Visual perception and action pt2 Flashcards
Whats perceiving?
involves combining information from the senses with what we already know
whats the constructivist approach to perception?
constructivist as sensory information is incomplete. Perception must be constructed from this incomplete input.
•Top-down processes “fill the gaps”
whats gregory’s (1972) theory of indirect perception?
Top-Down: The image arriving on the retina is incomplete and needs to be “worked on” and supplemented by stored knowledge, past experience, etc.
•Recognition Driven: The end point (or purpose) of perception is to identify what we are looking at
key principles of this theory
The senses provide raw data, but stored knowledge enables us to construct a perception of the input
- The key principles:
- Perception is active
- Sense input is insufficient for perception – need interaction between sensory input and knowledge
- Much of the information that reaches the eye is lost by the time it reaches the brain
- Perception involves hypothesis testing to make sense of information from our sense organs
- Incorrect hypotheses will lead to perceptual errors
Depth cues - evidence supporting constructivism.
what are depth cues?
Depth Cues: Evidence in Support of Constructivism
- Depth cues: often taken as evidence for top-down processing in perception
- Critical because the perceptual system needs to transform the 2D retinal image into a 3D interpretation of the external world
3 main categories of depth cues?
Monocular cues (can be seen with one eye)
- Oculomotor cues (need both eyes: based on muscle movements)
- Binocular cues (need both eyes
evidence supporting constructivism.
whats monocular cues?
Give the perceptual system the impression of 3D
•Seen with one or two eyes
•AKA pictorial cues as artists use them to create the perception of depth in paintings etc
Monocular Cues: Linear Perspective- what is it?
The cue is so powerful that it can give rise to visual illusions (e.g., the Ponzo illusion)
.•Our perceptual system expects the upper line to be further away in 3D space due to the convergence of the line of pillar
Monocular Cues: Aerial Perspective - what is it?
Light is scattered as it travels through the atmosphere, making more distant objects look hazy
•Used in paintings to create the perception of depth
•Top-down knowledge about the world convince us the image is 3D
Monocular Cues: Interposition - what is it?
Where a nearer object hides a more distant one
•The fact that one object is in front of another gives a powerful sense of depth
•These objects are on the same plane
•Overlap = depth
Monocular Cues: Shading
Provides good evidence of the presence of 3D (2D images don’t cast shadows)
•The perceptual system makes inferences about the structure of the image based on top-down knowledge of where the light source (typically) is
Monocular Cues: Familiar/Relative Size
If we know the size of an object, we can use this to judge how far away it is
•Achieved by comparing the size of the image on the retina with long-term knowledge (top-down control) of how big objects are
Monocular Cues: Familiar/Relative Size
Ittleson 1951
used three sizes of playing cards: normal size, half size and double size
- Participants had to judge the distance of the card
- Distance judgments were based on familiar size
- The normal size card was judged to be 2.28 meters away.
The half size card was judged to be twice as far as this and the double size card half as far away
LimitationsL hypothesis testing
Hypothesis testing:
•How are hypotheses generated, and how to we know when to stop and accept one as correct?
•Why does knowledge sometimes help and at other times hinder perception?
•Put another way: how can we ‘know’ something is wrong, and yet still perceive it incorrectly?
Limitations - the hollow face illusuon
Some familiar stimuli cause a strong bias towards accepting an incorrect hypothesis
Although the face viewed from the back is hollow, it still appears perceptually as a normal face
Therefore, the perceptual hypothesis conflicts with what you know
