In this talk Andrea Fella says that (1) according to Abhidhamma the sense base of touch is always either pleasant or unpleasant and that it's never got a neutral tone to it. She also says that (2) according to Abhidhamma that the other four sense bases are all inherently neutral (of 2 adds that she isn't convinced).
Which part of the Abhidhamma did she get this from? I only have a copy of the CMA and couldn't find any parallel statements in there.
Comments are at about 33:15 to about 33:14 and from about 46:45 to about 48:25.
