Visual Perception Flashcards
First thing light hits when it enters the eye…
Cornea (outer protector of the eye)
Vision is our most
Predominant sense
From the cornea light then enters the
Pupil
Pupil can expand and contract which lets
More and less light in
The order of light travel into the eye…
Cornea - pupil - lens - retina
Focusing of the lens is done by
Contracting and expanding of muscles
We can focus our vision at different distances by
Contracting and expanding our muscles in the lens
For objects that are near you need to
Expand your muscles tightens the lense
For far away object we need to
Contract the muscles which pulls lens out flatter
Technical name for short sighted
Myopia
Myopia is when
Light that enters into the eye focusing on the front of the eye, causing a blurred image. By the time light enters the retina it’s gone out of focus
Technical name for far sighted
Hyperopia
Hyperopia
When light enters eye it’s focused on a point that is behind your retina causing a blurry unfocused image
Myopia can be corrected with
Negative or concave lenses
Hyperopia can be fixed with
Positive or convex lenses
Retina is the
Light sensitive membrane in the back of the eye that contains photoreceptors
Photoreceptors in the retina send signals to the optic nerve which then send signals to the
Brain
Blind spot in the retina is where
The optic nerve exits the retina to get signals/info to brain
Dark spot on your retina is called
Fovea
Fovea
The point at which an image would be projected onto through the lens if you were focusing on an object.
Area around the fovea (macula) is the most
Densest in photoreceptors
The lens project an image on the the retina
Upside down (brain flips it)
Retina contains over
100 million photoreceptors
Two types of photoreceptors are
Rods and cones
Cones are photoreceptors responsible for
Daylight vision visual acuity and colour
Cones are most dense in the
Foveal centre
How many types of cones are there?
3
Rods are a photoreceptors that we rely on more for
Night vision
Rods can’t give you
Colour vision
Rods are more highly concentrated in the
Periphery
Ganglion cells are in
Front of the rods and cones on the back of the retina
Ganglion cells send info from your cones and rods to the
Brain
There are …………….. Less ganglion cells than photoreceptors
100x
When nothing is happening a ganglion cell will
Fire rapidly at a resting rate
Each ganglion cell is responsible for
A area of photoreceptors
When light hits the retina the ganglion cell firing rate
Goes up or down depending on what sort of light and where it hits in the receptor field
The smaller the field of photoreceptors synapsed onto the ganglion cell the more
Visual acuity you will have
Ganglion cell have
Centre-surround receptive fields
Centre surround receptive field allow ganglion cells to
Processing different info in the centre field and surrounding field
Two types of ganglion cells
‘On’ centre receptive field
‘Off’ centre receptive field
Ganglion cells with ‘on’ centre fields will get turned on more if
Light hits the centre of the receptor field
If light hits the edge of the ‘on’ ganglion cell then the
Firing rate will reduce (inhibitive)
Ganglion cells work to
Filter and amplify info that has been sent by the photoreceptors
Each photoreceptors is only able to detect a
Small area
Ganglion cells ……………….incoming info from photoreceptors
Filter, smooth out and amplify
Ganglion cells in crease our sensitivity to
Contrast (in our visual field) ie find edges and identify shapes etc even in poor lighting conditions
Herman grid is an example of
A visual illusion that gives us a hint at how our ganglion cells are working (spots in the intersection)
Hermans grid - if we focus on the intersection then
The illusion isn’t there. It’s white with no dark spot
When the dark spot are at periphery of vision you
Get the dark spots more
Why do you see black spots when look at the whole hermans grid without focusing
The receptive fields at the periphery are larger
Ganglion cells nearer to fovea are……and when focused can see there are no black spots in the Herman grid
Smaller
Another visual illusion
Mach bands
Mach bands suggest that
When you have a gradient that’s moving from one particular type of brightness to another brightness you may notice darker grey band towards dark and lighter grey band as you move towards lighter band
We use spatial perception to
Identify how far away object are
Spatial perception works by
The light from various objects projecting onto the retina
Two things that help in spatial perception
Monocular depth cues
Binocular depth cues
Monocular depth cues are
You can just use info from one eye. Seem like common sense. They produce visual images that represent 3D space.
Occultation (monocular depth cue)
If an object is behind another object we can assume the one that is in front is closest to us.
Relative size and position (monocular depth cues)
Smaller objects tend to appear further away compared to larger objects
Aerial perspective (monocular depth cues)
The more hazy something is assume it’s further away.
Linear perspective (monocular depth cues)
Rail tracks. Lines that lead away from us and in an up indicate that something is retreating in distance.
Accommodation (monocular depth cue)
Amount of contraction you have to do with your lens to focus on an object etc
Binocular vision
Using two eyes.
Being able to see the work in depth with two eyes (binocular) is called
Stereopsis
We don’t have exactly the same visual field for both eyes this is called
Binocular disparity
Our visual field is limited to ……….from left to right
190o
With one eye covered our visual field is
110-120o
Why do horses have bad binocular vision
Because of the positioning of the eyes at the side if their heads and don’t overlap
Why did horses evolve to have better monocular vision than binocular?
Prey needs to be able to see danger anywhere. More important than depth perception. Periphery super important
Predators have eyes at the front of their faces because
Larger area for binocular vision and depth perception not very good periphery.
Horopter is the
Circle from both eyes to the object that is your point of focus
Horopter circle
Any point on this circle will cast images on the same point for both retinas
Image will be cast onto different points in the retina if the
Objects not on the Horopter circle (ie inside or outside circle)
If the Image is closer than the Horopter circle it has
Crossed disparity
If the object is further away than the Horopter circle than it has
Uncrossed disparity
Binocular disparity can be
Crossed or uncrossed
Stereoscopes are
Devices that present a slightly different image to each eye
Stereogram is
An image that can be viewed in 3D
Free fusion technique for stereograms is the technique of
Converging (crossing) or drive thing the eyes in order to view a stereogram
How does free fusion work?
It fuses the images together causing the visual system to calculate the retinal disparity btwn each eye - giving the perception of stereopsis
Two methods of free fusion technique are
Parallel viewing (diverging) Cross-eyed (converging)
Cross eyed viewing is where
The eyes focus on something closer than the real image
Parallel viewing is where the eye focus on something
Further away from the real image
How do magic eyes work?
Cut out a shape
How do 3D movies work?
Tricking the brain into thinking you two eyes are recovering similar but slightly different images. Tricks brain into using the images together giving 3D vision
Left hemisphere is responsible for processing info from the
Left visual field
Info from right eye also gets sent to the
Left eye
Image projected onto the retina actually gets
Turned upside down
Info from Your right side retina
Stays on the right side hemisphere
Right side of your retina if your left eye is processed by
Your right hemisphere
