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PSYCH 1XX3 Chapter 5: Vision (Full Notes)
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  • April 22, 2024
  • 6
  • 2023/2024
  • Class notes
  • Michelle cadieux, joe kim
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Chapter 5: Vision

Muller-Lyer Illusion: When 2 identical lines are made to look like they ● Cornea: Dome-shaped, transparent lens that allows light into
are a diff length by a placement of arrows on the line ends the eye and focuses it (responsible for 80% of eye’s focusing
Necker Cube: A line drawing of a transparent cube that has an power)
ambiguous perception with regards to its 3D shape ● Iris: Ring-shaped membrane giving eye its colour, sits
● Your brain alters your perception despite stimuli remaining behind cornea, responsible for controlling the diameter of
relatively constant (which side is front? Doesn’t give up but the pupil, permitting the optimal amount of light to enter the
alternates between diff plausible perceptions when faced eye
with ambiguity) ● Pupil: Hole in the centre of the iris
● Illusion arises because brain infers depth when none exists ● Lens: Curved, flexible structure that changes shape through
(creating 3D percept based on 2D evidence) a process called accommodation (lens= adjusted by the
contraction of muscles around it), projecting light onto the
proper areas of the retina, responsible for the remaining 20%
of the eye's focusing power, curvature of lens causes images
to land on the retina upside-down + reversed but the final
perceived image is a product of brain activity
○ Nearby muscles = relaxed, → lens becomes
flattened/elongated → max focal length → helps
us see distant objects
Sensation: Our sensory systems (ie eye/ear) gathering raw data from ○ Muscles = contracted →lens becomes rounder →
the physical environment helps us see closer objects
● Our sensory organs have inherent physical limitations (ie *Study Hack: When your friends are around, your
visual system only responds to a narrow segment of the lens gets round; and when your friends are far,
electromagnetic spectrum and wavelengths that are too short you long for them, so your lens gets long
(ultraviolet light) or too long (infrared light) are not ○ Refractive Errors: Lens can only bend light so
captured, so we don’t perceive them, however, many other much, if refractive error occurs, light rays may be
species can) focused behind /in front of the retina causing
● Only a tiny fraction of all the info gathered by our sensory image to be out of focus
organs makes it to the level of conscious awareness (much ■ Hyperopia/farsightedness: Can see
of it is filtered out at various stages of perceptual processing distant objects with ease, but closer
so huge amounts of sensory input, especially if doesn’t objects appear blurry because light =
change over time, goes largely unnoticed by us) focused to a hypothetical location
● Transduction: The process by which physical behind the retina
aspects/characteristics of our environment are converted into ■ Myopia/nearsightedness: Can see closer
electrical signals that the brain can interpret objects with ease, but distant objects
● Perception: The outcome of the brain’s processing of the appear blurry because light = focused to
raw data a hypothetical location in front of the
Inferences of the Brain: Our brains excel at ‘making things up’ by retina
inferring things about the world/ ‘filling in the blanks’ ○ Abnormalities can occur for several reasons:
● We can rarely tell the diff between the info obtained from ■ Length of eyeball = abnormal
the real world and the info invented by our brains (nearsighted = usually slightly longer,
● Ie. You are likely unaware of a large blind spot in the visual farsighted = slightly shorter eye length)
field of your eyes due to your brain using input from areas ■ Curvature of cornea = abnormal
around the blind spot to infer what ought to be there, as if (farsighted = usually less curved lenses)
seamlessly inserting that inferred info into our visual input ■ Accommodation process = disrupted
● However due to natural selection, our sensory and ○ Corrective lenses/laser eye surgery can be used to
perceptual systems are not perfect but still serve us well ameliorate these refractive error problems by
(allowing us to become successful as a species) redirecting incoming light to its correct location
Vision = extensively studied sensory modality on the retina
● Our everyday decisions are shaped by what we can directly Vitreous Humour: Clear, jelly-like substance that comprises the main
see (eyes are describes as the ‘window’ to the brain, used as chamber inside the eyeball
diagnostic tools for health of our CNS) Retina: Transparent sheet of neural tissue with multiple layers,
● Magnitude of processing power devoted to vision is sometimes referred to as ‘duplex’ since it contains many very diff
staggering (estimates suggest 50% of the cortex is involved cells, where physical stimulus of light = first translated into neural
in visual processing) impulses
● Relatively easy to manipulate visual stimuli to understand ● First Layer: Closest to very back of eye, contains specialized
how the brain develops/changes based on sensory cells called photoreceptors that detect light + transform
experience physical stimulus of light into neural impulses and pass this
● ⅓ of brain = dedicated to processing visual info info to the next layer
Outer Parts of the Eye: Purpose = projecting a clear, focused image of ○ To reach photoreceptors, light must first pass
the outside world onto the retina at the back of the eye, listed in order through two other layers of retinal tissue because
light passes through parts of eye the photoreceptors get their nutrients from a layer
● Sclera: Tough, opaque, fibrous outer sheath that offers of cells at the very back of the eye (retinal
protection + constitutes the white of the eye pigment epithelium/RPE) + would die without

, Chapter 5: Vision

○ access to the RPE cells (which they wouldn’t have limitation), causes a sizable portion of our visual
access to if they were located at the front of the field to go entirely uncaptured
retina) ○ Receptive field of a Ganglion Cell: Area of the
○ Two types of photoreceptors: retina which, when stimulated by light, affects the
○ Rods: Primarily responsible for scotopic/low firing rate of said ganglion cell, circular with a
light/night vision because they contain rhodopsin centre that elicits one type of response when
(photopigment highly sensitive to light), total loss exposed to light and an antagonistic surround
of rods produces only night blindness, outnumber (outer perimeter) that elicits an opposite response
cones by roughly 20:1, grant poor visual acuity when exposed to light (this property =
(converge more), densely packed across retina centre–surround antagonism)
except fovea ○ Retinal ganglion cell = ‘on-centre’ if light
○ Cones: Responsible for photopic/high light/day reaching centre of its receptive field causes
vision and contain iodopsin (photopigments less excitation, = ‘off-centre’ if light reaching the
sensitive to light), three main types of cones that surround causes excitation
are each maximally sensitive to a diff wavelength Evolution of the Eye:
of light (blue/red/green), granting us the ability to ● The eye is extraordinarily complex with many
perceive colour (referred to as chromatic), grant interdependent parts, leading some to question whether it
good visual acuity (converge less but discriminate could arise through natural selection
finer details = high resolution), have smaller ● However, there is now strong evidence to suggest that it
receptive fields evolved through many small, incremental changes that
○ Fovea: Section near centre of retina, directly in accumulated over successive generations, increasing the
line with whatever you are focusing your gaze on, sophistication of the eye (cumulative selection)
where most cones are present + visual acuity = ● Algae = first to use light as energy + create action potentials
greatest → eyes = simple light-sensitive patches that could detect the
○ Dark Adaptation: The transition from a bright presence/absence of light → random genetic mutations →
environment to a dark environment = multi-step individuals developed light-sensitive patch formed into a
process involving both rods + cones slight depression/curve allowing the direction of light to be
■ During first few minutes of dark sensed, giving these individuals a survival advantage over
exposure, there is a lower threshold for those with a flat eye patch → curved eyes developed a
the activation of cones + rapid increase pinhole aperture allows organisms to resolve the detail of an
in our sensitivity to light image by changing the amount of light that enters the eye →
■ After about 5–10 minutes, the threshold individuals adapted crude lens, complete with a lens, cornea,
of rods decreases considerably (ie and a spherical shape, however its shape changes very little
‘rod–cone break’) so its best suited for animals who do not rely heavily on
■ The eye’s gradual adaptation to the dark visual acuity → developed adjustable lens which is quite
thus involves two distinct processes that flexible and allows accommodation
operate at diff timescales Visual Fields: Each eye can capture only a part of space ‘out there’
● Binocular Zone: regions where both visual fields overlap
extensively
● Monocular Zones: Areas of the visual field captured by only
one of the two eyes




● Second Layer: Contains bipolar cells which process the
signal further before it reaches the next layer
○ Horizontal + Amacrine Cells: Allow areas within
a retinal layer to communicate with each other +
allow info from adjacent photoreceptors to be
combined (visual processing done in retina, before
signal is sent to the brain)
● Third Layer: Closest to inner fluid of eye, contains ganglion
cells/retinal ganglion cells that relay the signals onto the
brain
○ Optic Disk/’Blind Spot’: Area in which the optic
nerve exits the retina, contains no photoreceptors
because it’s instead made up of converging axons
from the ganglion cells that are needed to carry
signals from the retina to the brain (structural Nasal Hemi-Retina: The half of a given retina closest to the nose

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