Week 3 - Visual Perception Flashcards
How is electromagnetic radiation (EMR) generated
EMR is generated when an atom emits a particle called a photon.
Principles of perception
- perception is dynamic, we perceive change
- we perceive constancies in a a changing environment
For an object to be visible is must emit or reflect_
Light
What determines the wavelength of a photon?
The energy of the photon.
What does the variation in wavelengths within the visible spectrum determine?
Different wavelengths give rise to the perception of different colours
eye movements (saccades)
- constantly moving
- if an image stays stabilised on the retina it disappears (photoreceptors stop firing) and brain fills in space
- blind spot at the optic nerve
Accomodation
ligaments (ciliary muscles) that attach the lens to the eye control the shape of the lens to accomodate near of far targets.
- stops working once you turn 40 years old so struggle to focus on middle distance
Vergence and stereopsis
two eyes converge on the information to produce two different but aligned images of the same target. Helps to tell how far away something is
Physiology of the retina
- densely packed with photoreceptors that point towards the back of the eye (light kills photoreceptors)
- structure of retina is upside down:
Ganglion Cells
Bipolar Cells
Photoreceptors
Choroid
Rods (photoreceptor)
- black and white vision
- low acuity (widely spaced throughout retina, in peripheral field)
- work well at night (scotopic vision)
Cones (photoreceptor)
- colour vision
- high acuity (can see fine detail bc densely packed in fovea)
- work in bright light (photopic vision)
Lateral Inhibition
every adjacent unit within the photoreceptor cell or ganglion cell slightly changes the output of the unit next to it
Passage of the visual signal
both eyes have a left and right visual field that send information to the left or right side of the brain.
- right visual field is on the left side of each eye and sends info the left side of the brain - vice versa
- Optic chiasm is where the nerves cross
Lateral Geniculate Nucleus (LGN)
- six layers all replicated
- same properties as ganglion cells
- ganglion and LGN cells respond to the present of a spot of light on the retina
- LGN cells receive input from visual cortex
Tectopulvinar System
- optic tract fibres that react to information that are fast moving (periphery)
- serves several functions:
1. localisation of objects in space
2. guidance of eye movements
3. gross pattern perception