion of Alpha relative to the other three bands increased. Hence, relative Alpha provided a good indication of the general maturational trend.

Age Factors↗
PubMed1996

Does the heart know what the ears hear? A heart rate analysis of auditory selective attention.

Between- and within-channel auditory selective attention were examined by presenting subjects with tone pips randomly to opposite ears; some pips had a slightly different pitch. Subjects were instructed to count rare, deviant tone pips at one ear and ignore all input to the other ear. Heart rate was sampled twice: once for the attended tone pips and once for the nonattended stimulus series. Heart rate responded differently to attended tone pips. While subjects were waiting for the rare stimulus to occur, heart rate slowed until the deviant stimulus was detected, which was followed by heart rate acceleration. Anticipatory heart rate deceleration was largely absent for nonattended series, and rare tone pips presented at the nonattended ear were not followed by acceleratory recovery. All tone pips elicited cardiac cycle time effects, that is, stimuli presented at short delays after the R wave prolonged the concurrent interbeat interval more than stimuli presented later. The cardiac cycle time effect was not altered by stimulus relevance (attended vs. nonattended) or significance (standard vs. rare). These results suggest that all stimuli receive preliminary perceptual analysis, but only attended stimuli are processed for further evaluation.

Acoustic Stimulation↗
PubMed1993

How are tonic and phasic cardiovascular changes related to central motor command?

We examined the influence of central motor command on heart rate, respiration, and peripheral vascular activity. Central command was enhanced or reduced using tendon vibration. Muscle tension was held constant permitting the examination of variation in central command. Experiment 1 demonstrated in 13 college-aged males an enhancement of heart rate and vascular responses to an isometric, extensor contraction when vibration of the flexor tendon was added. Experiment 2 asked whether changes in central command interacted with phasic cardiovascular changes such as stimulus-linked anticipatory cardiac deceleration. Twenty college-aged males performed either an isometric flexor or extensor contraction with or without flexor tendon vibration. As expected, vibration enhanced cardiovascular change with extensor contraction more than with flexor contraction. Relative to control contractions, however, the flexor change was not an absolute decrease in cardiovascular change. More importantly, tendon vibration failed to alter phasic cardiovascular changes. Force and central commands for force induce cardiovascular change, but this change seems independent of phasic changes induced by the anticipation and processing of environmental stimuli.

Adolescent↗
PubMed1992

On the synchrony of stopping motor responses and delaying heartbeats.

Recent evidence suggests that inhibition of a motor response may occur as late as the final stages of response execution. Response production involves central commands for autonomic support as well as motoric action. Autonomically controlled responses were used in conjunction with electromyographic and performance indices to examine the timing and flexibility of inhibition. Twenty young male Ss performed a choice reaction time task with stimuli timed according to when they occurred in relation to the R wave of the electrocardiogram. Stop signals, presented on 30% of the trials, induced inhibition. The performance and physiological results generally supported the horse-race model of inhibition. Inhibition was observed as late as during response execution. A short-latency, phasic lengthening of interbeat interval was suggested to reflect the midbrain coordination of the countermanding of response execution.

Adolescent↗
PubMed1991

Behavioral modulation patterns fit an animal model of vagus-cardiac pacemaker interactions.

The present study used a computer model of the dynamic interaction between the vagus nerve and the sinoatrial pacemaker membrane potential in the heart of the rabbit to reconstruct heart rate changes under vagal excitation conditions. We asked whether a hypothetical pattern of vagal acetylcholine (ACh) release, which was based on human heart rate results in a reaction time task, could be fit to this model. The reconstructed heart rate results showed changes that were highly consistent with experimental human heart rate changes. The model reliably reproduced effects of parameters such as intrinsic heart rate level, ACh stimulus intensity, and ACh stimulus duration. In addition, the effects of anticipatory vagal ACh release, stimulus-induced ACh, and subsequent blocking of ACh, which usually interact in human cardiac cycle time functions, could be untangled in the reconstructed heart rate results. We concluded that the mathematical model may be useful for formulating hypotheses and constructing experimental task designs for studies of human heart rate.

Acetylcholine↗
PubMed1991

Graphical and statistical techniques for cardiac cycle time (phase) dependent changes in interbeat interval.

Cardiac cycle time effects refer to the relative lengthening or shortening of a single cardiac cycle as a function of when in the cycle brief sensorimotor events occur. These effects may provide short-latency measures of cardiac sensitivity to psychological events. Conventional representations have, however, failed to clearly separate changes in interbeat interval due to cycle time--i.e., phase dependent changes--from other types of change. This paper advocates a particular technique of plotting to solve these representation problems. Heartbeat timing is represented in real time and in the context of beats both preceding and following the event of interest. The plot, a phase-sensitive plot, conceptualizes phase-sensitive (cardiac cycle time) effects as a change in linear or higher order trend. Thus, an adaptation of trend analysis is proposed as an efficient statistical analysis that follows directly from the proposed representational technique.

Data Display↗
PubMed1991

Weak sensory stimuli induce a phase sensitive bradycardia.

We attempted to demonstrate that significant perceptual stimuli would induce different degrees of heart rate deceleration depending on when (phase) in the cardiac cycle they occurred. Relative to previous work, we concurrently examined a number of factors that might alter the amplitude of such a cardiac cycle time effect. Stimulus intensity and presence or absence of a speeded response were manipulated. Liminal stimuli and a perceptual rather than motor set were expected to maximize any cardiac cycle time effect. Respiratory phase, length of average interbeat interval, and number of trials were also investigated. Twenty-four college aged, male volunteers were randomly separated into equal groups receiving instructions either to judge which of two weak visual stimuli occurred or to execute a speeded, discriminative response to the stimuli. Discriminative stimuli were presented at either 0, 150, 250, 350, or 500 ms after the R-wave of the electrocardiogram. Stimuli were presented with an intensity that had yielded either 63% or 90% correct detections in a prior psychophysical assessment. A phase dependent deceleration occurred after both intensities of stimuli. Poststimulus deceleration was greater for stimuli in early to mid cycle as suggested by earlier work. As expected, this result was clear when the stimuli were presented during the expiratory phase of respiration. Neither perceptual/motor set nor stimulus intensity altered the phase sensitive deceleration. Thus, phase sensitive deceleration was confirmed using demanding sensory stimuli and an improved representational technique.

Adolescent↗
PubMed1991

Response inhibition initiates cardiac deceleration: evidence from a sensory-motor compatibility paradigm.

Two experiments tested the hypothesis that response selection processes alter the timing of the shift between anticipatory cardiac deceleration and acceleratory recovery. Experiment 1 compared changes in cardiac interbeat interval induced by the manipulation of sensory-motor compatibility in a four choice reaction time task. A direct spatial mapping between a linear array of light-emitting diodes (LEDs) was compared to randomly assigned, indirect (non-compatible) mappings. Experiment 2 repeated these two tasks and added a two choice condition with direct spatial mapping, a task frequently employed to examine heart rate deceleration. Fifteen college aged males participated in Experiment 1; 18 college aged males participated in Experiment 2. In both experiments anticipatory cardiac deceleration either reached a plateau or shifted to acceleration by the interbeat interval in which the stimulus occurred. In contrast to previous reports, a secondary deceleration, rather than cardiac acceleration, often followed the stimulus. The secondary deceleration was greater with non-compatible mapping, slow response speeds, and short intertrial intervals. The findings suggested that the motoric inhibition required during response selection induces a phasic cardiac deceleration.

Adolescent↗
PubMed1990

On the shift from anticipatory heart rate deceleration to acceleratory recovery: revisiting the role of response factors.

The influence of inducing motor responses of low and high force at different times in the cardiac cycle was examined. A handgrip response was used which allowed the separation of response initiation from response completion. Based on earlier work, we expected initiation, rather than completion, to initiate poststimulus cardiac acceleration. We also thought that preparation for a high force response might alter preparatory changes of interbeat interval differently from preparation for a low force response. Fifteen college-aged male subjects performed a warned reaction time task in which a visual stimulus signalled a handgrip requiring either a high or a low force to close. NoGo trials in which an inhibit signal was presented occurred on 12% of the trials. Stimuli occurred either on the R-wave of the electrocardiogram or 300 ms later. Reaction speed was varied in different trial blocks by rewarding response times of 200 ms (+/- 50 ms), 300 ms, or 400 ms. Results based on the timing of response initiation were essentially identical to those based on the timing of response completion. High force relative to low force was associated with both earlier response initiation and earlier cardiac acceleration. Force did not alter preparatory cardiac deceleration. Force and response speed did, however, alter the level of heart rate after response occurrence. Thus, response initiation (or an earlier response process) appears to induce a cardiac acceleration whose level is influenced by the speed and force of the motor response.

Adult↗