Vision Flashcards
What is light?
Narrow range of electromagnetic spectrum; part of the spectrum that is visible to the human eye
What are cones?
Type of photoreceptor; good for daytime vision, higher resolution visual acuity
Where are cones found?
Highly concentrated in the fovea
What are rods?
Type of photoreceptor; good for seeing form/outline and mediating vision in dim illumination
What is the optic disk?
where ganglion cell axon exits the eye; there are no photoreceptors here and thus creates a blind spot
Where does ipsilateral visual information cross?
the optic chasm; neurons carrying info from nasal side cross to contralateral hemisphere
How many pathways occur from the optic chiasm?
Three; 1 pathway - superior colliculus, 2 pathway - hypothalamus; or lateral geniculate
True or false: Contralateral visual information crosses over to opposite hemisphere
False; contralateral info stays on the same side (e.g., left visual field processed in right eye)
What is the lateral geniculate body?
Nucleus of thalamus; comprised of 6 layers plus sublayer: magnocellular, parvocellular, and koniocellular
What are magnocellular layers?
Make up 1st and 2nd layer of the lateral geniculate body (LGN); they receive input from rods and are sensitive to light; they are NOT sensitive to color
What are parvocellular layers?
Make up 3rd-6th layers of LGN; they receive input from cones (so…color!)
What is the koniocellular pathway?
Found between each mangocellular and parvocellular pathway; it also receives info from cones
What do layers of the LGN do?
Each layer projects to a specific area in the striate (visual) cortex; segregation of the information is preserved in the cortex
Where is the central visual field processed?
Posterior primary visual cortex
Where is peripheral visual field processed?
Anterior primary visual cortex
True or false: the visual field is disproportionately represented
True; 25% of the primary cortex processes info from the fovea (but the fovea is a very small portion of our visual field)
The primary visual cortex is also know as…?
The striate cortex; V1
How does V1 process information?
Approx. 2,500 modules process information for color, form, and movement in discrete areas
What is subjective blindness?
When an individual still has visually-mediated behaviors; it is related to the pathway 1 where information is processed via the superior colliculus
What is “the where system”?
The dorsal stream of the association visual cortex; perceives location and mediation of one’s own movement
What is “the what system”?
The ventral stream of the association visual cortex; perceives objects/color (e.g., the identity of things, what objects are)
Where is the dorsal stream located and where does its input come from?
Located in parietal lobe; input mostly from magnocellular pathways
Where is the ventral stream located and where does its input come from?
Located in temporal lobe; input equally from magnocellular and parvo + some koinocellular
What is visual agnosia?
A sensory impairment where visual acuity remains intact but the person cannot identify objects by sight
