PSYA01H3 Chapter Notes - Chapter 5.8: Parietal Lobe, Basilar Membrane, Fundamental Frequency
Detecting and Localizing Sounds in the Environment
Loudness and Pitch
Sounds of different frequencies stimulate different groups of hair cells, therefore brain informed
of the pitch by activity of different sets of axons from auditory nerve. Damage to certain area of
basilar membrane cause inability to hear certain frequencies
Low frequencies detected by the very tip of the basilar membrane flexing at the same times as
the vibrations
Loudness is communicated through rate of firing, louder=faster, low frequency volume
determined by amount of hair cells stimulated
Timbre: perceptual dimension of sound determined by the complexity of the sound
Can determine which instrument is playing because each produce sounds consisting of a set of
unique simple tones called harmonics: component of complex tone, one of a series of tones
whose frequency is a multiple of the fundamental frequency. In music theory, also known as an
overtone.
Fundamental Frequency: lowest, usually most intense, frequency of a complex sound; most often
perceived as the sounds basic pitch.
Fundamental frequency causes one part of the basilar membrane to flex while each of the
harmonics causes another portion to flex, during complex sound multiple parts of membrane flex
simultaneously
Task of identifying sounds is that of pattern recognition
Locating the Source of a Sound
Relative loudness is most effective means of perceiving location of high-frequency sounds
Acoustic energy in form of vibrations cannot actually pass through solid objects, low frequency
sounds can actually make large solid objects like a wall vibrate and make a new sound on the
other side but can’t vibrate fast so no high frequency
Head is such object, so if sound on right is high-pitched, will be much more intense than in the
left ear. Brain uses difference to locate source of sound
Second method is detecting the arrival times of vibration in ears, best for sounds under 3000Hz
In 1000Hz tone it’s 0.3m apart, and our head is half that, so sound on left would pull left eardrum
out, and right pushed in
When sound off to side, axons from each ear will fire at different rates and brain will find the
discrepancy, capable to find it in difference of 1 millisecond
Information first processed in brainstem region known as superior olive
Spatial location in general processed quite widely in auditory cotex but when location concerns
particular object, processed in area close to parietal lobe
Dong, Swindale, Cynader: exp: loudspeaker frequency of tone increase moving to left, decreased
to the right, for 10 minutes, after stationary loudspeaker, asked participants about sound,
increased seemed to move left, decrease right, (after effects like in the visual)
Age-Related Losses in Hearing
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Document Summary
Sounds of different frequencies stimulate different groups of hair cells, therefore brain informed of the pitch by activity of different sets of axons from auditory nerve. Damage to certain area of basilar membrane cause inability to hear certain frequencies. Low frequencies detected by the very tip of the basilar membrane flexing at the same times as the vibrations. Loudness is communicated through rate of firing, louder=faster, low frequency volume determined by amount of hair cells stimulated. Timbre: perceptual dimension of sound determined by the complexity of the sound. Can determine which instrument is playing because each produce sounds consisting of a set of unique simple tones called harmonics: component of complex tone, one of a series of tones whose frequency is a multiple of the fundamental frequency. In music theory, also known as an overtone. Fundamental frequency: lowest, usually most intense, frequency of a complex sound; most often perceived as the sounds basic pitch.
