"Fit the sound and vision to the pattern of his brainwaves..."

In reality, of course, there is no clear difference between a "pitch" and a "rhythm"; both are subspecies of periodic phenomena related to the physical oscillation of air molecules, electric currents, or other media. In practice the distinction is somewhat provisional and is in principal a perceptual or psychoacoustic effect as opposed to a material property.

By definition a transient must spend at least some of its finite period in the "on" part of the cycle, meaning there can be no such thing as an ideal transient (also known as an ideal pulse), which would have zero duration and thus be infinitely thin. Such transients, although conceivable, would likely escape detection by anyone, and are therefore seldom encountered. 

Pitch and rhythm are ultimately just descriptions applied to collections of detectable transients that are variously interepreted by brains as being components of (re)cognizeable harmonic or rhythmic structures. The rate of oscillation, along with other cues like harmonic content, determines the mode of interpretation, so that a pitch or frequency is equally a very fast rhythm, and a rhythm is also like a kind of extremely low-frequency pitch or melody.