chapter 12 Flashcards
auditory space
perception of where sounds are located in space - auditory space extends around a listener’s head in all directions, existing wherever there is a sound
auditory localization
the locating of sound sources in auditory space
location cues
information created by the way sound interacts with the listener’s head and ears. the auditory information uses this information to determine location
what are the two types of location cues
binaural cues: depend on both ears
spectral cues: depend on just one ear
what are the three dimensions of sound position
azimuth: extends from left to right
elevation: extends up and down
distance: from the sound source to the listener (least accurate and works best when the sound source is familiar, or when cues are available from room reflections)
two types of binaural cues
interaural level difference and interaural time difference
interaural level difference
based on the difference in the sound pressure level of the sound reaching the two ears
acoustic shadow
the head acts as a barrier causing a difference in sound pressure level between the two ears, reducing the intensity of sounds that reach the far ear
when does the acoustic shadow occur
intensity is reduced in the far ear at high frequency sounds (greater than about 3000Hz for humans), but not for low frequency sounds
why does an interaural level difference occur for high frequencies but not for low frequencies?
because high frequency sounds have small spacing between them, meaning they are stopped by the head - whereas, low frequency sounds have large gaps in spacing, larger than the head, so are not affected
interaural time difference
the time difference between when a sound reaches the left ear and when it reaches the right ear
becomes larger as sound sources are located more to one side, and its magnitude can be used as a cue to determine a sound’s location
when is interaural time difference most effective
most effective at determining the locations of low frequency sounds
this makes it the dominant binaural cue because most sounds in the environment contain low frequency components
cone of confusion
an area extending from the ear that looks like a cone. sounds originating from different locations in this general area all have the same interaural level difference and interaural time difference, so location information provided by these cues is ambiguous
spectral cues
cues in which information for localization is contained in differences in the distribution of frequencies that reach each ear from different locations
caused by the fact that before the sound stimulus enters the auditory canal, it is reflected from the head and within the various folds of the pinnae
evidence for the pinae in determining elevation
when the inside contours of the pinnae are changed with a mold, localization for elevation coordinate is poor, but locations can still be judged along the azimuth coordinate
however, localization performance for elevation improves over time as people get used to the molds and is still good once molds come out (don’t have to readjust themselves)
jeffress model
proposes that neurons are wired so they each recieve signals from the two ears
coincidence detectors fire when signals from the left and right ears reach the neuron simultaneously - dif coincidence detectors fire to dif values of interaural time dif
itd is indicated by which itd neuron is firing
ITD Detectors
interaural time difference detectors - neurons in the jeffress model that fire when signals reach them from the left and right ears and are tuned to respond to a specific time delay between the two signals = information about possible locations of a sound source
ITD is indicated by which ITD neuron is firing
binaural localization in birds vs mammales
sharply tuned in birds: place code bc ITD id indicated by firing of neurons at a specific place in the nervous system
broadly tuned in mammals: population code bc ITD is determined by the firing of many broadly tuned neurons working together
superior olivary nucleus
first place that receives signals from the left and right ears
anterior vs posterior belt areas
two areas on either side of the auditory cortex
anterior: complex sounds/patterns of sounds - the what auditory pathway extends from the anterior belt to the front of the temporal lobe and then to the frontal cortex
posterior: localizing sounds - the where auditory pathway extends from the posterior belt to the parietal love and then to the frontal cortex
direct vs indirect sound
direct sound: sound that reaches your ears directly
indirect sound: reaches your ears after being reflected from a surface
precedence effect
when two identical or very similar sounds reach a listener’s ears separated by a time interval of less than about 50 to 100ms, the listener ears the first sound that reaches his or her ears
if the sounds are separated by a longer delay, they will hear two separate sounds
architectural acoustics
the study of how sounds are reflected in rooms - largely concerned with how indirect sound changes the quality of sounds we hear in rooms
reverberation time
the time it takes for the sound to decrease to 1/1000th of its original pressure
if reverberation time is too long: sounds become muddled because the reflected sounds persist for too long/echo
if reverberation time is too short: music sounds “dead” and it becomes more difficult to produce high intensity sounds
