Figure 1.

(a) Sequence of trial events. Each trial began when the monkey grabbed a response lever and fixated a small fixation target at the center of a computer screen. (b) Recording sites. Each symbol represents a recording site where neurons with what, where, or what-and-where delay activity were found. Typically, several neurons were found at the same site; hence, many symbols overlap and some symbols indicate more than one neuron. Data are combined across both monkeys. A.S., arcuate sulcus; P.S., principal sulcus. All recordings were from the surface of the lateral PF cortex.