Chapter 3: Neural Processing + Perception Flashcards
What is Lateral Inhibition?
Inhibition transmitted across the retina
Explain the experiment that was used to study Lateral Inhibition (Limulus experiment) (4)
- The Limulus experiment shows that lateral inhibition can cause response in neurons
- Its OMMATIDILIA contain lenses on the surface, directly over a single receptor, allowing recordings from single receptors
- Light shown at a receptor led to rapid firing rate of nerve fiber
- But! light shown at neibouring receptors led to reduced firing rate of initial receptor
Define Lightness
Perception of shades
What are the 3 illusions that can be explained by lateral inhibition?
- Hermann Grid: seeing spots at intersections
- Mach Bands: seeing borders more sharply
- Simultaneous Contrast: brightness of one area affected by another adjacent
(perceived lighter when surrounded by a dark area, vice versa)
Use the Hermann Grid to explain lateral inhibition (3)
- BIPOLAR CELLS respond to white, sending inhibiting signals to the receptors at intersection
- Bipolar cells inhibit each other by 10%, but at an intersection with 4 surrounding bipolar cells, inhibition is stronger at 40% total
- At a corridor with 2 surrounding white cells of 100 each and 2 black cells of 20, 10% inhibition only sums up to 24%
What is White’s Illusion? How can it be explained? (3)
In White’s Illusion, people see light and dark rectangles even though lateral inhibition would cause the opposite effect
Belongingness Theory: an area’s appearance is affected by where we perceive it belongs (gray area on the left appears to belong to the white background, contrasting with the white background SO! grey area on the left appears darker)
- The effect probably occurs in the cortex rather retina (top-down processing)
What is Adelson’s demos? How can they be explained?
In Adelson’s demos, 2 horses appear to be 2 different shades. They can be explained by lateral inhibition and top-down processing (additional lightness adjustment because shadows)
Define Receptive Field
The area on receptors/neurons that influence firing rate
What are Center-Surround Receptive Fields? Where can they be found? (3)
On C-S receptive fields, areas are arranged in a center region that responds one way (excite/inhibit) and a surrounding area that responds the opposite (inhibit/excite)
They can be found at the optic nerve and LGN
Explain Center-Surround Antagonism
Output of C-S fields changes depending on area stimulated
- If excitatory-center-inhibitory-surround, firing increases if light stimulates center but decreases if light expands to surrounding area
- If inhibitory-center-excitatory-surround, vice versa
- If both areas are stimulated, intermediate response
Outline the pathway signals travel from the optic nerve to the frontal lobe (4)
Lateral Geniculate Nucleus (LGN), Primary Visual Receiving area/Striate Cortex/area V1, temporal lobe + parietal lobe, frontal lobe
What is the function of LGN cells?
LGN cells regulate info from the retina to cortex. Signals are received from the retina, cortex, brain stem, and thalamus…then organized by eye, receptor type, and type of environmental info
Define Retinotopic Map
A map in which each point on the LGN corresponds to a point on the retina
What are Feature Detectors?
Elongated receptive fields in area V1, with side by side excitatory/inhibtory areas
(Receptive field properties become more complex in higher level cortical areas, like in the inferotemporal (IT) lobe and fusiform face area (FFA))
What are the 3 Feature Detectors?
- Simple Cortical Cells: respond best to specific orientation
- Complex Cortical Cells: respond best to moving shapes with specific orientation, and with direction of movement
- End-stopped Cortical Cells: respond best to moving lines with specific length or moving corners or angles, with particular direction of motion
What is Selective Adaptation?
Phenomenon where if neurons fire too long, they become fatigued/adapt, causing a decrease in neural firing
How can you test Selective Adaptation?
To test, measure sensitivity, have subject adopt to a stimulus, when remeasure sensitivity
What is Grating Stimuli?
Alternating light and dark bars, used to test for sensitivity to either orientation or contrast
What is Selective Rearing?
If animals are reared in environments that contain only certain types of stimuli, neurons that respond to these stimuli become predominant due to neural plasticity
Explain Blakemore + Cooper’s experiment related to selective rearing (and kittens)
Kittens were reared in tubes with only horizontal and vertical lines.
- Both behavioural and neural responses showed exceptional development of those neurons
- Experiment provided evidence that the visual cortex could be modified by visual experience
- Experiment led to identification of sensitive periods
Define Sensitive Period
Window of time during which neurons that code a function can be altered
Define Sensory Code
Representation of perceived objects through neural firing
What are the 3 coding theories?
- Specificity Coding: specific neurons respond to specific stimuli
- Problem: too many different stimuli to assign specific neurons
- Problem: most neurons respond to numerous stimuli - Distributed Coding: representation of specific objects through patterns of neural firing
- Sparse Coding: representation of specific objects through firing a few neurons (mid-point between 1 and 2)
What is the Grandmother Cell Hypothesis?
A hypothesis related to the specificity coding theory, proposing that there are ells in the hippocampus that respond to images and concepts related to grandmas
