Chapter 6 Flashcards
• is sometimes defined as waves of electromagnetic
energy that are between 380 and 760 nanometers (billionths
of a meter) in length
LIGHT
plays an important role in the perception of
color
WAVELENGTH
because it plays an important role in the
perception of brightness.
INTENSITY
regulates the amount of light
reached by the retinas and which
give our eyes their characteristic
color
IRIS
adjusts in response to
changes in illumination represents a
compromise between sensitivity
(the ability to detect the presence of
dimly lit objects) and acuity (the
ability to see the details of objects).
PUPIL
- focuses incoming light
on the retina.
• The process of adjusting the
configuration of the lenses to
bring images into focus on the
retina is called
accommodation.
LENS
• is the sensory
membrane that lies in the inner
surface of the back of the eyeball
• It is composed of several layers,
including one that contains
specialized cells called
photoreceptors.
Retina
are the primary cell type in the
innermost cellular layer of the
retina, responsible for carrying
visual information from the eye to
the brain
Retinal Ganglion Cells(RGCs)
are responsible for
complex processing of the retinal
image, specifically adjusting image
brightness and, by integrating
sequential activation of neurons,
detecting motion
Amacrine Cells
are the central
neurons of the retina which carry
light-elicited signals from
photoreceptors and horizontal
cells (HCs) in the outer retina to
amacrine cells (ACs) and ganglion
cells (GCs) in the inner retina.
Bipolar Cells
second-order
neurons in the vertebrate retina,
receiving direct excitatory input from
cone and rod photoreceptors.
Horizontal Cells
• takes light focused by the cornea
and lens and convert it into
chemical and nervous signals
which are transported to visual
centers in the brain by way of the
optic nerve.
Photoreceptors
• An indentation, about 0.33
centimeter in diameter, at the
center of the retina; it is the area
of the retina that is specialized for
high-acuity vision (for seeing fine
details).
• The thinning of the retinal
ganglion cell layer at the fovea
reduces the distortion of incoming
light.
Fovea
• Created by the inside-out
structure of the retina, requires a
more creative solution
Blind Spot
• the theory that cones and rods
mediate different kinds of vision.
Duplexity Theory
• the process by which we perceive surfaces; the visual system
extracts information about edges and from it infers the
appearance of large surfaces).
Surface Interpolation
(cone-mediated)
predominates in good lighting and
provides high-acuity (finely detailed)
colored perceptions of the world
Photopic vision
(rod-mediated) In
dim illumination, there is not
enough light
Scotopic vision
• graph of the relative
brightness of lights of
the same intensity
presented at different
wavelengths
Spectral
Sensitivity
• One evening, just before dusk, while Purkinje was
walking in his garden, he noticed how bright most
of his yellow and red flowers appeared in relation
to his blue ones. What amazed him was that when
viewed at night, appeared completely in shades of
gray, but most of the blue flowers appeared as
brighter grays than did the yellow and red ones.
• It is the tendency for the peak luminance sensitivity
of the eye to shift toward the blue end of the color
spectrum at low illumination levels as part of dark
adaptation.
Purkinje effect
• conversion of one form of energy to another
Transduction
is the conversion of light to neural signals by
the visual receptors.
• Visual transduction
• pigment-containing sensory
protein that converts light into
an electrical signal.
• it is required for vision in dim
light and is located within the
tightly packed disks that make
up the outer segment of the
retina’s photoreceptive rod cells,
which are specially adapted for
vision under low-light conditions.
Rhodopsin
The the correct term for
colors such as blue,
green, and yellow
Hues
The perception of object an object’s color
depends on the _____of the light.
wave lengths
Proposed by Thomas Young in (1802), and refined by
Hermann von Helmholtz in (1852)
Their theory that any color of the visible spectrum can be
matched by a mixing together of three different wavelengths of
light in different proportions. -
Component Theory
• Proposed by Ewald Hering in
(1878)
• There are two different
classes of cells in the visual
system for encoding color
and another class for
encoding brightness.
Opponent
Processing
are pairs of colors
(e.g., green light and red light) that produce
white or gray when combined in equal
measure
Complementary colors
Refers to the fact that the perceived
color of an object is not a simple
function of the wavelengths reflected
by it.
is the tendency for an
object to stay the same color despite
major changes in the wavelengths of
light that it reflects.
Color Constancy
• the color of an object is determined by its
reflectance the proportion of light of different
wavelengths that a surface reflects
Retinex Theory
• It is a failure of
recognition (gnosis
means to know ) that is
not attributable to a
sensory deficit or to
verbal or intellectual
impairment;
AGNOSIA
• A specific agnosia for visual
stimuli. Visual agnosics can
see visual stimuli, but they
don’t know what they are.
• Movement agnosia
• Object agnosia
• Coloragnosia a
VISUAL
AGNOSIA
• can usually
recognize a face as a face, but
they have problems recognizing
whose face it is.
• They often report seeing a
jumble of individual facial parts
(e.g., eyes, nose, chin, cheeks)
that for some reason are never
fused, or bound, into an easy-torecognize whole.
• In extreme cases,
prosopagnosics cannot
recognize themselves
PROSOPAGNOSIA
• is a deficiency in the ability to see movement progress in
a normal smooth fashion.
•It can be triggered by high doses of certain antidepressants
•It is often associated with damage to the middle temporal (MT) area
of the cortex
Akinetopsia
