auditory perception

Azimuth

Horizontal angle

elevation

Vertical angle

ITD

The difference in time between sound arriving at one ear vs the other; good for low frequencies, accurate localization for low frequencies, processed in the medial superior olive (MSO)

interaural time difference

Itd

azimuth, elevation, distance

elements to localize sound

MSO

relay station in the brain stem where inputs from both ears contribute to detection of ITDs

Medial superior olive

Mso

jeffress model

coincidence - detector model; responds to sounds coming from opposite ear neurons that respond maximally when inputs arrive from the two ears simultaneously – innervated from each ear by a series of delay lines – axons of variable path length

ILD

the difference in intensity (loudness) between a sound arriving at one ear versus the other; not very accurate for localizing stationary sounds, processed in lateral superior olive (LSO)

Interaural level difference

Ild

LSO

relay station in the brain stem where inputs from ears contribute to the detection of ILDs

lateral superior olive

lso

ipsilateral ear

excitatory connections to LSO come from…

contralateral ear

inhibitory connections to LSO come from …

cones of confusion

positions in space where all sounds produce identical ITDs and ILDs

head-related transfer functions (HRTF)

describes how pinnae, ear canals, head, and torso change the intensity of sounds with different frequencies as the sound location changes (aka DTF)

inverse square law

intensity decreases as the square of distance (quieter = farther away)

spectral composition

higher frequencies decrease in energy more than low frequencies as sound waves travel (like scattering of short vs. long wavelengths of light) - distant v. nearby thunder; cue only works for long distances (> 1km)

reverberant energy

whether sound is arriving directly (nearby source) or from reverberations is conveyed by timing info

harmonics

objects tend to vibrate at multiple “resonant frequencies” that are integer multiples of some fundamental frequency

timbre

psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are different

attack

part of a sound during which amplitude increases (onset)

decay

part of a sound during which amplitude decreases (offset)

missing fundamental

structure of harmonic sounds causes listeners to hear a low frequency that is absent