With the aim of automatically generating head motions during speech utterances, analyses are conducted for verifying the relations between head motions and linguistic and paralinguistic information carried by speech utterances. Motion captured data are recorded during natural dialogue, and the rotation angles are estimated from the head marker data. Analysis results showed that nods frequently occur during speech utterances, not only for expressing specific dialog acts such as agreement and affirmation, but also as indicative of syntactic or semantic units, appearing at the last syllable of the phrases, in strong phrase boundaries. Analyses are also conducted on the dependence on linguistic, prosodic and voice quality information of other head motions, like shakes and tilts, and discuss about the potentiality for their use in automatic generation of head motions. The paper also proposes a method for controlling the head actuators of an android based on the rotation angles, and evaluates the mapping from the human head motions.