PSYCO275 Chapter Notes - Chapter 6: Temporal Lobe, Edwin H. Land, Lateral Geniculate Nucleus
6 Jun 2018
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PSYCO 275 - Chapter 6
The Visual System
●Understanding the visual system required the integration of two types of research:
○Research that probes the visual system with sophisticated neuroanatomical,
neurochemical and neurophysiological techniques
○Research that focuses on the assessment of what we see
●Light Enters the Eye and Reaches the Retina
○The light reflected in your eyes from the objects around you is the basis for your
ability to see them
○No animal can see in complete darkness
○Light can be photons or waves
○Light is sometimes defined as waves of electromagnetic energy between 380 and
760 nanometers in length
■Nothing special about these wavelengths except that the human visual
system responds to them
■Rattlesnakes can see infrared waves (better locating warm-blooded prey)
○Two properties of light:
■Wavelength (ƛ - lambda)
●Plays an important role in the perception of color
■Intensity
●Perception of brightness
○Pupil and Lens
■Iris
: controls the amount of light that reaches the retina and gives the color
of our eyes
■Light enters the pupil (hole in the iris); adjustment of pupil size in
response to changes in illumination represents a compromise between
sensitivity and acuity
●Sensitivity
: ability to detect the presence of dimly lit objects
○Not important when illumination is high
○Visual system constricts the pupils
○Pupils are constricted: the image falling on each retina is
sharper and there’s a greater depth of focus
●Acuity
: ability to see the details of objects
○No use when the illumination is low
○Pupils dilate to let more light in
■Lens:
located behind each pupil and focuses incoming light on the retina
●Ciliary muscles
: the ligaments holding each lens in places
○Adjusts the tension when we gaze at something near
(assumes natural cylindrical shape)
■This increases the ability of the lens to refract
(bend) light and brings the objects into sharp focus
○When we gaze at something far, the lens is flattened
●Accommodation:
the process of adjusting the configuration of
lenses to bring images into focus on the retina
○Eye Position and Binocular Disparity
■An arrangement that’s an important basis for our visual system’s ability to
create 3D perceptions from 2D retinal images
■Predators have front-facing eyes so that they can perceive how far away
prey animals are
■Prey tend to have side-facing eyes because this gives them a larger field of
vision and the ability to see predators approaching form most directions
■The movements of our eyes are coordinated so that each point of the
visual world is projected corresponding points on your two retinas
●Eyes must converge (turn slightly inward)
●Convergence is greatest when inspecting things up close
●The positions of images on your two retinas can never correspond
exactly because our two eyes don’t view the world from the exact
position
■Binocular disparity
: difference in the position of the same image on the
two retinas
●Greater for close objects rather than distant objects
●The VS can use the degree of binocular disparity to construct 3D
perception from two 2D retinal images (depth perception)
●The Retina and Translation of Light into Neural Signals
○After light passes through the pupil and lens, it gets to the retina
○The retina converts light to neural signals, conducts them towards the CNS and
participates in the processing of these signals
○Structure of the Retina
■5 different types of neurons:
●Receptors
●Horizontal cells
●Bipolar cells
●Amacrine cells
●Retinal ganglion cells
■Amacrine and horizontal cells are specialized for lateral communication
(comms across the major channels of sensory input.
■Retinal neurons communicate both chemically via synapses and
electrically via gap junctions
■Inside out: light reaches the receptor layer only after passing through the
other four layers
●After the receptors have been activated → the neural message is
goes back out through the retinal layers → retinal ganglion cells,
Document Summary
Understanding the visual system required the integration of two types of research: Research that probes the visual system with sophisticated neuroanatomical, neurochemical and neurophysiological techniques. Research that focuses on the assessment of what we see. Light enters the eye and reaches the retina. The light reflected in your eyes from the objects around you is the basis for your ability to see them. No animal can see in complete darkness. Light is sometimes defined as waves of electromagnetic energy between 380 and. Nothing special about these wavelengths except that the human visual system responds to them. Rattlesnakes can see infrared waves (better locating warm-blooded prey) Plays an important role in the perception of color. Iris : controls the amount of light that reaches the retina and gives the color of our eyes. Light enters the pupil (hole in the iris); adjustment of pupil size in response to changes in illumination represents a compromise between sensitivity and acuity.
