Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.1 Audition Anatomy –outer ear –middle ear –inner ear Ascending auditory pathway –tonotopic mapping Physical and Psychological qualities of sound –The complex relationship between the physical and psychological variables

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.2 Audition The encoding of pitch The encoding of loudness The perception of complex tone combinations –Ohm’s law –exceptions

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.3 Anatomy * * Tympanic membrane

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.4 Anatomy Outer ear –pinna (pinnae) - visible ear funnels sound towards ear drum helps in sound localization –external auditory canal –tympanic membrane vibrates to transmit sound wave Middle ear –ossicles - malleus, incus, stapes amplifies vibrations –Eustachian tube equalizes pressure

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.5 Anatomy

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.6 Anatomy Inner ear - cochlea –oval window sets up waves in the fluid filled cochlea –helicotrema opening between the two outer tubes –transduction basilar membrane tectorial membrane hair cells –round window releases pressure of waves –auditory nerve carries signal to brain

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.7 Anatomy Tectorial membrane Hair cells

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.8 Ascending Auditory Pathway Superior Olivary Nucleus reflexive localization Inferior Colliculus combines auditory with visual location information MGN selective attention Temporal Lobe left - language right - sounds tonotopic mapping

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.9 Tonotopic Mapping Orderly representation of sound in the cortex –frequencies are represented parallel to the surface lower frequencies are represented inferior (lower) than higher frequencies –loudness is represented as distance from the surface soft sounds are represented near the surface louder sounds are represented deeper in cortex

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.10 Tonotopic map of Temporal Lobe

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.11 Sound - Physical Qualities Vibration in a medium Alternating compressions and rarefactions of pressure Physical variations in sound –frequency number of cycles per second (cps) often written as Hertz (Hz) –amplitude degree of change in pressure measured in decibels (Db) –complexity number of different frequencies present

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.12 Amplitude Note: prolonged exposure to sounds over 85Db produces permanent hearing loss

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.13 Sound - Psychological Qualities Pitch –varies from low to high –primarily based on frequency Loudness –varies from soft to loud –primarily based on amplitude Timbre –based on complexity –overtones

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.14 Complex Relationships Unlike color perception, there is not a simple relationship between the physical and psychological variables in audition Background –human range of hearing ,000 (16K) Hz (or K) octave = a doubling in frequency –e.g 20 Hz and 40 Hz are an octave apart, but 1,000 and 2,000 Hz are also an octave apart

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.15 Complex Relationships Pitch is primarily based on frequency Two other factors influence perceived pitch –instructions –amplitude Instructions –when asked to indicate a change in tone subjects generate the jnd scale –when asked to indicate a change in musical note they generate the octave scale –therefore you need to know the instructions to know what the person will perceive

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.16 Pitch Scales * Octave scale results in a straight line * least noticeable change is 0.25 Hz at about 15K, therefore for good recording equipment the wow and flutter must be less than.25Hz

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.17 Complex Relationships Amplitude also influences pitch –as amplitude increases high tone get higher, low tones get lower, middle remain the same

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.18 Complex Relationships Loudness is primarily based on amplitude –frequency also influences loudness equal loudness contours “loudness” control, graphic equalizer

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.19 Equal Loudness Contours

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.20 Encoding Pitch Von Bekesy’s Place Theory –peak of the envelope of the traveling wave is at different locations along the basilar membrane for different pitches –high frequency near stapes –low frequency near helicotrema

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.21 Encoding Pitch

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.22 Encoding Pitch Wever’s Volley Theory –nerves fire in a volley (sequence) to match frequency of pitch Both types of encoding are used –above 5,000 Hz - place theory – ,000 - both (very sensitive) –below volley

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.23 Encoding Loudness Cells respond to a specific range of firing –within the range an increase in firing rate –e.g. a specific set of hair cells might respond to Db at 10 Db these cells fire slowly, at 20 Db they fire more rapidly, at 30Db they fire maximally, over 30 Db a new group of cells take over

Sensation and Perception - audition.ppt © 2001 Laura Snodgrass, Ph.D.24 Complex Tone Combinations Ohm’s Law –the ear is a frequency analyzer (Fourier analysis) –given a complex waveform we hear the component frequencies Exceptions to Ohm’s Law –Harmonics - we hear the multiples as timbre not separate tones e.g. if 100 Hz is the fundamental, 200 Hz is the first harmonic and 300 Hz is the second harmonic if 225 is the fundamental, the 450 is the first harmonic, and 675 is the second harmonic –Beats small differences (1-6 Hz) are hear as a waxing and waning of amplitude