Hello! This is the summary of the needed information for the 7 problems of Block 2 - Thinking and Remembering. I used the best mandatory sources for each problem and understandably explained the subjects. It includes checklists for all the keywords.
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Vison
Humans depend on the sense of vision. It lets us perceive info at a distance – remote seeing/ exteroceptive
perception.
Visual info is in the light reflected from objects, so we need sensory detectors that respond to the reflected light. As
light passes through the lens of the eye, the image is inverted and focused to project on the back surface of the eye.
Visible light has wavelengths from about 400-700 nanometres.
Near point (distance where a person is not able to bring a nearby object into focus.
Gets worse with age presbyopia: The lens loses accommodative ability with age.
Far point: distance at which lens cannot bring distant object into focus.
there is Myopia (near-sightedness) and hyperopia (farsightedness) which affect focus.
Vision Correction: glasses, lenses, corrective lenses or surgery (e.g., LASIK) can address vision problems.
The eye is where vison begins, is spherical, which allows it to rotate and move.
Optical axis - imaginary diameter line running through the center of the lens from the front to the back of the eye.
Cornea - First layer encountered when light enters the eye. It’s fixed in place, provides about 80% of the eye's
focusing power, while the lens contributes the remaining 20%. The cornea bends or refracts the light: crucial
for focusing light on retina.
The iris – the coloured part of the eye, it’s a muscles
Lens - a transparent structure at the front of the eye that refracts or bends so light falls onto the retina –
focal length - the ability of a lens to refract light:
o is the distance from the lens to the retina (through which the image of an object is sharp).
o For distant objects, the focal length is large; for near objects, it is small.
o For near objects, lens is convex and for far one’s concave.
The eye has three different chambers:
1. The anterior chamber: the space between the cornea and the iris, filled with aqueous humour (a clear, thin
liquid);
2. The posterior chamber: the space between the iris and the lens, filled with aqueous humour:
3. the vitreous chamber: the main interior portion of the eye, filled with vitreous humour (a clear liquid with a
gel-like consistency)
The eye has 3 membranes:
1. The sclera: a hard protective layer. It consists of the white of the eye and the transparent cornea
2. The choroid: lines the interior of the sclera and contains blood vessels that supply the eye with oxygen and
nutrients.
3. The retina: the innermost membrane composed of neurons, including the rods and cones (The image enters
the retina in reverse: top becomes bottom and left becomes right.). it has layers and 3 main nuclear that
have nuclei from different neurons. The layers are interconnected:
a. outer nuclear layer
b. the inner nuclear layer
c. the ganglion cell layer
d. two synaptic layers that separate the three nuclear layers:
, i. inner and outer synaptic layer, containing different types of cells
Photoreceptors – light receptors– translate external stimulus of light not internal neural signals that the brain can
interpret – deepest layer of the retina has millions of photoreceptors, each has light-sensitive molecules (visual
pigments), that when exposed to light became unstable and split apart. This decomposition alters the flow of the
electrical current around the photoreceptors which triggers action potentials in downstream neurons. 2 types:
e. Rods – sensitive to low levels of stimulation, most useful at night, because replenishing the
photopigments in rods takes time They are distributed all over the retina. They are better for
detecting peripheral stimuli and detecting motion, because they are distributed all-over the retina
and have high convergence onto ganglion cell + Rod vision is more sensitive than cone vision.
Dark adaptation – 2 stages:
i. early, rapid phase that occurs due to adaptation of the cones (green line)
ii. later, somewhat slower phase that occurs due to adaptation of the rods (blue line). In the
second part of dark adaptation, only the rods are active
iii. high converge of rods provides sensitivity, low convergence leads to slower dark adaption of
cones.
f. Cones – require intense levels of light and use photopigments that are quick, so they are useful
during the day. They are essential for colour vision. They have 3 types – short-wavelength, medium-
wavelength, and long-wavelength– which differ in sensitive of their photopigments to different
wavelengths of visible light. Cones have less convergence, meaning that signals from fewer cones
contribute to the activity of a single ganglion cell. This results in finer spatial resolution and is
especially important for tasks like reading or recognizing faces
i. They are packed in the fovea, a small area in the center of the retina cones is concentrated.
But not much convergence. Here, each rod often connects to its own ganglion cell, providing
high acuity.
ii. In the peripheral retina, (includes all the retina outside of fovea) rods dominate, there is
more convergence. Here, each ganglion cell integrates signals from multiple rods, providing
better sensitivity but reduced acuity.
iii. The blind spot / optic disk - contains no receptors. It’s a point where optic nerve leaves the
eye, but were usually not aware (only when focusing on it) and our brain fills in missing spot
Scotopic vison - This is the vision under low-light conditions, typically provided by the rods. The higher convergence
of rods onto ganglion cells allows for greater sensitivity to low levels of light. this increased sensitivity comes at the
cost of reduced acuity.
Photopic Vision: This is the vision in bright-light conditions, usually provided by the cones.
Visual Acuity: Visual acuity is better in the fovea (cone-rich region) than in the periphery. - cones in the fovea
Dark Adaptation - reduces acuity, and rod vision takes over in dim illumination. Rods provide better sensitivity in low
light conditions but sacrifice detail vision.
Light enters photoreceptors -> transmitted to horizontal cells -> pass to bipolar cells/other photoreceptors -> further
to amacrine cells and the retinal ganglion cells -> those provide action potential in the brain via the optic nerve.
Neural convergence – when neurons signals from several other neurons and merges them together. Signals from
rods converge more than signal from cones, which results in more spatial summation in rods – more rods converge
than cones, so a stronger signal will taster at the rods. On average, about 120 rods converge on a single ganglion cell,
while only 6 cones send signals to a single ganglion cell.
The neural convergence difference cause 2 differences in perception:
1. Rod vision is more sensitive than cone vision, because it takes less light to generate a response from a single
rod receptor than from a single cone receptor and because there are more rods in the retina which leads to
higher spatial summation.
2. The cones have better visual acuity, or detailed vision. This is because they have less neural convergence.
a. So we can see details with cone in the light
, b. In low light, with rods we can only see the difference in things that are dimly lit, but not much detail.
Transduction is the transformation of light into electricity, or the transduction of info from a stimulus to the nervous
system. It works through specialized neurons, making energy into electronical signals. This is done by rods and cones.
It begins at the outer segment – because it has stacks of discs, each containing thousands of visual pigment
molecules – each has one retinal molecule crucial for transduction because its sensitive to light.
How it happens – 1. is triggered when the retinal picks up a photon ('a packet of energy') of light
2. When this happens, the retinal changes shape so that it protrudes from the opsin.
3. This change of shape (called isomerisation) causes light to be transformed into electricity.
Later inhibition – the inhibitory signals transmitted across neurons. It explains 3 different perceptual:
1. The Hermann grid: sees grey spots at the intersections between a cluster of black squares.
2. Mach Bands - are illusory light and dark bands near a light-dark border. Explained by lateral inhibition
enhancing the perception of borders, we see the boundaries between light and dark more strongly = more
contrast.
3. Simultaneous Contrast: occurs when the perception of one area is influenced by the presence of an adjacent
area. (not fully explained by later inhibition)
4. White's Illusion: challenges the explanation based on lateral inhibition.
Yes overall anatomy of the eye
Yes rods and cones - also distribution in the retina
Yes convergence
Yes other cells in the retina - bipolar, horizontal, amacrine, ganglion
Yes dark adaptation
Yes lateral inhibition and contrast illusions
yes – make sure you understand the functions of the different parts of the eye
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