Abstract
It has been previously demonstrated by our group that a visual stimulus made of dynamically changing luminance evokes an echo or reverberation at ∼10 Hz, lasting up to a second. In this study we aimed to reveal whether similar echoes also exist in the auditory modality. A dynamically changing auditory stimulus equivalent to the visual stimulus was designed and employed in two separate series of experiments, and the presence of reverberations was analyzed based on reverse correlations between stimulus sequences and EEG epochs. The first experiment directly compared visual and auditory stimuli: while previous findings of ∼10 Hz visual echoes were verified, no similar echo was found in the auditory modality regardless of frequency. In the second experiment, we tested if auditory sequences would influence the visual echoes when they were congruent or incongruent with the visual sequences. However, the results in that case similarly did not reveal any auditory echoes, nor any change in the characteristics of visual echoes as a function of audio-visual congruence. The negative findings from these experiments suggest that brain oscillations do not equivalently affect early sensory processes in the visual and auditory modalities, and that alpha (8–13 Hz) oscillations play a special role in vision.
Highlights
It has been known for close to a century that the brain operates within the context of intense oscillatory activity [1]
We chose an experimental design including both visual and auditory trials in an interleaved manner, so that the presence of visual perceptual echoes could be confirmed on the same group of subjects, and serve as a baseline against which to evaluate the magnitude of any auditory perceptual echoes
We failed to observe any modification of the visual echo by congruent or incongruent auditory stimulation. In both of our experiments, brain responses to visual stimulation solidly verified the findings of our original study [7], i.e. that a long-lasting visual perceptual echo in the alpha (,10 Hz) frequency range followed the broadband transient response (Figure 6, top, and Figure 9)
Summary
It has been known for close to a century that the brain operates within the context of intense oscillatory activity [1]. In a previous study [7] our group showed that a visual stimulus dynamically changing its luminance with a random Gaussian distribution (i.e., with equal power at all temporal frequencies) evokes a selective echo or reverberation at the alpha frequency (,10 Hz) of the individual’s EEG. This echo, revealed by crosscorrelating the EEG response with the random visual stimulation sequence, included several cycles and lasted for up to a second (much longer than the standard VEP components evoked by luminance changes in the random sequence). The echo was interpreted as a reverberation of perceptual information either directly in visual cortex, or as a result of corticothalamic circuitry, and we proposed that it could serve a functional role in the maintenance of sensory information over time
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