Task 8: Auditory Localization Flashcards
Auditory localization
Locating of sound sources in auditory space.
Name the 2 dimensions in which sounds can be located in addition to distance
- azimuth = left to right
2. elevation = up to down
Name the 2 cues for localization
- binaural
2. monaural
Binaural cues
- define
- name 2 examples
Uses information reaching both ears to determine azimuth of sounds e.g. ITD + ILD
Interaural time difference (binaural cue)
Difference between when sound reaches left ear and when it reaches right ear. Provides information about location of low-frequency sounds.
-> ITD becomes larger as sources are located more to the side. When distance is equal, ITD is equal
Interaural level difference (binaural cue)
Difference in sound pressure level of sound reaching two ears.
- Acoustic shadow: reduces intensity of sounds reaching far ear.
- Reduction of intensity occurs only for high-frequency sounds because if object is larger than distance between waves, it has higher effect than if object is smaller.
Cone of confusion
Time and level differences provide info that enables us to judge location along azimuth, but they provide little info about elevation of sound source.
Monaural cue
one ear to determine elevation
Define spectral cue
Information for localization is contained in differences in distribution (spectrum) of frequencies reaching each ear from different locations
- best for judging elevation at high frequencies
Directional transfer function
Explains how head, pinna and ear canal change intensity of sounds with different frequencies arriving at each ear from different locations in space (azimuth and elevation).
Superior olivary nucleus
place where signals from left and right ears meet
Inferior colliculus
place where further binaural processing occurs
A1
signal arrive here, travel to other cortical auditory areas (core, belt and parabelt areas)
What do neurons of the belt area do?
provide more precise information than A1 neurons about location of sound sources
Jeffress neural conicidence model of auditory localization
model that proposes that neurons are wired so they each receive signals from two ears (blue is left ear and red is right)
Coincidence detectors
Neurons that only fire when both signals coincide by arriving at same time at neuron.
ITD tuning curves
Curve that plots neuron’s firing rate against ITD. Useful to measure properties of ITD neurons, because each respond best to certain ITD.
What kind of neurons is coding for localization based on? Where are they? What does the amount of firing indicated
- Broadly tuned neurons
- Right hemisphere when responding to sound on left and vice versa
- How much these neurons fire indicates the location of sound. If sound is in left side, right hemispheric neurons respond faster
Distributed code
Code of localization for mammals because ITD is determined by firing of many broadly tuned neurons working together.
Name the 2 auditory pathways extending from temporal to frontal lobe
What and where
What pathway
- location
- responsibility
- neurons
- effect of deactivation
- Anterior part of core and belt and extends to prefrontal cortex
- Responsible for identifying different types of sounds.
- Neurons in anterior belt respond to more complex sounds.
- Deactivating disrupts ability to distinguish two patterns of sounds
Where pathway
- location
- responsibility
- neurons
- effect of deactivation
- Posterior part of core and belt and extends to prefrontal cortex.
- Associated with locating sounds.
- Neurons in posterior belt have better spatial tuning than those in A1.
- Deactivating disrupts ability to localize sounds
Sound waves from all sound sources in environment are summed into ______ But our auditory system can distinguish events or objects
single complex wave
Auditory scene analysis
Process by multiple sound sources in auditory scene are separated into sound images.
Name 5 seperating sources to help us perceptually organise auditory scences
- location
- onset time
- pitch and timbre
- auditory continuity
- experience
Location
To analyze auditory scene into separate components, we can use information about where each source is located
- sounds can be separated based on localization cues e.g. ITD and ILD
- when source moves, it follows continuous path
Onset time
If two sounds start at different times, it is likely that they came from different sources, if so more likely to group tones by spatial location
Pitch & Timbre
Sounds that have same timbre or pitch range are often produced by same source.
Auditory stream segregation
Separation of different sound sources into perceptually different streams. It depends on pitch and rate at which tones are presented.
Grouping by similarity of pitch
- what illusion is associated?
Instrument plays notes alternating rapidly between high and low tones, creating perception of two separate melodies. High and low notes are perceived to be playing by two different instruments.
- scale illusion
Explain the scale illusion
Effect in which notes in each ear jump up and down, making listener perceive smooth sequence of notes.
Auditory continuity
Sound stimuli with same frequency or smoothly changing frequencies are perceived as being continuous even when interrupted by another stimulus (good continuation principle). Longer than a certain period and it stops.
Experience
When people know which melody is present, they compare what they hear to their stored schema and perceive melody.
Melody schema
Representation of familiar melody that is stored in person’s memory.
Acoustic startle reflex
Very rapid motor response to abrupt loud sound. It is unselective, so any loud sound produces this effect.
-> Time between ear (sound) and spinal cord (movement) is brief – Very few neurons are involved in basic startle reflex.
Inattentional deafness
- limitation?
When we attend to particular sound source strongly and miss out on hearing other sounds.
- When surrounding sounds are made sufficiently loud, listeners had more trouble focusing in particular sound.
Why is it misleading to group componenets of an orchestra by location?
due to reflections therefore must rely on other cues
What cues do we rely on to differentiate between orchestral sounds? x 3
- harmonicity
- timing
- pitch proximity
Harmonicity
When two complex tones are played simultaneously by instruments built on same fundamental (unison) or different fundamentals they will be fused and only one tone will be perceived
- degree of fusion depends on frequency between fundamentals (complex tones fuse best when played in perfect unison with a 1:1 ratio and second best at an octave 2:1)
octave: same pitch but double frequency
Continuous frequency modulation
Natural sounds generated by instruments undergo small frequency fluctuations that preserve ratios formed by their component frequencies.
Pitch proximity
Hearer tends to link successive tones that are close in pitch and separate those that are further apart.
- tempo: the faster the tempo between 2 varying pitches, the smaller the threshold pitch difference at which one perceives separate streams
- frequency: when frequency difference between tones is small, we perceive ‘galloping’ rhythm. When difference is increased, two unrelated streams of tones are heard.
Theory of unconscious inference in perception
When faced with complex configuration, our perceptual system adopts most plausible interpretation in terms of our knowledge of environment. Similar sounds are likely to be coming from same source and different sounds from different sources
