Spatial Hearing Flashcards
When will the maximal inter aural time difference occur?
When the sound is directly to the left or to the right.
How fast does sound travel?
It travels at 330 metres per second.
When are ITDs the most important cues for sound location?
When low frequency components are present.
When will the ITD be zero?
For a sound directly in front, directly behind, and anywhere in the median plane (nose to head)
What is the maximum time difference for adults?
0.65ms
Distance between the two ears divvied by the speed of sound.
What is the smallest detectable inter aural time difference?
10 microseconds.
At what frequency and why might a pure tone appear to come from the right when in actual fact it arose from the left?
For a frequency above 750HZ (continuos pure tone) a waveform peak at the left ear will be closely followed by a peak in the right ear. So although the sound originates in the left ear it may appear as though it originated in the right ear.
Which from ITDs and ILDs is more dominant for natural sounds?
ITDs are more dominant for natural sounds.
What frequency components are ITDs useful for?
They’re useful for the localisation of low frequency components.
Why do ILDs arise?
Mainly because of the shadowing effect of the head. Low frequencies diffract more than high frequencies. So level cues are more important for higher frequencies.
What does our incredible sensitivity to ITDs imply?
It implies very accurate phase locked encoding of the time of arrival at the two ears. The information is extracted by neurons in the brainstem that receive input from both ears and are sensitive to differences between the arrival times at each ear.
However ITDs and ILDs can be ambiguous. How can this ambiguity be resolved?
The cone of confusion can be resolved by head movements and by the use of monaural information based on the effects of the pinna. Which imposes a direction specific signature on the spectrum of sounds arriving at the ear.
What are the most important cue for the distance of a sound?
Level (because quiet sounds are usually from sound sources that are further away) and the ratio of direct to reflected sound (which decreases with increasing distance). The auditory system combines the cues, but tends to underestimate.
In a reverberant environment how is the ear able to identify the location of the sound source?
It’s able to identify the location of a sound source by suppressing the (misleading) location information from reflections. You still perceive the reverberation, however it provides information regarding the dimensions and reflective properties of the walls and surfaces in the space around us.
How are sounds presented over headphones to be made to sound external?
By simulating the filtering characteristics of the pinnae. Addition of appropriate reverberation helps produce the impression of a natural space.
