Auditory Perception II: Space Perception Flashcards
How do we use two ears to infer information about depth and distance
differences in the arrival of sound at the two ears allow us to use the ONSET of a sound to localize
– time difference in onset of sound allows us to infer direction (arrives first in left, must come from left)
What are the difference sources of spatial information in auditory perception?
ITD
IPD
ILD
Interaural Time Difference (ITD)
The difference in TIME between a sound arriving at one ear versus the other
- amount of time delay gives us info about location
- more useful at low frequencies, not good at high frequencies
Azimuth
An imaginary circle that extends around us, in a horizontal plane; allows us to measure direction of sound (organized by degrees)
What location in space would give us 0 ITD
right in front, right behind us
- equal distance from both ears
- 0 degrees, 180 degrees
What location in space would give us maximum ITD
directly on one side (right or left)
- longest path to travel from one ear to the other
- 90 degrees, -90 degrees
What units are used to describe ITD?
microseconds (1000th of 1 millisecond)
– extremely small time differences
Interaural Phase Difference (IPD)
Differences in the PHASE of soundwaves arriving at the two ears can be used for localization
What is the maximum time difference from one ear to another?
about 0.6 milliseconds
Interaural level difference (ILD)
the difference in level (intensity) between a sound arriving at one ear versus the other
- sounds are more intense at the ear closer to sound source
- generally correlates with angle of sound source (like ITD), but correlation is not quite as great as it is with ITDs
Where is ILD highest?
90 degrees and –90 degrees
Where is ILD lowest?
0 degrees and 180 degrees
_____ and _____ differences play a complementary role
PHASE and INTENSITY
How do phase and intensity differences complement each other?
1) Phase differences work for low frequency sounds.
2) Intensity differences work for high frequency sounds.
3) The combination allows us to localize most sounds.
Phase differences work best for ____ frequency sounds
low frequency
Intensity differences work best for ___ frequency sounds
high frequency
Cone of Confusion
The limitation to time and intensity differences for finding location
There are symmetries that give the same ITD and ILD cues for both ears (up/down and front/behind)
How do we deal with the Cone of Confusion?
- head movements (tilting head)
- shape of the pinnae, primarily for high- frequency sounds
How do the pinnae in the outer ear help with resolving ambiguities in sound location
pinnae funnel certain sound frequencies better than others, and the intensity of each frequency varies depending on the direction of the sound
What is the simplest cue for listeners to judge distance of sounds?
Relative intensity of sound
Inverse-square law
As distance from a source increases, intensity decreases faster such that decrease in intensity is distance squared
*our brain knows and uses this to estimate distance based on intensity
Spectral composition of sounds
Higher frequencies decrease in energy more than lower frequencies as sound waves travel from source to one ear
- the further something is, the less high frequency content we have
- if a sound has a lot of high frequency content, it is probably closer by
Direct vs. reverberant energy
Direct: sound directly coming from the source
Indirect/reverberant: sound coming from bouncing off environment
- the closer you are, the greater ratio of direct sound you have
- the brain judges the ratio of direct to reverberant in order to determine how close or far something is
Inverse accoustics
our brain inverts the laws of physics for sound in order to perceive them accurately
What happens when you remove the first harmonic/fundamental frequency?
the brain fills it in somehow, and we still perceive the same pitch
Missing-fundamental effect
when you remove the first harmonic/fundamental frequency, the brain fills it in somehow and we still perceive the same pitch
–brain may be looking at the peaks, which corresponds to the fundamental harmonic
Timbre
quality of sound; psychological sensation by which a listener can judge that two sounds that have the same loudness and pitch are dissimilar
- -> conveyed by harmonics
- -> influenced by ONSET (attack)
Cocktail party problem
How does auditory system sort out multiple sound sources occurring simultaneously?
AKA source segregation or auditory scene analysis
What are the strategies for sound source segregation?
– Spatial separation between sounds – Grouping on basis of sounds’ spectral or temporal qualities – Auditory stream segregation – Grouping by frequency – Grouping by timbre – Grouping by onset
Auditory stream segregation
strategy for sound source segregation; the perceptual organization of a complex acoustic signals into separate auditory events for which each stream is heard as a separate event
Grouping by onset
sounds that start together/end together tend to get grouped together
note: similar to gestalt law of common fate
Filling in/Restoration
brain fills in missing sounds so that they are continuous
** interpolation, described as principle of continuity in gestalt
