Chapter 6 Flashcards
Light
waves of electromagnetic energy between 380 and 760 naometers
Fovea
an indentation
about 0.33 centimeter in diameter, at the center of the retina
it is the area of the retina that is specialized for high-acuity vision (for seeing fine details)
Retina
neural component of the eye that contains photoreceptors
Sensitivity
the ability to detect the presence of dimly lit objects
Acuity
The ability to see the details of objects
Binocular Disparity
The difference in the position of the same image on the two retinas
Retinal ganglion cells
the output stage of retinal information processing
blind spot
the second of the two visual problems created by the inside-out structure of the retina
completion
the visual system uses information provided by the receptors around the blind spot to fill in the gaps in your retinal images
when the visual system detects a straight bar going into one side of the blind spot and another straight bar leaving the other side, it fills in the missing bit for you; and what you see is a continuous straight bar, regardless of what is actually there.
Photoreceptors: Rods and Cones
Rods - low light levels or scotopic vision
Cones - vision at higher light levels or photonic vision
Transduction
the conversion of one form of energy to another
visual transduction is the conversion of light to neural signals by the visual receptors
rhodopsin
G-protein-coupled receptor that responds to light rather than neurotransmitter molecules
it initiate a cascade of intracellular chemical events when they are activated
retina-geniculate-striate pathways
conduct signals from each retina to the primary visual cortex, striate cortex, via the lateral geniculate nuclei of the thalamus
primary visual cortex (striate cortex)
Makes up a small portion of the visible surface of the cortex in the occipital lobe
essential to the conscious processing of visual stimuli
Lateral geniculate nuclei
nucleus in the thalamus that receives visual information from the retina and sends it to the visual cortex for processing
optic chiasm
all signals from the left visual field reach the right primary visual cortex, either ipsilaterally from the temporal hemiretina of the right eye or contralaterally via the optic chiasm
contrast enhancement
every edge we look at is highlighted for us by the constrast-enhanceing mechanisms of our nervous systems
- our perception of edges is better than the real thing
mach bands
the nonexistent stripes of brightness and darkness running adjacent to the edges
lateral inhibition
the second that when a receptor fires, it inhibits its neighbors via the lateral neural network
because it spreads laterally across the array of receptors
receptive field
area of the visual field within which it is possible for a visual stimulus to influence the firing of that neuron
component theory
proposed by Thomas Young in 1902 and refined by Hermann von Helmholtz in 1852
according to this theory there are three different kinds of color receptors(cones) each with a different spectral sensitivity and the color of a particular stimulus is presumed be encoded by the ratio of activity in the three kinds of receptors
opponent process theory
proposed by Ewald Hering
suggested that there are two different classes of cells int he visual system for encoding color and another class for encoding brightness
posterior parietal cortex
areas of association cortex that receive visual input are located in several parts of the cerebral cortex, but the largest single area is in the posterior parietal cortex
inferotemporal cortex
cortex of the inferior temporal lobe
scotoma
an area of blindness
conscious awareness
we assume that someone who has seen something will be able to acknowledge that he or she has seen it and be able to describe it
people who see things but have no conscious awareness of them
Blindsight
the ability to respond to visual stimuli in a scotoma with no conscious awareness of them
Dorsal stream
flows from the primary visual cortex to the dorsal prestriate cortex to the posterior parietal cortex
Ventral stream
flows from the primary visual cortex to the ventral prestriate cortex to the inferotemporal cortex
where versus what theory
damage to some areas of cortex may abolish certain aspects of vision while leaving others unaffected
most convincing support for the influential “where” versus “what” theory has come from he comparison of the specific effects of damage to the dorsal and ventral streams
Visual agnosia
can see things, but they don’t know what they are
often specific to a particular aspect of visual input and are named accordingly
Prosopagnosia
is a visual agnosia for faces that can be acquired either during development (developmental prosopagnosia) or as a result of brain injury(acquired prosopagnosia)
fusiform face area
the area of human cortex
parts of it are selectively activated by human faces
and because electrical stimulation of this brain area in humans can metamorphose a viewed face into a completely different face
Akinetopsia
deficiency int he ability to see movement progress in a normal smooth fashion
MT Area/VS
akinetopsia is often associated with damage to the MT area (middle temporal area) of the cortex
near the junction of the temporal,parietal and occipital lobes
