Neural mechanisms underlying specific visual tasks during self-motion
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Object movement detection during observers’ self-motion is critical in navigation. Given ample optical available variables, which of them would be used would help us reveal the strategies being employed. In this work, using functional magnetic resonance imaging (fMRI) methods, we investigated the neural substrate underlying specific visual motion related tasks, such as time to passage (TTP), depth parallax, and collision. Using a visual search paradigm implemented with MATLAB, we developed a psychophysical task to investigate how the target characteristics (initial depth, initial eccentricity, and independent velocity), spatial attention, and heading estimation would affect visual search, for better understanding the mechanisms involved in object movement detection during self-motion. The fMRI analysis shows that: 1. Bilateral precentral sulcus (PreCS), postcentral sulcus (PostCS) and bilateral hMT are strongly activated during the TTP task. 2. Cortical regions along the dorsal visual processing pathway, including bilateral hMT, superior parietal gyrus (SPG), PostCS, PreCS and superior frontal gyrus (SFG), play important roles in our depth perception test. 3. In the collision test, similar activation pattern has been found in normal controls and stroke patients with visual deficits, intraparietal sulcus (IPS), SPG, supplementary area (SMA) and premotor regions are highly activated. The psychophysical results in visual search tasks indicate targets located in central visual field and target placed closer to the observer are easier to detect, looming distractor demands attention, the detrimental effect increases with the increasing of the target eccentricity level, no preference has been found in visual search among different heading directions in this test. In summary, cortical regions along visual motion processing pathway are highly involved in object movement detection during self-motion, the observers will take flexible strategies when different optical cues are provided.