Abstract
Neural processing of dynamic continuous visual input, and cognitive influences thereon, are frequently studied in paradigms employing strictly rhythmic stimulation. However, the temporal structure of natural stimuli is hardly ever fully rhythmic but possesses certain spectral bandwidths (e.g. lip movements in speech, gestures). Examining periodic brain responses elicited by strictly rhythmic stimulation might thus represent ideal, yet isolated cases. Here, we tested how the visual system reflects quasi-rhythmic stimulation with frequencies continuously varying within ranges of classical theta (4–7Hz), alpha (8–13Hz) and beta bands (14–20Hz) using EEG. Our findings substantiate a systematic and sustained neural phase-locking to stimulation in all three frequency ranges. Further, we found that allocation of spatial attention enhances EEG-stimulus locking to theta- and alpha-band stimulation. Our results bridge recent findings regarding phase locking (“entrainment”) to quasi-rhythmic visual input and “frequency-tagging” experiments employing strictly rhythmic stimulation. We propose that sustained EEG-stimulus locking can be considered as a continuous neural signature of processing dynamic sensory input in early visual cortices. Accordingly, EEG-stimulus locking serves to trace the temporal evolution of rhythmic as well as quasi-rhythmic visual input and is subject to attentional bias.
Highlights
The Human visual system excels in organising the massive and continuous inflow of sensory impressions into meaningful and behaviourally relevant entities
Current day Human visual neuroscience features two lines of research on dynamic visual input processing: Entrainment studies focus on the ability of the visual system to synchronize intrinsic rhythms of the brain, such as theta (4–7 Hz) or alpha (8–13 Hz), to temporal regularities embedded in continuous visual input (Adrian and Matthews, 1934; Notbohm et al, 2016; Thut et al, 2011)
We provide the number of outliers and report statistics based on outlier-removed data
Summary
The Human visual system excels in organising the massive and continuous inflow of sensory impressions into meaningful and behaviourally relevant entities. Temporal structure aides in separating figure from ground (Alais et al, 1998; Guttman et al, 2007), extrapolating the origin and destination of moving objects (Nijhawan, 1994; Whitney, 2002) and increasing sensitivity to upcoming sensory input (Correa and Nobre, 2008; Lasley and Cohn, 1981). Despite these vital aspects of visual perception, little is known about how neural processing of continuous visual stimulation unfolds in time. It enables precise predictions of future stimulus occurrences when using visual presentation rates within theta (Cravo et al, 2013) or alpha bands (Spaak et al, 2014)
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