Abstract
In daily life the brain is exposed to a large amount of external signals that compete for processing resources. The attentional system can select relevant information based on many possible combinations of goal-directed and stimulus-driven control signals. Here, we investigate the behavioral and physiological effects of competition between distinctive visual events during free-viewing of naturalistic videos. Nineteen healthy subjects underwent functional magnetic resonance imaging (fMRI) while viewing short video-clips of everyday life situations, without any explicit goal-directed task. Each video contained either a single semantically-relevant event on the left or right side (Lat-trials), or multiple distinctive events in both hemifields (Multi-trials). For each video, we computed a salience index to quantify the lateralization bias due to stimulus-driven signals, and a gaze index (based on eye-tracking data) to quantify the efficacy of the stimuli in capturing attention to either side. Behaviorally, our results showed that stimulus-driven salience influenced spatial orienting only in presence of multiple competing events (Multi-trials). fMRI results showed that the processing of competing events engaged the ventral attention network, including the right temporoparietal junction (R TPJ) and the right inferior frontal cortex. Salience was found to modulate activity in the visual cortex, but only in the presence of competing events; while the orienting efficacy of Multi-trials affected activity in both the visual cortex and posterior parietal cortex (PPC). We conclude that in presence of multiple competing events, the ventral attention system detects semantically-relevant events, while regions of the dorsal system make use of saliency signals to select relevant locations and guide spatial orienting.
Highlights
In any everyday life situation the sensory system receives more information from the outside world than the brain can fully process, with many objects and events that compete for the limited processing resources
The same study showed that semantically-relevant, gaze/attention-grabbing events were processed in the ventral attention system, indicating a possible dissociation between the dorsal and the ventral frontoparietal systems when orienting attention within complex visual environments, in the absence of any explicit goal-directed task. We extend this line of investigation by enquiring how competing visual events are processed in the attention control networks, and how such competition interacts with stimulus-driven signaling
The aim of this study was to investigate the role of stimulusdriven salience and competition between distinctive visual events during free-viewing of naturalistic stimuli, in the absence of any explicit goal-directed task
Summary
In any everyday life situation the sensory system receives more information from the outside world than the brain can fully process, with many objects and events that compete for the limited processing resources. When the target is characterized by a very distinctive feature (e.g., a red target-letter among green distractor-letters), the target seems to ‘‘pop-out’’ of the visual array, the detection is fast and the search times are largely independent of the number of distractors (efficient search). In this situation, the sensory characteristics of the visual input guide the selection process and attention is attracted automatically towards the salient pop-out target (stimulus-driven control, Theeuwes, 1992; Yantis, 1993). The selection process is governed primarily by internal knowledge about the target-defining features and attention is controlled in a voluntary manner (goal-directed control, Bacon and Egeth, 1997; see Duncan and Humphreys, 1989, 1992)
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