Week 5 Flashcards
Pareidolia
is the phenomenon of perceiving a vague stimulus as something of importance.
The visual system may be biased to create (recognize) a perception that is ambiguous in the stimulus
parahippocampal cortex
PPA
Responds best to spatial layout (including
buildings and places, top row)
Extrastriate body area (EBA), in
occipitotemporal cortex
Responds best to pictures of full bodies and body parts (top row, not faces)
Binocular rivalry
each picture shown to one eye at the same time.
Picture of a house shown to one eye and a face to another. You can only perceive (i.e. be aware of) one at a time.
Experiment by Tong et al.
Used Binocular rivalry
Participants pushed button to indicate
what they perceived.
fMRI showed an increase in activity in
* Parahippocampal place area for the house
* Fusiform face area for the face
– Demonstrates how perception and
recognition correlate with specific brain
activity.
Inverse projection problem
An image on the retina can be caused by an infinite number of objects. [Many different distal stimuli can create similar proximal stimulus.]
Object perception is hard
- The stimulus on the receptors is ambiguous.
- the inverse projection problem - Objects can be hidden or blurred.
- Objects look different from alternative viewpoints
- viewpoint invariance
Viewpoint invariance
the ability to recognize an object regardless of the viewpoint/perspective.
hard for computers to perform
structuralism
Established in late 1800s by Wilhelm Wundt
– Stated that perceptions are created by combining elements called “sensations.”
– Hierarchical, well-ordered approach to perception. Strongly “bottom-up.”
– However, structuralism could not explain apparent movement
Apparent Movement
Motion is perceived when separated objects (e.g. dots, bars, etc.) flash in different locations, but without the necessary sensory atoms predicted by structuralism
Gestalts approach to object perception
-
The whole differs from the sum of its parts.
– Perception is not built up from sensations, but is a result of perceptual organization. [strong top-down influence]
– The mind (somehow) makes simple assumptions about objects in order to recognize them in the environment. -
Principles of perceptual organization
– 8 principles for organizing objects within perceptual scenes have been offered: pragnatz (good figure/simplicity), similarity, good continuation, proximity (nearness), common region, uniform connectedness, common fate, and meaningfulness.
- Pragnanz
(good figure/simplicity)
* Every stimulus is seen as simply as possible
* The easiest interpretation takes fewer cognitive resources.
- Similarity
- Similar things are grouped together
- Color is one measure of similarity (e.g. grouped into columns), but it could be shape, orientation, etc.
- Good continuation
Connected points resulting in straight or smooth curves belong together.
– Lines are seen as following the smoothest path
– Holds true even complex images
- Common region
elements in the same defined region tend to be grouped together.
- Proximity
Things that are near to each other are grouped together.
- Uniform connectedness
connected regions of visual stimuli are perceived as a single unit.
- Meaningfulness or familiarity
Stimuli form groups if they appear familiar or meaningful8
- Common fate
Things moving in same direction are grouped together
figure-ground segregation
determining what part of the environment is the figure and which is the background.
Properties of figure
More “thinglike” (i.e. can be acted upon) and more memorable than ground.
– The figure is seen in front of the
ground.
Properties of ground
– The ground is more uniform (e.g. one color or texture) and extends behind the figure.
– The contour separating figure from ground belongs to the figure (border ownership).
Factors that determine which are is the figure:
Elements located in the lower part of displays tend to be interpreted as figures (objects of interest)
– Units that are symmetrical
– Elements that are small
– Units that are oriented vertically
– Elements that have meaning
RBC theory
Definition: We recognize objects by volumetric features called geons.
(36 geons (cylinder, rectangular solids, pyramids, etc.) that combine to make
all 3D objects.)
Geons have the following properties to solve problems of object perception:
● View-invariant properties
● Non-accidental properties
● Discriminability
View-invariant properties
The ability to recognize an object regardless of the viewpoint/perspective.
○ Edges that are usually visible.
○ Because of these edges, we can tell that it’s a rectangle.
Non-accidental properties
Edges in the retinal image correspond with the 3-D environment.
○ We can always recognize TYPICAL objects, but not accidental objects.
Discriminability
The ability to distinguish geons from one another.
○ Because we have the view-invariant and non-accidental properties, we can distinguish each of the geons very easily.
Principle of componential recovery
Definition: The ability to recognize an object if we can identify its geons.
scene
A scene is a real-world environment that contains:
- background elements.
- objects organized in meaningful ways with each other and the background.
gist
A gist of a scene is a quick understanding and recognition of major elements in a complex picture or sequence.
● Potter, Mary (1976) showed that people can do this very accurately when a picture is only presented for 250 ms (90% in trial below).
● Li Fei Fei (2007) extended this research to demonstrate the range of information that becomes available with more viewing time, extending from 27–500ms.
Physical regularities
regularly occurring physical properties
Oblique effect:
people perceive horizontals and vertical more easily than other orientations.
Uniform connectedness
objects are defined by areas of the same color or texture.
Light-from-above assumption
light in natural environment comes from above us.
Theory of unconscious inference
Perceptions are result of unconscious assumptions about the environment. (top-down)
Likelihood principle
objects are perceived based on what is most likely to have caused the pattern. (so we can make the unconscious inference.)
Bayesian Inference
○ A modern interpretation of the Likelihood Principle.
○ Takes prior experience/ probabilities into account.
Predictive coding
suggests that prior information establishes expectations that are compared with current inputs.
if signal normal you proceed, if its unexpected you get a prediction error PE. this pe may cause you to reconsider your expectations or reevaluate the stimuli.
Contextual modulation
Stimuli (images) outside of a neuron’s receptive field can affect neural firing. happens when:
● when these stimuli follow good continuation.
● when the stimuli are perceived as part of the figure.
● when the stimuli are consistent with the role of top-down influence on perception and
recognition.
Good continuation: connected points
result in a straight line
Real motion
an object is physically moving across space.
Illusory motion
no real motion present, but it is perceived.
Apparent motion
Stationary stimuli are alternately presented in different locations.
(Basis of movement in movies and TV)
Induced motion
Real movement of one object results in the perception of movement in another object.
○ moving clouds may make the moon appear to move.
Motion After Effect
a. Observer looks at (perceives) movement of object for 30 to 60 seconds.
b. Then observer looks at a stationary object.
c. Movement occurs in the opposite direction from the original perceived movement.
(The waterfall illusion is an example of this)
What accounts for the motion after effect?
MT Medial Temporal Lobe
Spiral Motion After Effect
– MT cells converge on cells in the medial superior temporal – dorsal (MSTd) area.
– These cells respond to ‘optic flow’ – the relative motion of you going through your environment.
– Watching an expanding optic flow pattern can selectively adapt MSTd neurons.
Reichardt detectors
are circuits that fire to real movement in a specific direction, while the eye is stationary.
Aperture problem
observing a small portion of a larger stimulus may lead to misleading (ambiguous) information about the direction of movement
- Activity of a single complex cell does not provide sufficient information about
direction of movement.
Solution to Aperature Problem
A number of cells in V1 have hierarchical convergence into higher areas. One of which is middle temporal (MT) cortex , which is part of dorsal (where/how) stream. This area is responsible for directional motion, and more specifically, coordinated motion.
