J. pz)&iat. Res., 1977, Vol. 13 .pp. 185-191. PcrgamonPress.Printedin Great Britain.
AFFECT AND VIGILANCE PERFORMANCE DEPRESSIVE ILLNESS D. G. NH
and
MRC
IN
BYRNE*
Social Psychiatry Research Unit, Australian National University (Received 25 May 1976. Revised 23 December 1976)
Abstract-The relationships between the affective states of depression and anxiety on the one hand, and vigilance performance on the other, were examined for 10 neurotic depressive patients, 10 psychotic depressive patients and 10 normal controls. Affect did not consistently and systematically influence vigilance performance for individual subject groups. Combination of all 3 groups did however produce some significant relationships in the hypothesized directions. A significant negative relationship between severity of depressive affect and signal detection performance and a significant curvilinear (inverted U) relationship between anxiety and signal detection performance allowed confirmation of the hypotheses. The results were discussed in terms of a cognitive deficit among patients with depressive illness.
VIGILANCE, the maintenance of attention over a long, monotonous watch, is difficult even under ideal conditions. It has been shown1-3 that vigilance declines with time, even in normal subjects where central information processing is unimpaired. The presence of psychopathology impairs information processing in certain afllicted groups4 and may produce marked attentional defects.5 In particular, patients with depressive illnesses have been shown to exhibit significantly worse vigilance performance than normal controls,6 the degree of impairment varying with the clinical type of depressive state. Among some depressive patients, severity of depressive affect exerts a systematic influence on reaction time,4*7 that function itself being an attention dependent skill. It is likely also, to exert a systematic influence on vigilance performance among similar depressive patients. In fact both the affective states of depression and anxiety are evident to varying degrees among depressive patients,* and it is conceivable that both, either independently or in concert, exert some influence on vigilance performance, though it is likely that the nature of this influence will differ as a function of the affective state. The possibility of such influences was examined employing two measures of vigilance performance; the signal detection rate and the false positive error rate or the rate of signal reports where no signal has occurred. More specifically the following hypotheses were tested:
(a) Severity of depressive affect This influences information processing in a linear fashion .4 Therefore it is expected that signal detection rate will decline with increasing severity of depressive affect. However, it is *Reprint requests and correspondence Canberra, Australia, 2601.
to: Dr. D. G. Byrne, Social Psychiatry,
185
A.N.U.,
P.O. Box 4,
186
D. G. BYRNE
likely that severity of depressive affect and false positive errors will be related in a more complex way, particularly if the relationship is examined in a mixed diagnostic group of depressive patients. It has been suggested9 that neurotic depressives are less severely depressed than psychotic depressives. It has been shown however6 that neurotic depressives exhibit a greater false positive error rate that do psychotic depressives. If these findings are assumed to be correct, then a curvilinear (inverted U) relationship is expected between severity of depressive affect and false positive errors. (b) Anxiety This is more likely to coexist with and reflect levels of arousal.“’ Arousal influences signal detection in a curvilinear (inverted U) fashion 3*6~11 It is thus expected that signal detection rates will be low with low levels of anxiety, improve with moderate levels of anxiety, and decline again with high levels of anxiety. However, it has been suggested that high levels of arousal produce an inefficient information processing mechanism, initiating responses which are “impetuous and ill-controlled”. Therefore it is expected that the tendency to make false positive errors will increase as a linear function of anxiety. METHOD
Subjects
These were 20 hospitalized depressive patients (10 neurotic and 10 psychotic according to the criteria of KILOH and GARSIDE~~),of age range 22-67, and 10 normal controls of age range 23-47. Patients were selected so that: (a) they were acute admissions with no more than 2 weeks’ hospitalization; (b) they were free from medication and convulsive therapy for 4 days prior to testing; (c) they were sufficiently in touch with reality to understand experimental instructions. The vigilance task An auditory task of 30 min duration
was used. The noise background consisted of random digits spoken by a female voice at a rate of 1 set-l. Signals consisted of 3 odd digits in sequence. Thirty signals were presented, at an average rate of 1 min-l, but randomized over each minute block of stimulation (60 digits). The whole sequence was recorded onto tape in such a way that the signal on one track of a stereo recording co-incided with a tone on the other track (inaudible to the subject) which served to inform the experimenter that a signal had occurred. It did so by triggering a light visible only to the experimenter. Playback of the signal and noise sequence was by headphones. Subjects were instructed to report signal occurrence by pressing a hand-held switch. This also activated a light visible only to the experimenter. Simultaneous activation of the two lights indicated signal detection. Activation of the response light in the absence of the toneactivated light, indicated a false positive error. The apparatus has been described in more detail elsewhere.s Procedure
Subjects were individually tested in a sound attenuated, dimly lit room containing both
AFFECTAND VIGILANCE PERFORMANCE IN DEPREWVEILLNESS
187
subject and experimenter. The subject sat with back to experimenter and apparatus, so that no cues as to signal occurrence could be transmitted. External stimulation was minimized by the subject facing a blank wall. No communication took place between subject and experimenter during the task. All subjects were tested in the afternoon to control for possible diurnality of affect. Psychometric instruments
Both depression and anxiety were assessed psychometrically, using established and validated intruments. Two independent instruments were used to assess each of depression and anxiety. (a) Depression. (i) The Zung Self-Rating Depression Scale (SDS)13*‘” (ii) The severity scale from the Levine-Pilowsky Depression (LPD) scale.lS*16 (b) Anxiety. (i) The Taylor Manifest Anxiety Scale (TMAS).” (ii) A visual analogue anxiety scale based on a self-rating.le*rs Questionnaires were administered prior to vigilance testing. RESULTS
Means and standard deviations of vigilance performance scores (signal detections and false positive errors) for each of the 3 groups are presented in Table 1. TABLE1. VIGILANCE PERFORMANCE INDICES OF NEUROTIC AND PSYCHOTIC DEPRESSIVES,AND CONTROLS
Signal detection score (/30) False positive error rate
Neurotic depressives N= 10
Psychotic depressives N= 10
Controls N= 10
x
=
21.70
7.50
26.40
S.D.
=
4.30
4.28
2.46
X
=
3160
6.80
2.10
S.D.
=
42.69
14.69
1.79
Depression and vigilance
Product-moment correlation coefficient+ were calculated to examine the relationships between severity of depressive affect and vigilance performance. Table 2 presents these results for individual depressive groups and the control group. Only one significant result, a negative correlation between LDP and signal detection rate was obtained, for the control group. Combination of all groups did however produce some significant relationships in the hypothesized directions. Significant negative correlations between severity of depressive affect and signal detection rate (SDS and signal detection rate, r = -0.58, p < 0.05; LPD and signal detection rate, r = -0.64, p < 0.05) allowed confirmation of the hypothesis of an inverse linear relationship between the two. The hypothesis of a curvilinear relationship between severity of depressive affect and false positive errors was tested on combined groups using a second degree polynomial
188 TABLE
D.G. 2.
BVRNE
INTERCORRELAT~ONSBETWEENDEPREWONMEASURESAND
VIGILANCEPERFORMANCE
FOR INDMDUAL
GROUPS
Zung and signal detection Zung and false positives LPD and signal detection LPD and false nositives *p < 0.05.
Controls
Neurotic depressives
Psychotic depressives
r = to.36
r = to.11
r = -0.23
I’ = iO.49
Y = $045
r = +0.14
r = -0.56’
Y = +025
r=
r = --0.02
Y = to.51
Y = -0.26
-044
model of curvilinear repression. 2o Insignificant curvilinear relationships between SDS and false positive errors (F = 2-13) and LPD and false positive errors (F = 3.28) did not allow confirmation of that hypothesis. Anxiety
and vigilance
Again product moment correlation coefficients were used to examine the relationship between anxiety and vigilance performance for individual groups, and Table 3 presents the results of these correlations. Two significant results, a positive correlation between visual analogue scale and signal detection for the control group, and a negative correlation between visual analogue scale and signal detection for the psychotic depressive group were obtained. TABLE
3. INTERCORRELATIONS
BETWEEN
TMAS and signal detection TMAS and false positives Visual analogue and signal detection Visual analogue and false positives *p < 0.05.
ANXIETY MEASURES GROUPS
AND
VIGILANCEPERFORMANCE
FORINDIVIDUAL
Controls
Neurotic depressives
Psychotic depressives
r = j-o.53
r = -0.14
r = -0.14
r _ -i-O.17
r = +w49
r = +w13
r = +0.56*
I’ = 10.46
r = -0.66*
r = $0.02
r = +0.47
r = -0.32
The hypothesis of a curvilinear relationship between anxiety and signal detection performance was tested on combined groups using a second degree polynomial model of curvilinear repression. 2OA significant curvilinear relationship was found between TMAS and signal detection (F = 9.17; 2, 27; p < 0.01) and between visual analogue scale and signal detection (F = 344; 2, 27; p < 0*05), allowing confirmation of the hypothesis. The hypothesis of a positive, linear relationship between anxiety and false positive errors was tested on combined groups using product moment correlation coefficients. Neither the correlation between TMAS and false positives (r = + 0.32) nor visual analogue scale and false positives (r = +0*36) were significant, though they were in the hypothesized direction. This hypothesis was thus not able to be conlkned.
AFFECTAND VIGILANCEPERFORMANCE IN DEPRESSIVE ILLNESS
189
DISCUSSION
The lack of consistent correlations between affect and vigilance performance within individual groups, indicates that the influence of affect on vigilance only becomes apparent when a wide range of levels of affect and of vigilance scores are considered. Combination of all groups produced some significant and substantial relationships in the hypothesized directions. In particular the relationships between affect (both depression and anxiety) and signal detection performance were well demonstrated in the study. There was, however, no evidence of a systematic relationship between affect and the tendency to make false positive errors. Of some importance was the finding that the ability to detect signals presented against a background of noise, declines as a function of the severity of depressive affect. This accords well with the clinical finding that patients with depressive illness typically exhibit some loss of concentration.ll It is therefore interesting to speculate that the degree to which this clinical feature is evident, may to an extent reflect the clinical state of the individual patient. The failure of severity of depressive affect to relate significantly to the tendency to make false positive errors may indicate the complexity of the hypothesized relationship. It might be argued that the tendency to make false positive errors reflects not so much the capacity of the information processing channel to receive and process information, as it does the ability to control the output of motor responses. l1 Severity of depressive affect has however been shown to influence central information processing efficiency rather than motor functions.4 Consequently the failure to demonstrate a relationship between severity of depressive affect and false positive errors is not altogether surprising. Both measures of anxiety related in a significantly curvilinear fashion to signal detection performance. There was also however a significant linear component to the relationship (first degree polynomial,20 TMAS and signal detection, F = 16.57; 1, 28; p < 0.01; and visual analogue scale and signal detection, F = 6.07; 1, 28; p < 0.05). Neither measure of anxiety significantly correlated with false positive error rate. It was expected that vigilance performance would vary with measures of anxiety in the same way that it varies with measures of arousal. 3*6*11 This was not completely borne out in the results. Vigilance performance among depressive patients has been shown to relate to arousal,s although this relationship is not consistent over the various clinical categories of depressive illness. It was interesting to note then that while neither anxiety20 nor hyperarousa121*22have been found evident in psychotic depressive illness, the psychotic depressive patients in this study scored higher as a group on both measures of anxiety than did either of the other two groups (TMAS x score = 35.30 compared with 33.10 for the neurotic depressive group, and visual analogue R score = 6.30 compared with 6.20 for the neurotic depressive group). This is consistent with the observation lo that scales of depression and anxiety typically contain sufficient common items to be measuring much the same affective state. It invites the speculation that high anxiety scale scores among the psychotic depressive subjects reflect neither actual anxiety nor arousal. Removal of the psychotic depressive group from the collective data strengthened at least the correlations between anxiety and false positive errors (TMAS and false positives, r = +0*52, p < O-01; visual analogue and false positives, r = f0.59, p < O-01). The results of this study suggest that the relationships between affect and vigilance
190
D. G. BYRNE
performance are not clear cut. The diagnostic category into which a patient is placed appears to have some bearing on the issue. It has been suggested that the diagnostic category determines to some extent, not only the nature of the affective states but also the degree to which it is present. It is possible therefore that the mixture of diagnostic categories employed in this study contributed to the failure to demonstrate clearer relationships between vigilance and affect. The clearest relationship was that between severity of depressive affect and signal detection performance. This is understandable in terms of previously documented relationships between depression and central information processing,4*23 which suggest a reduced cognitive capacity to be a more general characteristic of depressive states. It may be concluded therefore that affect, and in particular depressive affect, exerts an influence over the ability of an individual to detect signals presented against a background of noise. This demonstrated relationship between clinical state and a laboratory measure of cognitive functioning poses the question as to whether the apparent deterioration in cognitive functioning is due to the deleterious effects of depressed mood, or to some more fundamental, and perhaps physiological change occurring in depressive illness. There is some evidence21922to suggest the latter. Future research might well be usefully devoted to an elucidation of the reasons why people with depressive illnesses exhibit such marked incapacities of cognitive functioning. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
19. 20. 21.
MACKWORTH, J. F. Vigilance and Habituation. Penguin, Harmondsworth, 1969. MACKWORTH, J. F. Vigilance and Attention. Penguin, Harmondsworth, 1970. DAVIES,D. R. and TUNE,G. S. Human Vigilance Performance. Staples Press, London, 1970. BYRNE,D. G. Choice reaction times in depressive states. Br. J. Sot. Clin. Psychok 15, 149, 1976. MCGHIE,A. Pathology ofdttention. Penguin, Harmondsworth, 1969. BYRNE,D. G. Vigilance and arousal in depressive states. Brit. J. sot. clin. Psychol. 15, 267, 1976. COURT,J. H. Psychomotor concomitants of psychological disorder. Unpublished doctoral dissertation, University of Adelaide, 1967. ROTH,M., GURNEY,C., GARSIDE,R. F., KERR,T. A. and SCHAPIRA,K. Studies in the classification of affective disorders. Br. J. Psychiat. 121, 147, 1972. MENDELS,J. Concepts of Depression. John Wiley, New York, 1970. MARTIN,B. and SROUFE,L. A. Anxiety. In Symptoms of Psychopathology, COSTELLO, C. G. (Editor), pp. 216-259. John Wiley, New York, 1970. WELFORD, A. T. Arousal, channel capacity and decision. Nature 194,365,1962. KILOH,L. G. and GARSIDE,R. F. The independence of neurotic depression and endogenous depression. Br. J. Psychiat. 109, 451, 1963. ZUNG,W. W. K. A self rating depression scale. Archsgen. Psychiat. 12,63, 1965. ZUNG,W. W. K. Factors influencing the self-rating depression scale. Archsgen. Psychiat. 16,543, 1967. PILOWSKY, I. and SPALDING,D. A method for measuring depression: validity studies on a depression questionnaire. Br. J. Psychiat. 121, 411, 1972. BYRNE,D. G. Some preliminary observations on a questionnaire technique for classifying depressive illness. dust. N.Z. J. Psychiat. 9, 25, 1975. TAYMR, J. A. A personality scale of manifest anxiety. J. abnorm. sot. Psychol. 48,285, 1953. CLARK,P. R. F. and SPEAR,F. G. Reliability and sensitivity of the self-assessment of well-being. BUN. Br. psycho/. Sot. 17, 18, 1964. RUN-ON, R. P. and HABER,A. Fundamentals of Behavioural Statistics. Addison-Wesley, California, 1968. SNEDECOR, G. W. and COCHRAN, W. G. Statistical Methods. Iowa University Press, Iowa, 1967. BYRNE,D. G. and TOTTMAN,V. The galvanic skin response inhibition threshold: a preliminary study with an Australian sample. dust. N.Z. J. Psychiat. 8,261, 1974.
AFFECTAND VIGILANCEPERFORMANCE IN DEPRESSIVE ILLNESS
IYI
22. BYRNE,D. G. A psychophysiological distinction between types of depressive states. Amt. N.Z. J. Psych&. 9,181,1975. 23. BECK, A. T., FLESHBACH,S. and LEGG, D. The clinical utility of the digit symbol test. .I. consult. Psychol. 26, 263, 1962.
AFFECT AND VIGILANCE PERFORMANCE DEPRESSIVE ILLNESS D. G. NH
and
MRC
IN
BYRNE*
Social Psychiatry Research Unit, Australian National University (Received 25 May 1976. Revised 23 December 1976)
Abstract-The relationships between the affective states of depression and anxiety on the one hand, and vigilance performance on the other, were examined for 10 neurotic depressive patients, 10 psychotic depressive patients and 10 normal controls. Affect did not consistently and systematically influence vigilance performance for individual subject groups. Combination of all 3 groups did however produce some significant relationships in the hypothesized directions. A significant negative relationship between severity of depressive affect and signal detection performance and a significant curvilinear (inverted U) relationship between anxiety and signal detection performance allowed confirmation of the hypotheses. The results were discussed in terms of a cognitive deficit among patients with depressive illness.
VIGILANCE, the maintenance of attention over a long, monotonous watch, is difficult even under ideal conditions. It has been shown1-3 that vigilance declines with time, even in normal subjects where central information processing is unimpaired. The presence of psychopathology impairs information processing in certain afllicted groups4 and may produce marked attentional defects.5 In particular, patients with depressive illnesses have been shown to exhibit significantly worse vigilance performance than normal controls,6 the degree of impairment varying with the clinical type of depressive state. Among some depressive patients, severity of depressive affect exerts a systematic influence on reaction time,4*7 that function itself being an attention dependent skill. It is likely also, to exert a systematic influence on vigilance performance among similar depressive patients. In fact both the affective states of depression and anxiety are evident to varying degrees among depressive patients,* and it is conceivable that both, either independently or in concert, exert some influence on vigilance performance, though it is likely that the nature of this influence will differ as a function of the affective state. The possibility of such influences was examined employing two measures of vigilance performance; the signal detection rate and the false positive error rate or the rate of signal reports where no signal has occurred. More specifically the following hypotheses were tested:
(a) Severity of depressive affect This influences information processing in a linear fashion .4 Therefore it is expected that signal detection rate will decline with increasing severity of depressive affect. However, it is *Reprint requests and correspondence Canberra, Australia, 2601.
to: Dr. D. G. Byrne, Social Psychiatry,
185
A.N.U.,
P.O. Box 4,
186
D. G. BYRNE
likely that severity of depressive affect and false positive errors will be related in a more complex way, particularly if the relationship is examined in a mixed diagnostic group of depressive patients. It has been suggested9 that neurotic depressives are less severely depressed than psychotic depressives. It has been shown however6 that neurotic depressives exhibit a greater false positive error rate that do psychotic depressives. If these findings are assumed to be correct, then a curvilinear (inverted U) relationship is expected between severity of depressive affect and false positive errors. (b) Anxiety This is more likely to coexist with and reflect levels of arousal.“’ Arousal influences signal detection in a curvilinear (inverted U) fashion 3*6~11 It is thus expected that signal detection rates will be low with low levels of anxiety, improve with moderate levels of anxiety, and decline again with high levels of anxiety. However, it has been suggested that high levels of arousal produce an inefficient information processing mechanism, initiating responses which are “impetuous and ill-controlled”. Therefore it is expected that the tendency to make false positive errors will increase as a linear function of anxiety. METHOD
Subjects
These were 20 hospitalized depressive patients (10 neurotic and 10 psychotic according to the criteria of KILOH and GARSIDE~~),of age range 22-67, and 10 normal controls of age range 23-47. Patients were selected so that: (a) they were acute admissions with no more than 2 weeks’ hospitalization; (b) they were free from medication and convulsive therapy for 4 days prior to testing; (c) they were sufficiently in touch with reality to understand experimental instructions. The vigilance task An auditory task of 30 min duration
was used. The noise background consisted of random digits spoken by a female voice at a rate of 1 set-l. Signals consisted of 3 odd digits in sequence. Thirty signals were presented, at an average rate of 1 min-l, but randomized over each minute block of stimulation (60 digits). The whole sequence was recorded onto tape in such a way that the signal on one track of a stereo recording co-incided with a tone on the other track (inaudible to the subject) which served to inform the experimenter that a signal had occurred. It did so by triggering a light visible only to the experimenter. Playback of the signal and noise sequence was by headphones. Subjects were instructed to report signal occurrence by pressing a hand-held switch. This also activated a light visible only to the experimenter. Simultaneous activation of the two lights indicated signal detection. Activation of the response light in the absence of the toneactivated light, indicated a false positive error. The apparatus has been described in more detail elsewhere.s Procedure
Subjects were individually tested in a sound attenuated, dimly lit room containing both
AFFECTAND VIGILANCE PERFORMANCE IN DEPREWVEILLNESS
187
subject and experimenter. The subject sat with back to experimenter and apparatus, so that no cues as to signal occurrence could be transmitted. External stimulation was minimized by the subject facing a blank wall. No communication took place between subject and experimenter during the task. All subjects were tested in the afternoon to control for possible diurnality of affect. Psychometric instruments
Both depression and anxiety were assessed psychometrically, using established and validated intruments. Two independent instruments were used to assess each of depression and anxiety. (a) Depression. (i) The Zung Self-Rating Depression Scale (SDS)13*‘” (ii) The severity scale from the Levine-Pilowsky Depression (LPD) scale.lS*16 (b) Anxiety. (i) The Taylor Manifest Anxiety Scale (TMAS).” (ii) A visual analogue anxiety scale based on a self-rating.le*rs Questionnaires were administered prior to vigilance testing. RESULTS
Means and standard deviations of vigilance performance scores (signal detections and false positive errors) for each of the 3 groups are presented in Table 1. TABLE1. VIGILANCE PERFORMANCE INDICES OF NEUROTIC AND PSYCHOTIC DEPRESSIVES,AND CONTROLS
Signal detection score (/30) False positive error rate
Neurotic depressives N= 10
Psychotic depressives N= 10
Controls N= 10
x
=
21.70
7.50
26.40
S.D.
=
4.30
4.28
2.46
X
=
3160
6.80
2.10
S.D.
=
42.69
14.69
1.79
Depression and vigilance
Product-moment correlation coefficient+ were calculated to examine the relationships between severity of depressive affect and vigilance performance. Table 2 presents these results for individual depressive groups and the control group. Only one significant result, a negative correlation between LDP and signal detection rate was obtained, for the control group. Combination of all groups did however produce some significant relationships in the hypothesized directions. Significant negative correlations between severity of depressive affect and signal detection rate (SDS and signal detection rate, r = -0.58, p < 0.05; LPD and signal detection rate, r = -0.64, p < 0.05) allowed confirmation of the hypothesis of an inverse linear relationship between the two. The hypothesis of a curvilinear relationship between severity of depressive affect and false positive errors was tested on combined groups using a second degree polynomial
188 TABLE
D.G. 2.
BVRNE
INTERCORRELAT~ONSBETWEENDEPREWONMEASURESAND
VIGILANCEPERFORMANCE
FOR INDMDUAL
GROUPS
Zung and signal detection Zung and false positives LPD and signal detection LPD and false nositives *p < 0.05.
Controls
Neurotic depressives
Psychotic depressives
r = to.36
r = to.11
r = -0.23
I’ = iO.49
Y = $045
r = +0.14
r = -0.56’
Y = +025
r=
r = --0.02
Y = to.51
Y = -0.26
-044
model of curvilinear repression. 2o Insignificant curvilinear relationships between SDS and false positive errors (F = 2-13) and LPD and false positive errors (F = 3.28) did not allow confirmation of that hypothesis. Anxiety
and vigilance
Again product moment correlation coefficients were used to examine the relationship between anxiety and vigilance performance for individual groups, and Table 3 presents the results of these correlations. Two significant results, a positive correlation between visual analogue scale and signal detection for the control group, and a negative correlation between visual analogue scale and signal detection for the psychotic depressive group were obtained. TABLE
3. INTERCORRELATIONS
BETWEEN
TMAS and signal detection TMAS and false positives Visual analogue and signal detection Visual analogue and false positives *p < 0.05.
ANXIETY MEASURES GROUPS
AND
VIGILANCEPERFORMANCE
FORINDIVIDUAL
Controls
Neurotic depressives
Psychotic depressives
r = j-o.53
r = -0.14
r = -0.14
r _ -i-O.17
r = +w49
r = +w13
r = +0.56*
I’ = 10.46
r = -0.66*
r = $0.02
r = +0.47
r = -0.32
The hypothesis of a curvilinear relationship between anxiety and signal detection performance was tested on combined groups using a second degree polynomial model of curvilinear repression. 2OA significant curvilinear relationship was found between TMAS and signal detection (F = 9.17; 2, 27; p < 0.01) and between visual analogue scale and signal detection (F = 344; 2, 27; p < 0*05), allowing confirmation of the hypothesis. The hypothesis of a positive, linear relationship between anxiety and false positive errors was tested on combined groups using product moment correlation coefficients. Neither the correlation between TMAS and false positives (r = + 0.32) nor visual analogue scale and false positives (r = +0*36) were significant, though they were in the hypothesized direction. This hypothesis was thus not able to be conlkned.
AFFECTAND VIGILANCEPERFORMANCE IN DEPRESSIVE ILLNESS
189
DISCUSSION
The lack of consistent correlations between affect and vigilance performance within individual groups, indicates that the influence of affect on vigilance only becomes apparent when a wide range of levels of affect and of vigilance scores are considered. Combination of all groups produced some significant and substantial relationships in the hypothesized directions. In particular the relationships between affect (both depression and anxiety) and signal detection performance were well demonstrated in the study. There was, however, no evidence of a systematic relationship between affect and the tendency to make false positive errors. Of some importance was the finding that the ability to detect signals presented against a background of noise, declines as a function of the severity of depressive affect. This accords well with the clinical finding that patients with depressive illness typically exhibit some loss of concentration.ll It is therefore interesting to speculate that the degree to which this clinical feature is evident, may to an extent reflect the clinical state of the individual patient. The failure of severity of depressive affect to relate significantly to the tendency to make false positive errors may indicate the complexity of the hypothesized relationship. It might be argued that the tendency to make false positive errors reflects not so much the capacity of the information processing channel to receive and process information, as it does the ability to control the output of motor responses. l1 Severity of depressive affect has however been shown to influence central information processing efficiency rather than motor functions.4 Consequently the failure to demonstrate a relationship between severity of depressive affect and false positive errors is not altogether surprising. Both measures of anxiety related in a significantly curvilinear fashion to signal detection performance. There was also however a significant linear component to the relationship (first degree polynomial,20 TMAS and signal detection, F = 16.57; 1, 28; p < 0.01; and visual analogue scale and signal detection, F = 6.07; 1, 28; p < 0.05). Neither measure of anxiety significantly correlated with false positive error rate. It was expected that vigilance performance would vary with measures of anxiety in the same way that it varies with measures of arousal. 3*6*11 This was not completely borne out in the results. Vigilance performance among depressive patients has been shown to relate to arousal,s although this relationship is not consistent over the various clinical categories of depressive illness. It was interesting to note then that while neither anxiety20 nor hyperarousa121*22have been found evident in psychotic depressive illness, the psychotic depressive patients in this study scored higher as a group on both measures of anxiety than did either of the other two groups (TMAS x score = 35.30 compared with 33.10 for the neurotic depressive group, and visual analogue R score = 6.30 compared with 6.20 for the neurotic depressive group). This is consistent with the observation lo that scales of depression and anxiety typically contain sufficient common items to be measuring much the same affective state. It invites the speculation that high anxiety scale scores among the psychotic depressive subjects reflect neither actual anxiety nor arousal. Removal of the psychotic depressive group from the collective data strengthened at least the correlations between anxiety and false positive errors (TMAS and false positives, r = +0*52, p < O-01; visual analogue and false positives, r = f0.59, p < O-01). The results of this study suggest that the relationships between affect and vigilance
190
D. G. BYRNE
performance are not clear cut. The diagnostic category into which a patient is placed appears to have some bearing on the issue. It has been suggested that the diagnostic category determines to some extent, not only the nature of the affective states but also the degree to which it is present. It is possible therefore that the mixture of diagnostic categories employed in this study contributed to the failure to demonstrate clearer relationships between vigilance and affect. The clearest relationship was that between severity of depressive affect and signal detection performance. This is understandable in terms of previously documented relationships between depression and central information processing,4*23 which suggest a reduced cognitive capacity to be a more general characteristic of depressive states. It may be concluded therefore that affect, and in particular depressive affect, exerts an influence over the ability of an individual to detect signals presented against a background of noise. This demonstrated relationship between clinical state and a laboratory measure of cognitive functioning poses the question as to whether the apparent deterioration in cognitive functioning is due to the deleterious effects of depressed mood, or to some more fundamental, and perhaps physiological change occurring in depressive illness. There is some evidence21922to suggest the latter. Future research might well be usefully devoted to an elucidation of the reasons why people with depressive illnesses exhibit such marked incapacities of cognitive functioning. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.
19. 20. 21.
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