(Fig. 10D). The retinal motion in these optic flow patterns is more complex, and although they contain a location with no motion (a false FOE), this no longer corresponds to the direction of motion. Recent experiments have shown that humans are able to accurately perceive their self-motion in these conditions, suggesting that the brain performs a more complex computation than simply identifying the location of the FOE. Eye movements can also play a role in heading perception. Information about eye rotation has been found to improve the accuracy of heading estimation in some conditions.

The brain appears to process optic flow patterns in area MST and adjacent parietal areas such as area 7A. Complex motion-sensitive neurons are found in the dorsal portion of area MST (MSTd), which receives direct input from area MT and eye movement areas, such as the superior colliculus, the lateral intraparietal area, and the frontal eye fields. Many MSTd neurons have large receptive fields, some of which cover nearly the entire visual field. Instead of responding best to the simple motion of bars, these large-field neurons respond optimally to specific patterns of motion. Some of these cells respond best to the expansion optic flow patterns produced by translations, other cells respond best to rotational optic flow patterns, and still others appear to respond best to specific combinations of expansion and rotation. Recently, Lee Stone and John Perrone developed a model that predicts both the response of MSTd neurons and the ability of humans to perceive their self-motion. In their model each neuron is tuned to a specific type of self-motion. The neurons have large receptive fields that receive input from MT neurons. Direct support for a role for MST in self-motion perception comes from microstimulation studies in area MST of awake behaving monkeys that were trained on a heading discrimination task. Ken Britten and coworkers showed that electrical microstimulation of MST frequently biased the monkeys' decisions about their heading, and these induced biases were often quite large. These results suggest that MST has a direct role in the perception of heading from optic flow.

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