Dissociation of salience-driven and content-driven spatial attention to scene category with predictive decoding of gaze patterns

Scene content is thought to be processed quickly and efficiently to bias subsequent visual exploration. Does scene content bias spatial attention during task-free visual exploration of natural scenes? If so, is this bias driven by patterns of physical salience or content-driven biases formed through previous encounters with similar scenes? We conducted two eye-tracking experiments to address these questions. Using a novel gaze decoding method, we show that fixation patterns predict scene category during free exploration. Additionally, we isolate salience-driven contributions using computational salience maps and content-driven contributions using gaze-restricted fixation data. We find distinct time courses for salience-driven and content-driven effects. The influence of physical salience peaked initially but quickly fell off at 600 ms past stimulus onset. The influence of content effects started at chance and steadily increased over the 2000 ms after stimulus onset. The combination of these two components significantly explains the time course of gaze allocation during free exploration.