This term is sometimes used to describe man's mechanical nature. This applies to common man in general but especially to the organic portal or Preadamic man and even more to the psychopath.
The idea is that man simply responds to stimuli and learns via a feedback system coupled with some innate preferences such as desire for food and sex. The behaviorist school of psychology starts from the assumption that man always is and can be no more than a reaction machine. Although the premises are simple, the behaviors can be highly complicated and guided by much abstract thinking.
People have a tendency to project their own internal landscape on others. Thus they are liable to incorrectly assume that the inner life of others resembles their own. Likewise, people may consider their own activity as unique or inspired when it is only a composite of reactions.
Man being a reaction machine applies to all the lower centers. This is most obvious in the moving/instinctive center, where actual physical reflexes belong. The emotional center version of this is expressed as categorical value judgements of like and not like, right and wrong, as blanket denial of the unpleasant, as automatic aggression and any range of quick, unthinking reactions that most often are simply taken for granted and not further analyzed by the rest of the mind. The intellectual version of the reaction machine behavior is expressed in 'formatory thinking,' i.e. black and white thinking without adequate awareness of context or simple rote repetition of facts.
Mouravieff compares man to a juke box with a number of records. Once a record has stopped playing, another record is brought in via association. The basic records are formed at an early age and later only new variations of the same are added. The records may be physical, emotional or intellectual in their emphasis, the mechanicity involves all these functions, although one or another may be more expressed with a specific individual.
The reaction machine can have symbolic representations for all physical/emotional/intellectual contents of the human experience. However the symbolic representation Is not the same thing as the experience. Distinguishing the mimicry of the experience from the experience itself is very difficult from the outside.
Thinking in terms of evolution, we could say that the organic portal mimics and steals from the individually souled in order to get the form, even if without the content. Mimicking the form may later prepare a space for the content itself. However, the mimicry-based being is not choosing the content and thus is subject to the prevailing winds of the psychic climate, which may tend to either STS or STO. At a subsequent level, the student of the 4th Way can be said to prepare a space for the soul to manifest by 'fusing a real I.' Thus the passage between reaction machine and conscious being may be incremental over a lifetime. However, according to the 4th Way, the embryonic soul in potential must be present from birth for the process to go beyond mimicking form.
Specially in the case of psychopaths, the effects of the reaction machine on a souled individual may be very confusing. The souled individual will typically invent excuses and fill in the gaps in the psychopath's behavior in order to avoid facing the reality of facing a qualitatively different, alien life form. People sometimes tend to take even a very poor simulation of ethics or conscience for the real thing because facing the complete absence of same in another is too unpleasant or scary. It may also happen that people be attracted to 'reaction machine' or psychopaths because these can reflect the people's expectations without being encumbered by any fundamentally own nature, at least for a time. However, such mimicry is generally predatory, working as a camouflage mechanism for other intentions.