Increased repetition blindness in schizophrenia patients and first-degree relatives of schizophrenia patients

Comparable repetition blindness effect in patients with schizophrenia

BACKGROUND AND OBJECTIVES

Repetition blindness (RB) refers to the difficulty to report repetitions of stimuli visually presented in a rapid list. To date only two studies have examined RB in patients with schizophrenia and the results are not clear-cut. The current study was designed to employ a task with reduced memory load, more trials in each experimental condition, and more participants to obtain a more reliable RB effect.

METHODS

A 2x2x3x2 mixed factor repeated measure design was used, with stimulus repetition, lag, and presentation rate as within-subject factors, and group (patient or control) as a between-subject factor. A rapid serial visual presentation (RSVP) procedure was used. Twenty eight inpatients with schizophrenia and 28 healthy controls participated in the experiment.

RESULTS

The patient group showed significantly impaired performance when compared tothe control group in every experimental condition. Nevertheless, the patient group demonstrated similar RB effect as the control group. Furthermore, the overall RB effect observed in patients did not relate to their illness severity or psychotic symptoms. Neither was it related to their age or education.

LIMITATIONS

It was difficult to match the age and education of the control group to that of the inpatient group.

CONCLUSIONS

Patients with schizophrenia performed worse than healthy controls in each experimental condition. Both the control and patient group showed robust RB effect in the short lag with faster rates. In addition, RB effect seemed to be irrelevant to patients' illness severity and clinical symptoms.

Attentional blink and repetition blindness

When two masked, to-be-attended targets are presented within half a second of each other, report accuracy for the second target (T2) is impaired relative to when the two targets are presented farther apart in time or relative to when the first target (T1) can be ignored. This effect is known as the attentional blink (AB). An additional T2 accuracy deficit is observed if T1 and T2 are identical or highly similar on a task-relevant dimension. This effect is known as repetition blindness (RB). For both AB and RB, targets are typically imbedded in rapid serial visual presentation (RSVP) streams and the dual-task attention cost lasts approximately half a second. Given the high degree of superficial similarity, AB and RB are often considered to be related phenomena. Although research thus far has suggested that both phenomena reflect limits of the attentional system and how attention is allocated when needing to organize stimuli for entrance into awareness, these two phenomena are dissociable; RB is not simply an enhanced AB. Furthermore, investigations of AB and RB have taken quite different courses over the last two decades. The AB has been investigated extensively with a variety of experimental, behavioral, neurophysiological, and clinical approaches, and has become widely used as a paradigm of convenience with which to study other effects. In contrast, studies of RB have tended to manipulate the nature of the target information to understand the level of representation that supports RB. WIREs Cogni Sci 2011 2 336-344 DOI: 10.1002/wcs.129 For further resources related to this article, please visit the WIREs website.

Impaired visual working memory consolidation in schizophrenia

This study investigated working memory (WM) consolidation, that is, the time required to create durable WM representations, at different levels of WM load in schizophrenia. Twenty-three schizophrenia spectrum patients and 16 control subjects participated in a change-detection task in which a sample array of 1-3 squares appeared followed by a delay and a test array. An array of pattern masks was inserted into the delay interval--covering the locations of the sample-array squares--100-800 ms after the offset of the sample array. If a durable WM representation is formed prior to mask onset, the mask should not impair performance. The degree of masking at an interval reflects the degree of WM consolidation at that time. Neither group showed masking at set size 1. Unlike controls, patients demonstrated robust masking effects at set size 2. Both groups showed masking at set size 3, but masking effects were larger and longer lasting in patients. These data demonstrate abnormally prolonged WM consolidation in schizophrenia. This impairment may slow the formation of stable representations of the visual environment, impacting everyday visually guided behavior.

Working Memory Consolidation Is Abnormally Slow in Schizophrenia

This study reports evidence that patients with schizophrenia demonstrate a slowing of working memory (WM) consolidation, which is the process of transforming transient perceptual representations into durable WM representations. Sixteen schizophrenia patients and 16 healthy control participants performed a task measuring the visual WM consolidation rate in a change-detection paradigm. A target display containing 3 colored squares was followed by a variable delay of 17-483 ms, a pattern mask, and then a test stimulus. This pattern mask does not interfere with perception but disrupts WM consolidation. Control participants reached no-mask performance by 250 ms, indicating completed WM consolidation, whereas patients failed to reach no-mask performance by 483 ms. Slowed consolidation may play an important and largely unrecognized role in schizophrenia.

Critical evaluation of cognitive dysfunctions as endophenotypes of schizophrenia

OBJECTIVE

Cognitive dysfunctions are potential endophenotypes of schizophrenia. The aim of this study was to investigate whether recent evidence indeed suggests that cognitive dysfunctions are potent indicators of specific genetic traits that represent susceptibility for schizophrenia.

METHOD

Studies including large, well-defined samples and controlled cognitive assessment have been reviewed.

RESULTS

Evidence suggests that schizophrenia patients and their unaffected biological relatives are impaired in several cognitive domains, including working memory, executive functions, sustained attention, verbal episodic memory, processing of visual and auditory stimuli, and smooth pursuit eye movements. However, these impairments are present only in a limited proportion of subjects, showing low specificity and sensitivity and high variability. Linkage with specific genes is weak.

CONCLUSION

Although some results are promising, at present cognitive dysfunctions cannot be considered as highly sensitive and specific endophenotypes of schizophrenia.