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M E Dawson

Publications and source records attributed to M E Dawson.

At least 37 records · Page 2Linked to original sources
PubMed1994

Information-processing abnormalities as neuropsychological vulnerability indicators for schizophrenia.

Studies of schizophrenic patients in psychotic and clinically remitted states and of biological relatives indicate that subtle anomalies in information processing may be critical components of neuropsychological vulnerability to schizophrenia. We describe a conception of possible abnormalities and several recent strategies to differentiate these possibilities. Within Continuous Performance Test conditions, varying the perceptual load vs. the active, working memory load yields a distinction between a stable vulnerability factor across clinical states and a potential mediating vulnerability factor. Specialized backward masking paradigms offer ways to separate two initial sensory-perceptual processes from attentional shifting processes. Top-down attentional influences on sensorimotor gating allow examination of the role of central executive processes in modulating early sensory processes. Initial results are discussed.

Adolescent↗
PubMed1993

Modification of the acoustic startle-reflex eyeblink: a tool for investigating early and late attentional processes.

The present experiment examined the sensitivity of short and long lead interval startle eyeblink modification to attentional processing. Eighteen college student subjects were presented with a series of intermixed high and low pitched tones and instructed to attend to tones of one pitch and to ignore tones of the other pitch. The majority of the attended and ignored tones served as prepulses for an eyeblink-eliciting burst of white noise presented at lead intervals of 60, 120, 240 and 2000 ms following prepulse onset. Results indicate that both attended and ignored prepulses produce significant startle eyeblink modification: significant blink inhibition at the 60, 120 and 240 ms short lead intervals, and blink facilitation at the 2000 ms long lead interval. In addition, compared with the ignored prepulse, the attended prepulse produced significantly greater blink inhibition at the 120 ms lead interval as well as significantly greater blink facilitation at the 2000 ms lead interval. These results suggest that both short and long lead interval startle eyeblink modification measures may be useful tools for future investigations of the early and later stages of attentional processing.

Acoustic Stimulation↗
PubMed1993

Reduced regional brain glucose metabolism assessed by positron emission tomography in electrodermal nonresponder schizophrenics: a pilot study.

This pilot study examined whether electrodermal nonresponder and responder subgroups of schizophrenic patients differ in regional brain metabolism assessed by Positron Emission Tomography during a continuous performance test. In comparison to both normal controls (n = 6) and responder schizophrenics (n = 3), the nonresponder schizophrenics (n = 3) showed about a 20% reduction in metabolic rate across the entire brain. Nonresponder schizophrenics tended to have lower absolute metabolic rates than responders in lateral and medial frontal, thalamic, and hippocampal areas. Nonresponders also had significantly lower relative metabolic rates in medial frontal and hippocampal areas as well as the right amygdala. These data suggest that electrodermal subgroups of schizophrenics differ in both regionally specific brain metabolic processes thought to be involved in electrodermal activity and in generalized brain metabolism.

Adult↗
PubMed1993

Attention and schizophrenia: impaired modulation of the startle reflex.

The startle reflex (SR) elicited by abrupt stimuli can be modified by attention to nonstartling stimuli that shortly precede the startle-eliciting stimulus. The present study of 15 recent-onset, relatively asymptomatic schizophrenic outpatients and 14 demographically matched normal control subjects demonstrated that attentional modulation of SR is impaired in schizophrenic patients. Specifically, the control group exhibited greater startle eye-blink modification following to-be-attended prestimuli than following to-be-ignored prestimuli, whereas the patients failed to show the attentional modulation effect. These results suggest traitlike attentional deficits in schizophrenia because the patients were relatively asymptomatic. The measurement of attentional modulation of SR may provide a nonverbal, reflexive, state-independent marker of the vulnerability to schizophrenia.

Adult↗
PubMed1992

Concurrent and predictive electrodermal correlates of symptomatology in recent-onset schizophrenic patients.

Electrodermal activity and symptomatology were interrelated in a group of 56 male and 13 female recent-onset schizophrenic patients. Electrodermal activity was indexed by the frequency of nonspecific skin conductances responses and the number of trials to habituation of the skin conductance orienting response. Symptomatology was assessed by the Brief Psychiatric Rating Scale (BPRS) on two separate test occasions. The first test occasion was during the inpatient period when psychotic symptoms were prevalent and medications were variable. The second test occasion was several months later during an outpatient period when symptoms were stabilized and medications held constant. Electrodermal activity was positively and significantly related to a number of symptoms in male patients, most reliably the BPRS factors Activation and Hostility/Suspiciousness. These relationships were most consistent during the outpatient period. Of particular theoretical interest, greater electrodermal activity during the inpatient period was associated with greater outpatient psychopathology. The results suggest that heightened inpatient electrodermal activity is predictive of poor short-term symptomatic recovery in recent-onset, acute, male schizophrenic patients.

Adolescent↗
PubMed1992

Electrodermal anomalies in recent-onset schizophrenia: relationships to symptoms and prognosis.

Electrodermal activity was measured in recent-onset schizophrenic patients (n = 98) and matched normal control subjects (n = 40) as part of an ongoing longitudinal study. Results at the initial inpatient test were generally consistent with the current consensus in the literature. A large subgroup of the patients was found to be nonresponsive with the phasic skin conductance orienting response measure, whereas the remaining subgroup of patients was found to be electrodermally tonically hyperaroused. Heightened electrodermal activity at the inpatient test was associated with a number of symptoms in male patients and with poor recovery from the acute schizophrenic episode. Followup tests conducted when the patients were in states of remission and psychotic relapse revealed that tonic electrodermal arousal measures qualify as state-sensitive episode indicators, whereas phasic nonresponding may qualify as an atypical vulnerability indicator. Moreover, preliminary data from three patients suggest that increases in tonic electrodermal arousal may temporally precede psychotic relapses. The principal findings are consistent with a vulnerability/stress model that posits that electrodermal hyperarousal is part of a transient intermediate state that may lead to a psychotic episode in a vulnerable individual.

Adult↗
PubMed1992

Developmental Processes in Schizophrenic Disorders: longitudinal studies of vulnerability and stress.

The Developmental Processes in Schizophrenic Disorders project is a longitudinal study of schizophrenic patients who have recently had a first episode of psychosis. The project focuses on discriminating characteristics of schizophrenic patients that are "stable vulnerability indicators," "mediating vulnerability factors," and "episode indicators" by comparing normal subjects to schizophrenic patients assessed in clinically remitted and psychotic states. A parallel project goal is to identify predictors of relapse, social and work impairment, and illness course among potential psychobiological vulnerability factors and environmental potentiating factors. Hypothesized vulnerability factors and potential environmental stressors are examined first under standardized maintenance antipsychotic medication conditions for at least 1 year. Patients showing stable remission of psychosis after 1 year of maintenance antipsychotic medication are invited to enter drug crossover and withdrawal protocols to determine the need for continuous antipsychotic medication. Vulnerability and stress factors are again assessed. A summary of results to date is presented. Deficits in early components of processing visual arrays and in sustained discrimination of successive ambiguous perceptual inputs are relatively stable across psychotic and clinically remitted states in the schizophrenic patients. Performance on a vigilance task demanding active, working memory also remains abnormal during clinical remission but covaries significantly with psychotic state and is a candidate for a mediating vulnerability factor. Autonomic activation level does not appear to be an enduring vulnerability factor, but it predicts the extent of short-term symptomatic recovery and may mediate the impact of stressors. Under conditions of standardized, injectable antipsychotic medication, independent stressful life events and highly critical attitudes toward the patient in the social environment predict relapse risk. Prospective data suggest that signs and symptoms prodromal to psychotic relapse may be present in about 60 percent of patients.

Adolescent↗
PubMed1992

Electrodermal lability: individual differences affecting perceptual speed and vigilance performance in 9 to 16 year-old children.

Studies on adults have suggested that a deterioration in performance (within session vigilance decrement) on a continuous performance task may be related to individual differences in baseline levels of electrodermal activity (electrodermal lability). This study investigated this relationship in 153 children, aged 9-16 years. A significant vigilance decrement was observed, as indicated by average decreases in perceptual sensitivity (d') over an 11.5-min time period. Although electrodermal labiles were overall more perceptually sensitive than electrodermal stabiles, results did not support the premise that the performance of stabiles decreases over time more than that of labiles. Performance on other cognitive tasks, involving tests of perceptual speed ability, did not appear to be highly related to vigilance performance. However labiles were not only better able to sustain their attention, but also performed better and faster on these cognitive tasks.

Adolescent↗
PubMed1992

A major effect of recording site on measurement of electrodermal activity.

Although the medial phalanx has been recommended as the preferred site for recording skin conductance activity, a review of articles published in Psychophysiology indicates that a large minority (34%) of studies employ the distal phalanx. Informal observations also suggest that the distal site may be more reactive than the medial site. This study formally tests this observation by recording skin conductance from both medial and distal phalanges. Twenty-four right-handed subjects (12 male, 12 female) were exposed to a series of 10 orienting and defensive stimuli. Electrodes were placed on the fore and middle fingers of each hand, with distal sites used on one hand and medial sites on the other for each subject. Skin conductance amplitudes were 3.5 times larger at distal than medial sites (p less than .002), while skin conductance levels were 2.08 times larger at distal sites (p less than .0005). A significant Site X Stimulus interaction (p less than .025) indicated that the distal site was more sensitive to habituation over trials and to increases in skin conductance amplitudes with increasing stimulus intensity than the medial site. On the basis of these findings it is recommended that distal sites be used in preference to medial sites in the recording of skin conductance activity.

Adult↗
PubMed1991

Effects of potentially phobic conditioned stimuli on retention, reconditioning, and extinction of the conditioned skin conductance response.

Discriminative classical conditioning of skin conductance responses (SCRs) was studied in 163 college students as a function of four variables: CS type (potentially phobic versus neutral conditioned stimuli), Sex of the subject, Interstimulus interval (ISI) during conditioning (.5 versus 8 s), and Retention interval between conditioning and retention assessment (1 versus 6 months). CS type did not affect acquisition, retention, or reconditioning of the differential conditioned responses. The effect of CS type was highly significant during extinction, with differential SCRs to CS+ and CS- being greater with potentially phobic conditioned stimuli. This was true for both sexes, both the .5-s and the 8-s ISI, and after a 1-month or a 6-month retention interval. Moreover, SCRs conditioned to phobic conditioned stimuli with the .5-s ISI persisted even after subjects' cognitive expectancy of the UCS, which was measured on a trial-by-trial basis, had completely extinguished. The results indicate that the effect of potentially phobic conditioned stimuli on the conditioned skin conductance response is unique to resistance to extinction-they affect not learning but unlearning of the autonomic response.

Adult↗
PubMed1991

The relationship between skin conductance orienting and the allocation of processing resources.

Information processing models of autonomic orienting suggest that the elicitation of an orienting response is associated with either the call for, or the actual allocation of, limited attentional processing resources. However, Dawson, Filion, and Schell (1989) reported a directional dissociation between elicitation of the skin conductance orienting response and resource allocation, as indexed by reaction time slowing on a secondary task. Although larger skin conductance responses were elicited by a task-relevant stimulus than by a task-irrelevant stimulus, reaction time showed the opposite pattern (i.e., greater slowing to secondary task probes presented shortly following the onset of the task-irrelevant stimulus). In the present report, we describe three experiments which examine the generality of this dissociation effect and test specific hypotheses regarding its nature. Results of the first two experiments revealed that the dissociation effect is observed reliably when the task-relevant and task-irrelevant stimuli consist of left ear and right ear tones or high and low pitched binaural tones, across a range of secondary task probe presentation times. However, the third experiment demonstrated that when task-relevant and task-irrelevant stimuli are presented to different sensory modalities (auditory and visual), orienting and resource allocation are both greater during the task-relevant than the task-irrelevant stimuli, thus eliminating the dissociation effect. These results support the hypothesis that the dissociation effect is due to a switch of attention initiated because of the physical similarity of the task-relevant and task-irrelevant stimuli, and suggest that there is a fundamentally positive relationship between skin conductance orienting and resource allocation under selective attention conditions.

Adult↗
PubMed1991

Probing the time-course of the auditory oddball P3 with secondary reaction time.

An elementary neural model of the P3 is proposed in which the P3 is held to manifest a brief, widely-distributed, inhibitory event. A preliminary and indirect test of the model is described using secondary-task methodology. Manual reaction times were measured to probe clicks delivered during the presumed time-course of an auditory oddball P3. We observed that reaction times to probes presented after oddball stimuli were significantly slowed as compared to reaction times to probes presented after standards. The latency of maximum reaction time slowing corresponded generally to the latency of the P3. The latency of maximum reaction time slowing did not respond to a manipulation varying the latency of the P3. Thus, some of the obtained results were consistent with the P3-inhibition hypothesis, whereas others were not. Secondary-task methodology may provide a valuable new approach to understanding the late event-related potentials.

Adult↗
PubMed1990

Psychophysiology at the interface of clinical science, cognitive science, and neuroscience.

Research in schizophrenia illustrates that the field of psychophysiology lies at the interface of clinical science, cognitive science, and neuroscience. Electrodermal abnormalities in schizophrenic patients have been found reliably across laboratories, and data reported here demonstrate that these abnormalities are at least partially dependent upon the clinical state of the patients. Both tonic and phasic electrodermal activity increased when schizophrenic patients entered into a psychotic episode, and preliminary evidence suggests that the increases may serve as early prodromal signs of an impending episode. Significance of the electrodermal abnormalities for understanding cognitive and attentional deficits is suggested by associations with secondary reaction time and startle blink probe findings. Neuroscience implications are highlighted by the correlation of the electrodermal abnormalities with regional brain metabolic activity indexed by positron emission tomography. An important task for the future is to interrelate measures from these various domains. The field of psychophysiology is particularly well positioned for this task.

Arousal↗
PubMed1989

Awareness of the CS-UCS contingency and classical conditioning of skin conductance responses with olfactory CSs.

The possibility of demonstrating acquisition of classically conditioned responses without awareness of the conditioned stimulus-unconditioned stimulus (CS-UCS) contingency using olfactory stimuli with 58 college student subjects was tested. A classical discrimination delay conditioning paradigm was employed, with electric shock as the UCS and two pleasant odors (perfumes) as the conditioned stimuli (CS+ and CS-). Trial-by-trial measures of skin conductance conditioned responses served as dependent variables. A masking task in the form of an olfactory memory task was employed for the purpose of delaying the onset of awareness of the conditioning contingency. Awareness of the conditioning contingency was assessed by a concurrent and a post hoc measure, and subjects who satisfied both criteria were considered aware of the CS-UCS contingency. Conditioning was observed only in the aware subjects, and only after the onset of awareness of the CS+-UCS contingency. Respiratory activity, measured as a check against possible artifacts, had no effect on the SCR measures. It was concluded that the awareness of the CS-UCS contingency is necessary for acquisition of discriminative conditioned responses in humans, regardless of the sensory modality in which CSs are presented. Sex differences in skin conductance measures and performance on the olfactory memory task were observed.

Adult↗
PubMed1989

Is elicitation of the autonomic orienting response associated with allocation of processing resources?

Two experiments investigated whether elicitation of the autonomic orienting response is associated with active allocation of processing resources as indexed by the slowing of reaction time to secondary task probes. In Experiment 1, 75 college student subjects performed a dual task consisting of a primary auditory orienting task and a concurrent secondary visual reaction time task. The primary orienting task included task-relevant tones presented to one ear and task-irrelevant tones presented to the other ear. The last trial of the primary task included an unexpected novel tone presented binaurally. The secondary task consisted of a series of brief light flashes presented at critical times throughout the primary task; the reaction time of the subjects' motor responses to these flashes was measured. Consistent with the resource allocation view of orienting, the results demonstrated that resources were allocated during the primary task tones and the novel tone, and this allocation was greater during the early trials than the late trials of the primary task. However, a directional dissociation was observed in that resource allocation was greater during the task-irrelevant tone whereas autonomic orienting responses were larger to the task-relevant tone. Experiment 2 replicated all of these effects and demonstrated that the directional dissociation was sensitive to the predictability and ease of discrimination between the task-relevant and task-irrelevant tones. Taken together, these findings indicate that the relationship between resource allocation and autonomic orienting is a reliable but complex one in need of further research.

Adult↗