Span of apprehension in schizophrenic patients as a function of distractor masking and laterality

On the centrality and significance of stimulus-encoding deficit in schizophrenia

Increased latency of stimulus encoding is presented as a central deficit in schizophrenia cognition. Encoding, here, entails the internal representation of presenting stimuli in a format facilitating their implementation in other cognitive processes, such as those taking place in working memory. Historical roots of suspected encoding debility in schizophrenia briefly are reviewed, and its singular empirical robustness is described. More recently, this deficit has been subjected to stochastic mathematical modeling, resulting in its decomposition into discrete cognitive functions. A nonmathematical exposition of this account is provided, and substantial behavioral study support is illustrated. Implications for clinical assessment of individuals and of treatment regimens, with respect to encoding-related cognitive efficiency, are noted. Finally, because stochastic dynamic trajectories of process duration are modeled, times of measurement interest, complementing neuroanatomical regions of interest, become available for enhanced temporal navigation of event-related fMRI. Results from recent implementations of such process-defined events are described.

Is filtering difficulty the basis of attentional deficits in schizophrenia?

The distractibility that schizophrenia patients display may be the result of a deficiency in filtering out irrelevant information. The aim of the current study was to assess whether patients with schizophrenia exhibit greater difficulty when task-irrelevant features change compared to healthy participants. Thirteen medicated outpatients with a diagnosis of schizophrenia and thirteen age- and parental education-matched controls performed a target selection task in which the task-relevant letter or the task-irrelevant features of color, and/or location repeated or switched. Participants were required to respond by pressing the appropriate key associated with the target letter. These patients with schizophrenia were slower when the task-relevant target letter switched than when it repeated. In contrast, schizophrenia patients performed similarly to controls when task-irrelevant information changed. Thus, we found no evidence that patients with schizophrenia were impaired in inhibiting irrelevant perceptual features. In contrast, changes in task-relevant features were problematic for patients relative to control participants. These results suggest that medicated outpatients who are mild to moderately symptomatic do not exhibit global impairments of feature processing. Instead, impairments are restricted to situations when task-relevant features vary. The current findings also suggest that when a course of action is not implied by an irrelevant feature, outpatients' behavior is not modulated by extraneous visual information any more than in healthy controls.

Early visual information processing deficit in depression with and without Borderline Personality Disorder

Backward masking is a measure of early visual information processing usually abnormal in psychotic disorders. Previous studies of subjects with Borderline Personality Disorder have been inconsistent regarding their impairment or lack of impairment on backward masking. We examined visual backward masking performance in samples of unmedicated depressed patients with (n=12) and without (n=16) Borderline Personality Disorder, and healthy volunteers (n=18). Accuracy was poorer in depressed BPD patients, relative to both non-BPD depressed and healthy comparison subjects. As in previous studies, no differences in accuracy were found between non-BPD depressed patients and healthy comparison subjects. Differences in BPD subjects' accuracy were most evident at the fastest ISI and were not attributable to intercurrent psychotic symptoms. Beyond these group differences, accuracy at faster ISI's correlated with self-ratings of impulsiveness in all patients, and may be a general correlate of this trait. Poor early information processing appears to be a feature of Borderline Personality Disorder, and may play a role in the impulsive behavior that is characteristic of the disorder.

Neural anomalies during visual search in schizophrenia patients and unaffected siblings of schizophrenia patients

Schizophrenia patients and their unaffected first-degree relatives exhibit performance deficits on attention tasks, perhaps indicating genetic influence over attentional abnormalities in schizophrenia. To identify anomalous brain function associated with attention in individuals who likely have unexpressed genetic liability for schizophrenia, we studied electrophysiological characteristics of unaffected siblings of schizophrenia patients during a visual serial search task. We gathered behavioral and electrophysiological data from 19 schizophrenia patients, 18 unaffected biological siblings of schizophrenia patients, and 19 nonpsychiatric control participants during performance of the Span of Apprehension (Span) task and a control task. Schizophrenia patients had lower Span task accuracy than the other two groups. Schizophrenia and sibling groups exhibited diminished late positive potentials (P300) over parietal brain regions during Span trials. Compared to control task stimuli, attentional demands of Span stimuli elicited augmented early negative potentials (N1, P2) over posterior brain regions. The degree of augmentation was reduced in schizophrenia patients but not in siblings compared to control subjects. Unaffected siblings of schizophrenia patients appear to modulate early attentional functions of posterior brain regions more effectively than schizophrenia patients but show later electrophysiological anomalies suggestive of abnormal updating of task-relevant information. While the latter may reflect neural mechanisms predisposing performance deficits on attentional tasks, the former may reflect compensatory processes present in unaffected relatives of schizophrenia patients.

The use of neurophysiological endophenotypes to understand the genetic basis of schizophrenia

Specifying the complex genetic architecture of the “fuzzy” clinical phenotype of schizophrenia is an imposing problem. Utilizing metabolic, neurocognitive, and neurophysiological “intermediate” endophenotypic measures offers significant advantages from a statistical genetics stand-point. Endophenotypic measures are amenable to quantitative genetic analyses, conferring upon them a major methodological advantage compared with largely qualitative diagnoses using the Diagnostic and Statistical Manual of Mental Health, 4th Edition (DSM-IV). Endophenotypic deficits occur across the schizophrenia spectrum in schizophrenia patients, schizotypal patients, and clinically unaffected relatives of schizophrenia patients, Neurophysiological measures, such as P50 event-related suppression and the prepulse inhibition (PPI) of the startle response, are endophenotypes that can be conceptualized as being impaired because of a single genetic abnormality in the functional cascade of DNA to RNA to protein. The “endophenotype approach” is also being used to understand other medical disorders, such as colon cancer, hemochromatosis, and hypertension, where there is interplay between genetically conferred vulnerability and nongenetic stressors. The power and utility of utilizing endophenotypes to understand the genetics of schizophrenia is discussed in detail in this article.

Eye tracking in normals: spem asymmetries and association with schizotypy

SPEM was recorded electro-oculographically during visual tracking of sinusoidal targets oscillating at .4 and .8 cycles per second in one hundred nineteen undergraduates. The logarithms of median root mean square values were used to assess tracking accuracy for leftward and rightward halfcycles of tracking. Over the entire sample, there was a significant superiority of rightward over leftward tracking, which, given evidence for the ipsilateral mediation of SPEM at the cortical level, suggests a right hemisphere predominance in the control of SPEM in normal subjects. Individual tracking asymmetry was associated with overall tracking accuracy such that subjects with relatively deficient leftward tracking and those with a larger absolute magnitude of asymmetry had poorer overall tracking. High scores on an MMPI schizotypy measure (Sum 2-7-8-0) were significantly related to poorer overall SPEM accuracy, individual tracking asymmetry, the absolute magnitude of tracking asymmetry, and phase lag, though the subjects' sex, handedness, and crossed hand-foot dominance were found to affect the relationships between schizotypy and tracking accuracy. These findings suggest that although control of SPEM may be predominantly right hemispheric, in some persons with a vulnerability to schizophrenia spectrum disorders, expressed as poorer overall SPEM accuracy and high schizotypy scores, left hemisphere-mediated (leftward) SPEM may be particularly impaired.

Preattentive information processing as measured by backward masking and texton detection tasks in adolescents at high genetic risk for schizophrenia

Schizophrenic patients have consistently been reported to show deficits in preattentive information processing as demonstrated by impairments in visual backward masking and texton detection tasks. Texton detection refers to Julesz's texton theory, which defines a certain limited number of texton elements (e.g., one 'L' among many '+') that can be detected readily and simultaneously without attentional effort irrespective of the size of the rest of the visual field. The present study investigated whether deficits of preattentive information processing are more prevalent in a group of adolescents of high genetic risk for schizophrenia compared to matched control subjects. Although differences in the performance in visual backward masking tasks could not be detected with our experimental approach, preattentive texton detection was to a certain extent disturbed in subjects at risk. Moreover, subjects at risk did not show the advantage of the right hemisphere in processing texton elements which was found in the control group. This may point to a subtle dysfunction of the right hemisphere in the risk group. It is concluded from the present study that deficits in preattentive texton detection may represent an indicator for a schizophrenic disposition. However, further studies including other high risk groups, schizophrenics in remission and individuals with a schizotypal personality disorder are needed to confirm this hypothesis.

Perceptual and conceptual information processing in schizophrenia and depression

Schizophrenic patients (n = 20), depressive patients (n = 20), and normal adults (n = 20) were compared on global vs local analyses of perceptual information using tachistoscopic tasks and on top-down vs bottom-up conceptual processing using card-sort tasks. The schizophrenic group performed more poorly on tasks requiring either global analyses (counting lines when distracting circles were present) or top-down conceptual processing (rule learning) than they did on tasks requiring local analyses (counting heterogeneous lines) or bottom-up processing (attribute identification). The schizophrenic group appeared not to use conceptually guided processing. Normal adults showed the reverse pattern. The depressive group performed similarly to the schizophrenic group on perceptual tasks but closer to the normal group on conceptual tasks, thereby appearing to be less dependent on a particular information-processing strategy. These deficits in organizational strategy may be related to the use of available processing resources as well as the allocation of attention.

Nonverbal perceptual organization output disability and schizophrenia spectrum symptomatology

Patients with neurodevelopmental syndromes often receive numerous psychiatric diagnoses before the true nature of their disorder becomes apparent. We present a case in which the neuropsychological evaluation played a significant role in reconceptualizing a patient who had received, at various times, diagnoses of schizotypal personality disorder, schizoaffective disorder, and schizophrenia. The identification of specific cognitive deficits in executive functioning, perceptual organization, visual-spatial problem solving, and abstraction led to: 1) a diagnosis of nonverbal perceptual-organization-output disabled; 2) the adoption of a rehabilitative treatment model; and 3) a greater understanding of the way in which the patient's social deficits represented adaptations to her cognitive impairments. Research data and theoretical models relating cognitive deficits to psychiatric symptoms are discussed, and evidence is presented that schizophrenia and certain neurodevelopmental syndromes may share commonalities of pathophysiology. Diagnostic issues arising from similarities between these disorders are discussed. It is suggested that direct comparisons between these groups can aid in clarifying the specific nature of cognitive deficit-symptom relationships, as well as leading to improvements in the understanding, diagnosis and treatment of schizophrenic and neurodevelopmental syndromes.