視覚探索における注意と記憶

Neural Mechanisms of Visual Search and Working Memory

視覚探索の効率を上げるためには，一度見たものを記憶し，再び注意が向かないようにする必要がある。多数の物体の中から標的を探し出す採餌課題中の二度見行動に着目し，短期記憶の容量，忘却率，利用率を定量化する方法を考案した。サルの採餌行動の成績はケタミン投与で低下し，ニコチン投与で向上したが，いずれも短期記憶の利用率の変化を伴っていた。複雑な教示を必要としない本課題を用いれば，さまざまな被験者で作業記憶を定量化できる。

Abstract

Visual search is a useful experimental paradigm investigating various aspects of attention. For efficient search, participants must avoid revisiting previously viewed objects. Inhibitory tagging and inhibition of return are phenomena related to this process, but their neural mechanisms are yet to be elucidated. Recent studies have shown that the rate of revisit behavior during visual search correlates with working memory capacity. This suggests that top-down signals from the frontal executive system alter the priority map that guides attention and eye movements. With this in mind, we have developed a novel visual search paradigm with many identical distractors and an evaluation model that assesses multiple parameters of working memory. The model incorporated memory capacity, memory decay, and utility rate, and when applied to data obtained from experimental animals, these parameters could be reliably evaluated. Furthermore, using the behavioral paradigm and model, we found that systemic administration of subanesthetic dose of ketamine decreased utility rate and memory capacity, while nicotine administration increased utility rate. Since our behavioral paradigm does not require complex instruction, it can be applied to a variety of patients in future clinical studies.