H8 the Hearing Brain

• Pure tones

  Sounds with a sinusoid waveform (when pressure change is plotted against time)
• Pitch


  The perceived property of sounds that enables them to be ordered from low to high
• Pitch range for humans

  • 20 Hz and 20,000 Hz
• Loudness


  The perceived intensity of the sound (measured in decibels)
• Fundamental frequency

  The lowest frequency component of a complex sound that determines the perceived pitch. Also the difference between harmonics
• Fundamental frequency example


  • From the harmonics 100 Hz, 200 Hz, 300 Hz, then 100 Hz is the lowest it could go and is the fundamental frequency
• Missing fundamental phenomenon


  If the fundamental frequency of a complex sound is removed, then the pitch is not perceived to change (the brain reinstates it)
• Missing fundamental phenomenon example


  • When the pitches 200 Hz, 300 Hz, 400 Hz etc are all played together → Brain will recognize the difference is 100 Hz and will hear this pitch too
• Timbre


  The perceptual quality of a sound enables us to distinguish between different musical instruments even when pitch is the same
• Timbre example


  • a piano and a violin playing the same note sound different due to intensity of the sinusoids
• Pinna (Earlobes)


  • Collects sound waves and directs them into the auditory canal
  • Helps in locating the direction of sound sources due to its shape and folds
• Auditory Canal


  • Channels sound waves from the pinna to the eardrum
  • Amplifies certain sounds through reflections within the canal
• Eardrum


  • Vibrates in response to sound waves, converting airborne sound waves into mechanical vibrations
• Ossicles (Three Tiny Bones)


  • Amplifies and transfers mechanical vibrations to the inner ear with minimal energy loss
• Malleus (Hammer)


  Attached to the eardrum and transfers vibrations to the incus
• Incus (Anvil)


  Transfers vibrations from the malleus to the stapes
• Stapes (Stirrup)


  Transfers vibrations from the incus to the oval window of the cochlea
• Oval Window


  • Receives vibrations from the stapes and transmits them into the fluid-filled cochlea
• Cochlea


  • Part of the inner ear that converts liquid-borne sound into neural impulses
• Basilar membrane


  • A membrane within the cochlea containing tiny hair cells linked to neural receptors
  • Different parts of the basilar membrane respond to different frequencies (high frequencies near the oval window, low frequencies near the center)
• Primary auditory cortex


  The main cortical area to receive auditory-based thalamic input
• Belt region


  Part of the secondary auditory cortex, with many projections from the primary auditory cortex
• Parabelt region


  Part of the secondary auditory cortex, receiving projections from the adjacent belt region
• The belt and parabelt regions are involved in higher-level processing
• Auditory Scene Analysis


  • Separating and identifying individual sound sources in complex auditory environments
• Tonotopic organization


  The principle that sounds close to each other in frequency are represented by neurons that are spatially close to each other in the brain
• Inter-aural time difference


  The difference in timing between a sound arriving in each ear (used to localize sounds)
• Inter-aural intensity difference


  The difference in loudness between a sound arriving in each ear (used to localize sounds)
• Head-related transfer function

  An internal model of sounds get distored by the unique shape of one's own ears and head
• Planum temporale


  A part of the auditory cortex (posterior to the primary auditory cortex) that integrates auditory information with non-auditory information, for example to enable sounds to be separated in space
• Auditory stream segregation


  The division of a complex auditory signal into different sources or auditory objects (like different voices or instruments)
• Mismatch negativity (MMN)


  An ERP component that occurs when an auditory stimulus deviates from previously presented auditory stimuli
• Cocktail party problem


  The problem of attending to a single auditory stream in the presence of competing streams (with different acoustic and spatial properties)—for instance, attending to one person's voice in a noisy room of other voices
• Amusia


  An auditory agnosia in which music perception is affected more than the perception of other sounds. Amusia is a condition that impacts musical perception and production, affecting pitch, rhythm, and emotional engagement with music
• Tone-deafness (or congenital amusia)


  A developmental difficulty in perceiving pitch relationships
• Prosody


  Changes in the stress pattern of speech (e.g., to add emphasis), the rhythm of speech or the intonation (e.g., rising/falling pitch to indicate questioning or sarcasm)
• Melody


  Patterns of pitch over time
• Pure word deafness

  Type of auditory agnosia in which patients are able to identify environmental sounds and music but not speech. → damage in left hemisphere
• Spectrogram

  Plots the frequency of sound (on the y-axis) over time (on the x-axis) with the intensity of the sound represented by how dark it is
• Allophones


  Different spoken/acoustic renditions of the same phoneme