Yes, it is ambiguous. 1) It could refer to "certain kinds of signal processing" (in which case I would have said " they are visual, auditory, or tactile"). 2) It could refer to "signal processing" (not "signal," which is an adjective telling you what kind of processing it is).
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.