TAILIEUCHUNG - Visual perception - part 10

Để đảm bảo rằng AD của sự chú ý được tập trung vào các chữ cái trình bày, chúng tôi yêu cầu của mình để báo cáo, ở cuối mỗi khối, số lượng trình bày. Trước đó electroencephalography não đồ (EEG) và từ não đồ (MEG) nghiên cứu cho thấy rằng phản ứng với vật liệu orthographic | 266 target letter I synesthetic color white . To ensure that AD s attention was focused on the presented letters we requested her to report at the end of each block the number of I s presented. Earlier electroencephalography EEG and magnetoencephalography MEG studies showed that responses to orthographic vs. nonorthographic material diverge at posterior temporal locations as early as 150-200ms after stimulus presentation Bentin et al. 1999 Tarkiainen et al. 1999 . We examined the N1 N170 component 150-170ms for AD elicited by congruently and incongruently colored letters. Mean ERP amplitudes relative to a nose reference at this time range in eight blocks of trials were used as random factor. These were measured at PO7 and PO8 the posterior scalp locations at which the negative component N1 evoked by letters was maximal. AD s N1 was significantly more negative in congruent than in the incongruent condition showing for the first time an early effect of synesthesia on evoked potentials recorded over the posterior scalp within an individual subject. Additionally the N1 was larger on the right PO8 than on the left PO7 side a somewhat unusual pattern for a right-handed participant however there was no interaction between congruency and hemisphere Fig. 3 . What are origins of this congruency effect Note that in both conditions a synesthetic color is induced. The only difference is that we present lettercolor combinations that match or mismatch Fig. 3. Event-related potentials evoked by letter stimuli colored either congruently or incongruently with AD s synesthetic colors. The approximate location of scalp locations PO7 and PO8 is shown on the schematic drawing on the lower left. AD s individual synesthetic correspondences. This could have implications on both perceived stimulus contrast and stimulus categorization. The larger N1 recorded in the congruent condition is more consistent with the latter. Because AD reports seeing both her synesthetic color and the actual .

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