Activities of two typical sample-selective delay neurons showing decreasing (left column) and increasing (right column) trends. Note that all neuronal data during sample stimulus presentation and delay periods are sorted by a sample stimulus tilt angle. The broken-line graphs at the bottom indicate average discharge rates for different tilt angles during sample stimulus presentation (filled circles), former (F) half of delay (open triangles), and latter (L) half of delay (inverted open triangles). Dotted lines in the broken-line graphs indicate the spontaneous activity, and error bars indicate SE. FP, Frontoparallel orientation. Rasters and histograms above each broken-line graph display neuronal activities for three representative sample stimulus tilt angles. Bars at the top of the rasters indicate when the sample and test stimuli were on. Markers in each raster line indicate stimulus onset and offset. Other conventions of rasters and histograms are the same as in Figure 3.