9.4 Flashcards
Neuronal Activity
What do RGCs respond to in their receptive field? Why?
They respond to the presence or absence of light. They are too small to detect shape.
What shape is an RGC’s receptive field?
Concentric circle (like a donut!)
What excites an on-center cell? What inhibits it?
Excited when light falls directly on the center. Inhibited when light falls on the surround.
What happens when light shines on an entire on-center cell?
It becomes weakly excited.
What excites of off-center cell? What inhibits it?
Excited when light falls on the surround. Inhibited when light falls on the center.
What happens when a light shines on the entire receptive field of an off-center cell?
It becomes weakly inhibited.
What is luminance contrast?
Amount of light an object reflects relative to its surroundings.
How RGCs can give the brain information about shape.
What kind of information about shapes are RGCs sending the brain (because of luminance contrast)?
They are sending signals about edges. Edges form shapes
What are V1 cells also known as (when talking about processing shapes)?
Orientation detectors
What are orientation detectors with rectangular shape called?
Simple cells
What are the three types of orientation detectors in V1?
Simple cells, complex cells, hypercomplex cells
What are complex cells?
Orientation detectors that are maximally excited by bars of light moving in a particular direction through the receptive field
What are hypercomplex cells?
Orientation detectors that are maximally responsive to moving bars with a strong inhibitory area at one end of the receptive field
What shape is a complex cell and hypercomplex cell’s receptive field?
Circular (not concentric like RGCs)
How are neurons organized in the cortical structure in V1?
Organized into functional columns with a vertical connectivity pattern
What is selective orientation in V1?
V1 neurons respond best to bars or edges in the orientation that matches their input alignment
What is an ocular dominance column?
A functional column in the visual cortex that is maximally responsive to information coming from one eye
What layer of V1 do inputs arrive to? How does it connect to other layers (orientation)
Inputs arrive in layer IV and connect vertically with other layers.
What excites neurons in the temporal lobe region TE?
Complex visual stimuli (e.g faces)
Can be very specific in what they respond to
What is stimulus equivalence?
Recognizing an object as remaining the same despite being viewed from different orientations
How are stimulus preferences different in V1 vs. the TE region of the temporal lobe?
V1 neurons are not modified by experience whereas TE neurons are.
What is trichromatic theory?
Explanation of color vision based on the coding of three primary colors: red, green, and blue
What is subtractive color mixing?
Mixing red blue and yellow to make all the colors. Mixing the three makes black. What painters use.
What is additive color mixing.
Reflects light waves we see as red, blue, and green. When all visible wavelengths are reflected, we see white.
What is protanopia?
The lack of red cones. Inability to see red
What is deuteranopia?
The lack of green cones.
What is tritanopia?
The lack of blue cones
Where is color vision processed in primates?
V1 and V4
What is the opponent process?
Explanation of color vision that emphasizes the importance of the apparently opposing color pairs: red vs green and blue vs yellow.
According to the opponent process, if an RGC is excited by a blue wavelength, what would it be inhibited by?
Yellow wavelengths
What is color constancy?
The property of perception whereby colors appear to remain the same relative to one another despite changes in light
What area of the brain is speculated to be important for color constancy?
V4
What is the role of neurons in the posterior parietal cortex (dorsal stream)?
Processing visual information for action
Neurons in the primary visual cortex respond to properties of shapes, especially to ______ oriented in a certain direction
Bars of light
Recognition of complex visual stimuli such as faces is completed in the _______ lobe
Temporal (Inferotemporal cortex as stated in slides)
The idea that the color we see is determined by the relative responses of the three cone types in the retina is called _________
Trichromatic Theory
RGCs mediate color vision by _________ processes
Opponent
Describe the opponent process in the retinal ganglion cells
RGCs are excited by one wavelength of light and inhibited by another, producing two pairs of what seem to be color opposites - red vs green and blue vs yellow
