Chapter 2: The beginning of perceptual processes Flashcards
Accommodation
the change in the lens’s shape that occurs when the ciliary muscles at the front of the eye tighten and increase the curvature of the lense so that it gets thicker
blind spot
area of the eye with no receptors, where the optic nerve leaves the eye
cones
found in the fovea, a type of visual receptor
cornea
focuses light in the eye, transparent covering of the front of the eyes accoutns for about 80 of the eyes focusing power, but it is fixed in place and cannot adjust
eyes
contains the receptors for vision (earliest eyes were eyespots that could distinguish between light and dark)
fovea
one small area that contains ONLY cones, and when we look directly at an object, the object’s image falls into the fovea
lens
focuses light in the eye, 20% of the focusing power, but can change its shape to adjust the eye’s focus for objects located at different distances
macular degeneration
when the fovea is destroyed and the small area around it, which creates a blind region in the central vision, so when someone looks directly at something they loose sight of it
optic nerve
signals go through the back of the eye through this, it contains a million optic nerve fibers that conduct signals toward the brain
outer segments
the part of the receptor that contains light sensitive chemicals called visual pigments that react to light and trigger elec signals
peripheral retina
all the retina outside the fovea, with both rods and cones, more rods than cones, about 120M R to 6M C
pupil
where light enters through the eye
retina
the netweokr of neurons that covers the back of the eyes and contains the receptors for vision
retinitis pigmentosa
generational condition, attacks the peripheral rod recpetors and results in poor vision in the periphery
rods
visual receptor, more common than cones, only found in the periphery
visible light
small subset of the electromagnetic spectrum that humans can percieve with wavelengths from 400-700 nm
visual pigments
light sensitive chemical that triggers electrical signals
wavelength
the distance between the peaks of electromagnetic waves
describe how the cornea and lens focus image on the retina
the cornea focuses about 80% of the light but its unmoving, and the lens focuses the other 20% but can change and adjust based on the distance and light that it avaliable
absorption spectrum
a plot of the amount of light absorbed versus the wavelength of the light
axial myopia
the eyeball is too long, so the image doesnt focuses too far ahead of the retina
cone spectral sensitivity
measured y having a subject look directly as a test light so taht it stimulates only the coens in teh fovea
dark adapted sensitivity
the sensitivity at the end of dark adaptation is about 100,000 time greated than the light-adapted sensitivity measured before dark adaptation began
dark adaptation curve
measures dark adaptation, the function relating sensitivity to light to time in the dark, beginning when theh light are extinguished
dark adaptation
the process in which a person starts to see better in the dark after a little while after adjusting
detached retina
when the retina becomes deattached from the pigment epithelium, which is required for visual pigment regeneration, makes people blind at that part
farsightedness
can see distant objects clearly but have trouble seeing nearby objects because the focus point for parallel raus of light is located behind the retina, usually because the eyeball is too short
hyperopia
can see distant objects clearly but have trouble seeing nearby objects because the focus point for parallel raus of light is located behind the retina, usually because the eyeball is too short
light-adapted sensitivity
1/threshold, sensitivity measured inthe light, mesured while the eyes are adapted to the light
monochromatic light
light of a single wavelength, can be measured using a spectrometer
myopia
an inability to see distant objects cleary, and affects more than 70 million americans - occurs when the optical ssystem brings parallel rays of light into focus at a point in front of the retina, so the image that reaches the retina is blurred.
nearsightedness
an inability to see distant objects cleary, and affects more than 70 million americans - occurs when the optical system brings parallel rays of light into focus at a point in front of the retina, so the image that reaches the retina is blurred.
presbyopia
the loss of ability to accomodate enough to see objects or read at a close range (fixed by wearing reading glasses)
refractive myopia
the cornea/the lens bends the light too much
rod spectral sensitivity
measured after the eyes is dark apadated (when rods control visio) and presenting test flashes inthe peripheral retina
spectral sensitivity curve
the relationship between wavelength and sensitivity
spectral sensitvity
a point of the spectral sensitivity curve
visual pigment bleaching
the change in shape of the retinal and seperations from the opsin causes the molecule to become lighter in color
visual pigment regeneration
the process of reforming the visual pigment molecule, because whenth epigments are in their bleached state they are no longer useful for vision
describe the role of visual pigments in transduction
visual pigments are important to seeing, and the convert the light energy into electrical energy via transduction
describe the method for measuring dark adaptation and the overall results
dark adaptatation is better for the cones than rods
discuss the difference between the distributions of the rods and the cones
rods are inthe periphery, cones are very concentrated in the fovea and also dispered throughout the erphery but muchhhh less than rods
explain why the “blind spot” exists and why we are not usually aware of it
it occurs because that is where the optic nerve leaves the eye, and we are usually unaware of it because out brain tried to fill it in
action potential
axon rises 40mV and then decreases again, lasts about 1millisecond, remains the same size no matter how intense the stimulus is
axon
filled with fluid that conducts electrical signals
cell body
contains mechanisms to keep the neuron alive
dendrites
branch out from the cellbody to recive eelctrical signals from other neurons
depolarization
when the inside of the neuron becomes more postive
(excitatory response)
excitatory response
when the inside of the neuron becomes more postive (depolarization), increases neuron firing
falling phase of the action potential
potassium rushes out of the axon which causes the axon to become more negative (+40mV back to -70mV)
hyperpolerization
the inside of the neuron becomes more negative (inhibitory response)
inhibitory response
the inside of the neuron becomes more negative (hyperpolarization) decreases nerve firing
ions
molecules that carry an electrical charge
isomerization
when the visual pifment molecule absorbs light and the retinal changes its shape from bent to stract which creates a chemical reaction that activates thousands of charged moleciles to create electrical signals in receptors
nerve fiber
filled with fluid that conducts electrical signals (also an axon)
neurons
where electrical signals occur
neurotransmitters
small chemicals stored in synaptic vesicles in the sending neuron that flow into the synapse to small areas on the recieving neurons
permeability
the ease in with which a molecule can pass through the mebrane, in reerence to teh sodium channels when an action potential travels through the axon
propagated response
one the response it trigger, it travels all the way down the axon without decreasing in size ( enables signals to go across long distances)
receptor sites
areas on the neuron that are sensitive to specifi neurotransmitters
refractory period
the interval between the time one nerve impulse occurs and the next one cam be generated in the axon (about 1 ms) so the upper rate of firing is about 500-800 impulses per second
rising phase of the action potential
the increase in potential from -70mV to +40mV (sodium rushes in)
resting potential
-70 mV, no signals outside the neuron
spontaneous activity
action potentials that occur in the absense of stimuli from the enviornment
synapse
the small space between neurons
transduction
visual transduction occurs int he rods and cones which transform light into electricity using visual pigments
identify the key components of neurons
cellbody, axon, dendrites, synapse
define propagated response and discuss how this is related to measuring activity in a single neuron
once a signal is released it travels down the neuron without decreasing in size, which means that it can travel long distances. also it means that the speed of firing doesnt change but the RATE of firing varies
describe depolarization, hyperpolarization, and inhibition
depolatization is a exitatory reponse that means there is more positive in the neuron, verus hyperpolizaiton which is an inhibitory response which is more negative in the neuron
amacrine cells
allows signals ot travel between bipolar and ganglion cells
bipolar cells
right after the receptors
convergence
multiple signals going to one cell, happens alot with ganglion cells in the eye
ganglion cells
right after bipolar cells, have long axons like neurons, which transmit signals out of he retina in the optic nerve
horizontal cells
allows signals to travel between receptors
neural circuits
interconnected groups of neurons within the retina
neural convergence
happens when a number ofneurons synapse onto a signle neuron (happens opften in the retina)
visual acuity
refers to the ability to see details, like being able to see very small letters on an eye, increases in cones
visual evoked potential
electrical response that is generated by the visual cortex that occures when the stimukus is large enought to be detected by the visual system (used for babies)
describe what convergence is, and how it related to acuity in rods and cones
cones have higher acuity while rods have higher sensistivity
rod-cone break
the place where the rods begin to determine the dark adaptation curve (20-30 minutes)
