Antecedent occipital alpha band activity predicts the impact of oculomotor events in perceptual switching

Abstract

Oculomotor events such as blinks and saccades transiently interrupt the visual input and, even though this mostly goes undetected, these brief interruptions could still influence the percept. In particular, both blinking and saccades facilitate switching in ambiguous figures such as the Necker cube. To investigate the neural state antecedent to these oculomotor events during the perception of an ambiguous figure, we measured the human scalp electroencephalogram (EEG). When blinking led to perceptual switching, antecedent occipital alpha band activity exhibited a transient increase in amplitude. When a saccade led to switching, a series of transient increases and decreases in amplitude was observed in the antecedent occipital alpha band activity. Our results suggest that the state of occipital alpha band activity predicts the impact of oculomotor events on the percept.

Keywords: Necker cube; ambiguous figures; blinking; electroencephalogram (EEG); perception; saccade.

Figure 1

Necker cube used as visual stimulus in our experiment. The stimulus was presented as a white line-drawing on a black ground. The visual angle of presentation was 5.0°. The stimulus was continuously presented for 240 s.

Figure 2

An amplitude increase in occipital alpha band activity preceded blinking, when blinking was followed by perceptual switching. (A) Average waveform of the occipital recordings (O2) aligned with the pre-switch blinkings that were followed by perceptual switching. The amplitude was Z-transformed, and the amplitude zero indicates baseline amplitude. (B) Statistical difference between average waveform aligned with the pre-switch blinkings and baseline amplitude. The colors red and blue denote that amplitude was larger in average waveform or baseline amplitude, respectively (P < 0.05). (C) Average waveform of the occipital recordings (O2) aligned with the no-switch blinkings that were not followed by perceptual switching. The amplitude was Z-transformed, and the amplitude zero indicates baseline amplitude. (D) Statistical difference between average waveform aligned with the no-switch blinkings and baseline amplitude. The colors red and blue denote that amplitude was larger in average waveform or baseline amplitude, respectively (P < 0.05). (E) Statistical difference between average waveform aligned with pre-switch blinks and average waveform aligned with the no-switch blinks. The colors red and blue denote that amplitude was larger in the pre-switch blinking-related average waveform or the no-switch blinking-related average waveform, respectively (P < 0.05).

Figure 3

Probabilities of preceding saccades transiently increased when blinking led to perceptual switching. Time 0 indicates onset of blinking. (A) The color red denotes saccade probabilities when blinking led to a switch response (button press) approx. 1000 ms after blinking. Blue denotes saccade probabilities when blinking did not lead to a switch response. Green denotes periods that exhibited increased saccade probabilities when blinking led to a switch response (P < 0.05). (B) The color red denotes the probabilities of the pre-blink saccades whose directions were consistent with the preferred interpretation of the Necker cube after the switch. Blue denotes the probabilities of the pre-blink saccades whose directions were inconsistent with the preferred interpretation. Green denotes periods that exhibited increased probabilities of the pre-blink saccades whose directions were consistent with the preferred interpretation (P < 0.05). Purple denotes periods that exhibited increased probabilities of the pre-blink saccades whose directions were inconsistent with the preferred interpretation (P < 0.05).

Figure 4

A series of amplitude increase and decrease in occipital alpha band activity preceded saccade, when saccade was followed by perceptual switching. (A) Average waveform of the occipital recordings (O2) aligned with the pre-switch saccades that were followed by perceptual switching. The amplitude was Z-transformed, and the amplitude zero indicates baseline amplitude. (B) Statistical difference between average waveform aligned with the pre-switch saccades and baseline amplitude. The colors red and blue denote that amplitude was larger in average waveform or baseline amplitude, respectively (P < 0.05). (C) Average waveform of the occipital recordings (O2) aligned with the no-switch saccades that were not followed by perceptual switching. The amplitude was Z-transformed, and the amplitude zero indicates baseline amplitude. (D) Statistical difference between average waveform aligned with the no-switch saccades and baseline amplitude. The colors red and blue denote that amplitude was larger in average waveform or baseline amplitude, respectively (P < 0.05). (E) Statistical difference between average waveform aligned with pre-switch saccades and average waveform aligned with the no-switch saccades. The colors red and blue denote that amplitude was larger in the pre-switch saccade-related average waveform or the no-switch saccade-related average waveform, respectively (P < 0.05).

Figure A1

EEG amplitude preceding blinking, when the mother wavelet with a size of 3 cycles was used for the continuous wavelet transform. (A) Average waveform of the occipital recordings (O2) aligned with the pre-switch blinks. Amplitude was Z-transformed, and the amplitude zero constitutes the baseline. (B) Statistical difference between average waveform aligned with the pre-switch blinks and baseline amplitude. The colors red and blue denote that amplitude was larger in the average waveform or baseline amplitude, respectively (P < 0.05). (C) Average waveform of the occipital recordings (O2) aligned with the no-switch blinks. The amplitude was Z-transformed, and zero indicates baseline amplitude. (D) Statistical difference between average waveform aligned with the no-switch blinks and baseline amplitude. The colors red and blue denote that amplitude was larger in average waveform or baseline amplitude, respectively (P < 0.05). (E) Statistical difference between the average waveform aligned with the pre-switch blinks and the average waveform aligned with the no-switch blinks. The colors red and blue denote that amplitude was larger in the pre-switch blinking-related average waveform or the no-switch blinking-related average waveform, respectively (P < 0.05).

Figure A2

EEG amplitude preceding a saccade, when a mother wavelet with a size of 3 cycles was used for the continuous wavelet transform. (A) Average waveform of the occipital recordings (O2) aligned with the pre-switch saccades that were followed by perceptual switching. The amplitude was Z-transformed, and the amplitude zero indicates baseline amplitude. (B) Statistical difference between average waveform aligned with the pre-switch saccades and baseline amplitude. The colors red and blue denote that amplitude was larger in the average waveform or baseline amplitude, respectively (P < 0.05). (C) Average waveform of the occipital recordings (O2) aligned with the no-switch saccades. The amplitude was Z-transformed, and the amplitude zero indicates baseline amplitude. (D) Statistical difference between average waveform aligned with the no-switch saccades and baseline amplitude. The colors red and blue denote that amplitude was larger in average waveform or baseline amplitude, respectively (P < 0.05). (E) Statistical difference between the average waveform aligned with the pre-switch saccades and the average waveform aligned with the no-switch saccades. The colors red and blue denote that amplitude was larger in the pre-switch saccade-related average waveform or the no-switch saccade-related average waveform, respectively (P < 0.05).