Figure 5. Electrical stimulation could also impair performance on the frequency discrimination task (A, B) or shift behavior away from the BF of the neurons at the stimulation site (C, D). The site illustrated in A had a BF of 454 Hz, which was lower than the RF of 827 Hz, but stimulation at this site produced only a small shift in the direction of the BF (B; Fisher's exact test, n = 1169, p = 0.022). Rather, the psychometric function was slightly but consistently flattened on stimulation trials compared with nonstimulated trials. C, D, Example “paradoxical” effect in which the stimulation exerted a shift in the psychometric function in the direction opposite to what would be expected based on the frequency-tuning properties of the site. The site had a BF of 509 Hz, lower than the RF of 827 Hz, but stimulation increased the proportion of high-frequency judgments relative to the control trials (Fisher's exact test, n = 197, p = 0.0039).