Abstract
Visual attention is thought to be driven by the interplay between low-level visual features and task dependent information content of local image regions, as well as by spatial viewing biases. Though dependent on experimental paradigms and model assumptions, this idea has given rise to varying claims that either bottom-up or top-down mechanisms dominate visual attention. To contribute toward a resolution of this discussion, here we quantify the influence of these factors and their relative importance in a set of classification tasks. Our stimuli consist of individual image patches (bubbles). For each bubble we derive three measures: a measure of salience based on low-level stimulus features, a measure of salience based on the task dependent information content derived from our subjects' classification responses and a measure of salience based on spatial viewing biases. Furthermore, we measure the empirical salience of each bubble based on our subjects' measured eye gazes thus characterizing the overt visual attention each bubble receives. A multivariate linear model relates the three salience measures to overt visual attention. It reveals that all three salience measures contribute significantly. The effect of spatial viewing biases is highest and rather constant in different tasks. The contribution of task dependent information is a close runner-up. Specifically, in a standardized task of judging facial expressions it scores highly. The contribution of low-level features is, on average, somewhat lower. However, in a prototypical search task, without an available template, it makes a strong contribution on par with the two other measures. Finally, the contributions of the three factors are only slightly redundant, and the semi-partial correlation coefficients are only slightly lower than the coefficients for full correlations. These data provide evidence that all three measures make significant and independent contributions and that none can be neglected in a model of human overt visual attention.
Highlights
In daily life, eye movements center parts of a scene on the human fovea several times a second [1]
Recent arguments emphasize the influence of tasks and motor constraints
The stimuli are composed of small image patches
Summary
Eye movements center parts of a scene on the human fovea several times a second [1]. The selection process is an important aspect of attention, and it has a profound impact on our perception [3]. Goal-driven, top-down mechanisms adapt eye movements to the specific task [4,5]. Bottom-up mechanisms that consider only sensory-driven aspects, such as local image features [6], contribute to the fixation selection process. Characteristics inherent to the visual apparatus, such as the spatial bias to the center region [7] and geometric properties of saccades [8], are widely acknowledged to influence the selection of fixation points. The relative roles and the interaction of these mechanisms are not understood, and a quantitative understanding of the principles of fixation selection is still lacking
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