- Email: [email protected]
Psychometric schizotypy and sustained attention in young males
Person. indiuid.Di’ Vol. 14, No. 2, pp. 381-384, 1993 Printed in Great Britain. All rights reserved
Psychometric
schizotypy
0191-8869/93 $5.00 + 0.00 Copyright 0 1993 Pergamon Press Ltd
and sustained
JORDI E. OBIOLS, MERCB GARCIA-DOMINGO,
attention
in young males
ISABEL DE TRINCHERIA and EDELMIRA DO~~NECH
L.aboratori de Psicopatologia, Depariament de Psicologia de la Salut, Facultat de Psicologia, Universitat Auidnoma de Barcelona, Bellaterra (Barcelona), Spain (Received 10 November 1991; received for publication 12 June 1992) Summary-A sample of 343 young males in military duties were studied by means of two schizotypy scales (Claridge’s STA and Chapman’s PAS). A psychosis-prone group (n = 35) was compared with a control group on a standard sustained attention task, the Continuous Performance Task (CPT, identical pairs version). The expected association between high schizotypy scores and low CPT performance was confirmed by our results. These findings add evidence to the view supported from high-risk research and attention research with schizophrenics, that subtle attention deficits are present among schizophrenia spectrum subjects. We also discuss the role of state anxiety as a possible nuisance variable.
INTRODUCIlON The detection of abnormal behavior patterns that bridge normality and schizophrenic psychosis is as old as the same concept of schizophrenia. Family and adoption studies in the sixties (Kety, 1988) demonstrated the genetic link between schizotypic Ss and their schizophrenic relatives. Later, advances were made in the theory of schizotypy (Meehl, 1962, 1989) and in the psychological evaluation of these personality/behavior traits (Chapman, Edell& Chapman, 1980; Claridge & Broks, 1984). Recently, clinical instruments have appeared (Loranger, Susman, Oldham & Russakoff, 1987; Spitzer, Williams & Gibbon, 1986) that improve the diagnosis Nevertheless, we still lack objective correlates, of oersonalitv disorders related to the so-called “schizophrenia spectrum”. either biological or psychological, for these disorders. _ Until now. schizouhrenia “high-risk” studies have been the onlv ones to shed some light onto the field. So, deficits in sustained attention, evaluated by the Continuous Performance Test(CPT) seem to be the most robust indices or “markers” for the risk/vulnerability of schizophrenic psychosis (Erlenmeyer-Kimling & Cornblatt, 1987; Neuchterlein & Dawson, 1984). These and similar information processing deficits have been detected in active and remitted patients, and in high genetic risk children. Our goal is to study the psychometric schizotypy in a normal population and examine its relationship with sustained attention performance evaluated by means of the CPT. We chose to study an army recruit population for two main reasons: (1) the draft provides a sample of the general population, with no a priori bias concerning the schizotypy dimension and (2) we eliminate the gender variable by studying only young males. There is growing evidence (Goldstein & Tsuang, 1990) of the importance of gender as a confounding variable in schizophrenia research. We hypothesized that schizotypic traits of personality would be associated with poor CPT performance. Secondarily, we were also interested in the possible influence of socio-educational level and intelligence on our principal variables, i.e. schizotypy and sustained attention. Our hypothesis was that none of these variables would correlate at a significant level with psychometric schizotypy and/or sustained attention performance. The study was completed with the assessment of anxiety as a possible modulating variable. Our hypothesis was that neither trait nor state anxiety would be significantly associated with sustained attention performance. This study is part of a larger ongoing research project on schizotypy and vulnerability markers in our laboratory. METHOD Subjects A total of 343 male Ss voluntarily participated in the study. Mean age was 20.8 (SD = 1.9). All Ss were non-professional soldiers in their first semester of military duties. The general aim of the study was explained to them and eventual refusal to participate was accepted. The sample completed a general socio-demographic questionnaire that rated educational and social level, both on a 5-point scale. Mean educational level was 3.28 (SD = 0.82) and mean social level was 2.82 (SD = 0.78). From the initial sample, 292 Ss correctly completed the personality and intelligence tests (see below) and 68 were selected (see the procedure below) to form the schizotypic (n = 35) and control (n = 33) groups. Both groups were tested on a sustained attention task. the CPT. MEASURES AND PROCEDURES Sustained attention measure Sustained attention was measured using the CPT (Rosvold, Mirsky, Sarason, Bransome & Beck, 1956). We actually used a computerized version developed in our laboratory, following the CPT-IP (Identical Pairs) of Cornblatt. Rish, Farrs, Friedman and Erlenmeyer-Kimling (1988). There were two types of stimuli used (four digit numbers and nonsense shapes) which appeared for 50 msec in the center of the screen at a rate of l/set. 381
NOTE? AND SHORTER COMMUNICATIONS
382 Table
I.
Sustained schizotvoics
attention results, comparison (n = 35) and controls (n = 33)
Schizotypics t~/SD~
Index
OE
5.60/3.7 4.2812.0 2.31/0.8 0.25/0.8 0.6310.6
CE d I-B LDE
Controls (R/SD) 3.9512.9 4.38/3.4 2.6410.7 0.08/0.9 0.63/0.5
between
t-Test nob. 0.02 NS 0.04 NS NS
Table
2. Anxiety, social and intelligence measures, comparison between schizotypics and controls
MeWlIe
State anxiety Trait anxiety EL Social level Raven P.M.
Schizotypics (f/SD)
Controls @/SD)
26.30/I I .4 28.06/I I .6 3.00/0.7 2.5510.9 69.85121.9
r-Test prob
15.80/6.3 15.87/6.7 3.41/0.7 3.00/0.8 76.21119.2
0.001 0.001 0.03 NS NS
OE = omission errors; CE = comission errors; d’ = discriminability; Lb = response bias; LDE = log distraction errors; NS = not significant.
Four conditions were tested: (1) Numbers, (2) Shapes, (3) Distraction * Numbers and (4) Distraction Shapes. Each condition had 150 trials, with 30 (20%) target trials. Target trials were those on which the second of a pair of two identical stimuli appeared. Each condition also included 30 (20%) catch trials, on which the stimulus presented was very similar to that of the preceding trial but not identical (e.g. 5081 following 5681). The CPT-IP was administered by an IBM-PS2 computer system. A computer program was designed to generate the different types of stimuli and patterns of presentation. The stimuli appeared on a standard non-color monitor and the S was instructed to respond as fast as possible by pushing a control button whenever two identical stimuli were presented one after the other. A short training trial block of 50 stimuli was given before starting the experiment in order to assess the comprehension of the task. The same computer program recorded the three different kinds of errors (comission, omission, distraction), and reaction times for all the responses. Schizotypy measures The following questionnaires were administered to each S: (1) The STA (Claridge & Broks, 1984). This questionnaire is aimed at measuring schizotypal (2) The Perceptual Aberration Scale (PAS; Chapman, Chapman & Raulin, 1978). Ss were instructed to accurately complete the questionnaires without discussing their responses
personality with other
traits. peers.
Other measures We used the Raven Progressive Matrices (general form-Raven, 1986) as a measure Anxiety Inventory (STAI; Spielberger, Gorsuch & Lushene, 1982), a well-known self-report state and trait anxiety (in the Spanish version the score scale range is O-3).
of intelligence. The State-Trait inventory, was used to measure
Procedure Ss completed the psychological battery, in a group of 40 people under the scrutiny and instructions of our research team. After the schizotypy data were analyzed, Ss who scored 1.5 SD above the mean on the STA and the PAS were selected as “schizotypic”. The control group was randomly selected from the rest of the sample, provided they scored below the cut-off point on both the STA and the PAS. The CPT and the STAI were completed individually, between 9 and 12 a.m., in a quiet conventionally lighted room. A short training session on the CPT was given first in order to ensure proper execution. The assistant team was blind to a S’s group membership during the CPT procedure. Data analysis All the psychological scales provide direct scores which reflect the degree of presence of that particular personality trait. Performance on the CPT-IP was analyzed using five major indices closely following the methodology of Cornblatt et al. (1988). (1) (2) (3) (4) (5)
“Omission errors”, i.e. the proportion of missing responses to target trials; of responses to catch trials; “Comission errors” or “False alarms”, i.e. proportion “Ln randoms”, i.e. proportion of responses to filler trials converted into natural logs; d’, a measure of discriminability, and Ln/?, i.e. the natural log of 8, a measure of response bias.
These two signal detection indices, (Davies & Parasuraman, 1981) d’ and /I, were calculated as outlined by Rutschmann, Cornblatt and Erlenmeyer-Kimling (1977), using hits and false alarms. Since the goal in this study is focused on the overall CPT performance level we present summary performance values, i.e. overall means across the four conditions, for each CPT index. *For both numbers and shapes, distraction consisted of a specific type of visual distraction. For numbers, the computer generates sets of 3 four-digit numbers, identical in size to the target number. The 3 distracters appear randomly all over the screen except in the central point, which is exclusive for the target stimulus. The 3 distracters appear simultaneously with the target, also for SOmsec. Distracters are administered all along the 150 trials in the distraction condition. The distraction condition for shapes follows essentially the same pattern as referred to for the numbers. The only difference is that the distractor stimuli are shapes instead of numbers. In both distraction conditions, the S is instructed to pay attention only to the central stimuli and to ignore all other stimuli appearing on screen.
NOTES AND
Table 3. Pearson correlation
Trait anxiety State anxiety I-Tail sianif.
SHORTER
383
COMMUNICATIONS
coefficients between trait/state
anxiety and CPT indices
OE
LB
LDE
CE
0.29 0.33.
0.17 0.10
0.11 0.28
0.10 0.33*
l0.01
d -0.29 -0.39’.
**0.001
OE = omission errors; CE = comission errors; d’ = discriminability; bias; LDE = log distraction errors.
LB = response
RESULTS
The comparison between schizotypic and control Ss on the CPT performance (see Table 1) reveal, as expected, poorer discriminability (d’) and more omission errors (i.e. less hits) in the experimental group. No significant differences were found in the rest of the CPT indices, i.e. comission errors, random errors and response bias (Lnp). Table 2 contains the results and comparisons between groups of the rest of the variables. We found no significant differences in social level but control Ss had a higher educational level than schizotypics. Nevertheless, our measure of intelligence, the Raven Progressive Matrices, did not reveal significant differences between groups. Finally, results on the STAI revealed significant differences, the schizotypic Ss being more anxious than control Ss. We performed a correlational analysis of the combined sample (n = 68) to examine the association between anxiety and the attentional performance variables (see Table 3). We found no correlations between trait anxiety and the CPT indices, but state anxiety (SA) did positively correlate with both omission and comission errors, being the strongest (and negative) correlation with discriminability (d’). No significant correlations were found between SA and response bias (Lt$) or distraction errors. In order to examine the influence of SA on the attentional index d’, we performed an analysis of covariance between the two groups, with d’ as the dependent variable and SA as the covariate. The regression slope was significant (F = 6.78; sig. at F = 0.012) but when SA was partialled out, the difference between groups was not significant (F = 0.35; sig. at F = 0.56). The assumption of parallel slopes was warranted since the group by SA interaction was not significant (F = 1.63; sig. at F = 0.21). Therefore, the hypothesis of SA being a relevant variable on the CPT performance index d’ cannot be rejected.
DISCUSSION
Schizotypic Ss, defined by means of two well-known and sensitive measures of psychometric schizotypy, displayed poorer discriminability (d’) than controls, based on a higher rate of omission errors in a high processing load attentional test. Other indices of the attentional task like comission errors, response bias (Lnp) or distraction errors did not reveal differences between groups. It is interesting to note that these results are the same as those found in other studies (Lenzenweger, Cornblatt & Putnick, 1991), that used a comparable methodology. The definition used of “control S” enhances the significance of our results. Had we used a more conservative cut-off point in the schizotypy scales, as was done in the study referred to above, the differences would have probably been larger. Schizotypes displayed more trait anxiety and SA than controls. Did anxiety affect schizotypes in their CPT performance? Our global correlation analyses indicate a negative influence of SA over CPT performance. Anxious Ss did make more omission and comission errors, and their discriminability was poorer. Moreover, when the influence of SA was partialled out, we found no differences between the two groups on the CPT performance index. Thus, our results do not allow us to reject the influence of SA on the attentional task. This is in contrast with other similar studies (Lenzenweger et al., 1991) that also found greater levels of state variables, i.e. anxiety and depression in schizotypes compared to controls, but could rule out their influence on attentional performance. Since our schizotypic group had a lower educational level (EL) (see Table 2), we wondered about the possibility that state anxiety in schizotypes was a consequence of their lower EL. In order to rule out this hypothesis we performed a comparison between the highest EL schizotypes (n = 23, R = 3.3) and the lowest EL controls (a = 16, R = 2.6): results revealed that “high EL” schizotypes still show more SA than “low EL” controls (t = - 1.87; P < 0.03). No differences were found in the CPT performance between the two groups (t = 0.56; P < 0.30). These results suggest that SA is related to schizotypy rather than to EL. Furthermore, we think that anxiety is an essential component of the schizotypy construct. We performed a statistical partialling out of anxiety as the only way to clarify our ambiguous results, but we think that statistical procedures are not the best way to rule out the effects of nuisance variables. These effects should be controlled in carefully designed experimental ad hoc studies. We still conclude that our results add evidence to the notion that different high-risk for schizophrenia populations show attentional deficits comparable to the ones found in actual schizophrenia. The CPT-IP confirms its potential to pick-up subtle information-processing deficits in non-clinical populations, hence its putative value as a biological marker in schizophrenia vulnerability research seems to be robust. We also add support for the validity of the psychometric schizotypy scales used in the present study. Nevertheless, our study suggests a possible spurious distorting effect of SA. We think future research in the field should use different and larger samples to control the influence of other psychological and state variables and pursue longitudinal studies to assess the predictive validity of such findings.
REFERENCES
Buchsbaum, M. S. & Sostek, A. S. (1980). An adaptive-rate continuous performance test: vigilance characteristics and reliability for 400 male students. Perceptual and Motor Skills, 51, 707-713. Chapman, L. J. & Chapman, J. P. (1979). Revised physical anhedonia scale. Unpublished Test. Chapman, L. J., Chapman, J. P. & Raulin, M. C. (1978). Body image aberration in schizophrenia. Journal of Abnormal Psychology, 85, 399407.
384
NOTES AND
SHORTER
COMMUNICATIONS
Chapman, L. J., Edell, W. S. & Chapman, J. P. (1980). Physical anhedonia, perceptual aberration and psychosis proneness, Schizophrenia Bulletin, 6, 639-653. Claridge, G. & Broks, P. (1984). Schizotypy and hemisphere function-l. Theoretical considerations and the measurement of schizotypy. Personality and Individual Differences, 5, 633449. Cornblatt, B. A., Rish, N. S., Farrs, G., Friedman, D. & Erlenmeyer-Kimling, L. (1988). The Continuous Performance Test, Identical Pairs Version (CPT-IP). New findings about sustained attention in normal families. Psychiatry Research, 26, 223-238. Davies, R. R. & Parasuraman, R. (1981). The psychology of vigilance. London: Academic Press. Eckblad, M. L. & Chapman, L. J. (1983). Magical Ideation as an indicator of schizotypy. Journal of Consulting and Clinical Psychology, 51, 215-225. Eckblad, M. L., Chapman, L. J., Chapman, J. P. & Mishlove, M. (1982). The revised social anhedonia scale. Unpublished Test. Erlenmeyer-Kimling, L. & Cornblatt, B. A. (1987). High-risk research in schizophrenia: a summary of what has been learned. Journal of Psychiatry Research, 21, 401411. Eysenck, H. J. & Eysenck, S. B. G. (1975). Manual of the Eysenck Personality Questionnaire. London: Hodder and Stoughton. Goldstein, J. M. & Tsuang, M. T. (1990). Gender and schizophrenia: an introduction and synthesis of findings, Schizophrenia Bulletin, 16, 179-184. Kety, S. S. (1988). Schizophrenic illness in the families of schizophrenic adoptees: Findings from the Danish national sample. Schizophrenia Bulletin, 14, 217-222. Lenzenweger, M. F., Cornblatt, B. A. & Putnick, M. (1991). Schizotypy and sustained attention. Journal of Abnormal Psychology, 100, 8489. Loranger, A. N., Susman, V. L., Oldham, J. M. & Russakoff, L. M. (1987). The Personality Disorder Examination: A preliminary report. Journal of Personality Disorders, 1, l-13. Meehl, P. E. (1962). Schizotaxia, schizotypy, schizophrenia. American Psychologist, 17, 827-838. Meehl, P. E. (1989). Schizotaxia revisited. Archives of General Psychiatry, 46, 935-944. Muntaner, C., Garcia-Sevilla, L., Fernandez, A. & Torrubia, R. (1988). Personality dimensions, schizotypal and borderline personality traits and psychosis proneness. Personality and Individual Differences, 9, 257-268. Neuchterlein, K. H. & Dawson, M. E. (1984). Information processing and attentional functioning in the developmental course of schizophrenic disorders. Schizophrenia Bulletin, IO, 160. Raven, J. C. (1986). Test de Matrices Progresivas para la Medida de la Capacidad Inte/ectua/. Escala General. Buenos Aires: Paidos. Rosvold, H. E.. Mirsky, A., Sarason, M., Bransome. E. D. Jr & Beck, L. H. (1956). A continuous performance test of brain damage. Journal of Consulting Psychology, 20, 343. Rutschmann. J.. Cornblatt, B. A. & Erlenmever-Kimlina. L. (1977). Sustained attention in children at risk for schizophrenia. Archives of General Psychiatry, 34, 5711575. Spielberger, C. D., Gorsuch, R. L. & Lushene, R. E. (1982). Cuestionario de Ansiedad Estado-Rasgo (Spanish adaptation from the Manual,for the State-Trait Anxiety Inventory. CA: Madrid: TEA ediciones. Spitzer, R. L., Williams, J. B. W. & Gibbon, M. (1986). Structured clinical interview for DSM-III-R personality disorders (SCID-II). Biometrics Research Department, New York State Psychiatric Institute, New York.
Psychometric
schizotypy
0191-8869/93 $5.00 + 0.00 Copyright 0 1993 Pergamon Press Ltd
and sustained
JORDI E. OBIOLS, MERCB GARCIA-DOMINGO,
attention
in young males
ISABEL DE TRINCHERIA and EDELMIRA DO~~NECH
L.aboratori de Psicopatologia, Depariament de Psicologia de la Salut, Facultat de Psicologia, Universitat Auidnoma de Barcelona, Bellaterra (Barcelona), Spain (Received 10 November 1991; received for publication 12 June 1992) Summary-A sample of 343 young males in military duties were studied by means of two schizotypy scales (Claridge’s STA and Chapman’s PAS). A psychosis-prone group (n = 35) was compared with a control group on a standard sustained attention task, the Continuous Performance Task (CPT, identical pairs version). The expected association between high schizotypy scores and low CPT performance was confirmed by our results. These findings add evidence to the view supported from high-risk research and attention research with schizophrenics, that subtle attention deficits are present among schizophrenia spectrum subjects. We also discuss the role of state anxiety as a possible nuisance variable.
INTRODUCIlON The detection of abnormal behavior patterns that bridge normality and schizophrenic psychosis is as old as the same concept of schizophrenia. Family and adoption studies in the sixties (Kety, 1988) demonstrated the genetic link between schizotypic Ss and their schizophrenic relatives. Later, advances were made in the theory of schizotypy (Meehl, 1962, 1989) and in the psychological evaluation of these personality/behavior traits (Chapman, Edell& Chapman, 1980; Claridge & Broks, 1984). Recently, clinical instruments have appeared (Loranger, Susman, Oldham & Russakoff, 1987; Spitzer, Williams & Gibbon, 1986) that improve the diagnosis Nevertheless, we still lack objective correlates, of oersonalitv disorders related to the so-called “schizophrenia spectrum”. either biological or psychological, for these disorders. _ Until now. schizouhrenia “high-risk” studies have been the onlv ones to shed some light onto the field. So, deficits in sustained attention, evaluated by the Continuous Performance Test(CPT) seem to be the most robust indices or “markers” for the risk/vulnerability of schizophrenic psychosis (Erlenmeyer-Kimling & Cornblatt, 1987; Neuchterlein & Dawson, 1984). These and similar information processing deficits have been detected in active and remitted patients, and in high genetic risk children. Our goal is to study the psychometric schizotypy in a normal population and examine its relationship with sustained attention performance evaluated by means of the CPT. We chose to study an army recruit population for two main reasons: (1) the draft provides a sample of the general population, with no a priori bias concerning the schizotypy dimension and (2) we eliminate the gender variable by studying only young males. There is growing evidence (Goldstein & Tsuang, 1990) of the importance of gender as a confounding variable in schizophrenia research. We hypothesized that schizotypic traits of personality would be associated with poor CPT performance. Secondarily, we were also interested in the possible influence of socio-educational level and intelligence on our principal variables, i.e. schizotypy and sustained attention. Our hypothesis was that none of these variables would correlate at a significant level with psychometric schizotypy and/or sustained attention performance. The study was completed with the assessment of anxiety as a possible modulating variable. Our hypothesis was that neither trait nor state anxiety would be significantly associated with sustained attention performance. This study is part of a larger ongoing research project on schizotypy and vulnerability markers in our laboratory. METHOD Subjects A total of 343 male Ss voluntarily participated in the study. Mean age was 20.8 (SD = 1.9). All Ss were non-professional soldiers in their first semester of military duties. The general aim of the study was explained to them and eventual refusal to participate was accepted. The sample completed a general socio-demographic questionnaire that rated educational and social level, both on a 5-point scale. Mean educational level was 3.28 (SD = 0.82) and mean social level was 2.82 (SD = 0.78). From the initial sample, 292 Ss correctly completed the personality and intelligence tests (see below) and 68 were selected (see the procedure below) to form the schizotypic (n = 35) and control (n = 33) groups. Both groups were tested on a sustained attention task. the CPT. MEASURES AND PROCEDURES Sustained attention measure Sustained attention was measured using the CPT (Rosvold, Mirsky, Sarason, Bransome & Beck, 1956). We actually used a computerized version developed in our laboratory, following the CPT-IP (Identical Pairs) of Cornblatt. Rish, Farrs, Friedman and Erlenmeyer-Kimling (1988). There were two types of stimuli used (four digit numbers and nonsense shapes) which appeared for 50 msec in the center of the screen at a rate of l/set. 381
NOTE? AND SHORTER COMMUNICATIONS
382 Table
I.
Sustained schizotvoics
attention results, comparison (n = 35) and controls (n = 33)
Schizotypics t~/SD~
Index
OE
5.60/3.7 4.2812.0 2.31/0.8 0.25/0.8 0.6310.6
CE d I-B LDE
Controls (R/SD) 3.9512.9 4.38/3.4 2.6410.7 0.08/0.9 0.63/0.5
between
t-Test nob. 0.02 NS 0.04 NS NS
Table
2. Anxiety, social and intelligence measures, comparison between schizotypics and controls
MeWlIe
State anxiety Trait anxiety EL Social level Raven P.M.
Schizotypics (f/SD)
Controls @/SD)
26.30/I I .4 28.06/I I .6 3.00/0.7 2.5510.9 69.85121.9
r-Test prob
15.80/6.3 15.87/6.7 3.41/0.7 3.00/0.8 76.21119.2
0.001 0.001 0.03 NS NS
OE = omission errors; CE = comission errors; d’ = discriminability; Lb = response bias; LDE = log distraction errors; NS = not significant.
Four conditions were tested: (1) Numbers, (2) Shapes, (3) Distraction * Numbers and (4) Distraction Shapes. Each condition had 150 trials, with 30 (20%) target trials. Target trials were those on which the second of a pair of two identical stimuli appeared. Each condition also included 30 (20%) catch trials, on which the stimulus presented was very similar to that of the preceding trial but not identical (e.g. 5081 following 5681). The CPT-IP was administered by an IBM-PS2 computer system. A computer program was designed to generate the different types of stimuli and patterns of presentation. The stimuli appeared on a standard non-color monitor and the S was instructed to respond as fast as possible by pushing a control button whenever two identical stimuli were presented one after the other. A short training trial block of 50 stimuli was given before starting the experiment in order to assess the comprehension of the task. The same computer program recorded the three different kinds of errors (comission, omission, distraction), and reaction times for all the responses. Schizotypy measures The following questionnaires were administered to each S: (1) The STA (Claridge & Broks, 1984). This questionnaire is aimed at measuring schizotypal (2) The Perceptual Aberration Scale (PAS; Chapman, Chapman & Raulin, 1978). Ss were instructed to accurately complete the questionnaires without discussing their responses
personality with other
traits. peers.
Other measures We used the Raven Progressive Matrices (general form-Raven, 1986) as a measure Anxiety Inventory (STAI; Spielberger, Gorsuch & Lushene, 1982), a well-known self-report state and trait anxiety (in the Spanish version the score scale range is O-3).
of intelligence. The State-Trait inventory, was used to measure
Procedure Ss completed the psychological battery, in a group of 40 people under the scrutiny and instructions of our research team. After the schizotypy data were analyzed, Ss who scored 1.5 SD above the mean on the STA and the PAS were selected as “schizotypic”. The control group was randomly selected from the rest of the sample, provided they scored below the cut-off point on both the STA and the PAS. The CPT and the STAI were completed individually, between 9 and 12 a.m., in a quiet conventionally lighted room. A short training session on the CPT was given first in order to ensure proper execution. The assistant team was blind to a S’s group membership during the CPT procedure. Data analysis All the psychological scales provide direct scores which reflect the degree of presence of that particular personality trait. Performance on the CPT-IP was analyzed using five major indices closely following the methodology of Cornblatt et al. (1988). (1) (2) (3) (4) (5)
“Omission errors”, i.e. the proportion of missing responses to target trials; of responses to catch trials; “Comission errors” or “False alarms”, i.e. proportion “Ln randoms”, i.e. proportion of responses to filler trials converted into natural logs; d’, a measure of discriminability, and Ln/?, i.e. the natural log of 8, a measure of response bias.
These two signal detection indices, (Davies & Parasuraman, 1981) d’ and /I, were calculated as outlined by Rutschmann, Cornblatt and Erlenmeyer-Kimling (1977), using hits and false alarms. Since the goal in this study is focused on the overall CPT performance level we present summary performance values, i.e. overall means across the four conditions, for each CPT index. *For both numbers and shapes, distraction consisted of a specific type of visual distraction. For numbers, the computer generates sets of 3 four-digit numbers, identical in size to the target number. The 3 distracters appear randomly all over the screen except in the central point, which is exclusive for the target stimulus. The 3 distracters appear simultaneously with the target, also for SOmsec. Distracters are administered all along the 150 trials in the distraction condition. The distraction condition for shapes follows essentially the same pattern as referred to for the numbers. The only difference is that the distractor stimuli are shapes instead of numbers. In both distraction conditions, the S is instructed to pay attention only to the central stimuli and to ignore all other stimuli appearing on screen.
NOTES AND
Table 3. Pearson correlation
Trait anxiety State anxiety I-Tail sianif.
SHORTER
383
COMMUNICATIONS
coefficients between trait/state
anxiety and CPT indices
OE
LB
LDE
CE
0.29 0.33.
0.17 0.10
0.11 0.28
0.10 0.33*
l0.01
d -0.29 -0.39’.
**0.001
OE = omission errors; CE = comission errors; d’ = discriminability; bias; LDE = log distraction errors.
LB = response
RESULTS
The comparison between schizotypic and control Ss on the CPT performance (see Table 1) reveal, as expected, poorer discriminability (d’) and more omission errors (i.e. less hits) in the experimental group. No significant differences were found in the rest of the CPT indices, i.e. comission errors, random errors and response bias (Lnp). Table 2 contains the results and comparisons between groups of the rest of the variables. We found no significant differences in social level but control Ss had a higher educational level than schizotypics. Nevertheless, our measure of intelligence, the Raven Progressive Matrices, did not reveal significant differences between groups. Finally, results on the STAI revealed significant differences, the schizotypic Ss being more anxious than control Ss. We performed a correlational analysis of the combined sample (n = 68) to examine the association between anxiety and the attentional performance variables (see Table 3). We found no correlations between trait anxiety and the CPT indices, but state anxiety (SA) did positively correlate with both omission and comission errors, being the strongest (and negative) correlation with discriminability (d’). No significant correlations were found between SA and response bias (Lt$) or distraction errors. In order to examine the influence of SA on the attentional index d’, we performed an analysis of covariance between the two groups, with d’ as the dependent variable and SA as the covariate. The regression slope was significant (F = 6.78; sig. at F = 0.012) but when SA was partialled out, the difference between groups was not significant (F = 0.35; sig. at F = 0.56). The assumption of parallel slopes was warranted since the group by SA interaction was not significant (F = 1.63; sig. at F = 0.21). Therefore, the hypothesis of SA being a relevant variable on the CPT performance index d’ cannot be rejected.
DISCUSSION
Schizotypic Ss, defined by means of two well-known and sensitive measures of psychometric schizotypy, displayed poorer discriminability (d’) than controls, based on a higher rate of omission errors in a high processing load attentional test. Other indices of the attentional task like comission errors, response bias (Lnp) or distraction errors did not reveal differences between groups. It is interesting to note that these results are the same as those found in other studies (Lenzenweger, Cornblatt & Putnick, 1991), that used a comparable methodology. The definition used of “control S” enhances the significance of our results. Had we used a more conservative cut-off point in the schizotypy scales, as was done in the study referred to above, the differences would have probably been larger. Schizotypes displayed more trait anxiety and SA than controls. Did anxiety affect schizotypes in their CPT performance? Our global correlation analyses indicate a negative influence of SA over CPT performance. Anxious Ss did make more omission and comission errors, and their discriminability was poorer. Moreover, when the influence of SA was partialled out, we found no differences between the two groups on the CPT performance index. Thus, our results do not allow us to reject the influence of SA on the attentional task. This is in contrast with other similar studies (Lenzenweger et al., 1991) that also found greater levels of state variables, i.e. anxiety and depression in schizotypes compared to controls, but could rule out their influence on attentional performance. Since our schizotypic group had a lower educational level (EL) (see Table 2), we wondered about the possibility that state anxiety in schizotypes was a consequence of their lower EL. In order to rule out this hypothesis we performed a comparison between the highest EL schizotypes (n = 23, R = 3.3) and the lowest EL controls (a = 16, R = 2.6): results revealed that “high EL” schizotypes still show more SA than “low EL” controls (t = - 1.87; P < 0.03). No differences were found in the CPT performance between the two groups (t = 0.56; P < 0.30). These results suggest that SA is related to schizotypy rather than to EL. Furthermore, we think that anxiety is an essential component of the schizotypy construct. We performed a statistical partialling out of anxiety as the only way to clarify our ambiguous results, but we think that statistical procedures are not the best way to rule out the effects of nuisance variables. These effects should be controlled in carefully designed experimental ad hoc studies. We still conclude that our results add evidence to the notion that different high-risk for schizophrenia populations show attentional deficits comparable to the ones found in actual schizophrenia. The CPT-IP confirms its potential to pick-up subtle information-processing deficits in non-clinical populations, hence its putative value as a biological marker in schizophrenia vulnerability research seems to be robust. We also add support for the validity of the psychometric schizotypy scales used in the present study. Nevertheless, our study suggests a possible spurious distorting effect of SA. We think future research in the field should use different and larger samples to control the influence of other psychological and state variables and pursue longitudinal studies to assess the predictive validity of such findings.
REFERENCES
Buchsbaum, M. S. & Sostek, A. S. (1980). An adaptive-rate continuous performance test: vigilance characteristics and reliability for 400 male students. Perceptual and Motor Skills, 51, 707-713. Chapman, L. J. & Chapman, J. P. (1979). Revised physical anhedonia scale. Unpublished Test. Chapman, L. J., Chapman, J. P. & Raulin, M. C. (1978). Body image aberration in schizophrenia. Journal of Abnormal Psychology, 85, 399407.
384
NOTES AND
SHORTER
COMMUNICATIONS
Chapman, L. J., Edell, W. S. & Chapman, J. P. (1980). Physical anhedonia, perceptual aberration and psychosis proneness, Schizophrenia Bulletin, 6, 639-653. Claridge, G. & Broks, P. (1984). Schizotypy and hemisphere function-l. Theoretical considerations and the measurement of schizotypy. Personality and Individual Differences, 5, 633449. Cornblatt, B. A., Rish, N. S., Farrs, G., Friedman, D. & Erlenmeyer-Kimling, L. (1988). The Continuous Performance Test, Identical Pairs Version (CPT-IP). New findings about sustained attention in normal families. Psychiatry Research, 26, 223-238. Davies, R. R. & Parasuraman, R. (1981). The psychology of vigilance. London: Academic Press. Eckblad, M. L. & Chapman, L. J. (1983). Magical Ideation as an indicator of schizotypy. Journal of Consulting and Clinical Psychology, 51, 215-225. Eckblad, M. L., Chapman, L. J., Chapman, J. P. & Mishlove, M. (1982). The revised social anhedonia scale. Unpublished Test. Erlenmeyer-Kimling, L. & Cornblatt, B. A. (1987). High-risk research in schizophrenia: a summary of what has been learned. Journal of Psychiatry Research, 21, 401411. Eysenck, H. J. & Eysenck, S. B. G. (1975). Manual of the Eysenck Personality Questionnaire. London: Hodder and Stoughton. Goldstein, J. M. & Tsuang, M. T. (1990). Gender and schizophrenia: an introduction and synthesis of findings, Schizophrenia Bulletin, 16, 179-184. Kety, S. S. (1988). Schizophrenic illness in the families of schizophrenic adoptees: Findings from the Danish national sample. Schizophrenia Bulletin, 14, 217-222. Lenzenweger, M. F., Cornblatt, B. A. & Putnick, M. (1991). Schizotypy and sustained attention. Journal of Abnormal Psychology, 100, 8489. Loranger, A. N., Susman, V. L., Oldham, J. M. & Russakoff, L. M. (1987). The Personality Disorder Examination: A preliminary report. Journal of Personality Disorders, 1, l-13. Meehl, P. E. (1962). Schizotaxia, schizotypy, schizophrenia. American Psychologist, 17, 827-838. Meehl, P. E. (1989). Schizotaxia revisited. Archives of General Psychiatry, 46, 935-944. Muntaner, C., Garcia-Sevilla, L., Fernandez, A. & Torrubia, R. (1988). Personality dimensions, schizotypal and borderline personality traits and psychosis proneness. Personality and Individual Differences, 9, 257-268. Neuchterlein, K. H. & Dawson, M. E. (1984). Information processing and attentional functioning in the developmental course of schizophrenic disorders. Schizophrenia Bulletin, IO, 160. Raven, J. C. (1986). Test de Matrices Progresivas para la Medida de la Capacidad Inte/ectua/. Escala General. Buenos Aires: Paidos. Rosvold, H. E.. Mirsky, A., Sarason, M., Bransome. E. D. Jr & Beck, L. H. (1956). A continuous performance test of brain damage. Journal of Consulting Psychology, 20, 343. Rutschmann. J.. Cornblatt, B. A. & Erlenmever-Kimlina. L. (1977). Sustained attention in children at risk for schizophrenia. Archives of General Psychiatry, 34, 5711575. Spielberger, C. D., Gorsuch, R. L. & Lushene, R. E. (1982). Cuestionario de Ansiedad Estado-Rasgo (Spanish adaptation from the Manual,for the State-Trait Anxiety Inventory. CA: Madrid: TEA ediciones. Spitzer, R. L., Williams, J. B. W. & Gibbon, M. (1986). Structured clinical interview for DSM-III-R personality disorders (SCID-II). Biometrics Research Department, New York State Psychiatric Institute, New York.