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PSYCH 1XX3 (1,000)
Joe Kim (1,000)
Lecture 8

PSYCH 1XX3 Lecture Notes - Lecture 8: Basilar Membrane, Sound, Coevolution


Department
Psychology
Course Code
PSYCH 1XX3
Professor
Joe Kim
Lecture
8

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The$tree$dilemma$
The$auditory$system$can$translate$sound$waves$from$vibrating$objects$into$the$
psychological$experience$of$audition.$
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The$sound$waves$themselves$do$not$make$sound$unless$an$auditory$system$is$
present$to$translate$those$waves$into$the$perceptual$experience$of$hearing.$
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The$auditory$mechanisms$of$different$species
Species$vary$in$the$range$of$frequencies$they$can$detect
Ex.$A$dog$whistle$does$not$produce$any$sound$to$a$human$but$can$easily$get$a$
dogs$attention$as$they$are$able$to$hear$higher$frequencies$than$humans.$
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Audible$frequency$range$is$determined$in$part$by$the$evolution$of$the$structures$of$
the$auditory$system.
One$key$structure$is$the$basilar$membrane which$contains$the$hearing$
receptors;$sounds$of$different$frequencies$are$processed$along$different$areas$
of$the$basilar$membrane.$
The$basilar$membrane$varies$in$length$across$species,$a$longer$basilar$
§
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Audition
Saturday,$March$10,$2018
1:18$PM

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The$basilar$membrane$varies$in$length$across$species,$a$longer$basilar$
membrane$allows$processing$of$a$wider$range$of$frequencies.
§
The$Stimulus$-Sound$Waves
Sound$travels$in$waves$and$requires$some$medium$to$travel$through.$
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Sound$waves$are$initiated$by$either$a$vibrating$object,$like$vocal$chords$or$a$guitar$
sting,$a$sudden$burst$of$air,$like$a$clap,$or$by$forcing$air$past$a$small$cavity,$like$a$pipe$
organ.$
This$causes$the$air$molecules$surrounding$the$source$of$the$sound$to$move,$
causing$a$chain$reaction$of$moving$air$particles.$
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Similar$to$the$ripple$in$a$pool$of$water,$travels$in$all$direction.$
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The$alternating$bands$of$compressed$air$molecules$interact$with$the$eardrum$to$
begin$auditory$processing.$A$band$of$compressed$air$molecules$causes$your$ear$drum$
to$get$pushed$$slightly$inwards,$whereas$a$band$of$less$dense$air$particles$causes$the$
eardrum$to$move$outwards.$
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