Class Notes (1,000,000)
CA (610,000)
McMaster (50,000)
PSYCH (6,000)
PSYCH 1XX3 (1,000)
Joe Kim (1,000)
Lecture 1

PSYCH 1XX3 Lecture Notes - Lecture 1: Low Frequency, Hair Cell, Cochlea


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

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lAudition
Unit 1: introduction
-“If a tree falls in the forest and no one is around to heat it, does it still make a
sound?”
-Sound, is it strictly the produce of an external stimulus or a result of our own
sensory processing
-A falling tree would produce sound waves, and the auditory system translates
sound waves form vibrating objects into the psychological experience of
audition
-Does produce sound waves, but they don’t make sound unless an auditory
system is present to translate those waves into the perceptual experience of
audition
Unit 2: The Auditory Mechanisms of Dierent Species
Introduction to Auditory Mechanisms
-Mechanisms vary across di$erent species depending on speci%c needs
oWhere do they live? Water, land or air?
oDo they need to communicate over long distances?
oNeed to be able to receive high or low frequency sounds?
Sound Frequency
-Species di$er in range of frequencies that they can detect
oEx. Dog whistle – doesn’t produce audible sound to your own ears, but
get a dogs attention
oProduces a sound at high frequency beyond the range of human ears,
but well within the range of the
dog’s auditory system
- In Vertebrates
oHumans – 20 to 20,000 Hz
oWhales, dolphins and dogs have
a wider hearing range
oFrogs and birds have a much
narrower range
oLower frequency detection –
%sh, higher frequency detection
– bats and rodents
oIf %sh and bats were to
communicate, it would have to
be in a narrow band of
frequencies, ~2000 Hz – sounds
high-pitched to %sh and low-
pitched to bats

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Environmental Impacts on Auditory
Structure
-Audible frequency is determined in part by
the evolution of the structures of the
auditory system
- Basilar membrane contains
hearing
receptors
– sounds of di$erent frequencies
are processed along di$erent are of the
basilar membrane
The Basilar Membrane
- Varies in length across species, shortest in amphibians and reptiles,
longer in birds, longest in mammals
- Longer membrane = wider range of frequencies
Unit 3: The Stimulus – Sound Waves
-Sound travels in waves, but is much slower and requires a medium to
travel through
-Initiated by a vibrating object, or by forcing air past a small cavity
oVocal cords, guitar string, or pipe organ
-Causes air molecules surrounding the source of sound to move, and a chain
reaction of moving air particles
The Eardrum Responds to Air Pressure Changes
-Alternating bands of more and less compressed air molecules interact with
the eardrum to begin auditory processing
-Band of compressed air (crest) – eardrum gets pushed inwards
-Band of less dense air (trough) – eardrum moves outwards
Sine Waves
-Changes in air pressure over time that make up sound can be graphed as a
sine wave
-Three physical characteristics: amplitude, wavelength, purity: loudness,
pitch, and timbre
Amplitude – Measure of Loudness
-Greater amplitude are vibrations of greater intensity, higher waves =
louder sounds
-Humans are sensitive to a wide range of sound amplitudes
-Loudness is measured with a logarithmic scale of decibels (dB)
-Perceived loudness of a sound doubles for every 10 dB increase
oNormal conversation ~ 60 dB
oWhisper ~ 27 dB
oFront row of a rock concert ~ 120 dB
Brief exposure to sounds this loud can cause physical pain and
permanent damage

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Frequency – Measure of Pitch
-Distance between successive
peaks – wavelength/frequency
of the sound
-A$ects the perception of pitch
measured in Hertz (Hz)
-Cycles per second
-High frequency = high pitch,
low frequency = low pitch
-Audible zone humans can
detect are only a portion of
possible frequencies that can be produced
Timbre – Measure of Complexity/Purity
-Perception of timbre = complexity of the sound
-Most of the sounds we hear are complex and composed to multiple sound
waves that vary in frequency
oEx. Pluck a guitar string, vibrates as a whole – fundamental tone
oAlso vibrates at shorter
segments along the string –
overtones
oFinal sound is a mixture of
both tones, this combination
timbre
oPiccolo and Bassoon may
both play the same note, but
each instrument produces a
unique combination of
fundamental frequency and
overtones – still sound
di$erent to us even though
they’re producing the same frequency and amplitude
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