Chapter 5: Perceiving Objects and Scenes Flashcards
object recognition
the process of detecting objects in an image and matching those objects to existing, stored representations of what those objects are
inverse projection problem
the task of determining the object responsible for a particular image on the retina involves starting with the retinal image and extending rays out of the eye
viewpoint invariance
the ability to recognize an object seen from different viewpoints
why is it difficult to design a perceiving machine?
The stimulus on the receptors is ambiguous
Objects can be hidden or blurred
Objects look different from different viewpoints
perceptual organization
The process by which elements in a person’s visual field become perceptually grouped and segregated to create a perception
grouping
the process by which elements are put together into coherent units
segregation
the process of separating one area or object from another
Gestalt psychologists
psychologists in the early 1900s who stated that perception is the result of perceptual organization. “the whole differs from the sum of its parts”
structuralism
a school of thought proposed by Wilhelm Wundt in 1879 that distinguished between sensations and perceptions
apparent movement
the illusion of movement
illusionary contours
contour that is perceived even though it is not present in the physical stimulus
gestalt principles
A set of principles that determine how elements in a scene become grouped together
principle of good continuation
points that when connected, result in straight or smoothly curving lines are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path
principle of Pragnanz (good figure)
every stimulus pattern is seen in such a way that the resulting structure is as simple as possible
principle of similarity
similar things appear to be grouped together
principle of proximity
things that are near each other appear to be grouped together
principle of common fate
things that are moving in the same direction appear to be grouped together
principle of common region
elements that are within the same region of space appear to be grouped together
principle of uniform connectedness
a connected region of the same visual properties is perceived as a single unit
what principles overpower proximity?
common region & uniform connectedness
figure-ground segregation
The division of a scene into a figure and a ground
figure
the object that stands out
ground
its background
reversible-figure-ground
a pattern that can be perceived alternatively as either a figure or a ground
properties of figures vs. grounds
- The figure is more “thing-like” and memorable
- The figure is seen as being in front of the ground
- The ground is seen as unform and extends behind the figure
- Border ownership
- Areas lower in the field of view are more likely to be perceived as a figure
border ownership
The border separating the figure from the ground appears to belong to the figure
figural cues
cues within an image that indicate which image is perceived as a figure
2 main figural cues
- areas lower in the field of view are more likely to be perceived as figure
- Figures are more likely to be perceived on the convex side of borders
Vecera et al., 2002 figure-ground experiment
flashed a stimulus at participants and determined which image was seen as the figure. He found that stimuli presented in the lower field were more likely to be figures
Peterson & Salvagio, 2008 convexity experiment
provided participants with displays of stimuli and asked them to indicate whether they perceived the red square as a figure or ground. They found that convex regions were perceived as a figure 89% of the time. They also found that displays with fewer components decreased the likelihood that convex regions were seen as a figure
Gibson & Peterson, 1994 meaningfulness experiment
found that ground formation can be affected by the meaningfulness of a stimuli
recognition by component theory
States that objects are comprised of geons and that we recognize objects based on the arrangement of those geons
geons
Individual 3-dimensional component shapes
how many individual geons are there?
36
who proposed recognition by component theory?
Irving Biederman in the 1980s
benefit of recognition by component theory
Accounts for viewpoint invariance
weaknesses of recognition by component theory
- Couldn’t explain grouping or organization
- Some objects can’t be represented by assemblies of geons
- The RBC theory also doesn’t allow for distinguishing between objects within a given category
components of a scene
Scenes contain 1) background elements 2) multiple objects that are organized in a meaningful way relative to each other and the background
objects vs. scenes
Objects are acted upon and scenes are acted within
gist of a scene
the general description of the type of scene
Potter, 1976 gist of a scene experiment
showed observers a target picture and then asked them to indicate whether they saw that picture as they viewed a sequence of 16 rapidly presented pictures. The observers could do this with almost 100% accuracy even when the pictures were only flashed for 250 ms. Even when the target picture was only specified by a written description, observers achieved an accuracy of almost 90%
Fei-Fei et al., 2007 describing scenes experiment
tried to determine the “absolute threshold” of what people can perceive in a scene by showing them a scene for a limited amount of time. Found that people mainly were guessing up until 40 ms. At 500 ms, people were able to perceive the gist of the scene
masking stimulus
a random pattern that covers the original stimulus so that the stimulus is visible only for a particular amount of time
global image features
features that can be perceived rapidly and are associated with specific types of scenes
global image features include
Degree of naturalness
Degree of openness
Degree of roughness
Degree of expansion
Colour
physical regularities
regularly occurring physical properties of the environment
semantic regularities
characteristics associated with activities that are common in different types of scenes
scene schemas
the knowledge of what a given scene typically contains
palmer 1975 scene schemas experiment
presented a context scene and then flashed a target picture. Palmer then asked participants to identify the object in the target picture and they correctly identified it more often when it corresponded to the scene schema
who proposed the theory of unconscious inference
Hermann von Helmholtz in the 18th century
likelihood principle
we perceive the object that is most likely to have caused the pattern of stimuli we have received
unconsious inference
the process by which we decide which stimulus is most likely to have occurred
prediction
the idea that our past experiences help us make informed guesses about what we will perceive
bayesian inference
the estimate of the probability of an outcome is determined by two factors:
1) prior probability
2) likelihood
prior probability
our initial estimate of the probability of an outcome
likelihood
The extent to which the available evidence is consistent with that outcome
predictive coding theory
A theory that describes how the brain uses our past experiences to predict what we will perceive
The brain determines whether what we’re seeing matches what we expect to be seeing. If the incoming signal matches, nothing happens. However, if it doesn’t a prediction error signal is generated, which is sent back up to higher levels so that the existing prediction can be modified
Lateral occipital complex (LOC)
a brain region within the ventral pathway that is activated when a person views any type of object, but not a texture
Fusiform face area (FFA)
a brain region located in the fusiform gyrus below the inferotemporal (IT) cortex that is specialized to respond to faces (basic face processing)
Prosopagnosia
difficulty recognizing the faces of familiar people following damage to the FFA
occipital cortex function
initial face processing
amygdala function
emotional reaction and familiarity of faces
frontal lobe function
evaluation of attractiveness of faces
superior temporal sulcus (STS)
gaze direction, mouth movements, general face movements
Extrastriate body area (EBA)
a specialized brain area that is activated by pictures of bodies and parts of bodies
Parahippocampal place area (PPA)
a specialized brain area in the temporal lobe that responds to places
spatial layout hypothesis
proposes that the PPA responds to the surface geometry or geometric layout of a scene
3D space hypothesis
the role of the PPA is to represent 3D space more generally, even if there is no scene
contextual relations hypothesis
the role of the PPA is to represent how related objects are organized in space
binocular rivalry
a condition in which the observer perceives either the left-eye image or the right-eye image but not both at the same time because the eyes are receiving totally different images
Tong et al., 1998 binocular rivalry experiment
When the observers perceive the house, activity occurs in the PPA in the left and right hemispheres. When observers perceived the face, activity occurred in the FFA in the left hemisphere
gestalt psychologists beliefs on experience in figure-ground segregation
built-in principles can override experience when determining figure-ground segregation
what are examples of computer vision
autonomous vehicles, cell phones
can computers accurately perceive scenes?
Computers are becoming more accurate, but they often fall short in identifying objects under degraded conditions
critique of structuralism
Structuralism couldn’t explain apparent movement
critique of gestalt approach
Gestalt psychologists’ emphasis on perceptual principles led them to minimize the role of a person’s past experiences in determining perception
how does our brain infer where light is coming from?
using shadows
ockham’s razor
the simplest explanation is the most likely
prediction error signal
errors that occur when we perceive things differently than our predictions
perceptual explanation for anxiety
Some psychologists believe prediction errors are the cause of some anxiety disorders
who discovered the FFA
Nancy Kanwisher
measuring brain activity in the FFA
Used fMRI to determine brain activity in response to pictures of faces and other objects, then subtracted the response to other objects from the response to faces
Helmhotz’s Theory
viewed consciousness as an unconscious inference
Huth et al., 2012 brain activation experiment
participants viewed 2 hours of film clips while in a brain scanner. They analyzed how brain areas were activated by different objects and actions in the films
