Response patterns of single auditory-nerve fibers are compared under two conditions. The first condition is similar to the stimulus condition customarily used to determine pulsation threshold psychophysically. A 100-ms duration signal at a fiber's characteristic frequency (CF) is presented at 10 dB above threshold at a rate of 5/s. A 100-ms duration tonal masker is introduced during the interval between signal pulses, raised in intensity and PST response patterns collected at each masker level. The second condition is the same except that the signal is continuous rather than pulsed. In the pulsed-signal condition when the masker-evoked discharge rate equals the signal-evoked discharge rate, the response pattern resembles the firing pattern to a continuous tone. When the masker-evoked rate exceeds the signal-evoked rate, the response pattern is indistinguishable from the pattern evoked by a continuous signal plus a pulsed masker. For different masker frequencies the results are essentially the same when masker level is expressed relative to the fiber's excitatory response threshold at the frequency of the masking stimulus. It is suggested that “pulsation threshold” is an auditory illusion in which the central processor is presented with ambiguous information and accepts as a “perceptual hypothesis” the more likely possibility that a continuous signal is superimposed on a pulsed masker. Data presented previously on forward masking and unmasking [J. Acoust. Soc. Am. 62, S45–S46 (A) (1977)] will be reviewed and compared to the pulsation threshold data.