Mislocalizations in saccadic and mask-induced suppression of displacement

摘要

'Saccadic suppression of displacement' (e.g., Deubel, Schneider, & Bridgeman, 1996) denotes a difficulty in discriminating small 'jumps' (displacements) of a visual target when these jumps occur during a saccadic eye movement. The effect is supposed to reflect some aspect of spatial updating across saccades. More specifically, it is assumed to result from the necessity to compare pre- to post-saccadic coordinates. Recently, we have reported a similar difficulty in a condition without saccades, when the jump was obscured by a full-screen pattern mask (Zimmermann, Born, Fink, & Cavanagh, 2014). We suggested that, rather than spatial updating, saccadic suppression of displacement may also primarily reflect the saccade's masking effect on the visual input stream. We further hypothesized that masking may cause an underestimation in the perceived size of the target jump. Here, instead of using the classic binary response mode ('leftward or rightward jump?'), participants were asked to precisely indicate the target's perceived starting position by mouse click. In accordance with a smaller perceived jump, the initial target position was systematically mislocalized towards the target's final position in both mask and saccade conditions. The systematic bias increased with larger target jumps, reminiscent of the phenomenon of saccadic or mask-induced compression of space (Ross, Morrone, & Burr, 1997; Zimmermann et al., 2014). In contrast, in a control condition without saccades or masks, small displacement sizes ( 1 deg) were slightly overestimated. Finally, when a short blank interval between the disappearance of the target at its initial position and its reappearance at the displaced position was introduced, no systematic mislocalizations occurred, suggesting that the effect depends on a critical time window for integration of spatial positions, again reminiscent of the saccadic compression window. These results are further evidence for a common mechanism underlying saccadic and mask-induced mislocalization and suppression effects.