Abstract
The phase and frequency of neural oscillations in the alpha band (8–12 Hz) have been recently proposed as key parameters for the temporal resolution of visual perception. Here, we tested the possible causal links between these oscillatory features and temporal integration/segregation. The individual alpha frequency (IAF) peak as obtained from resting-state electroencephalography was used to set the frequency of sensory (audio-visual) entrainment for the lower (IAF − 2 Hz) and upper (IAF + 2 Hz) alpha. Entrainment at IAF ± 2 Hz was administered in the prestimulus interval to align oscillations to a faster or slower rhythm. We densely sampled in time the accuracy for integration/segregation by using identical stimuli with different instructions. The spectral peaks of performance fluctuations over time were found in the upper or lower alpha band for the IAF + 2 and IAF − 2 Hz entrainment, respectively, implying that faster entrainment resulted in faster behavioral fluctuations. Moreover, the entrainment frequency had opposite effects on temporal resolution: faster entrainment improved segregation while slower entrainment improved integration. Performance fluctuations were almost in anti-phase between the two tasks, such that highest integration performance coincided with lowest segregation performance. These findings provide evidence for a direct link between changes in the alpha band and the temporal resolution of perception.
Highlights
Despite our subjective impression of a continuous and smooth reality, the continuous flow of information coming from the sensory world is not elaborated in an analog fashion
Other studies have investigated the role of neural oscillations in the temporal resolution of visual perception, defined as whether two items in a sequence are perceived as separate, individual events or instead combined into a single unique percept[11,12,13,14,15,16,17,18,19]
From the resulting Fast Fourier Transform (FFT) spectra (Fig. 3B), the frequencies corresponding to the maximum power observed in the frequency range of interest (2–18 Hz), was used as the dependent variable in a repeated-measure analysis of variance (ANOVA), where within-subjects factors were the ‘entrainment frequency’ (IAF + 2Hz vs. individual alpha frequency (IAF) − 2 Hz) and ‘task condition’
Summary
Despite our subjective impression of a continuous and smooth reality, the continuous flow of information coming from the sensory world is not elaborated in an analog fashion. The idea that perceptual processing depends on the rhythmic sampling of sensory information was initially introduce in seminal neurophysiological studies[3,4,5] and later confirmed using electroencephalographical (EEG) recording in humans, which consistently show a relationship between oscillatory phase and sensitivity to new input[6,7,8,9]. Together, these findings argue that fluctuations in detection, reflecting sensitivity to new input, are related to alpha rhythms. We showed that the alignment of the ongoing oscillations to a particular entrained rhythm can impact the temporal pattern of segregation of stimuli over time, and this occurred only within a certain frequency range that includes the alpha band (8–12 Hz)[17], in agreement with previous M/EEG studies reviewed above
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