Reconstruction of target speed for the guidance of pursuit eye movements

We studied how object speed is reconstructed from the responses of motion-s elective cells for the generation of a behavior that is tightly linked to t he speed of visual motion. In theory, the speed of an object could be estim ated either from the speed tuning of the active population of motion-select ive cells or from the rate of displacement of activation across the cortica l map of visual space. We measured the pursuit eye movements evoked by stim uli containing two conflicting motion components: a local component designe d to excite motion-selective cells with a particular speed tuning and a dis placement component designed to excite cells with a sequence of spatial rec eptive fields. Pursuit eye movements were driven primarily by the local-mot ion component and were affected to only a small degree by the rate of targe t displacement across visual space. Extracellular single-unit recordings us ing the same stimuli revealed that the responses of cells in the middle tem poral visual area (MT) depended primarily on the local-motion component but were influenced by the displacement component to the same degree as were p ursuit eye movements. We conclude that the initiation of pursuit is consist ent with a reconstruction of target speed based on the speed tuning of the active population of MT cells.