Speed skills: measuring the visual speed analyzing properties of primate MT neurons

Knowing the direction and speed of moving objects is often critical for survival. However, it is poorly understood how cortical neurons process the speed of image movement. Here we tested Mi neurons using moving sine-wave gratings of different spatial and temporal frequencies, and mapped out the neurons' spatiotemporal frequency response profiles, The maps typically had oriented ridges of peak sensitivity as expected for speed-tuned neurons. The preferred speed estimate, derived from the orientation of the maps, corresponded well to the preferred speed when moving bars were presented. Thus, our data demonstrate that MT neurons are truly sensitive to the object speed. These findings indicate that MT is not only a key structure in the analysis of direction of motion and depth perception, but also in the analysis of object speed.