Maria Nordfang

Visual Attention Lab, Brigham & Women’s Hospital

Selection of color singletons, nonspatial features, and locations – separate influences on attentional weights?

 

An object with a high local feature contrast is more readily encoded than an otherwise similar object with lower local feature contrast (e.g., Theeuwes, 1992). Likewise, an object with a feature that is relevant to the current task is more readily encoded than an otherwise similar object without this task-relevant feature (e.g., Shibuya & Bundesen, 1988; Wolfe, Cave, & Franzel, 1989). The attentional weight of an object thus seems to depend on two components: the feature contrast of the object and the task-relevance of the features belonging to the object. It is highly debated how these two components relate to each other and whether both come into play at early stages of visual selection (e.g., Theeuwes, 2010; Töllner, Müller, & Zehetleitner, 2012; Yantis & Egeth, 1999). We investigated relations between feature contrast and task relevance through a series of experiments with very brief exposure durations and analyzed the data by detailed computational modeling. The results revealed concurrent effects of feature contrast and task relevance. Both effects were present at exposure durations of 20 milliseconds. We estimated attentional weights by fitting the data to a mathematical model based on Bundesen’s (1990) theory of visual attention (TVA). The weight of a singleton object was proportional to an otherwise similar nonsingleton object. Furthermore, both target weights and distractor weights showed strong variations across spatial locations, but for each subject, the ratio of the weight of a distractor to the weight of a target at the same location was approximately constant. The results suggest that attentional weights are products of local feature contrast, task relevance and location pertinence.