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Sensation and perception test 1
Terms in this set (121)
Plato's Cave illusion
All we have access to is our imperfect senses, but can use reason too
Plato is a _________
Aristotle | Q - How does perception lead to thinking?
M - Reasoning, some observing.
Perceptions set up "vibrations" of the soul.
Acknowledged 5 senses, but also a "common sense"/central authority
Augustine was in the ____ era
Augustine | Q - Is there a God/are we created by God?
M - casual observations, generally anti-intellectual.
A - non sensing inner awareness of "truth", right/wrong, personal identity
Augustine's tactile vision theory
You are emitting something from the eye that interacts with something physical on outside vision.
Galen/scientific alternative | Q - how does this "machine" (body) work?
M - anatomy, dissection, functionalism.
A - born with instincts that affect what we learn, both innate and learned.
Empiricism (modern) - the authority of experience. | Q - All Q's valid
M - scientific method (Bacon).
A - Mind must be pre-organized to make sense of all perceptions
Rationalist | Q - how do we work? Sense/perc/thinking?
M - limited to thought, proofs.
A - we have innate ideas/knowledge/universal truths; there are also eternal truths we may never know. Perception is based on geometric calculations of eye angles, triangular convergence, etc.
Materialists - the "enlightened machine" | Q - separate spirituality from psych & science (but acknowledge existence)
M - metaphor of a machine / perception can be used to study perception.
A - perception/the mind is a process of the brain; no ideas innate, all ideas enter the mind through observation (sensation) and tradition (memory)
Want to find basic, fundamental units of matter to explain sensation/perception
a structuralist/reductionist, wanted to break down sensation into its most basic elements
Were against structuralists; the whole is more than the sum of its parts; perception is gotten from how the different elements are arranged; pacman triangle example
Perception is an active process; knowledge you have will influence how you perceive new things; top-down
J.J. Gibson's theory - previous knowledge has little/no effect on new perception; get all perception from senses/env as necessary; opposite of constructivist approach
David Marr; primal sketches to simulate activity in our cells
Neurophysiological approach (criticism)
very reductionist, similar to structuralists; goal is to break down everything to the interaction of neurons, but much of psychology isn't like this
Similar to neurphys approach but on a bigger scale
Franz Gall; diff. areas of the brain differ in size based on most used faculties. By feeling your skull, you could tell what someone was good at. Brain map - some elements still alive (localization of brain function)
The study of perception needs two levels of analysis:
Phenomonological method - interested in subjective experience
stimulation -> neuron firing; brain as center of perception (materialist); the neuron doctrine - most impt, neuron is a discrete unit/cell with space between them .All human behavior is due to interaction amongst these neurons
Clinical observations are mostly done in people with ____
3 electrical techniques (list)
Single Cell Recordings (invasive), electrocorticography (EcoG), EEG, MEG
Single cell recordings
An invasive electrical technique typically done in non-human studies; see how diff. stimuli affect single neurons
Single cell stimulation
a type of single cell recording; sending electrical impulses to simulate an action potential to stimulate a cell and see the reaction
electrocorticography; an invasive technique, puts electrodes on the surface of the brain; good for localizing seizure focus, very temporally precise, decent spatial precision
electrodes on surface of skll; direct measure of brain activity (post-synaptic potentials); temporally precise (timing), but not spatially precise (can't localize the activity to one area)
Event-related potentials (ERPs)
present an event and measure the EEG and get the avg. to get the ERP
uses magnetic fields of neurons (current down axon) instead of electric fields; temporally and spatially precise; the magnetic field isn't distorted by the skull as much as the E-field is.
Disruptive techniques (list)
Lesion techniques, TMS (transcranial magnetic stimulation)
physically damage the brain to see if a certain behavior is involved in a certain area; large electrical current, chemicals also work; temporary lesions also possible (cooling or anasthetic)
TMS (transcranial magnetic stimulation)
sends a magnetic field to the outer layer of cortex to create a reversible lesion; non-invasive
x-ray based, good for structure
uses large magnets to interfere with hydrogen in blood and uses those properties to figure out structure
Diffusion tensor imaging (DTI)
similar to MRI (non-invasive), tells you how water is flowing in the brain; water flows well in axon bundles, but not well outside, so you can track where bundles of nerve fibers are
indirect measure of brain activity (not like EEG); more active -> changes magnetic properties -> more blood flow -> shows up in fMRI.
Pros - good spatial precision
Cons - bad temporal precision (blood flow increases happens 6 min after the activity)
insert radioactive isotopes into patient; radioactive glucose -> more glucose in active areas.
Pros: good spatial prec.
Cons: bad temporal prec.
pass light into brain and see how the light is scattered by the brain; neurons that are firing scatter light differently.
pros - good spatial + temporal precision
cons: light can only penetrate surface of the cortex, takes long time
Fechner - founder of experimental psychology, developed most of psychophysical techniques;
Came up with ways to relate intensity of physical stimulus to the subjective intensity of the psychological experience/perception
Classical psychophysics (absolute and difference threshold)
absolute threshold - minimum physical stimulus necessary for you to have a psychological perception
difference threshold - min. difference between 2 physical stimulus for you to detect the difference psychologically
problem with absolute threshold
gradual transition, variability in people (even same person), thus you have to estimate the threshold
Psychophysical methods (list)
method of constant stimuli, method of limits, method of adjustment
method of constant stimuli
a psychophysical method; present varying levels of stimuli at random and ask patient if they detect it or not
cons: need many trials for each stimuli; have to have some idea of the threshold before hand
pros: will get a function of the varying levels of stimuli and detection levels and can find the "absolute threshold" at the stimulus level that is detected 50% of the time;
method of limits
Pros: Don't need to know abs. threshold before hand; start at either a very low or very high point and make small incremental changes in stimulus intensity until the observer can/cannot detect it. The cross-over value is where they first detect/can't detect the stimuli is the absolute threshold (take the avg. for all trials)
Cons: expectations of observer (since stimulus is changed in order), habituation of observer (keeps saying yes even though he can't actually hear it). Cons can be combatted by varying starting points and starting closer to threshold so the switchover is sooner.
method of adjustment
subject has control over magnitude of stimulus; turn knob until can/can't hear stimulus
Pros: intuitive, don't have to know abs. threshold, quick estimate
Cons: less reliable b/c participants aren't that precise every trial
How is the difference threshold (JND) measured using the different classical methods?
Method of constant stimuli: one stiulus is standard (doesn't change), and a comparison stimulus is compared by the patient and asked if it is less,equal, or greater than the standard. Doing this for many trials and finding where they are equal is how to find the JND.
Method of limits: go successfully below the standard stimulus with a comparison stimulus and see when they can tell them apart -> take avg of crossovers as the JND
Method of adjustment: participant adjusts the comparison stimulus and tells you when he can't tell it apart from the standard stimulus; aka "method of error" b/c you can see what the error is between them finding the JND and the actual difference
Weber - is the difference threshold constant for different intensities?
No - the difference threshold changes with stimulus intensity; if the stimulus is low, you only need a small change to notice. A larger stimulus intensity will have a larger difference threshold.
ΔI / I = k or ΔI = k*I; where ΔI = difference threshold, I = stimulus intensity, k = weber fraction.
Weber's fraction (k) examples
electric shock .01
Weber's law candle example
k = .08 for brightness; ΔI = k*I
ΔI = (0.08)(1 candle) = 0.08 more candles to notice a change (JND) -> 1.08 total candles
ΔI = (0.08)(500 candles) = 40 more candles to notice a change (JND) -> 540 candles total to notice a change in brightness
S = klogR
S = sensation intensity;
k = constant (adjusts scale)
R = physical stimulus intensity
Better for getting absolute threshold; derived from Weber's law. Says JND's are perceptually equal to one another; physical change required to produce a JND increases with stimulus magnitude. To get the same increase increment of stimulus intensity, a larger and larger physical stimulus intensity is required.
S.S. Stevens (1906-73); Says we shouldn't use Fechner's law.
Wanted participants to label a number (intensity level) to a physical stimulus and then to compare it to other physical stimulus and assign those numbers in relation.
Relies on participant -> more direct route
Steven's power law
S = aI^b
S = sensation intensity
a = scaling factor
I = physical intensity
b = exponent that differs by stimuli
Is similar to Fechner's law but more flexible.
If b < 1, concave down, psychological response grows slower than the physical stimulus (ex: brightness)
If b > 1, concave up, psychological response grows faster than the physical stimulus (ex: electric shock)
If b = 1, direct relation, psychological response grows at the same rate as the physical stimulus (ex: apparent length)
Signal detection theory
Good for cases of uncertainty; in psychophysics cases - present a stimulus and see if they detected it or not, while the tester knows if the stimulus was there or not.
Shows the bias present in a participant -> can have a Hit, False alarm, Miss, or correct rejection
Signal detection theory graphs
light (visible spectrum) reflects off of surfaces that humans care about seeing; light can reflect, refract, transmit, diffract
The outside, white part of the eye that reflects everything
Anterior chamber (aqueous humor)
in the cornea of the eye, continually recycled b/c it brings nutrients to the cornea; in glaucoma, pressure builds up in the anterior chamber b/c of no recycling of the fluid
has most of the optic power, refracts light; is clear to allow light through
also has refractive power; attached to muscles which can alter the shape of the lens (accomadation)
makes up most of the space of the eyeball, collects biodebris over time, is not recycled ever
gap in the retina where axons + blood vessels leave the eye, no photoreceptors here
at the back of the eye, contains the photoreceptors
What happens to the lens when looking at near objects?
It becomes fatter
What happens to the lens when looking at far objects?
It becomes flatter
Near-sightedness (you can only see well near); either b/c the eye is too long, or the lens is too strong, causing rays to converge in front of the retina instead of on it
Far-sightedness (you can only see well far); either b/c eye is too short, or lens is too weak, causing rays to converge behind the retina instead of on it
How is myopia treated?
Use a lens that weakens the power (negative diopters)
people with normal vision; have infinity far point, normal near point.
people with near-sightedness; have a closer far point and near point than emmetropes
people with far-sightedness; have infinity far point, but farther near point than emmetropes
"old-eye" - losing cells from lens, becomes less flexible and less able to accomadate; NP gets farther (like hyperopia).
A 20 yr old has a 15 cm NP
A 60 yr old has a 60 cm NP
low light threshold, low acuity, no color
high light threshold, high acuity, color.
Blue, red, and green cones sensitive to blue (short), red(long), and green wavelengths
collects info from photoreceptors; horizontal cells, bipolar cells, amacrine cells
Retinal ganglion cells (RGC)
axons of the RGCs form the optic nerve (exit it to the brain); takes info from bipolar/intermediate cells and transmits the info the brain
Pigment epithelium/reflecting tapetum
absorbs (in humans) or reflects (cats) excess photons to prevent the photons from reflecting backwards into the eye, or reflect it back for a "second chance" at perception (in cats)
contains only cones, highest visual acuity area.
Discs contained in rods/cones that determine what they are sensitive to. Have 2 parts: 1 part that determines what the photoreceptor is sensitive to (ex: opsin), 2nd part is retinal [retinal + opsin = rhodopsin, in rods].
There are different opsins in different cones; ~100 million photopigments. When a photon hits photopigment, it changes the conformation of the photopigment causing a bunch of intracellular rxn's that change the output of that photoreceptor
Transducin, phosphodiesterase, cGMP system
Net effect is to multiply the impact of the photon; phosphodiesterase affects cGMP by dephosphorylation, cGMP interacts with Na+ ions flowing into the membrane, slowing Na+ flow. Slowed Na+ flow affects neurotransmitter release.
Before any light interacts with the photoreceptor, it has "dark current" b/c of the flow of Na+ flow in, AT REST, is releasing neurotransmitter. Photons slow the Na+ flow in.
the area on the retina corresponding to which photoreceptors are activated. These excitatory/inhibitory regions help us see changes/edges more profoundly.
How is receptive field found with single cell recordings?
get a microelectrode near RGC, stimulate retina with light, and find out where it needs to be stimulated to fire the most APs in the RGCs.
Excitatory region in the receptive field
The excitatory region in the receptive field is where it fires many AP's (center for on-center cells)
Inhibitory region in receptive field
Where there are the least amount of APs firing (at the border of the cell for on-center cells)
What determines what type of cells the RGCs are?
intermediate cells determine "centerness" of RGCs
Off-center RGC is stimulated by what kind of light?
A dark center with light surrounding it
an illusion due to the bands adjacent to each other; our visual system enhances the edges and makes it look stronger than they actually are within a band.
The edges look stronger because:
1. excitatory region in center
2. inhibitory region on the edges
See notes for picture; remember black light = no light
If excitatory region receives no light (black) -> perceived as dark
If inhibitory region receives light -> perceived as dark
Types of retinal ganglion cells
P cells (parvocellular) - small, 70% of the RGCs
M cells (magnocellular), big, 10% of the RGCs
have small dendritic fields -> take in less info from intermediate cells; small receptive fields. High acuity because they are only processing a small portion of the retina, but low sensitivity
large receptive fields due to large dendritic fields; much less visual acuity, more sensitivity
Going from reliance on cones to rods
cone based vision, peak sensitivity at λ = 555 nm
rod based vision, peak sensitivity at λ = 507 nm
Blues will look brighter than reds in high light or low light?
Blues will look brighter in low light than rods because of the shift to the scotopic/rod system which is most sensitive to λ = 507 nm, lower wavelength than cone based/photopic system
How do we keep rods sensitive to low light at night?
Use red light at night to keep rods sensitive to low light since red isn't on the peak sensitivity for rods. When light hits photopigments, it breaks them up they arent sensitive anymore to low light (bleached); takes about 30 minutes for the photopigments to regenerate (rhodopsin in rods)
the minimal spatial frequency where you can still differentiate from black/white
Measuring visual acuity
eye doctors: use distance (e.g. 20/20)
vision scientists: use smallest visual angle of a cycle of grating (light to dark)
the number of cycles of light/dark per visual degree
the difference between the light/dark cycles
Left visual field goes to which hemisphere?
Goes to right hemispheres of your retinas, nasal retina and temporal retina
Where does the nasal optic nerve cross?
At the optic chiasm
Where does the nasal optic nerve go after it crosses at the optic chiasm?
After the chiasm, it goes to the LGN, and then to the primary visual cortex (V1/striate nucleus), the pathway to conscious vision
Right visual field ->
Right visual field -> Left hemispheres of retinas -> left LGN -> left primary visual cortex
Left visual field ->
Left visual field -> Right LGN -> Right visual cortex
How is contralateral (opposite) organization of the vision pathway accomplished?
by having the nasal nerve fibers cross at the chiasm
Structures of the eye -> hits photopigment on receptors and interacts with and breaks up, starting some intracellular processes; retinal blocks Na+ flow in and thus slows down NT release.
Afterwards intermediate cells receive the info from photoreceptors and pass it to RGCs (center/surround setup)
Next the info crosses at the optic chiasm, contralateral organization as a result of crossing nasal fibers.
First stop in the brain is thalamus -> routes/proceeses/emphasizes certain info -> LGN -> optic radiations -> primary visual cortex -> other areas of occipital lobe.
LGN (lateral geniculate nucleus)
Part of the thalamus, 80% of RGCs project to LGN, other 20% to superior colliculus.
->Fuction: plays a role in attention
->Gets 80% of input from areas other than the retina (top-down, from higher visual areas)
->Thalamus -> conscious vision
->Superior colliculi -> unconscious/reflexive vision
->Axons of retinal ganglion cells synapse at the lateral geniculate nucleus
Layers of LGN
-First 2 layers are M-cellular layers, specialized for motion, but not good for detail.
-Layers 3-6 are P-cellular layers, acute detailed vision, slower.
-Each layer only receives input from one eye (hemiretina).
-Layers 2,3,5 are ipsilateral -> receive input from same side of eye (temporal fibers).
-Layers 1,4,6 are contralaeral -> receive input from the other side of the eye (nasal fibers)
2 things out in the environment are going to stimulate layers close together on the LGN
Receptive field properties of the LGN neurons
Similar to RGC's with center/surround setup, keeps the correspondence.
Parvo vs. magno layers of LGN receptive field properties
-Parvo layers - much smaller receptive fields, much more detail, have ability to compare wavelengths/hue. Smaller axons -> slower respond, but specialized for color/form
-Magno layers - large axons, fast, no contribution to color vision at all; specialized for motion, location, how things change over time
one thing different in a picture; see if the patient detected the difference by tracking their eye movement towards the difference
Lesions in the parvo layers of the LGN cause deficits in what?
Severe color, texture, fine shape, and 3-D shape deficits.
Mild coarse shape deficits (since magno layers contributing some here)
No deficits in motion and flicker.
Lesions in the magno layers of the LGN cause deficits in what?
No deficits in color, texture, fine shape, 3-D shape, or coarse shape.
Moderate deficit in motion.
Severe deficit in flicker.
Damage in the parvo layers of the left LGN will cause a deficit in what visual field?
right visual field (mostly)
Primary visual cortex features
-Primary functional area of occipital lobe.
-Two features of V1 organization:
-->1. Retinotopic mapping - photoreceptors on retina adjacent to each other will get processed in an adjacent area of the retina, LGN, and primary visual cortex.
-->2. Cortical magnification - specialized areas, such as the fovea, are over-represented in the brain (compared to the periphery). The fovea has a large area represented in the V1 relatively, giving more detail to the fovea. In the center of the visual field, corresponding to the fovea of the retina, a very large number of neurons process information from a small region of the visual field. If the same stimulus is seen in the periphery of the visual field (i.e. away from the center), it would be processed by a much smaller number of neurons. Fovea has high cortical magnificatino factor.
Receptive fields in primary visual cortex/striate cortex
->Have preferred stimulus, usually lines for neurons in striate cortex.
->Have also a preferred orientation, more action potentials fire in the neurons in V1 for lines orientated optimally (vertically for example).
How are the circular receptive fields in the LGN transformed into the elongated receptive fields in striate cortex?
Hubel & Weisel - very simple scheme, each cortical cell receives info from many LGN cells, and the optimum orientation is determined by the average output of the LGN cells.
Many cortical cells respond equally well to:
moving lines (specific direction), bars, edges, and gratings.
Different receptive fields of the striate cortex:
1 - Edge detector
2 - stripe detector
Complex cells: doesn't matter where is stimulated, still going to get a good response. HOWEVER, both simple and complex cells have orientation tuning with a preferred orientation of lines, even though the stimulus location in receptive field doesn't matter for complex cells.
End-stopping cells: most sensitive to stimuli that stop at the edge of a receptive field. If it extends past or is too short, it won't fire optimally.
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