The Neural Control of Visually Guided Eye Movements
C. Cortical Mechanisms of Visually Guided Saccadic Eye Movements

Figure 16 shows how the data were plotted. The percent of time the monkey selected the target in the receptive field is plotted as a function of the temporal asynchrony between the targets as shown on the abscissa. If the stimulation were to increase the probability with which the target in the receptive field of stimulated neurons is chosen, the curve should shift to the left; this we call facilitation. If stimulation were to decrease the probability of choosing the target in the receptive field, the curve should shift to the right; this we call interference.