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Vision
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Vision
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Gives us an enormous biological
advantage by helping us detect…
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Targets
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Threats
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Changes in our physical environment,
allowing us to adapt our behavior
accordingly
Evolutionary pressure has made vision the
sense that is the
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The most complex
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Best developed
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And most important sense for humans
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Process of Visual Sensation
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Eye is like a camera the brain uses to make
motion pictures of the world
The eye…
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Gathers light
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Focuses it
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Converts it to neural signals
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Sends signals to be processed into image
The eye is unique in that it extracts images
from light waves
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Transduces characteristics of light into
neural signals
The lens of the eye helps refract light on to
the retina
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Transduction happens in the retina
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thin light-sensitive layer at the back of the eye
ball that contains millions of photoreceptors
Photoreceptors – Light – sensitive cells (neurons) in
the retina that convert light energy to neural
impulses
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Rods – especially sensitive to dim light but not
colors (rod shaped)
Cones – especially sensitive to colors but not
dim light (cone shaped)
Cones concentrate in the very center of the
retina called the fovea
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Area of sharpest vision
Young – Hemholtz Theory: theory that the
retina contains three different color receptors
(red, green, blue)
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Other cells in the retina that do not respond directly to light
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Bipolar cells – collect impulses from photo receptors and
shuttle them on to the ganglion cells
Ganglion cells – collect neural impulses from bipolar cells
and shuttle them through the brain via the optic nerve
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Left and right optic nerve come together at the optic
chiasm
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The bundle of neurons that carries visual information
from the retina to the brain
The crossing/connection point of the left and right optic
nerves
Place where the optic nerve meets the retina is known as
the blind spot (no photo receptors)
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Visual Processing
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Eyes sit just below the forebrain
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Forebrain is the front part of the brain
Optic nerves run to the thalamus where visual information is relayed
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Thalamus relays visual information to the occipital lobe (specifically the visual
cortex) where the information is processed and an image is created
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Thalamus is the brain's central relay station, situated just atop the brain stem.
Nearly all the messages going into or out of the brain go through the thalamus
Occipital lobes are the cortical regions at the back of the brain that house the
visual cortex
The visual cortex is the visual processing areas of cortex in the occipital lobes
Brain uses parallel processing while taking in visual information
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Parallel processing – the processing of many aspects of a problem
simultaneously; the brain’s natural mode of information processing for many
functions including vision. Contrasts conscious problem solving
Visual Processing
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What the Brain Uses
- Monocular Cues – depth cues, such as interposition
and linear perspective available to either eye alone
- Binocular Cues - depth cues, such as retinal disparity
that depend on the use of two eyes
- Retinal disparity – a binocular cue for perceiving
depth: by comparing images from the retinas in the
two eyes, the brain computes distance – the greater
the distance the greater the disparity between two
objects
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Visual Adaption
- Accommodation – process by which the eye
adjusts to maintain a clear image (focus) as
distances in an image change
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Dark Adaption – Changes in the sensitivities
of rods and cones to account for the change
in brightness and amount of visual light
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Electromagnetic Spectrum
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The entire range of electromagnetic energy
Wavelength- the distance between the crest of two successive
peaks
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Impacts the type of wave
Amplitude - the height of
a wave
– determines intensity
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Radiant light – light that
is emitted from an object
rather than reflected
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How the Visual System Creates Color
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Reflected light - Color depends on
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the light an object reflects
Color (hue) is a sensation
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doesn’t exist outside the brain
Visible Spectrum
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a tiny part of the
Electromagnetic spectrum which
our eyes are sensitive to
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Colors differ in wavelength
Color(or hue), form , position, and depth are based off the same stream of sensory information
in different parts of the visual cortex
Saturation - how pure a color is
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Ways of Sensing Colors
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Trichromatic theory –(color processing in cones)
colors are sensed by three different types of cones
sensitive to light in the red blue and green
wavelengths
Opponent-process theory – (color processing in
bipolar cells and past) cells in the visual system
process colors in complementary pairs
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Afterimages – Sensations that linger after the
stimulus is removed, most appear in opposite
colors
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Activity
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Color Deficiencies
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Color Blindness
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Inability to distinguish
colors
It’s more common for
people have a color
weakness. This is minor
problem s in distinguishing
colors
Monochromats - one who is
color blind
Dichromats – a person that
has one of the three cone
pigments missing
Acuity
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Visual acuity - Clarity or Sharpness of vision
Nearsightedness - is when light entering the eye is focused
incorrectly, making distant objects appear blurred
Farsightedness - more difficulty to see near objects than far
ones
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