Week 2 - Visual Perception Flashcards
What are the benefits of the visual system?
We see things very accurately and externally verifiable. Our perceptual system allows us to get information we need, exactly when we need it. It allows us to then process information & work with this information to respond to our environment in a timely manner. We can’t afford much ambiguity, and we need to get things right to stay alive.
What are we actually doing with all of this light coming from around us?
- We have photons coming in and chaotic patterns of light from infinite number of angels, in a scattered way.
- Everything except for our central visual field, is out of focus.
- We make sense of jumbled patterns & extract meaning from it.
- Positions of objects, their identity, characteristics.
- We need to identify what these are, their position and movement with respect to ourselves. All of this is critical for survival.
What does it mean when we say that we ‘perceive constancies in a change environment’?
Anything that doesn’t change, becomes background noise. We extract things from our environment that is important/ salient. For example, an object constant in a position when environment around us is moving, we can identify the characteristics of the object.
Describe some characteristics of light.
- For an object to be visible, it must reflect light.
- The energy of photons determines the wavelengths of light (short & long).
- Light is on an electromagnetic spectrum.
- Different colours are denoted by wavelength of light (violet = short end), (red = long end).
Describe some characteristics of the eye.
Eye = like a camera lens.
Opening in eye = pupil.
Lens = focusses light (directly behind the pupil).
- The largest amount of light is focussed in a straight line (where eye is pointing is where largest amount of light will come through).
- Fovea = where largest amount of light will focus.
What is Microsaccades?
Tiny movement (wabbling), to keep information updated on the retina. If an image stays stablised on the retina, it disappears (the photoreceptors stop firing), and the brain will fill the missing space.
Stationary blind spot = we all have one, it is directly where the optic nerve goes into the eye. We are not aware of it because it’s always in the same place, and our brain fills this with missing information.
EXAMPLE: when things are stationary long enough, they disappear. The colours in the background will turn grey. Snow blindness is also a known thing that can happen.
What are ciliary muscles?
They sit behind the pupil and control the shape of the lens, to accomodate for near or far targets.
Near in focus = lens is round
Far in focus = lens flattens
As you move something towards you, your lens should accomodate for this to be able to focus. The ciliary muscles can refract light at different angels, which changes focal point of the light.
What is vergence & stereopsis?
Vergence = two eyes converge to prodouce two different, but aligned images of the same target.
Stereovision = important for depth perception. Two copies of an image which are both slightly different versions (as they come from the same angle
What is the choroid and where is it located?
The choroid is a dense line behind the eye. The choroid layer absorbs light.
What are rods and cones?
Cones are densely packed into the fovea, can perceive fine detail (high acuity). Cones go to sleep at night and stop functioning.
Rods have high dark sensitivity. Low acuity, green sensitive. Only active at night.
What is photopic vs scotopic?
Photopic = bright light vision via cones
Scotopic = dim light vision via rods.
What is the retina and where is it located?
It lines the back of the eye near the optic nerve. The purpose of the retina is to receive light that the lens has focused, convert the light into neural signals, and send these signals on to the brain for visual recognition.
Bipolar cells = middle layer of the retina. Bipolar cells integrates information from the visual field. E.g. if they were cones it will also tell you the colour of the light & intensity.
Ganglion cells = tells you what area of space the light is coming from.
How does communication happen between cells?
Receptor cells synapse with bipolar cells
Bipolar cells synapse with ganglion cells
Horizontal cells connect different receptor or different bipolar cells
Amacrine cells connect different bipolar or different ganglion cells – these connecting cells allow events at one location to influence events at others (communication)
Ganglion cells integrating information from whole region of visual field
What is lateral inhibition?
Lateral inhibition refers to the capacity of excited neurons to reduce the activity of their neighbors. E.g. high intensity light edge (bright pane), low intensity dark edge (dark pane) = ganglion cells can communicate to neighbour how much information they are receiving. E.g. lateral connections can be sent to adjacent neighbours with inhibition. E.g. sending 10% inhibition to neighbours whilst the cells receive stimulation. My inhibition/ excitation less than neighbours. If you’re neighbour is receiving bright light, you are firing less/ receiving less light. Constant inhibtion
Increased excitation for those receiving stimulation/ light
Ganglion cells.
Ganglion cells act like a lens = captures image over the area of the retina
Example: Grey scale light spectrum picture (lighter edge/ darker edges for panes of colour)
At the edges, your visual system is reinforcing the edge, discontinuity. Reinforcing by making colour lighter and darker on each side to reinforce contrast.
Ganglion cells = have excitatory & inhibitory connections (within their receptive fields)
Knows environment we are looking at
