Lecture 17 Flashcards
On average, people can localize sounds most accurately ____ (and least accurately to their sides and behind their heads)
On average, people can localize sounds most accurately directly in front of them (and least accurately to their sides and behind their heads)
Auditory localization
locating sounds in space
Azimuth coordinates
left to right position
Elevation coordinates
up and down position
Distance coordinates
position relative to observer
Location cues
are created based on how sound waves interact with our head/ears
Binaural cues
location cues based on the comparison of the signals received by the left and right ears (intramural time and level differences) to determine the azimuth (i.e. left-right) positions of sounds
Intramural level difference (ILD)
is a binaural cue related to differences in sound pressure levels reaching each ear
Reduction in intensity occurs for high frequency sounds for the far (relative to audio source) ear, due to the head casting an __ ___
Reduction in intensity occurs for high frequency sounds for the far (relative to audio source) ear, due to the head casting an acoustic shadow
acoustic shadows do not occur for ___ frequency sounds because the distance, or spacing, between waves i.e. frequency for low frequency is relatively ___, in comparison to the object casting the acoustic shadow i.e. your head
acoustic shadows do not occur for low frequency sounds because the distance, or spacing, between waves i.e. frequency for low frequency is relatively large, in comparison to the object casting the acoustic shadow i.e. your head
intramural time difference (ITD)
is a binaural cue related to differences in the timing of when a sound reaches each ear
When distance to each ear is the same, there is ___ ___ in ___ (___=0)
When distance to each ear is the same, there is no difference in timing (ITD=0)
When the source is to the side of the observer, the times ___ ___
When the source is to the side of the observer, the times will differ
__ and ___ are useful binaural cues for judging azimuth and distance
ILD and ITD are useful binaural cues for judging azimuth and distance
ILD and ITD cannot reliably indicate the ___ of a sound source
ILD and ITD cannot reliably indicate the elevation of a sound source
‘cone of confusion’
in reference to the (many) conical space(s) around the ears for which various possible pairs of points on an ‘imaginary cone’ would produce the same ITD and ILD
monoaural cues
location cues based on signals reaching a single ear
__ __ are particularly important for judging elevation, given that ILD and ITD are not effective for doing so since they may be zero in many different locations
monoaural cues are particularly important for judging elevation, given that ILD and ITD are not effective for doing so since they may be zero in many different locations
The monaural cue we primarily rely on is referred to as a __ __, because it involves using information related to the distribution of intensities of a particular spectrum of frequencies experienced
The monaural cue we primarily rely on is referred to as a spectral cue, because it involves using information related to the distribution of intensities of a particular spectrum of frequencies experienced
Spectral cues occur because the __ and ___ affect the intensity of sound waves entering the system
Spectral cues occur because the pinna and head affect the intensity of sound waves entering the system
Sound waves are reflected off the __, as well as within the folds of the __, before stimulating the ear drum
Sound waves are reflected off the head, as well as within the folds of the pinnae, before stimulating the ear drum
Frequency spectra
recorded by a microphone placed inside the ear for the same stimulus being played at different elevations
Gardner and Gardner found that changing the pinnae (by smoothing out nooks/crannies using a molding compound) resulted in participants producing worse localization judgements about ___
Gardner and Gardner found that changing the pinnae (by smoothing out nooks/crannies using a molding compound) resulted in participants producing worse localization judgements about elevation
Cue summary for sound source localization:
___ and ___ work for judging azimuth
___ works best for high frequency sounds
____ works best for low frequency sounds
___ cues helps us judge elevation
____ cues are also relevant i.e. vision
Cue summary for sound source localization:
ILD and ITD work for judging azimuth
ILD works best for high frequency sounds
ITD works best for low frequency sounds
Spectral cues helps us judge elevation
Multi-modal cues are also relevant i.e. vision
Jeffress neural coincidence model
proposes that some neurons receive input from both ears and respond to ITD (are essentially ITD detectors)
___ detectors only fire if they receive input from both axons simultaneously or in other words only fire if they receive signals originating from each ear simultaneously
Coincidence detectors only fire if they receive input from both axons simultaneously or in other words only fire if they receive signals originating from each ear simultaneously
Jeffress Neural Coincidence model: Example 1- sound originating directly in front of listener
each ear receives stimulation at same time, resulting in transmission from each ear to the cortex to happen at same time, ‘meeting’ in the middle of the neural coincidence detector e.g. meeting at the middle at neuron 5. Firing of neuron 5 indicates a sound is directly in front of the listener i..e ITD=0
Jeffress Neural Coincidence model: Example 2- sound originating to the right of a listener
Signal from right ear gets a ‘head start’ to going to cortex relative to the signal from the left ear, point which they ‘meet’ is skewed to left from middle e.g. instead of 5 it is at Neuron 3, firing of this neuron would indicate that sound is skewed to a right
It may be more likely that mammals use ___ coding to encode ITD for the purpose of localizing sounds (whereas birds may sue something more akin to ___ coding)
It may be more likely that mammals use population coding to encode ITD for the purpose of localizing sounds (whereas birds may sue something more akin to specificity coding)
Neurons in the left hemisphere respond best to sound from the ___, neurons in the right hemisphere respond best to sounds from the ___
Neurons in the left hemisphere respond best to sound from the right, neurons in the right hemisphere respond best to sounds from the left
Evidence that A1 is involved in localization: Neff et al.
Cats rewarded with food for approaching boxes emitting a sound, no longer able to localize sounds after bilateral lesions to A1 (even after 5 months of training)
Evidence that A1 is involved in localization: Nodal et al.
Lesioning A1 in ferrets detrimentally impacted (but did not eliminate) their ability to localize sound
Evidence that A1 is involved in localization: Malhorta and Lomber
deactivating via cooling A1 in cats impairs their sound localization
Evidence that the posterior belt is involved in localization: Recanzone
single-cell recordings of monkeys revealed neurons that only respond to sounds coming from particular locations in space
Evidence that the posterior belt is involved in localization: Lomber and Malhotra
temporarily disputing the posterior belt again via cooling, disrupts localization. This did not affect their ability to distinguish between differences in patterns of timing related to sound stimuli
Evidence that anterior belt is involved in perceiving sound: Rauschecker and Tian
while some neurons in A1 respond to pure tones, those in the anterior belt respond to more complex sounds e.g. monkey vocalizations
Evidence that anterior belt is involved in perceiving sound: Lomber and Malhorta
Cooling this area in cats disrupts their ability to discern differences in timing patterns related to sound (but not localization)
Where or dorsal stream
used to locate sounds
What or ventral stream
used to identify sounds
Direct sound
sound that reaches the listener’s ears straight from the source
Indirect sound
sound that is reflected off of the environmental surfaces and then to the listener
When listener is outside, most sound is __
When listener is outside, most sound is direct
Architectural acoustics
study of how sounds are reflected in rooms
Reverberation time
time it takes sound to decrease to 1/1000th of its original pressure
If the reverberation time is too long sound will seem ‘___’
If the reverberation time is too long sound will seem ‘muddled’
If the reverberation time is too short sound will see ‘___’
If the reverberation time is too short sound will see ‘dead’
Intimacy time
time between the sound leaves its source and when the first reflection arrives
Bass ratio
ratio of low to middle frequencies reflected from surfaces
Spaciousness factor
fraction of all the sound received by listener that is indirect
___ spaciousness factors are typically perceived as most pleasing
High spaciousness factors are typically perceived as most pleasing
Auditory scene
array of all sound sources in the environment
Auditory scene analysis
process by which sound sources in the auditory scene are separated into individual perceptions, this does not happen at the cochlea since simultaneous sounds are processed together in the pattern of vibration of the basilar membrane
Onset time
sounds that start at different times are likely to come from different sources
Location
a single sound source tends to come from one location, individual sources of sound also tend to move in a smooth and continuous way
