THEORIES EXPLAINING THETHEORIES EXPLAINING THE
APPRECIATION OF DIFFERENTAPPRECIATION OF DIFFERENT
FREQUENCIES OF SOUNDSFREQUENCIES OF SOUNDS
► FIRST GROUP:FIRST GROUP:
Analysis of sound frequency is a function of cerebralAnalysis of sound frequency is a function of cerebral
cortex and cochlea merely transmits the sound.cortex and cochlea merely transmits the sound.
TELEPHONE THEORY OF RUTHERFORDTELEPHONE THEORY OF RUTHERFORD
VOLLEY THEORYVOLLEY THEORY SECONDSECOND
Frequency analysis is done by cochlea,which sendsFrequency analysis is done by cochlea,which sends
the information to the cerebral cortex.the information to the cerebral cortex.
► RESONANCE THEORY OF HELMHOLTZRESONANCE THEORY OF HELMHOLTZ
► PLACE THEORYPLACE THEORY
PLACE PRINCIPLE OFPLACE PRINCIPLE OF
FREQUENCY DISCRIMINATIONFREQUENCY DISCRIMINATION
It states that the perception 0f sound depends onIt states that the perception 0f sound depends on
where each component frequency produceswhere each component frequency produces
vibrations along the basilar membrane.vibrations along the basilar membrane.
CONCEPT OF RESONANACE POINT:CONCEPT OF RESONANACE POINT:
That point on the basilar membrane which is mostThat point on the basilar membrane which is most
strongly activated/stimulated by a travelling wave.strongly activated/stimulated by a travelling wave.
Distance between stapes and resonanceDistance between stapes and resonance
point is inversel proportional to thepoint is inversel proportional to the
frequency of sound waves .frequency of sound waves .
► high frequency sounds cause maximalhigh frequency sounds cause maximal
activation of basilar membrane near theactivation of basilar membrane near the
base of cochlea.(close to oval window andbase of cochlea.(close to oval window and
► Low frequency:Low frequency: at apex of cochlea(helicotrema)at apex of cochlea(helicotrema)
► Intermediate frequency sounds:Intermediate frequency sounds: in betweenin between
two extremestwo extremes
BASIS OF PLACE PRINCIPLEBASIS OF PLACE PRINCIPLE
STRUCTURE OF BASILAR MEMBRANE:STRUCTURE OF BASILAR MEMBRANE:
20000_30000 basilar fibres projecting from modiolus20000_30000 basilar fibres projecting from modiolus
toward outer wall.toward outer wall.
Basal end_fixed at modiolusBasal end_fixed at modiolus
Distal end_embedded in basilar membrane.Distal end_embedded in basilar membrane.
AT BASEAT BASE: basilar membrane: basilar membrane stiffstiff due todue to thick,thick,
short reed like fibresshort reed like fibres
AT APEX:AT APEX:basilar membranebasilar membrane compliantcompliant due todue to
thin,long fibresthin,long fibres
EXPERIMENTAL EVIDENCEEXPERIMENTAL EVIDENCE
SUPPORTING PLACE THEORYSUPPORTING PLACE THEORY
► Long exposure to loud noise of a particularLong exposure to loud noise of a particular
frequency destroys a specific portion of organ offrequency destroys a specific portion of organ of
► InIn high tone deafness,high tone deafness, organ of corti near base oforgan of corti near base of
cochlea or nerve supplying cochlea near basecochlea or nerve supplying cochlea near base
► During exposure to high frequency sound,cochlearDuring exposure to high frequency sound,cochlear
microphone potentials show greater voltage in hairmicrophone potentials show greater voltage in hair
cells near base of cochlea.cells near base of cochlea.
► There is point to point representation of basilarThere is point to point representation of basilar
membrane in auditory cortex.membrane in auditory cortex.