Which visual pathway is responsible for processing motion?
The Where (dorsal) pathway, which ends at the Parietal Lobe (responsible for processing spatial attention)
What part of vision is good at processing motion? How does this relate to the LGN?
The periphery is good at detecting when there is motion (not necessarily what is moving)
This also means the magnocellular layers of the LGN are good at motion detection
How do we know that there is some kind of higher-level processing for motion beyond receptive fields?
We can perceive motion when there isn’t any
- Motion Aftereffects (MAE)
- Apparent Motion
What is the MAE? What does it tell us about motion? How is it similar to color adaptation?
The illusion of motion in a stationary object after prolonged exposure to movement
- The afterimage appears to move in the opposite direction of the original motion, meaning motion adaptation works through an opponent system similar to color adaptation
- There is also evidence for interocular transfer as well (like color)
What is Apparent Motion?
Lights flickering or alternating between locations can give the appearance of motion even when there isn’t any
- ex: marquee lights outside a theater
How do V1 cells detect local motion?
They have an additional system to detect timing between cells
- Delay Cells: process a delay from cell one
- Multiplication Cells: only fire when delay cell and cell two fire at the same time
What is the aperture problem? How does it relate to binocular disparity?
Small receptive fields in V1 make motion detection limited because they’re only getting a small window to the world, meaning that different types of motion may appear similar because they aren’t seeing the whole picture
This can be thought of as another form of the correspondence problem, where the brain has to decide whether two points are the same (but instead of occurring between the two eyes, it’s occurring in the same eye across two points in time)
How does motion detection in V1 feed into global motion detection?
The information from these cells gets fed into brain area MT (or V5), which is responsible for overall shared motion across a large area
What were the Newsome and Paré experiments and what did they find about global motion? What variable did they manipulate that is similar to a variable in visual search tasks?
They tested global motion by having monkeys detect which direction most dots were moving - they varied conditions by the amount of noise (set size? distractor complexity?)
Eventually found that damage to MT causes impairment in the ability to detect global motion (also found that lesions to the magnocellular portion of LGN impairs detection of large, fast objects)
What is Akinetopsia?
Motion Blindness
Vision is like a set of still images (like a flip book), often leaving afterimages
What is First-order motion? How is Second-order motion different?
First-order: changes in luminance over space and time
Second-order: overall luminance stays the same, but motion is detected by changes in contrast and texture
What is Biological Motion good for identifying? What brain regions does it activate?
Can identify actions, gender, and other information by broad movements
- Activates the visual system (MT) as well as the motor region associated with the action being seen
How can motion be used to perceive depth?
Parallax Effect
Optic Flow
What is Optic Flow? What is the Focus of Expansion?
We experience changes in the angular positions of points in space as we move through the world
This is experienced through the focus of expansion, or the center point from which motion seems to emanate or expand outward from
How is optic flow important for things such as landing planes?
At far distances, triangulation doesn’t work very well at providing depth
Instead, we can focus on whether the runway is expanding symmetrically
How can we calculate time-to-collision (TTC) in situations where things are moving towards us?
Tau: the size of a retinal image relative to the expanding rate (aka a heuristic estimate of whether an object is rapidly expanding towards us compared to its surroundings, implying motion)
What is Motion Induced Blindness?
Motion can cause static parts of an image to seemingly vanish
Our brain focuses on change, sometimes ignoring things that stay the same
What are the different ways in which our eyes can move?
Fixations, saccades, micro-saccades, smooth pursuit, reflexive movement, and vergence
Fixations & Micro-Saccades
Our eyes are focused on one area
Even though we are fixated on something, our eyes are still making small movements to prevent adaptation and inform depth through parallax
Saccades
Sharp eye movements between locations
Smooth Pursuit
Steadily moving our eyes to follow something across space
Reflexive eye movements
Automatic movements that occur to maintain our fixation point as we move our head
Vergence
Rotating eyes inward (convergence) or outward (divergence)
Critical for depth
How do we know the difference between our eyes moving and the world itself moving?
Our brain knows when the eyes move because of information from the eye muscles and the efference copy
Comparing the muscle information with the retinal information to see if they match
