Feature-based surround suppression in the motion domain
Creators: name: Yoo, Sang-Ah
name: Tsotsos, John K.
name: Mazyar Fallah
Publisher: name: F1000Research
Year: 2017

description: The Selective Tuning model of visual attention (ST, Tsotsos, 1995) proposed feature-based attentional surround suppression. That is, when a certain feature is attended, processing of other features represented nearby in the feature map is suppressed (e.g., orientation (Tombu &amp; Cutzu, 2008), action (Loach <i>et al.</i>, 2008), colour (Störmer &amp; Alvarez, 2014), and VWM (Kiyonaga &amp; Egner, 2016)). We investigated whether feature-based surround suppression occurs in the motion domain using motion repulsion (Marshak &amp; Sekuler, 1979): When two superimposed motions moving in different directions are presented, people tend to overestimate the directional difference between the two motions. A previous study suggested that attention to one motion surface reduces motion repulsion by inhibiting the unattended motion surface (Chen <i>et al.</i>, 2005). Motion repulsion is also affected by the speed of motion, showing lesser repulsion as the speed increases (Curran &amp; Benton, 2003; Perry <i>et al.</i>, 2014). We hypothesized that attention to one motion surface will reduce motion repulsion to a greater degree when two motions move in similar directions than in dissimilar directions due to feature-based surround suppression. We also studied the relationship between motion direction and speed and their interactive effects on motion repulsion. In Experiment 1, participants reported directions of two superimposed motions presented for 2 sec. In the unattended condition, participants viewed both motion surfaces equally, whereas in the attended condition, they were attended to a cued motion surface and detected brief directional shift on the surface as an attentional task. Then, they reported directions of the motions. Experiment 2 controlled the task load between the two attentional conditions. Participants detected directional shift in the unattended condition as well but there was no attentional cue. The other experimental conditions were identical to those in Experiment 1. There were 5 directional differences (10~50 deg) and 2 speeds (3 and 6 deg/sec). Motion repulsion was defined by difference between the perceived and the actual directional differences and attentional modulation was defined by difference in motion repulsion between the attended and the unattended conditions. In Experiment 1, there was no significant attentional modulation on motion repulsion for a slower speed (3 deg/sec) but significant difference between the two attentional conditions was observed when motion speed was faster (6 deg/sec). There was greater motion repulsion in the attended condition at 10, 40, and 50 deg difference. Although this is opposite to the previous results (Chen <i>et al.</i>, 2005), many differences in experimental settings can explain this. Especially, our participants reported both motion directions even in the attended condition, thus, they could not totally filter out the unattended motion direction. Importantly, difference in motion repulsion between the two attentional conditions disappeared at 20~30 deg directional differences. It suggests that in the attended condition, the unattended motion direction was inhibited by feature-based attentional surround suppression so motion repulsion decreased. Faster motion speed reduced motion repulsion only in the unattended condition, indicating that top-down (attention) and bottom-up (speed) factors independently influenced motion repulsion. Experiment 2 is still in progress. However, it shows similar patterns as in Experiment 1. Therefore, feature-based attentional surround suppression occurs in the motion domain as Selective Tuning model proposed.