NSCI 225 Unit 1
Cones
- Found in the fovea - can have a 1:1 ratio for receptor:ganglion cell - Become fully adapted in the dark after about 5 minutes - Have good acuity - Help us see color - Have a tapered top
Macular Degeneration
- Fovea affected - The only thing you can't see is the thing you're looking at (center of vision)
Both rods and cones
- Have varying sensitivity for varying wavelengths of light - Found in the periphery - Have varying thresholds of activation for different wavelengths of light - Is responsible for the transduction step in vision (change light activity into electrical activity)
Rods
- More abundant in the retina - Contain rhodopsin, specifically - Slower to adapt to the dark - Sensitive to low levels of light
Hyperopia (farsightedness)
-Can't view close up images - Lens can't accommodate (round/tighten ciliary muscles) any further - Light is not bent enough, image is focused behind the retina
Steps of an action potential
1. Depolarization - threshold is reached 2. Sodium channels open 3. Sodium channels close/refractory period @ peak 4. Sodium channels opening causes voltage-gated K+ channels to open - repolarizes the cell 5. Refractory period where AP cannot occur 6. Back to resting potential - 70 mV
Signal travel from neuron to neuron
1. Neuron receives signal in either a chemical or physical form 2. Sodium passively diffuses down through the dendrites and cell body 3. The electrical signal is activated (threshold reached) and travels quickly down the axon to the axon terminals 4. This causes the release of NT's at the synapse and the process starts all over in the next neuron
Which weight difference would likely be most difficult to detect?
11 and 14 pounds
Cornea
1st part of the eye that light will go through - Transparent covering on the front of the eye - Focuses light (does most of the work)
sodium-potassium pump
2 K+ in, 3 Na+ out Maintains RMP
Cones and wavelengths
3 different types of cones absorb different wavelengths: short - blue, medium - green, long - red
Humans can only see what part of the electromagnetic spectrum?
400 - 700 nm
What type of cortical cell were Hubel and Weisel most likely recording from when they accidentally discovered the receptive field by slipping a slide into the projector?
A complex cell (certain orientation and movement)
Which of the following measures of threshold is an appropriate example of the method of limits?
A participant is asked to record at what point they hear a sound. The sound begins very low, and volume is incrementally increased, and on the next trial incrementally decreased.
LGN (lateral geniculate nucleus)
A structure in the thalamus, part of the midbrain, first place that info stops on the way to the primary visual cortex
What is true about the distribution of cones in the retina?
A. There are many in the fovea B. There are none in the blind spot
What is not part of the process for neural firing? A. There is an active current of K+ through the dendrites and cell body B. After the neurotransmitters are released, the process begins again in the next neuron. C. If threshold is reached, the action potential is activated at the top of the axon D. Neuron receives a physical or chemical signal
A. There is an active current of K+ through the dendrites and cell body There is a passive current of Na+ through the dendrites and cell body.
Myelin
AP DOESN'T happen on myelin (happens on Nodes of Ranvier - jumps) Myselin: Increases speed of the signal Saves energy for the neuron
With which of our senses do we use top-down processing?
All of them
dark adaptation
Amount of light needed to stimulate rods decreases over time spent in the dark. Threshold decreases
3 ways waves (the way by which light travels) can vary
Amplitude Wavelength Purity
Aurelia is holding a 1lb hamster in one hand and 6lb bunny in the other. Brenda is holding a 20lb dog in one hand and a 25lb dog in another. According to Weber's Law, who would have an easier time feeling the difference?
Aurelia
Which step does NOT occur in an action potential? A. Sodium channels open when the threshold is reached B. Sodium flows quickly out of the axon C. Potassium rushes out of the axon D. Sodium Potassium pump brings K+ into the cell while taking Na+ out.
B. Sodium flows quickly out of the axon
You have been shown a Hermann grid and are confused how grey dots appear when you look at the side of the grid, but when you look at the dots directly they have disappeared. Give one explanation of why this illusion is formed.
Because the area surrounding the grey dot has more brightly lit areas, you receive a greater amount of lateral inhibition, and consequently see the area as darker
Transduction of light stimuli into electrical activity occurs in the retina. What is this process called?
Bleaching
A drug that blocks the sodium gates of a neuron's membrane will ____.
Block the action potential from occurring
Diabetic Retinopathy
Blood vessels on the front surface of the eye become leaky and as the blood pools it causes blind spots - blood pools block light from being able to reach visual receptors
I am standing outside thinking about what I have been learning in my plant biology class. I come across a tall object that is green and brown. From my class, I realize it is a specific type of pine tree. Is bottom-up or top-down processing occurring?
Both
When viewing the ambiguous image from the Homework #1, which type of processing is involved in you seeing a seal?
Both top-down and bottom-up
larger amplitude=
Brighter
Brightness (rods and cones)
Brightness in the dark (rods) varies much more than it does in the daylight (cones)
Cataracts
Build up of protein and gunk on the lens (clouds lens so light is unable to pass through) Image is blurry
Solar Retinopathy
Caused by looking directly at the sun - blurry/distorted vision - blind spot in eyes - increased sensitivity to light - Chromatopsia - Happens on the retina. Visual pigment becomes bleached out = splotchy missing pieces of vision Normal retina is rosy, this causes it to be yellow/red
Receptive fields of the LGN
Center-surround like ganglion cells
Chemical vs. Physical Signal
Chemical signal used by interneurons Physical signal used by receptor cells (sensory neurons)
Has a higher threshold
Cones
The fovea of the eye contains which of the following?
Cones
Astigmatism
Cornea is misshapen, blurred/distorted image
Path light takes through the eye
Cornea, aqueous humor, pupil, lens, vitreous humor, retina
Surgery for cataracts
Cut open cornea Emulsify lens and suck it out Insert artificial lens New lens can't adjust/focus - have to wear bifocals
Weber's Law
DL = k x s. Harder to tell a difference between strong stimuli, easier to tell a difference between low stimuli. Ex) radio on 20/25 vs. radio on 5/10
Dark adaptation curve
Decreasing threshold of rods and cones overtime. Bump is due to differences in the curves for rods and cones - Cones reach peak adaptivity around 7-10 minutes - Rods reach it around 25 minutes
Neuron is made up of
Dendrites, cell body, axon
What we experience as different colors are
Different wavelengths of light that are being reflected into our eye
Physical Tasks & Judgement
Different weights in each hand can you tell the difference? Attention with driving, etc.
Con of single cell recording
Difficult to find a stimulus that will make the cell fire
Transduction process in rods and cones
Discs on outside of rods and cones that are full of rhodopsin and retinal - Retinal is sensitive to light - Absorbs a photon and changes shape = isomerization - Causes cascade of reactions that change activity in sodium channels = light changing into electrical activity
Lens
Does 20-30% of the focusing of light after the cornea has done most of it
Recognition Test
Eye doctor letters
Primary visual Cortex (V1/Striate cortex)
First processing area for vision
How do you get rid of bias in studying S & P?
Forced choice procedure! 2 time intervals, 1 with the stimulus, 1 without. Ask which one has the stimulus.
Neither
Found in the optic nerve
The optic nerve is made up of this type of cell
Ganglion cell
Rods and cones communicate to the brain via
Ganglion cells (retina output) and the optic nerve
Which would be true about what is happening in the retina when you walk into a dark room?
Given enough time, rods will adapt more fully and become more sensitive than cones.
Which of the following is LEAST LIKELY to be related to a problem with the lens? Cataracts Glaucoma Presybyopia Myopia
Glaucoma
More ganglion cell is firing =
Greater perception of brightness
Purkinje Shift
Green/blue appears brighter than red
Glaucoma (optic nerve damage)
Gunk from the iris clogs the canals that the aqueous humor normally drains from. It is still being replenished but can no longer drain = pressure build up. The outside nerves of the optic nerve slowly get crushed (tunnel vision) until you go completely blind.
All of the following describe the cones as compared to rods EXCEPT for which? A. Greater number of types B. Lower convergence C. Higher acuity D. Higher sensitivity
Higher sensitivity
Super pure light =
Highly saturated
What is the equivalent of the lateral plexus in a human eye?
Horizontal and Amacrine Cells (responsible for lateral interactions in the retina)
These cells are important in the process of lateral inhibition
Horizontal cells
Purity of light
How much achromatic light (black/white) is mixed in
ERP Effects of Attention
Ignored stimuli (in peripheral vision) are still processed, just not as much as attended stimuli
How does information get to the receptors in your eye?
In the form of light
Brighter border on gray box
Increased inhibition = less firing = inside of box appears darker.
Left LGN
Info from both eyes and only the right visual field
Shine light on the outside of an ON-Center, OFF-Surround ganglion cell
Inhibition. Firing rate will decrease.
The first part of the brain where attention has been shown to have an effect
LGN
Red Wavelength Blue Wavelength
Large wavelength, low amplitude Shorter wavelength, high amplitude
Which of the following would occur if horizontal and amacrine cells were not in the retina?
Lateral inhibition would be impaired
light from the right visual field would be processed by this side of the brain after the optic chiasm
Left side
The part of the eye that is affected by cataracts
Lens
Presbyopia (old eye)
Lens loses the ability to accommodate and becomes stiff as you age. Muscles are getting weaker, it is harder to squeeze. - Wear bifocals to fix
Myopia (nearsightedness)
Light is bent too much - image is focused in front of the retina instead of on it- blurry - Either the cornea or the lens is bending the light too much - Can't view things that are far away
Suppose a patient experiences a traumatic injury to their optic chiasm; what symptoms would they present with?
Loss of vision in right eye, right visual field and left eye, left visual field
Layers 1 & 2 of the LGN
Magnocellular layers. Process movement. One layer from each eye
Which is the best definition for absolute threshold?
Minimum amount of stimulus energy necessary to detect a stimulus
Cell membrane
More Na+ outside more K+ inside. Inside charge is negative in comparison to the outside
Rod Sensitivity
Multiple rods connected to one bipolar/ganglion cell sum their information to make the ganglion cell fire. With signals coming into multiple dendrites from multiple ganglion/bipolar cells, there would be a better chance of firing.
Light from the left visual field would hit this side of the left eye
Nasal retina
The bleaching of rhodopsin by light
Normally rosy in color Retinal and opsin separate and over time retina goes from rosy to colorless/yellow
Where is the receptive field for a cell?
On the receptor for that cell type
Convergence of rods and cones
Oneish cone per bipolar/ganglion cell - lower convergence = higher acuity Many rods per bipolar/ganglion cell - higher convergence = lower acuity
Action Potentials
Only occur in axons Can travel up to 100 m/s Constant in strength as they move All-or-none
Retinis Pigmentosa
Opposite effect of macular degeneration - Loss of outside vision - Now have tunnel vision
95% of cells coming from the fovea are
Parvocellular cells
The LGN layers coding color for the right visual field would be ________.
Parvocellular layers in the Left LGN
Layers 3-6 of LGN
Parvocellular layers. Proces color, texture, and pattern. 2 layers from each eye
Top-down Processing
Past experience/knowledge affects how you recognize things
Method of Adjustment
Patient adjusts knob until stimulus is just barely there. Continuous. Has the most bias. Easiest/quickest to conduct
Purkinje shift
Perception of brightness changes from daytime to nighttime. Using rods at night, blue end of color spectrum is much more pigmented than other colors. Caused by different thresholds of activation across wavelengths for both rods and cones
A Rorschach test (when you ask someone what they see in a random ink blot test) would be best described as which type of method?
Phenomenological Report
Cells in the retina back to front
Photoreceptors (rods and cones) Bipolar cells Ganglion cells - make up optic nerve and send info to the brain
Which if the following is NOT a problem with single cell recording?
Poor temporal (timing) resolution
Bottom-up Processing
Previous information does not affect recognition. You process sensory information as it is coming in
In the Blue/Black vs White/Gold dress image, why do people see the two different color schemes?
Prior experience is affecting the perceptual process
Magnitude estimation
Rate how intense a stimulus is
As threshold goes down
Regeneration of rhodopsin goes up (rhodopsin isn't being bleached by light, it regenerates in the dark)
Receptive Field of a cell
Region on the receptors in which stimulation causes that cell to change its activity (excitation or inhibition). With vision the receptive field is an area on the retina.
simple cells in V1
Respond to bars of light in a specific orientation (can receive info from the LGN (O-c, O-S) that has been put together to make a bar of a specific orientation)
End-stopped cells
Respond to corners and bars of a specific length. Care about orientation, movement, and length.
Complex cells
Respond to orientation and direction of movement
A green flower will
Retain its brightness better than a red flower
Left visual field is taken in by
Right temporal retina and left nasal retina (goes to right side of the brain)
Are rods or cones more sensitive to light?
Rods
Has higher sensitivity
Rods
Absorption of different wavelengths of light
Rods - absorb 500 nm best. Only need a little bit of this light to be stimulated Cones - absorb 560-600 nm best. Lower threshold means they are more sensitive to different wavelengths - rods have a lower threshold and higher sensitivity than cones
Professional stargazers always look slightly to the side of the stars they are viewing because...
Rods in the periphery are more sensitive to light in dark environments
Color is to Wavelength as...
Saturation is to Purity
Lateral Inhibition
Shining light on an individual receptor will increase it's firing and decreased the firing of any neighboring receptors (inhibition)
Absolute threshold
Smallest amount of stimulus energy necessary to detect a stimulus
Difference Threshold (DL)
Smallest difference between two stimuli that can be detected.
Visual Receptive Fields
Start out small in the fovea and increase as you move out towards the periphery. Lots of rods converging on a single ganglion cell makes for bigger receptive fields in the periphery.
Reaction Time Test
State colors as fast as you can when you see them
Method of Limits
Stimuli presented in ascending or descending order. Find mean crossover. "Can you see it yet?/Can you still see it?"
Method of Constant Stimuli
Stimuli presented in random order. Threshold stimulus is that that is detected 50% of the time. Hardest to cheat on/has the least bias
The action potential relies on the cell to depolarize and transmit the impulse. What is the best description of the beginning for this process?
The drifting of sodium causes the Na+ channels at the top of the axon to open and allow positive ions to rush in
Naima is playing hide and seek with her friends with the lights off. Which friend's shirt would likely appear the brightest?
The green shirt
The right visual field projects to
The left side of the retina
Where is the receptive field for a visual cell?
The retina/on a rod or cone
Which is another name for the Primary Visual Cortex
The striate cortex or V1
In the fovea
There are only cones. Super clear and acute vision
Which of the below is TRUE of Dendrites for typical neurons?
There can be many for one neuron
What do the pupil and the iris do?
They close and expand to let less or more amounts of light in. In the dark pupil is wider to more light can get in
lens accommodation
Tighten ciliary muscles to make the lens more round, fibers slack, fat lens - near vision Relax ciliary muscles, fibers taut, normal lens - distant vision
Which stage of the perceptual process is knowledge/top-down processing LEAST likely to influence?
Transduction
Which step in the perceptual process is most likely to only include bottom-up processing?
Transduction
T or F: The correct order in which LIGHT passes through the physical eye BEFORE being transduced is: cornea > iris/pupil > lens > ganglion cells > bipolar cells > rods/cones.
True
True or False: as you move down the visual field, the size of the receptive fields get bigger
True
True or false: the receptive field is always going to be a spot on the retina.
True
True or False: both LGNs receives info from both eyes.
True! But they each only have info from one visual field (either right or left)- opposite of the LGN.
Single Cell Recording
Used to look at receptive fields of different cells. Stimulus on or near receptive field - neuron fires
This is where you could find simple cells
V1
What happens if we never have exposure to a certain orientation?
We are unable to respond to that orientation Ex.) kittens that have only seen horizontal stripes run into chair legs bc they are vertical lines
According to ______ Law as the size of the standard increases, the difference threshold _________.
Weber's; Increases
Retina
What light is focused on. Has to be focused directly on the retina or else vision will be blurry
Sclera
White part that holds the eyeball together
Does attention affect processing in the LGN?
Yes. Neurons in the LGN fire more for what you are paying attention to than what you are ignoring. This is evidence top-down processing can affect how much the image is being processed in the LGN.
Phenomenological Report
Your explanation of what you are seeing
If you have been told you have Astigmatism, which best describes your symptoms?
Your vision as a whole becomes distorted and blurred especially for particular orientations.
Blindsight
a condition in which a person can respond to a visual stimulus without consciously experiencing it
Part of the neuron with an active current
axon
these cells care about the orientation of a line and movement, but not about line length.
complex cells
A neural signal is _____________ in a ___________ axon.
quicker; myelinated
Select the best description of a problem that can cause myopia
the cornea or lens bends the light too much. the eyeball is too long.
Cones are most abundant in
the fovea
Rods are most abundant in
the periphery
Blind spot
the point at which the optic nerve leaves the eye, creating a "blind" spot because no receptor cells are located there
Optic Chiasm
the point in the brain where the visual field information from each eye "crosses over" to the appropriate side of the brain for processing. Nasal and temporal pathways split here
Lateral Inhibition
the reduction of activity in one neuron by activity in neighboring neurons Gives us edges when looking at things
blind spot (optic disc)
where the optic nerve leaves the eye; there are no photoreceptor cells here
