VOL. 18, NO. 4,1992
Disorder of Attention in Individuals With Schizotypal Personality
by Soraya Wllklns and Peter H. Venebles
Abstract
Reaction time (RT) studies have been used extensively in research on schizophrenic patients, and it has been reported consistently that they exhibit longer RTs than normals. More specific deficits also have been reported. In a review of cross-modal RT studies of schizophrenia, Mannuzza (1980) found evidence that schizophrenic patients show, in addition to general slowness, a deficit when shifting attention across sensory modalities. Cross-modal RT experiments in the study of schizophrenic patients were first used by Mettler (1955), who found that they have great difficulty switching attention from one sensory modality to another. Many studies have replicated this finding: Sutton et al. 1961; Sutton and Zubin 1965; Waldbaum et al. 1975; and Spring 1980. In 1961, Sutton and colleagues carried out the first systematic study of modality shift in schizophrenia. They measured the RT performances of 23 chronic schizophrenic patients and 25 normal controls. The subjects were presented with green and red lights and high- and low-frequency tone stimuli. It was found that both
schizophrenic and control subjects had longer RTs in response to ipsimodal stimuli when there was a change in stimulus type from one stimulus to the next than to ipsi-modal stimuli that were successively identical. However, the RT was longer for schizophrenic patients than for normals. The researchers found that for trials in which there was a change in the modality of the stimuli, schizophrenic patients showed significantly slower RTs in crossing from visual to auditory stimuli than in changing from auditory to visual stimulation. Based on these results Sutton and colleagues (1961) suggested that the disorder of switching attention shown by schizophrenic patients is related not only to changes in the stimuli but also to differences in sensory modality. A similar study was carried out by Sutton and Zubin in 1965. They confirmed that schizophrenic subjects were slow in response to both ipsimodal nonidentical and cross-modal changes when the change was to sound stimuli. Several other studies (Kristofferson 1967; Verleger and Cohen 1978) have also reported that schizophrenic patients had slower responses when crossing to auditory than to visual stimuli. The defidt of shifting attention across sensory modalities has been shown to persist even when schizophrenic and control subjects have been matched for their general speed of RT (Sutton and Zubin 1965; Waldbaum et al. 1975) and when the subjects were given advance warning as to which stimulus would come next (Spring 1980). It appears that defidts in switching attention between different stimuli are Reprint requests ahould be sent to Dr. S. Wilkins, Genetics, Institute of Psychiatry, Denmark Hill, London SES 8AF, England.
Downloaded from http://schizophreniabulletin.oxfordjournals.org/ at University of Georgia on June 9, 2015
This study was designed to examine disorder of switching attention in normal individuals with schlzotypal personality. High scorers on the physical anhedorda (PA) and schizophrerdsm (SZ) scales of a questionnaire constructed to measure schizotypy were compared with a group of control subjects. A reaction time test was used that required switching attention across or between auditory and visual modalities. It was found that the high PA scorers and the high SZ scorers showed a defidt of shifting attention across modalities compared with the control subjects.
717
718
The authors are aware of only one study that examines attention switching in subjects who are vulnerable to the development of schizophrenia by reason of being children of schizophrenic parents. Phipps-Yonas (1984) carried out a study in which crossmodal RTs of 22 children, between 9 and 16 years of age, of schizophrenic mothers and 24 matched control subjects were examined. The task consisted of responding to sound and light stimuli presented in a sequence in which, on occasion, there was a switch from one stimulus modality to the other. In addition, a series of conditions was included in which the subjects were given information concerning the modality of the stimulus. Phipps-Yonas included this condition to examine the subjects' ability to benefit from the information concerning the upcoming stimuli. The results showed that the performance of children of schizophrenic mothers was indistinguishable from that of their matched controls in terms of the speed of their reactions and the variability of their performance. Further examination of her data led Phipps-Yonas to conclude that these negative results could be due to the fact that the highrisk sample used in this study consisted of a subsample of healthy children, as indexed by their scores on peers ratings, sodometric status, and achievement test scores, and that this group of children did not form a truly representative sample of children of schizophrenic mothers.
The view that schizophrenic characteristics are on a continuum has been extensively reviewed by Venables and colleagues (1990). This view, in general, steins from the notion put forward by Meehl (1962) that a tendency to develop schizophrenia ("schizotaxia") may be inherited, but whether the person with a schizotaxic predisposition develops schizophrenia or remains a functionally normal person with schizotypic traits depends on whether he or she is exposed to malignant or benign environmental influences ("environmental" refers to a wide variety of possible effects, ranging from intra-uterine to social). Chapman and colleagues (1980) and Siever and colleagues (1990) have demonstrated that schizotypic subjects are at increased risk for schizophrenia. Studies measuring schizotypy using the scales developed by the Chapmans and their colleagues (Chapman et al. 1976,1978; Eckblad and Chapman 1983) have shown—perhaps paralleling the notion of positive and negative schizophrenia (Crow 1980; Andreasen and Olsen 1982)—that two forms of schizotypy may be exhibited. (See review by Venables et al. [1990] and data provided by Kendler et al. [1991].) It is also important, however, to consider the relationship of schizotypy as measured by questionnaires to the concept of DSM-III-R (American Psychiatric Association 1987) schizotypal personality disorder (SPD) identified clinically. Claridge and Broks (1984) have developed a schizotypy scale more directly related to DSMIII-R SPD, and this has been shown (Muntaner et al. 1988; Raine and Allbutt 1989) to measure the more positive aspects of schizotypy insofar as it correlates with the Chapmans' Perceptual Aberration and Magical Ideation Scales (Per-Mag Scales; Chapman et al. 1976, 1978; Eckblad and Chapman
1983). Thus, on the basis of the present data, it appears that a person showing SPD characteristics may be considered as being on a borderline state between positive symptom schizophrenia and positive characteristic schizotypy. In this study, the "schizophrenism" scale (see below) measures positive aspects of schizotypy and thus is related to SPD as defined in DSMIII-R, whereas "physical anhedonia" (see below) is related to the negative aspects of schizotypy and not directly related to SPD as defined. The studies that support these relationships are covered in detail by Venables and colleagues (1990). We are not aware of any studies that examine the performance of schizotypic subjects or subjects diagnosed as exhibiting SPD on the crossmodal RT paradigm. Two studies are available that examine the performance of schizotypal subjects on other RT paradigms. Simons and colleagues (1982) showed that subjects with high scores on the Perceptual Aberration Scale (Chapman et al. 1978) showed the "crossover effect" (a measure of the ability of a subject to benefit from warning intervals of repeated regular durations) in an RT procedure with a regular and an irregular preparatory interval paradigm. That schizophrenic patients show the crossover effect has been a well-established finding in the literature since it was first reported by Rodnick and Shakow in 1940. Simons and colleagues (1982) also showed that subjects with high scores on the Physical Anhedonia Scale (Chapman et al. 1976) showed the crossover effect but less strongly than those with high perceptual aberration scores. A study by Chapin and colleagues (1987) provided further evidence of a crossover effect in patients diagnosed as exhibiting SPD, whereas
Downloaded from http://schizophreniabulletin.oxfordjournals.org/ at University of Georgia on June 9, 2015
characteristic of schizophrenic patients; thus, it is pertinent to ask whether this is a state phenomenon, only evident when the subject is exhibiting schizophrenic symptoms, or is a trait characteristic of subjects vulnerable to schizophrenia or possessing some of the characteristics of schizophrenia in a normal state.
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selected from the original 470. The 42 selected subjects were mainly undergraduate and postgraduate students, chosen on the basis of their scores on the 25-item version of the questionnaire. They were formed into three groups. The first group consisted of 12 subjects (6 males and 6 females) with high scores on the PA scale. The second group consisted of 15 subjects (9 males and 6 females) who scored high on the SZ scale. The third group, the control subjects, consisted of 8 males and 7 females with the lowest overall scores. A very small number of subjects scored high on the SA scale, but
there were not enough to form a group based on this dimension. Test subjects ranged in age from 21 to 30; there were 19 females and 23 males. As far as possible the groups were matched for age and sex. The subjects were highly intelligent undergraduate and postgraduate students. Table 1 presents the subjects' demographic characteristics. The scores on each scale for all the groups is given in table 2. The high SZ group had low scores on the PA scale and the high PA group scored low on the SZ scale. Two subjects who scored high on both scales were excluded.
Method and Procedure In this study, deficit of switching attention across sensory modalities was examined in subjects with schizotypal personality characteristics, identified on the basis of their scores on a questionnaire constructed to measure schizotypy in the general population. In brief, the questionnaire consists of 25 items derived from factor analysis of the earlier (86-item) version of the questionnaire. (The full description of this questionnaire is presented in Venables et al. [1990].) The shortened version consists of three scales: SZ (schizophrenism), PA (physical anhedonia), and SA (social anhedonia). The SZ scale contains items that could be considered to be parallel to "positive symptom" schizophrenia. The PA and SA scales contain items tapping some aspects characteristic of "negative symptom" schizophrenia. Subjects. The schizotypy questionnaire, described above, was presented to 470 subjects between the ages of 20 and 35 (mean 25.3 ± (SD] 3.8 years). Forty-two percent of the subjects were male and 58 percent were female. The subjects were drawn from university staff and students and their acquaintances. A total of 42 subjects were
Table 1.
Demographic characteristics of the groups Ag* (years)
Sax Qroups
n
M
F
Mean
(SD)
High physical anhedonia score
12
6
6
24.80
(3.01)
15 15 42
9 8 23
6 7 19
25.04
(1.64)
High schizophrenism score Control Total or average
25.77
(2.39)
25.3
(3.8)
Note.—8D = standard deviation.
Table 2. Subjects' scores on the physical anhedonia (PA) and schizophrenism (SZ) scales Control
Sampla1
High PA
HlghSZ
SD
0.67 0.72
1.40 1.06
4.42 1.08
0.93 0.79
Range
0-2
0-3
3-6
0-2
SD
1.07 1.03
2.13 1.30
1.17 1.03
Range
0-3
1-4
0-3
8.27 2.15 6-12
Scale 2
PA
Mean
3
SZ
Mean
More.—8D = standard deviation. Total sample excluding the high and low scorers on the PA and the SZ scales. 'Contains 6 Items. 'Contains 13 Items.
Downloaded from http://schizophreniabulletin.oxfordjournals.org/ at University of Georgia on June 9, 2015
patients with affective disorder or borderline personality disorder behaved the same way as normal subjects. The present study examines the performance of normal subjects who have questionnaire scores that suggest positive or negative schizotypic characteristics on a task on which schizophrenic patients show impaired performance, and on the basis of the performance of schizotypal subjects on another RT paradigm where the most impaired performance might be expected in those subjects showing high "positive" schizotypic scores.
720
A key press terminated the current stimulus and started the time interval before a new stimulus. No ready signal was given but the termination of a signal indicated that a new stimulus was to appear. Any response occurring after 5 seconds was regarded as an error. The stimuli consisted of 64
trials, with 16 trials of each stimulus type. The stimuli were presented with random intertrial intervals (ITIs) that varied from 1.5 to 3.5 seconds, to reduce the possibility of anticipation that occurs with fixed ITIs. Stimuli were presented in a semirandomized order in such a way that there were no more than three successively occurring stimuli in a given modality. The subjects were uncertain about what stimulus to expect on each trial. The order of stimulus presentation was identical for all the subjects. Before starting the experiment, the subjects practiced until there was no uncertainty about the task. The RTs produced by key presses were measured in milliseconds as the interval between the onset of a stimulus and the subjects' responses. False responses that occurred before stimulus presentation were discarded. Subjects worked continuously throughout the task. Data Analysis. The RT scores of each subject were classified in terms of their relationship to the preceding trials. The trials were grouped into cross-modal, ipsi-modal nonidentical, and ipsi-modal identical conditions. Each of these three conditions was subdivided into two conditions (six conditions total). The cross-modal trials consisted of sounds that were preceded by lights (L-S) and trials consisting of lights preceded by sounds (S-L). In the ipsi-modal nonidentical condition, a red light preceded a green light or vice versa (G-R/R-G) and a low tone preceded a high tone or vice versa (Hi-Lo/Lo-Hi). In the ipsi-modal identical condition, a red light was followed by a red light or a green light was followed by a green light (R-R/ C-G), and a low tone was followed by a low tone or a high tone was followed by a high tone (Hi-Hi/Lo-Lo).
Results A Group X Conditions analysis of variance (ANOVA) compared the RT performances of the high-PA, highSZ, and control subjects. A significant main effect of groups (f — 7.51; df — 2,39; p < 0.002) was found, indicating that the RT performances of the three groups differed. A highly significant main effect of conditions (F «• 43.15; df - 5,195; p < 0.0001) and a significant Group X Conditions interaction effect were also found (F — 2.98; df - 10,195; p < 0.009). The means, standard deviations, F ratios, and p values of the RT data for the three groups in response to crossmodal conditions, ipsi-modal nonidentical conditions, and ipsi-modal identical conditions are presented in table 3. Both high-PA and high-SZ groups showed considerably longer RTs compared with control subjects in response to the cross-modal sequences. These slow RTs were not as marked in response to changes in stimuli in the same modality as they were in reaction to shifts across modalities. ANOVAs were carried out separately for each of the cross-modal, ipsi-modal nonidentical, and ipsimodal identical conditions. The results revealed a highly significant difference (F - 21.56; df - 2,39; p < 0.0001) between the RT performances of the three groups for the crossmodal reaction to sound, that is, the condition under which subjects had to switch from visual to auditory stimuli. Post-hoc analysis (Tukey's HSD) showed a significant difference between the mean RTs of high-PA scorers compared with control subjects ip < 0.01). This indicated a lengthening of RT for shifting from light to sound stimuli for high-PA scorers
Downloaded from http://schizophreniabulletin.oxfordjournals.org/ at University of Georgia on June 9, 2015
Method. An attention switching experiment was designed using auditory and visual stimuli. The experimental design and measurement strategies closely resembled those employed by Sutton and colleagues (1961). The stimuli consisted of a red and a green light and sound stimuli of high and low frequency. The red and green lights and high- and low-frequency tones were presented randomly to the subjects, one stimulus at a time. The light stimuli were presented from two small boxes, each of which had a semitransparent, circular, colored plastic aperture of 5 cm in diameter, behind which the low wattage light sources were mounted. The auditory stimuli consisted of tones of 1,200 and 400 Hertz (Hz), set at 70 decibel (dB) intensity. The subjects wore headphones through which the auditory stimuli were heard. The stimulus boxes were placed in front of the subjects, approximately 30 cm apart at eye level. The subjects were seated approximately 1.5 meters from the stimulus lights and were instructed to make their responses as quickly as possible by pressing a response key with the preferred hand at the onset of any one of the four stimuli. The subjects' task was to respond every time a stimulus was presented and they were instructed to respond to all of the stimuli. The essential factor in producing a fast response is attention to the stimulus. Because it has frequently been reported that schizophrenic subjects show a long key-press RT, their slow RT is interpreted as an attentional defidt.
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Table 3. Mean reaction time scores for cross-modal, Ipsi-modal nonldentlcal, and Ipsl-modal Identical conditions for the high physical anhedonia (PA), high schlzophrenlsm (SZ), and control subjects HlghSZ (SD)
Control (SD)
F
P
Cross-modal Light-sound Sound-light
373 (34.6) 290 (38.8)
369 (47.9) 313 (36.1)
296 (18.0) 270 (43.3)
21.6 4.61
< 0.0001
Disorder of Attention in Individuals With Schizotypal Personality
by Soraya Wllklns and Peter H. Venebles
Abstract
Reaction time (RT) studies have been used extensively in research on schizophrenic patients, and it has been reported consistently that they exhibit longer RTs than normals. More specific deficits also have been reported. In a review of cross-modal RT studies of schizophrenia, Mannuzza (1980) found evidence that schizophrenic patients show, in addition to general slowness, a deficit when shifting attention across sensory modalities. Cross-modal RT experiments in the study of schizophrenic patients were first used by Mettler (1955), who found that they have great difficulty switching attention from one sensory modality to another. Many studies have replicated this finding: Sutton et al. 1961; Sutton and Zubin 1965; Waldbaum et al. 1975; and Spring 1980. In 1961, Sutton and colleagues carried out the first systematic study of modality shift in schizophrenia. They measured the RT performances of 23 chronic schizophrenic patients and 25 normal controls. The subjects were presented with green and red lights and high- and low-frequency tone stimuli. It was found that both
schizophrenic and control subjects had longer RTs in response to ipsimodal stimuli when there was a change in stimulus type from one stimulus to the next than to ipsi-modal stimuli that were successively identical. However, the RT was longer for schizophrenic patients than for normals. The researchers found that for trials in which there was a change in the modality of the stimuli, schizophrenic patients showed significantly slower RTs in crossing from visual to auditory stimuli than in changing from auditory to visual stimulation. Based on these results Sutton and colleagues (1961) suggested that the disorder of switching attention shown by schizophrenic patients is related not only to changes in the stimuli but also to differences in sensory modality. A similar study was carried out by Sutton and Zubin in 1965. They confirmed that schizophrenic subjects were slow in response to both ipsimodal nonidentical and cross-modal changes when the change was to sound stimuli. Several other studies (Kristofferson 1967; Verleger and Cohen 1978) have also reported that schizophrenic patients had slower responses when crossing to auditory than to visual stimuli. The defidt of shifting attention across sensory modalities has been shown to persist even when schizophrenic and control subjects have been matched for their general speed of RT (Sutton and Zubin 1965; Waldbaum et al. 1975) and when the subjects were given advance warning as to which stimulus would come next (Spring 1980). It appears that defidts in switching attention between different stimuli are Reprint requests ahould be sent to Dr. S. Wilkins, Genetics, Institute of Psychiatry, Denmark Hill, London SES 8AF, England.
Downloaded from http://schizophreniabulletin.oxfordjournals.org/ at University of Georgia on June 9, 2015
This study was designed to examine disorder of switching attention in normal individuals with schlzotypal personality. High scorers on the physical anhedorda (PA) and schizophrerdsm (SZ) scales of a questionnaire constructed to measure schizotypy were compared with a group of control subjects. A reaction time test was used that required switching attention across or between auditory and visual modalities. It was found that the high PA scorers and the high SZ scorers showed a defidt of shifting attention across modalities compared with the control subjects.
717
718
The authors are aware of only one study that examines attention switching in subjects who are vulnerable to the development of schizophrenia by reason of being children of schizophrenic parents. Phipps-Yonas (1984) carried out a study in which crossmodal RTs of 22 children, between 9 and 16 years of age, of schizophrenic mothers and 24 matched control subjects were examined. The task consisted of responding to sound and light stimuli presented in a sequence in which, on occasion, there was a switch from one stimulus modality to the other. In addition, a series of conditions was included in which the subjects were given information concerning the modality of the stimulus. Phipps-Yonas included this condition to examine the subjects' ability to benefit from the information concerning the upcoming stimuli. The results showed that the performance of children of schizophrenic mothers was indistinguishable from that of their matched controls in terms of the speed of their reactions and the variability of their performance. Further examination of her data led Phipps-Yonas to conclude that these negative results could be due to the fact that the highrisk sample used in this study consisted of a subsample of healthy children, as indexed by their scores on peers ratings, sodometric status, and achievement test scores, and that this group of children did not form a truly representative sample of children of schizophrenic mothers.
The view that schizophrenic characteristics are on a continuum has been extensively reviewed by Venables and colleagues (1990). This view, in general, steins from the notion put forward by Meehl (1962) that a tendency to develop schizophrenia ("schizotaxia") may be inherited, but whether the person with a schizotaxic predisposition develops schizophrenia or remains a functionally normal person with schizotypic traits depends on whether he or she is exposed to malignant or benign environmental influences ("environmental" refers to a wide variety of possible effects, ranging from intra-uterine to social). Chapman and colleagues (1980) and Siever and colleagues (1990) have demonstrated that schizotypic subjects are at increased risk for schizophrenia. Studies measuring schizotypy using the scales developed by the Chapmans and their colleagues (Chapman et al. 1976,1978; Eckblad and Chapman 1983) have shown—perhaps paralleling the notion of positive and negative schizophrenia (Crow 1980; Andreasen and Olsen 1982)—that two forms of schizotypy may be exhibited. (See review by Venables et al. [1990] and data provided by Kendler et al. [1991].) It is also important, however, to consider the relationship of schizotypy as measured by questionnaires to the concept of DSM-III-R (American Psychiatric Association 1987) schizotypal personality disorder (SPD) identified clinically. Claridge and Broks (1984) have developed a schizotypy scale more directly related to DSMIII-R SPD, and this has been shown (Muntaner et al. 1988; Raine and Allbutt 1989) to measure the more positive aspects of schizotypy insofar as it correlates with the Chapmans' Perceptual Aberration and Magical Ideation Scales (Per-Mag Scales; Chapman et al. 1976, 1978; Eckblad and Chapman
1983). Thus, on the basis of the present data, it appears that a person showing SPD characteristics may be considered as being on a borderline state between positive symptom schizophrenia and positive characteristic schizotypy. In this study, the "schizophrenism" scale (see below) measures positive aspects of schizotypy and thus is related to SPD as defined in DSMIII-R, whereas "physical anhedonia" (see below) is related to the negative aspects of schizotypy and not directly related to SPD as defined. The studies that support these relationships are covered in detail by Venables and colleagues (1990). We are not aware of any studies that examine the performance of schizotypic subjects or subjects diagnosed as exhibiting SPD on the crossmodal RT paradigm. Two studies are available that examine the performance of schizotypal subjects on other RT paradigms. Simons and colleagues (1982) showed that subjects with high scores on the Perceptual Aberration Scale (Chapman et al. 1978) showed the "crossover effect" (a measure of the ability of a subject to benefit from warning intervals of repeated regular durations) in an RT procedure with a regular and an irregular preparatory interval paradigm. That schizophrenic patients show the crossover effect has been a well-established finding in the literature since it was first reported by Rodnick and Shakow in 1940. Simons and colleagues (1982) also showed that subjects with high scores on the Physical Anhedonia Scale (Chapman et al. 1976) showed the crossover effect but less strongly than those with high perceptual aberration scores. A study by Chapin and colleagues (1987) provided further evidence of a crossover effect in patients diagnosed as exhibiting SPD, whereas
Downloaded from http://schizophreniabulletin.oxfordjournals.org/ at University of Georgia on June 9, 2015
characteristic of schizophrenic patients; thus, it is pertinent to ask whether this is a state phenomenon, only evident when the subject is exhibiting schizophrenic symptoms, or is a trait characteristic of subjects vulnerable to schizophrenia or possessing some of the characteristics of schizophrenia in a normal state.
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V O L 18, NO. 4,1992
selected from the original 470. The 42 selected subjects were mainly undergraduate and postgraduate students, chosen on the basis of their scores on the 25-item version of the questionnaire. They were formed into three groups. The first group consisted of 12 subjects (6 males and 6 females) with high scores on the PA scale. The second group consisted of 15 subjects (9 males and 6 females) who scored high on the SZ scale. The third group, the control subjects, consisted of 8 males and 7 females with the lowest overall scores. A very small number of subjects scored high on the SA scale, but
there were not enough to form a group based on this dimension. Test subjects ranged in age from 21 to 30; there were 19 females and 23 males. As far as possible the groups were matched for age and sex. The subjects were highly intelligent undergraduate and postgraduate students. Table 1 presents the subjects' demographic characteristics. The scores on each scale for all the groups is given in table 2. The high SZ group had low scores on the PA scale and the high PA group scored low on the SZ scale. Two subjects who scored high on both scales were excluded.
Method and Procedure In this study, deficit of switching attention across sensory modalities was examined in subjects with schizotypal personality characteristics, identified on the basis of their scores on a questionnaire constructed to measure schizotypy in the general population. In brief, the questionnaire consists of 25 items derived from factor analysis of the earlier (86-item) version of the questionnaire. (The full description of this questionnaire is presented in Venables et al. [1990].) The shortened version consists of three scales: SZ (schizophrenism), PA (physical anhedonia), and SA (social anhedonia). The SZ scale contains items that could be considered to be parallel to "positive symptom" schizophrenia. The PA and SA scales contain items tapping some aspects characteristic of "negative symptom" schizophrenia. Subjects. The schizotypy questionnaire, described above, was presented to 470 subjects between the ages of 20 and 35 (mean 25.3 ± (SD] 3.8 years). Forty-two percent of the subjects were male and 58 percent were female. The subjects were drawn from university staff and students and their acquaintances. A total of 42 subjects were
Table 1.
Demographic characteristics of the groups Ag* (years)
Sax Qroups
n
M
F
Mean
(SD)
High physical anhedonia score
12
6
6
24.80
(3.01)
15 15 42
9 8 23
6 7 19
25.04
(1.64)
High schizophrenism score Control Total or average
25.77
(2.39)
25.3
(3.8)
Note.—8D = standard deviation.
Table 2. Subjects' scores on the physical anhedonia (PA) and schizophrenism (SZ) scales Control
Sampla1
High PA
HlghSZ
SD
0.67 0.72
1.40 1.06
4.42 1.08
0.93 0.79
Range
0-2
0-3
3-6
0-2
SD
1.07 1.03
2.13 1.30
1.17 1.03
Range
0-3
1-4
0-3
8.27 2.15 6-12
Scale 2
PA
Mean
3
SZ
Mean
More.—8D = standard deviation. Total sample excluding the high and low scorers on the PA and the SZ scales. 'Contains 6 Items. 'Contains 13 Items.
Downloaded from http://schizophreniabulletin.oxfordjournals.org/ at University of Georgia on June 9, 2015
patients with affective disorder or borderline personality disorder behaved the same way as normal subjects. The present study examines the performance of normal subjects who have questionnaire scores that suggest positive or negative schizotypic characteristics on a task on which schizophrenic patients show impaired performance, and on the basis of the performance of schizotypal subjects on another RT paradigm where the most impaired performance might be expected in those subjects showing high "positive" schizotypic scores.
720
A key press terminated the current stimulus and started the time interval before a new stimulus. No ready signal was given but the termination of a signal indicated that a new stimulus was to appear. Any response occurring after 5 seconds was regarded as an error. The stimuli consisted of 64
trials, with 16 trials of each stimulus type. The stimuli were presented with random intertrial intervals (ITIs) that varied from 1.5 to 3.5 seconds, to reduce the possibility of anticipation that occurs with fixed ITIs. Stimuli were presented in a semirandomized order in such a way that there were no more than three successively occurring stimuli in a given modality. The subjects were uncertain about what stimulus to expect on each trial. The order of stimulus presentation was identical for all the subjects. Before starting the experiment, the subjects practiced until there was no uncertainty about the task. The RTs produced by key presses were measured in milliseconds as the interval between the onset of a stimulus and the subjects' responses. False responses that occurred before stimulus presentation were discarded. Subjects worked continuously throughout the task. Data Analysis. The RT scores of each subject were classified in terms of their relationship to the preceding trials. The trials were grouped into cross-modal, ipsi-modal nonidentical, and ipsi-modal identical conditions. Each of these three conditions was subdivided into two conditions (six conditions total). The cross-modal trials consisted of sounds that were preceded by lights (L-S) and trials consisting of lights preceded by sounds (S-L). In the ipsi-modal nonidentical condition, a red light preceded a green light or vice versa (G-R/R-G) and a low tone preceded a high tone or vice versa (Hi-Lo/Lo-Hi). In the ipsi-modal identical condition, a red light was followed by a red light or a green light was followed by a green light (R-R/ C-G), and a low tone was followed by a low tone or a high tone was followed by a high tone (Hi-Hi/Lo-Lo).
Results A Group X Conditions analysis of variance (ANOVA) compared the RT performances of the high-PA, highSZ, and control subjects. A significant main effect of groups (f — 7.51; df — 2,39; p < 0.002) was found, indicating that the RT performances of the three groups differed. A highly significant main effect of conditions (F «• 43.15; df - 5,195; p < 0.0001) and a significant Group X Conditions interaction effect were also found (F — 2.98; df - 10,195; p < 0.009). The means, standard deviations, F ratios, and p values of the RT data for the three groups in response to crossmodal conditions, ipsi-modal nonidentical conditions, and ipsi-modal identical conditions are presented in table 3. Both high-PA and high-SZ groups showed considerably longer RTs compared with control subjects in response to the cross-modal sequences. These slow RTs were not as marked in response to changes in stimuli in the same modality as they were in reaction to shifts across modalities. ANOVAs were carried out separately for each of the cross-modal, ipsi-modal nonidentical, and ipsimodal identical conditions. The results revealed a highly significant difference (F - 21.56; df - 2,39; p < 0.0001) between the RT performances of the three groups for the crossmodal reaction to sound, that is, the condition under which subjects had to switch from visual to auditory stimuli. Post-hoc analysis (Tukey's HSD) showed a significant difference between the mean RTs of high-PA scorers compared with control subjects ip < 0.01). This indicated a lengthening of RT for shifting from light to sound stimuli for high-PA scorers
Downloaded from http://schizophreniabulletin.oxfordjournals.org/ at University of Georgia on June 9, 2015
Method. An attention switching experiment was designed using auditory and visual stimuli. The experimental design and measurement strategies closely resembled those employed by Sutton and colleagues (1961). The stimuli consisted of a red and a green light and sound stimuli of high and low frequency. The red and green lights and high- and low-frequency tones were presented randomly to the subjects, one stimulus at a time. The light stimuli were presented from two small boxes, each of which had a semitransparent, circular, colored plastic aperture of 5 cm in diameter, behind which the low wattage light sources were mounted. The auditory stimuli consisted of tones of 1,200 and 400 Hertz (Hz), set at 70 decibel (dB) intensity. The subjects wore headphones through which the auditory stimuli were heard. The stimulus boxes were placed in front of the subjects, approximately 30 cm apart at eye level. The subjects were seated approximately 1.5 meters from the stimulus lights and were instructed to make their responses as quickly as possible by pressing a response key with the preferred hand at the onset of any one of the four stimuli. The subjects' task was to respond every time a stimulus was presented and they were instructed to respond to all of the stimuli. The essential factor in producing a fast response is attention to the stimulus. Because it has frequently been reported that schizophrenic subjects show a long key-press RT, their slow RT is interpreted as an attentional defidt.
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Table 3. Mean reaction time scores for cross-modal, Ipsi-modal nonldentlcal, and Ipsl-modal Identical conditions for the high physical anhedonia (PA), high schlzophrenlsm (SZ), and control subjects HlghSZ (SD)
Control (SD)
F
P
Cross-modal Light-sound Sound-light
373 (34.6) 290 (38.8)
369 (47.9) 313 (36.1)
296 (18.0) 270 (43.3)
21.6 4.61
< 0.0001
