Chapter 5 Flashcards
law of specific nerve energies
activity by a particular nerve always
conveys the same type of information to
the brain
ex. impulses in one neuron indicate
light; impulses in another neuron indicate
sound
Bipolar cells
Cells, located closer to the center of the
eye, that receive messages from visual
receptors at the back of the eye
These cells send messages to ganglion
cells that are even closer to the center of
the eye
The axons of ganglion cells join one another
to form the optic nerve that travels to the brain
Fovea
the central portion of the retina and
allows for acute and detailed vision
Packed tight with receptors
Each cone in the fovea has a direct line to
the brain which allows the registering of
the exact location of input
Our vision is dominated by what we see in
the fovea
Rods
most abundant in the periphery of the
eye and respond to faint light (120 million per
retina)
Cones
most abundant in and around the fovea (6 million per retina) Essential for color vision and more useful in bright light provide about 90% of the brain’s input
Photopigments
Chemicals contained by both rods and
cones that release energy when struck by
light
trichromatic theory (or YoungHelmholtz theory)
Color perception occurs through the relative rates of response by three kinds of cones – Short wavelength – Medium-wavelength – Long-wavelength
Each cone responds to a broad range of
wavelengths, but some more than other
The ratio of activity across the three types
of cones determines the color
Three kinds of cones are unevenly
distributed
The Opponent-Process Theory
Suggests that we perceive color in terms
of paired opposites
color vision deficiency
An impairment in perceiving color
differences
Caused by either the lack of a type of cone or
a cone that has abnormal properties
Mamillian visual system
Rods and cones of the retina make
synaptic contact with horizontal cells and
bipolar cells
Horizontal cells are cells in the eye that
make inhibitory contact onto bipolar cells
Bipolar cells make synapses onto
amacrine cells and ganglion cells
Different cells are specialized for different
visual functions
Ganglion cell axons form the optic nerve
The optic chiasm is the place where the
two optic nerves leaving the eye meet
In humans, half of the axons from each
eye cross to the other side of the brain
Most ganglion cell axons go to the lateral
geniculate nucleus, a smaller amount to
the superior colliculus, and fewer to other
areas
lateral geniculate nucleus
– Part of the thalamus
– Specialized for visual perception
– Destination for most ganglion cell axons
– Sends axons to other parts of the thalamus
and to the visual areas of the occipital cortex
sight goes to the Later Good Night
Lateral inhibition
Sharpens contrasts to emphasize the
borders of objects
• The reduction of activity in one neuron by
activity in neighboring neurons
• The response of cells in the visual system
depends upon the net result of excitatory
and inhibitory messages it receives
receptive field
the part of the visual field that either excites or inhibits a
cell in the visual system of the brain
blindsight
an ability to respond to visual
stimuli that they report not seeing
damage to V1
Simple cells
Fixed excitatory and inhibitory zones
The more light that shines in the excitatory
zone, the more the cell responds
Bar-shaped or edge-shaped receptive
fields with
respond to vertical and horizontal orientations
responds to a stimulus in only one location
