- Email: [email protected]
Visual vigilance and psychopathology
Psvc‘hiatry Research, 18, 285-287 Elsevier
285
Letter Visual Vigilance
and Psychopathology
To the Editors: We have developed two psychometrically matched visual continuous performance tasks (CPTs) to determine the role of perceptual processing deficits in the poor vigilance performance of schizophrenic patients and those at risk for schizophrenia (Nuechterlein and Dawson, 1984). During the standardization of these tasks, an unanticipated relationship was found between performance and psychometrically defined psychopathology. After pilot testing, three conditions of a visual CPT were preliminarily standardized by administering them to 30 undergraduate volunteers. After this, the tasks were administered to paid volunteers. Testing followed the procedures of Nuechterlein et al. (1983) and used identical equipment. Subjects were required to press a button to the digit zero and to withhold responses to the other digits (l-9). Stimuli were rear-projected for 40 ms with an interstimulus interval of 1 second. The three conditions were: (1) Standard, in which the stimuli were in clear focus; (2) Perceptual Degradation, in which the stimuli were blurred, by defocusing the lens 2.25 diopters, and viewed through a mask of + signs; and (3) Memory Load, in which a zero was a target only if it followed a 2 or a 9 within three trials. The subject was also required to keep a mental tally of the number of responses made. The last is a newly developed condition. For each form of the task, a period of practice was followed by486 trials. The target appeared on 25% of the trials in Standard and Perceptual Degradation conditions. It appeared on only 11% of the Memory Load trials, since it was also necessary to have zeros not preceded by 2 or 9. The Standard condition, which was treated as extended practice, was always administered first. The order
of the other two conditions was counterbalanced. Subjects were paid volunteers who had responded to newspaper advertisements for studies of memory and attention. Forty of 97 respondents were eliminated after telephone screening for history of head injury, psychiatric disorder, current illness or medication, or drug/alcohol abuse. Thirty subjects were then tested with the vigilance tasks and also administered the Minnesota Multiphasic Personality Inventory (MMPI)-168, which was not scored until all testing was completed. All MMPIs were valid. Eight subjects had one clinical scale above 70, and replacement subjects with normal MMPIs were tested. The data from the subjects with deviant MMPIs were not used in determining the discriminating power of the degraded and memory load vigilance tasks, since this should be done with normals (Chapman and Chapman, 1978). A Task Conditions (2) by Trial Block (3 successive blocks of 162 trials) analysis of variance (ANOVA) showed that average sensitivity (A’) for the Perceptual Degradation condition (mean = 0.91; SD = 0.09) and for the Memory Load condition (mean q 0.94; SD q 0.09) did not differ (F = 2.22, df = l/29; p < 0.2). Sixty-five subjects would be needed for this mean difference to be significant (p < 0.05) with power of 0.8 (Cohen, 1977). Sensitivity did not vary over trial blocks, nor was the interaction significant @ > 0.20). The reliability of the tasks was estimated by scoring all trials as correct or incorrect and computing the odd-even correlation. These coefficients, corrected for test length, were 0.96 and 0.95 for the Perceptual Degradation and Memory Load conditions, respectively.
0165-I 78 I 86 $03.50 0 1986 Elsevier Science Publishers B.V.
286
These equivalent reliability coefficients, along with comparable means and SDS, suggest that the tasks have comparable true score variance, or discriminating power, although this requires confirmation in a larger sample (Chapman and Chapman, 1978). One of the eight subjects with deviant MMPIs did not perform the tasks in a meaningful way, missing 34 of 120 degraded targets and making 281 false alarms. The average profile of the other seven subjects and that of the psychometrically normal group are shown in Fig. I. Lachar’s (1974) compendium describes the deviant profile (8-4/4-8) as straddling the fence between character disorder and psychosis. Persons with this profile are characterized as schizoid, although it must be emphasized that they were not patients and denied histories of psychological or psychiatric treatment. The A’ scores of these seven subjects were examined in a Condition by Trial Block ANOVA. Although the n is small, sensitivity was significantly lower (F= 12.49. df’= I /6,p < 0.02) in the Perceptual Degradation condition (mean q 0.82, SD q 0.10) than in the Memory Load condition (mean q 0.90, SD q 0.09). The interaction was also significant (F= 68.64, df= 2/ 12, p < 0.005). Performance in the degraded condition tended to deteriorate
over time (Block 5 - Block I = -5.4), while it improved slightly with the memory load (Block 5 - Block 1 = 3.0). Thus, the difference between degraded and memory conditions was larger in the third block of trials (I 1.9) than in the first (3.5). The two versions of the CPT described here have different psychological processing demands but equal discriminating power for the parameter of sensitivity to signals (A’). The degradation CPT performance of the subjects with deviant MMPls is like that reported in Nuechterlein and Dawson’s (1984, pp. 175176) review of the relations between psychometric indicators of the schizophrenic spectrum and impaired vigilance. The present findings require replication in larger samples selected for psychometric indicators of schizophrenic spectrum disorders. Larger psychometrically deviant groups are necessary to determine whether there is an interaction between MMPI group and vigilance condition. This more conservative test was not used here because of the disproportionately small size of the deviant MM Pl group. If replicated, the present findings would suggest that the sensitivity of this behavioral marker is due to perceptual factors rather than to greater task difficulty.
Fig 1. Average profiles on the Minnesota Multiphasic Personality Inventory (MMPI) for psychometrically normal and deviant subjects
,1
a.?,
70--
-
-
-
-
30_-_--.-__--_-__--/ /
/
L
F
K
12 Hs
0
3 Hy
4 Pd
MMPIScale
5 Mf
6 Pa
7 Pt
6 SC
9 Ma
0 Si
287
This work was supported by grants from the NIMH (MH-38387) and NIH (NS-16375). The authors thank Dr. Keith Nuechterlein for advice and aid in establishing the vigilance task in our laboratory, and Dr. Jean Chapman for the suggestion to estimate task reliability with splithalf correlation. Acknowledgment.
Nuechterlein, K.H., and Dawson, M.E. Information processing and attentional functioning in the developmental course of schizophrenic disorders. Schizophrenia Bulletin, 10, 160 (1984). Nuechterlein, K.H., Parasuraman, R.. and Qiyuan, J. Visual sustained attention: Image degradation produces rapid sensitivity decrement over time. Science, 220, 327 (1983).
References
Chapman, L.J., and Chapman, J.P. The measurement of differential deficit. Journalof Ps.vchiatric Research, 14, 303 ( 1978). Cohen, J. Statistical Power Analvsisfor the Behavioral Sciences. Rev. ed. Academic Press, New York (1977). Lachar, D. The MMPI: Clinical Assessment and Automated Interpretation. Western Psychological Services, Los Angeles (1974).
Milton E. Strauss, Ph.D. Jason Brandt, Ph.D. Patricia McSorley, B.S. Department of Psychiatry Osler 320 Johns Hopkins Hospital Baltimore, MD 2 1205, USA. Received April 15, 1985; revised May 5, 1986; accepted May 29, 1986.
285
Letter Visual Vigilance
and Psychopathology
To the Editors: We have developed two psychometrically matched visual continuous performance tasks (CPTs) to determine the role of perceptual processing deficits in the poor vigilance performance of schizophrenic patients and those at risk for schizophrenia (Nuechterlein and Dawson, 1984). During the standardization of these tasks, an unanticipated relationship was found between performance and psychometrically defined psychopathology. After pilot testing, three conditions of a visual CPT were preliminarily standardized by administering them to 30 undergraduate volunteers. After this, the tasks were administered to paid volunteers. Testing followed the procedures of Nuechterlein et al. (1983) and used identical equipment. Subjects were required to press a button to the digit zero and to withhold responses to the other digits (l-9). Stimuli were rear-projected for 40 ms with an interstimulus interval of 1 second. The three conditions were: (1) Standard, in which the stimuli were in clear focus; (2) Perceptual Degradation, in which the stimuli were blurred, by defocusing the lens 2.25 diopters, and viewed through a mask of + signs; and (3) Memory Load, in which a zero was a target only if it followed a 2 or a 9 within three trials. The subject was also required to keep a mental tally of the number of responses made. The last is a newly developed condition. For each form of the task, a period of practice was followed by486 trials. The target appeared on 25% of the trials in Standard and Perceptual Degradation conditions. It appeared on only 11% of the Memory Load trials, since it was also necessary to have zeros not preceded by 2 or 9. The Standard condition, which was treated as extended practice, was always administered first. The order
of the other two conditions was counterbalanced. Subjects were paid volunteers who had responded to newspaper advertisements for studies of memory and attention. Forty of 97 respondents were eliminated after telephone screening for history of head injury, psychiatric disorder, current illness or medication, or drug/alcohol abuse. Thirty subjects were then tested with the vigilance tasks and also administered the Minnesota Multiphasic Personality Inventory (MMPI)-168, which was not scored until all testing was completed. All MMPIs were valid. Eight subjects had one clinical scale above 70, and replacement subjects with normal MMPIs were tested. The data from the subjects with deviant MMPIs were not used in determining the discriminating power of the degraded and memory load vigilance tasks, since this should be done with normals (Chapman and Chapman, 1978). A Task Conditions (2) by Trial Block (3 successive blocks of 162 trials) analysis of variance (ANOVA) showed that average sensitivity (A’) for the Perceptual Degradation condition (mean = 0.91; SD = 0.09) and for the Memory Load condition (mean q 0.94; SD q 0.09) did not differ (F = 2.22, df = l/29; p < 0.2). Sixty-five subjects would be needed for this mean difference to be significant (p < 0.05) with power of 0.8 (Cohen, 1977). Sensitivity did not vary over trial blocks, nor was the interaction significant @ > 0.20). The reliability of the tasks was estimated by scoring all trials as correct or incorrect and computing the odd-even correlation. These coefficients, corrected for test length, were 0.96 and 0.95 for the Perceptual Degradation and Memory Load conditions, respectively.
0165-I 78 I 86 $03.50 0 1986 Elsevier Science Publishers B.V.
286
These equivalent reliability coefficients, along with comparable means and SDS, suggest that the tasks have comparable true score variance, or discriminating power, although this requires confirmation in a larger sample (Chapman and Chapman, 1978). One of the eight subjects with deviant MMPIs did not perform the tasks in a meaningful way, missing 34 of 120 degraded targets and making 281 false alarms. The average profile of the other seven subjects and that of the psychometrically normal group are shown in Fig. I. Lachar’s (1974) compendium describes the deviant profile (8-4/4-8) as straddling the fence between character disorder and psychosis. Persons with this profile are characterized as schizoid, although it must be emphasized that they were not patients and denied histories of psychological or psychiatric treatment. The A’ scores of these seven subjects were examined in a Condition by Trial Block ANOVA. Although the n is small, sensitivity was significantly lower (F= 12.49. df’= I /6,p < 0.02) in the Perceptual Degradation condition (mean q 0.82, SD q 0.10) than in the Memory Load condition (mean q 0.90, SD q 0.09). The interaction was also significant (F= 68.64, df= 2/ 12, p < 0.005). Performance in the degraded condition tended to deteriorate
over time (Block 5 - Block I = -5.4), while it improved slightly with the memory load (Block 5 - Block 1 = 3.0). Thus, the difference between degraded and memory conditions was larger in the third block of trials (I 1.9) than in the first (3.5). The two versions of the CPT described here have different psychological processing demands but equal discriminating power for the parameter of sensitivity to signals (A’). The degradation CPT performance of the subjects with deviant MMPls is like that reported in Nuechterlein and Dawson’s (1984, pp. 175176) review of the relations between psychometric indicators of the schizophrenic spectrum and impaired vigilance. The present findings require replication in larger samples selected for psychometric indicators of schizophrenic spectrum disorders. Larger psychometrically deviant groups are necessary to determine whether there is an interaction between MMPI group and vigilance condition. This more conservative test was not used here because of the disproportionately small size of the deviant MM Pl group. If replicated, the present findings would suggest that the sensitivity of this behavioral marker is due to perceptual factors rather than to greater task difficulty.
Fig 1. Average profiles on the Minnesota Multiphasic Personality Inventory (MMPI) for psychometrically normal and deviant subjects
,1
a.?,
70--
-
-
-
-
30_-_--.-__--_-__--/ /
/
L
F
K
12 Hs
0
3 Hy
4 Pd
MMPIScale
5 Mf
6 Pa
7 Pt
6 SC
9 Ma
0 Si
287
This work was supported by grants from the NIMH (MH-38387) and NIH (NS-16375). The authors thank Dr. Keith Nuechterlein for advice and aid in establishing the vigilance task in our laboratory, and Dr. Jean Chapman for the suggestion to estimate task reliability with splithalf correlation. Acknowledgment.
Nuechterlein, K.H., and Dawson, M.E. Information processing and attentional functioning in the developmental course of schizophrenic disorders. Schizophrenia Bulletin, 10, 160 (1984). Nuechterlein, K.H., Parasuraman, R.. and Qiyuan, J. Visual sustained attention: Image degradation produces rapid sensitivity decrement over time. Science, 220, 327 (1983).
References
Chapman, L.J., and Chapman, J.P. The measurement of differential deficit. Journalof Ps.vchiatric Research, 14, 303 ( 1978). Cohen, J. Statistical Power Analvsisfor the Behavioral Sciences. Rev. ed. Academic Press, New York (1977). Lachar, D. The MMPI: Clinical Assessment and Automated Interpretation. Western Psychological Services, Los Angeles (1974).
Milton E. Strauss, Ph.D. Jason Brandt, Ph.D. Patricia McSorley, B.S. Department of Psychiatry Osler 320 Johns Hopkins Hospital Baltimore, MD 2 1205, USA. Received April 15, 1985; revised May 5, 1986; accepted May 29, 1986.