Cortical organization
What is a hypercolumn?
A V1 “module” that contains a full set of orientation preferences for both eyes for a small region of visual space
What is visual agnosia?
A neurological disorder characterized by an inability to process sensory information (visual information)
In Gestalt psychology, what’s the core idea about wholes vs. parts?
The whole is not equal to the sum of its parts
What is the basic “problem” the visual system must solve for depth perception?
There’s a fundamental ambiguity between size and distance (the same visual angle can come from a small-near object or a large-far object).
Explain the difference between additive and subtractive color mixing, including the primary colors for each and what you get when you mix “all” colors
Additive (light): add light waves; primaries RGB; mixing all → white. Subtractive (paint/ink): absorbs/subtracts light; primaries CMY; mixing all → black/dark
In selective adaptation, what happens to a neuron’s firing when the stimulus is repeated after extended exposure?
The firing rate decreases (the neuron fires less)
In the “two-stream” framework, which stream is linked to perception and which to action?
Ventral stream → perception; dorsal stream → action
What are the three stages of object perception and what happens at each stage?
Early vision (detecting/combining features), mid-level vision (constructing surfaces and then 3-D objects), high-level vision (identifying the objects).
What is motion parallax?
When an observer moves, objects at different distances appear to move at different speeds (relative to the observer’s movement)
What is metamerism (in one sentence)
Two different light spectra can produce the same cone responses and therefore look like the same color
Which lobe is tied to object discrimination task vs landmark discrimination task?
Temporal lobe → object discrimination; parietal lobe → landmark discrimination
What is cerebral achromatopsia, and what area is damaged?
Cortical color blindness caused by damage to V4, leading to a world perceived in shades of gray despite normal retinal function
List three properties that distinguish figure from ground
Figure is more thinglike/memorable, is seen in front, and the contour belongs to the figure; ground is unformed, extends behind the figure
What is the horopter, and how do crossed vs. uncrossed disparity relate to it?
The horopter is an imaginary surface in space where points fall on corresponding retinal locations (same perceived location in both eyes). Crossed disparity = object in front of the horopter; uncrossed disparity = object beyond/behind the horopter.
Name the three cone types and give their approximate peak sensitivities.
S-cones ~420 nm, M-cones ~530 nm, L-cones ~560 nm
Compare and contrast the dorsal and ventral visual streams (location + function)
Dorsal stream (“where/how”): V1 → parietal regions; supports spatial processing, visually guided action, motion/spatial relationships.
Ventral stream (“what”): V1 → temporal regions; supports object identity, form recognition, color-related object information.
Name the three major extrastriate areas for motion, color, and faces recognition
V5/MT → motion
V4 → color
FFA → faces recognition
Give two pieces of evidence that “faces are special.”
We have an area in the brain that is specialized in face recognition - Fusiform Face Area (FFA)
We can perceive faces even in non-face objects (pareidolia)
We can easily recognize even blurred faces.
What is binocular disparity, and what feature of our body makes it possible?
Binocular disparity is the difference in the images on the two eyes, made possible because the eyes are separated by about ~6 cm, so they view the world from slightly different angles.
Define color constancy and name three factors/cues that help it work
Color constancy is the brain’s ability to perceive colors as stable despite lighting changes. It’s supported by chromatic adaptation, comparisons to surrounding colors, and memory/expectations
What are the three steps in the orientation/contrast grating selective-adaptation procedure?
(1) Measure sensitivity to different orientations
(2) Adapt to one orientation
(3) Re-measure sensitivity to different orientations.
How do we call impaired face recognition and which brain area is damaged?
Prosopagnosia, damage/dysfunction in the fusiform face area (FFA)
Name four cues the visual system uses to decide what’s figure vs. ground.
Position in the visual field, convexity, symmetry, familiarity
How do red–cyan anaglyph (3D) glasses create depth? Be specific about what each lens filters and what each eye ends up seeing.
Two slightly different images are overlaid (one red, one cyan). The red lens filters out the red image so the left eye sees only the cyan-tinted image; the cyan lens filters out the cyan image so the right eye sees only the red-tinted image. The brain fuses the offset images and interprets the position differences as depth.
In achromatic (black&white) perception, what is the ratio principle, and how can you tell a reflectance edge from an illuminance edge?
Ratio principle: two areas look the same if the ratios of their intensities are the same (under even illumination). A reflectance edge is a real material/color change; an illuminance edge is a lighting change (like a shadow) on the same surface.