Perception-Chapter 5

Geons

**Geometric ions *Irving Biederman proposed 36 different Geons and suggested this number of geons is enough to enable us to mentally represent a large proportion of the objects that we can easily recognize.

The principle of uniform connectedness

*A connected region of visual properties, such as lightness, color, texture, or motion, is perceived as a single unit.

Apparent movement

*An illusion of movement because there is actually no movement in the display just two stationary stimuli flashing on and off.

Non-accidental properties (NAPs)

*Are properties of edges in the retinal image that correspond to the properties of edges in the three-dimensional environment.

Physical regularities

*Are regularly occurring physical properties of the environment. 1) Oblique effect 2) Uniform connectedness 3) Light-from-above heuristic

Semantic regularities

*Are the characteristics associated with the functions carried out in different types of scenes. *Study by Hollingworth (2005) 1) Observers were presented with a scene either with or without a target object. 2) They then saw the target followed by a blank screen and were asked where the object was in the scene or where they would expect it to be. 3) Both groups could accurately predict where the object would be. *Context used to identify images (Stephen Palmer) *The multiple personalities of a blob (Oliva &Torrabla)

Regularities in the environment

*Characteristics of the environment such as, the sky is associated with blue, and forests are associated with green and brown. 1) Physical regularities 2) Semantic regularities

The principle of common region

*Elements that are within the same region of space appear to be grouped together.

Figure-Ground Segregation

*Factors that determine which area is figure: 1) Elements located in the lower part of displays 2) Units that are symmetrical 3) Elements that are small 4) Units that are oriented vertically 5) Elements that have meaning

What causes perceptual segregation>

*Figure-ground segregation - determining what part of environment is the figure so that it "stands out" from the background *Properties of figure and ground 1) The figure is more "thinglike" and more memorable than ground. 2) The figure is seen in front of the ground. 3) The ground is more uniform and extends behind figure. 4) The contour separating figure from ground belongs to the figure (border ownership).

Gist of a scene

*General description of the type of scene *Research has shown that it is possible to perceive the gist of a scene within a fraction of a second. *The overall gist of a scene is perceived first, followed by perception of details and smaller objects within the scene.

Global image properties

*General property of perception: -Our past experiences in perceiving properties of the environment plays a role in determining our perceptions.

Gestalt psychologists

*Gestalt: -a whole configuration that cannot be described merely as the sum of its parts. *A group of psychologists in the 1900s who were trying to discover why it is so difficult to make a perceiving machine.

Law of perceptual organization

*Having rejected the idea that perception is built up of sensations, Gestalt psychologists proposed a number of principles which they called this.

Voxel

*IS a small cube shaped area of the brain about 2 or 3 mm on each side.

Perceptual organization

*Involves the grouping of elements in an image to create larger objects.

Algorithm

*Is a procedure guaranteed to solve a problem.

A scene

*Is a view of a real-world environment that contains: 1) background elements 2) multiple objects that are organized in a meaningful way relative to each other and the background. *Objects are compact and are acted upon *Scenes are extended in space and are acted within.

Bayesian inference

*Modern researcher use this statistical technique *Takes probabilities into account

Specificity coding

*Occurs if an object is represented by the firing of a neuron that fires only to that object.

Distributed coding

*Occurs if an object is represented by the pattern of firing of a number of neurons

Law of Pragnanz

*Or the law of good figure *Or the law of simplicity **Is the central law of Gestalt Psychology *Every stimulus pattern is seen in such a way that the resulting structure is as simple as possible.

The law 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.

Grill-Spector experiment

*Region-of-interest approach: the FFA for each person was determined first by: 1) Showing participants faces and non-faces 2) Finding the area that responded preferentially to faces

Law of Similarity

*Similar things appear to be grouped together. *Grouping also occurs for auditory stimuli.

Contextual modulation

*Stimuli outside of a neuron's receptive field can affect neural firing -happens when these stimuli follow good continuation -happens when the stimuli are perceived as part of the figure.

Viewpoint invariance

*The ability to recognize an object seen from different viewpoints. *Computers have trouble with this.

Light from above heuristic

*The assumption that light is coming from above. *Apparently, people make the light from above assumption because most light in our environment comes from above. -sun -artificial light sources

Viewpoint invariance for geons

*The fact that NAPs are visible from most viewpoints results in another property of geons, viewpoint invariance-the geon can be identified when viewed from most viewpoints.

The Gestalt Laws as heuristics

*The gestalt principles are more accurately described as heuristics. *The reason for rejecting the term "laws" is that the rules of perceptual organization and segregation proposed by the Gestalt Psychologists don't make strong enough predictions to qualify as laws. *We say the Gestalt principles are heuristics because like heuristics, they are best guess rules that work most of the time, but not necessarily all of the time.

The principle of componential recovery

*The main principle of recognition-by-components theory. *If we can perceive an object's geons, we can identify the object. *This principle is what is behind out ability to identify objects in the natural environment even when the parts of the objects are hidden by other objects.

Persistence of vision

*The perception of any stimulus persists for about 250 ms after the stimulus is extinguished. -A picture that is presented for 27ms will be perceived as lasting about 275ms *To eliminate this phenomenon, we use a masking stimulus.

Perceptual segregation

*The perceptual separation of one object from another.

The law of common fate

*Things that are moving in the same direction appear to be grouped together.

The law of proximity or nearness

*Things that are near each other appear to be grouped together.

The law of familiarity

*Things that form patterns that are familiar or meaningful are likely to become grouped together.

Accidental viewpoint

*This edge-on viewpoint that occurs rarely

Recognition-by-Components Theory

*This is how we recognize objects in the environment based on the image on the retina. 1) Objects are recognized by volumetric features called geons -Theory proposes there are 36 geons that combine to make all 3-D objects. -Geons include cylinders, rectangular solids, and pyramids. *According to this theory, the image of a curved edge on the retina indicates the presence of a curved edge in the environment. *This theory also states that we can recognize objects based on a relatively small number of geons

Border ownership

*This property of figure means that, although figure and ground share a contour, the border is associated with the figure.

Masking stimulus

*Used to eliminate the persistence of vision *Usually a pattern of randomly oriented lines, immediately after presentation of a picture.

The principle of synchrony

*Visual events that occur at the same time are perceived as belonging together. *Synchrony can occur without movement, and the elements don't have to change in the same direction as they do in common fate.

Global image features

*Which can be perceived rapidly and are associated with specific types of scenes. *These features are holistic and rapidly perceived.

Discriminability

*each geon can be discriminated from other geons.

Likelihood principle

*objects are perceived based on what is most likely to have caused the pattern

Perceiving Scenes and Objects in Scenes

1) A scene contains: -background elements. -objects organized in meaningful ways with each other and the background. 2) Difference between objects and scenes -A scene is acted within -An object is acted upon

Neuron firing is distributed in two ways:

1) Across groups of neurons within a specific area. 2) Across different areas in the brain.

The Structuralist Approach

1) Approach established by Wundt (late 1800s) 2) States that perceptions are created by combining elements called sensations 3) Structuralism could not explain apparent movement 4) Stimulated the founding of Gestalt psychology in the 1920s by Wertheimer, Koffka, and Kohler

Experiment by Tong et al.

1) Binocular rivalry used again with people 2_ Picture of a house shown to one eye and a face to another 3) Participants pushed button to indicate perception. 4) fMRI showed an increase in activity in -Parahippocampal place area for the house -Fusiform face area for the face

Neurons that respond to perceptual grouping and Figure-ground

1) Contextual modulation

Theory of unconscious inference

1) Created by Helmholtz (1866/1911) to explain why stimuli can be interpreted in more than one way 2) Main Principle - perceptions are result of unconscious assumptions about the environment 3) likelihood principle

Global image features of scenes proposed by Olivia and Torralba:

1) Degree of naturalness 2) Degree of openness 3) Degree of roughness 4) Degree of expansion 5) Color *Such features are holistic and rapidly perceived. *These contain information that results in perception of a scene's structure and spacial layout.

Brain modules involved in perceiving faces

1) Fusiform face area (FFA)- responds only to faces 2) Amygdala (AG)- activated by emotional aspects of faces 3) Superior temporal sulcus (STS)- responds to where the person is looking and to mouth movements 4) Frontal cortex (FC)- activated when evaluating facial attractiveness. *This has led to the conclusion that there is a distributed system in the cortex for perceiving faces.

Experiment by Kamitani & Tong

1) Gratings with different orientations were presented to participants. 2) Responses from fMRI voxels were measured. 3) Activity patterns across voxels varies by grating orientation. 4) An orientation decoder was used to analyze the voxel activity. 5) The decoder could accurately predict which orientation had been presented.

Experiment by Sheinberg & Logothetis

1) Monkey was trained to pull two levers: one for a sunburst one for a butterfly 2) Binocular rivalry was used - each picture shown to one eye at the same time 3) Neuron in the IT cortex that responded only to the butterfly was monitored. 4) Firing was vigorous for only the butterfly

Palmer experiment

1) Observers saw a context scene flashed briefly, followed by a target picture. 2) Results showed that: -Targets congruent with the context were identified 80% of the time . -Targets that were incongruent were only identified 40% of the time.

Research on perceiving gists of scenes

1) Potter showed that people can do this when a picture is only presented for 1/4 second 2) Fei-Fei used masking to show that the overall gist is perceived first followed by details.

The Gestalt Laws of Perceptual Organization

1) Pragnanz 2) Similarity 3) Good Continuation 4) Proximity 5) Common region 6) Uniform connectedness 7) Synchrony 8) Common Fate 9) Meaningfulness or familiarity

Experiment by Kay et al.

1) Presented 1,750 photographs to an observer 2) Measured activity in 500 voxels to -Position of image -Orientation of image -Degree of detail in image 3) Decoder was tested by using new images -Performance was 92% and 72% for two observers

Review of sensory coding

1) Specificity coding 2) Distributed coding

The Challenge of Object Perception

1) The stimulus on the receptors is ambiguous. -Inverse projection problem: An image on the retina can be caused by an infinite number of objects. 2) Objects can be hidden or blurred. -Occlusions are common in the environment.

Why is it so difficult to design a perceiving machine?

1) The stimulus on the receptors is ambiguous. 2) Objects can be hidden or blurred 3) Objects look different from different view points.

The Gestalt Approach

1) The whole differs from the sum of its parts. 2) Perception is not built up from sensations, but is a result of perceptual organization. 3) Principles of perceptual organization. -Pragnanz - every stimulus is seen as simply as possible -Similarity - similar things are grouped together

Properties of geons

1) View-invariant properties - aspects of the object that remain visible from different viewpoints 2) Non-accidental properties - properties of edges in the retinal image that correspond with the 3-D environment 3) Discriminability - the ability to distinguish geons from one another 4) Principle of componential recovery - the ability to recognize an object if we can identify its geons

For trials that only included Harrison Ford's face, results showed that FFA activation:

1) was greatest when picture was correctly identified as Ford. 2) was less when picture was identified as other object. 3) Showed little response when there was no identification of a face **Neural processing is associated with both the presentation of the stimulus and with the response to the stimulus.

Uniform connectedness

Objects are defined by areas of the same color or texture.

Oblique effect

People perceive horizontals and verticals more easily that other orientations.