"Non-vocalization" (N-V) is a newly described phonological error process in hearing impaired speakers. In N-V the hearing impaired person actually articulates the phoneme but without producing a voice. The result is an error process looking as if it is produced but sounding as if it is omitted. N-V was discovered by video recording the speech of two groups, "profoundly" and "severely" hearing impaired adults in four elicitation tasks of varying difficulty, and analysing 2065 phonological error processes (substitutions, omissions, and N-V) according to 24 criteria resulting in 49,560 data points. Results, which are discussed in view of the theory "Phonology as Human Behaviour" (PHB), indicate that: (a) The more communicative the error process was; the more effort was made for its production and the more frequent its distribution; (b) The easier the elicitation task was, the more frequent the use of communicative error processes; c) The more difficult the elicitation task was, the more frequent the use of the relatively less communicative and easier to produce error processes; and d) The process of N-V functioned like a communicative error process for the group of profoundly hearing impaired adults. (Contains 4 figures.)