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The visual system
Vision starts with
Light
Intensity corresponds to the perceptual experience of
Brightness
Wavelength corresponds to the perceptual experience of
Color
The first eye evolved
600 million years ago
A wavelength of visual light is in between __ and __ nanometers
400 and 700 nanometers
The dark circle in the center of your eye is your
Pupil
The colored part of your eye is the
Iris
The lens focuses light on the
Retina
More light means
Constriction (higher activity, lower sensitivity)
Less light means
Dilation (Lower activity, higher sensitivity)
Accommodation
Lens changing its shape
Accommodation happens through
Ciliary muscles
The purpose of accommodation is to
Focus light on the back of the eye
If something is near, the lens is more
Cylindrical
If something is further away the lens is more
Flat
Binocular disparity
Eyes see things from different perspectives to create depth perception
A predators eyes are faced
Forward
A preys eyes are faced
To the side
Structure of the Mammalian Retina from where the light enters to the back of the eyeball is
Retinal ganglion cells, amacrine cells, bipolar cells, horizontal cells, receptors,
The fovea processes in
High detail
The fovea works because the layer of cells
Is thinner
Completion
Your brain guesses what is in a blind spot to complete the image
Surface interpolation
Understanding the edges of something for your brain to fill in the rest
The two visual systems (duplexity theory)
Photopic (cone) and Scotopic (rod)
Photopic vision
Active in bright lights, high acuity, low sensitivity, low convergence
Scotopic vision
Active in dim conditions, low acuity, high sensitivity, high convergence
High convergence
Many rods going to one ganglion cell
Low convergence
One cone going to one ganglion cell
As you move away from the Fovea, __ density decreases and __ density increases
Cones decrease, rods increase,
Wavelength significantly influences __ perception
Brightness
Spectral sensitivity curves graph
The relative brightness of same-intensity lights at different wavelengths
Temporal integration
What we perceive is the sum of the input that has been received during the last few fixations (why things dont disappear when we blink)
Saccades
Movements between fixations
Fixations
The pauses (about 3 per second)
Most visual system neurons respond to __ not steady input
Change
Visual transduction
Converting light into neural signals by visual receptors
Retina-Geniculate-Striate Pathway
Largest visual pathway (90% of signals)
Cortical magnification
Primary visual cortex has a disproportionately large representation for the fovea
On the retina, the edge is a region of
High contrast
Contrast enhancement
Visual system that enhances our perception of brightness contrast
Mach bands illusion is the result of
Contrast enhancement
Receptive field
The area of the visual field to which a neuron responds
Hubel and Wiesel studied
Individual neurons in the retina-geniculate-striate system of a cat by recording activity from the neuron
Hubel and Wiesel’s question was
What visual features does each neuron respond to?
Hubel and Wiesel found that
All receptive fields are circular and different sizes
Neurons are __ with each neuron responding to a stimuli in only one eye
Monocular
Many neurons had receptive fields with both excitatory and inhibitory areas, separated by
A circular boundary
On-center cell
If center is stimulated, there is an “on” response
Off-center cell
If center is stimulated, there is an “off” response
Hubel and Wiesel concluded that
The cells were responding to contrast, rather than just stimulation
Component theory
Suggests there are three types of color receptors, each with different spectral sensitivities
In component theory, color perception is encoded by the
Ratio of activity in the three receptors
In component processing, every color will create
Different patterns of activity
Opponent processing theory
Suggests two classes of cells, one for color encoding and one for brightness encoding
In opponent processing, each color-coding cell signals complementary colors in an
Opponent fashion
In opponent processing, when stimulating one color, your brain
Responds with the opposite
In opponent processing, complimentary colors do not
Exist together (no bluish-yellow or reddish-green)
Mechanisms proposed by __ theories appear to exist in the visual system
Both component and opponent
Color constancy
Objects are perceived as the same color despite changes in wavelengths of the light across the surface (due to different lighting conditions)
Retinex theory
The brain has to also analyze the environment to figure out the color of something
Cortical Mechanisms of awareness
More than just the visual cortex helps to process visual information
Three different classes of visual cortex
Primary, secondary, visual association
Primary visual cortex
Receives most inputs from visual relay nuclei of thalamus
Secondary visual cortex
Receives input from primary visual cortex
Visual association cortex
Receives input from secondary visual cortex
Damage to primary visual cortex results in
Scotomas
Scotomas are an
Area of blindness in corresponding areas of the visual field
Scomas are plotted by
Perimetry tests
Many patients with scotomas are unaware because of
Completion
Is awareness required for sight?
Not really
Blindsight
Patients can respond to something even when they are not actually aware of it
Dorsal stream
Neurons respond to spatial location or movement (“where” system)
Ventral stream
Neurons respond to difficult objects (“what” system)
Dorsal damage means
You know what something is, but not how to interact with it
Ventral damage means
You know how to interact with something, but not what it is
Agnosia
Failure to recognize objects
Prosopagnosia
Inability to recognize faces
Akinetopsia
Deficiency in the ability to see smooth movement because of damage to the medial temporal area
Note 
Flashcard (20)