Journal of Abnormal Psychology 1977, Vol. 86, No. S, 461-469
Selective Attention, Breadth of Attention, and Shifting Attention in Chronic Nonparanoid Schizophrenics Susanne Davies-Osterkamp, Fred Rist, and Anne Bangert University of Konstanz, West Germany The performance of normals, chronic schizophrenics, and hospitalized alcoholics was compared in a reaction time task with simultaneous presentation of two stimuli and the offset of one stimulus as the signal. The stimuli were either of one or two different modalities, and the signal was known or was not known to the subjects in advance. The data were analyzed according to two different models of attentional deficit in chronic nonparanoid schizophrenics. No empirical support could be found for Broen's model, which attributes the difficulties that chronic nonparanoid schizophrenics experience in tasks with stimuli of different sense modalities to narrowed attention. On the other hand, Kristofferson's findings on slower attentional shifts in chronic schizophrenics could be replicated; and, as an extension of her work, it was shown that this slower shifting process is confined to cross-modal shifts—no differences being found between normals, chronic schizophrenics, and alcoholics in ipsimodal shifts.
The present article is concerned with certain theoretical explanations of attention disorders in chronic nonparanoid schizophrenics that have been presented by several authors in the context of interference theory. Concurrent reports have been given by Broen (1973), Broen and Nakamura (1972), Kristofferson (1967), Sutton and Zubin (196S), and Kriegel-Waldbaum, Sutton, and Kerr (1975) on specific deficits in chronic nonparanoid schizophrenics when simultaneous attention to stimuli of different sense modalities (auditory and visual) is relevant for a specified task. Although the empirical findings of these authors were partly obtained under very similar experimental conditions, the theoretical assumptions are quite divergent as to which aspects of attention under heterogeneous stimuli are subject to specific disturbances. The following article attempts to clarify these divergences by replicating and extending some of those findings. Broen (1973) proposes that attentional disorders in chronic nonparanoid schizophrenics Requests for reprints should be sent to Susanne Davies-Osterkamp, who is now at the University of Giessen, Zentrum fur Psychosomatische Medizin, Medizinische Psychologic, Friedrichstrasse 36, 6300 Lahn-Giessen, West Germany.
can only be understood with reference to the cognitive disturbances in the earlier phases of the illness. As a protective mechanism against the (central) overstimulation in the acute stage of their illness, chronic schizophrenics develop a peripheral narrowing of attention breadth. This narrowing occurs along modality lines, that is, chronic nonparanoid schizophrenics restrict their monitoring of the environment more exclusively to sensations in single sensory modalities. The gain of this mechanism is that schizophrenics are less disturbed by irrelevant stimuli of other sense modalities; the cost is that their performance is diminished when they are confronted with relevant stimuli of different modalities. The works of Feeney (1971) and Broen and Nakamura (1972) are quoted by Broen (1973) as the main empirical support for these assumptions. In Broen and Nakamura, acute paranoid and chronic nonparanoid schizophrenics carried out simultaneously a visual tracking task and an auditory signal detection task. As part of the instruction, the experimenter gave the auditory monitoring either primary or secondary importance. With acute schizophrenics, these instructions produced no substantial changes in the number of correctly detected signals, whereas chronic schizophrenics showed a significant drop in auditory per-
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formance when the visual problem was emphasized. Feeney (1971) compared acute schizophrenics, chronic schizophrenics, and normals in a reaction time paradigm with simultaneous presentation of auditory and/or visual stimuli and with stimulus offset as the signal. In the assessment of selective attention, the relevant stimulus was known to the subjects in advance; in the assessment of breadth of attention, it was not. In comparison with the other two groups, chronic nonparanoid schizophrenics showed a specific deficit in selective attention in the case of stimuli within the same modality. On the other hand, they showed a specific deficit in breadth of attention when dual-modality monitoring was required. Kristofferson (1967) used the same experimental setup as Feeney (1971)—although confined to the condition of stimuli in two modalities—when comparing chronic schizophrenics and normal subjects. In contrast to Feeney (1971), Kristofferson analyzed her data from the perspective of cross-modal attentional shifting. In continuation of the works of Sutton and co-workers (for a summary, see Sutton & Zubin, 1965), who found a particularly strong deterioration in reaction time in schizophrenics with sequential presentation of auditory and visual stimuli, Kristofferson concluded that these specific deteriorations could best be explained by a slower intermodal switching. This explanation increases in importance in view of the recent data by Kriegel et al. (197S). No support was found for the hypothesis that the increased cross-modal reaction times of schizophrenics are primarily due to expectancies overly influenced by the preceding stimulus. Schizophrenics and normals did not differ in the frequency of cross-modal versus ipsitnodal expectations. Furthermore, the schizophrenics' greater impairment on cross-modal reaction time trials occurred even when the schizophrenics' expectations of the next stimulus were correct. In the present experiment, we have chosen an experimental design that is based on and also extends the work of Kristofferson (1967) and Feeney (1971) and that allows an evaluation of the data in terms of Broen's (1973) model as well as Kristofferson's. In this way,
we can determine by a direct comparison of the results which of the two models has the better explanatory power. Furthermore, the inclusion of an additional psychopathological group, chronic alcoholics, allows inferences about the specifity of any deficits. Method Subjects Subjects were 16 chronic nonparanoid schizophrenics and 16 alcoholics from the Reichenau Psychiatric Hospital; 16 health}' employees of the hospital served as the controls. All subjects were male and had completed secondary education. The subjects were matched according to age and years of education. Mean ages were as follows: For the chronic nonparanoid schizophrenics, M = 42.2 years, SD = S . l ; for the alcoholics, M = 41.2 years, SD = 8.2; and for the healthy control subjects, M = 41.S years, SD = &.1. The diagnosis of chronic schizophrenia had remained unchanged for at least 6 years and had been confirmed by at least two psychiatrists during this time. Only those patients were selected for the study who had no evidence of paranoid symptoms in their files. Since the last admission the schizophrenics had been hospitalized continuously for at least 2 years. Mean length of illness since the first hospitalization was 13.3 years. In this respect, our group may be even more "chronic" than the groups studied by Feeney (1971) and Broen and Nakamura (1972), who reported a mean hospitalization time of 8.S and 9.9 years, respectively. However, it should be noted that the attentional deficits postulated by Broen (1973) to be specific for chronic schizophrenics should be, according to his model, more marked as the illness progresses. Kristofferson (1967) did not report on the mean length of hospitalization, but as in our own study, her criterion for including subjects was hospitalization for a minimum of 2 years. Her subjects and our subjects are also comparable in age. (It should be noted that in Europe, the definition of schizophrenia is somewhat more restricted than it is in the States. However, we do not believe that these differences are as marked in the case of chronic schizophrenia as they may be in selecting groups of acute schizophrenics.) All schizophrenic patients were under phenothiazine medication, and we ascertained that medication had not been changed during the 2 weeks before they took part in the experiment. The possible influence of antipsychotic medication on the attentional variables under study is not clear. Feeney (1971) as well as Broen and Nakamura (1972), whose subjects were also under phenothiazine medication, gave indirect evidence on this problem by showing that the differences between their acute and chronic schizophrenics in attentional behavior could not be attributed to differences in subjects' medication level. Furthermore, Broen and Nakamura reported no differ-
ATTENTION IN CHRONIC NONPARANOID SCHIZOPHRENICS ences between some medicated and some unmedicated subjects in the attentional variables under study. In contrast to our own as well as to Feeney's and to Broen and Nakamura's procedure, Kristofferson (1967) selected subjects who had not been on medication for at least 1 month prior to her study. Therefore, differences between our results and her results might be due to different approaches in handling the medication problem. At the time of the present investigation, the alcoholics were undergoing a 3-month treatment program in the hospital and no longer showed withdrawal symptoms. This group was included to allow an assessment of general motivational influences on the results. All subjects were paid for taking part in the experiment. Stimuli Visual stimuli were two round, opaque glass lights of medium intensity, 3.5 cm in diameter and placed 26 cm apart at eye level. Acoustical stimuli were pure tones of 300 and 1,000 Hz presented from a tape recorder via relays to headphones. At the start of the session, subjects had adjusted the tones for equal subjective intensity. Reactions were recorded via a morse key. An IBM 1130 computer connected to an interface (Wissenschaftliche Datenverarbeitung, Munich) controlled stimulus presentation and randomization and processed the reaction times.
Procedure On 2 separate days, subjects were tested on a total of 24 sets of 43 trials. The results of the first three trials of each set were ignored. Two additional sets at the beginning of each session were used to determine baseline reaction times. The subjects started each trial by pressing the key. A key press was followed immediately by either two lights or two tones (the homogeneous condition) or one light and one tone (the heterogeneous condition). After either 1 or 3 sec at random, one of the stimuli was switched off. The subject had to react by lifting his finger off the key as fast as possible; this action switched off the other stimulus. In each session, each of the three stimulus combinations was presented in four different sets. In two of the sets (the certain condition), the first stimulus to be turned off was the same in all 43 trials; that is, in the homogeneous condition, either the right-hand or left-hand stimulus was turned o f f ; and in the heterogeneous condition, either the light or the tone was turned off. In the remaining two sets (the uncertain condition), one of the two stimuli was switched off at random on each trial, with the constraint that each stimulus was switched off approximately equally often and never more than three times in succession. The 12 sets in each session were sequenced in such a way that two identical stimulus combinations never occurred in succession, and two heterogeneous sets were always separated by two homogeneous sets.
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Certain and uncertain conditions always alternated. In the certain condition, the side or type of stimulus that was turned off first was also systematically alternated. The resulting eight possible sequences of sets were distributed evenly over the 16 subjects in each group. The second session was identical to the first session for each subject. Before starting each set of trials, the subject was informed of the type of stimulus combination that was to follow (certain/uncertain or homogeneous/heterogeneous) ; in the case of the certain condition, subjects were informed of the type of stimulus (right/left or light/tone). Baseline reaction times were determined in sets of trials in which either one light or one tone was presented. Duration of presentation was either 1 or 3 sec at random. Half the subjects in each group started with the sets of light stimuli. In the second session, the order was reversed for each subject.
Results The results are presented in the following three sections: (a) reaction times to a single light or sound stimulus ("baseline" reaction times), (b) reaction times as applied to testing the selective attention and the breadth of attention according to Broen (1973), and (c) the indices of attention switching, which—extending the work of Kristofferson (1967) — were calculated both intermodally and intramodally. All the data were subjected to analyses of variance. Significant interactions were analyzed by the calculation of simple effects according to Winer (1962). The statistical tests were performed on the logarithms of the reaction times; however, for simplicity of exposition in the tables, antilogs and their standard deviations are presented. Baseline Reaction Times The log-transformed reaction times were subjected to a four-way analysis of variance with repeated measurement on the last three factors. (Factor A was the experimental group; Factor B was the experimental session; Factor C was the length of the preperiod; and Factor D was the modality.) All the main effects proved to be statistically significant: For Factor A, F(2, 45) = 22.28, p < .01; for Factor B, F(l, 45) = 4.45, p < .05; for Factor C, ^(1,4$) = 70.63, p< .01; and for Factor D, F(l, 45) = 53.23, p < .01. As expected, the normal subjects had the fastest reaction times and the schizophrenics
S. DAVIES-OSTERKAMP, F. RIST, AND A. BANGERT
464 Table 1
Antilogs of Baseline Reaction Times jor Combined Sessions Light condition Group
Sound condition
1 sec
3 sec
1 sec
3 sec
425 72
424 77
378 200
353
338
317
283
93
87
68
267 64
275 35
256 31
230
216
23
24
Schizophrenics
M SD
75
Alcoholics
M SD
Normal controls
M SD
the slowest (see Table 1). The reaction times of all groups were longer in the first session than in the second, and they were longer for the 1-sec interval than for the 3-sec interval. Finally, all groups displayed a shorter reaction time to sound than to light. This result corresponds to the findings of Kriegel-Waldbaum et al. (1975) but contradicts those of Feeney (1971), who found that schizophrenics in contrast to normals had shorter reaction times to light than to sound. According to our analyses, the interaction between experimental group and modality was not significant. As the analysis of the significant interaction between interval length and experimental group showed, F(2, 45) = 3.75, p < .05, the effects of interval length on reaction time was stronger for schizophrenics than for the other two groups. Selective Attention and Breadth of Attention To test the hypotheses of Broen (1973), the data obtained under conditions of simultaneous presentation of two stimuli were evaluated using two four-way analyses of variance with repeated measurement on the last three factors. Factor A was the experimental group; Factor B, the conditions of stimulus uncertainty (in Broen's terminology, breadth of attention) and certainty (in Broen's terminology, selective attention); Factor C, the two levels of interval length; and Factor D, the homogeneity of the stimuli (the irrelevant stimulus was either of the same modality as
the relevant stimulus or of a different modality). One of the analyses concerned those trials with sound as the relevant stimulus; the other one concerned those with light. In both analyses, the dependent variables were the difference of the log-transformed reaction times and the correspondingly transformed baseline reaction times. An evaluation of the reaction time to light and sound in separate analyses seemed necessary to us to prevent confounding of modality and homogeneity. The alternative procedure of Feeney (1971), in which the reaction times to light and sound are combined and relativized with respect to the average baseline reaction times, seems to be somewhat problematic because this procedure eliminates any effects due specifically to the modality (effects that are, according to our results, certainly present). The data of both sessions were combined because a preliminary analysis had revealed no statistically significant interaction between this and the experimental groups. Means and variances of the reaction times of each group can be found in Table 2. In both analyses, the main effects due to the experimental groups were not significant. The deviation of the reaction time from the baseline was no more marked for the schizophrenics than for the normal or alcoholic subjects. Moreover, testing for the simple main effects of groups in those cases (to be individually described later) in which significant interactions between these factors and other experimental conditions were obtained yielded no significant differences. The analyses of such interactions showed, on the whole, that the change in the reaction times of schizophrenics under varying experimental conditions was in the same direction as for normals and alcoholics, the differences between the groups being solely in the extent of such changes. The critical test for examining Broen's (1973) hypothesis of a relatively stronger deterioration of selective attention in schizophrenics under homogeneous conditions as against a relatively stronger deterioration of their breadth of attention under heterogeneous stimuli conditions is the test for the interaction between group, certainty, and homoge-
ATTENTION IN CHRONIC NONPARANOID SCHIZOPHRENICS
neity of stimuli. In contrast to this hypothesis, the analyses yielded no significant interactions. This finding, which also contradicts the results of Feeney (1971), appeared again in additional analyses in which the dependent variable instead of being the difference from the baseline was, respectively, the percentage change from baseline as employed by Feeney and the reaction time not relativized to the baseline. We had to apply a log transformation because the reaction times were (in accordance with the experimental literature) definitely skewed. Could the transformation explain our negative findings? To check on this, we analyzed the antilogs of each subject's mean of the log-transformed reaction times for each condition. This transformation, without resulting in too badly skewed data, is halfway between our previous analyses and the one using the means of untransformed values (cf. Feeney, 1971), but here too the critical interactions did not approach significance. The interaction between certainty and homogeneity was significant for all groups: For sound, P(l, 4 S ) = 3 . 9 4 , p < .05; and for light, F(l, 45) - 5.74, p < .05. As the main effects show, the reaction time was slower under conditions of uncertainty (breadth of attention) than under conditions of certainty (selective attention); For tone, F(l, 45) = 72.94, p< .01; and for light, F(l, 45) = 163.99, p < .01. Reaction time was also slower under homogeneous than under heterogeneous stimuli: For tone, F(l, 45) = 58.69, p < .01; and for light, F(l, 45) = 14.86, £ < .01. Further, the analysis of the simple main effects of homogeneity of stimulus conditions showed that under certainty conditions, the homogeneity of the stimuli caused a larger deterioration in reaction time than under uncertainty. Tests of significance for the deviations of the reaction times from the baseline average by means of t tests showed a statistically significant increase under all the above experimental conditions, with the exception of those in which the relevant stimulus was known to the subject and the irrelevant stimulus was of another modality. In the case of the relevant signal being a light and the irrelevant signal being a sound stimulus, the
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Table 2 Antilogs of Reaction Times (in msec} in the Different Experimental Conditions j or Combined Interval Lengths Homogeneous condition Group
Heterogeneous condition
Certain Uncertain Certain Uncertain Light
Schizophrenics 447 M SD 125 Alcoholics 317 M SD 64 Normal controls 281 M SD 29
497 121
386 86
450 99
353 86
299 S4
357 90
321 40
261 26
308 42
410 98
308 56
356 84
55
302 81
247 47
274 57
Normal controls 229 M SD 32
250 38
210 25
234 23
Sound Schizophrenics 377 M SD 92 Alcoholics 280 M SD
deviations from the baseline were not significant for any group. The deviations from the baseline showed a shortening of reaction time for all groups when the relevant stimulus was a sound and the irrelevant stimulus a light. This finding corresponds to one aspect of Broen's (1973) model inasmuch as his model postulates a stronger deterioration of selective attention under homogeneous stimuli than under heterogeneous stimuli. However, because this effect according to our results is not specific to schizophrenics and is, moreover, in agreement with the findings on intersensory facilitation of reaction time (Nickerson, 1973), this cannot be interpreted as a confirmation of Broen's model. Significant interactions of group with particular experimental conditions occurred in both analyses. In no case, however, did these results yield any support for the validity of Broen's (1973) model. The Group X Certainty X Preperiod interaction was significant
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S. DAVIES-OSTERKAMP, F. RIST, AND A. BANGERT
for light as well as sound: For sound, F(2, 45) = S.06, p < .05; and for light, F(2, 45) = 7.62, p < .01. When sound was the relevant stimulus, the Group X Preperiod X Homogeneity of Stimuli interaction was also significant, F ( 2 , 45) = 4.77, p < .05. As analyses of these interactions showed, the length of the preperiod influenced the reaction times of the three groups in the same direction, although the extent of the change was different according to the experimental conditions. The deterioration of the reaction time relative to the baseline was greater for all groups for a preperiod of 3 sec than for a period of 1 sec. However, the influence of the preperiod turned out to be significant as a main effect only with light as the relevant stimulus, ^(1, 45) = 18.06, p < .01. With sound as the relevant stimulus, a lengthening of reaction time with increasing preperiod occurred only for the group of schizophrenics and only under heterogeneous stimuli and uncertainty about the relevant stimulus. For schizophrenics, this last finding also held when light was the relevant stimulus; whereas in contrast, normals and alcoholics reacted with a lengthening of reaction time with increasing preperiod precisely when the relevant stimulus was known. An interpretation of this finding on the differential influence of the preperiod on the reaction time cannot be given here because it was not a primary concern of our investigation; the length of the preperiod, therefore, was varied only on two levels. It should be noted, however, that schizophrenics—in agreement with the findings of Shakow (1963) — reacted with an increase in reaction time particularly under those conditions that are conducive to the influence of "minor sets." Intermodal and Intro-modal Attention Switching The index of attention switching (A) was calculated using Kristofferson's (1967) method from the difference of the reaction times of each subject under uncertainty conditions (UC) and under certainty conditions (C). With our experimental design, a crossmodal (light/sound ^LS]) as well as an ipsimodal (light/light [LL] and sound/sound
[SS]) determination of this index was possible. ALS = Lightuc + Sounduc — Lightc — Soundc. ALL = Light luc + Light 2 UC - Light lc - Light 2C. ASS = Sound IDC + Sound 2uc — Sound lc — Sound 2c. To calculate this measure, the untransformed reaction times in milliseconds were used. As Kristofferson (1967) states, the construction of this index is based on an attention model that makes the following assumptions: (a) Attention cannot be paid simultaneously to two different channels; (b) if the irrelevant channel is being monitored, a certain time is necessary to switch attention to the relevant channel; (c) an input in the currently not monitored channel can cause attention to switch to that channel. The indices were subjected to a four-way analysis of variance with repeated measurement on the last three factors (Factor A: experimental group; Factor B: experimental session; Factor C: length of preperiod; Factor D: stimulus condition [sound/light, light/light, sound/ sound]). Figure 1 shows the A values for each group. The main effect of group proved not to be statistically significant; therefore, general group differences in the A indices could not be detected. On the other hand, the experimental session factor, F(l, 45) — 4.81, p < .05, was significant (in the second session, the indices were smaller for all groups) as well as the preperiod factor, F(l, 45) = 5.62, p < .05, and stimulus condition, F ( 2 , 90) =5.36, p < .05. As an analysis of the significant Preperiod X Stimulus Condition interaction, F(2, 90) = 6.81, p < .01, as well as the Group X Preperiod X Stimulus Condition interaction, F(4, 90) = 3.44, p < .05, showed, the normals and the alcoholics differed from the schizophrenics in regard to which experimental conditions had a statistically significant effect on the A indices: For the normals as well as for the alcoholics, only the length of the preperiod had an influence on the attention switching; for both groups, greater
ATTENTION IN CHRONIC NONPARANOID SCHIZOPHRENICS PREPERIOO I SEC
467
PREPERIOO 3 SEC
IN MSEC
ISO
100
SOUND/ SOUND
SOUND/ LIGHT
LIGHT/ LIGHT
SOUND/ SOUND
SOUND/ LIGHT
LIGHT/ LIGHT
Figure 1. Mean cross-modal (sound/light) and ipsimodal (sound/sound and light/light) values in milliseconds for normal controls (white columns), schizophrenics (dark columns), and alcoholics (lined columns).
differences occurred with a short preperiod, as was to be expected from the baseline data. For the schizophrenics, on the other hand, the simple main effect of preperiod was not significant. However, in this group, significant effects due to stimulus condition as well as to the Stimulus Condition X Preperiod interaction were present. With a preperiod of 1 sec, the A indices under the ipsimodal condition with two light stimuli were significantly higher than under the other two conditions. With a preperiod of 3 sec, the A values were highest under the intermodal condition with a light and sound stimulus. An additional analysis of the simple effects of group, moreover, showed that this was the only condition in which the A values for schizophrenics were significantly different from those of normals and alcoholics. In correspondence with the results of Kristofferson (in her experimental scheme, the preperiod was held constant at 2 sec),.the cross-modal switching time was significantly higher for schizophrenics than for normals and alcoholics, although only with a preperiod of 3 sec. On the other hand, no difference in the ipsimodal switching time could be ascertained within the auditory and visual modality. Discussion Our experimental data were analyzed by two methods that were based on different
models of specific deficits of attention in chronic schizophrenics. A comparison of the results of these two methods permits some conclusions on the validity of the assumptions deduced from these models. Our investigation furnished no support for Broen's (1973) assumptions that in the case of chronic schizophrenics, a deficit of selective attention or breadth of attention occurs depending on the homogeneity or heterogeneity of stimulus conditions: (a) The critical interaction between experimental group, stimulus condition, and certainty about the relevant stimulus was not significant, regardless of whether the general retardation in reaction time of chronic schizophrenics was eliminated by control of baseline reaction time. When such an elimination was carried out, the extent of the deterioration of schizophrenics was not greater than for normals or alcoholics under those experimental conditions, which according to Broen are relevant for breadth of attention and selective attention. From this, it would even be possible to conclude that chronic nonparanoid schizophrenics do not have any specific attentional disorders, and that the variance between the groups can be explained solely by the schizophrenics retardation in information processing (Yates & Korboot, 1970). (b) In addition, it was found that with simultaneous presentation of two stimuli, the reaction times of all three groups were affected differently
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by certain experimental conditions (preperiod theoretical considerations of Broen (1973) and heterogeneity of stimuli) depending on and Broen and Nakamura (1972) could be whether sound or light was denned as the integrated into the model of a retarded intersignal. This finding casts further doubt on modal shift in schizophrenics. The narrowed the usefulness of Broen's model. As an ex- attention and narrowed monitoring across moplanation of such specific effects, the concept dalities postulated by these authors could of breadth of attention does not seem to be operate through less reliable shifts of attensufficient. tion from the irrelevant to the relevant signal. A detailed analysis of the divergencies be- Further research is necessary to clarify tween our results and Feeney's (1971) is ex- whether the attention shifting of acute and cluded by the fact that she did not take into paranoid schizophrenics is independent of the account that selective attention and breadth heterogeneity of stimuli as Broen (1973) of attention might be differentially affected suggests. when light and sound are the relevant stimuli. Finally, it should be noted that the differWith respect to the experimental design and ences in intermodal shifting between the to the selection of the group of chronic schizo- schizophrenic subjects and the other two phrenics, our procedure and her procedure groups did not hold for a preperiod of 1 sec, seem to be rather similar; therefore, in our which should caution against a generalization opinion, they cannot be relevant in explain- of our findings. With a preperiod of 1 sec, ing the divergent results. the schizophrenics' shifting process was longIn terms of another model in which in the est with two light stimuli, although the differcase of simultaneous presentation of two ences between them and the other two groups stimuli a decisive role is attributed to the were not statistically significant. It could be process of attention switching between several speculated that with very short preperiods, input channels, the analysis of our data aspects of the stimuli other than modality yielded a confirmation of the findings of (such as discriminability in spatial location, Kristofferson (1967) on the retardation of intensity, etc.) might become relevant for the intermodal shifting in chronic schizophrenics. process of attentional shifts. A test of this Moreover, by comparison with a further psy- could consist of a replication of the present chopathological group, it could be shown that study with a broader variability in length of this deficit might be specific to schizophrenics preperiod and kind of stimuli. A further imand that it occurs only for cross-modal but provement would be an experimental setup of not for ipsimodal shifting. According to our the certainty condition in which knowledge of results, the often reported deficit in chronic the signal is not confounded with consistency schizophrenics with heterogeneous stimuli of the source of stimuli, for example, by incould be explained by a retardation of the cluding discriminative stimuli that announce shifting process. the kind of signal to be expected. Our results do not permit the retarded intermodal shifting to be interpreted as due References purely to a longer switching process. As Kristofferson (1967) points out, the value of Broen, W. E., Jr. Limiting the flood of stimulation: the A index is also dependent on how cerA protective deficit in chronic schizophrenics. In R. Solso (Ed.), Contemporary issues in cognitive tainly a signal in the currently not attended psychology: The Loyola symposium. New York: but relevant channel can cause an attentional Wiley, 1973. switch to that channel. An empirical separa- Broen, W. E., Jr., & Nakamura, C. Y. Reduced tion of these two components is not possible. range of sensory sensitivity in chronic, nonparaIf we assume that it is precisely this second noid schizophrenics. Journal of Abnomal Psychology, 1972, 79, 106-111. component that is responsible for the retardaFeeney, S. Breadth oj cite utilization and ability to tion of reaction time in schizophrenics under attend selectively in schizophrenics and normals. heterogeneous stimuli and conditions of unUnpublished doctoral dissertation, University of California, Los Angeles, 1971. certainty, then the empirical findings and
ATTENTION IN CHRONIC NONPARANOID SCHIZOPHRENICS Kriegel-Waldbaum, J., Button, S., & Kerr, J. Shift of sensory modality and reaction time in schizophrenia. In M. Kietzman, S. Sutton, & J. Zubin (Eds.), Experimental approaches to psychopathology. New York: Academic Press, 1975. Kristofferson, M. W. Shifting attention between modalities: A comparison of schizophrenics and normals. Journal oj Abnormal Psychology, 1967, 72, 388-394. Nickerson, R. S. Intersensory facilitation of reaction time. Psychological Review, 1973, 80, 489-509. Shakow, D. Psychological deficit in schizophrenia. Behavioral Science, 1963, 8, 275.
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Sutton, A., & Zubin, J. Effect of sequence on reaction time in schizophrenia. In A. T. Welford & J. E. Birren (Eds.), Behavior, aging and the nervous system. Springfield, 111.: Thomas, 196S. Winer, B, J. Statistical principles in experimental design. New York: McGraw-Hill, 1962. Yates, A. T., & Korboot, P. Speed of perceptual functioning in chronic nonparanoid schizophrenics. Journal of Abnormal Psychology, 1970, 76, 453.
Received October 26, 1976 Revision received May 17, 1977 a
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