As an alternative measure of difference in neural activity elicited by task conditions, we also computed the mean rate for each multi-unit’s preferred, intermediate, and nonpreferred WM items (objects × upper/lower locations; Figures S1C and S1D). This was computed separately for each multi-unit and time point, since PFC units often have complex dynamics with different preferences at different time points. To avoid circularity, calculation of item preference and of mean rates for the preference-sorted items was performed on odd and even-numbered trials, respectively.
