Precisely timed oculomotor and parietal EEG activity in perceptual switching

Blinks and saccades cause transient interruptions of visual input. To investigate how such effects influence our perceptual state, we analyzed the time courses of blink and saccade rates in relation to perceptual switching in the Necker cube. Both time courses of blink and saccade rates showed peaks at different moments along the switching process. A peak in blinking rate appeared 1,000 ms prior to the switching responses. Blinks occurring around this peak were associated with subsequent switching to the preferred interpretation of the Necker cube. Saccade rates showed a peak 150 ms prior to the switching response. The direction of saccades around this peak was predictive of the perceived orientation of the Necker cube afterwards. Peak blinks were followed and peak saccades were preceded by transient parietal theta band activity indicating the changing of the perceptual interpretation. Precisely-timed blinks, therefore, can initiate perceptual switching, and precisely-timed saccades can facilitate an ongoing change of interpretation

Traveling EEG slow oscillation along the dorsal attention network initiates spontaneous perceptual switching

An ambiguous figure such as the Necker cube causes spontaneous perceptual switching (SPS). The mechanism of SPS in multistable perception has not yet been determined. Although early psychological studies suggested that SPS may be caused by fatigue or satiation of orientation, the neural mechanism of SPS is still unknown. Functional magnetic resonance imaging (fMRI) has shown that the dorsal attention network (DAN), which mainly controls voluntary attention, is involved in bistable perception of the Necker cube. To determine whether neural dynamics along the DAN cause SPS, we performed simultaneous electroencephalography (EEG) and fMRI during an SPS task with the Necker cube, with every SPS reported by pressing a button. This EEG–fMRI integrated analysis showed that (a) 3–4 Hz spectral EEG power modulation at fronto-central, parietal, and centro-parietal electrode sites sequentially appeared from 750 to 350 ms prior to the button press; and (b) activations correlating with the EEG modulation traveled along the DAN from the frontal to the parietal regions. These findings suggest that slow oscillation initiates SPS through global dynamics along the attentional system such as the DAN

Analysis of the electroencephalographic activity during the Necker cube reversals by means of the wavelet transform

In previous studies, a perceptual switching related potential was obtained during the observation of a multistable dynamic reversal pattern, where the averaging of the single responses was triggered by subjects pressing a button. The present methodological study aims to increase the signal quality of perceptual switching related potentials considering the dependence of the measurement method on the reaction time of the subject, which may vary significantly during a session, leading to low-amplitude waveform in the averaged event-related-potential (ERP). To overcome this problem in measuring the electrophysiological correlate of an internal event, a pattern selection method based on the wavelet transform (WT) is proposed to choose a subset of single ERPs with more homogenous latencies. Nine subjects observed a Necker cube and were instructed to press the button immediately after perceptual switching. A slow, low-amplitude positive wave with frontocentral amplitude maxima was observed around 250 ms prior to the button press. After the application of a 5 octave WT on single sweeps, the time-frequency coefficients obtained in each octave were averaged across trials. The most dominant feature representing the averaged ERP was the delta (0.5-4 Hz) coefficient occurring between 250 and 125 ms before the button press. By averaging the subset of the single sweeps containing this property, a sharpening and significant amplitude increase of the response peak was observed

Electrophysiological Correlates of Reversal Processes in Ambiguous Figure Perception

Ambiguous figures provide an opportunity to study fluctuations in perceptual experience without corresponding changes in sensory input. Researchers have taken great interest in the mechanisms that generate them using electrophysiology because of the potential to track these processes across time as perceptual reversals of these figures unfold. This work has highlighted brain activity both before and after perceptual reversals involving a wide range of mechanisms. Some of the known electrophysiological correlates of perceptual reversals, like the Reversal Negativity (RN) and Reversal Positivity (RP), have the potential to be explained by demands of the tasks used to elicit them. In addition, many findings on perceptual reversals and ambiguous figure interpretation originate from studies using univariate analyses that do not take full advantage of the multivariate nature of EEG data. In four experiments, I used psychophysics, ERP, and multivariate pattern analysis (MVPA) of EEG data to address the interpretation of two reversal-related ERP components and to identify new multivariate correlates of perceptual reversals. First, I found that the reversal-related RP only appears when reversals are response targets. This result suggests that the RP is not a pure correlate of perceptual processing of endogenous perceptual reversals but rather may reflect response-related monitoring processes. Second, using MVPA, I found that activity linked to perceptual reversals in the post-stimulus period is an ongoing process that involves a wide range of frequency bands (1-30Hz) and spans over a substantial amount of time (~550 ms). Finally, I found that I was able to isolate in time and frequency pre- stimulus activity that is predictive of the upcoming subjective interpretation of the ambiguous stimulus and of perceptual reversals. Overall, these results provide a new interpretation for some extant reversal-related electrophysiological markers as well as identify a set of new phenomena to guide neural theories of perceptual reversals going forward