Week 6 Flashcards
What frequency range is speech?
400-3000Hz
What does ear damage depend on? What level?
Level and duration of frequency
85+ dB is damaging
What is the cocktail party effect?
We can understand a conversation from individuals speaking amongst others
*What is sound localisation ?
Distance (range) and bearing/direction (azimuth and elevation)
*Principles of sound conduction?
An oscillating object creates sound by causing the surrounding air to undergo cycles of compression (increased density) and rarefaction (decreased density). These alternating pressure waves propagate through the air, transmitting sound energy to the ear.
What factors define sound?
Frequency (Hz) and amplitude (dB)
What is human hearing range?
20 Hz to 20,000 Hz
*Ear Anatomy?
Outer Ear: Captures sound waves.
Middle Ear: Contains ossicles (bones) that amplify sound vibrations and match impedance to the inner ear.
Inner Ear: Comprises the cochlea, which performs frequency analysis (Fourier analysis) via the basilar membrane.
*Types of hair cells?
Inner Hair Cells: Convert mechanical energy into electrical signals for the auditory nerve.
Outer Hair Cells: Amplify sound via motor proteins like prestin.
Special functions of the ear?
Stapedius reflex reduces sound transmission during loud noises to protect hearing.
Cochlear amplification sharpens frequency tuning for clearer sound discrimination.
Otoacoustic emissions (sounds generated by the ear) are diagnostic tools
What is pitch perception?
Based on the place theory: Different basilar membrane regions respond to specific frequencies
*What is the Fourier Analysis?
The ear decomposes sounds into frequency components, akin to a Fourier analyser.
*Auditory Pathway?
Sound travels from the cochlea to the auditory cortex via structures like the superior olive and brainstem.
*How do we judge sound?
Judging Distance:
1. High Frequencies vs. Bass: High frequencies attenuate faster over distance, so distant sounds are bass-dominated.
- Expectation: Known loudness of a source helps judge its distance (e.g., a quieter voice seems farther).
- Relative Attenuation (Timbre): Bass travels better than high-frequency sounds like sibilants, altering the timbre.
- Echoes and Reverberation: Far sounds have more reverberation and less direct sound, aiding distance perception.
Judging Direction:
1. Interaural Timing/Phase Differences (ITD): Low-frequency sounds are localized by the time delay or phase difference between ears.
- Interaural Volume Differences (ILD): High-frequency sounds are localized by intensity differences caused by the head’s sound shadow.
- Spectral Coloring: The head and pinna modify sound frequencies based on their angle, aiding in determining elevation and direction.
*Startle Response?
The startle response is a rapid, involuntary reaction to loud sounds, bypassing the cerebral cortex for faster response.
Evoked by very loud sounds (~120 dB).
Blink Reflex: Occurs in ~40 ms.
Neck Contraction: Follows at ~80 ms.
Mediated by the brainstem via the reticular formation, avoiding higher processing centers for speed.
When a loud sound accompanies a “go” signal, reaction times can decrease significantly (e.g., from ~170 ms to ~80 ms in extreme cases).
