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Biomedical subjects

J L Andreassi

Publications and source records attributed to J L Andreassi.

At least 19 recordsLinked to original sources
PubMed1991

Cardiodynamic response to psychological and cold pressor stress: further evidence for stimulus response specificity and directional fractionation.

In the present study 36 police officers were exposed to a psychological stressor (IQ quiz) and to cold pressor stress while several cardiovascular variables were monitored. Impedance cardiography was used to provide measures of heart rate, stroke volume, cardiac output, myocardial contractility, and total peripheral resistance. In addition, measures of systolic and diastolic blood pressure and peripheral skin temperature were obtained. A multivariate analysis of variance (MANOVA) indicated that significant increases in diastolic and systolic blood pressure during the cold pressor test were mediated by large increases in total peripheral resistance, whereas blood pressure elevation during the IQ quiz were accompanied by significant increases in heart rate and, to a lesser extent, cardiac output. Peripheral skin temperature decreased in response to each stressor. Additional analysis indicated a degree of stimulus specificity for several variables. For example, diastolic blood pressure showed greater increases to cold pressor than quiz, whereas systolic blood pressure increased more with the psychological than the physical stressor. Directional fractionation occurred for both myocardial contractility and cardiac output.

Adult↗
PubMed1991

Effects of stress management on blood pressure and other cardiovascular variables.

Blood pressure and impedance cardiography derived measures of heart rate, stroke volume, cardiac output and total peripheral resistance were measured in 16 persons before and after participation in a comprehensive program of stress management that included home monitoring of blood pressure and feedback of finger skin temperature during relaxation. Ten of the subjects were hypertensive and six were normotensive. Baseline measures of systolic and diastolic blood pressure and heart rate decreased significantly after participation in the program. In addition, reactivity to a psychological stressor (oral quiz) was significantly lower as revealed in reduced systolic and diastolic pressure, heart rate and cardiac output at the second assessment. A reduction in sympathetic nervous system activity is postulated as a possible mechanism for the changes observed.

Adult↗
PubMed1988

Interactive effects of type A personality and psychological and physical stressors on human cardiovascular functions.

The first part of this study examined the relationship(s) between Type A behavior scores and heart rate, blood pressure and impedance derived cardiovascular measures in response to discrete stressors during a standardized psychophysiological assessment. Expts. 2A and 2B considered cardiovascular responses to dynamic exercise stress alone and in combination with psychological and cold pressor tests. Gender and stroke volume changes during the psychological stress correlated 0.45 (P less than 0.02) with Type A score. Subscale scores of Job Involvement correlated 0.78 (P less than 0.02) with stroke volume, total systemic resistance and heart rate during the psychological stressor, and systolic blood pressure during the cold pressor task. The combined effects of psychological stress and dynamic exercise on systolic and diastolic blood pressure were significantly greater than the individual effects of these stressors. The use of impedance cardiography in measuring cardiovascular variables that correlate with Type A behavior, during psychophysiological assessments, may further elucidate our understanding of Type A behavior in addition to providing information about how stress interacts with aerobic exercise.

Adult↗
PubMed1987

Performance and physiological responses of type A and type B individuals during a cognitive and perceptual-motor task.

A total of 36 male individuals, 18 classified as Type A and 18 as Type B performed a cognitive (tonal memory) and a perceptual-motor (simulated race car driving) task along with a secondary reaction time (RT) task. Heart rate (HR), skin temperature, and skin conductance (SC) were measured. Multiple linear regression analysis revealed that tracking was related to Jenkins Activity Survey indicating superior performance for those scoring high in overall Type A behavior and low in the H sub-scale (hard driving, competitive behavior). Persons scoring high in the S scale (speed and impatience) and low in the H scale performed better in the short-term memory task. Type A subjects had higher HR and performed better (faster RTs and higher scores) than Type Bs, but only while engaged in the cognitive task. The Type As also had higher SCs than Bs, although they were not differentiated according to task. Sub-scale patterns may have important implications for refining the Type A behavior concept.

Adolescent↗
PubMed1985

An investigation of hemispheric asymmetry in size and semantic discriminations and related visual ERPs.

The present study examined possible hemispheric differences in discriminations of different sizes of geometric shapes (rectangles) and different meanings of words, and determined whether left and right hemisphere derived visual event related potentials (ERPs) were related to performance. Eighteen right-handed subjects (10 male and 8 female) participated in two separate sessions conducted on different days. The visual ERPs were recorded from over left parietal (P3) and right parietal (P4) scalp locations. Subjects were required to make discriminations of three words (PARE, PAIR, PEAR) and three sizes of rectangles (small, medium, large). Each word and rectangle was singly presented for 40 msec at 1 degree 24 minutes of arc to the left and right of central fixation (LVF and RVF respectively). The major findings were as follows: 1) there were no performance and ERP differences between hemispheres in the verbal task; 2) the left hemisphere excelled in the spatial task; however, ERPs derived from the two hemispheres were similar; 3) subjects experienced greater difficulty in their discriminations of geometric size, as compared to words, regardless of field of presentation. Discrimination of size seemed to have influenced P3 (P300) latency, i.e., it was longer (both hemispheres) when subjects made size discriminations as compared to words. It was proposed that the more difficult discriminations involved in size discrimination required a greater time for stimulus evaluation and that this was reflected in the delayed P3 response.

Adult↗
PubMed1984

An investigation of hemispheric specialization and visual event related potentials in discriminations of line length.

The purpose of the present study was to examine possible hemispheric differences in discriminations of line length and to determine whether the visual event related potential (ERP) recorded from over left and right hemispheres was related to performance. Twelve right-handed subjects participated on each of 2 separate days. The visual ERPs were derived from left occipital (O1) and right occipital (O2) placements. Eye blinks and vertical and lateral eye movements were also monitored. A single vertical 1.0 cm line (Standard) was displayed for 40 ms and was followed 2 s later by either a 0.9 cm, 1.0 cm or 1.1 cm (Comparison) line (also 40 ms). Subjects were asked to judge whether the second of the lines (Comparison) was "shorter" or "longer" than the first. Stimuli appeared at the center of a screen or at 1 degree 24' to the left and right of central fixation. Accuracy of line length judgements were similar in all 3 visual fields indicating a lack of hemispheric performance asymmetry for this type of discrimination task. In addition, there was no evidence of hemispheric asymmetry in the ERPs. The ambiguous discrimination involving the 1.0 cm standard and comparison lines seems to have influenced P3 latencies at both hemispheres. Namely, P3 latency was significantly longer in response to the 1.0 cm line than to the 0.9 cm or 1.1 cm lines. We propose that the ambiguous discrimination required a greater time for simulus evaluation and that this was reflected in the delayed P3 latencies.

Adult↗
PubMed1984

Interactions between target and masking stimuli: perceptual and event-related potential effects.

TWo separate experiments were conducted to determinge the nature of the visual event related potential (ERP) at two different cortical areas under conditions of backward visual masking and to see the effects of varied inter-stimulus-intervals (ISIs) upon both masking and the ERP. The results of the first experiment clearly demonstrated visual ERP attenuation at a target-mask ISI of 40 ms, an ISI which consistently produced masking. Both experiments showed that this effect was specific for the occipital recording site since amplitude reductions were not observed at the vertex under this condition. The mask alone condition produced the largest amplitude ERPs in both experiments. Again, this was specific for Oz. In the second experiment target-mask ISIs which did not produce backward masking (i.e., 10 ms and 100 ms) were not accompanied by ERP amplitude reductions. The results may be explained by a cortical excitatory-inhibitory model. That is, when successive stimuli are presented to the visual system, the visual cortical excitation produced by the initial stimuli is inhibited by the presentation of subsequent stimuli when temporal and spatial intervals are appropriate.

Evoked Potentials, Visual↗
PubMed1983

Hemispheric asymmetries in a signal detection task.

Reaction time and signal detection performance were measured during a 78-min. vigilance task. 12 right-handed male subjects served in two experimental sessions. Subjects focused on a central fixation point and responded to signals presented at unpredictable times in one of three locations: 2.5 degrees to right of central fixation, central, and 2.5 degrees to the left of center. Subjects decided whether to press a response key with either the left or right hand with each presentation. Over-all vigilance performance (signal detections and response time) was similar for left and right visual-field presentations. Evidence from reaction times indicated that responses controlled by the left hemisphere were faster to a verbal stimulus (T) while reactions controlled by the right hemisphere were faster to an apparent non-verbal stimulus, an inverted T.

Adult↗
PubMed1979

Monocular and binocular visual evoked potentials before and after cataract surgery.

Visual evoked cortical potentials (VEPs) were recorded from an individual with a mature cataract in one eye. Stimulation was both monocular and binocular and VEPs were obtained from three occipital scalp sites. Comparisons of recordings taken prior to cataract removal and after removal showed a dramatic increase in amplitude of potentials derived through stimulation of the affected eye. Slight differences in hemispheric amplitude prior to surgery suggest a greater degree of opacity in one portion of the affected lens.

Cataract↗
PubMed1976

Amplitude changes in the visual evoked cortical potential with backward masking.

A series of three experiments examined backward visual masking effects and visual evoked cortical potential correlates of such masking. In Experiment I, which was concerned with the effects of sequential sets of like stimuli (grids), it was found that when backward masking occurred, it was accompanied by decreased visual evoked potential (VEP) amplitudes. Experiment II replicated the first experiment using different stimuli (letter B's) and several new subjects. Again, backward masking was accompanied by decreased VEP amplitudes. In Experiment III, which examined the effects of sequential sets of unlike stimuli (B's and grids), it was found that when earlier stimuli differed in configuration from later stimuli, there was an absence of backward masking and VEP amplitude changes also failed to appear. Thus, when backward masking did not occur, no changes in the VEP were observed. The results are discussed in terms of interactions between excitatory and inhibitory activities produced at the visual cortex by the earlier and subsequently presented stimuli. Various concepts regarding the visual system mechanisms involved in backward masking, including integration and interruption hypotheses, may help to explain the complexity of findings obtained thus far in studies using VEP correlates of backward visual masking.

Evoked Potentials↗
PubMed1976

Hypnotic suggestion of stimulus change and visual cortical evoked potential.

Two experiments were conducted to determine whether the hypnotic suggestion of stimulus intensity change would affect the physical parameters (latencies, amplitudes) of the visual cortical evoked potential. Stimulus intensity was kept constant as visual cortical evoked potentials were measured under conditions in which it was suggested that stimuli were "bright" or "dim". The results of both experiments led to the conclusion that, under the present condition, hypnotic suggestion of stimulus intensity change did not result in changes in visual cortical evoked potentials.

Electrophysiology↗