Problem 8 - DONE Flashcards
auditory localisation
auditory localisation
= locating of sound sources in auditory space
- auditory space = exists all around
- -> created by each sound in a room/sounds all around
- -> each sound is heard as coming from different locations
localisation cues
= information used to determine auditory location
- created by way sound interacts with listener’s head + ears (pinnae)
two kinds:
(1) binaural cues
(2) monaural cues
three dimensions of sound
- azimuth = extends from left to right
- elevation = extends up and down
- distance = distance of sound source from the listener
binaural cues
= information reaching both ears
- locate along azimuth coordination
- based on comparison of sound signals reaching the left + right ears
=> sounds that are off to the side: reach one ear before the other (1) + louder at one ear than the other (2)
(1) inter-aural time difference (ITD)
(2) inter-aural level difference (ILLD)
–> superior olivery nuclei
inter-aural time difference (ITD)
= difference between when a sound reaches the one ear and when it reaches the other; phase delays
- location of low-frequency sounds (< 1500 Hz)
- source directly in front of listener: distance to each ear is the same/sound reaches the left and right ears simultaneously
- -> ITD = 0
- source is located off to the side: sound reaches right/left ear before it reaches the other
- -> ITD becomes larger as sound sources are located more to the side
- magnitude of ITD: cue to determine sound’s location
inter-aural level difference (ILD)
= difference in the sound pressure level (amplitude/loudness) of the sound reaching the two ears; intensity
- location of high-frequency sounds (> 1500 Hz)
- acoustic shadow = head is a barrier
–> reducing intensity of sounds that reach the far ear (for high-frequency, not low)
=> high-frequencies: (small compared to size of head) are disrupted by head
=> lower frequencies: smaller difference between the ILDs for sounds coming from two locations
=> very low frequencies: ILD is a very poor indicator of a sound’s location
cone of confusion
= ITD + ILD illustrate ambiguous places
- ITD/ILD differences can be the same at different elevations
=> no reliable indication of elevation of sound source (only azimuth, distance)
solution:
- move our heads: additional ITD/ILD + spectral information
–> helps locate continuous sounds
monaural cues
= information from one ear
- locate sounds along elevation coordinate
- spectral cues
spectral cues
= information for localisation is contained in differences in distribution (spectrum) of frequencies that reach each ear from different locations
cause:
- reflection from head and within folds of pinnae before stimulus enters auditory canal
–> importance of pinnae: nooks and crannies of pinnae makes it easy to locate sounds along the elevation coordinate
jeffress neural coincidence model
= proposes that neurones are wired so they receive signals from two ears
- coincidence detectors = only fire when both signals coincide by arriving at same time at neurone
- proposes: series of detectors, each tuned to respond best to a specific ITD
- -> place code = ITD is indicated by place (which neurone) where activity occurs
ITD tuning curves
= plots neurone’s firing rate against ITD
- measure properties of ITD neurones, because each respond best to certain ITD
broadly tuned neurones
- in right hemisphere: respond when sound comes from the left
- in left hemisphere reason when sound comes from the right
- location of sound: indicated by ratio of responding of these two types of broadly tuned neurones
- distributed coding = determined by firing of many broadly tuned neurones working together
auditory pathways
- from temporal lobe to frontal lobe
- what pathway
- where pathway
what pathway
- starts: anterior part of score + belt
- extends: prefrontal cortex
- -> identifying sounds
where pathway
- starts: posterior part of core + belt
- extends: prefrontal cortex
- -> locating sounds
auditory scene analysis
= multiple sound sources in auditory scene are separated into sound images
- no spatial information on auditory receptors
problem:
- sounds from different sources are combined into single acoustic signal
–> difficult to tell which part of signal is created by which source (just by looking at waveform of sound stimulus)
- uses spectral cues + ITD + ILD
segregation principles
- similar to Gestalt in vision
- perceptually organise elements of auditory scene
- basis: how sounds occur in environment
location
= information about where each source is located
- -> separate sounds based on localisation cues (ITD, ILD)
- when a source moves: continuous movement of sound (rather than jumping from one to another place)
- -> perceive sound from a passing car as originating from a single source
onset time
= if two sounds start at slightly different times: likely that they came from different sources
- in environment: sounds from different sources rarely start at exactly the same time
- when sound components start together: likely that created by same source
pitch and timbre
= same timbre or pitch: often produced by same source
auditory continuity
= sounds that stay constant/change smoothly are often produced by the same source
- Gestalt principle: good continuation
- -> sound stimuli with same frequency/smoothly changing frequencies are perceived as continuous even when interrupted by another stimulus = continuity illusion
experience
= effect of past experience on perceptual grouping
- melody schema = representation of a familiar melody that is stored in a person’s memory
localisation in A1 and belt area
- neurones in A1: respond when sound is moved within specific area of space + don’t respond outside that area
- neurones in posterior belt area: respond to sound within an even smaller area of space
–> spatial tuning is better
=> neurones in belt area provide more precise information than A1 neurones about location
auditory stream segregation
pitch and timbre
= separation of different sound sources into perceptually different streams
–> depends on pitch and rate at which tones are presented
scale illusion
auditory illusions
= melodic channeling = effect in which notes in each ear jump up and down, making listener perceive smooth sequence of notes
–> accurately interpret what is happening in the environment
