Chapter 6 Flashcards
The law of specific nerve energies states that:
every stimulation of the optic nerve is perceived as light.
In the human retina, messages go from receptors at the back of the eye to ____.
bipolar cells
Night-active species are more likely than day-active species to have:
a greater rod to cone ratio.
According to the trichromatic theory of color vision, the most important factor in determining the color we see is the:
relative activity of short, medium, and long wavelengths.
Which theory can best explain why people that are wearing yellow-colored glasses can still identify the color of a green apple?
retinex theory
Cortical area ____ appears to be where conscious visual perception occurs.
V1
People with motion blindness probably have suffered damage to the:
middle-temporal cortex.
When individuals with intact brains recognize faces, activity:
increases in the fusiform gyrus.
If we compare the receptive fields of two simple cells in the primary visual cortex, chosen at random, in what way are they most likely to differ?
orientation (angle) of a line that they respond to
What would the effect be if an experimenter covered the eye of a kitten in an alternating pattern (left eye one day; right the next)?
Most cortical neurons would respond to stimuli in one eye or the other, but not both.
whatever excites a particular nerve establish a special kind of energy unique to that nerve
law of specific nerve energies (Johannes Muller)
center of the iris; light enters the eye thru an opening in the center of the iris
pupil
rear surface of the eye; light is focused by the lens (adjustable) and the cornea (fixed) onto the rear surface of eye
retina
located closer to the center of the eye-receive msgs from receptors at back of the eye
bipolar cells
bipolar sends to this; located still closer to center of eye-receive msgs from bipolar cells
ganglion cells
light from left side striked right side of retina (vice versa)
contralidal arrangement
additional cells that get info from bipolar cells and send it to other bipolar cells other amacrine cells, and ganglion cells
amacrine cells
consists of ganglion cell axons- exits thru back of eye and travel to the brain
optic nerve
has no receptors; the point at which the optic nerve leaves the back of the eye
blind spot
central portion of retina; tiny area specialized for acute, detailed visions
fovea
ganglion cells in fovea of humans and primates
midget ganglion cells
better for details, not faint light
foveal vision
greater number of receptors converge into ganglion and bipolar
peripheral vision
have more receptors on the top 1/2 of retina; b/c they’re usually looking down while flying
eyes in birds
abundant in periphery of retina-respond to faint light, not useful in bright light
rods
abundant in and near fovea- less active in dim light, more useful in bright light, and essential for color vision
cones
ration of rods to cones
1/20th to rods; 90% of the input
where do you have good color vision?
right in the middle (fovea)
chemicals in both rods and cones that release energy when struck by light
photo-pigments
color perception occurs thru the relative rates of response by 3 kinds of cones
The Trichromatic (Young-Helmholtz) theory
we perceive color thru the relative rates of response by three kinds of cones, each kind maximally sensitive to a different set of wave lengths
young-helmholtz theory
Suggests that we perceive color in terms of paired opposits
The Opponent-Process Theory
proposed opponent-process theory
ewald hering
We perceive color in terms of opposite
red to green
yellow to blue
white to black
ability to recognize colors despite changes in lighting
color constancy
suggests the cortex compares info from various parts of the retina to determine the brightness and color for each area
Better explains color and brightness constancy
retinex theory
you perceive differences in brightness when there are none – perception of brightness of an object requires comparing it with other objects
Brightness constancy
whenever we see anything, we make an inference
purves and colleagues
an impairment in perceiving color differences; Some people lack one or two of the types of cones; Some people have three kinds of cones, but one is abnormal
color vision deficiency
Color vision deficiency AKA
color blindness
What is the most common form of color vision deficiency?
difficulty distinguishing between red and green; more common in men
a smaller amount to the superior colliculus, and fewer to other areas; part of the thalmus
lateral geniculate nucleus
the reduction of activity in one neuron by activity in neighboring neurons; Main function is to sharpen contrasts to emphasize the borders of objects
lateral inhibition
part of the visual field that excites or inhibits it – each cell in the visual system of the brain has this
receptive field
circular center with antagonistic (doughnut-shaped) surround
receptive field of ganglion cell
3 categories of ganglion cells in primates
parvocellular neurons
magnocellular neurons
koniocellular neurons
have small cell bodies and small receptive fields – located mostly in or near fovea; are highly sensitive to detect color and visual detail
parvocellular neurons
have larger cell bodies and receptive fields and are distributed evenly throughout the retina; are highly sensitive to large overall pattern and moving stimuli
magnocellular neurons
have small cell bodies, but occur throughout the retina; have several functions and their axons terminate in many different places
koniocellular neurons
located in occipital cortex
Also known as area V1 or striate cortex
Receives info from the lateral geniculate nucleus and is the area responsible for the 1st stage of visual processing
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Primary visual Cortex
an ability in people with damage to area V1 – they respond to visual information that they report not seeing
blindsight
looks like things are going up b/c those cells are fatigued
waterfall effect
recorded from cells in brains of cats and monkeys
Hubel and wiesel (1959)
has receptive field with fixed excitatory and inhibitory zones
simple cells
located in areas V1 and V2 – does not respond to exact location of a stimulus. Responds to pattern of light in a particular orientation (e.g., a vertical bar) anywhere within its large receptive field; Have large receptive field that can’t be mapped into fixed excitatory or inhibitory zones
complex cell
you present the stimulus in different locations
classifying cell as simple or complex
resembles complex cell, but has a strong inhibitory area at one end of it bar-shaped receptive field
end-stopped (hypercomplex) cell
neuron that indicates the presence of a particular feature
feature detector
Early lack of stimulation of one eye:
leads to synapses in the visual cortex becoming gradually unresponsive to input from that eye
Early lack of both eyes
cortical responses become sluggish but don’t cause blindness
when experiences have particularly strong and enduring influence
sensitive period
the discrepancy between what the left and right eyes see
Requires the brain to detect retinal disparity
don’t point in same direction, usually develops in childhood
strabismus
aka lazy eye
strabismus
Early exposure to a limited array of patterns;
Leads to nearly all of the visual cortex cells becoming responsive to only that pattern
blurring of vision for lines in one direction ; Caused by an asymmetric curvature of the eyes
astigmatism
(cloudy spots) on one or both eyes during infancy
cataracts
visual path in parietal cortex
dorsal stream
o The “where” pathway – helps motor system locate objects and move towards them
dorsal
receives information from primary visual cortex, processes it further, and transmits it to additional areas
secondary visual cortex (area V2)
ppl w/damage to dorsal stream
know what things are, but not where they are
collection of visual paths in temporal cortex
The “what” pathway
Specialized for identifying and recognizing objects
Ventral stream
damage to ventral stream
can’t describe what they see
how is info transferred between area V1 and V2
reciprocal Nature
As visual information goes from the simple cells to the complex cells and then to other brain areas, the receptive fields become______
more specialized
the ability to recognize an object’s shape despite changes in direction or size
shape constancy
inability to recognize objects despite otherwise satisfactory vision
visual agnosia
damage in temporal cortex usually results in this
visual agnosia
area (especially in right hemisphere) that responds strongly to faces, much more than to anything else
fusiform gyrus of ITC
Ability to recognize faces develops gradually, all the way into adolescence
ability depends largely on exposure
face recognition depends on several brain areas
Parts of occipital cortex
Anterior temporal cortex
Prefrontal cortex
Fusiform gyrus of inferior temporal cortex (especially in right hemisphere)
inability to recognize faces; Some people are poor throughout life
prosopagnosia
Born with a shortage of connections to and from fusiform gyrus
prosopagnosia
MST
medial superior temporal cortex
area V5; MT
Middle temporal cortex
Able to see objects but impaired at seeing whether they are moving or, if so, which direction and how fast
motion blind
ppl w/damage to areas of MT and MST
motion blind
a decrease in the activity of the visual cortex during quick eye movements
saccades
