Influence of visual motion on reversal speeds in an ambiguous Necker cube experiment: an eye-tracking study

International audienceMultistability is the oscillation between different perceptual states under constant physical stimulus. Although either or both bottom-up and top-down processing can explain such oscillations (Leopold & Logothetis, 1999), we focus here on bottom-up information processing in which perceptual reversal is associated with passive neural adaptation and noise, early in visual processing (Kornmeier & Bach, 2005). Objectives. We had focused on bottom-up factors governed by low-level visual features, to study the effects of adaptation and noise on reversal speed. Methods. Inspired by the experimental design in (Blake, Sobel & Geloy, 2003) we manipulate the adaptation level by moving the stimulus following a smooth Lissajous trajectory (LJ). We expected a decrease in reversal speed compared to a fixed stimulus (FX), serving as our control condition. Ocular noise was controlled through pseudo-random movements of the stimulus (random walk, RW). Under this “random walk” condition, an increased reversal speed was expected by assuming a higher noise level. The three conditions were randomly sequenced. Participants were instructed to stare at a central point during the stimulus presentation (Necker cube) at the screen centre, and to report their perceptual changes by keypress. After removing outliers, data (eye movements and behavioural responses) from sixteen participants were analysed. Results. The hypothesis concerning the ocular noise was supported by a significant increase of reversal speed (RW > FX) as a consequence of a continuous spatial jitter of the retinal image. However, we also found LJ > FX, in contrast to our initial hypothesis following (Blake, Sobel & Geloy, 2003). Upon further inspection of eye fixational movements during the “Lissajous” condition, we observed a systematic smooth gaze pursuit following the centre of gravity of the moving stimulus, increasing retinal image stability. Through this stabilisation, adaptation could set in earlier, provoking faster reversals