Michael Heap (1988) conducted a systematic review of the research literature on NLP and found, after analysis of over 60 research studies, that it was lacking in evidence.
The present author is satisfied that the assertions of NLP writers concerning the representational systems have been objectively and fairly investigated and found to be lacking. These assertions are stated in unequivocal terms by the originators of NLP and it is clear from their writings that phenomena such as representational systems, predicate preferences and eye-movement patterns are claimed to be potent psychological processes, easily and convincingly demonstrable on training courses by tutors and trainees following simple instructions, and, indeed, in interactions in everyday life.
Adding,
Therefore, in view of the absence of any objective evidence provided by the original proponents of the PRS hypothesis, and the failure of subsequent empirical investigations to adequately support it, it may well be appropriate now to conclude that there is not, and never has been, any substance to the conjecture that people represent their world internally in a preferred mode which may be inferred from their choice of predicates and from their eye movements. […] These conclusions, and the failure of investigators to convincingly demonstrate the alleged benefits of predicate matching, seriously question the role of such a procedure in counselling.[24]
Heap (1988) remarks [25] that if the assertions made by proponents of NLP about representational systems and their behavioural manifestations are correct, then its founders have made remarkable discoveries about the human mind and brain, which would have important implications for human psychology, particularly cognitive science and neuropsychology. Yet there is no mention of them in learned textbooks or journals devoted to these disciplines. Neither is this material taught in psychology courses at the pre-degree and degree level. When Heap spoke to academic colleagues who spend much time researching and teaching in these fields, they showed little awareness, if any, of NLP.[25][26]
Heap (1988) argued that to arrive at such important generalisations about the human mind and behaviour would certainly require prolonged, systematic, and meticulous investigation of human subjects using robust procedures for observing, recording, and analysing the phenomena under investigation. "There is just no other way of doing this". Yet the founders of NLP never revealed any such research or investigation, and there is no evidence of its existence.[25] Indeed, Bandler himself claimed it was not his job to prove any of his claims about the workings of the human mind, "The truth is, when we know how something is done, it becomes easy to change" (ibid).[27]