Hearing and Language Flashcards
How do sensory receptors convert stimuli into useable information?
(Vision) Light to chemical energy
(Audition) Sound to mechanical energy
(Somatosensory) Pain, touch, pressure to mechanical energy
Vibration and sound
Vibration = sensation
Sound = perception
Sound = vibrations of air molecules that are transmitted to the ear and are perceived by the brain
Physical and perceptual dimensions of sound waves
Amplitude - loudness
Frequency - pitch
Complexity - timbre
Amplitude
Perceived intensity of sound (loudness dB)
Human auditory system is sensitive to quiet sounds
Soft = below 20 dB
Loud = above 70 dB
Frequency
Sound waves travel at a fixed speed but vary in wavelength
Perceived as low and high pitch (Hz, 1 Hz = 1 cycle per second)
Human hearing range = 20 to 20,000 Hz
Complexity
Corresponds to our perception of timbre or uniqueness
Pure = sounds with single frequency
Complex = sounds with a mixture of frequencies
Portions of the ear
Outer ear - Capturing and amplifying vibrations in the air
Middle ear - Transduction of sound waves from air pressure to mechanical energy; amplification (ossicles)
Inner ear - Conversion of mechanical signal to neural signal
Cochlea
Part of inner ear involved in hearing
A spiral-shaped, fluid-filled organ in the inner ear that converts sound waves into electrical impulses that the brain can interpret as sound
Basilar membrane (separates sound into frequencies):
Narrow thick base = tuned for high frequencies
Wide, thin apex = tuned for low frequencies
Tonotopic organization (organ of corti)
Closest to oval window = more sensitive to high frequency
At apex = more sensitive to low frequency
Outer hair cells outnumber inner hair cells …
3:1
Outer hair cells = tune cochlea
Inner hair cells = receptors
Pathways of the thalamus
Ventral = identifies what a sound is and projects to A1
Dorsal = identifies the sounds spatial location and projects to secondary auditory regions
Primary auditory cortex
A1, or Heschl’s gyrus
Secondary auditory cortex
A2, Planum temporale
How is the audiory cortex viewed (practically)
Retractor opens the lateral fissure to reveal the auditory cortex
What is hearing pitch related to?
Tonotopic organization
- tonotopic organization of cochlea is preserved in primary auditory cortex
- cochlea base = high frequencies
- cochlea apex = low frequencies
- cortex posterior = high frequencies
- cortex anterior = low frequencies
Detecting loudness
Cochlear cells fire more when amplitude is greater
Detecting location
Differences in arrival time (interaural time difference)
Relative loudness on the left and right (interaural intensity difference)
Detecting patterns
Music and speech are sound wave patterns
Music = right hemisphere
Language = left hemisphere
Language and music
Capacity of each is innate
Language = left lateralized
Music = right lateralized
Likely evolved together
Typical pattern of lateralization allows for processing of aspects of language in the right hemisphere and music in the left hemisphere (although language/music is not exclusively a LH/RH process)
Wilder Penfield
Worked with epilepsy
Montreal’s first surgeon (1934)
Penfield and Jasper map the somatosensory and motor cortices (1954)
Directly stimulated auditory and language areas with electrical current (disrupt or elicit speech)
Paul Broca
‘First higher cognitive function to be localized - location of language’
Usually left (dominant) frontal lobe, anterior to central fissure
Wernicke-Geschwind model
1) Comprehension is extracted from sounds in Wernicke’s area
2) Passed over the Arcruate Fasciculus (important to process of language) pathway to …
3) Broca’s area for speech articulation
Aphasia
The inability to speak or comprehend language despite the presence of normal comprehension and intact vocal mechanisms.
Broca’s Aphasia
Understands speech, but speech production is laborious
- left frontal lobe damage
- speech production deficits
- comprehension spared
Wernicke’s Aphasia
Fluent speech, with the meaning of speech severely compromised
- left temporal lobe damage
- speech production spared
- comprehension deficits
- Neologisms = not a real word but sounds like one
Right hemisphere damage
Deficits: global structure processing of the discourse (e.g. how to link sentences to form stories); Sentence reassembly; Story order; Theme detection; Doesn’t get the joke
Aprosodia
RH orbitofrontal lesions
- RH Broca’s area produces prosody
- RH Wernicke’s area comprehends prosody
- double dissociation, some patients can’t produce prosody (monotone) but can understand it, others can produce it but can’t understand it
Pinna (outer ear)
Funnel-like external structure of the outer ear - designed to catch sound waves in surrounding environment and deflect them into external ear canal
External ear canal (outer ear)
Amplifies sound waves and directs them to the eardrum at its inner end
Ossicles (middle ear)
Hammer, anvil, stirrup
- Connected in a series and contained in an air-filled chamber
- Amplify sound vibrations from the eardrum and send them to the inner ear
- Attach the eardrum to the oval window (opening to bony casing of cochlea)
Summary of pathway to the auditory cortex
Auditory inputs cross to the hemisphere opposite the ear in the hindbrain and midbrain, then recross in the thalamus. In this way, the information from each ear reaches both hemispheres. Multiple nuclei process inputs en route to the auditory cortex
Where is the primary auditory cortex (A1)?
Heschl’s gyrus
- surrounded by secondary cortical areas (A2)
- secondary cortex behind Heschl’s gyrus is the planum temporale
