How we perceive motion. The ecological theory of perception
18 important questions on How we perceive motion. The ecological theory of perception
What did Helmholtz argue was a problem with the Constructivist theory of perception?
---> Perception is the end product of external stimulation and internal hypotheses, expectations and knowledge
---> Most of the experimental demonstrations are based on artificial stimuli – very top down in nature; you see what you expect to see…not bottom up
What is the Ecological Theory of Depth Perception? Who proposed it?
He thought perception was a bottom up process and saw it as the “direct pick-up” of information
i.e. everything that we need is in the environment, we just need to pick it up
- The purpose of vision is to enable interaction between the organism and the environment
- Emphasised the importance of motion in the environment, both in the observer and the object: Optic Flow (a primary cue in Constructivism)
Optic Flow ---> a cue related to the physiology of the eyes
What are 2 types of Optic Flow?
---> the focus, or centre of the outflow, specifies the direction of locomotion in the environment
---> a shift in the centre of outflow from one visual solid angle to another specifies a turn
2. Inflow (to the visual target) indicates retreat
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Regarding motion parallax, why do distant objects move more slowly?
---> the angle of near objects changes much more, so we perceive them as moving faster
Why is optic flow important?
2. Catching balls/avoiding collisions
What is the importance of perceiving movement?
For the predator looking for prey and the potential prey on the lookout for predators, the perception of movement is crucial for survival
This is why although many animals have poor depth or colour perception, none lacks the ability to perceive motion
What is meant by apparent motion?
What is the wagon wheel illusion?
---> It occurs when a wheel that is clearly moving forward, is perceived to move backwards because we do not match the appropriate spokes of the wheel
When perceiving motion, how does the brain take eye movements into account?
---> By comparing these two signals the visual system can determine whether an image has moved or not
---> Saccadic suppression stops us from seeing a blurred world during an eye-movement. The visual system shuts down for the duration of a saccade
What are direction selective cells?
- Most of the neurons in MT are directionally selective, when compared to area V4 (colour area)
---> In addition, it has been found that stimulating neurons in MT increases behavioural sensitivity to a particular direction of motion.
= These results suggest that our perception of movement is based on the activity of neurons in MT
Where does MT get its input from?
(p. 227 perceptual textbook)
Apart from MT, what other visual areas detect other aspects of movement?
---> these signals may be involved in analyzing optic flow
How does context affect our ability to see movement?
- In a blank homogeneous field, we are only able to detect whether an object is moving or not if its displacement is greater than 0.2 degrees per second
- However, if the same object is perceived in a visual scene that contains vertical lines, we are able to detect movements as slow as 0.02 degrees per second!
How does context affect the direction of moving objects?
How does movement tell us about the world?
What can moving signals offer?
(see slide 2, p. 9 lecture notes and there is a video on duo)
(more info p. 233 perceptual textbook)
What is the motion after-effect?
i.e. after viewing motion in a constant direction for a sustained period of time, we see stationary objects that we view afterwards as moving in the opposite direction
(p. 221 & 222 perceptual textbook)
Does sensitivity to visual motion develop all at once?
e.g. reflexive eye movements to moving targets are present in newborns (as long as the targets are sufficiently large)
e.g. physiological studies show that neurons in V1 have adultlike sensitivity to visual direction
e.g. on the other hand, sensitivity to global motion (which is thought to reflect processing in the MT), appears to develop more slowly reaching maturity at 3-4 years old, while sensitivity to motion-defined form and biological motion takes even longer
(p. 240 perceptual textbook)
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