Evidence of speed gradient sensitive neurons in the monkey extrastriate area MSTd

Optic flow is the changing array of light that is reflected from objects in the environment and is projected on the retinae during motion. Speed gradients are a natural component or optic flow and they are the result of the relative ordering of objects in depth. It has been proposed that speed gradient information may signal the direction and speed of self-motion as well as the three-dimensional structure of the environment. The dorsal region of the medial superior temporal area of the visual cortex, or MSTd, is believed to be the neuronal basis for the analysis of optic flow and therefore it could convey information about the direction and speed of self-motion and the three-dimensional structure of the environment. In our study, cells in MSTd were tested with random dot stimuli moving at different speeds (speed gradients). We found that cells in MSTd are sensitive to stimuli containing speed gradients. This supports a role for MSTd in determining the speed of self motion or the three-dimensional structure of the environment or both