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Jian Ding, Ramesh Srinivasan, George Sperling; Flicker elicits eeg responses in two distinct cortical networks depending on attention and flicker frequency. Journal of Vision 2006;6(6):515. doi: 10.1167/6.6.515.
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Frequency-tagging is an experimental design for EEG or MEG in which two or more stimuli are presented simultaneously but flickered at different frequencies. Steady-state responses (SSVEP) elicited by the flicker are detected at each stimulus frequency by Fourier analysis of EEG responses. We studied attentional modulation of EEG flicker responses using 15 “tag” frequencies ranging from 2.5–20 Hz. The stimuli were confined to two color-coded concentric annuli. On each annulus, a sequence of search arrays (concentric disks with, possibly a target triangle) was superimposed. The two sequences were updated independently; one updated at a fixed frequency (flicker) and the other updated at random intervals to generate a white noise temporal-frequency distribution. On each trial, observers were instructed to attend one of the two annuli and to detect target triangles that appeared occasionally. Results. The choice of whether the annulus with flicker is attended or not, whether the unattended annulus (the competing annulus) was inner or outer, and flicker frequency all influence SSVEP amplitude and cortical distribution. There are two cortical response configurations (networks) with different sensitivities to attention. At low flicker frequencies in the delta band (2–4 Hz), and in the upper-alpha band (10–11 Hz), an occipital-frontal network appears to phase-lock to the flicker when attending to the flicker, increasing the steady-state response. When attention is directed away from the flicker in the lower-alpha (8–10 Hz) band and towards a competing stimulus in the fovea, a global resonance, including parietal cortex and posterior-frontal cortex, responds preferentially to the unattended flicker.
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