lecture 13 - motion and depth Flashcards
(41 cards)
why is it important to detect motion
because moving things can be dangerous
Barlow-Levick model (1965)
example of a detector for rightward movement
how does the rightmoving model work? (Barlow-Levick)
when something appears in front of a receptor, it triggers a * signal that travels down the pathway. delay holds onto the signal for a bit before allowing it to continue its way. moving right only activated when it receives two * at the same time
the rightward motion detector is one part of a larger system
imagine similar detectors for leftward, upward and downward movements, each responding to its own specific direction. all of these detectors cover all possible directions.
smooth persuit
follow objects with our eyes - voluntary eye movement
Masson and Stone 2002
when we see an object, our eyes will initially track its features (colour and shape), later after these have been associated with the object, our eyes will track the whole objects trajectory
Saccades
when we read, look at a scene or search for an object, we continually make eye movements called saccades, which bring our central vision to new regions of interest
Fixations
inbetween saccades, our eyes remain still during fixations that last between 200ms to 300ms
Rothman et al 2006
showed that in a block stacking task, participants would saccade to the next block before the reaching movement was complete
what did Rothman et al 2006 demonstrate
demonstrated that some of our saccades are planned and can support our movements and actions
vision during saccades - saccadic suppression
during a saccade, your eyes can reach a peak speed of 500 deg/sec and the movement would blur the retinal image. one of the main mechanisms that prevent us seeing this blur is called the saccadic suppression
Latour 1962
presented participants with two light sources (A and B) and asked them to look at the one that is lit. the lights would light up alternatively so the participants would move their eyes back and forth. Latour measured how sensitive participants were to a flash (C)
how long does a saccade last
typically they last 150ms
when is the lowest saccade sensitivity
the lowest sensitivity is immediately before a saccade
when is there reduced visual sensitivity
reduced visual sensitivity is 50ms before the saccade
improved saccade sensitivity
improved sensitvity from 50-100 ms
what is saccadic suppression
when you make a saccade, there is a period when your visual sensitivity is decreased and your vision is suppressed
when an object moves
when an object moves, their projection on your retina moves. this signals to your brain that an object is not moving
when your eyes move
when your eyes move, the projection of objects also moves on your retina, but you do not think that objects are moving
corollary discharge theory
when your eyes move, the signal sent (to the motor cortex) to move your eyes is accompanied by another signal that tells the brain (motion processing centre) that your eye movements, not objects, cause any movements across your retina.
no signal to eye muscles
no accompanying signal to cancel motion perception in the brain
optic flow
when you move, the objects in your environment create this. these flow lines help you determine the direction and speed of your movements
implied motion
implied motion is so powerful that it activates areas of the brain that processes actual motion
close objects
move quickly across yout field of vision
