Week 8 - Hearing: Physiology and Psychoacoustics Quiz

Hearing: Physiology and Psychoacoustics

• Hearing is secondary to vision, but it plays a crucial role in our daily lives, and its absence would make life more difficult to navigate.
• Sound is created when objects vibrate, causing molecules to vibrate and resulting in waves of pressure changes in the medium.

Physical Quality of Sound Waves

• Sound waves have two main qualities: amplitude (intensity) and frequency.
• Amplitude (dB) measures the difference between the highest and lowest pressure in the wave.
• Frequency (Hz) measures the number of times per second that a pattern of pressure change repeats.
• Sound waves travel at different speeds through media: 340 m/s through air and 1500 m/s through water.
• Light waves travel approximately 1 million times faster than sound waves.

Qualities of Sound

• Loudness: the psychological aspect of sound related to perceived amplitude (or intensity).
• Pitch: the psychological aspect of sound related mainly to the perceived frequency.
• Timbre: the quality of the sound.
• Frequency is associated with pitch: low-frequency sounds correspond to low pitches, and high-frequency sounds correspond to high pitches.
• Amplitude is associated with loudness: high-amplitude sounds are louder, and low-amplitude sounds are quieter.

Measuring Sound Pressure Levels

• Sound levels are measured on a logarithmic scale, in decibels (dB).
• Relatively small decibel changes correspond to large physical and perceptual changes.

Sine Waves and Complex Sounds

• Sine waves dictate how they sound to us: a single sine wave results in a pure tone.
• Complex sounds (speech, instruments, environmental noise) are made up of combinations of sine waves.
• Complex sounds have a spectrum of amplitudes present at multiple frequencies.
• Complex sounds have harmonic spectra: one vibrating object will emit a spectrum of frequencies.

Physiology of the Human Ear

• The pinna funnels sound into the ear via the ear canal.
• Only mammals have pinnae (external ear structures).
• The side and shape of pinnae vary greatly between species.

Physiology of the Human Ear: Outer Ear

• The outer ear amplifies sounds in the 2000-6000 Hz range and protects the eardrum from damage.
• The pinna and ear canal make up the outer ear.

Physiology of the Human Ear: Middle Ear

• The tympanic membrane (eardrum) is a thin sheet of skin that moves in and out in response to sound pressure changes.
• The middle ear contains three ossicles (small bones) that amplify sound and transmit it to the inner ear.
• The three ossicles are: malleus, incus, and stapes.

Physiology of the Human Ear: Inner Ear

• The inner ear is where transduction of pressure changes into neural signals happens.
• The main structure of the inner ear is the cochlea.
• Activity in the cochlea is sent to the auditory nerve, then transmits info to auditory processing.

Physiology of the Human Ear: The Cochlea

• Vibrations in the middle ear push and pull the oval window from the vestibular canal.
• Pressure changes (traveling waves) flow in the fluid of the vestibular canal.
• Because the cochlea is closed, pressure can build up, and is then relieved via the round window.