0022-3956/78/1001-0035502.0010

J. psychiaf. Res.. 1978. Vol. 14, pp. 3545. 0 Pergamon Press Ltd. Printedin Great Britain.

INFORMATION

PROCESSING

STAGES

IN SCHIZOPHRENIA

JULIUS WISHNER and MARSHA K. STEIN

and AUGUST L. PEASTREL Department of Psychology, University of Pennsylvania, Philadelphia, Pennsylvania, U.S.A. Norristown State Hospital, Norristown, Pennsylvania, U.S.A.

General background FROM

Kraepelin on, and perhaps before, investigators have been intrigued by the slowness of schizophrenics as one reflection of their disorder. The modern history can be said to begin with the Worcester group,l,z starting with the work of SHAKOW and HUSTON3 and extending to the current scene.4*5 Ignoring minor exceptions, it is a universal finding that schizophrenics are slower than controls, with the smallest differences appearing in simple reaction time (RT) at very short preparatory intervals. The details of the relevant experiments have been reviewed extensively.6-8 Most germane to our current concerns are the hypotheses offered to account for the results. In general, they concentrate on input dysfunctions. Thus, SHAKOWg proposed that retardation of RT resulted from the inability of the schizophrenic to maintain the major set required by the situation, with the concomitant arousal of erratic minor sets. WISHNER~~ has argued that the “segmental set” theory is a special case of inefficiency in schizophrenic behavior, which is generally diffuse in relation to task requirements. MCGHIE” emphasized attentional dysfunction localized at the filtering mechanism postulated by BROADBENT.‘~,~~ At the physiological level, VENABLES 14.15 adduced evidence to support a theory of extreme levels of arousal as accounting for the variability of schizophrenic performance. None of these theories are sufficiently precise to generate critical experiments. It is not surprising, therefore, that the overall results of the research undertaken to test them are inconclusive.7 The most detailed attempt to deal with attentional dysfunction in schizophrenia has been that of YATES.16 He proposed that there are four “levels” at which dysfunction can occur in schizophrenic information processing: receptor, data processing, cognitive, and motor. These look very similar to the stages proposed by Sternberg. Indeed, there is reason to view Yates’ idea as a first approximation to the more refined and operationally precise paradigm of Sternberg. Yates’ theory has been criticized precisely for failing to prescribe experiments which could lead to clear-cut conclusions ,17 for whatever dysfunctions are found at any of his “levels” could originate at any other level. No paradigm is provided for identifying loci of dysfunction. Sternberg’s paradigm, as will be seen below, is not subject to such criticism.

35

36

JULIUS WISHNER, MARSHA

K.

STEIN

and

AUGUST

L.

PEASTREL

Sternberg’s paradigm

As a result of a series of experiments (for original experiments, see STERNBERG~*,~~ - fat summaries and theoretical development, see STERNBERG 20~23).Sternberg postulated four stages in information processing, as shown in Fig. 1. Further, he has specified a set of experimental operations which affect each of the stages exclusively (top line of Fig. I), so that appropriate experimentation can yield information concerning specific loci of effect on RT.

(2) SIZE OF POSITIVE SET __7_____-T--_---~__--_;~___

1 STIMULUS

W+ESFWSE TYPE (PCISITIM OR NEGATIVE J

1

14) RELATIVE FREWEHC( OF RESPONSE

1

STIMULUS

RESPOME

ENCODING

FIG. 1. Processing stages in binary classification. Above the broken line are shown the four factors examined. Below the line is shown the analysis of RT inferred from additive relations between factor pairs l&2, l&3, 2&3, 2&4, and 3&4, the linear effect of factor 2, and other considerations described in the text. The quality of the test stimulus influences the duration of an encoding stage in which a stimulus representation is formed. This representation is then used in a serial-comparison stage, whose duration depends linearly on size of positive set; in each of its substages the representation is compared to a memory representation of one member of the set. In the third stage a binary decision is made that depends on whether a match has occurred during the serial-comparison stage that precedes it; its mean duration is greater for negative than for positive decisions. The selection of a response based on the decision is accomplished in the final stage whose duration depends on the relative frequency with which a response of that type is required. (Copied from Sternbergzl, Fig. 6).

A paradigmatic experiment is as fo 110~s: (a) the subject memorizes a set of digits; (b) a test digit is then presented; (c) if this digit is a member of the memory set, the subject responds in one way; if it is not, he responds in another. The measure is RT, measured from time of onset of the test stimulus to time of response. Sternberg has shown the operational effects of the independent variables at the top of Fig. 1 on each of his postulated stages. Thus, manipulating stimulus quality, e.g. intact vs degraded stimuli, affects RT via retardation of encoding with degraded stimuli, but affects no other stage. Varying the size of the memory set affects speed of comparison of the stimulus serially with the items in the memory set. The presence or absence of the stimulus in the memory set affects decision time, absence resulting in longer RT, but again, without interaction with either stimulus quality or memory set size. Finally, the relative frequency of presentation of members of the positive set affects a translation and response organization stage, the greater the frequency the shorter the RT. Sternberg’s additive-factor model provides for a test of whether a variable affects only one stage of the RT process or more than one stage, by testing for interaction between factors. It is precisely this power of the model and paradigm that is the focus of this research program. Application of Stemberg’s

paradigm to schizophrelliu

Suppose we introduce the variable, paradigm outlined above. The questions

schizophrenia are:

vs control,

into

the experimental

INFORMATION PROCESSING STAGES IN SCHIZOPHRENIA

37

1. Does schizophrenia simply add a processing stage (perhaps negativistic or withdrawn attitudinal stage prior to encoding) or cause simple delay without affecting any other stages? (i.e. there is no interaction between schizophrenia and any of the other factors, but it retards RT.) 2. Does schizophrenia are found.

affect one or more of the other stages? i.e. one or more interactions

3. Are both additive (main effects) and interaction

effects present?

The only previous attempt to apply Sternberg’s paradigm to study schizophrenia is that of Checkosky.* He studied chronic schizophrenics, acute schizophrenics and alcoholic controls using letters, digits, geometric figures and colors. He varied intactness (implicating the encoding stage), memory set size (implicating the serial comparison stage), and presence vs absence (implicating the decision stage). In all cases there were significant main effects, i.e. differences in intercept between the three groups, but no differences in slope. In brief, for acute and chronic schizophrenics, Checkosky found no evidence of qualitatively different functioning from controls in the first three stages of Sternberg’s model. For example, with respect to memory set size, the extrapolated intercept at zero set size for chronic schizophrenics was 705 msec with a slope of 35 msec/item for acute schizophrenics, the respectice ligures were 598 and 35; for alcoholics 488 and 34. The equivalent figures for Sternberg’s subjects were 367 and 39. One apparent exception to this conclusion has been reported by YATES and KORBOOT,~” who studied inspection time as a function of “complexity” of stimuli (akin to set size in the current study), using three types of materials (lines, words, symbols) in four groups of schizophrenics and two groups of neurotics. Unfortunately, they reported only log transformations of their real time data. As STERNBERG~~has pointed out, additivity is in general destroyed by nonlinear transformations. He therefore specified the use of real time as the datum for all calculations. It is extremely difficult to interpret the YATES and KORBOOT data in the current context. Although an interaction between type of schizophrenia and set size appears to be implied, it must be remembered that their experiment does not fit in the memory search paradigm. Their analysis of variance (on transformed data only) indicates also an interaction of diagnosis by type of stimulus material. Although type of material has been shown to be implicated in schizophrenic performance in various types of experiments,25,*6 it is by no means certain that it will constitute either an interactive or additive factor in the STERNBERGparadigm. It may simply affect one of the stages in the model; the serial comparison stage is a likely candidate. However, Checkosky’s data do not support even this notion, in that he found no interactions regardless of type of material. Thus, the use of log transformations by Yates and Korboot may be responsible for statistical interactions even when none may exist in untransformed data. Checkosky’s data show no interactions between diagnosis and any of the factors implicating the first three stages. The fourth stage, translation and organization of the response, was not tested. Analysis of the experimental literature on output dysfunction in schizophrenia indicates that the omitted stage may be important in differentiating schizophrenics from normals. *Unpublished

data kindly made available to us by Dr. Stephen Checkosky.

38

JULIUS WISHNER, MARSHA K. STEINand AUGUST I-. PEASTREL

For example, HOLZMAN et u/.27,28 have described two experiments in which the subject is required to look at a moving pendulum while his eye movements are recorded. Fifty-two percent of their “recent” schizophrenics, and 86 o/;;of their chronic schizophrenics showed deviant eye-tracking, compared to 22 % of the manic-depressives, 21 % of nonpsychotic patients, and 8 7; of a normal control group. Moreover, 44’%; of the relatives of schizophrenics but only 10% of the relatives of nonschizophrenics showed this phenomenon. The authors concluded that it was quite unlikely that the results were attributable to motivational and set variables. Rather, they point to the implication of the muscles themselves and their neural control mechanisms.‘” At a directly physiological level, MELTIZER and his associates?“-31 have examined enzymatic and structural changes in the musculature of acutely psychotic patients and conclude that both myopathic and neuropathic components are involved. At the level of organization of memory, BAUMAN and KOLISNYK~~~~~ concluded that output interference had a more profound effect on the recall of schizophrenics than input interference. In one of their experiments33 subjects learned 35 different 7-digit lists one at a time. Different serial positions were probed randomly after each list. When the interference was of the input variety, resulting from the interpolation of iten~s between presentation and recall of the probed item, the results were the same for both groups. But when the interference was of the output, resulting from the interpolation of YeS/TO/I.ye,s between presentation and recall, the schizophrenics were significantly poorer than controls. They concluded that “output interference is the major causative factor in the schizophrenic recall deficit”. In a similar vein, WISHNER and WAHL,“4 in a dichotic listening task, showed that at very slow rates ofpresentation, schizophrenics and controls did not differ significantly in accuracy of shadowing. At the same time, in later recall and recognition tests, schizophrenics show marked inaccuracy in differentiating between the shadowed and distractor words. Thus, it was inferred that the dysfunction noted had to be beyond the input stage. Thus, Checkosky may have omitted a critical variable in his survey of Sternberg’s paradigm as it applies to schizophrenia. In the present study, a variable was included with the intention of testing for differences in psychomotor functioning. In addition, it was decided to sample paranoid and nonparanoid schizophrenics, in view of the usual findings that paranoids function at a level between nonparanoids and normals. In terms of the Sternberg paradigm, we were interested in whether this represents quantitative differences in intercepts, or whether we will find differential slopes, indicating different loci of dysfunction. Spec#ic aims qf the,first espcrimcnt The present study was designed to examine the information processing of paranoid and nonparanoid schizophrenics over the last three Sternberg stages: serial comparison, binary decision, and translation and organization of the response. The factors varied were the size of the positive set (2, 3 or 4 digits), response type (positive or negative), and the number of hands used in responding (1 vs 2). The task was memory search and the fixed set procedure was used. As a test of the translation and response organization stage, 1 vs 2 hands was *See Holzman’s contribution

to this volume for a possible reinterpretation.

39

INFORMATION PROCESSING STAGESIN SCHIZOPHRENIA

chosen over relative frequency, the usual factor varied for this stage. The manipulation of the latter variables has been shown in one study to influence the encoding stage as well as the translation and response organization stage. 35Based on pilot data, 1 vs 2 hands appeared to be a clearer measure of at least one aspect of the final stage. This, along with the other stages, are always subject to further analysis and breakdown into several stages, as Sternberg has recognized. Subjects. The subjects were 10 nonparanoid schizophrenics, 10 paranoid schizophrenics, at Norristown State and 12 alcoholic control subjects. * They were drawn from populations Hospital, Norristown, Pennsylvania. Alcoholics were chosen to control partially for the effects of institutionalization and for effects not specific to the schizophrenic process which might occur generally in any psychopathological group. 36 Criteria for selection of subjects were: (1) male; (2) right-handed; (3) age: 18-55 years; (4) race: white; (5) education: minimum of 8 years; (6) no electroconvulsive shock treatments within 3 months of testing; (7) no brain damage or mental retardation; (8) paranoid schizophrenics must display an organized delusional system.

The selection of schizophrenics proceeded as follows: the third author reviewed the computer printouts of the patient population, which include staff diagnoses, and selected likely candidates. He made initial contact with ward administrators and patients and obtained the necessary consents. The patient was then interviewed by two of us. The object of the interview was to establish whether there existed an obvious schizophrenic syndrome, including thought disorder, and, if so, whether organized delusions existed. If there was disagreement on the diagnosis, the patient was excluded. The patient was also excluded if he did not meet any of the criteria above. If the patient passed this test, all existing data on him was consulted, with his consent. The patient was included if there was agreement that the interview, case record, and psychological studies (when available) supported our diagnosis. The mean ages for the groups were: paranoids

33, nonparanoids

34, alcoholics

39.

Almost all schizophrenics in the hospital are on antipsychotic medication, primarily phenothiazines. However, two studies37,38 concerned with the effects of phenothiazine medication on performance of psychomotor tests showed little difference before and after drugs. The study which included a reaction time task37 found a decrease in variability, but no change in mean speed. In any case, there is no apriori reason to expect these drugs to affect slopes differentially. The subjects were paid $lO*OO for their participation in the experiment, session and the balance at the completion of the experiment.

$1.00 after each

Apparatus. Thetest stimuli were digits mountedon 35mmslides.Thedigits,whenprojected onto a screen, were 2.5 cm tall. The apparatus included two tables on one of which was mounted a screen and a track with two movable telegraph keys. The track was mounted on a board whose position could be adjusted by the subject. The subject was told to rest his fingers lightly on the keys. The travel of the telegraph keys was 0.09 cm and their tension was approximately 125 gm. Surrounding the screen were lights whose illumination served as the warning stimulus. The second table, in back of the first and separated by the screen, held *The full design calls for 12 per group (see addendum).

40

JULIUSWISHNER, MARSHA K.

STEIN and AUGUST L. PEASTREL

a projector, a shutter, a digital counter which recorded RT in msec., and two lights indicating the nature of the subject’s response. Trial events. A trial consisted of the following events: (1) an intertrial interval of 4 set, (2) warning signal (illumination of lights) for 1.25 set, and (3) display of the test stimulus for 3 set whether or not the subject responded. Set selection. The positive memory sets were composed of 2,3 or 4 digits. Each group of 6 subjects received a different group of memory sets. The sets were selected using a table of random numbers, picking 2, 3 or 4 digits from the table. Obvious patterns, for example ail even or odd, were excluded. Once selected, the positive sets for a given set size were balanced so that all digits were represented more or less equally. The digits 2 through 9 were used in composing the memory sets and as test stimuli. Zero and 1 were excluded, since experience indicates that responses to these numbers tend to be faster than to the other digits. For each group of set sizes 2 through 4 presented to each subject, one digit was not represented and two digits were represented twice. For example, Subject 1 received, in different sessions, the memory sets 29, 378, and 2469. Here, the number 5 is excluded and the numbers 2 and 9 are repeated. The numbers excluded and repeated differed for each subject. Stimulus selection. A number of lists consisting of the digits 1 to 24 in random order was generated by a computer. Each test session was composed of 144 trials divided into 6 blocks of 24 digits each. The order of the digits presented in each of these blocks was determined by matching each digit with one of the numbers, I to 24. The number to which the test digit was matched determined its place in the trial block. Two further constraints were applied to the order of the stimuli: (1) no digit was presented consecutively more than 3 times, and (2) no more than 3 of the same response types occurred consecutively. Procedure. It was intended to test each subject twicea day for 6 sessions over aperiod of3 successive days. This was not possible in the case of 6 subjects, whose sessions were extended over 1 or more extra days when their schedules interfered. Each session lasted 35 min to 1 hr, and the sessions were separated by at least 2 hr.

At the beginning of each session, the subject was given an index card with the members of the positive set. After stating that he had memorized the numbers, the subject was presented with a set of cards, one digit per card, which he was instructed to sort into two piles, one containing the positive and the other, the negative numbers. If the subject made a mistake, he was asked to sort the cards again. This was repeated until the subject sorted the cards perfectly. Each session was composed of 24 practice trials and 144 test trials. informed of his errors during the practice trials to further insure that memorized the numbers. The subject was stopped during the test trials number of errors. If this occurred, the subject was asked to repeat the memorized and then indicate the appropriate key response. The 144 test trials were divided into 3 memory set appeared half of the time. The were maintained within each 24-trial block. when further information and instructions after each block of 48 trials. The sub.ject

The subject was he had correctly if he had made a numbers that he

blocks of 48 trials each. The members of the frequencies of the positive and negative stimuli There was a short break after the practice trials were given and approximately a 2-minute break was asked to respond as fast as possible while

41

INFORMATION PROCESSING STAGESIN SCHIZOPHRENM

maintaining accuracy. Any error trials were repeated at the end of each block of 48 trials. Records of errors were kept. One digit was presented on each trial of the experiment. The subject decided whether or not the digit was a member of the positive set. He then pressed 1 of 2 keys. In the l-hand condition, half of the subjects responded to the positive set with their right hand and half with their left hand. Within the l-hand condition, half of the subjects responded “yes” with their index finger and “no” with their middle finger. This was reversed for the other half of the subjects. In the 2-hand condition, half of the subjects responded to the positive set with the index finger of their right hand and to the negative set with the index finger of their left hand. Again, this was reversed for the other half of the subject. RESULTS

AND

INTERPRETATIONS

Between groups Mean error rates were 0.77 % for alcoholics, 3.04 % for paranoids, and 1.84 % for nonparanoids, indicating the possibilities for valid RT results from these groups. A summary of the results of the analysis of variance of RT is given in Table 1. TABLE 1. SUMMARY OF RESULTS OF ANOVA OF RT

Schizophrenic Group Separately

df

Variable Diagnosis (D) Set Size (S) Positive-Negative Hand (H) DxS DxP-N DxH SxP-N SxH P-NxH DxSxP-N DxSxH DxP-NxH SxP-NxH DxSxP-NxH

(P-N)

2,29 2.58 1;29 1,29 4,58 2,29 2,29 2,58 2,58 1.29 4;58 4,58 2,29 2,58 4.58

F 3.81 23.25 30.73 1.28 1.47 1.50 0.24 0.17 0.53 5.04 0.10 0.73 0.54 2.75 0.76

P 0.03 0~0001 00IOl 0.27 0.22 0.24 0.79 0.84 0.60 0.03 0.98 0.58 0.59 0.07 0.55

Schizophrenic Group Combined

df 1,30 2,60 1,30 1,30 2.60 1;30 1,30 2.60 2;60 1.30 2160 2,60 1.30 2;60 2.60

F 7.32 23.09 31.72 1.33 1.72 3.03 0.48 0.18 0.55 5.19 0.10 1.37 1.02 2.76 0.62

P 0.01 oxtOO 0~0001 0.26 0.18 0.09 0.50 0.83 0.59 0.03 0.90 0.26 0.32 0.07 0.55

The results of central interest are those involving interactions of diagnosis by the other independent variables. These are illustrated in Fig. 2. There were no significant interactions involving diagnosis; i.e. the slopes for the schizophrenics were not significantly different from the slopes for the alcoholics. Since the paranoid and nonparanoid schizophrenics were not significantly different from each other, their data were combined, and these results are shown in the right half of Table 1 and by the dotted lines in Fig. 2. Again, there were no significant interactions involving diagnosis. There were significant main effects for the groups; i.e. intercepts of the schizophrenics

JULIUSWISHNER, MARSHA K. STEIN and AUGUST L. PEASTREL

42

FIG.

2.

TR

m

A-Alcoholics

N=l2

c

.

F -Poranolds

N=lO

------

as a function

of the independent

NP

Non-Pxonolds

N=IO

P and NP combixd

variables

and their interactions.

were significantly different from that of the alcoholics. Thus, as is usually the case, schizophrenics were slower than controls. The significant interaction of hands by positive (P)-negative (N) results from a mean difference of 37 msec between P and N with 1 hand responding, as compared to a mean difference of 63 msec with 2 hands responding. Such an interaction indicates that the hand factor may be affecting the third stage (Fig. I) in Sternberg’s model, but in view of our failure to find this with college students in our pilot work, further speculation appears hazardous. The tendency of paranoids to be slower than nonparanoids seen in Fig. 2, although not significant, may reflect our diagnostic procedure. It will be recalled that overt evidence of a delusion was required to justify classification as paranoid. It may well be that this requirement (in the face of medication) selected for a greater intensity of disorder. From the standpoint of our central interest in differential slopes between groups, the results are negative. In the stages thus far surveyed by Checkosky and LIS,there is no evidence of a different mode of functioning for schizophrenics in the type of information processing tested by these methods. Within

groups

As a further check on the applicability of the Sternberg method to our groups, analyses of variance were carried out for each group separately. In all three groups, the analyses yielded significant main effects for set size and P-N, none for hands, and no significant interactions. Thus, the classical factors, set size and P-N, yielded the standard results, while our innovation, the hand factor, showed no significant effects, despite positive indications in our pilot results. It must be concluded that 1 vs 2 hands is too weak a variation to affect significantly the fourth stage, as was intended. This may be due to the fact that this factor samples fine motor activity, whereas reports of motor dysfunction in schizophrenia emphasize patterned, gross motor activity. In all, possible schizophrenic dysfunction in the fourth stage of the model remains untested.

INFORMATION PROCESSING STAGESIN SCHIZOPHRENIA

43

By individuals

The number of trials for each individual is sufficiently large to enable analyses of individual results. To make these useful requires matching of the experimental performance to clinical status. This aspect of the analysis is not yet complete, and we shall reserve it for the full report on the completed experiment. DISCUSSION Within the limits of the methods and materials utilized to this point, the results indicate that there is no special dysfunction of schizophrenics in the serial comparison and binary decision stages, the second and third stages in Sternberg’s model. In these respects, this is a replication of Checkosky’s results. Checkosky has also shown convincingly that there is no special dysfunction in the first stage, encoding. Our attempt to test the fourth stage, translation and organization of the response, must be considered unsuccessful. It might be useful to attempt to experiment with Sternberg’s factor for the fourth stage, relative frequency, as well as with a stronger psychmotor variable, which would implicate gross movements. The intercept differences remain unexplained in ways other than the theories outlined in the introduction to this report. It may well be that we are dealing with an overall disorganization factor in schizophrenia which is not specific to any stage of information processing in short term memory experiments; thus, the greatly raised intercepts. Before accepting such a conclusion, however, it would seem wise to eliminate decisively the possibilities of the sorts of more precise analyses offered by modern cognitive psychology. There are the suggestions offered above, as well as other potentially fruitful approaches. For example, there is every reason to attempt to study the effects of distraction on information processing using visual stimuli, analogously to what has been done in the aural mode.34 In our laboratory, we are proceedin, 0 in this direction via visual stimuli with built-in distracters. In view of the focus of this conference, such manipulations seem natural to try. In any case, systematic, step-by-step attempts to analyze the schizophrenic retardation in RT, utilizing the techniques made available to us by cognitive psychology, as well as others yet to be invented, would appear to be the surest road to a psychological understanding of this phenomenon. The scattered attempts thus far, while laying some foundation, seem destined to leave us in puzzlement, if continued in unsystematic fashion. ADDENDUM

AS OF MARCH

1977

The experiment has now been completed. Analysis of the data according to the scheme detailed above yielded results identical in significance levels to those reported. However, additional analysis revealed one positive result and one trend of interest. The trend is for more schizophrenics (13 of 24) than controls (3 of 12) to be slower with two hands than with one. Although not significant statistically, we are inclined to place some weight on this trend because in a subsequent study by Jacqueline Persons with female schizophrenics, the proportion of patients and controls exhibiting slower RTs with two hands was quite similar: 4 of 8 and 1 of 8 (with 1 equal), respectively. The modal difference among these patients was about 100 msec; for the controls it was about 10 msec.

JULIUS WISHNER, MARSHA K. STEIN and AUGUST L. PEASTREL

44

The positive result arose from dividing the schizophrenics and controls into fast and slow RT groups at their respective medians for mean RT over all conditions. Mathematically, mean RT is independent of the slope for any condition. A significant interaction (p

Information processing stages in schizophrenia.

0022-3956/78/1001-0035502.0010 J. psychiaf. Res.. 1978. Vol. 14, pp. 3545. 0 Pergamon Press Ltd. Printedin Great Britain. INFORMATION PROCESSING S...
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