Journal of Abnormal Psychology 1996, Vol. 105, No. 3, 410--420
Copyright 1996 by the American Psychological Association, Inc. 0021-843X/96/$3.00
Stimulus Configuration and Context Effects in Perceptual Organization in Schizophrenia Steven M. Silverstein
Raymond A. Knight
University of Rochester Medical Center
Brandeis University
Steven B. Schwarzkopf, Laura L. West, Leah M. Osborn, and Don Kamin University of Rochester Medical Center Two studies assessed perceptual organization in schizophrenia to determine (a) whether inpatient and outpatient groups with poor premorbid schizophrenia have comparable levels of perceptual organization deficit; and (b) whether the deficit could be eliminated by task manipulations. In Study l, inpatients demonstrated clear evidence of a perceptual organization deficit, whereas outpatients performed similarly to the control groups. In Study 2, a performance pattern that operationally defined a perceptual organization deficit was eliminated by a task manipulation thought to aid in context processing. The perceptual organization deficit is most pronounced in actively symptomatic patients with poor premorbid schizophrenia, and the deficit reflects, in part, deficient top-down influences to basic perceptual processes.
One model of the visual information processing dysfunction in schizophrenia posits an impaired ability to rapidly and automatically organize stimulus elements into object representations (Cox & Leventhal, 1978; Knight, 1992; Place & Gilmore, 1980; Wells & Leventhal, 1984). This perceptual organization (PO) deficit hypothesis is based on more general models of norreal human visual perception that have traditionally postulated two stages in early visual information processing: (a) an initial global, parallel, or holistic analysis (up to 200 ms) that occurs preattentively, or prior to allocation of attentional resources, in which stimulus components are grouped on the basis of gestalt principles (e.g., similarity, proximity, etc.) into object represen-
Steven M. Silverstein, Steven B. Schwarzkopf, Laura L. West, Leah M. Osborn, and Don Kamin, Department of Psychiatry, University of Rochester Medical Center; Raymond A. Knight, Department of Psychology, Brandeis University. Leah M. Osborn is now at the Department of Neurology, University of Rochester Medical Center. This research was supported by a Biomedical Resarch Support Grant from the University of Rochester Medical Center and by a grant from the Scottish Rite Benevolent Foundation's Schizophrenia Research Program, N.M.J., USA. Preliminary results of this study were presented at the meeting of the Society for Research in Psychopathology, Palm Springs, CA, 1992, and at the meeting of the Society of Biological Psychiatry, Philadelphia, PA, 1994. We thank Clifford Jacobson and Michael McGrath for their help in recruiting patients for this study, the staff'and patients of Strong Memorial Hospital and Strong Ties for their help and cooperation with our research program, and Donna Palumbo and David Hamilton for their helpful comments on an earlier draft of this article. Correspondence concerning this article should be addressed to Steven M. Silverstein, University Services Psychiatric Rehabilitation Program, Rochester Psychiatric Center, l I I l Elmwood Avenue, Rochester, New York 14620. Electronic mail may be sent via Internet to
[email protected].
tations; and (b) a stage of serial, local, or analytic processing (from 200 to as late as 600 ms), during which attentional resources are allocated for processing the most behaviorally relevant object, while other objects receive little or no subsequent processing (Baylis, 1994; Broadbent, 1977; Duncan, 1984; Kahneman, 1973). The PO deficit hypothesis implies that • Stage l is impaired in schizophrenia. Such impairment is thought to lead to the following perceptual and attentional failures: (a) poor figural articulation of stimulus objects in the visual field; (b) weak figure-ground distinctions; (c) an increased amount of information competing for attentional resources; (d) an allocation ofattentional resources to a wider range of stimuli than is adaptive; (e) poorly defined loci of attention and rapid shifting of attention between stimuli; and (f) a slowness in the assessment of meaning of relevant visual stimuli. PO dysfunction has been demonstrated in both inpatient (Cox & Leventhal, 1978; Knight, 1992; Place & Gilmore, 1980; Rabinowicz, Opler, Owen, & Knight, 1992) and outpatient schizophrenia patients (Wells & Leventhal, 1984), and it is most consistently found among those with a history of poor pre: morbid social functioning (Knight, 1992). In addition, the greater degree of PO dysfunction in poor premorbid schizophrenia patients has not been found to be an artifact of age, amount of hospitalization, medication levels, education, or intelligence (Knight, 1992). A PO deficit has not been demonstrated in other psychiatric groups (Cox & Leventhal, 1978; Knight, 1992; Knight, Elliott, & Freedman, 1985; Place & Gilmore, 1980; Wells & Leventhal, 1984) and was not found among high scorers on the schizotypy Scales (Silverstein, Raulin, Pristach, & Pomerantz, 1992 ). The PO deficit has been demonstrated and replicated with a variety of tasks including visual search (Cox & Leventhal, 1978; Knight, 1992) and numerosity (Place & Gilmore; 1980; Wells & Leventhal, 1984) paradigms. In several of these studies, 410
CONFIGURATION AND CONTEXT EFFECTS schizophrenia patients demonstrated superior target detection or counting of elements compared to controls in conditions with little stimulus grouping. In those cases, controls' tendency to engage in global processing appeared to delay the onset of serial processing and thus to hinder performance. Whereas the majority of past studies of PO in schizophrenia have assumed the traditional two-stage, global to serial model, a variety of recent data suggest that this model should be revised and that the nature of the PO deficit should be reconceptualized. For example, recent electrophysiologicaldata indicate that global and local processes are initiated at the same time, although they are largely localized in different areas of the brain ( Heinze & Miinte, 1993). In addition, a recent series of studies (Friedman-Hill & Wolfe, 1995) indicated that, in nonschizophrenic individuals, under the control of top--down influences such as memory and attentional strategies, global and serial processes interact. In short, in contrast to the reflexive, invariant global to serial sequence posited in early studies, recent data indicate a more reciprocal and complex relationship between global and serial processes that implies a shift in the way the PO deficit in schizophrenia should be conceptualized. A second body of data suggesting that the PO deficit should be reconceptualized involved demonstrations that among nonpatients, PO often developed over time as individuals became more familiar with stimuli (Lassaline & Logan, 1993; Rabbitt, 1984). These data suggest that individuals were using contextual information or information in working memory (Goldman-Rakic, 1991 ) to guide perceptual processing so that, after repeated exposure, certain stimulus configurations could be processed as single units. These data are consistent with the recent Friedman-Hill and Wolfe (1995) studies, which indicated that processes that have traditionally been considered automatic and preattentive can be controlled by top--down factors such as context processing and attentional strategies. Place and Gilmore (1980) reported that controls demonstrated superior grouping of stimuli that occurred 33% of the time when these stimuli were presented in the context of other grouped stimuli (Study 2 ) compared to when they were presented among nongrouped stimuli (Study 1 ). In contrast, schizophrenia patients did not demonstrate this superiority in their Study 2. This implies that the PO deficit may reflect an impairment in the ability to generate top-down feedback to earlier perceptual processes. This hypothesis is supported by Knight (1992), who demonstrated that schizophrenia patients performed normally on a PO task involving the detection of symmetrical relationships, a form of PO that does not require matching current percepts to memory representations (i.e., top-down influences; Peterson, 1994). Finally, several investigators have demonstrated that PO of even relatively simple stimuli requires attentional resources (Ben-Av, Sagi, & Braun, 1992; Rock & Mack, 1994). These data suggest that schizophrenia patients' PO difficulties may reflect a lack of attentional resources being allocated to the processing of global stimulus features, a dysfunction that implies reduced top-down control over perceptual processes. In short, recent data indicate that PO is not simply a product of b o t t o m - u p processing, wherein stimulus components are grouped solely on the basis of physical characteristics such as color, texture, and edges. Rather, PO also involves top-down
41 1
factors, which can be defined as the influence of previous experience on the manner in which stimulus components are organized (Kosslyn & Koenig, 1992). Top--down factors are thought to operate when a combination of affective and perceptual information related to previous experiences with the stimulus can be recreated in parallel with current stimulus input. This is thought to provide the basis for an understanding of context (Patterson, 1987 ). The data reviewed above suggest that the poor performance of schizophrenia patients on PO tasks may reflect, in part, deficient top--down control over perceptual processes. More specifically, they suggest a schizophrenia-related deficit in the ability of current sensory input to initiate a simultaneous recreation of aspects of experience associated with past occurrences of the stimulus (Patterson, 1987). The latter would lead to nonuse of contextual information in PO. This hypothesis, however, has received little attention. Therefore, the purpose of the present studies was to evaluate PO in schizophrenia (Study 1 ) and then to determine whether a performance abnormality indicating an impairment in PO could be eliminated by a task manipulation thought to enhance top--down influences and context processing (Study 2). An additional goal of Study 1 was to determine whether PO dysfunction is found to an equivalent degree in acute and remitted patients (suggesting a stable trait), or whether it is found to a lesser degree among remitted patients (supporting a state-related phenomenon). Study 1
Method Participants Participants were 11 acutely psychotic good premorbid schizophrenia patients (GPM; 8 men, 3 women), 14 poor premorbid schizophrenia patients (PPM; 12 men, 2 women), and 14 patients with psychotic disorders other than schizophrenia (8 men, 6 women) from the psychiatric inpatient units at the University of Rochester Medical CenterStrong Memorial Hospital. An additional 10 PPM patients (8 men, 2 women ) from Strong Ties Clinic, an outpatient facility for chronic psychiatric patients, comprised the outpatient group. Individuals with a history of traumatic brain injury, seizure disorder, mental retardation, or ongoing substance abuse were excluded. The psychotic nonschizophrenic group consisted of patients with bipolar disorder with psychotic features, schizoaffective disorder, depression with psychotic features, and delusional disorder. All inpatients in this study were experiencing psychotic symptoms at the time they were tested. Patients were diagnosed by a clinical psychologist (Steven M. Silverstein or Don Kamin ) or a trained research assistant ( Laura L. West) using the Structured Clinical Interview for DSM-III-R Diagnosis-Patient version (SCID-P; Spitzer, Williams, Gibbon, & First, 1990) and chart information. Interviewers were unaware of the patient's performance on the PO task. Premorbidity status was determined by ratings on Farina's (Farina, Garmezy, & Barry, 1963; Farina, Garmezy, Zalusky, & Becker, 1962) adaptation of the Phillips (1953) scale of premorbid social adjustment, based on responses to DeWolfe's (1968) General Information Questionnaire and chart information. Phillips ratings were determined by Steven M. Silverstein, Don Kamin, and Laura L. West and were done without awareness of patient identity. Interrater reliabilityfor Phillips scores ( intraclass correlation) was .92, based on a sample of 16 General Information Questionnaires from patients in a
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SILVERSTEIN ET AL. Condition 1
3-
3-
Condition 2
3-3-3-
3-
3-3-
3-
T
Condition 3
3-
-T-
3-
33--I-
T 3- -I-
Condition 4
Condition 5
-F-I--I-
3-
3-3-
-I-3-
T
3-
3-
T q..- -1-
Figure 1. Examples of stimuli from target detection task.
different study. Schizophrenia patients with Phillips scores o f 14 or less were classified as good premorbid, and patients with scores o f 15 or greater were classified as poor premorbid (Knight, 1992; Knight, EIliott, & Freedman, 1985 ).
Medication For several reasons, we made no attempt to control patient medication. First, withdrawing patients from antipsychotic medication before testing has been shown to create disabling sampling biases. The inclusion o f only those patients who agree to be withdrawn from medication, and the loss of a subgroup o f these patients because o f relapse, coalesce to produce a sample that is not representative of the clinical population being studied (Spohn & Fitzpatrick, 1980). Second, research has generally found that medicated psychotic patients perform better than unmedicated acutely ill patients on cognitive and information processing tasks ( Spohn, 1984). In this study, all patients were receiving neuroleptic medication at doses that were considered therapeutic by their attending psychiatrists. In addition, the majority o f patients in the nonschizophrenic psychotic control group were receiving (in addition to neuroleptic medication) medications such as lithium carbonate that have been shown to impair concentration. Thus, if medication effects influenced our data, it is most likely that they made it mote difficult to confirm our hypotheses. Third, previous research has not found relationships between either oral dose or blood level o f depot medication and performance on PO tasks (Knight, 1992 and personal communication, March 1, 1992). Fourth, medicated and unmedicated patients do not perform differently on PO tasks (Rabinowicz, Knight, Owen, & Gotman, 1994), and the PO deficit has been demonstrated among unmedicated schizophrenic patients (Frith, Stevens, Johnstone, Owens, & Crow, 1983). These data suggest it is unlikely that a PO deficit could be caused or mediated by medication.
Procedure Experimental task and predicted performance patterns. After obtaining informed consent, all patients completed the information processing task. The PO paradigm used was an adaptation o f Banks and Prinzmetal's (1976) procedure. Examples of stimuli are shown in Figure 1. These arrays consist of T-F hybrid characters and either one T or one F. The patient's task is to report, after each stimulus presentation, whether a Tor an F w a s present. The arrays in Condition 1 are arranged in a "good form" (Banks & Prinzmetal, 1976; Garner, 1970), where the target is perceptually grouped with the noise elements, making it difficult to detect rapidly and requiring a serial search o f all elements. In Condition 2, the noise elements are grouped together, making it easier for the target to be isolated as a distinct perceptual group. In past research (Banks & Prinzmetal, 1976; Silverstein et al., 1992), performance among nonpatients was better in Condition 2 than in Condition 1, even though Condition 2 has more elements. Thus, organizational and configural effects override display size effects among nonpatients? In Conditions 3, 4, and 5 the target is grouped with the noise elements and is therefore more difficult to detect than in Condition 2,
where it forms its own perceptual group. The differences between Conditions 3, 4, and 5 involve controlling for the relative positioning o f target and noise elements. Conditions 3 and 4 are mirror images of each other and are typically associated with similar performance. Condition 5 is typically associated with the poorest performance because of the greatest degree of target-noise grouping. I f P P M schizophrenia patients are less responsive than other groups to configural qualities o f the stimuli, they should display either a relatively smaller difference between Conditions l and 2 than produced by controls or superiority in Condition 1 over Condition 2 (i.e., a display size effect). Similarly, if PPM schizophrenic patients are less responsive to stimulus structure-grouping than controls, they should show smaller differences between Condition 2 and Conditions 3-4 and between Conditions 3-4 and 5. The five conditions in the Banks and Prinzmetal (1976) task can be translated into four between-condition contrasts to assess the degree o f PO that is occurring: (a) Condition 1 versus 2 (a test o f display size vs. organizational effects); (b) Condition 2 versus Condition 3 / 4 (pooled; a test o f sensitivity to moderate changes in grouping o f target and noise elements with equal numbers o f elements); (c) Condition 2 versus Condition 5 (a test o f sensitivity to strong changes in grouping o f target and noise elements with equal numbers o f elements); and (d) Condition 3/ 4 versus Condition 5 (a test o f sensitivity to increasingly difficult degrees o f target-noise grouping with equal numbers o f elements). The specific hypotheses of the study can be tested by examining the interaction between the above contrasts and participant group. If these tests are significant, more specific contrasts can be performed to examine whether the differences between conditions are significantly different for PPM schizophrenia patients compared to the other groups. These can be followed by within-group contrasts to determine specifically which groups performed normally or abnormally across the critical stimulus conditions. The hypothesized performance patterns for both groups o f PPM patients compared to the other two groups can be expressed as follows. For RT: (RTcondltion i - RTconditi~ 2) for PPM < (RTcondition t - RTco~ition 2) for controls; (RTc,~aia,~ 3/4 - RTco.,aiao. 2) for PPM < (RTcondition 3/4 - RTcondition2) for controls; (RTco~a,~ 5 - RTco.~iao. 2) for PPM < ( RTconaitio~5 - RTc~iuo~ 2) for controls; and (RTco~aitio~5 RTc~dition 3/4) for PPM < (RTco,~ia,~ 5 - RTco~iao. 3/4) for controls. For accuracy (ACC): (AfC¢ondition 2 - ACfcoa~liti~ 1) for PPM < (ACCcondition 2 ACCceqadition t) for controls; (ACCco~a,,. 2 ACCcondition3/4) for PPM < (ACCconditio~2 - ACCcoadition3/4) for controls; (ACCcondition 2 -- ACCconditioa5) for PPM < (ACCcondititm2 ACCco.~tio, 5) for controls; and (mccconditioa 3/,I - ACfcondition 5) for PPM < ( ACCco~lition 3/,; - mCCcoadition 5 ) for controls. Stimulus presentation. Each of the two target stimuli (either T or F) could appear at any o f the four corners (maintaining the relative posi-
=The presence of display size effects (i.e., RTs increasing and accuracy decreasing linearly with additional elements) is usually interpreted as evidence for pure serial processing and an absence o f organizational effects.
CONFIGURATION AND CONTEXT EFFECTS tion of target to noise elements), producing eight stimuli for each of the five conditions. In each set of trials, stimuli from one stimulus condition were shown twice for a total of 16 trials. Patients were presented trials from each of the five conditions before any condition was repeated. Altogether, they were shown four blocks of five conditions of 16 stimulus presentations for a total of 320 stimulus presentations. The order of presentation of stimulus ( Tor F), stimulus location, and conditions ( 15 ) within each block was randomized for each patient. RTs were recorded for correct responses only. Each stimulus consisted of white target and noise elements against a dark screen. The boundaries of each array subtended approximately 2.75* of visual angle in height and width. 2 Patients were instructed to press the left button if they saw a T and the right button if they saw an F. The letters T or F were affixed to the left and right buttons respectively of a Gravis (Advanced Gravis Computer Technology, Burnaby, British Columbia) analog response device that interfaced with the computer through a Gravis game card. The initial trials in each condition were single Ts or Fs. After four consecutive correct responses to the single letter stimuli (a check for attentiveness), the 16 stimulus arrays from one of the five conditions were shown. Each trial began with a fixation point that was displayed for 500 ms, followed by a stimulus array and then a blank dark screen. Responses were recorded for up to 1,500 ms after stimulus onset. There was then an additional 500 ms before the onset of the next fixation point. After each set of 16 trials the computer program paused; when patients indicated that they were ready, the experimenter initiated the next set of trials. All stimuli were presented centrally. Stimulus exPosure for each of the four blocks was 100, 50, 40, and 20 ms, respectively. Stimuli were displayed on an NEC MultiSync 3D monitor in screen mode 1. Timing was accomplished using a Keithley CTM-05 clock board (Keithley Metrabyte, Taunton, MA). After completion of the perceptual task, patients completed the Shipley Institute of Living Scale Vocabulary subtest (to screen for low IQ; Zachary, 1991 ) and the General Information Questionnaire (GIQ; DeWolfe, 1968). As soon as possible after this session (usually 1-2 days later), patients were interviewed with the SCID-P, and chart information was reviewed to check for inaccuracies in the SCID-P and GIQ data.
Results Demographic Data D e m o g r a p h i c data are presented in Table 1. The four groups o f patients did not differ significantly in age, F ( 3 , 45) = .03, p > .99; IQ, F ( 3 , 43) = 1.87, p > .14; or age at first hospitalization, F ( 3 , 41 ) = . 16, p > .92. The three inpatient groups did not differ in the n u m b e r o f days they had been in the hospital when testing occurred, F ( 2 , 32) = 0.21, p > .81. Significant differences were observed in Phillips scores, F ( 3 , 44) --- 12.94, p < .0001. Differences between the G P M schizophrenia group and the inpatient and outpatient P P M schizophrenia groups were the result of group assignment. Post hoc Tukey tests indicated that the psychotic nonschizophrenia group had significantly lower Phillips scale scores than the outpatient P P M schizophrenia group (p < .01 ), but not the inpatient P P M group, and there was a trend toward higher scores compared to the G P M schizophrenia group (p < . 1 ). Although there was a significant effect o f group for total n u m b e r o f psychiatric hospitalizations, F ( 3 , 45 ) = 3.16, p < .04, no intergroup differences were significant at the .05 level. Trends (p < . 10) indicated more hospitalizations for the inpatient P P M group c o m p a r e d to the inpatient G P M and outpatient P P M groups.
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PO Data from the first presentation o f each of the conditions (i.e., Block 1 ) were considered practice and were excluded from all analyses. Performance on the PO task was analyzed with two (one each for RT and accuracy) three-way analyses of variance (ANOVAs: 4 G r o u p s X 3 Blocks x 5 Conditions), with repeated measures on the block and condition variables. Each o f the four contrasts was then conducted to determine whether significant differences between conditions existed. Following each contrast, the G r o u p × Contrast interaction was e x a m i n e d to test hypotheses that the groups would differ in their performance patterns. When this was significant, further contrasts were performed to determine whether PPM patients differed from the other groups in the manner hypothesized above.
RT RT data are graphically presented in Figure 2. These data reflect the difference between each group's RT for each condition minus the group's overall mean RT collapsed across all five conditions, weighted by accuracy in each condition. Relative RT scores were used because, using raw scores, there was a trend toward a significant main effect o f group, with the outpatient PPM group achieving longer RTs in all conditions, F ( 3, 45) = 2.45, p < .08. Whereas there were no significant group differences in raw RT in any o f the individual conditions, the mean differences in raw RT made it more difficult to visually interpret the data, whereas the use of relative RTs controls for baseline RT and more clearly reveals differences in performance patterns between groups. Because the transformation involves simply subtracting each patient's grand mean RT from the mean RT in each condition, all data analyses except the main effect o f group ( reported above) are identical when using raw or relative RTs. Prior to performing group comparisons, the RT data were explored to determine whether they were skewed, which would necessitate a further transformation to normalize the data. Shapiro and Wilk's W statistic was computed for RT data for each condition for each group. All tests were nonsignificant for the G P M schizophrenia, outpatient P P M schizophrenia, and psychotic nonschizophrenia groups, indicating that the normality assumption was not violated for any o f the RT variables for these groups. For the inpatient PPM group, the p value o f the IV statistic was between .04 and .05 for two of the five RT variables. Nevertheless, the ratios of kurtosis-standard error and skewness-standard error were within the normal range for these two variables. Therefore, overall, the data do not violate assumptions to a degree that would preclude the use o f parametric statistics or require a further transformation of the data before these statistics could be used. The main effect of block was significant, with RTs decreasing from the second to the fourth block, F ( 2 , 90) = 3.25, p < .05. The interaction effect of Block X Condition was not significant, F ( 8 , 360) = .55, p > .8. There was a significant main effect of
2 Coordinates of stimuli, as written in Microsoft Corporation (1990) QuickBASIC Version 4.5, are available from Steven M. Silverstein on request.
SILVERSTEIN ET AL.
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Table 1 Descriptive Data o f Patient Groups in Study I PPM SCZ
OP-PPM SCZ
GPM SCZ
NONSCZ PSY
Characteristic
M
SD
M
SD
M
SD
M
SD
Age IQa Phillipsb Hosps. c Ageat 1st hosp. (ns) Days ind Days oute
33.36 88.58 18.36 5.50 24.71 13.50 N/A
7.06 14.32 2.98 4.20 7.33 10.57 N/A
32.20 94.70 21.60 2.40 22.37 N/A 1,555.78
7.33 12.48 2.80 1.96 8.40 N/A 1,598.83
32.46 87.00 I 1.00 2.64 24.90 11.20 N/A
12.59 13.72 3.80 2.46 5.71 10.89 N/A
32.79 98.00 15.15 3.00 24.77 11.55 N/A
10.42 12.47 5.94 2.04 12.04 6.87 N/A
Note. SCZ = schizophrenia; PPM = inpatient poor premorbid; OP = outpatient; GPM = inpatient good premorbid; NONSCZ PSY = psychotic nonschizophrenia patient. =Estimate is based on Shipley Institute of Living Scale Vocabulary subscale scores (ns). b Phillips scale score: GPM < NONSCZ (p < . 10) < OP-PPM (p < .01 ). c Mean number of known hospitalizations (hosps.) including index episode: GPM, OP-PPM < PPM (p .83. The G r o u p × Condition interaction effect, the critical test o f this study's hypothesis, was not significant, F ( 2 , 39) = .38, p > .68. Thus, the differences between Conditions l and 2 were not different across groups in this modified version of the task wherein Conditions 3-5 were eliminated.
Accuracy Method Participants Acutely psychotic GPM schizophrenia (N = 9; 5 men, 4 women), PPM schizophrenia (N = 12; 9 men, 3 women), and psychotic nonschizophrenia (N = 21; 13 men, 8 women) patients from the same psychiatric inpatient units as in Study 1 participated in the research. Because no differences between outpatient PPM schizophrenia patients and other participants were observed in Study 1, this group was not included in Study 2. Inclusion and exclusion criteria were the same as in the previous study, as were diagnosti c and premorbidity rating procedures and 1Q estimation. There was no overlap of participants between Studies 1 and 2.
Procedure The procedure was identical to the previous study except that only Conditions 1 and 2 were included in the task. Thus, participants were shown four blocks of two conditions of 16 stimulus presentations for a total of 128 stimulus presentations. Stimulus exposure duration times for each block were identical to those used in the previous study.
There was a significant main effect o f condition, F ( 1, 39) = 5.75, p < .03. There was no main effect o f group, F ( 2 , 39) = 0.91, p > .41, and the G r o u p X Condition interaction was not significant, F ( 2 , 39) = 0.27, p > .76.
Discussion The PPM schizophrenia group demonstrated the normal pattern of organizational effects in Study 2, as evidenced by significantly faster RTs in Condition 2 than l, when Conditions 3 5 were not present in the task. This is in striking contrast to Study 1 in which organizational effects were not present, and RTs in Condition l were nonsignificantly faster than in Condition 2 in the full five-condition version o f the task. It is noteworthy that the Conditions 1 and 2 stimuli and exposure durations
590 580,
Results 570 -
Demographic Data In general, participant characteristics in Study 2 were similar to those in Study 1. The groups did not differ in age, F ( 2 , 39) = .23, p > .79. There was a significant difference in IQ, F ( 2 , 39) = 3.27, p < .05, with the G P M schizophrenia group achieving the lowest scores. Post hoc Tukey tests revealed that both the P P M and psychotic nonschizophrenia groups differed from the G P M group at t h e . 1 level only. Significant differences were observed in Phillips scale scores, F ( 2 , 38) = 8.94, p < .001. Differences between G P M and P P M schizophrenia groups were the result o f group assignment; however, the P P M group also had higher scores than the psychotic nonschizophrenia group (p < .01 ).
PO Data from the first presentation of each o f the conditions (i.e., Block 1 ) were considered practice and excluded from all analy-
• PPM SCZ • GPM SCZ ~ O N - S C Z PSY
560
-'
550
--
.¢::: ~:
540 530
-
520 Condition in Target Detection Task
Figure4. Mean reaction time (RT) by group by condition in the modified, two-condition version of the target detection task. PPM = poor premorbid; SCZ = schizophrenia; GPM = good premorbid; PSY = psychosis.
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S1LVERSTEIN ET AL. 95-
¢O O
•
PPM SCZ
•
GPM SCZ
•
NON-SCZ PSY
90
ss
N 75 2
Condition in Target Detection Task Figure 5. Percentage correct by group by condition in the modified,
two-condition version of the target detection task. PPM = poor prernorbid; SCZ = schizophrenia; GPM = good premorbid; PSY = psychosis.
were identical across the two studies. Therefore, this reversal cannot be accounted for in terms of stimulus differences. Instead, it is hypothesized that the normalization of PO in Study 2 was due to the development of top--down influences to perceptual processes among PPM schizophrenia participants. They appear to have been able to attend rapidly to the isolated target in Condition 2 after elimination of similarly structured stimuli (i.e., Conditions 3-5) that required a different processing strategy. By changing the task so that the response of directing attention to the small element was adaptive 100% of the time in the 7-element arrays (i.e., in Condition 2 only), as opposed to only 25% of the time (i.e., among Conditions 2-5 in Study 1 ), PPM schizophrenia participants were able to apply consistently a processing strategy wherein PO occurred. General Discussion Study 1 provides further evidence for a PO deficit in schizophrenia that is most pronounced in patients with a history of PPM functioning. Study 2 indicates that a pattern of performance indicating a PO deficit can be eliminated through task manipulations. Other investigators have reported attenuation or elimination ofa PO deficit by increasing the salience of those stimulus components requiring grouping (Cox & Leventhal, 1978; Rabinowicz et al., 1992). The present data suggest that reversals can also be accomplished by altering task conditions to heighten recognition of stimulus context. This is thought to encourage the development of top--down feedback to perceptual • processes (Kosslyn & Koenig, 1992), wherein attentional resources are consistently allocated to processing global aspects of stimuli and the use of global information to determine the subsequent focus of attention. The greater PO impairment in PPM schizophrenia inpatients compared to outpatients suggests that the PO deficit is both a trait variable in that it has been found among both PPM schizo-
phrenia inpatients and outpatients in past studies, and a state variable, in that the deficit appears to be more pronounced in acutely psychotic patients. Clarifying the manner in which the PO deficit is related to schizophrenia in general and disruptions associated with florid psychotic symptoms in particular should be an important goal of future research. Ongoing studies in this laboratory are attempting to determine more precisely the relationship of PO dysfunction to course of illness, clinical state, and specific symptom clusters within schizophrenia. Future studies should clarify the sequelae of the PO deficit in schizophrenia. For example, this deficit may reduce access to object-related semantic information. Among controls, access to semantic information proceeds automatically when attention is fixed to global information about the form of an object (Boucart & Humphreys, 1994; Boucart, Humphreys, & Lorenceau, 1995). As a result of their PO deficit, individuals with PPM schizophrenia may be characterized by interference in accessing semantic information about objects, thus causing the slowness in the processing of meaning found by Knight (1992). In addition, if object parts, rather than the full objects themselves, are defined as "figure" relative to "ground," this may lead to activation of memory representations and semantic information about different objects, leading to inappropriate verbal associations to the objects being perceived. Data from the present study suggest several areas for further exploration of the PO deficit. For example, our data suggest impairment in context processing in PO tasks among schizophrenia patients. Further evidence for this would be demonstrated if, on versions of the Banks and Prinzmetal (1976) task that systematically reintroduced Conditions 3, 4, and then 5, the performance of PPM schizophrenia participants in Conditions 1 and 2 reverted back to a display size effect in a linear fashion as each condition was added. Also, it is typically assumed on the basis of two-stage models of visual perception (Broadbent, 1977; Duncan, 1984; Kahneman, 1973) that an impairment in PO leads to relatively random subsequent processing of details (i.e., inefficient serial processing). The temporal course of visual information processing in schizophrenia, however, has not been directly investigated. In light of recent data suggesting inadequacies in traditional two-stage models, investigations of the ways in which the normal interaction of global and serial processes is abnormal in schizophrenia appear worthy of undertaking. The use of more naturalistic stimuli in PO experiments (Venturino & Gagnon, 1992) would also add external validity to the now compelling set of laboratory studies using conventional visual primitives such as lines and shapes. Finally, attempts to integrate findings from PO and other paradigms can lead to greater conceptual clarity regarding the nature of information processing dysfunction in schizophrenia. Data from these two studies overlap conceptually with some of the older RT literature in suggesting a schizophrenia related disturbance in establishing a "major set" (Shakow, 1963) during task performance. In addition, the normalization of PO in Study 2 is reminiscent of Kaplan's (1974) temporary elimination of the RT crossover effect in schizophrenia patients after giving them training in time interval estimation, a form of context processing relevant to that task (Cromwell, 1975; Nuechterlein, 1977). The data from this and other PO studies
CONFIGURATION AND CONTEXT EFFECTS also share commonalities with the latent inhibition literature, in that loss o f latent inhibition is most associated with the acute stage of the illness and has been attributed to a reduced organization of current sensory input caused by the weakened influence o f past regularities (Baruch, Hemsley, & Gray, 1988; Gray et al., 1991; Lubow, Weiner, Schlossberg, & Baruch, 1987; Nuechterlein & Green, 1991 ). Attempts to determine relationships between performance on these paradigms, as well as more sensory-based information processing tasks (e.g., prepulse inhibition) may help to untangle the complex interactions among basic and higher level processing dysfunctions associated with schizophrenia.
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