Visual and memory search by process schizophrenics

Brain-performance correlates of working memory retrieval in schizophrenia: a cognitive modeling approach

Correlations of cognitive functioning with brain activation during a sternberg item recognition paradigm (SIRP) were investigated in patients with schizophrenia and in healthy controls studied at 8 sites. To measure memory scanning times, 4 response time models were fit to SIRP data. The best fitting model assumed exhaustive serial memory scanning followed by self-terminating memory search and involved one intercept parameter to represent SIRP processes not contributing directly to memory scanning. Patients displayed significantly longer response times with increasing memory load and differed on the memory scanning, memory search, and intercept parameters of the best fitting probability model. Groups differed in the correlation between the memory scanning parameter and linear brain response to increasing memory load within left inferior and left middle frontal gyrus, bilateral caudate, and right precuneus. The pattern of findings in these regions indicated that high scanning capacity was associated with high neural capacity among healthy subjects but that scanning speed was uncoupled from brain response to increasing memory load among schizophrenia patients. Group differences in correlation of the best fitting model's scanning parameter with a quadratic trend in brain response to increasing memory load suggested inefficient or disordered patterns of neural inhibition among individuals with schizophrenia, especially in the left perirhinal and entorhinal cortices. The results show at both cognitive and neural levels that disordered memory scanning contributes to deficient SIRP performance among schizophrenia patients.

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.

Changes in short-term memory processes in patients with multiple sclerosis

In this study we compared the performance of 39 multiple sclerosis (MS) patients with 28 age-, sex- and education-matched controls on both the Mini-Mental State Examination, a global cognitive assessment tool, and the Sternberg Short-Term memory scanning task, a standardized test of short-term memory (STM) processes. While the STM span of our MS patients did not differ from that of our controls, STM scanning time of the MS group was reliably slower than that of the controls and a significant correlation was observed between STM scanning time and duration but not severity of illness. Our results suggest that processing stages other than the manipulation of data within the STM buffer are also affected by MS.

Visual search, eeg, and psychopathology in schizophrenic patients

Twenty acutely admitted schizophrenic inpatients diagnosed according to RDC and 8 normal controls were instructed to search for a randomly located target letter (Z) in ten lists of 284 distractor letters of either rounded or angular shape projected on a screen (23 degrees x 15 degrees). Eye movements were recorded using infrared corneal reflection-pupil centre measurement. Search performance was defined as the search time in seconds from onset of the display until localization of the target. The EEG was recorded simultaneously in schizophrenics, in whom assessment took place shortly after admission and before discharge. The psychopathological status was assessed at the same time with the Brief Psychiatric Rating Scale and the Scale for the Assessment of Negative Symptoms. Search performance was not significantly different in schizophrenics and normal controls, but was heavily affected by target/distractor similarity in both groups. Moreover, search performance in schizophrenics was not significantly affected by illness severity. However, search performance was differently related to negative and positive symptoms. Schizophrenics and normal controls differed with respect to the relationship between search performance and visuomotor microbehaviour. Additionally, two relatively time-stable eye movement patterns in schizophrenics could be distinguished, which were differently related to psychopathology, performance measures and EEG.

Decisional processing in paranoid and non-paranoid schizophrenics

40 schizophrenic subjects, divided into paranoid/non-paranoid categories and 14 normal controls were presented a task which involved making "same-different" judgments during random presentations of a series of visual comparison stimuli with a standard which represented the midpoint of the stimulus continuum. Using Sternberg's Choice RT paradigm for studying the locus of cognitive deficit, difficulty at the response-selection stage was manipulated while holding other stages constant. It was predicted that paranoids would have shorter RTs at easy decision points and longer RTs at difficult decision points relative to non-paranoids. The directions of the differences were as predicted but did not attain statistical significance. Both schizophrenic groups, compared to normals, made significantly fewer "same" responses on those trials where the comparison and standard were most similar.

Abolition of the expression but not the acquisition of latent inhibition by chronic amphetamine in rats

The animal amphetamine model of schizophrenia has been based primarily on stereotyped behavior. The present study sought to demonstrate an amphetamine-induced deficit in attentional processes. To this end, the effects of acute and chronic (14 days) 1.5 mg/kg dl-amphetamine administration on the ability of rats to ignore irrelevant stimuli were examined using the paradigm of latent inhibition (LI) in a conditioned emotional response (CER) procedure. The procedure consisted of three stages: pre-exposure, in which the to-be-conditioned stimulus, tone, was presented without being followed by reinforcement; acquisition, in which the pre-exposed tone was paired with shock; and test, in which LI was indexed by animals' suppression of licking during tone presentation. Experiment 1 showed that chronic but not acute treatment abolished LI. Experiment 2 showed that animals receiving chronic amphetamine pretreatment but pre-exposed and conditioned without the drug, exhibited normal LI. In Experiment 3, animals which received chronic amphetamine pretreatment and were pre-exposed under the drug but conditioned without it, also showed normal LI. The implications of these results for the animal amphetamine model of schizophrenia are discussed.