Spatio-temporal tuning in macaque area MT

Motion detection in apparent motion of random dot patterns (RDP) requires correlation across space and time. It has been difficult to study the temporal requirements for the initial correlation step because temporal measurements jointly depend on temporal filtering, delay-tuning and successive temporal integration. Moreover, it has been difficult to construct a stimulus containing a single delay only. To measure delay tuning independent of temporal integration, we constructed a motion stimulus containing a single delay value only, and with constant motion energy, irrespective of delay. The stimulus consists of a sparse random dot pattern with a two frame, single step dot lifetime. It is constructed by generating a dynamic random dot pattern on each stimulus frame, and showing this pattern once again at a delay of n frames later, superimposed on the newly generated RDP. Each frame thus consists for 50% of new random dots and 50% displaced random dots. The delay between corresponding dot patterns can be chosen freely, without affecting the number of steps per second, steps, in total, and temporal frequency content. We measured the activity of motion-sensitive neurons in area MT in anesthesized monkeys as a function of both step size and delay. The data will be compared to the spatio-temporal characteristics found in human motion perception.