Effects of severe traumatic brain injury on visual memory.

The study aimed to clarify the effects of severe traumatic brain injury (TBI) on visual memory. Three groups of participants (14 late-recovery and 14 early-recovery TBI individuals and 18 controls) were administered the following: The Shum Visual Learning Test (SVLT), a test that measures the ability to remember visual patterns, an electronic maze test, a test that measures the ability to remember spatial positions, and the Rey Auditory Verbal Learning Test (RAVLT), a test of verbal memory and learning. The individuals with TBI (late- and early-recovery) were found to be impaired on the SVLT and the RAVLT but not on the electronic maze. Specifically, on the SVLT, they were found to learn at a slower rate and make more false-positive errors than the controls. The advantages of the SVLT over visual memory tests used in previous studies and the significance of findings of the present study were discussed.

Normative data for a new memory test: the Shum Visual Learning Test.

This study reports normative data and test-retest reliabilities for a visuo-spatial memory test, the Shum Visual Learning Test (SVLT). Participants were 146 Caucasians (70 males and 76 females, age range between 17-83 years). The test was administered to 116 participants once and 30 participants twice (1 month apart). Age (but not gender and education) was found to affect SVLT test performance. The norms, therefore, were presented according to seven age groups (viz., 17-19, 20-29, 30-39, 40-49, 50-59, 60-69, 70+ years). Three indices (learning, retention after interference, and delayed retention) were derived for descriptive and clinical purposes. The test-retest reliabilities for all trials of the SVLT (except Trial 6) were found to be significant (rs ranged from .63 to .82). Normative data reported allow neuropsychologists to compare patient performances with those of appropriate controls and are important for fostering clinical application of this test.

Ethical issues in research on adolescent depression and suicidal behaviour.

The codes of ethical conduct of the Australian Psychological Society and the American Psychological Association imply that researchers of adolescent depression and suicidal behaviour must plan to intervene to assess risk where a participant in a study indicates an intention to commit suicide. Participants in research of this kind need to be advised of this possibility in advance. The obligation to intervene, and to advise of the possibility of intervention, pose practical and methodological problems for research in this area but do not, it is argued, absolve the researcher of the primary responsibility to contribute to the welfare of the research participant.

Individual differences in the orienting response: nonresponding in nonclinical samples.

The complete failure of the electrodermal orienting response (OR), although widely studied in clinical samples, has received little systematic attention in work with healthy adults. The published studies of nonresponding using nonclinical samples are reviewed, with data from three unpublished studies pertinent to the question, to identify the characteristics of nonresponders. The most durable findings to date are that nonresponding shows both trait and state characteristics, and that nonresponders are more likely to be female than male, to show hypoarousal in the electrodermal system but not complete unresponsiveness in this system or low arousal in other systems, and to show higher scores on measures of impulsiveness and antisociality but not to differ from responders in terms of sensation seeking. Most of these data can be reconciled with two different accounts of the OR mechanism. One is that proposed by I. Maltzman which postulates a difference between voluntary and involuntary ORs, and the other is that of J. A. Gray which proposes that the OR is a function of activity in a Behavioural Inhibition System. Taken together, these accounts imply that the OR reflects attentional and affective processes, and that both cognitive style and temperamental differences in the appraisal of threat can lead to electrodermal nonresponding.

Methods and mechanisms in electrodermal studies of omission responding.

Barry and O'Gorman (1987) employed a response-averaging technique to investigate the electrodermal orienting response (OR) to stimulus omission. We obtained reliable evidence of increased response latency to stimulus omission, supporting an explanation of the missing-stimulus effect in terms of Maltzman's voluntary OR. Wilson's (1989) commentary on our article addresses both methodological and theoretical aspects. This response first examines his methodological difficulties, and provides simulation exercises which serve as a validation of our procedure. We then examine Wilson's theoretical points. His alternative theoretical explanation of the missing-stimulus effect, in terms of a systematic bias in the time-keeper of the stimulus-comparator process, is shown to be untenable. His remaining problem, concerning what he terms "assessment of stimulus significance", appears to have arisen through misinterpretation of our theory. A clarification of our theoretical position indicates the internal consistency of our use of "significance" and "voluntary OR".

Stimulus omission and the orienting response: latency differences suggest different mechanisms.

Following response habituation to a regularly-presented innocuous stimulus, omission of that stimulus may elicit a response. The missing-stimulus effect has been of some importance in the development of Orienting Response (OR) theory, particularly Sokolov's neuronal model/stimulus comparator mechanism. Western work on this effect has been somewhat equivocal, with only some subjects emitting small responses at stimulus omission. Barry (1984b) proposed that the fragility of the data might reflect the elicitation of a voluntary OR (Maltzman, 1979) rather than the more robust (reflexive) involuntary OR commonly emphasised in OR work. A prediction generated from this hypothesis, that the OR to stimulus omission has a longer latency than that associated with physical stimuli, was tested here. The first experiment found such an effect in the electrodermal responses to simple visual stimuli and their omission. This was replicated in a second experiment with both significant and indifferent visual stimuli. These latency delays (group mean differences ranged from 1.15 to 1.65 s) imply an intervening process in the elicitation of the electrodermal response to stimulus omission, compatible with it being viewed as a voluntary OR. An implication of these results for the conceptualization of other ORs to stimulus change is discussed.

Extraversion and the EEG: II. A test of Gale's hypothesis.

The study sought to test A. Gale's hypothesis that only under moderately arousing conditions will introverts be shown to differ from extraverts in EEG defined arousal. Alpha activity was recorded for 45 subjects under each of six conditions, and extravert and introvert groups formed on the basis of subject's score on the E scale of the Eysenck Personality Questionnaire (EPQ). Contrary to the hypothesis, extraverts showed more prestimulus alpha activity than introverts under all conditions except opening and closing eyes on instruction where the reverse was the case. It is argued that the failure to confirm the hypothesis is not due to faults in design or execution of the study, and that future research may profit more from ignoring interactions of the sort demonstrated.

Extraversion and the EEG: I. An evaluation of Gale's hypothesis.

The hypothesis of A. Gale that extraverts differ from introverts in EEG defined arousal only under moderately arousing conditions is examined. It is argued that the hypothesis is not entirely internally consistent and lacks empirical support. A re-analysis of the literature on which it was based points to problems in the measurement of extraversion as a more significant source of confounding than variation in conditions of testing.

Consistency of individual differences in non-specific electrodermal activity.

The study sought to determine whether, as implied by a trait interpretation of individual differences in non-specific electrodermal responding, the frequency of NSRs is a consistent characteristic of subjects across conditions. 40 male subjects completed two 1-hour sessions spaced at an interval of 2 weeks. In each session, three 12-min conditions were administered: relaxation, vigilance, and mental arithmetic. Continuous recordings were made throughout each condition of electrodermal and respiratory activity, and at the end of each condition subjects completed an Adjective Checklist (ACL). Counts were made of the total number of 10-sec intervals during each condition in which at least one NSR was recorded. Separate counts were made for large amplitude (equal to or greater than 1% of baseline) and for small amplitude (less than 1%) responses. Analyses of variance performed on the NSR data indicated that the major component of variance was that due to subjects, and that the interactions between subjects and conditions and subjects and sessions, which would contradict a trait interpretation, were negligible. Consistency in subject's responding was estimated by intraclass correlations across conditions and sessions. For NSR large, the coefficient was 0.58 and for NSR small 0.50. The data were interpreted as support for a trait interpretation of NSR frequency.

Further observations on the incremental stimulus intensity effect and habituation of the human electrodermal response.

Two studies are reported which examined the relative effectiveness of an incremental series of stimulus intensities for reducing electrodermal responsiveness to a test stimulus. In the first study, employing five pairs of male undergraduates matched on electrodermal responsiveness, habituation to a 100 db (re 20muN/m2) noise burst was compared following two training procedures. In one, stimulation began at 64 db and increased by 4 db up to 96 db whenever two consecutive presentations of the stimulus failed to elicit a response. In the other, an equivalent number of presentations with a 100 db noise burst were provided. While habituation occurred during both training conditions, subsequent habituation to a 100 db test stimulus was more rapid following incremental training. In the second experiment, employing 40 female undergraduates, incremental and fixed conditions of training were compared for effectiveness using more moderate intensities of test stimulus: viz., 60 db and 80 db. A these levels, the fixed training series was superior to the incremental in reducing responsiveness. The data extend previous findings on the incremental stimulus intensity effect with the human electrodermal response but suggest limiting conditions for its demonstration.

Perception of hostility in the TAT as a function of defensive style.

Groups of male and female students with high, intermediate, and low scores on Byrne's Scale of Repression-Sensitization judged the amount of hostility and the darkness of 10 TAT cards, including the blank. The groups' judgments for each card were expressed in terms of the statistic E, a non-parametric index of discriminability derived on the basis of the theory of signal detection. Subjects with low scores on the scale showed significantly lower E values for hostility (p less than .05), but not for darkness, than the other two groups. It was concluded that differences in sensitivity to affective stimulation underlie the dimension of Repression-Sensitization.

Individual differences in habituation of human physiological responses: a review of theory, method, and findings in the study of personality correlates in non-clinical populations.

Studies up to 1976 of the relationship between psychometrically defined dimensions of personality and individual differences in habituation of EEG and autonomic responses were examined. Attention was confined to reports employing persons who were not diagnosed as suffering from mental disorder, institutionalized for this reason of for delinquent or criminal behaviour. The dimensions of extraversion and anxiety were most frequently found to be implicated in predictions about individual differences in response habituation, though no consistent rationale for these predictions was identified. Methodological problems involved in studying the predictions were considered, and a number of factors relating to measurement of personality and habituation and the experimental conditions under which response habituation is studied were suggested as possible sources of confounding. A survey of the empirical literature led to the conclusions that anxiety as defined by the Manifest Anxiety Scale is related to habituation of the finger vasomotor response but probably not to habituation of the electrodermal response, while extraversion, as defined by Eysenck's scale, is related to habituation of the electrodermal response. For other scales and other dimensions, including cognitive factors, the available data are inconsistent or too meagre to permit conclusions being drawn. It is suggested that future research be directed to a systematic investigation of the conditions under which personality factors contribute significantly to individual differences in response habituation, rather than seek to identify general relationships.

Short-latency acceleration of human heart rate as a function of stimulus intensity.

The study examined the effectiveness of three intensities of white noise in evoking short-latency acceleration of human heart rate. 3 groups of 10 female subjects were presented with 1-sec. bursts of white noise with virtually instantaneous rise times at intensities of 100 db (re 20 mu N/m2), 90 db, or 80 db SPL as measured at the headset. 5 bursts were presented at intervals of 45 sec. while the EKG was recorded. An increase in heart rate during poststimulus beats 3 and 4 compared with the mean rate of the three beats prestimulus was reliably evoked on the first two trials in the 100-db and 90-db groups but not in the 80-db group. Apart from a recovery of acceleration on Trial 5 for the 100-db group, the 100-db and 90-db groups did not differ in amplitude or rate of habituation of the response. Poststimulus heart-rate level was not significantly related to prestimulus level as expected in terms of the law of initial values. The results were interpreted as consistent with F.K. Graham's interpretation of short-latency cardiac acceleration as a component of startle.