He was responding inappropriately to questions (i.e. saying "no" when he meant to say "yes"), but appeared to understand what was being said to him.
 The patient is able to speak normally. 
(ROOT (S (NP (PRP He)) (VP (VP (VBD was) (VP (VBG responding) (ADVP (RB inappropriately)) (PP (TO to) (NP (NP (NNS questions)) (PRN (-LRB- -LRB-) (PP (FW i.e.) (S (VP (VBG saying) (`` ``) (NP (DT no) ('' '') (SBAR (WHADVP (WRB when)) (S (NP (PRP he)) (VP (VBD meant) (S (VP (TO to) (VP (VB say) (INTJ (`` ``) (UH yes) ('' '')))))))))))) (-RRB- -RRB-)))))) (, ,) (CC but) (VP (VBD appeared) (S (VP (TO to) (VP (VB understand) (SBAR (WHNP (WP what)) (S (VP (VBD was) (VP (VBG being) (VP (VBD said) (PP (TO to) (NP (PRP him))))))))))))) (. .)))
(ROOT (S (NP (DT The) (NN patient)) (VP (VBZ is) (ADJP (JJ able) (S (VP (TO to) (VP (VB speak) (ADVP (RB normally))))))) (. .)))
( He ( ( ( ( ( was ( ( responding inappropriately ) ( to ( questions ( -LRB- ( ( i.e. ( ( saying `` ) ( ( no '' ) ( when ( he ( meant ( to ( say ( `` ( yes '' ) ) ) ) ) ) ) ) ) ) -RRB- ) ) ) ) ) ) , ) but ) ( appeared ( to ( understand ( what ( was ( being ( said ( to him ) ) ) ) ) ) ) ) ) . ) )
( ( The patient ) ( ( is ( able ( to ( speak normally ) ) ) ) . ) )