TY - JOUR T1 - Visual Perceptual Echo Reflects Learning of Regularities in Rapid Luminance Sequences JF - The Journal of Neuroscience JO - J. Neurosci. DO - 10.1523/JNEUROSCI.3714-16.2017 SP - 3714-16 AU - Acer Y.-C. Chang AU - David J. Schwartzman AU - Rufin VanRullen AU - Ryota Kanai AU - Anil K. Seth Y1 - 2017/08/01 UR - http://www.jneurosci.org/content/early/2017/08/01/JNEUROSCI.3714-16.2017.abstract N2 - A novel neural signature of active visual processing has recently been described in the form of the ‘perceptual echo', in which the cross-correlation between a sequence of randomly fluctuating luminance values and occipital electrophysiological (EEG) signals exhibits a long-lasting periodic (∼100ms cycle) reverberation of the input stimulus (VanRullen & Macdonald, 2012). As yet, however, the mechanisms underlying the perceptual echo and its function remain unknown. Reasoning that natural visual signals often contain temporally predictable, though non-periodic features, we hypothesized that the perceptual echo may reflect a periodic process associated with regularity learning. To test this hypothesis, we presented subjects with successive repetitions of a rapid non-periodic luminance sequence, and examined the effects on the perceptual echo, finding that echo amplitude linearly increased with the number of presentations of a given luminance sequence. These data suggest that the perceptual echo reflects a neural signature of regularity learning.Furthermore, when a set of repeated sequences was followed by a sequence with inverted luminance polarities, the echo amplitude decreased to the same level evoked by a novel stimulus sequence. Crucially, when the original stimulus sequence was re-presented, the echo amplitude returned to a level consistent with the number of presentations of this sequence, indicating that the visual system retained sequence-specific information, for many seconds, even in the presence of intervening visual input.Altogether, our results reveal a previously undiscovered regularity learning mechanism within the human visual system, reflected by the perceptual echo.Significance StatementHow the brain encodes and learns fast-changing but non-periodic visual input remains unknown, even though such visual input characterises natural scenes. We investigated whether the phenomenon of ‘perceptual echo' might index such learning. The perceptual echo is a long-lasting reverberation between a rapidly changing visual input and evoked neural activity, apparent in cross-correlations between occipital EEG and stimulus sequences, peaking in the alpha (∼10 Hz) range. We indeed found that perceptual echo is enhanced by repeatedly presenting the same visual sequence, indicating that the human visual system can rapidly and automatically learn regularities embedded within fast-changing dynamic sequences. These results point to a previously undiscovered regularity learning mechanism, operating at a rate defined by the alpha frequency. ER -