The mammalian motor cortex sends efferent motor commands and receives two kinds of feedback, internal and external. The avian vocal command center, robustus archistriatalis (RA) which corresponds to the mammalian motor cortex, also receives internal and external feedback which are integrated in the hyperstriatum ventralis pars caudalis (HVc) . The present study clarifies the avian feedback path by analysing neural substrates in the HVc: the HVc contains 3 kinds of neurons in which auditory responses interact and constitute both feedback paths. A speculative theory of the song production mechanism is discussed on the basis of the evidence of synaptic connections between three kinds of the HVc neurons.
The followings ermerged from the study of Japanese speech sound perception of seven patients with Nucleus multichannel cochlear implant. For nonsense monosyllable sounds, the percent recognition in the cochlear implant alone or in lipreading alone did not correlate to that of cochlear implant plus lipreading. For words or sentences, however, the percent recognition in the cochlear implant alone correlated highly with that of the cochlear implant plus lipreading. The auditory and the visual signals provided mutually complementary information for monosyllable sound recognition, whereas the auditory signal provided major information for word or sentence recognition. The role of the visual signal was not only supplemental, but more active in semantic identity for Japanese word and sentence recognition.