CHAPTER 4
Factual
LO 1 to 4
Pages: 92-99
WWW
1. Trace the path of energy from a visual stimulus from the environment, through
the eye, to the brain.
Concept/Applied
LO 14
Pages: 113-114
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2. Provide an overview of the place and frequency theories of pitch perception,
and resolve the “debate” between the two.
Light passes through the cornea, enters the pupil, is focused by the lens, and
projected onto the retina. The retina converts the light rays into nerve impulses,
which then travel via the optic nerve to the optic chiasm. At the optic chiasm, the
axons from the inside half of each eye cross over and project along two divergent
pathways to the opposite cerebral hemisphere.
Place theory proposes that specific sound frequencies vibrate specific portions of the
basilar membrane, producing different pitches. Frequency theory, on the other hand,
proposes that pitch perception corresponds to the frequency at which the entire
basilar membrane vibrates.
Currently, it is believed that both theories are needed to fully account for pitch
perception. It appears that, for low-frequency sounds (under 1000 Hz), pitch
perception depends on frequency coding only; for moderate-frequency sounds (1000
Hz to 5000 Hz), pitch perception depends on a combination of place and frequency
coding; for high-frequency sounds (over 5000 Hz), pitch perception depends on
place coding only.
Integrative
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3. Compare vision and hearing with regard to the proximal stimulus and
information processing for each sense.
The proximal stimulus for vision is light waves oscillating over distance. Light
waves have three properties: (1) amplitude, affecting the perception of brightness;
(2) wavelength, affecting the perception of color; and (3) purity, affecting the
perception of saturation. Similarly, the proximal stimulus for hearing is sound waves
oscillating over time. Sound waves have the same three properties as light waves:
(1) amplitude, affecting the perception of loudness; (2) wavelength, affecting the
perception of pitch; and (3) purity, affecting the perception of timbre.
Both the eye and the ear convert physical energy (light and sound waves,
respectively) into the neural energy that travels to the brain, producing sensory
experience. In the eye, this conversion is done by the rods and cones at the retina; in
the ear, this conversion is done by the hair cells, located on the basilar membrane in
the inner ear. Visual information is routed to the visual cortex in the occipital lobes;
auditory information is routed to the auditory cortex in the temporal lobes.