Audition Anatomy outer ear middle ear inner ear

Audition • The encoding of pitch • The encoding of loudness • The perception

Anatomy * * Tympanic membrane Sensation and Perception - audition. ppt © 2001 Laura

Anatomy • Outer ear – pinna (pinnae) - visible ear • funnels sound towards

Anatomy Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 5

Anatomy • Inner ear - cochlea – oval window • sets up waves in

Anatomy Tectorial membrane Hair cells Sensation and Perception - audition. ppt © 2001 Laura

Ascending Auditory Pathway Superior Olivary Nucleus reflexive localization Inferior Colliculus combines auditory with visual

Tonotopic Mapping • Orderly representation of sound in the cortex – frequencies are represented

Tonotopic map of Temporal Lobe Sensation and Perception - audition. ppt © 2001 Laura

Sound - Physical Qualities • Vibration in a medium • Alternating compressions and rarefactions

Amplitude Note: prolonged exposure to sounds over 85 Db produces permanent hearing loss Sensation

Sound - Psychological Qualities • Pitch – varies from low to high – primarily

Complex Relationships • Unlike color perception, there is not a simple relationship between the

Complex Relationships • Pitch is primarily based on frequency • Two other factors influence

Pitch Scales * Octave scale results in a straight line * least noticeable change

Complex Relationships • Amplitude also influences pitch – as amplitude increases high tone get

Complex Relationships • Loudness is primarily based on amplitude – frequency also influences loudness

Equal Loudness Contours Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph.

Encoding Pitch • Von Bekesy’s Place Theory – peak of the envelope of the

Encoding Pitch Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D.

Encoding Pitch • Wever’s Volley Theory – nerves fire in a volley (sequence) to

Encoding Loudness • Cells respond to a specific range of firing – within the

Complex Tone Combinations • Ohm’s Law – the ear is a frequency analyzer (Fourier

Slides: 24

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Audition • Anatomy – outer ear – middle ear – inner ear • Ascending auditory pathway – tonotopic mapping • Physical and Psychological qualities of sound – The complex relationship between the physical and psychological variables Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 1

Audition • The encoding of pitch • The encoding of loudness • The perception of complex tone combinations – Ohm’s law – exceptions Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 2

Anatomy • Outer ear – pinna (pinnae) - visible ear • funnels sound towards ear drum • helps in sound localization – external auditory canal – tympanic membrane • vibrates to transmit sound wave • Middle ear – ossicles - malleus, incus, stapes • amplifies vibrations – Eustachian tube • equalizes pressure Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 4

Anatomy • Inner ear - cochlea – oval window • sets up waves in the fluid filled cochlea – helicotrema • opening between the two outer tubes – transduction • basilar membrane • tectorial membrane • hair cells – round window releases pressure of waves – auditory nerve carries signal to brain Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 6

Ascending Auditory Pathway Superior Olivary Nucleus reflexive localization Inferior Colliculus combines auditory with visual location information MGN selective attention Temporal Lobe left - language right - sounds tonotopic mapping Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 8

Tonotopic Mapping • Orderly representation of sound in the cortex – frequencies are represented parallel to the surface • lower frequencies are represented inferior (lower) than higher frequencies – loudness is represented as distance from the surface • soft sounds are represented near the surface • louder sounds are represented deeper in cortex Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 9

Sound - Physical Qualities • Vibration in a medium • Alternating compressions and rarefactions of pressure • Physical variations in sound – frequency • number of cycles per second (cps) • often written as Hertz (Hz) – amplitude • degree of change in pressure • measured in decibels (Db) – complexity • number of different frequencies present Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 11

Sound - Psychological Qualities • Pitch – varies from low to high – primarily based on frequency • Loudness – varies from soft to loud – primarily based on amplitude • Timbre – based on complexity – overtones Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 13

Complex Relationships • Unlike color perception, there is not a simple relationship between the physical and psychological variables in audition • Background – human range of hearing • 16 - 16, 000 (16 K) Hz (or 20 -20 K) • octave = a doubling in frequency – e. g 20 Hz and 40 Hz are an octave apart, but 1, 000 and 2, 000 Hz are also an octave apart Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 14

Complex Relationships • Pitch is primarily based on frequency • Two other factors influence perceived pitch – instructions – amplitude • Instructions – when asked to indicate a change in tone subjects generate the jnd scale – when asked to indicate a change in musical note they generate the octave scale – therefore you need to know the instructions to know what the person will perceive Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 15

Pitch Scales * Octave scale results in a straight line * least noticeable change is 0. 25 Hz at about 15 K, therefore for good recording equipment the wow and flutter must be less than. 25 Hz Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 16

Complex Relationships • Amplitude also influences pitch – as amplitude increases high tone get higher, low tones get lower, middle remain the same Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 17

Complex Relationships • Loudness is primarily based on amplitude – frequency also influences loudness • equal loudness contours • “loudness” control, graphic equalizer Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 18

Encoding Pitch • Von Bekesy’s Place Theory – peak of the envelope of the traveling wave is at different locations along the basilar membrane for different pitches – high frequency near stapes – low frequency near helicotrema Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 20

Encoding Pitch • Wever’s Volley Theory – nerves fire in a volley (sequence) to match frequency of pitch • Both types of encoding are used – above 5, 000 Hz - place theory – 500 - 5, 000 - both (very sensitive) – below 500 - volley Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 22

Encoding Loudness • Cells respond to a specific range of firing – within the range an increase in firing rate – e. g. a specific set of hair cells might respond to 10 -30 Db • at 10 Db these cells fire slowly, at 20 Db they fire more rapidly, at 30 Db they fire maximally, over 30 Db a new group of cells take over Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 23

Complex Tone Combinations • Ohm’s Law – the ear is a frequency analyzer (Fourier analysis) – given a complex waveform we hear the component frequencies • Exceptions to Ohm’s Law – Harmonics - we hear the multiples as timbre not separate tones • e. g. if 100 Hz is the fundamental, 200 Hz is the first harmonic and 300 Hz is the second harmonic • if 225 is the fundamental, the 450 is the first harmonic, and 675 is the second harmonic – Beats • small differences (1 -6 Hz) are hear as a waxing and waning of amplitude Sensation and Perception - audition. ppt © 2001 Laura Snodgrass, Ph. D. 24