In a discussion of the MLAT and PLAB, Wesche (1981) Wesche, M.B. (1981). Language aptitude measures in streaming, matching students with methods, and diagnosis of learning problems. In: Individual differences and universals in language learning aptitude. K.C. Diller, Editor. Rowley, MA: Newbury House Publishers, pp. 119-154. noted that PLAB part 4 is a measure of inductive learning of foreign language grammar, while the MLAT (mentioned above) does not include a direct measure of inductive learning. She further notes that PLAB part 5 also measures the inductive learning of foreign language tones in different contexts. She states that low PLAB scores on parts 5 and 6 are often reflective of hearing problems and that PLAB Part 6 (Sound-Symbol Association) measures the phonetic coding ability described by Carroll in his description of the components of foreign language aptitude.
