Cog & Bio Auditory Spatial Processing Flashcards
(48 cards)
What does sound provide?
Provides useful information and plays a role in many daily activities
What are applications for sound processing?
It effects hearing loss and aging
It used to help know how to deign aids that restore various aspects of hearing
Also used to help design mobility aids for the blind that rely on sound
What is a good starting assumption?
The perceptual system wants to give you the most accurate information about your surroundings, by combining the information from all the sense
An ideal internal representation would thus be a complete, accurate reproduction of the external world
However, especially when making judgements using sound, this does not happen
What is allocentric?
Where is a sound in relation to other sounds
What is egocentric
Where is the sound in relation to me
Why might internal representations be inaccurate? 4 points
- Limited info - this could lead to ‘fuzzy’ noisy internal representations
- Spatial biases, such as underestimation for auditory distance judgements, or a bias for looming sounds
- Conflicting cues e.g vision vs sound in ventriloquism
- Hard to track multiple, moving objects in space, or get an accurate sense of surroundings in a busy environment / auditory scene
What is a major advantage of hearing?
It is not limited to frontal space, as vision is - locating the azimuth of sound sources is mostly achieved by having 2 ears
What does spatial perception rely on?
Relies on cues
What may be the problem with cues?
- various location cues might be available e.g distance of a sound source: level, reverberation (DRR), spectral (frequency) cues, binaural cues, dynamic cues
- all these cues need to be combined to give you the most accurate perception of the surroundings - the perceptual system can flexibly weight the reliable ones more
- available cues may vary depending on the environment or situation
Binaural meaning?
Listening with two ears
Localisation meaning?
Judging sound source location in terms of left-right direction (azimuth), distance, and/or elevation
Azimuth cues - what are the 2 primary cues for locating sound?
Interaural time difference - medial superior olive (MSO)
Interaural level differences - lateral superior olive (LSO)
How long does it take for sound to travel across the head approximately?
0.6ms
Low frequency in the head :
Low frequency sounds are not substantially attenuated by the head, so ILD cues are better for localising high frequency sounds
Absolute tasks example?
Localise a single sound
What does discrimination involve?
Involves more than one sound e.g minimum audible angle - the smallest detectable difference between the azimuth of 2 sound sources
The smallest possible values for discriminating ITD and ILD (the thresholds) can be measured using what?
can be measured using headphones, using a set reference (e.g 0 degrees for straight head)
For sinewaves….
A change in ITD of 10 microseconds is detectable at 900Hz
When can ITDs not be detected?
Cannot be detected above 1500Hz
When are ILDs discrimination thresholds smallest?
ILDs discrimination thresholds are smallest (i.e best) for frontal sounds, where ILDs of approximately 1-2 dB are detectable, and this varies little with changes in frequency
Azimuth cues - what is the duplex theory?
The perceived azimuth of low-frequency sounds (below 1-2kHz) is dominated by the ITD
For high frequency stimuli (above 1-2kHz), the auditory system weights the ILD more when determining the azimuth
I.e ITD for low frequencies, ILD for high frequencies
When is sound localisation poorest?
Poorest where neither ITD or ILD cues work well, around 1500Hz
Auditory level - lower level sounds and sound levels
Lower level sounds are perceived as further away
Sound level falls by 6dB for each doubling of the source distance
Reverberation - reverberant sounds & what they’re dependent on
Reverberant sounds are judged as more distant (direct-to-reverberant energy ratio)
Dependent on absorption by the surrounding walls, floor, and ceiling
