Aiming at natural F_0 control for conversational speech synthesis, F_0 characteristics are analyzed from both generation and perception viewpoints. By systematically designing conversational situations and utterances with adverb phrases expressing different degree of markedness, their F_0 characteristics are compared. The comparison shows the consistent F_0 control dependencies not only on adverbs themselves but also on the attribute of neighboring adjective phrases. Strong positive/negative correlation is observed between the markedness of adverbs and F_0 height when an adjective phrase with a positive/negative image is followed to the current adverb phrase. These consistencies have been perceptually confirmed by naturalness evaluation tests using the same two-phrase samples with different F_0 heights. These results indicate the possibility of F_0 control for natural conversational speech using lexical markedness information and adjacent word attributes.