Handbook of Psychology, Volume 4: Experimental Psychology

130 Audition

nerve represents the relative amplitude of a particular fre-
quency in the sound. The temporal discharge pattern of the
fiber indicates the time domain properties of the sound in this
frequency region. The overall level of neural discharge rate
indicates the sounds’s overall amplitude. Individual auditory
nerve fibers are topographically organized within the audi-
tory nerve bundle; fibers carrying low-frequency information
are toward the middle of the XIIIth bundle, and fibers carry-
ing high-frequency information are toward the outside of the
bundle. Thus, a spatial (spectral)-temporal representation of
the stimulating sound is transmitted via the auditory nerve to
the auditory brain stem. This spatial-temporal pattern repre-
sents the neural code for the sound waveform that is the com-
posite of the sounds generated from all of the sources in the
acoustic environment.

Central Auditory Nervous System

Figure 5.9 depicts a schematic diagram of the gross anatomy

of the major components of central auditory nervous system.

In addition to the afferent pathways indicated in Figure 5.9,

there is a network of efferent centrifugal connections as well

(Altschuler, Hoffman, Bobbin, & Clopton, 1989).

The cochlear nucleus has many different fiber types and

connections in its three main subdivisions. There is evidence

for lateral inhibitory networks in the cochlear nucleus that

may aid it in performing different types of spectral pattern

processing (Young, 1984). Processing of binaural informa-

tion occurs in the olivary complex, where the first significant

bilateral interactions occur. The medial superior olive is most

sensitive to interaural (between the ears) time differences,

Figure 5.9 Highly schematic diagram of the ascending (afferent) pathways of the central auditory sys-

tem from the right cochlea to the auditory cortex. No attempt is made to show the subdivisions and con-

nections within the various regions, cerebellar connections, or connections with the reticular formation.

Source: From Yost (2000), a compilation of similar diagrams by Ades (1959); Whitfield (1967);

Diamond (1973); Harrison and Howe (1974).

Ipsilateral

Sylvian

fissure Sylvianfissure

auditory

cortex

auditory

cortex

medial

geniculate

body

lateral

lemniscus

medial

geniculate

body

inferior

colliculus

lateral

lemniscus

cochlear

nucleus

right

cochlea

trapezoid body

superior

olivary

complexes

Contralateral

Commissure

of

inferior

colliculus

Commissure

of

Probst

inferior

colliculus