Normalizing the crossover effect: enhancement of cognitive attentional processing in schizophrenia

PSYCHIATRY RESEARCH ELSEVIER

Psychiatry Research 72 (1997) 167-176

Normalizing the crossover effect: enhancement of cognitive attentional processing in schizophrenia Gerald Rosenbauma,ba*, Michael J. Taylora, Gayane J. Minasianb aDeparh2ent of Psychiatry, University of California Medical School, La Jolla, CA 92093, USA bDeparmtent of Psychology San Diego State University, San Diego, CA 92120, USA

Received 28 January 1997; revised 8 April 1997; accepted 13 August 1997

Abstract Thirty male schizophrenic subjects Shakow reaction time (RT) procedure

and 20 male control subjects and a modified experimental

were administered both the classic Rodnick and procedure using a balanced design in an attempt

to enhance cognitive attentional processing and inhibit the crossover effect in schizophrenic patients. The experimental procedure increased the number of predictable trials, provided more information about the task and presented the regular trials in a simple ascending order. Analysis of the RT data showed the typical early schizophrenic crossover and late normal crossover on the standard task, while schizophrenic patients in the experimental condition showed a new finding of statistically significant normalization of the early crossover effect. The results support Shakow’s theory of attentional set deficit in schizophrenia and in conjunction with previous findings suggest that separate neuropsychological mechanisms of cognitive preparatory attention and a more automatic form of vigilance attention may, respectively, underlie the regular and irregular procedures of the traditional RT task. 0 1997 Elsevier Science Ireland Ltd. Keywords:

Schizophrenia;

Neuropsychology;

Cognition; Reaction time

*Corresponding author, SDSU/UCSD Joint Doctoral Program in Clinical Psychology, 6363 Alvarado Court, Suite 103, San Diego, CA 92120-4913, USA. Tel.: + 1 619 5942838; fax: + 1 619 594-6780. 0165-1781/97/$17.00 PZZSO165-1781(97)00100-5

0 1997 Elsevier

Science

Ireland

Ltd. AI1 rights reserved.

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1. Introduction The classic Rodnick and Shakow (1940) reaction time (RT) procedure for studying schizophrenic deficits in attention has identified early RT crossover as a robust and sensitive indicator of schizophrenic pathology (Nuechterlein, 1977; Nuechterlein and Dawson, 1984) and as a possible marker of schizophrenia (Chapin et al., 1987, 1996; Rosenbaum et al., 1988). This crossover deficit refers to the inability of schizophrenic individuals to benefit from the predictability of regular temporal preparatory intervals (PIs) compared with irregular unpredictable PIs when the PI duration exceeds 4 s. The crossover effect was originally reported in the Huston et al. (1937) study of schizophrenic and normal finger-lift RTs to an auditory stimulus presented at PIs of 0.5, 1, 2, 3, 5 and 10 s in a regular predictable serial order and an irregular unpredictable order of presentation. The term crossover refers to the finding that, when RTs were graphed as a function of PIs, the curve for schizophrenic RT latencies on the regular order tended to rise from the short PIs and to cross over the curve for the irregular PIs before the 5-s PI. Normal subjects showed a rising latency curve on the regular order, but the curve did not cross over the irregular curve. In 1940, Rodnick and Shakow investigated simple RT to a visual stimulus in schizophrenic and normal subjects. They extended the series of PIs out to 25 s and again found early crossover in schizophrenic patients at a PI of less than 7.5 s, while normal subjects also showed a crossover of the regular and irregular curves, but only at PIs longer than 20 s. The crossover paradigm has also proved to be a useful tool for investigating attentional brain mechanisms in epilepsy and schizophrenia. Greiffenstein et al. (1981) found the classical crossover deficit in schizophrenic and temporal lobe epilepsy (TLE) patients, but not in patients with generalized seizures (GSP). More recently, Goldstein et al. (1997) replicated these findings, but also showed that the GSP group displayed a deficit on the continuous performance test (CPT) that was not found in TLE, schizophrenic patients, or normal participants. The CPT findings con-

Research 72 (1997) 167-I 76

firmed prior reports of specific vigilance deficits on the CPT in GSP when compared to normal subjects and focal seizure groups (Mirsky et al., 1958, 1960, 1991; Kimura, 1964; Lansdell and Mirsky, 1964; Fedio and Mirsky, 1969). These results support a double dissociation hypothesis between cognitive expectancy (crossover) and sustained vigilance (CPT) forms of attention associated with two neuroanatomically distinct systems. The TLE and schizophrenic groups showed an inability to maintain a regular motor set on the predictable regular RT task (i.e. crossover effect), a cognitive expectancy process most likely dependent upon intact, anterior cortical functions. GSP and some schizophrenic patients displayed impairments in sustaining vigilant continuous attention to external stimuli (i.e. CPT deficit reflected in increased errors of omission), a more automatic attentional process likely dependent upon the integrity of subcortical arousal centers. In a previous attempt to explicate the mechanisms involved in the classic crossover effect, Rosenbaum and Taylor (1996) successfully demonstrated the experimental induction of early crossover in normal college students. In a dual task paradigm, participants were required to perform a simple version of the CPT during all regular and irregular PIs of the RT task. Under these conditions, normal subjects showed an early mean crossover of 8.01 s, which was very comparable and not significantly different from either the schizophrenic crossover of 8.36 s on the standard task found in this experiment, or the typical schizophrenic crossover means found in many other studies, including the original Rodnick and Shakow (1940) crossover of the regular and irregular curves at 7.00 s. These findings suggested that the additional cognitive processing required by the dual task procedure prevented normal students from maintaining the high level of preparatory set on the regular procedure that would typically lead to faster RTs and late crossing over of the slower irregular PI curve. The authors hypothesized that the ability to sustain heightened cognitive attention utilizing cortical functions during predictable regular PIs is impaired in normal subjects when they are required to attend simultaneously to a second task during

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the PI, and in schizophrenic subjects who are characterized by a basic marker deficit in the ability to take and maintain this cognitive set. This hypothesis regards early crossover in schizophrenic patients as a failure to keep the high level of cognitive attention required for rapid RTs on the regular PIs resulting in a return to the more automatic level of perceptual vigilance characteristic of the slower RTs found on the irregular procedure and on the very long regular PIS. The present investigation was designed to extend this hypothesis by attempting to experimentally induce later, more normal crossover in schizophrenic patients by providing additional cognitive information to enhance an expectancy set on the regular predictable trials. While the crossover effect has shown extremely consistent replication in studies of schizophrenia (Bellissimo and Steffy, 1972; Nuechterlein, 1977; Rist and Cohen, 19911, very few studies have tried to normalize this RT deficit. An early study by Rosenbaum et al. (1957a) using a foreshortened modification of the Rodnick and Shakow task showed that when an electric shock was emitted by the response key at the same instant as the reaction signal, schizophrenic RTs were normalized, but no significant effects on crossover were obtained. Using the Bellissimo and Steffy (1972) embedded set procedure, Steffy and Galbraith (1974) showed a decrease in the amount of crossing over in process schizophrenic subjects by introducing longer intertrial intervals presumably permitting greater dissipation of reactive inhibition between trials, but no difference in the point of very early crossover was produced by this experimental manipulation. Steffy and Galbraith (1980) also were able to produce a significant decrease in RT latencies on the embedded set procedure by use of verbal and monetary reward speed training with process schizophrenic subjects, but a strong form of the crossover pattern was found in posttraining performance. Proceeding from a cognitive rehabilitation perspective, Olbrich and Mussgay (1990) assessed the effects of a cognitive training procedure in reasoning, concept formation and recall on schizophrenic performance of complex and elementary tasks. This 3-week training program improved performance on complex

cognitive tasks (e.g. embedded figures test, letter cancellation), but not on elementary tasks including the crossover RT paradigm. The present study proposed to modify the crossover attention deficit in schizophrenia by enhancing cognitive predictability during the regular sequence to improve the maintenance of cognitive set. This cognitive training procedure made the following modifications of the standard procedure: (a) regular predictable trials were increased from 10 to 15 to strengthen and enhance PI expectancies; (b) following the findings of Zahn et al. (1961), regular PIs were presented in a simple ascending order (i.e. 1, 2, 4, 8 and 16 s) permitting the gradual acquisition of more difficult longer PI expectancies; cc>participants were initially instructed as to exactly how many trials would be conducted at each interval and the ascending order of presentation; and (d) participants were informed whenever a new block of regular trials started and when they finished. In the present experiment, 30 schizophrenic patients were tested on the standard RT crossover procedure and on the cognitive training procedure. A normal target group of 20 male students from San Diego State University were similarly studied to exemplify optimal performance on the RT task. Both samples were split in a balanced design so that half of the participants in each group were administered the standard procedure first and half had the experimental procedure first. It was anticipated that improved performance on the regular sequence would be produced by the experimental procedure leading to inhibition of the crossover effect in the schizophrenic patients. If the experimental procedure proved to be effective in enhancing predictability, it should lead to later, more normal crossing over of the regular and irregular RT curves, and possibly to some improvement in all RT latencies. Similar, but less dramatic effects were expected in the normal sample which typically shows much later RT crossover. 2. Methods 2.1. Subjects The

sample consisted

of 50 participants:

30

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male schizophrenic patients and 20 male college undergraduate volunteers. The patient sample contained 21 volunteer inpatients from a private hospital and nine outpatient volunteers from a Veterans Administration Medical Center. All patients met DSM-III-R criteria for schizophrenia and were screened for brain damage, alcohol or drug use and medical conditions likely to affect RT. Seventy-three percent of the patients were Caucasian, 20% were Hispanic and 7% were African-American. Seven of the outpatients were and two as chronic diagnosed as acute schizophrenic, while all of the inpatients were classified as chronic schizophrenic. Four of the outpatients and 11 of the inpatients were also receiving medication for treatment of depressive or bipolar symptoms supplementary to their antipsychotic medication. In addition to their conventional neuroleptics, 18 of the inpatients were also receiving clozapine. The mean Brief Psychiatric Rating Scale (BPRS) score of the patient sample was 74.06 (S.D. = 9.981, reflecting moderate to moderately severe symptomatology. The Global Assessment of Functioning (GAF) yielded a mean of 33.00 (S.D. = 13.04), indicating current impairment in reality testing among these patients. The mean length of illness for all patients was 16 years, with 7.20 previous hospitalizations. All patients were on neuroleptic medication at therapeutic levels. Spohn and Strauss (1989) reviewed the evidence on the effects of conventional neuroleptics on RT and concluded that neuroleptics probably have no effects on simple RT. More recently, Zahn et al. (1994) found that clozapine did not improve RT indices of attention in chronic schizophrenic patients compared to either placebo or conventional neuroleptic treatment, despite its clinical benefits. This patient sample had a mean of 11.86 years of education and ranged in age from 24 to 47 years with a mean of 36.63. The normal target sample consisted of 20 volunteer students ranging in age from 18 to 23 years with a mean of 19.15. Fifty-five percent were Caucasian, 20% were Asian, 15% were Hispanic and 10% were African-American. All normal subjects were screened for previous psychiatric history, drug or alcohol abuse, head injury

and illnesses likely to affect RT performance. While the normal subjects were obviously significantly younger than the schizophrenic sample (t,, = 11.32, P < .OOOl),the within group correlations between age and both mean RT and crossover ranged from 0.04 to 0.22 and were not statistically significant. 2.2. Instruments The apparatus consisted of an IBM compatible personal computer with an additional monochrome graphics card installed. The card was modified to allow an additional monitor and a response key mounted on Plexiglas to be linked to the personal computer. The modification allows the participant and the experimenter to view different information simultaneously. A computer program was developed to run the standard and experimental procedures, measure RT in milliseconds and save the data in files for each participant.

2.3. Procedures All participants were tested on both the standard and experimental regular series RT procedures in a balanced order design in which half of the participants had the standard task followed by the experimental task, and the other half had the reverse order. The same irregular series procedure was interposed between the standard and experimental tasks. A 2-min break was given following completion of each of the three tasks. Participants were seated before the additional monitor linked to the PC with the telegraph key placed on the side of their dominant hand. To reduce glare and make the stimuli more salient, the lights in the room were dimmed. Instructions were given to press down on the attached telegraph key at a ‘beep’ signal from the computer and to release the key as rapidly as possible when a light appeared in a l-inch box in the center of the screen. The interval between the ‘beep’ and presentation of the light is the preparatory interval (PI). Since our previous studies (Chapin et al., 1987; Rosenbaum et al., 1988) had shown that early crossover typically occurs before a 10-s PI,

G. Rosenbaum et al. /Psychiatry Research 72 (1997) 167-I 76

the Rodnick and Shakow task was modified by eliminating the 25-s PI and using only PIs of 1, 2, 4, 8 and 16 s in the interest of task brevity. Any RT greater than 1000 ms was scored as 1000 ms to minimize the effect of extreme scores. Any trial in which the RT was less than 100 ms (below the reaction threshold of the equipment/ participant interaction) and any trial in which the participant released the key before presentation of the reaction stimulus was regarded as a mistrial and was repeated. 2.3.1. Standard RTprocedure Ten trials at each of the five PIs were successively presented in the regular procedure in the order of 1, 16, 2, 8 and 4 s. Trials were separated by a 3- to 5-s intertrial interval and a 15-s rest occurred at the end of each regular block of 10 trials. During the irregular series, each of the five PIs was presented in a counterbalanced order so that every PI occurred on 10 trials and no PI was ever repeated on successive trials. All irregular series trials had a 3-5-s intertrial interval and a 60-s rest followed 25 trials. The irregular series was presented only once. Participants received no additional instructions regarding the number or length of RT trials on the standard procedure. 2.3.2. Experimental RT procedure This task was identical to the standard regular procedure with the following cognitive-expectancy enhancing modifications: (a> participants were initially instructed that ‘there will be 15 trials for each preparatory interval and the preparatory intervals are in the successive order of 1, 2, 4, 8 and 16 s with 3-5 s between trials’; (b) upon completion of each block of 15 regular trials, participants were informed during the 15-s rest break that they would now have 15 trials at the next regular PI. 3. Results The principal measures of interest in this study were the individual mean regular order RTs and crossover scores for the standard and experimental procedures. The irregular order RT means were also calculated, and the values obtained

171

were used in calculating crossover for both the standard and experimental procedures. The data were analyzed using two separate repeated measures ANOVAs with either the regular mean RT or RT crossover as the repeated measure for the standard and experimental procedures. Individual mean RTs were calculated as the mean of the 50 trials on the standard regular order, the irregular order and the mean of the 75 trials on the experimental regular order. Crossover scores were calculated for each participant as the point at which the curve for the regular order crosses the curve for the irregular order using the algorithm developed by Rosenbaum et al. (1988) and applied to the present abbreviation of the Rodnick and Shakow (1940) task described by Rosenbaum and Taylor (1996). The essential results of the experiment are presented in Fig. 1 and Table 1. Inspection of the upper portion of Fig. 1 reveals the traditional finding that schizophrenic patients tend to lose the advantage of the predictable regular order between the 4- and 8-s PI on the standard RT procedure. When these same patients were tested on the experimental procedure which enhances the predictability of the regular serial order, the regular order curve shows lower RTs particularly at the short PIs and does not cross over the irregular curve before a PI of approx. 14 s, closely resembling normal crossover. The lower portion of Fig. 1 shows the typical RT findings that normal subjects are much faster than patients and tend to show crossover only as they approach the longest PI of 16 s. The experimental procedure also lowers normal RTs, but the advantage of increased predictability appears to hold constant across PIs. 3.1. Regular order RT The means and standard deviations for the dependent variables are shown in Table 1. The regular order and crossover means were analyzed by a two groups (schizophrenic patients vs. normal subjects) X two orders of task presentation X two procedures (standard vs. experimental), mixed model ANOVA, with repeated measures on the two procedures. As may be seen from the first

G. R~~en~~~

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Table 1 Comparison of RT performance on standard and experimental procedures in normal and schizophrenic groups Sc~~ophre~c

Regular order Mean S.D.

subjects (n = 30)

Normal subjects (n = 20)

Standard

Experimental

Standard

Experimental

584.50 189.59

528.80a 203.41

307.05 31.21

300.00 38.29

Irregular orderb Mean S.D.

636.27 183.69

Crossover Mean S.D.

8.47 6.01

362.55 41.95 11.81’ 5.24

12.93 3.43

14.52 2.91

“This mean was significantly different from the schizophrenic mean for the standard procedure (P < 0.01). bThe irregular order was presented only once with standard instructions. The irregular order values were used in calculating crossover for both the standard and experimental procedures. ‘This mean was significantly different from the schizophrenic mean for the standard procedure (P < O.Ol), but was not significantly different from the normal crossover mean for the standard procedure.

row of Table 1, schizophrenic regular order means across tasks were appreciably slower than normal

means yielding a significant between-groups main The withineffect (FI,46 = 35.78, P < 0.001).

750 7006503600Schizophrenic LOFE SO.i 4!50GOOCC 350 -

Normal

300-

250 ’

,

12

,

I

I

I

4

8

18

PreparatoryInterval Fig. 1. Reaction time performance of normal subjects and schizophrenic subjects on both the standard (Rodnick and Shakow, 1940) and experimental procedures.

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groups main effect for procedure was also statistically significant (Fi,,, = 7.03, P < 0.011, with both groups benefiting from the experimental procedure. The group X procedure interaction was statistically significant (F,,,, = 4.23, P < 0.09, indicating that the schizophrenic group benefited more from the experimental procedure than did the normal group. Neither the main effect of order nor any of the interactions involving order were statistically significant, although the mean RT on the standard task for the schizophrenic group receiving the experimental training first was 92 ms faster than that for those receiving the training last. This effect was not statistically significant and was not observed in the normal group. Consistent with the hypothesis that the experimental procedure would produce improved schizophrenic performance on the regular order, a planned comparison for paired samples of schizophrenic mean RTs on the standard (mean = 584.50) vs. experimental task (mean = 528.80) was conducted. In keeping with the means and standard deviations shown in Table 1, the schizophrenic patients were significantly faster on the experimental procedure (t,, = 3.00, P < 0.01). 3.2. RT crossover Inspection of the crossover means in Table 1 shows appreciably earlier crossover in the schizophrenic group across tasks than in the normal subjects, yielding a significant main effect for group (F,,,, = 10.23, P < 0.01). Again, the main effect for task procedures was statistically significant (F,,46 = 10.20, P < 0.011, with the experimental procedure producing later crossover in both groups. Neither the main effect for order nor any of the interactions was statistically significant. Although the significant main effect for procedures confirmed our hypothesis that increased predictability would elevate schizophrenic crossover scores, a planned comparison for paired samples of schizophrenic crossover scores was run to test our specific major hypothesis. The schizophrenic group mean crossover score was 8.47 (SD. = 6.01) on the standard task and 11.81 (S.D. = 5.24) on the experimental task, resulting in a significant difference (t,, = 2.88, P < 0.01). To test the hy-

pothesis that the experimental procedure would normalize the schizophrenic crossover deficit, a planned comparison for independent samples was run comparing the normal crossover mean of 12.93 (SD. = 3.43) on the standard task with the schizophrenic crossover mean of 11.81 (S.D.= 5.24) on the experimental task, resulting in a non-significant difference (t,, = 0.91, P > 0.05). To separate out the effect of increasing the number of trials from 10 to 15 in the experimental procedure, mean RT and crossover was calculated for three blocks of five trials at each PI. The scores for each of the three blocks yielded nearly identical results to those presented for all 15 trials at each PI. We conclude from this finding that the other alterations in the procedure, namely the ascending order of PI presentations, expanded verbal instructions and more definitive separation of PIs, were the critical factors in lowering RT and producing later crossover in the experimental task. 3.3. Irregular order mean RTs The middle row of Table 1 shows the mean RTs for the irregular procedure. This procedure was presented only once and was interposed between the standard and experimental procedures. A two groups x two orders of presentation ANOVA showed the expected significant main effect for groups (F,,,, = 43.77, P < 0.001). Neither the main effect for order of presentation nor the interaction was statistically significant. 3.4. Effects

qf symptom

severity

In order to assess the association between symptom severity and RT measures, BPRS and Global Assessment of Functioning (GAF) scores were correlated with RT and crossover indices on the standard task. Significant correlations were found between BPRS total and mean RT for the standard regular (r = 0.43, P < 0.05) and irregular (r = 0.51, P < 0.01) series, indicating that patients reporting more symptoms also demonstrated slower RT. The correlations between GAF scores and mean RT for the standard regular and irregular procedures were statistically significant (r =

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-0.35, P < 0.05and r= -0.41, P < 0.05, respectively), indicating that patients with poorer ratings also had slower RTs. None of the correlations between symptom severity measures and RT crossover reached statistical significance, ranging from r = 0.11 to 0.22. When the 18 inpatients who were relatively unresponsive to conventional neuroleptics and who were receiving clozapine were compared with the 12 other schizophrenic patients, statistically significant differences were observed in BPRS scores (t2s = 2.13, P < 0.051, GAP scores (tzs = 2.84, P < 0.011, mean RT on the standard regular (t,, = 2.96, P < 0.01) and mean RT on the irregular series (t,, = 3.17, P < 0.01). No significant difference (P > 0.50) was found for the crossover measure. These findings support previous results from Goldstein et al. (1997) showing that mean RT reflects the vigilance component of attention which is correlated with general neuropsychological deficit, while crossover is unrelated to general symptom severity and assesses the cognitive expectancy component of attention. 4. Discussion The results of the present study showed that the cognitive procedures designed to enhance schizophrenic attention produced significant decreases in RT latency on the regular procedure and the inhibition of the classic crossover effect, a unique finding in studies of RT in schizophrenia. Improvement of cognitive attention was significantly induced in both schizophrenic and normal subjects by enhancing the predictability of the regular order through cognitive information designed to increase the expectancy set on the regular trials. While normal subjects also showed later crossover on the experimental task, our unique finding is the experimentally induced later crossover mean of 11.81 in the schizophrenic group, which was highly similar and not statistically different from the normal group standard crossover mean of 12.93. Table 2 displays the schizophrenic attentional deficit, namely the crossover effect, shown as consistently early crossover values (< 10 s> in a large number of studies. While this table represents

Table 2 Reaction time crossover comparisons of normal subjects on standard procedure with schizophrenic groups on experimental and standard procedures Crossover n

Mean

SD.

Present study Normal subjects: standard task 20 12.93 3.43 Schizophrenic subjects: experimental task 30 11.81 5.24 Schizophrenic subjects: standard task 30 8.47 6.01 Previous studies Normal subjects: standard task Rosenbaum and Taylor, 1996 Schizophrenic subjects: standard task Rosenbaum and Taylor, 1996 Rosenbaum et al., 1988 Chapin et al., 1987 Greiffenstein et al., 1981 Rodnick and Shakow, 1940

48 12.78 4.75 16 17 12 11 25

8.36 8.90 7.34 6.81 7.00a

6.56 7.36 6.34 4.37 -

aEstimated from the curves of group means; standard deviation was not available.

only a small sample of the many replications of the early crossover effect in schizophrenia, the investigations included are the only published studies using the same Rodnick and Shakow (1940) standard task to calculate individual crossover scores, rather than estimating RT crossover from group means. Inspection of the group means and standard deviations in Table 2 clearly shows that our schizophrenic patients on the experimental procedure closely approximated the crossover values for normal subjects and were significantly different (using t-test comparisons) from previous groups of schizophrenic subjects. Using the value of < 10 s as an index of early crossover, 18 of our 30 patients (60%) showed the effect on the standard task, while only nine patients (30%) showed the effect on the experimental task. When performance of the 21 outpatients and nine inpatients was compared, 66% of the outpatients and 44% of inpatients showed early crossover on the standard task versus only 33% of outpatients and 22% of inpatients on the experimental task, suggesting that the experimental procedure was effective with patients at different levels of symptomatology. Four normal

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subjects (20%) showed early crossover on the standard task compared with only two normal subjects (10%) on the experiment task. When schizophrenic and normal groups were compared on the standard task, schizophrenic patients show significantly more frequent early crossover, x 2(1, n = 50) = 7.79, P < 0.005; on the experimental task schizophrenic and normal groups were not significantly different in frequency of early crossover, x2(1, at = 50)= 2.80, P > 0.05. The experimental procedure employed to normalize the schizophrenic crossover deficit was based on strengthening the preparatory set or cognitive expectancy in patients on the regular order predictable trials. A special analysis of the effects of increased practice showed that more trials did not significantly improve preparatory set. On the other hand, following the lead of Zahn et al. (19611, we used an ascending order of PI presentation going essentially from the easiest to the most difficult preparatory set and we used exact procedural information with well-defined separation of PIs to enhance PI expectancies. Both patients and normal subjects showed faster latencies at all but the longest 16-s PI on the experimental task. The inhibition of the crossover effect was the result of a large drop in schizophrenic latencies on the 1, 2, 4 and 8-s PIs. These findings support the Shakow (1962) preparatory set theory of the attentional deficit in schizophrenic subjects and are consistent with information processing theory (Nuechterlein and Dawson, 1984) and our neuropsychological explanation of the crossover effect. The experimental provision of additional simplified cognitive information appears to have reduced the load on schizophrenic subjects’ limited processing capacities and/or increased cognitive expectancies, permitting schizophrenic patients to utilize the predictable information on the regular task and hence lowering PI latencies. While our experimental intervention also increased experimenter-subject communications, it seems unlikely that these greater social interactions improved RT performance, given previous failures of socially motivating procedures which provided information as to the speed of the last RT and encouragement to exceed that speed (Rosenbaum et al., 1957b).

17s

The present findings in conjunction with our previous results with normal volunteers (Rosenbaum and Taylor, 1996) appear to clarify considerably the mechanisms underlying the classic crossover effect. This study showed that experimental procedures designed to enhance cognitive attention resulted in the inhibition of this major schizophrenic attention deficit. Our previous study showed the unique finding of experimental induction of the crossover effect in normal subjects, by using a dual-task processing procedure designed to disrupt cognitive preparatory set. The combination of these joint findings seems to lend considerable credence to our formulation that crossover is a byproduct of the interaction between the cognitive preparatory attention required on the regular task (a schizophrenic deficit) and the more subcortical automatic vigilance form of attention required by the irregular task. In our most recent study (Goldstein et al., 1997), we found that mean RT, a very high correlate of irregular RT, had a high loading on the vigilance factor along with CPT measures and an impairment index of generalized neuropsychological deficit, while crossover loaded on a cognitive expectancy factor showing deficits only in the schizophrenic and temporal lobe epilepsy patients. The present abbreviated RT procedure appears to be an efficient tool for neuropsychological investigations of these separate forms of attention. It may also be noted that the standard RT crossover task is widely regarded as a laboratory microcosm of the attentional deficit in schizophrenia. In this experiment, we used very simple approximation and shaping of preparatory set to modify the crossover deficit. Our interactions analysis did not show a statistically significant profit on the standard task in those patients receiving the experimental intervention first. Perhaps, there was too little statistical power to demonstrate this trend in an interaction term. On the other hand, if crossover proves to be a marker deficit in schizophrenia and schizotypic disorders (Chapin et al., 1987; Rosenbaum et al., 19881, it is unlikely that shaping procedures will result in sustained improvement in schizophrenic attention. The term ‘psychiatric rehabilitation’ has been coined to designate the practical application of cognitive shaping procedures with patients and is

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