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内容記述 |
Selective attention has two main aspects: bottom-up attention and top-down<br />attention. Bottom-up attention is elicited or driven by the properties of<br />stimuli automatically. Top-down attention refers to a volitional focusing of<br />attention on a location and/or an object based on current behavioral goals,<br />while other processing is inhibited. Each attention is classified by subject to<br />which one directs attention. The attention to an object is called object-based<br />attention, whereas that to a location is spatial attention.<br /> Although numerous neuropsychological studies have investigated neural<br />mechanisms regarding to these kinds of attention, it is still unknown entail<br />neural mechanisms. Here, we used magnetoencephalography (MEG) and<br />investigated neural responses underlying to two kinds of selective attention.<br />In the first study, we investigated neural mechanisms regarding Inhibition<br />of return (IOR). IOR is a phenomenon of bottom-up spatial attention that<br />involves reaction times (RTs) to a spatially cued target that are longer than<br />RTs to an uncued target when the interval between the cue and target is<br />prolonged. Although numerous studies have examined IOR, no consensus<br />has yet been reached regarding the neural mechanisms responsible for it. <br />We used MEG and measured the neural responses underlying the time<br />course of IOR, applying a typical spatial cueing paradigm. The cue-target<br />interval was 600 ± 200 ms. Three following experimental conditions were<br />employed. (1) Cued: the cue and target were presented at the same location.<br />(2) Uncued: the two stimuli were presented at opposite locations. (3)<br />Neutral: the cue stimulus was presented bilaterally. We found differences in<br />the amplitudes of signals in the posterio-temporal and bilateral temporal<br />areas, and peak latencies in a central area between the cued and uncued<br />conditions. These signals were localized to the extrastriate cortex, bilateral<br />temporal-parietal junction (TPJ), and primary motor cortex, respectively.<br />Bilateral TPJ activities are related to the identification of salient events in <br />the sensory environment both within and independent of the current<br />behavioral context and may play an important role in IOR in addition to<br />extrastriate and the primary motor cortex.<br /> In the second study, we investigated neural responses concerning<br />top-down object-based attention. Although top-down attention to a specific<br />object, a volitional focusing of attention on an object based on current<br />behavioral goals, can modulate early neural activities in extrastriate<br />cortices for object-processing, no consensus has yet been reached regarding<br />early modulation for face and object-processing. To address this issue, we<br />adopted a double-exposure visual stimulus comprising superimposed<br />images of a face and a house and asked subjects to direct their attention at<br />either image. MEG revealed bilateral activities in the occipital, <br />occipito-temporal and superior temporal sulcus (STS) at 100 (M100R: right<br />occipital, M100L: left occipital), 170 (M170R: right occipito-temporal;<br />M170L: left occipito-temporal) and 230 (M230R: right STS, M230L: left<br />STS) ms, respectively. We found that top-down object-based attention<br />enhanced the activity in the right occipito-temporal area (M170R) and in<br />the right STS (M230R) for face-processing. For object-processing, only the<br />activity in the right STS activity (M230R) was modulated by top-down<br />attention. These results suggested that top-down attention has different<br />effects on face and object-processing with preferred and early access to<br />face-processing.<br /> In the third study, we investigated neural responses concerning top-down<br />spatial attention and revealed common and different neural basis with<br />top-down object-based attention dealt with Experiment 2. Images of a face<br />and object (a house) were presented in the peripheral visual field (same as <br />those used in Experiment 2) and subjects were asked to direct their<br />attention to a face or an object. MEG revealed bilateral activities in the<br />occipital, occipito-temporal and STS at 100 ms, 170 and 260 ms,<br />respectively. We found that top-down spatial attention enhanced the activity<br />in the right occipito-temporal area and in the right STS for face-processing.<br />For object-processing, only the activity in the right STS activity was<br />modulated by top-down spatial attention. These results suggested that<br />top-down spatial attention has different effects on face and<br />object-processing with preferred and early access to face-processing. The<br />study indicated that top-down spatial attention has similar effects on neural<br />activities of top-down object-based attention. |
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