Lecture 16 and 17 Flashcards
What is the relationship between sensation and perception
What we perceive depends on assumptions our visual system makes and on past learning
What is the pathway light takes in the retina
light goes through ganglion cells and bipolar cells to the rods and cones which are photoreceptor cells
rods (type of sensitivity, convergence)
dim light, very sensitive, lots of convergence to the next level
cones (type of sensitivity, convergence)
multiple kinds, sensitive to different ranges of wavelengths (color), high acuity, little convergence
how do the discs act within rods and cones with light
discs contain opsin molecules (when lit by light, they activate g proteins to second messengers)
visual transduction pathway before light and after light
visual receptor cells (rods and cones) release NTs continuously onto bipolar cells when not stimulated by light. Light stimulates a rhodopsin that causes second messenger cascades resulting in Na+ channels closing and the receptor cell becoming hyper polarized
stimulation by a light source is indicated by what
by stopping or reducing neurotransmitter release
In-depth pathway of rod photoreceptor being hit by light
light acts on rhodopsin molecule which changes shape of the overall molecule (retinal) which causes 500 molecules of G protein transducin to be made. Each molecule of transducin causes GTP molecule to replace GDP. The GTP then dissociates from retinal molecule and activates the phosphodiesterase which turns cGMP into GMP causing the Na+ channel to close. No positive ions coming in, makes it hyper polarized
dark adaptation
it takes time for photopigments to be recombined after being split by light. The levels go up in the dark
What is the composition of rods and cones in the retina from outside towards inside
densely packed cones on inside which causes high acuity and good detail, loosely packed cones on outside and densely packed rods which causes low acuity but good dim light
the fovea
high receptor density, cell bodies and axons are bent away from it so light doesn’t have to pass through other cell layers
the blind spot
where axons form the optic nerve so there are no receptors. When using both eyes you don’t have to fill in the gap
Lateral inhibition
a whole network of inhibitory connections going side by side throughout the retina. Each receptor cell is exerted by light but inhibits its neighbor cells mainly horizontal cells
if a spot of light comes and touches the ganglion cell…
it makes a bunch of APs
if there is a spot of light right next to the ganglion cell…
it turns off its APs and nearby cells stimulated (exhibition on ganglion)
light only on area around ganglion…
normal range of APs when light off, light on inhibits ganglion
diffuse light inside and outside of ganglion…
produce background levels of APs where some excitation and some inhibition
explain the pathway between light, cones, and bipolar cells
Light causes cones to be hyper polarized and decreases the amount of glutamate that it is releasing. The released glutamate has opposite effects on the two kinds of bipolar cells because they have different glutamate receptors. Causes decreased inhibition on one bipolar cell which results in increased release of the NT glutamate at the synapse. This causes increases firing rate of (APs) to brain
what is the difference between predator and prey receptive fields
Predators have front eyes because they want to see what they are attacking, the majority of their receptive field is both eyes in the front and a little of side for each individual eye. Prey wants to be aware of movement all around them. They have side eyes and the majority of their receptive field is on the periphery
What is the relationship between visual field image, retinal image, and which side of the brain they go to
The visual field is opposite to brain parts. Right visual field goes to the left brain and the left visual field goes to the right brain. The retinal image on the other hand is an inverted and reversed image of the visual field. Therefore the right half of the retina goes to the right side of the brain and the left half of the retina goes to the left side of the brain
most axons in optic tract terminate in… while some terminate in…
the lateral geniculate nucleus
while some terminate in the superior colliculus
day and night cycle happens in the
suprachiasmatic nucleus
cortical neurons are sensitive to
orientation as well as location
how do we experience the light illusions
lateral inhibition and summation
How do we experience light illusions (summation part)
in lateral geniculate only if all five cells have APs will a cell in visual cortex show an AP. Requires a bunch of input all at once.
How do we experience light illusions (later inhibition part)
Cortex can see lines of orientation and lines brightly distinguished from what is happening on other side of the line because inhibitory activity from neighbors can make dark look darker and make an edge of white look whiter
ocular dominance columns
2 kinds of columns, neurons that show substantial APs to one eye or to the other. As you go across cortex find zones responsive to one eye or the other eye and back again. In between the borders you see neurons responding to both eyes
hyper column in V1 (primary visual cortex)
whole cluster where all orientations are represented and all combinations of inputs from the two eyes
clusters of eeks
embedded in cortex responsible for analyzing color (blobs)
how do we see shapes
detecting spatial frequency and contrast
spatial frequency
how quickly things change from light to dark
Explain color perception (trichromatic theory)
Color perception is created by context and previous experience. The trichromatic theory is that there are three kinds of cones and each responds to a different range of wavelengths (colors). The color ranges are wide and overlapping (none peak in red). Precise hue discrimination depends on relative activity of different cones. Our color vision involves looking at the mixes of activation on these different receptor types
Axons carry information between the lateral geniculate and the striate cortex via
Optic radiations
Crossing of information from the eye happens at
Optic chasm
Notice a tiny flashy light by
Superior colliculus
