Effects of salience are both short- and long-lived

Abstract

A salient object can attract attention irrespective of its relevance to current goals. However, this bottom up effect tends to be short-lived (e.g. <150 ms) and it is generally assumed that top down processes such as goals or task instructions operating in later time windows override the effect of salience operating in early time windows. While the majority of studies on visual search and scene viewing comply with the assumptions of top down and bottom up processes operating in different time windows and that the former overrides the latter, we point to some possible anomalies in decision research. To explore these anomalies and thereby test the two key assumptions, we manipulate the salience and valence of one information cue in a decision task. Our analyses reveal that in decision tasks top down and bottom up processes do not operate in different time windows as predicted, nor does the former process necessarily override the latter. Instead, we find that the maximum effect of salience on the likelihood of making a saccade to the target cue is delayed until about 20 saccades after stimulus onset and that the effects of salience and valence are additive rather than multiplicative. Further, we find that in the positive and neutral valence conditions, salience continues to exert pressure on saccadic latency, i.e. the interval between saccades to the target with high salience targets being fixated faster than low salience targets. Our findings challenge the assumption that top down and bottom up processes operate in different time windows and the assumption that top down processes necessarily override bottom up processes.

Keywords: Bottom up control; Eye movements; Saccadic latency; Saccadic selection; Salience; Top down control.