Attentional asymmetry in schizophrenia: controlled and automatic processes.

Two versions of Posner's covert orienting task were administered to 14 drug-free schizophrenic patients and 12 normal controls. In the schizophrenic subjects, automatic orienting to exogenous cues in the right visual field was impaired. However, this lateralizing general deficit was not present when the schizophrenics were able to direct attention effortfully in the second version of the task using endogenous cues. These findings support the hypothesis that there is a deficit in left hemispheric mechanisms mediating visual spatial attention in schizophrenia. However, when schizophrenics are given the opportunity to use an attentional strategy they are able to partially overcome this lateralized processing deficit.     

Disengagement of attention in schizophrenia

We compared covert shift of visual attention in patients with schizophrenia or bipolar disorder, both in states of remission, to normal controls to examine the persistence of lateralized attentional deficits into nonpsychotic states. Although patients were slower in all conditions than normals, there was no difference in pattern of attentional shift among the groups. This suggests that the left-hemisphere deficit in shift of covert attention in schizophrenia may be limited to periods of florid illness.     

A simple clinical assessment of attention in schizophrenia

Although attentional dysfunction is considered a predominant feature of schizophrenia, it is seldom quantitatively assessed in clinical practice. A simple paper-and-pencil test of selective attention (Ruff et al., 1986) provides a 5-min assessment with theoretical relevance for schizophrenia. Thirty schizophrenic subjects performed the 2 and 7 Selective Attention Test, which measures speed and accuracy, and compares controlled and automatic information processing. Ninety percent of the subjects displayed automatic processing. Speed was severely impaired, and accuracy was less so. Sixty-seven percent of the schizophrenic subjects performed in the normal range (± 1 SD) for accuracy, but only 23% scored in the normal range for speed. Speed and accuracy were moderately correlated. Although theories of a lateralized deficit were not supported, the results are consistent with a hypothesized frontal lobe dysfunction. The automatic processing demonstrated may represent old learning. Poor controlled processing may preclude the acquisition of automatic functioning. This selective attention test may provide a measure of severity of cognitive impairment relevant to daily life functioning.     

Effects of the hallucinogen psilocybin on covert orienting of visual attention in humans

Hallucinogenic drug-induced states are considered as models for acute schizophrenic disorders (experimental psychoses). In a double-blind study with healthy volunteers we investigated the influence of the serotonergic hallucinogen psilocybin, the ecstasy-like drug 3,4-methylenedioxyethylamphetamine (MDE), the stimulant d- methamphetamine and placebo on covert orienting of spatial attention (n = 8 in each group). Reaction times were prolonged after ingestion of psilocybin > MDE, but not after d-methamphetamine. In addition, subjects on psilocybin exhibited particularly slow reaction times in invalid trials at short cue target intervals and failure of response inhibition in valid trials at long cue target intervals for right visual field targets. Despite some methodological limitations, these results are in line with both bilateral impairment of disengagement of attention and a lateralized impairment of inhibition of return (IOR) in productive psychotic states. Additional investigations with larger samples, different hallucinogenic substances (serotonergic agonists vs. NMDA antagonists) and different dose regimens are needed in order to further explore the suggested relationship between visuospatial attentional dysfunction and acute psychotic conditions.     

Schizophrenia Patients Show Deficits in Shifts of Attention to Different Levels of Global-Local Stimuli: Evidence for Magnocellular Dysfunction

Abnormalities of attention and visual perception are well documented in schizophrenia. The global-local task is a measure of attention and perceptual organization that utilizes visual stimuli comprised of large letters (global level) made up of smaller letters (local level). Subjects identify target letters appearing at either the global or local level of the stimulus. In this study, we used a version of the global-local task specifically designed to examine lateralized hemispheric processing and attention shifting in 30 schizophrenia patients and 24 normal controls. Global-local stimuli were presented in couplets (consecutive pairs). Reaction time for the second target in a couplet was compared under conditions in which the target remained at the same level (global-global, local-local) and when the target changed levels (global-local, local-global). Level-specific priming (ie, global to global and local to local) and the local-to-global level shift were similar in both groups. Schizophrenia patients were significantly slower, however, shifting attention from the global to the local level. These results implicate an impairment in shifting attentional resources from predominantly right lateralized magnocellular/dorsal stream processing of global targets to predominantly left lateralized parvocellular/ventral stream processing of local targets. Local interference effects in global processing provide further support for impaired magnocellular processing in schizophrenia patients.     

Parietal lobe mechanisms of spatial attention: modality-specific or supramodal?

Is the spatial attention system divided into separate, modality-specific subsystems, or is there a supramodal spatial attention system? More specifically, does the role of the parietal lobe in spatial attention involve modality-specific or supramodal mechanisms? We addressed this question using a variant of Posner's spatial cuing task. Parietal-lesioned patients performed a simple reaction time task to lateralized visual target stimuli, preceded on each trial by either non-predictive lateralized visual cue stimuli or non-predictive lateralized auditory cue stimuli. With both types of cues, we found disproportionate slowness in responding to invalidly cued contralesional targets, indicative of an impairment in disengaging attention from the ipsilesional to the contralesional side of space. The finding of an attentional disengagement impairment for visual targets with auditory cues implies that the parietal lobe's attentional mechanism operates on a representation of space in which both visual and auditory stimuli are represented, in other words, a supramodal representation of space.     

Specific impairment of visual spatial covert attention mechanisms in Parkinson's disease

Visual deficits in early and high level processing nodes have been documented in Parkinson's disease (PD). Non-motor high level visual integration deficits in PD seem to have a cortical basis independently of a low level retinal contribution. It is however an open question whether sensory and visual attention deficits can be separated in PD. Here, we have explicitly separated visual and attentional disease related patterns of performance, by using bias free staircase procedures measuring psychophysical contrast sensitivity across visual space under covert attention conditions with distinct types of cues (valid, neutral and invalid). This further enabled the analysis of patterns of dorsal-ventral (up-down) and physiological inter-hemispheric asymmetries. We have found that under these carefully controlled covert attention conditions PD subjects show impaired psychophysical performance enhancement by valid attentional cues. Interestingly, PD patients also show paradoxically increased visual homogeneity of spatial performance profiles, suggesting flattening of high level modulation of spatial attention. Finally we have found impaired higher level attentional modulation of contrast sensitivity in the visual periphery, where mechanisms of covert attention are at higher demands.These findings demonstrate a specific loss of attentional mechanisms in PD and a pathological redistribution of spatial mechanisms of covert attention.     

Perceptional and executive deficits of chronic schizophrenic patients in attentional and intentional tasks

The present study investigated whether schizophrenic patients could develop appropriate visual orientation and motor set under precuing conditions which contrasted attentional (input selective) and intentional (output selective) information. The aim was to evaluate perceptual performance in processing visuospatial information, and executive performance in response preparation. Stimuli and/or elicited responses were controlled for selective hemispheric engagement. Age, sex and handedness matched groups of 33 chronic schizophrenic patients and 33 normal subjects were tested on choice reaction time (RT) tasks in which warning signals were manipulated regarding either where a target stimulus would occur (selective attention) or which hand to use for responding (response preparation). All subjects benefited from precued information regarding subsequent responses. However, schizophrenic patients were not able to use intentional cues as effectively as control subjects did. Interhemispheric asymmetry of spatial attention was found in patients with schizophrenia, with slowing of responses to uncued targets presented in the right visual field. There was also a decreased advantage of within-hemisphere stimulus-response conditions in the schizophrenic group. Our results support the notion that a dysfunction involving parietal and premotor areas has potential importance in the schizophrenic illness. We replicated findings which indicate that deficits of information processing in schizophrenia may affect left hemispheric mechanisms to a larger extent. The results also point toward a possible abnormal connectivity between frontal and parietal circuits in schizophrenia.     

Visual orienting in schizophrenia.

Patients with schizophrenia demonstrate a variety of attentional impairments which have proven difficult to relate to specific neural systems. Posner et al. (1988) reported an asymmetric slowing of right visual field orienting in schizophrenia similar to that observed in patients with parietal lesions. We examined the visual orienting performance of 19 patients and controls using two different versions of the Posner paradigm. In overall ANOVAs we found main effects of group, cue condition, and delay interval. However, we did not observe any main effect of visual field or interactions involving visual field. There was some evidence of an asymmetric cost of invalid cues similar to those reported by Posner et al. The bulk of data suggests bilateral attentional deficits.     

Smoking and schizophrenia: epidemiological and clinical features

FREQUENCY: The prevalence of cigarette smoking is significantly higher among patients with schizophrenia (60-90%) than in the general population (23-30%). While tobacco smoking decreases in the general population (from 45% in the 1960's to 23-30% in the 2000's), smoking in patients with schizophrenia remains high. Patients with schizophrenia smoke more cigarettes than control subjects. Patients smoke more deeply, thereby increasing their exposure to the harmful elements in tobacco smoke. IMPACT OF SMOKING IN SCHIZOPHRENIC PATIENTS: As in the general population, smoking contributes to the reduced life expectancy in patients with schizophrenia. Patients with schizophrenia are at increased risk for cardiovascular disease due to high rates of cigarette smoking. In the Department of Mental Health of the commonwealth of Massachusetts, cardiovascular disease was the factor the most strongly associated with excess mortality. Cardiac deaths were elevated more than six-fold. Weight gain, insulin resistance, metabolic syndrome and diabetes mellitus are frequent in patients with schizophrenia, and may worsen the risk of cardiovascular diseases. It has been reported that the risk for lung cancer in patients with schizophrenia is lower than that of the general population, despite increased smoking. However, in a study conducted in Finland, a slightly increased cancer risk was found in patients with schizophrenia. Half of the excess cases were attributable to lung cancer. IMPROVEMENT OF COGNITIVE DEFICITS: Patients with schizophrenia may use nicotine to reduce cognitive deficits and negative symptoms or neuroleptic side effects. Smoking may transiently alleviate negative symptoms in schizophrenic patients by increasing dopaminergic and glutamatergic neurotransmission in the prefrontal cortex. In patients with schizophrenia, nicotine improves some cognitive deficits: (1) sensory gating deficits and abnormalities in smooth pursuit eye movements associated with schizophrenia are transiently normalized with the administration of nicotine ; (2) high-dose nicotine transiently normalizes the abnormality in P50 inhibition in patients with schizophrenia and in their relatives; (3) in tasks that tax working memory and selective attention, nicotine may improve performance in schizophrenia patients by enhancing activation of and functional connectivity between brain regions that mediate task performance (Jacobsen et al. 2004; Paktar et al.2002); (4) cigarette smoking may selectively enhance visuospatial working memory and attentional deficits in smokers with schizophrenia. However, Harris et al., found that nicotine affects only the attention without effects of nicotine on learning, memory or visuospatial/constructional abilities. In addition, smoking could facilitate disinhibition in schizophrenic patients.     

Specificity of smooth pursuit eye movement and visual fixation abnormalities in schizophrenia. Comparison to mania and normal controls

Smooth pursuit eye movements (SPEM) were assessed in 30 schizophrenic patients, 12 lithium-free manic patients, and 20 normal controls. Compared to schizophrenic patients, manic patients evidenced less SPEM impairment in an attention enhancing, sinusoidal target motion condition and had superior performance during a visual fixation condition. SPEM and visual fixation dysfunctions may be more common in schizophrenic than in acutely manic patients, even when the latter are characterized by marked attentional dysfunction, poor interepisode psychosocial functioning, and psychosis.     

Differential impairment on measures of attention in patients with paranoid and nonparanoid schizophrenia

The purpose of the present study is to investigate whether patients with different subtypes of schizophrenia are differentially impaired on measures of attention. Forty-eight patients with schizophrenia (19 paranoid and 29 nonparanoid) and 48 healthy controls (matched on chronological age, sex, and years of education) were administered five measures of attention including the Stroop Color-Word Test (SCWT; Stroop, 1935), the Digit Vigilance Test (DVT; Lewis, 1992), the Symbol Digit Modalities Test (SDMT; Smith, 1982), the Backward Digit Span Test (BDST; Wechsler, 1987), and the Color Trails Test (CTT; D'Elia et al., 1996) to assess selective attention, sustained attention, switching attention, and attentional control processing by the latter two tests respectively. Results from the present study showed that patients with schizophrenia performed poorer on the SCWT, the DVT, and the SDMT, relative to their healthy counterparts. Furthermore, patients with different subtypes of schizophrenia also had different degrees of attentional impairment. While patients with paranoid schizophrenia performed worse on the SCWT, those with nonparanoid schizophrenia performed worse on the SDMT. Nevertheless, these findings may suggest that patients with paranoid and nonparanoid schizophrenia may have different profiles with respect to their performances on measures of attention.     

Lateralized attentional deficits in drug-free and medicated schizophrenic patients

Performance on a cued reaction time (RT) task, theoretically linked to posterior and anterior neuroanatomical systems in the brain (Posner, M. I. et al., Science, 1988, 210, 1627–1631; Archives of General Psychiatry, 1988, 15, 811–821), was used to assess sensory orienting and maintenance of attention. In schizophrenic patients, Posner et al. found a lateralized abnormality in RT (longer RTs to uncued targets in the right visual field than in the left visual field), as did Maruff et al. (Neuropsychologia, 1995, 33, 1205–1223), but Strauss et al. (Journal of Psychiatric Research, 1991, 37, 139–146), among others, did not replicate this effect. However, the subjects in these studies differed in the percentage of schizophrenic patients taking neuroleptic medication at the time of testing and in the chronicity of the illness. In the present study, we used two groups of schizophrenic subjects to control for the use of neuroleptic medication. The lateralized abnormality in RT was observed in the drug-free group of schizophrenic subjects, but not in the group of drug-treated schizophrenic subjects.     

Spatial attention in hypothetically psychosis-prone college students

This study tested the hypothesis that psychosis-prone individuals show patterns of visual search that suggest a lateralized cerebral hemispheric abnormality, similar to one hypothesized by Venables (1980) to underlie cognitive dysfunction in schizophrenia. Self-report measures of psychiatric vulnerability were completed by 881 college students. Experimental subjects (n = 73) were those with high scores on one of four psychosis-proneness scales. Control subjects (n = 33) scored within 0.5 SD of the mean on all scales. Subjects were tested using verbal and nonverbal visual search tasks designed to detect abnormalities in the spatial distribution of attention. When searching random arrays of nonverbal stimuli, 53% of the experimental subjects used an erratic search strategy similar to that typically observed in right-brain-damaged patients, compared with 23% of controls. The most deviant search patterns were shown by subjects who scored high on Physical Anhedonia and Perceptual Aberration-Magical Ideation. The results suggest that early development of schizophrenic disorder might be associated with dysfunction of right-hemispheric mechanisms of attentional control.     

Event-related potentials and thought disorder in schizophrenia

We examined the relationship between event-related potentials and thought disorder in schizophrenia. The subjects were 29 chronic schizophrenic patients. Thought disorder was assessed using the Comprehensive Index of Positive Thought Disorder developed by Harrow and colleagues (Harrow and Quinlan, 1985; Marengo et al., 1986). Auditory event-related potentials were recorded during a standard oddball task. The P300 amplitude correlated negatively with the severity of the thought disorder. The P300 amplitude in the patients with thought disorder was significantly smaller than in the patients without thought disorder. These results suggest that a reduction in P300 amplitude is associated with a fundamental impairment of information processing in schizophrenic patients.     

Antisaccadic eye movements and attentional asymmetry in schizophrenia in three Pacific populations

Antisaccadic eye movements were examined in 50 patients with schizophrenia and in 77 controls in three Pacific populations, namely New Zealand, Palau and Papua New Guinea. Despite the great biocultural variation encompassed by these three populations, schizophrenic patients made significantly more antisaccadic errors than controls (36% vs. 13%), as has been demonstrated previously in other populations. This neurocognitive deficit may be consistent with frontal lobe dysfunction in schizophrenia. In addition, patients with schizophrenia made significantly more errors than expected when the target was presented in the right visual field (RVF). This trend was observed in patients from all three study areas, and was not seen in any of the control populations. Antisaccadic test performance in schizophrenia may be influenced by lateralized (left hemisphere) neuroanatomical impairment.     

Veränderte Wahrnehmung zeitlicher Relationen bei schizophrenen Psychosen

Basic perceptual skills involving the central nervous system require the orderly temporal integration of internal as well as external information. Current research in schizophrenia increasingly centers on the accompanying neurocognitive deficits. In association with schizophrenic psychoses, there have been frequent reports of altered temporal processes, but explicit research on the perception of temporal relationship is still rare. Using concrete operationalized neuropsychological procedures, the present pilot study addressed the question whether schizophrenic patients (n = 27) differ from a healthy control group (n = 18) concerning their ability to judge correctly the temporal order of visual stimuli. We found a significant impairment in basal temporal perception among patients. Moderating variables such as antipsychotic medication, attention deficits, or motivation effects did not appear to be essential explanatory factors for this finding. Thus, our findings indicate a fundamental disturbance in the temporal coordination of neuronal network functions in association with schizophrenic psychoses and are in line with neurophysiological, neuroanatomical, and neuropsychological overlappings of schizophrenia and temporal perception.     

Event-related brain potentials: a window on information processing in schizophrenia

The application of the P300 component of the event-related brain potential to the study of attentional impairment in schizophrenia is discussed, and two recent studies are described. In one, the relative effects on P300 of stimulus modality and probability were evaluated. The data showed that the P300 is smaller in schizophrenic patients relative to normal controls for low-probability auditory stimuli. Next is described a preliminary report that evaluated whether this P300 reduction reflects a core deficit (trait marker) or clinical symptomatology (state marker). To pursue this question, a group of schizophrenic patients was studied on and off neuroleptic medication. The data showed that improvement in clinical state was highly correlated with increased visual P300 but was uncorrelated with auditory P300. These findings suggest that P300 elicited in the visual modality has the characteristics of a state marker of schizophrenia. In contrast, auditory P300 remains a candidate for a vulnerability trait marker of schizophrenia. The core deficit in schizophrenia thus appears to involve the auditory information-processing system, whereas fluctuations in clinical state may be reflected in the visual processing system.     

Attentional dysfunction of chronic schizophrenia: No association with long-term institutionalization

Attentional processes play a central role in information selection, which is impaired in schizophrenic patients. In the present study, we attempted to characterize the attentional performance of chronic schizophrenics using a computerized assessment of the multiple components of attentional function. Two comparable samples, consisting, respectively, of out-patients and in-patients, were tested in order to assess the effect of chronic institutionalization. Twenty-four subjects (half in-patients and half out-patients) fulfillling DSM-IV criteria for schizophrenia were examined with a standard computerized battery for the assessment of attention, namely Testbatterie zur Aufmerksamkeitsprufung (TAP). Both groups were impaired on all measures of attentional processing (in terms of both reaction times and number of errors). There were no significant differences in attentional performance between in- and out-patients. In conclusion, the present findings confirm the presence of pervasive attentional dysfunction in chronic schizophrenia; the lack of significant differences in performance between in- and out-patients supports the hypothesis that the cognitive deficits are inherently associated with the illness and cannot be attributed to environmental/social factors.