Perception 2 Flashcards
Vision and Multimodal Perception
What are the steps in the visual pathway?
Stimulus = light
1. Eye (remote sensation)
2. Lens inverts and focuses
3. Retina (photoreceptors)
4. Light causes changes in photopigments
5. Photoreceptors connect with bipolar cells that synapse with retinal ganglion cells (neurons)
6. Retinal ganglion cells fire action potentials
7. Optic nerve
8. Optic chiasm
9. Thalamus (LGN)
10. Optic radiation
11. Primary visual cortex (V1)
12. Secondary visual areas (V2, V3, etc)
What are photoreceptors?
They are light sensitive cells not neurons.
Are photoreceptors involved with action potentials?
Photoreceptors don’t fire action potentials it is a chemical change instead
What are the 2 types of photoreceptors?
Rods and Cones
What are rods useful for?
Rods are useful at night
What are cones useful for?
Cones are useful for daytime vision and color (3 types of cones for color vision)
What is contralateral crossover in the visual pathway?
Left visual field to the right hemisphere
When do optic fibers project ipsilaterally in visual pathway?
Optic fibers from the temporal half of the retina project ipsilaterally (same side - don’t cross at chiasm)
When do optic fibers project contralaterally in the visual pathway?
Optic fibers from the nasal half of the retina cross over at the chiasm (contralateral)
What is the retinogeniculate pathway?
When input from both eyes joins together
What is retinotopy?
Neighboring regions in the brain respond to adjacent regions in visual space
What is cortical magnification?
Center of gaze is over-represented in cortex
How is the visual system organized?
Retinoptically (based on space)
What is the Visual Hierarchy?
As you go through the visual pathway optimal stimuli increase in complexity and receptive field size (from retina - the cortex)
Where is the primary visual cortex located?
V1 is located in the posterior occipital lobe
Where are the secondary visual areas located (V2, V3, etc)?
They surround the primary visual cortex
How do lateral geniculate nucleus (LGN) cells respond?
They are either on-center (off surround) or off-center (on-surround) cells that respond to light accordingly
What is surround inhibition?
When receptive fields in the visual cortex are organized so that light in the center of field will activate a cell, while light in the periphery will inhibit it
Why have surround inhibition?
It sharpens contrast and edge detection
What is the fundamental principle of perception?
The brain cares about change
What does the cortical area, V1 like?
Likes oriented lines at various angles
What does the cortical area, V4 like?
Likes colors and shapes
What is V4 responsible for?
Color vision
What does a lesion to the V4 area cause?
Achromatopsia
What is achromatopsia?
Color blindness (complete lack of color vision or grey scale)
What does the cortical visual area MT like?
Middle temporal (MT) like motion
Where would a lesion that affects the MT area occur?
Middle temporal gyrus
What does a lesion to the MT area cause?
Akinetopsia
What is akinetopsia?
Motion blindness, an individual sees the world as a series of snapshots and their ability to judge direction and speed of moving objects was impaired
What are rods?
They are photoreceptors in the retina that are sensitive to low levels of light (night vision) and have a higher density in periphery
What are the 3 types of cones
Blue, red, and green cones
What are the 3 types of cones sensitive to?
They are sensitive to different wavelengths of light
What are cones?
They are photorecpetors in the retina that are in charge of seeing color and have the highest density in fovea (focus of what we’re looking at)
What would happen if you only have one type of cone?
You wouldn’t see color but you would see changes in brightness
How do cones work?
Our perception of color is based on the ratio of activated cones
What would happen if you only have 2 types of cones?
You would be able to see 2 colors
What is dichromats?
When there aer only 2 types of cones in the retina (usually red or green –> can’t tell the difference between red and green all look the same)
What are some of the visual cognitive functions?
Spatial localization, detection/discrimination, object recognition, color/texture, motion cues, depth perception, and navigation
Where are all the multi-sensory areas located?
STS (temporal), parietal, frontal, superior colliculus
How does multimodal perception work?
Weak responses can sum together and spatial/temporal synchrony is important
What is synesthesia?
Mixing of 2 senses (ex: colored letters, seeing music, tasting words)
What is some research that can be conducted on synesthesia?
Behavioral: Stroop test
fMRI: more activation in V4 (color) and STS (multimodal)
DTI: greater white matter connectivity compared to controls
