Abstract
Research into the flanker congruency effect has previously focused on static stimuli free from perceptual noise, such as letters, digits and arrows. In a recent task using random dot kinematograms (RDKs), we manipulated perceptual noise through motion coherence and fitted the Dual-Stage Two-Phase Model (DSTP) of Hübner, Steinhauser & Lehle (2010) using Bayesian parameter estimation. DSTP posits competition between an early selection stage vulnerable to flanker interference and a later, highly selective stage driven only by the target. Our results suggested that the onset of this late selection (the point at which flankers are fully suppressed) is delayed in high compared to low noise conditions, leaving more time for flankers to interfere through the early selection stage. Previous work by Song and colleagues has shown that speeded choice reaching tasks (CRTs) allow us to better understand the time-course of selection. For example, movement trajectories have been shown to be curved in conditions of high interference, suggesting interference can persist past the point of movement onset. Here, we rerun the RDK flanker task as a CRT, in which participants respond by moving a stylus towards a response box. Interestingly, while congruency effects in high-noise conditions were reflected in curvature, congruency effects in low noise conditions were reflected in initiation latency. In agreement with the modelling results, this suggests the time at which flankers are suppressed is modulated by noise, occurring earlier in low noise conditions and later in high noise conditions. We discuss these results further along with their implications and alternative explanations.