Discretized Theta-Rhythm Perception Revealed by Moving Stimuli

Ryohei Nakayama,Takao Sato,Isamu Motoyoshi

doi:10.1038/s41598-018-24131-6

Ryohei Nakayama, Takao Sato + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-24131-6

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Abstract

Despite the subjective continuity of perception over time, increasing evidence suggests that the human nervous system samples sensory information periodically, a finding strongly exemplified by discretized perception in the alpha-rhythm frequency band. More recently, studies have revealed a theta-band cyclic process that manifests itself as periodical fluctuations in behavioral performance. Here, we used a simple stimulus to demonstrate that the theta-cyclic system can produce a vivid experience of slow discrete visual sampling: a Gabor texture pattern appears as a series of flickering snapshots if its spatial window moves continuously over a carrier grating that remains still or drifts continuously in the opposite direction. While the perceptual magnitude of this illusory saltation varied with the speed difference between grating and window components in head-centered coordinates, the perceived rhythm of saltation remained nearly constant (3–8 Hz) over a wide range of stimulus parameters. Results provide further evidence that the slow cyclic neural processes play a critical role not only in attentional task performance but also in conscious perception.

Highlights

In favor of this argument, several studies report illusions in which a continuously changing stimulus is perceived as a series of discrete snapshots (“discrete perception” in our definition), as is perhaps best exemplified by a chromatic line that appears to jitter at a temporal rate of 10–11 Hz when embedded in a luminance-defined moving target[11,12]
We found that opposite directional drifts elicited distinct percept of illusory saltation and that the range of grating speeds over which observers experienced illusory saltation depends on window speed
Illusory saltation occurs if the spatial window moves continuously over a carrier grating that remains stationary on screen or drifts in the opposite direction

Summary

Introduction

In favor of this argument, several studies report illusions in which a continuously changing stimulus is perceived as a series of discrete snapshots (“discrete perception” in our definition), as is perhaps best exemplified by a chromatic line that appears to jitter at a temporal rate of 10–11 Hz when embedded in a luminance-defined moving target[11,12]. Consider a visual Gabor pattern whose window changes location smoothly from left to right while its underlying carrier grating moves in the opposite direction (Fig. 1A,B). For such stimuli, the whole stimulus is perceived as a slow succession of discontinuous stationary snapshots (Fig. 1C). We found that the perceived rhythm of saltation remained nearly constant (3–8 Hz) over a wide range of stimulus parameters (Experiments 2 and 3) We take this as further evidence of the involvement of the theta-cyclic system in the conscious perception. We manipulated the speed of the spatial window, of the carrier grating, and of the tracking fixation

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