CHP. 3 - Visual Perception Flashcards
Points of refraction in eye
- Cornea
- Lens
* Contacts/glasses add an extra refraction point
Where is the focal point of light in the eye?
Fovea
Rods & cones
Pathway of light into the eye
- Light
- Cornea
- Lens
- Retina
Rods
- Color-blind
- Sensitive in low light levels
- Lower acuity
- None in fovea
Cones
- Color-sensitive
- Can’t function in dim light
- Higher acuity
- Mostly in/near fovea
Color perception problems
Color “blindness” or deficiency
* Due to overlap in cone sensitivities
* More common in males
Retina visual pathway
Right up to optic nerve
- Photoreceptors (rods & cones)
- Bipolar cells
- Ganglion cells
- Optic nerve
Brain visual pathway
- Optic nerve
- Optic chasm (optic nerves cross over)
- Optic tract to LGN of thalamus
- Optic radiations to V1 (visual cortex) in occipital lobe
Primary visual cortex
(aka) V1
* receives info from LGN in thalamus
* in occipital lobe
Emmetropia
Vision
Happy condition of no refractive error
Myopia
Vision
Near-sightedness
* When the light entering the eyes is focused in front of the retina & distant objects can’t be seen sharply
Hyperopia
Vision
Far-sightedness
* When light entering the eye is focused behind the retina
Presbyopia
Vision
“Old sight”
* Hardening of the crytal lens
* Lens becomes harder & capsule that encircles the lens loses its elasticity
* Can’t focus on things as closely
Astigmatism
Visual defecting involving unequal curving of 1 or more of the refractive surfaces of the eye (usually the cornea)
Cataracts
Cloudy lens - loss of transparency in lens
Lateral inhibition
When cells are stimulated, they inhibit the activity of neighboring cells
* Results in edge enhancement
Visual field
External stimuli
* Field of view
* Divided into left & right
Receptive field
The area that causes an increase/decrease in a firing rate of a cell when stimulated
Retinal receptive fields
Smaller in fovea (cones)
Larger in periphery (rods)
* Organized into Center-Surround
* On-Center
* Off-Center
Parallel processing
- Brain divides stimuli into separate components
- Processes each component separately
- Perception if formed by integrating them together
Summary of visual info processing
- Scene
- Retinal processing
- Feature detection
- Parallel processing
- Recognition
Advantages of parallel processing
- Speed & efficiency
- Mutual influence among multiple systems
Serial processing
Steps are done one at a time (bottom-up)
What system (Ventral pathway)
Connects occipital lobe & inferotemporal cortex
* Aids in ID of visual objects (object)
* Damage = visual agnosia
Where system (Dorsal pathway)
Connects occipital lobe & posterior parietal cortex
* Aids in perception of object’s location (spatial)
* Damage = difficulties reaching for objects
Binding problem
Task of reuniting elements of a stimulus that were addressed by different systems in different brain regions
Elements that help with the binding problem
- Spatial position
- Neural synchrony
- Attention
Reversible (ambigous) figures
One set of visual features results in multiple interpretation
ex. young woman vs. old woman, duck vs. bunny
Perceptual constancy
We perceive constant object properties (sizes, shapes, etc) even though sensory info can change viewing circumstances change
* Brightness/size/shape constancy
Accomodation
Depth
Eye changes its focus (lens gets fatter as gaze is directed toward nearer objects)
Convergence
Depth
Ability of the 2 eyes to turn inward (used to focus on nearer objects)
Divergence
Depth
Ability of the 2 eyes to turn outward (used to focus on farther objects)
Monocular depth cue
Depth/distance
Cue available even when the world is viewed with only 1 eye
Binocular depth cue
Distance/depth
Cue that relies on info from both eyes
Motion cue
Cue available when object is moving
Binocular disparity
ex. finger exercise
Difference between each eye’s view of a stimulus
* Can lead to perception of depth in absence of other cues
Motion parallax
Projected images of nearby objects move more than distant ones across retinas
Optic flow
As you move toward/away from an object, the pattern of stimulation across the entire visual field changes
Akinetopsia
Inability to detect motion, causing moving objects to appear as if they are jumping from one stationary position to another
* “Motion blindness”
* Linked to Area V5
