Task 8 a scene made of sounds Flashcards
What pathway
Starts in anterior part of core and belt and extends to prefrontal cortex.
o Responsible for identifying different types of sounds.
o Neurons in anterior belt respond to more complex sounds. ´
o Deactivating anterior auditory areas disrupts ability to distinguish two patterns of sounds but does not affect sound localization
Where pathway
Starts in posterior part of core and belt and extends to prefrontal cortex.
o Associated with locating sounds.
o A1 is important for localization but neurons in posterior belt have better spatial tuning than those in A1.
o Deactivating posterior auditory areas disrupts ability to localize sounds but does not affect sound identification.
auditory scene
Acoustic environment
Source segregation/auditory scene analysis
: Processing an auditory scene consisting of multiple sound sources into sperate sound images
Spatial segregation
Sounds that emanate from the same location in space can typically be treated as if the arose from the same source
Spectral/temporal segregation
sound with the same or similar pitch are more likely to be treated as coming from the same source
Auditory stream segregation
The perceptual organization of a complex acoustic signal into separate auditory events for which each stream is heard as a separate event
Interaural time difference (ITD)
The difference in time between a sound arriving at one ear versus the other (low frequencies more efficient)
Azimuth (ITD)
The angle of a sound source on the horizontal plane relative to a point in the centre of the head between the ears. Azimuth is measured in degrees, with 0 degrees being straight ahead. The angle increases clockwise toward the right, with 180 degrees being directly behind, we can detect delays of little as 10 us (1 degree)
Medial superior olive (MSO) (ITD)
a relay station in the brain stem where inputs from both ears converge to detection of the interaural time difference
Interaural level difference (ILD)
The difference in level (intensity) between a sound arriving at one ear versus the other (high frequency)
o Sounds are louder at the ear which is closer to the sound source
o The ILD is largest at 90 and -90 degrees, and it is non-existent at 0 and 180 degrees
o Less precise because of the irregular shape of the head compared to ITD
o Head blocks high-frequency sounds more efficient than low-frequency sounds
Lateral superior olives (LSOs) (ILD)
A relay station in the brain where inputs from both ears contribute to detection of the interaural level difference, excitatory comes ipsilateral and inhibitory comes contralateral
Cone of confusion
A region in space where all sounds produce the same time and level (intensity) differences (ITDs and ILDs)
Intensity (distance)
sound becomes less intense over space
Inverse-square law (distance)
A principle that as distance from a source decreases faster such decrease in intensity is equal to the distance squared. This general law also applies to optics and other forms of energy
Distance prediction
good for up to 1 meter farer distances are often underestimated, especially good for moving objects, e.g. hearing a frog hopping in your direction
Relative amount of direct versus reverberant energy (distance)
At close distance more direct energy hits your ear, where as reverberant energy provides a greater proportion of the total when the sound source is farther away
Pinnea (localisation)
tunnels certain frequencies more efficient the others
Body (localisation)
especially the upper torso affect which frequencies reach the ear most easily
Directional transfer function (localisation)
A measure that describes how the pinna, ear canal, head, and torso change intensity of sounds with different frequencies that arrive at each ear from different locations in space (azimuth and elevation)
Elevation
the bottom to top localization
Timbre
The psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar. Timber quality is conveyed by harmonics and other high frequencies
o Perception of timber is related to the relative energies of different acoustic spectral components
Attack (timbre)
The part of a sound during which amplitude increases (onset)
Decay (timbre)
The part of a sound during which amplitude decreases (offset)
Grouping by onset
sound components that begin at the same time are likely to be heard as they come from the same source
Similarity (gestalt)
sounds that are similar to each other tend to be grouped into streams
Common fate (gestalt)
grouping sounds by onset
Familiarity (gestalt)
you get used to certain sounds which makes it easier to sperate them from others (e.g. your name)
Good continuation (gestalt)
the continuous auditory stream is heard to continue behind the masking sound (perceptual restoration effect)
Precedence effect
If there is only a short delay between two sounds, then sound is perceived to come only from the that started playing the sound first. It means that we perceive sound as coming from its source, rather than from many different directions at once.
JEFFRESS NEURAL COINCIDENCE MODEL OF AUDITORY LOCALIZATION (Birds)
Model that proposes that neurons are wired so they each receive signals from two ears
Coincidence detectors
Neurons that only fire when both signals coincide by arriving at same time at neuron
How does coincidence of auditory localisation work
Axons transmit signals from left and right ear to neurons (= circles).
Sound in front – Signals start simultaneously in channels and meet at middle neuron (5), causing it to fire.
Sound to the right – Signal starts in right channel first and signals meet at neuron closer to left ear (3), causing it to fire.
ITD curves explained
When ITD tuning curves are measured in humans, curves are broader than in birds. Therefore, it was proposed that coding for localization is based on broadly tuned neurons for humans and sharply tuned neurons for birds.
Broadly tuned neurons in right hemisphere respond when sound is coming from left, while those in left hemisphere respond when sound is coming from right.
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.
