Transcript What are the physical and perceptual dimensions of light

Psychology 304:
Brain and Behaviour
Lecture 31
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Announcement
“Body Worlds and the Brain is now at
Science World at TELUS World of
Science for a limited time. This all-new
version of Dr. Gunther von Hagens’
world-famous exhibition looks at the
body in a previously unseen way! With
over 200 authentic human specimens,
and highlights on recent neuroscience
findings on brain development,
function and disease, it will excite even
those guests who visited when we
hosted BODY WORLDS 3 in 2006.”
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From last class ….
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Olfactory Epithelium
Olfactory Receptors and Pathways
of the Olfactory System
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Secondary olfactory cortex
Pathways of the Olfactory System
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The Visual System
1. What are the physical and perceptual dimensions of
light?
2. What is the structure of the eye and where are the
receptors for light?
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By the end of today’s class, you should be able to:
1. describe the three physical and three perceptual
dimensions associated with light.
2. describe the structural and functional features of the
eye ball and retina.
3. distinguish between cones and rods.
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What are the physical and perceptual dimensions of
light?
• Light waves vary on three physical dimensions. Each
physical dimension uniquely influences our perception
of colour.
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1. Wavelength
 Determines hue.
 Relatively long wavelengths: Yellow/red hue.
Relatively short wavelengths: Blue/purple hue.
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A Wavelength
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Wavelengths Associated with Distinct Hues
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 The human eye is only capable of detecting light
with a wavelength of 380 – 760 nanometers.
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Wavelengths and Colours Visible to the Human Eye
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2. Intensity
 Determines brightness (i.e., light vs. dark).
 Greater number of light waves of a given wavelength: bright.
Fewer number of light waves of a given wavelength: dark.
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Hue vs. Brightness
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3. Purity
 Determines saturation.
 One wavelength: saturated hue.
Many wavelengths: intermediate hue.
All wavelengths: no hue (white)
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Saturation
Brightness
Saturation vs.
Brightness
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The Perceptual Properties of Colour
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What is the structure of the eye and where are the
receptors for light?
• Light waves pass through the cornea, pupil, and lens
of the eye, ultimately falling on the retina, the interior
lining of the back of the eye.
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Vitreous humor
The Human Eye
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• The retina is composed of five layers of different types
of neurons: receptors, horizontal cells, bipolar cells,
amacrine cells, and retinal ganglion cells.
• Light reaches the receptor layer only after passing
through the other four layers; for this reason, the
cellular organization of the retina is described as
“inside-out.”
• The point at which the optic nerve exits the eye is
referred to as the optic disc and produces a “blind
spot” in the visual field.
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The Cellular Structure of the Retina
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A Section of the Retina
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A Section of the Retina and Optic Nerve
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• There are two types of receptors in the human retina:
cones and rods.
• Cones allow for high visual acuity because a single
ganglion cell receives input from only one or a few
cones (low convergence).
• Rods allow for high sensitivity to illumination because
a single ganglion cell receives input from many rods
(high convergence).
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Convergence of Cones and Rods on
Retinal Ganglion Cells
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The Visual System
1. What are the physical and perceptual dimensions of
light?
2. What is the structure of the eye and where are the
receptors for light?
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