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Sensation, Part 3 Gleitman et al. (2011), Chapter 4
Mike D’Zmura Department of Cognitive Sciences, UCI Psych 9A / Psy Beh 11A February 18, 2014
T. M. D'Zmura 1
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• Sound waves • can vary in amplitude and frequency • create vibrations in eardrum • transmitted by the auditory ossicles • to the oval window—movements create waves in the
cochlea • hair cell receptor neurons in the cochlea transduce sound
pressure waves into neural signals
Hearing - Audition
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A brief recap from last week on sound stimuli…
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A pure tone has a sound pressure wave described by a sinusoidal function.
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Pure tones vary in their • amplitude (related to the perceptual variable loudness) • frequency (related to the perceptual variable pitch)
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Units of frequency are Hertz (Hz): number of cycles (full waves) per second
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Almost all sounds are described by complex waveforms. These can be analyzed in terms of a sum of pure tone waveforms (Fourier analysis)
try the sound-generating Java applet at http://www.phys.hawaii.edu/~teb/java/ntnujava/sound/sound.html
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• Within the cochlea is the basilar membrane. • contains receptors stimulated by the membrane’s
deformation
Hearing
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Organ of Corti
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Organ of Corti with Inner and Outer Hair Cells (IHC and OHC)
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Inner and Outer Hair Cell Stereocilia
IHC cilia – not attached to the tectorial membrane OHC cilia – attached to the tectorial membrane
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Inner Hair Cell Stereocilia
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Tip links on haircell stereocilla
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Inner Hair Cell Transduction
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Dendrites of the spiral ganglion cells collect signals from the hair cells
AFF – afferent fibers to the brain EFF – efferent fibers out of the brain
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• Place theory • Pitch is based on the place
where the basilar membrane is most stimulated.
• Different places are more responsive to particular frequencies and generate particular pitch sensations.
• Frequency theory • Pitch depends on firing
frequency of the auditory nerve.
Theories About Pitch
Hermann von Helmholtz
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Idea behind place theory: the place of maximum stimulation along the basilar membrane depends on frequency, so that the hair cell receptor neurons convey frequency information simply by virtue of their position along the basilar membrane.
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• Evidence suggests that both theories are correct. • Perception of higher frequencies depends on the place
where the basilar membrane is stimulated. • Perception of the lower frequencies depends on firing
frequency.
Theories About Pitch
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Axons of the spiral ganglion neurons, which pass through the auditory nerve (VIIIth nerve), project to the cochlear nucleus
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Inferior colliculus neurons receive signals from ipsilateral and contralateral ears via the superior olive and the dorsal cochlear nucleus Commissural axons connect the inferior colliculi on either side of the head (not shown in the figure at right) Inferior colliculus neurons project primarily to the ipsilateral medial geniculate nucleus Some inferior colliculus neurons project to the superior colliculus (multimodal integration; not shown) MGN neurons project to auditory cortex (superior temporal gyrus)
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Tonotopic (or cochleotopic) organization of primary auditory cortex
High-frequency sounds stimulate best the base (oval window) end of the cochlea, while low-frequency sounds stimulate the apical end. There is a progression in best frequency ( tono – “tone” ) as one moves along the basilar membrane ( topus – “place” ).
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Tonotopic (or cochleotopic) organization of primary auditory cortex in cat Neuron preferred frequencies are shown in units of kiloHertz (kHz)
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• Vision is our primary distance sense. • Its stimulus is light, which varies in intensity and
wavelength. • Eye structures, like the cornea, iris and lens,
• control the amount of light entering the eye. • form the retinal image.
Vision
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Electromagnetic Spectrum
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UV and Lens Brunescence
infant
91-year-old
The lens absorbs UV radiation. This causes the lens to yellow and eventually become brown and more opaque. Moral: Wear UV-filtering sunglasses when outdoors!
photos of peoples lenses, arranged by age
UV
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The Eye cornea – transparent surface that acts as eye’s principal focusing element aqueous and vitreous humors - effectively salt water sclera – whites of the eyes iris – colored muscle that contracts and dilates pupil – disk in center of iris through which light passes lens – crystalline structure providing secondary focus ciliary muscle – changes shape of the lens retina – layered sheet of neurons lining back of the eye optic nerve – bundle of retinal ganglion cell axons passing up into the brain optic disk – blind spot fovea – region of retina used to view objects directly ahead T. M. D'Zmura 26
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The Eye
retina – sheet of nerve cells (part of central nervous system) lining back of the eye
fovea – small region of retina on which falls light from objects directly ahead (look straight at ‘em) T. M. D'Zmura 27
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Layers of the Retina
AC amacrine cell HC horizontal cell MC Müller cell
axons, dendrites
cell bodies
cell bodies
axons, dendrites
cell bodies
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direct path to the brain:
photoreceptor
to bipolar cell
to ganglion cell
to higher brain centers
via optic nerve: ganglion cell axons
rods and cones signal light absorption
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• The light stimulus is transduced by rods and cones • Rods and cone photoreceptors contain pigment molecules
that change shape when they absorb a photon of light • Rods and cones differ in function.
• rods: active at low light levels (night time: scotopic vision), shades of gray
• cones: active at high light levels (daytime: photopic vision), responsible for sensations of color
• Acuity is greatest in the fovea, where the most cones are located.
Rod and cone photoreceptors
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Rod and Cone Photoreceptors
from http://neuro.med.harvard.edu/site/dh/b11.htm
electron micrograph of a small part of monkey retina showing sheet of rod (small, numerous) and cone (surrounded by black, fewer) photoreceptors
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Rod and cone distribution across the retina • Cones: high density in the fovea • Rods: none in the fovea, many in the periphery
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Fovea and Optic Nerve
great site: webvision.med.utah.edu T. M. D'Zmura 34
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