Schizophrenia is a major mental disorder characterized by various clinical symptoms, but also shows perceptual and cognitive impairments that are important research topics in this field. For example, patients with schizophrenia consistently show impai ...
Schizophrenia is a major mental disorder characterized by various clinical symptoms, but also shows perceptual and cognitive impairments that are important research topics in this field. For example, patients with schizophrenia consistently show impaired visual motion perception and working memory. So far, most research on perceptual processing in schizophrenia tended to control any cognitive influence during the experimental tasks and vice versa. Efforts to scrutinize perceptual-cognitive processing integratively have been relatively ignored. The present study paid attention to the dynamic relationship among deficits in visual perception, working memory, and resulting social dysfunction. An unique type of visual motion stimuli, called biological motion(BM), that depicts characteristic movement of organism including humans with a couple of moving dots, and even contains rich social information such as gender and mood was used to understand interaction between visual deficits and impaired working memory representation, and to take more integrative approach to this issue. In the first year of the study, we investigated how biological motion (BM) would affect efficiency of working memory, specifically encoding and maintenance. We recruited patients with schizphrenia and healthy controls and administered a delayed-response task (DRT) which is one of a typical working memory task. In the delayed-response task, either BM, non-BM, or static random polygon was given as a stimus to be remembered, and its recognition was tested after a delay period. The results showed that the patients with schizophrenia had lower accuracy compared with controls in general, which is consistent with past researches. A novel finding was as follows. In the low memory load condition (one target is to be remembered), the patients with schizophrenia had relatively higher accuracy when they was to remember BM stimuli, compared with other types of stimuli. It seemed that BM had a facilitating effect for encoding process, resulting enhanced working memory. However, when the memory load was high (2 targets remembered), this effect was not valid any more. Whereas, the healthy controls showed consistent encoding facilitation effect by BM stimuli regardless of memory load. This results suggested that working memory impairments may have different manifestation depending on memory load and types of memory stimuli. Recently, the first year study has been published in the journal PLOS ONE. In the first experiment of the second year (experiment 2), we examined the unanswered questions from the first year study. Specifically, we attempted to understand more deeply how the encoding facilitation would be manifested by combinations of stimulus type and memory load. In this experiment, there were three conditions of presenting stimuli during the delayed response task: BM (load1 and load2), non-BM (load 1 and load2), BM and non-BM. The results showed similar accuracy between load 2 conditions regardless of BM or nonBM and BM-nonBM conditions. In general, encoding facilitation effect was observed in low load condition only, like in the first year study. Although the new condition of BM-nonBM presentation had similar accuracy with that from 2 BM or 2 nonBM stimuli in both groups, the underlying mechanisms appear to be quite different between groups. In healthy controls, they had strong encoding facilitation when BM was to be remembered, it was not the case for nonBM trials. Furthermore, the accuracy dropped a lot when the memory load increased in nonBM trials. When nonBM was the target in BM-nonBM trials, it seemed that BM was not helpful for encoding. Whereas, in the patients with schizophrenia group, it seemed that they may have processed nonBM as a “quasi” BM, as a results, the two different stimuli could interfere with each other leading dropped accuracy than other conditions. In the second experiment of the second year study (experiment 3), we investigated how long the facilitated encoding by BM in low load condition would last in the patients and controls group. There were three different delay periods conditions in the delayed response task: 0s, 5s, and 20s. Stimulus was either BM, nonBM or a random polygon. The results showed that the memory for BM stimuli was more accurate and lasted longer compared with the other two types of stimuli, in both groups. However, even when the delay period was 0s, overall accuracy for recognition in schizophrenia was lower than healthy controls, suggesting their abnormal perceptual encoding. Furthermore, the patients’ the facilitated encoding itself disappeared earlier than in controls. Therefore, the patients with schizophrenia do benefit from BM in working memory encoding, but its effect is limited and its influence on working memory is not as strong as in healthy cotrols. The results from the second year study is now under statistical analysis and the manuscript are being prepared.