Ch. 11 pt. 1&2

• There are 2 definitions of sound:

  • Physical definition: pressure changes in the air or other medium
  • Perceptual definition: the experience we have when we hear
• Frequency:

  • Number of cycles within a given time period
  • Measured in Hertz (Hz): 1 Hz is one cycle per second
  • Perception of pitch is related to frequency
  • Tone height: the increase in pitch that happens when frequency is increased
• Perceptual Aspects of Sound:

  • Loudness is the perceptual quality most closely related to the level or amplitude of an auditory stimulus
  • Human hearing range: 20 to 20,000 Hz
• Periodicity Pitch: Removal of the first harmonic results in a sound with the same perceived pitch, but with a different timbre
• Transduction takes place through this process:

  • Cilia bend in response to movement of the organ of Corti and the tectorial membrane
  • Movement in one direction opens ion channels
  • Movement in the other direction closes the channels
  • This causes bursts of electrical signals
• Pure Tone: created by a sine wave
• Amplitude: difference in pressure between high and low peaks of wave
• Loudness: perception of amplitude
• Frequency: number of cycles within a given time period

  • measured in herts (Hz) - 1 Hz is one cycle per second
  • perception of pitch is related to frequency
• The Decibel Scale: relates the amplitude of the stimulus with the psychological experience of loudness

  • Decibel (dB): used to measure the loudness
  • Number of dB: 20 logarithm (p/po)
• Tone Height: the increase in pitch that happens when frequency is increased
• Both pure and some complex tones are periodic tones
• Fundamental Frequency: the lowest frequency of a periodic waveform and serves as the base frequency for all other harmonic frequencies in the sound

  • called the first harmonic
• Period Complex Tones: consists of several pure tones called harmonics
• Additional Harmonics: multiples of the fundamental frequency
• Additive Synthesis: process of adding harmonics to create complex sounds
• Frequency Spectrum: display of harmonics of a complex sound wave, showing the frequencies of the sound wave
• Human Hearing Range: 20 to 20 000 Hz
• Perceptual Aspects of Sound: loudness is the perceptual quality most closely related to the level or amplitude of an auditory stimulus
• Audibility Curve: shows the threshold of hearing in relation to frequency

  • changes on this curve show that humans are most sensitive to 2000 to 4000 Hz
• Auditory Response Area: falls between the audibility curve and the threshold for feeling

  • it show the range of response for human auditionn
• Equal Loudness Curves: illustrate the varying sensitivity of the human ear to different frequencies at different loudness levels

  • curves demonstrate that the human ear is not equally sensitive to all frequencies
  • determined by using a standard 1000 Hz tone
• Pitch: the perceptual quality we describe as high and low
• Timber: the quality that distinguishes between 2 tones that sound different even though they have the same loudness, pitch & duration

  • it's closely related to the harmonics, attack, and decay of a tone
• Effect of Missing Fundamental Frequency:

  • Periodicity Pitch - removal of the first harmonic results in a sound with the same perceived pitch, but with a different timber
  • Attack of Tones - buildup of sound at the beginning of a tone
  • Decay of Tones - decrease in sound at end of tone
• Outer Ear consist of the Pinna & Auditory Canal:

  • Pinna: helps with sound localization
  • Auditory Canal: 3cm tube like structure through which air vibrations travel from environment to tympanic membrane
• The resonant frequency of the auditory canal amplifies frequencies between 1000 & 5000 Hz
• Middle Ear has 2 cubic cm cavity separating inner from outer ear & contains the 3 ossicles:

  1. Malleus - moves due to the vibration of the tympanic membrane
  2. Incus - transmits vibrations of malleus
  3. Stapes - transmits vibrations of incus to the inner ear via the oval window of the cochlea
• Functioning of Ossicles:

  • Ossicles act to amplify the vibration for better transmission to the fluid
  • Middle ear muscles dampen the ossicles vibrations to protect the inner ear from potentially damaging stimuli
• Pressure changes in air transmit poorly into the denser medium
• Outer & Inner ear are filled with air

  • inner ear is filled with fluid that is much denser than air
• Inner / Outer Hair Cells: are the receptors for hearing
• Tectorial Membrane: gel-like structure located within the cochlea of the inner ear, playing a crucial role in the auditory system

  • extends over the hair cells
• Basilar Membrane: component of the cochlea in the inner ear

  • vibrates in response to sound and supports the organ of corti
• Process of Transduction:

  1. Cilia bend in response to movement of the organ of Corti and the tectorial membrane
  2. Movement in one direction opens ion channels
  3. Movement in the other direction closes the channels; this causes bursts of electrical signals
• Békésy's Place Theory of Hearing: frequency of sound is indicated by the place on the organ of Corti that has the highest firing rate
• Tonotopic Map: an organized arrangement found within the auditory system where different frequencies of sound are systematically mapped to specific physical locations in the brain and cochlea

  • Apex responds best to low frequencies
  • Base responds best to high frequencies
• Neural Frequency Tuning Curves: are graphical representations that illustrate how neurons in the auditory system respond to different frequencies of sound

  • Pure tones are used to determine the threshold for specific frequencies measured at single neurons
  • Plotting thresholds for frequencies results in tuning curves
  • Frequency to which the neuron is most sensitive is characteristic frequency
• Place Theory: proposes the perception of sound frequency depends on the location of maximum vibration along the cochlea's basilar membrane

  • Different frequencies stimulate different regions of the cochlea, with higher frequencies causing peak vibrations closer to the base and lower frequencies peaking near the apex
  • Allowing the brain to discern pitch based on the specific area of stimulation
• Phase Locking: refers to the ability of neurons to fire action potentials (or spikes) at the particular phase of a sound wave cycle

  • nerve fibers fire in bursts
  • firing bursts happen at or near the peak of the sine-wave stimulus
  • thus, are "locked in phase" with the wave
  • groups of fibers fire with periods of silent intervals creating a pattern of firing