Abstract
Accumulating evidence suggests that visual perception operates in an oscillatory fashion at an alpha frequency (around 10Hz). Moreover, visual attention also seems to operate rhythmically, albeit at a theta frequency (around 5Hz). Both rhythms are often associated to "perceptual snapshots" taken at the favorable phases of these rhythms. However, less is known about the unfavorable phases: do they constitute "blind gaps," requiring the observer to guess, or is information sampled with reduced precision insufficient for the task demands? As simple detection or discrimination tasks cannot distinguish these options, we applied a continuous report task by asking for the exact orientation of a Landolt ring's gap to estimate separate model parameters for precision and the amount of guessing. We embedded this task in a well-established psychophysical protocol by densely sampling such reports across 20 cue-target stimulus onset asynchronies in a Posner-like cueing paradigm manipulating involuntary spatial attention. Testing the resulting time courses of the guessing and precision parameters for rhythmicities using a fast Fourier transform, we found an alpha rhythm (9.6Hz) in precision for invalidly cued trials and a theta rhythm (4.8Hz) in the guess rate across validity conditions. These results suggest distinct roles of the perceptual alpha and the attentional theta rhythm. We speculate that both rhythms result in environmental sampling characterized by fluctuating spatial resolution, speaking against a strict succession of blind gaps and perceptual snapshots.
Highlights
In our everyday life, we experience our visual perception as a seamless, continuous flow
We found a theta rhythm (4.8 Hz) for the guessing parameter for data collapsed across both cueing conditions, which was readily evident for data collapsed across both cueing conditions but was present in invalid trials in particular, and an alpha rhythm (9.6 Hz) for the precision parameter, mostly for invalid trials
We tested the hypothesis that perceptual and attentional rhythms are better characterized as oscillations in spatial resolution than as an alternating succession of perception during "perceptual snapshots" and guessing during "blind gaps." To this end, we used an exogenous cueing task and dense sampling of cue-target stimulus onset asynchrony. Edited by (SOA)
Summary
We experience our visual perception as a seamless, continuous flow. More than a century ago, Bergson (1911, p.332) introduced the metaphor of a "cinematograph inside us" taking "snapshots [...] of the passing reality," which seems to contradict our everyday experience. With his film metaphor, he postulated our visual perception to consist of a succession of "perceptual snapshots" and "blind gaps," comparable to a filmstrip. . |2 has inspired researchers to accumulate evidence for a rhythmic succession of such snapshots (see VanRullen, 2016; VanRullen & Koch, 2003, for a review). While this research has demonstrated that behavioral accuracy is best during the favorable “peaks” of this rhythm, less is known about the less favorable “troughs” in between two snapshots: do they reflect veritable gaps where nothing is processed, or moments of insufficient precision?
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