Chapter 5: Sound, Auditory System, and Pitch Perception

Physical Definition: sound as pressure changes in the air or other medium

Perceptual Definition: sound as the experience we have when we hear

Sound as Pressure Changes

• Soundwave: pattern of air pressure changes

• Amplitude: height of wave

• Wavelength: distance from one peak to the next (one full cycle)

• Compression: higher pressure

• Rarefaction: lower pressure

Pure Tones - Frequency

• Hertz: cycles per second

  • how many waves fit in a second

• Range of hearing - Humans

  • 20 Hz to 20,000 Hz

  • Dogs hear up to 45,000 Hz

• Frequency is associated with the perception of Pitch

Pure Tones - Amplitude

• Amplitude: difference in pressure between the high and low peaks

• Loudness: the perceptual quality of amplitude

• Decibels (dB): measure of loudness

• dB = 20 x logarithm(p/p0)

• p = sound of pressure of stimulus

• p0 is the sound pressure of the standard

Complex Tones

• Comprised of multiple frequencies

• Fundamental Frequency - the repetition rate of complex musical tone

• Harmonics - multiples of the fundamental frequency

• Most sounds are complex

Perceiving Sound

• Loudness

  • Most closely related to amplitude

  • Decibels are a physical measure

  • Loudness is a perceptual experience

• Pitch

  • Most closely related to frequency

  • Hz is the physical measure

  • Pitch is the perceptual experience

Aspects of Pitch

• Tone Height

  • increasing pitch associated with increasing frequency

• Tone Chroma

  • Notes with the same letter have the same chroma, octave apart

  • Frequency doubles with each octave

• Missing Fundamental

  • Removing the fundamental changes Timbre

  • Pitch stays the same

Timbre

• Character or quality of a sound separate from pitch and loudness

• Quality of waveform

  • frequencies

  • number of harmonics

  • relative intensities

• Different instruments and voices produce different timbre

• Attack - build-up

• Decay - decline

Outer Ear

• Pinna

• Auditory Canal

• Eardrum

Middle Ear

• Between eardrum and Oval Window

Inner Ear

• After Oval Window

Cochlea

• Organ of Corti

• Basilar membrane

• Tectorial membrane

• Hair cells

  • Inner hair cells - transmit

  • Out hair cells - amplify sounds

Coding of Frequency in Cochlea

• Place Theory

  • location on Basilar membrane signals frequency

• Timing Theory

  • phase locking and temporal coding

Place Theory

• sounds travel down the basilar membrane varying distances

• high frequency - travel less distance

• low frequency - travel further distance

• full range of frequencies not accounted for

Timing Theory

• Timing

  • firing of single neurons

• Volley Principle

  • firing of multiple neurons, phase locking

Primary Auditory Pathway

• cochlear nuclei

• superior olivary nucleus

• inferior colliculus

• medial geniculate of thalamus

• primary auditory cortex

Auditory Path

• main pathway for hearing

• information does cross over

• SONIC MG

Non-Primary Pathway

• cochlear nuclei

• reticular formation

• non specific thalamus

• poly-sensory cortex

Beyond A1

• Three main areas

  • core (A1)

  • belt area

  • parabelt area

• What pathway - identification

• Where pathway - localization

Hearing Loss

• conductive hearing loss

  • sound is blocked from reaching receptors

• sensorineural hearing loss

  • damage to hair cells, auditory nerve, or brain

Presbycusis

• loss of hearing associated with aging

• most common type of sensorineural hearing loss

• loss of higher frequencies

• due to gradual changes in the ear

• affects men more severely than women

• age and work/occupation related

Noise Induced Hearing Loss

• can occur at any age

• due to exposure to intense sound

• damages Organ of Corti

• damages hair cells

• work place noise - now regulated by OSHA

• leisure noise isn’t regulated

Conductive Hearing Loss

• hole in eardrum

• blockage in ear canal (ear wax, foreign body)

• damage or malformed ossicles

• ear infections

• tumors