reverse names 2 Flashcards
-Which fibers are responding
-Specific groups of hair cells on basilar membrane activate a specific set of nerve fibers
-Suggests that different frequencies will disturb different regions of the basilar membrane (i.e. different cells)
-Helmholtz first proposed a “resonance” theory
basilar membrane wider at apex
suggested that fibers in basilar membrane resonated at different frequencies at different locations along its length (long fibers at apex, short at base)
-Problems for resonance theory
no fibers
not under tension:
The Neural Encoding of Pitch: Place Theory
Bekesy observed the movement of the basilar membrane directly – drilled hole in cochlea of cadaver and viewed movement
sound produced ? along the basilar membrane
waves affected all of the membrane, but the location of maximum displacement varied with frequency
Peak of envelope moves towards basal end of basilar membrane with increasing frequency
low freq/long at apex, high freq/short at base
TRAVELLING WAVES
Rate or pattern of firing of nerve impulses
-Proposes the basilar membrane vibrates in synchrony with the pressure changes (at the same frequency as the sound)
-Frequency representation based on a match between the frequencies in incoming sound waves and the firing rates of auditory nerve fibers.
-similar to a diaphragm in a speaker
vibrates as a unit
results in impulses in the auditory nerve at same frequency as sound itself
-Two problems:
basilar membrane not like a diaphragm
Nerve fibres can’t fire above about 1000 Hz
The Neural Encoding of Pitch: Frequency Theory or Temporal Code
frequency could be coded by pattern of activity in a number of cells
Volley Theory & Phase Locking
~mechanical impediment to sound transmission~ Common causes -blockage in external ear -Otitis media (infection) -Otosclerosis Diagnosis -Relatively “flat” loss or low -frequencies more affected -Difference between bone and air thresholds -maximum loss no more than about 6o dB Treatment -Medical/surgical -Hearing aid
Conductive loss:
Persistent noise in the absence of any auditory stimulation
Chronic
Debilitating
May be related to “Phantom Limbs”
Tinnitus
The range of amplitudes that can be heard and discriminated; when applied to an individual auditory nerve fiber, the range of amplitudes over which the firing rate of the fiber changes.
dynamic range
~damage to neural transduction (i.e. hair cells)~
Common causes
-Age: gradual deterioration (presbycusis)
-Noise: progressive cumulative effects
-Ototoxic drugs: nicotine, aspirin, streptmycin
-Infections: mumps, maternal rubella, syphilis
Diagnosis
-Similar bone and air thresholds
-Typical high frequency loss (“ski-slope”)
-Loss may be profound
Treatment
-Hearing aids very limited
-In severe cases, cochlear implants
Sensori-neural loss:
Hearing loss with age
Progressive sensori-neural loss
More severe in males than females
Presbycusis:
preferred frequency
characteristic frequency
location cues based on the comparison of the signals received by the left and right ears
Binaural cues
- difference in sound pressure level reaching the two ears
- Reduction in intensity occurs for high frequency sounds for the far ear
- The head casts an acoustic shadow
- This effect is minimal for low frequency sounds
Interaural intensity (or level) difference
-Heuristics that help to perceptually organize stimuli
>Location - a single sound source tends to come from one location and to move continuously
>Similarity of timbre and pitch - similar sounds are grouped together
>Auditory stream segregation - separation of stimuli into different perceptual streams
Auditory Grouping
- the array of all sound sources in the environment
- process by which sound sources in the eviornment are separated into individual perceptions
Auditory Scene
Auditory Scene Analysis
Distributed coding – trichromatic theory of colour vision
Population code
Pattern Theory
-muscle stretch and joint angle, for monitoring limb position and movement
-Three different types of sensory organs provide information about joint angles:
muscle spindles
Golgi tendon organs
joint receptors
proprioception
-Specialized for the detailed perception of spatial patterns on surfaces
-Good acuity or spatial resolution
so small receptive fields
-??? receptors are densely packed on the fingertips - similar to cones in the fovea
-Both two-point thresholds and grating acuity studies show acuity was greatest on fingertips and that acuity is related to the spacing between ??? receptors at each location
Tactile Acuity
Merkel Cell Endings (SA I)
Feature detectors (grandmother cell)
Labeled lines - taste
Place theory – hearing
modular
Specificity Theory
object shape, perceived through touch and proprioception together
haptic
minimum separation needed between two points to perceive them as two units
Two-point threshold
placing a grooved stimulus on the skin and asking the participant to indicate the orientation of the grating
Grating acuity
- respond most strongly to low- frequency vibrations
- convey information about very small motions of the skin
- ideally suited for perceiving slip and maintaining control over the force of one’s grip on an object.
Grip Control
(Meissner corpuscles (FA I))
- Spatial cues are determined by the size, shape, and distribution of surface elements
- Temporal cues are determined by the rate of vibration as skin is moved across finely textured surfaces
- only the adaptation to the 250-Hz stimulus affected the perception of fine textures (adapt pacinian)
duplex theory of texture perception
Thermoreceptors that fire at an ongoing moderate rate in response to sustained skin temperatures in the range of 29– 43° C.
Respond if skin temperature is abruptly warmed from a sustained neutral temperature
warm fibers
-Very large receptive fields (poor spatial resolution)
-Important role in information about skin stretch
Critical to perception of hand conformation
Plays a role in perception of movement across the skin
Skin Stretch (SA II Mechanoreceptors... Ruffini endings)
-Onion-like structure
-Large receptive fields (poor spatial resolution, but high sensitivity)
-Very sensitive to vibration
Critical for perceiving texture of surfaces
The structure of the ???? is responsible for the response to vibration
without the ???? fibers respond when pressure is applied, as pressure continued, and when it was removed
with ?????, fibers only responded when pressure was applied and when it was removed
Vibration & Texture
Pacinian Corpuscles (FA II)
-The “” consists of substantia gelatinosa cells in the spinal cord (SG- and SG+)
-Input into the gate comes from:
Large diameter (L) fibers - information from tactile stimuli
Small diameter (S) fibers - information from nociceptors
Central control - information from cognitive factors from the cortex
-Pain does not occur when the gate is closed by stimulation into the SG- from central control or L-fibers into the T-cell
-Pain does occur from stimulation from the S-fibers into the SG+ into the T-cell
Gate Control Model of Pain Perception
Endogenous opioids that have an inhibitory effect on pain- related neural signals in many areas of the central nervous system, reducing the perceived intensity of pain.
endorphins
Compounds that belong to a class of substances called opiates; released by the body in response to painful or stressful experiences.
endogenous opioids
proprioceptive information carried by signals from muscle spindles and Golgi tendon organs, and
tactile information carried by signals from mechanoreceptors in the skin
Neurons in area 2
tactile information carried by signals from mechanoreceptors in the skin
Neurons in areas 3b and 1
proprioceptive information carried by signals from muscle spindles and Golgi tendon organs located in tissues below the skin
Neurons in area 3a
Thermoreceptors that fire at an ongoing moderate rate in response to sustained skin temperatures in the range of 17– 40° C.
Respond if skin temperature is abruptly cooled from a sustained neutral temperature
cold fibers
