Chapter 5

Chapter summary

Perception of loudness and pitch is based on responses in the cochlea. Loudness is coded by the rate of firing of cochlear cells, and pitch is coded by a combination of the place of maximum excitation (frequency-to-place conversion) and the rhythmic firing pattern of cochlear cells.

Our ability to locate sound sources in the horizontal plane is based on tiny differences in the time that a sound arrives at one ear relative to the other (inter-aural time difference or ITD), and on differences in intensity level between the ears (inter-aural level difference or ILD). Sound location in the vertical plane depends on the filtering effect of the outer ear.

Neuroimaging studies indicate that speech perception involves two parallel streams of processing in the cortex, a dorsal stream and a ventral stream. Spoken word recognition involves a pre-lexical stage in which the sound energy is broken up into primitive speech units, and a lexical stage in which the speech units are mapped onto known words.

Sounds are grouped perceptually on the basis of their location, spectral content, and timing (auditory scene analysis).

Disorders of hearing can be grouped into two categories: problems due to poor conduction of sound (conductive hearing loss) and damage to neural structures (sensori-neural hearing loss).