Cross-frequency phase synchrony around the saccade period as a correlate of perceiver's internal state

Abstract

In active vision, eye-movements depend on perceivers' internal state. We investigated peri-fixation brain activity for internal state-specific tagging. Human participants performed a task, in which a visual object was presented for identification in lateral visual field, to which they moved their eyes as soon as possible from a central fixation point. Next, a phrase appeared in the same location; the phrase could either be an easy or hard question about the object, answered by pressing one of two alternative response buttons, or it could be an instruction to simply press one of these two buttons. Depending on whether these messages were blocked or randomly mixed, one of two different internal states was induced: either the task was known in advance or it wasn't. Eye movements and electroencephalogram (EEG) were recorded simultaneously during task performance. Using eye-event-time-locked averaging and independent component analysis, saccade- and fixation-related components were identified. Coss-frequency phase-synchrony was observed between the alpha/beta1 ranges of fixation-related and beta2/gamma1 ranges of saccade-related activity 50 ms prior to fixation onset in the mixed-phrase condition only. We interpreted this result as evidence for internal state-specific tagging.

Keywords: EEG-eye movement co-registration; efference copy; information processing over multiple fixations; up-date of visual coordinates; visual tokens.

Figure 1

Experimental task. Examples of stimuli (top), a display sequence (middle, not to scale), and an example of horizontal eye movement (bottom).

Figure 2

ICA components. (A) Two ICA components, C1 and C2. Vertical dotted-lines indicate the fixation onset. Arrows indicate P1- and SP-equivalent activities, of which the scalp projections are shown in the head image. (B) Average of filtered signals.

Figure 3

Cross-frequency phase synchrony between C1 and C2. (A) The cfPSI in the single-fixation trials in the mixed and blocked conditions. The x and y axes in each matrix indicate C1 and C2 frequencies. (B) The cfPSI in the two-fixation trials, and (C) The cfPSI at the onset of the 1st/1, 1st/2, and 2nd/2 saccades.

Figure A1

EFRP before and after EOG artifact correction.

Figure A2

Twelve ICA components.