Linear vector models of time perception account for saccade and stimulus novelty interactions

Exploring the correlation and causation between alpha oscillations and one-second time perception through EEG and tACS

Alpha oscillations have been implicated in time perception, yet a consensus on their precise role remains elusive. This study directly investigates this relationship by examining the impact of alpha oscillations on time perception. Resting-state EEG recordings were used to extract peak alpha frequency (PAF) and peak alpha power (PAP) characteristics. Participants then performed a time generalization task under transcranial alternating current stimulation (tACS) at frequencies of PAF-2, PAF, and PAF+2, as well as a sham condition. Results revealed a significant correlation between PAP and accuracy, and between PAF and precision of one-second time perception in the sham condition. This suggests that alpha oscillations may influence one-second time perception by modulating their frequency and power. Interestingly, these correlations weakened with real tACS stimulations, particularly at higher frequencies. A second analysis aimed to establish a causal relationship between alpha peak modulation by tACS and time perception using repeated measures ANOVAs, but no significant effect was observed. Results were interpreted according to the state-dependent networks and internal clock model.

Sound reduces saccadic chronostasis illusion

The saccadic chronostasis illusion refers to the duration overestimation of the first visual stimulation after saccadic eye movement, which is also known as "stopped clock illusion." The present study investigated whether saccadic chronostasis would be observed in the auditory modality and whether the saccade-induced time dilation in the visual modality would be reduced by a synchronously presented sound. In each trial, a unisensory visual stimulus, unisensory sound, or bimodal audio-visual stimulus with a duration of 200-800 ms (probe stimulus) was presented at the saccade target location and temporally around the offset of the saccade, followed by a unisensory visual or auditory standard stimulus for a fixed 500 ms. Participants were required to identify which of the two stimuli (probe or standard) presented in the target modality (visual or auditory) was perceived as longer. The results showed that no saccadic chronostasis was observed in the auditory modality, regardless of whether the sound was presented alone or synchronously accompanied by a visual stimulus. Interestingly, the magnitude of the saccadic chronostasis illusion was reduced by the synchronously presented sound. Moreover, the combined effect of the saccade and sound on visual time perception fits well with the standard scalar model, and the weight of the cross-modal effect was higher than that of saccadic visual time dilation. These results suggest that sound dominates vision in time processing during saccades and linearly modulates saccadic chronostasis, which follows the Scalar Expectancy Theory.

Saccades and presaccadic stimulus repetition alter cortical network topology and dynamics: evidence from EEG and graph theoretical analysis

Parietal and frontal cortex are involved in saccade generation, and their output signals modify visual signals throughout cortex. Local signals associated with these interactions are well described, but their large-scale progression and network dynamics are unknown. Here, we combined source localized electroencephalography (EEG) and graph theory analysis (GTA) to understand how saccades and presaccadic visual stimuli interactively alter cortical network dynamics in humans. Twenty-one participants viewed 1-3 vertical/horizontal grids, followed by grid with the opposite orientation just before a horizontal saccade or continued fixation. EEG signals from the presaccadic interval (or equivalent fixation period) were used for analysis. Source localization-through-time revealed a rapid frontoparietal progression of presaccadic motor signals and stimulus-motor interactions, with additional band-specific modulations in several frontoparietal regions. GTA analysis revealed a saccade-specific functional network with major hubs in inferior parietal cortex (alpha) and the frontal eye fields (beta), and major saccade-repetition interactions in left prefrontal (theta) and supramarginal gyrus (gamma). This network showed enhanced segregation, integration, synchronization, and complexity (compared with fixation), whereas stimulus repetition interactions reduced synchronization and complexity. These cortical results demonstrate a widespread influence of saccades on both regional and network dynamics, likely responsible for both the motor and perceptual aspects of saccades.