Visual Perception (CH. 3) 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
Shape Constancy
Correct perception of an object’s shape despite changes in its shape on the retina
Brightness and Colour Constancy
Objects should not change brightness or colour under different light sources
Gestalt Principles
- Similarity
- Proximity
- Good continuation
- Closure
- Simplicity
Binocular Depth Information
The eyes get slightly different 2D views of the same 3D scene. You can reconstruct the 3D scene by comparing the 2D images
What are Monocular Distance Cues?
Features of the visual stimulus that indicate distance even if the stimulus is viewed with only one eye
What are Pictorial Cues?
Sources of depth information that can be extracted from static 2D images, such as pictures, even using only 1 eye
Occlusion, Relative height, Relative size, Perspective convergence, Familiar size, Familiar shape, Atmospheric perspective, Texture gradient, Shadows
What is a Conjunction Error?
An error in perception in which a person correctly perceives what features are present but misperceives how the features are joined
What is a Reversible (or Ambiguous) Figure?
Drawings that can be readily perceived in more than one way (e.g., Necker Cube)
Necker Cube
One of the classic reversible (or ambiguous) figures; a two-dimensional drawing that can be perceived as a cube viewed from above or as a cube viewed from below
What is the Motion Parallax?
A distance cue based on the fact that as an observer moves, the retinal images of nearby objects move more rapidly than do the retinal images of objects farther away
