Visual Perception Flashcards
What is the Retina?
Layer of photoreceptors at the back of your eyeball (where all of your vision comes from)
What are the Photoreceptors in the Retina?
Rods and Cones
Rods
- Sensitive to dim light (i.e., low levels of light)
- Lower acuity (fine detail)
- Colour-blind
- None in the fovea
Cones
- Cannot function in dim light
- Higher acuity (fine detail)
- Colour-sensitive
- Mostly in or near the fovea; none in the periphery
What Does the Optic Nerve Do?
Info from retina to the brain; all of the axons bundle together into a nerve and that nerve passes out through the back of the eyeball into the brain
Cornea
The transparent tissue at the front of each eye that plays an important role in focusing the incoming light
Lens
The transparent tissue located near the front of each eye that (together with the cornea) plays an important role in focusing incoming light
Fovea
The centre of the retina and the region on the eye in which acuity is best; when a person looks at an object, they are lining up that object with the fovea
What is Lateral Inhibition?
A pattern in which cells, when stimulated, inhibit that activity of neighbouring cells.
In the visual system, lateral inhibition in the optic nerve creates edge enhancement
Bipolar Cells
A type of neuron in the eye; bipolar cells receive their input from the photoreceptors and transmit their output to the retinal ganglion cells
Ganglion Cells
A type of neuron in the eye; ganglion cells receive their input from the bipolar cells, and then the axons of the ganglion cells father together to form the optic nerve, carrying info back to the lateral geniculate nucleus
What is the Lateral Geniculate Nucleus (LGN)?
An important way station in the thalamus that is the first destination for visual information sent from the eyeball to the brain
What is Edge Enhancement?
The neurons in the visual system give exaggerated responses to edges of surfaces
What is the Hermann Grid Illusion?
Dark patches at the intersection between two white pathways (only appear in the periphery, not the centre of vision)
What are Mach Bands?
A type of illusion in which one perceives a region to be slightly darker if it is adjacent to a bright region, and also perceives a region to be slightly brighter if it is adjacent to a dark region
Receptive Field
The size, shape, and location of the area in the visual world to which that cell responds
Centre-Surround Cells
A type of neuron in the visual system that has a “donut-shaped” receptive field. Stimulation in the centre of the receptive field has one effect on the cell; stimulation in the surrounding ring has the opposite effect
Receptive Fields in Visual Cortex
Simple Cells (primary visual cortex): edge detectors
- these detectors fire when a stimulus within the receptive field contains an edge of a particular orientation
- the less the edge is like the cell’s “preferred” edge, the less often it fires
Complex Cells (secondary visual cortex)
- angles, motion and direction, corners
Where vs. What Processing
After processing in early visual areas, information is processed hierarchically in two different pathways
“Where” System (top of the brain)
The “where” pathway processes relevant spatial information for the purposes of guiding action
“What” System (bottom of the brain)
The “what” pathway extracts shape and texture information to identify objects
Parallel Processing
A system in which many steps are going on at the same time
Serial Processing
A system in which only one step happens at a time (and so the steps occur in a series)
Constancy
We perceive constant object properties (sizes, shapes, etc.) even though sensory information about these attributes changes when viewing circumstances change
