Relations between two-flash discrimination and electrodermal activity, re-examined in schizophrenics and normals

J.psycbiot. Res.,1975. Vol. 12.pp. 73-85.Pergamon Press.Printedin GreatBritain.

RELATIONS BETWEEN TWO-FLASH DISCRIMINATION AND ELECTRODERMAL ACTIVITY, RE-EXAMINED IN SCHIZOPHRENICS AND NORMALS JOHN H.

GRUZELIER*

and PETER H.

VENABLES

Psychological Institute, Department of Psychiatry, Kommunehospitalet, Copenhagen, Denmark and Department of Psychology, Birkbeck College, University of London, London, England (Received 16 July 1973; in revisedform 22 August 1974)

INTRODUCTION IN SCIENTIFIC

investigations schizophrenics have been found to be either over or under reactive physiologically.1-4 However, such bidirectionality has seldom been acknowledged by any one investigator, a possible reason why attempts to define homogeneous groups of schizophrenics in terms of arousal processes have generally failed. The present report is one aspect of a series of experiments designed to investigate the psychophysiology of schizophrenics in the light of recent evidence that frontal-limbic processes are involved in the regulation of physiological reactivity to stimuli, orienting and habituation processes in particular, and the possibility that these brain structures are central to the formation of schizophrenic symptomatology. This approach has led to the subgrouping of high and low arousal groups of schizophrenics upon the basis of electrodermal orienting activity. The experiments and theory are presented in detail in a doctoral thesis5 and are the subject of a series of reports.6-12 This report focuses upon the tonic skin conductance activity of the two schizophrenic subgroups and upon the interrelation between two-flash discrimination and electrodermal activity in schizophrenics and normals. There are conflicting reports as to the nature of the tonic or generalized changes in electrodermal activity of schizophrenics. In a review LANG and BusP concluded that schizophrenics, especially chronic ones, are hyporeactive, though their resting levels of activity are high. To explain this effect they invoked the law of initial values which states that because of homeostatic constraints reactivity is inversely related to basal level. ZAHN~* and also FOWLES et a1.15noted that while the electrodermal levels of normals increased with task demands, the levels of schizophrenics remained invariant. In contrast, VENABLES~~ found quite pronounced lability in the tonic skin potential levels of schizophrenics during the course of a two-flash threshold task accompanied by white noise or in the presence of white noise alone. GRUZELIER, et a1.l’ found a paradoxical reduction in the skin conductance *Present address: University College Hospital Medical School, University of London, Clinical Pharmacology, 117 Gower Street, London WClE 6AP, England. 73

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JOHN H. GRUZELIER and PETERH. VENABLES

activity of non-paranoid schizophrenics under high levels of physiological activation, whereas levels increased with normal control subjects and paranoid schizophrenics. It was predicted here that the schizophrenics who exhibited skin conductance orienting responses to repeated tones would have tonic skin conductance responses of high amplitude. The schizophrenics without orienting responses would have minimal tonic activity. The relation between two-flash thresholds (interpreted as an index of cortical arousal) and electrodermal levels has been examined in a number of laboratories, but the results have been confusing. VENABLES,~~in this journal, reported negative correlations between two-flash thresholds and skin potential levels with non-paranoid schizophrenics, and positive correlations with paranoid schizophrenics and normal controls. LYKKEN and MALEY,~~ also in this journal, could not replicate these results, and in some cases they found opposite relations; in their patient control group correlations between two-flash threshold and both skin potential level and skin conductance level were negative, while in their non-paranoid group correlations between threshold and skin potential level were negative and between threshold and skin conductance level varied about zero. HUMJZand CLARIDGE~O also found positive but insignificant correlations between two-flash threshold and skin potential level in normal subjects. GRUZELIER,et a1.,17considered two separate issues which might account for the divergent results. Firstly, the application of signal detection theory to psychophysics has shown that traditional measures of perceptual thresholds confound sensory with non-sensory factors.21*22 Consequently correlations may vary because either impulsive or alternatively conservative response modes may have been adopted. Secondly, covariation between the variables may be altered by changes in arousal level. These authors used a forced-choice threshold measure which minimises the influence of attitudinal factors upon threshold. Arousal levels were manipulated with a bicycle ergometer. Whereas the basal arousal levels of the groups did not differ, when activated changes in threshold and electrodermal activity occurred in different directions with non-paranoid schizophrenics as distinct from paranoid schizophrenics and normal controls. Furthermore, curvi-linear relations between electrodermal levels and thresholds, measured with a traditional threshold measure, and obtained under a wide range of arousal conditions, followed a different form for the schizophrenics compared with the controls. However, because of the use of the traditional threshold measure the latter result could be a function of sensory factors, non-sensory factors, or both. Subsequently, the two-flash discrimination of paranoid, non-paranoid and normal subjects was re-examined with a signal detection procedure adapted for the two-flash threshold task.23-2s This method provides not only a measure of threshold, but also a measure of sensory sensitivity, defined by the slope of the psychophysical ogive, and a measure of response criterion. Patients were also categorised according to the presence or absence of skin conductance orienting responses to repeated tones of moderate intensity. Arousal was varied by taking measures, first in a resting condition to establish baseline functioning, then in the presence of continuous 75 dB white noise, and finally in the absence of noise. Differences between schizophrenics and normal controls were found with all three variables.‘O On the whole schizophrenics, especially those with paranoid symptomatology,

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75

had more lenient response criteria than the controls. They were more inclined to report “two” flashes when only “one” occurred, a response style which would act to lower twoflash threshold artificially. However, in most cases the thresholds of the schizophrenics were higher than those of the controls, suggesting that they were not substantially influenced by attitudinal factors. Rather, it is possible that phenothiazines, which were administered to all patients, may be responsible for the threshold effect; a phenothiazine has been shown to raise two-flash threshold and lower sensory sensitivity. 24 The sensory sensitivity of the schizophrenics was also in most cases lower than that of the controls, and overall the paranoid schizophrenics had lower sensory sensitivity scores than the non-paranoid schizophrenics. As predicted, in the baseline condition the schizophrenics with orienting responses, the more aroused group, had lower two-flash thresholds than the schizophrenics without orienting responses, the less aroused group. The schizophrenic subgroup differences could not be explained as drug effects for all groups had similar medication, an issue that is returned to in the Discussion. The introduction of white noise influenced all measures and produced one striking effect; marked increases in sensory sensitivity were found with some of the under-reactive non-paranoid schizophrenics. The sensory sensitivity of the control group was lowered in noise. Noise produced more lax criteria in the normal group and the aroused paranoid group. It brought about no significant changes in the thresholds of the controls or the aroused non-paranoid group, whereas the thresholds of the paranoid schizophrenics were raised in this and the subsequent condition. These results indicate that when comparing the sensory discrimination of schizophrenics and normal controls it is important to use threshold measures that permit assessment of sensory factors as well as response bias. Furthermore, both are influenced by changes in the state of arousal, and effects will differ according to the patient’s basal level of physiological reactivity. The present report examines correlations, not only between threshold and indices of electrodermal reactivity, but also with the independent measures of sensory sensitivity and response criterion. METHOD

Subjects

The subjects were all male. Thirty schizophrenics were tested in session I, of whom 24 were available for a second session on the following day. In both sessions half of the subjects had exhibited skin conductance orienting responses during a tone habituation sequence and half failed to exhibit responses. These were termed responders and non-responders respectively. Only patients diagnosed as unambiguously schizophrenic by the hospital psychiatrists were included in the sample. Each subgroup contained equal numbers of paranoid and non-paranoid schizophrenics. The control group consisted of 12 normal subjects employed in the hospital, and by the nature of their occupations (gate attendants, cleaners, nurses) of similar range in IQ. and variety of social background to the schizophrenics. All of the control subjects had exhibited skin conductance orienting responses which habituated quickly. In contrast the responses of the schizophrenic responders habituated slowly, if at all. In several investigations it has been found that schizophrenics may be dichotomised as responders and non-responders in roughly equal numbers. All

76

JOHN

H. GRUZELIER and

PETER

H. VENABLES

groups were age matched. The schizophrenics were drawn from short and long stay wards. All were prescribed moderate or low dosages of phenothiazine tranquilisers and were selected so that the variety of medication and dosage levels in all subgroups were approximately equal, see Table 1. TABLE1. AVERAGE DAILYDOSAGES OFPHENOTHIAZINE MEDICATION (mgs) D% Chlorpromazine Melleril Stelazine Modicate Moditen

Group Responder Non-responder Paranoid Non-paranoid Paranoid Non-paranoid 320 310 280 310 300 300 300 300 % 24 24 24 25 24 24 28 28 24 30

Apparatus

Skin conductance was recorded as described by GRUZELIER and VENABLES.~In brief, skin conductance was measured with a constant voltage system connected to one channel of a Grass 5 polygraph. Silver-silver chloride electrodes, 1 cm dia., were used with a 0.5% potassium chloride electrolyte. Placements were bipolar from the proximal phalanges of the first and second fingers of the right hand. Paired flashes, 1 set in duration, were 360 ft lamberts and were presented with a cathode ray-tube.ls Timing was controlled electronically and the flash sequence presented via an Epsilon paper-tape reader connected to a Digitimer (Devices Ltd.). The flashes were viewed binocularly from a distance of 8 ft. Continuous 75 dB white noise from a white noise generator was presented binaurally through earphones during the treatment condition. PROCEDURE

In session I the subjects were familiarized with the two-flash task and thresholds were determined with the method of limits procedure. In session II thresholds were obtained with the method of constant stimuli. Prior to session I skin conductance orienting response activity was examined to fifteen, 1000 Hz, 85 dB tones presented at irregular intervals between 30 and 60 sec. The constant stimuli threshold was measured under three conditions in the following sequence for all subjects: (1) a baseline condition in the absence of white noise, (2) in the presence of continuous 75 dB white noise, (3) in the absence of noise as in condition 1 and termed the recovery condition. Each condition consisted of 80 flash presentations for a duration of 3 min. Average tonic skin conductance level was calculated at thirty second intervals during the two-flash threshold procedure. When evaluating group differences in skin conductance level by analyses of variance, conventional and conservative degrees of freedom (GEISSER and GREENHOUSE)were employed. WINER~~ recommends the latter procedure to counteract the effects of serial correlation of means occurring in a repeated measures design, and hence the use of this precaution when tonic changes are compared across conditions. Sensory

RELATIONS BETWEEN TWO-FLASHDISCRIMINATION AND ELECTRODERMAL ACTIVITY

II

1 sensitivity was calculated, -, where I1 is the probability of a report of two flashes 1.2- II p(T), and Z, is wherep(T) is 0.84. p is the ratio of the p(T) when two flashes were presented and the p(T) when one flash was presented. RESULTS

Results obtained with the two-flash variables are reported in detaiLlo Here group differences in tonic skin conductance are first reported and then correlations between the twoflash and electrodermal variables are considered. TONIC

SKIN CONDUCTANCE

LEVELS

Mean tonic skin conductance levels for the responder, non-responder and control groups at 30 set intervals during the method of limits two-flash threshold procedure are illustrated in Fig. 1. When comparing the schizophrenic groups with the control group, highly significant differences were found with analyses of variance. The responder group had higher levels (F = 15.15, df 1,28, p < 0.001) and the non-responder group lower levels 23 00 ,Responders

22 00

21 00 1 20 00 t

30010’

I 05

!

IO

Time,

I 15

I 20

I 25

I 30

mtn

Fm. 1. Mean tonic skin conductance levels of schizophrenic responders, non-responders and controls during the method of limits two-flash threshold procedure.

(F = 8.26, df = 1,28, p < O*OOl).A significant Group X intracondition effect in a three group analysis could be attributed to highly significant within condition changes in the responder (F = 3.91, df = 6,84, p < 0.002; df = 2,14, p < 0.05) and control groups

78

JOHN H. GRUZELIER

and PETER H. VENABLES

(F = 16.28, df = 6,84, p < 0401; df = 2,14, p < O.OOl), in the direction of an initial increase in conductance during the first 30 set followed by a gradual decrease, in contrast to insignificant tonic changes in the non-responder group (F = 2.07, df = 6,84, N.S.). Similar group differences and changes in tonic skin conductance within blocks were observed during the constant stimuli threshold procedure, see Fig. 2. The responder group had higher levels than the control group (F = 3.90, df = 1,22, p < 0*06), while the nonresponder group had lower levels (F = 6.05, df = 1,22, p < 0.02). In a three group analysis 0-O

Baseline

e--o

Treatment

G----O

Recovery

Controls

FIG. 2. Mean tonic skin conductance levels of schizophrenic responders, non-responders and controls during the method of constant stimuli procedure in baseline, noise and recovery conditions.

there was a highly significant condition effect (J’ = 14.45, df = 2,66, p -C O*OOl);levels decreased across conditions. There was also a significant intracondition effect (F = 9.00, df = 6,198, p < O-001; df = 1,33, p < 0.01) and a group X intracondition interaction (F = 2.67, df = 12,198, p < OW3; df = 2,33, p < 0.01). In general, the same pattern of change was observed in the responder and control groups as seen during the method of limits procedure, namely an increase in conductance during the first 30 set followed by a gradual decrease. The impression that the non-responder group did not show the same tonic increases during the first 30 set in all conditions, nor a more pronounced increase during the noise condition was implied by the group X condition effects obtained only in the non-responder group comparisons: control group (F = 2.82, df = 2,44, p < 0.07) responder group (F = 3.80, df = 244, p < O-03); control-responder comparison (F = O-47, df = 2,44, N.S.). Similarly with group X intracondition effects: control group (F = 3.72,

RELATIONSBETWEENTWO-FLASHDISCRIMINATIONAND ELECTRODERMAL ACTMTY

19

df = 6,132, p < 0.002); responder group (F = 3.98, df = 6,132, p < 00Il); controlresponder comparison (F = 2.61, df = 6,132, N.S.), and with group X condition and group X intracondition interactions: (F = 4.46, df = 1,22, p < 0.05) and (F = 7.52, df = 1,22, p -c O-OS), respectively. The responder group showed a tonic increase under the noise condition which reached the baseline level, while the non-responder group showed little variation in levels during parison only an intracondition

the three conditions. X group interaction

In the control, non-responder comwas significant (F = 5.44, df = 1,22,

p <

0.05). The control group also showed increases in tonic conductance in each condition though their responses were smaller than those of the responder group. CORRELATIONS BETWEEN TWO-FLASH THRESHOLD AND ELECTRODERMAL VARIABLES

Correlations were obtained with the following two-flash threshold variables: method of limits threshold, constant stimuli threshold, p and sensitivity, under the baseline, noise and recovery conditions. Electrodermal variables included mean skin conductance level under the four threshold conditions and mean orienting response amplitude during the tone habituation sequence. The latter was necessarily obtained only for the control and schizophrenic responder group as the non-responder group had no responses. The interest of earlier investigators lay in the correlations between two-flash threshold and electrodermal levels. Here these are shown in Table 2. With the control group negative correlations were found between method of limits threshold and skin conductance level, TABLE 2. THE CORRELATIONS OF TWO-FLASHTHRESHOLD WITH Ti'SKIN CONDUCTANCE LEVEL

AND

~ORIENTINGRESPONSEAMPLITCJDE

Two-flash threshold Group Control Responder Non-resoonder *p < 0.05.

Electrodermal variable Level Response Amplitude Level Response Amplitude Level

Method of limits -0.65* -0.76t

Baseline 0.23 0.08

-0*63* -056

-0.61* -0.53

-0.50 -0.35

-0.42 -0.44

-O-72?

-0.75t

-0.77.k

-0.55

Noise 0.51 060*

Recovery 044 0.66*

tp < 0.01.

r = -0.68, p < 0.05. Across conditions this relation varied until in the noise condition a moderate correlation in the opposite direction occurred, r = 0.51. From examination of correlations between skin conductance levels under the various conditions, and interrelations between thresholds, see Table 3, it can be inferred that the reversal in sign was due to changes in threshold rather than skin conductance. Correlations between skin conductance levels were all higher than O-78, p < 0.01, whereas correlations between thresholds varied; for example the correlation between method of limits threshold and baseline threshold was r = -0.05, and between method of limits threshold and threshold in noise, r = -0.51. The thresholds of the schizophrenics did not show the same variation

80

JOHN H. GRUZELIERand

PETER H. VENABLES

TABLE 3. CORRELATIONS BETWEEN METHOD OF LIMITS THRESHOLD AND STIMULITHRESHOLDSANDBETWEENSKINCONDUCTANCELEVELSUNDERCORRESPONDlNG CONDITIONS

Two-flash threshold Group

Responder Non-responder *p < 0.05.

condition

Variable Baseline

Control

CONSTANT

Method of limits Skin conductance Method of limits Skin conductance Method of limits Skin conductance

tp < 0.01.

threshold level threshold level threshold level

-0.05 0.8lt 0.59* 0.72t 0.75t o.ssl:

Noise -0.51 0.84: 0.61* 0.65* 0.89$ 0.85$

Recovery -0.42 0.781 0.47 0.69* 0.843 O-84$

$p < O+Ol.

across conditions. With the responder group moderate correlations were found between method of limits threshold and baseline threshold, r = 0.59, p -c 0.05, and between method of limits threshold and threshold in noise, r = O-61,p < O-05. With the responder group these correlations were r = O-78, p -=cO-01 and r = O-89, p -=c0.001, respectively. Consistent with this uniformity was the constant relation between thresholds and skin conductance levels, in the direction of high electrodermal activity and low thresholds. This was most evident with the non-responder group in whom all correlations between levels and thresholds were higher than r = -0.55. Correlations were also examined between the mean amplitude of the skin conductance orienting response and two-flash threshold, see Table 2. In most cases correlations were in the same direction as those obtained with skin conductance levels. With the responder group they were in the direction of high electrodermal reactivity and low two-flash thresholds. With the control group, just as correlations between thresholds and levels varied, so did those between thresholds and response amplitude: method of limits threshold, r = -0.76, p < 0.01; threshold in noise, r = 0.60, p < 0.05; threshold in recovery, r = O-66, p < 0.05. Thus with the schizophrenics relations remained constant between the electrodermal and perceptual variables in the direction of high skin conductance reactivity and low thresholds, i.e. high two-flash resolution. In the control group relations between measures began in the same direction but reversed with repeated testing. However, as threshold may be influenced by sensory and non-sensory factors correlations were next examined with the measures of perceptual sensitivity and response criterion. Parallels with the correlations relating to threshold were found when examining correlations between perceptual sensitivity and electrodermal activity, see Table 4. With the control group in the baseline condition the correlation with response amplitude was negative, r = -0.46, whereas in noise it was positive, r = O-74,p < 0.01. The correlation with skin conductance level was low in the baseline condition, r = O-05, whereas in the recovery condition the correlation was moderate, r = O-51. In contrast, correlations with the schizophrenics were moderate and remained positive in sign. Correlations between p and the electrodermal measures remained stable across conditions in all groups, see Table 4. Correlations with response amplitude were positive in sign for both the schizophrenic group and the control group, i.e. a cautious response criterion was

RELATIONSBETWEENTWO-FLASH DISCRIMINATIONAND ELECTRODERMALACTIVITY

81

TABLE 4. CORRELATIONSOF SENSORY SENSITIVITY AND 13 WITH SKIN CONDUCTANCE LEVELAND 8 SKIN CONDUCTANCERESPONSE AMPLITLJDE Two-flash Group

Baseline Control N= 12

Level/sensitivity level/R Response/sensitivity response/B Level/sensitivity level/I3 Response/sensitivity response/l3

Schizophrenic N = 24

* p < 0.05.

threshold condition

Variable

tp

< 0.01.

0.38 -o-59* -0.46 0.69* 0.6O.r

Noise

Recovery

0.43 -0.61* 0.74t 0*70* 0.44*

0.51 -064* 0.65* 0.711. 0.55t

0.43*

0.31

0.35

0.67: 0.53”r

0.61.t 0.80$

0.73$ 0.79$

$ p < 0.001

associated with high response amplitudes. Differential group correlations were found between p and skin conductance levels. With the schizophrenics correlations were positive, with the control group they were negative. Thus high electrodermal levels were associated with an impulsive response mode amongst the control group but a cautious response mode amongst the schizophrenics. This may reflect learned constraints upon performance occurring with the most aroused schizophrenics. DISCUSSION

The sub-classification of schizophrenics according to the presence or absence of phasic electrodermal responses to non-signal tones, and examination of their tonic changes in skin conductance during the two-flash discrimination task, provided clarification of earlier reports of either pronounced lability or invariance in tonic levels of activity in schizophrenia. The schizophrenic responder group exhibited tonic changes of a higher magnitude than those of the control group. On the other hand the schizophrenic non-responders showed minimal changes. This is plausible evidence that lability of levels characterises the schizophrenic responder and invariance of levels characterises the non-responder. The results suggest several factors that may have contributed to the ambiguity surrounding the covariation of two-flash threshold and electrodermal activity. The reversal in sign of correlations occurring with repeated testing with the control group support the earlier finding of a similar change as the arousal levels of normal controls fell. Here, repeated testing was also accompanied by a decrease in skin conductance levels. The concurrent estimates of /3 enable one hypothesis to be tested, namely that the variation in threshold was due to a change in response criterion; there was no corresponding change in p. An alternative hypothesis, namely that the variation in threshold was due to sensory perceptual factors was supported by changes in the sensory sensitivity measure which paralleled the changes in threshold. This is not to be taken to imply that two-flash threshold and sensory sensitivity mirror the same processes. Sensory sensitivity is defined by the slope of the psychophysical ogive which represents the variability of the central effect. High scores of sensory sensitivity reflect a high signal-to-noise ratio. Two-flash threshold, on the other hand, is understood to be related to the recovery cycle of the visual evoked response; VAUGHAN and COSTAR’

82

JOHN H. GRUZELIERand PETERH. VENABLES

have shown that the two-flash threshold is positively correlated with the duration of the visual evoked response. That the two measures may vary independently of one another is illustrated by the results here. For example, noise produced no change in the thresholds of the control group yet 75 per cent of this group showed a decrease in sensory sensitivity. In the same group the electrodermal measures were correlated in opposite directions with the two sensory perceptual measures. The schizophrenic group did not show variation in correlations between electrodermal levels and two-flash thresholds across conditions. Correlations throughout were similar to those found in the control group during the first condition of measurement. The schizophrenics exhibited an impulsive response mode throughout the two-flash threshold task. Correlations opposite in sign were obtained between response criterion and electrodermal levels with schizophrenics and normal controls, the more aroused schizophrenics showed a conservative attitude whereas the more aroused normals adopted a lax criterion. The influence of such attitudinal factors upon two-flash threshold might well have influenced previous results. Consideration of the neuropsychological frame of reference underlying the responder, non-responder distinction may provide an explanation of these effects. Briefly, it is proposed that this distinction reflects a difference in excitatory activity of origin in functional systems related to the amydala; activity which is accentuated in the responder and diminished in the non-responder. Monkeys with lesions of the amydala have an absence of electrodermal orienting responses.28 Electrical stimulation of the amydala produces an electrodermal response,2s and increases the rate of recovery of the visual evoked response.gO It will be recalled that enhanced phasic and tonic skin conductance activity and low two-flash thresholds differentiate the responder from the non-responder. It is also proposed that a loss of hippocampal inhibitory activity is common to both schizophrenic responders and non-responders. Both groups were found to have lower scores than the normal control group, and an impulsive response mode is characteristic of hippocampal animals.31*32 The recovery times of the electrodermal responses of schizophrenics are faster than those of controls,s as are the electrodermal response recovery times of hippocampal monkeys compared with unoperated control monkeys.33 An association between fast electrodermal response recovery and impulsivity is supported by a correlation of r = O-61, p -c 0.05 between b and the mean skin conductance orienting response recovery times of the responder group. Electrical stimulation of the hippocampus produces a decrease in electrodermal activity and levels and an increase in cortical recovery cycles.34*36 REDDING~~ has shown that electrical stimulation of the hippocampus has differential effects upon the reticular activating system and cortex. Whereas activity of the reticular system is inhibited, cortical recovery cycles are shortened. This implies that as hippocampal inhibitory effects accumulate skin conductance levels will be lowered through action upon the reticular formation, while phasic activity, mediated via the cortex, will be augmented. This may account for the reversal in sign in correlations between skin conductance levels and two-flash thresholds in the control group. Repeated stimulation, and lowering of arousal as the task becomes familiar, will result in a decrease in skin conductance levels, through the action of the hippocampus upon the descending reticular formation. The opposite effects upon the cortex may lead to an improvement in two-flash resolution and

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83

an increase in the signal to noise ratio. This would account for the coexistence with repeated testing of low two-flash thresholds, high sensitivity and lower levels of skin conductance in the control group. This may also account for the consistency of correlations in the schizophrenic group, in whom it is hypothesised that there is a loss of this inhibitory effect. The negative feedback properties of hippocampal inhibitory influences upon the brain stem may keep the arousal properties of this system under homeostatic control. The lack of these homeostatic constraints in schizophrenics may underlie the correspondence of high skin conductance response amplitudes and high skin conductance levels which were found in the schizophrenic responder group but not in the control group. Finally, to what extent might these results reflect the action of phenothiazine medication? It is unlikely that phenothiazines, which act to reduce the activating properties of the reticular system,38 could give rise to correlations which imply the loss of such inhibitory effects. With regard to the responder, non-responder distinction, the groups were on similar medication and did not differ in terms of chronicity or length of hospitalisation.6 Nor could a difference in the metabolism of the drugs account for the results. Responders differ from non-responders not only in terms of skin conductance reactivity and levels but also with heart rate variability and levels, systolic blood pressure and finger skin temperature, all in the direction of higher levels of arousal in the responder group.6*g*11,12In contrast phenothiazines act to increase heart rate, reduce heart rate variability, increase skin temperature, while effects upon blood pressure and skin conductance are inconclusive.38*3g Furthermore, cases of unilateral non-responding and the high incidence of bilateral electrodermal response asymmetries are not easily explained. Nevertheless, the first author is currently examining these issues with schizophrenics both on and off chlorpromazine and experimental evidence will be forthcoming. SUMMARY

The tonic skin conductance responses of schizophrenics and normals were examined while they performed a two-flash discrimination task before, during and after the presentation of continuous white noise. Schizophrenics were subdivided into groups of responders and non-responders on the basis of whether or not skin conductance orienting responses occurred to repeated tones. The electrodermal levels and tonic response amplitudes of the responders were higher than those of the control group. The non-responders had the lowest levels and their tonic responses were minimal. Correlations between the electrodermal variables and two-flash threshold, perceptual sensitivity, and response criterion or p, revealed variations in threshold and perceptual sensitivity with repeated testing in the control group but not the schizophrenic group. Correlations with p did not change. Results are related to previous divergent reports of the differential relations between two-flash threshold and electrodermal activity in schizophrenics and controls and a neurophysiological explanation for these effects is proposed. Acknowledgements-The research was carried out at Springfield Hospital, South London. The support of the Mental Health Trust and Research Fund, England, is gratefully acknowledged together with a grant from the National Institute of Mental Health, USPHS, MH 19225.

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