Midterm #2 Flashcards
Computer vision: Object recognition
Detection of objects in an image and then matching those objects to existing, stored representations of what those objects are to create a secene.
Why is it hard to design a perceiving machine?
The stimulus on the receptors is ambiguous (inverse projection problem). Objects can be hidden or blurred (occlusions are common in the environment. Objects look different from different viewpoints (Viewpoint invariance).
Inverse projection problem
The fact that a particular image on the retina (or a computer vision machine’s sensors) can be caused by an infinite number of objects.
Viewpoint invariance
The ability to recognize an object regardless of the viewpoint. This is a difficult task for computers to perform.
Perceptual Organization
Approach established by Wundt in the late 1800s. States that perceptions are created by combining elements called sensations. Stimulated the founding of Gestalt psychology. The whole differs from the sum of its parts: perception is not built up form sensations but is a result of perceptual organization.
Structuralism
Wilhelm Wundt. Perceptions are created by combining elements called sensations. Distinguished between sensations and perceptions.
Apparent movement
An illusion of movement. When two stimuli that are in slightly different positions are flashed one after another with the correct timing, movement is perceived between the two stimuli. But there is actually movement in the display, just two stationary stimuli flashing on and off.
Illusory contours
Appear real but have physical edge. Illusory contours represent the edges of the cube. Called illusory because they aren’t actually present in the physical stimulus.
The Gestalt Laws of Perceptual organization
Involves the grouping of elements in an image to create larger objects.
Gestalt law of Pragnanz
Every stimulus is seen as simply as possible.
Gestalt law of Similarity
Similar things appear to be grouped together.
Gestalt law of Good Continuation
Connected points resulting in straight or smooth curves are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path.
Gestalt law of Proximity
Things that are near each other appear to be grouped together.
Gestalt law of Common Region
Elements that are within the same region of space appear to be grouped together.
Gestalt law of Uniform connectedness
A connected region of visual properties, such as lightness, colour, texture, or motion, is perceived as a single unit.
Gestalt law of Common Fate
Things that are moving in the same direction appear to be grouped together.
Perceptual Segregation
The perceptual seperation of one object from another. Figure-ground segregation: determining what part of the environment is the figure, so that it “stands out” from the background.
The properties of figure and ground
- The figure is more “thinglike” and more memorable than the ground.
- The figure is seen in front of the ground.
- The ground is more uniform and extends behind figure.
- The contour separating figure from the ground belongs to the figure (border ownership).
Figural cues proposed by the Gestalt psychologists
Areas lower in the field of view are more likely to be perceived as figure.
Heuristics
Rules of thumb that provide a best-guess solution to a problem. Gestalt principles are more accurately described as heuristics instead of laws.
An algorithm
A procedure that is guaranteed to solve a problem.
The role of perceptual principles and experience in determining which area is figure.
Gestalt psychologists’ emphasis on perceptual principles led them to minimize the role of a person’s past experiences in determining perception.
Meaningfulness experiment, Gibson and Peterson (1994)
Experiment that argued against the idea of minimizing the role of a person’s past experiences in determining perception by showing that figure-ground formation can be affected by the meaningfulness of a stimulus.
Recognition by Components (RBC) theory
Objects are comprised of individual geometric components called geons. Geons: three-dimensional shapes, like pyra-mids, cubes, and cylinders.
Shortcomings of RBC theory
Many aspects of object perception that the RBC theory could not explain:
Grouping or organization like the Gestalt principles do. Some objects can’t be represented by assemblies og geons. The RBC theory doesn’t allow for distinguishing between objects within a given category.
Non-accidental properties (NAPs).
Properties of edges in the retinal image that correspond to the properties of edges in the three-dimensional environment.
Perceiving Scenes and Objects in Scenes
Scene: 1) background elements, 2) multiple objects that are organized in a meaningful way relative to each other and the background.
Objects: compact and acted upon.
Scenes: Extended in space and are acted within.
Discriminability of geons
The fact that each geon has a unique set of NAPs results in a property of geons called discriminability - each geon can be discriminated from other geons.
Geons and Viewpoint invariance
The fact that NAPs are visible from most viewpoints results in property of geons called viewpoint invariance - the geon can be identified when viewed from most viewpoints.
Principle of componential recovery
The ability to identify an object if we can identify its geons. This principle is what is behind our ability to identify objects in the natural environment even when parts of the objects are hidden by other objects.
Gist of a scene
Perceiving scenes presents a paradox: scenes are often large and complex, however, despite this size and complexity, you can identify most scenes after viewing them for only a fraction of a second.
What enables observers to perceive the gist of a scene so rapidly?
Global image features: can be perceived rapidly and are associated with specific types of scenes. Past experiences in perceiving properties of the environment: blue associated with open sky, landscapes are often green and smooth, verticals and horizontals are associated with buildings.
Degree of naturalness
Natural scenes have textured zones and undulating contours. Man-made scenes are dominated by straight lines and horizontals and verticals.
Degree of openness
Open scenes, such as the beach, often have a visible horizon line and contain few objects. The forest is an example of a scene with a low degree of openness.
Degree of roughness
Smooth scenes (low roughness) like the beach contain fewer small elements. Scenes with high roughness like the forest contain many small elements and are more complex.
Degree of expansion
The convergence of parallel lines (railroad tracks that appear to vanish in the distance).
Color in scenes
Some scenes have characteristics colours, like the beach scene (blue) and the forest (green and brown).
Physical Regularities
Regularly occurring physical properties of the environment. There are more vertical and horizontal orientations in the environment than oblique (angled) orientations. This occurs in human-made and natural environments.
Light-from-above heuristic
The assumption that light is coming from above. People make this assumption because most light in our environment comes from above.
Semantic Regularities
The characteristics associated with the functions carried out in different types of scenes. What we expect to see in different contexts influences our interpretation of the identity blurry “blobs” in scenes.
The Role of Inference in Perception
People use their knowledge of physical and semantic regularities to infer what is present in a scene.
Helmholtz’s Theory of Unconscious Inference
States that some of our perceptions are the result of unconscious assumptions we make about the environment. Was proposed to account for our ability to create perceptions from stimulus information that can be seen in more than one way.
Likelihood principle
Aspect of the theory of unconscious inference, which states that we perceive the object that is most likely to have caused the pattern of stimuli that we have received.
Bayesian inference
We perceive what is most likely to have created the stimulation we have received in terms of probabilities.
Contextual Modulation
When we add a field of randomly oriented lines, these lines, which fall outside the neuron’s receptive field, cause a decrease in how rapidly the neuron fires to the single vertical line. This effect of the stimuli that fall outside of the neuron’s receptive field is called contextual modulation, because the context within which the bar appears affects the neuron’s response to the bar.
How does the brain respond to objects?
Objects are represented by distributed coding, so a specific face would be represented by the pattern of firing of a number of neurons that respond to faces. There is a distributed system in the cortex for perceiving faces. The activation caused by other objects is also distributed, with most objects activating a number of different areas in the brain.
Binocular rivalry
Connections between neural responses and perception have been determined by using this perceptual phenomenon: if one image is presented to the left eye and a different image is presented to the right eye, perception alternates back and forth between the two eyes.
Predictive coding
A theory that describes how the brain uses our past experiences - our our “priors,” as Bayes put it - to predict what we will perceive. A way that the brain implements prediction.
Lateral occipital complex (LOC)
Active when the person views any kind of object (animal, face, house, or tool) but not when they view a texture, or an object with the parts scrambled. Builds upon the processing that took place in lower-level visual regions.
The Neural Correlates of Face Perception (FFA)
Fusiform face area (FFA): fMRI to determine brain activity in response to pictures of faces and other objects such as household objects, houses, and hands. Subtracted the response to the other objects form the response to the faces.
Prosopagnosia
Difficulty recognizing the faces of familiar people.
Neural representation of other categories of objects
Exrastriate body area (EBA): activated by pictures of bodies and parts of bodies.
Neural representation of other categories of objects, Alex Huth and coworkers (2012).
Participants viewed 2 hours of film clips while in a brain scanner. Analyze how individual brain areas were activated by different objects and actions in the films.
Brain responses to Scenes
Parahippocampal place area (PPA) (parahippocampal cortex (PHC)). Spatial layout hypothesis.
The relationship between perception and brain activity, Frank Tong and coworkers (1998).
Binocular rivalry. When the observers perceived the house, activity occured in the parahippocampal place area (PPA) in the left and right hemispheres (red ellipses). When observers perceived the face, activity occurred in the fusiform face area (FFA) in the left hemisphere (green ellipse).
Akinetopsia
Motion blindness. Motion is either very difficult or impossible to perceive. Traumatic brain injury. Neurodegenerative disease such as Alzheimer’s. Epilepsy, hallucinogen persistent perception disorder (HPPD). Damage to V5 medial temporal.
L.M.
Lost the ability to perceive motion when she suffered a stroke that damaged an area of her cortex involved in motion perception. Her condition is called motion agnosia, and made it difficult for her to pour tea or coffee into a cup because the liquid appeared frozen. Another effect was the sudden appearance or disappearance of people and objects.
Attentional capture
The ability of motion to attract attention. This effect occurs not only when you are consciously looking for something, but also while you are paying attention to something else.
Real motion
Actual motion of an object. Perceiving a car driving by, people walking. Observers perceive shapes more rapidly and accurately when an object is moving.
Illusory motion
Perception of motion when there actually is none. Eg., apparent motion: no actual motion between the stimuli.
Induced motion
Occurs when motion of one objects (usually a large one) causes a nearby stationary object (usually a smaller one) to appear to move.
Motion aftereffects
Occur after viewing a moving stimulus for 30 to 60 seconds and viewing a stationary stimulus, which appears to move. Eg,, waterfall illusion.
Movement as an organizing function
Movement serves an organizing function which groups smaller elements into larger units. The motion of individual birds becomes perceived as the larger unit of the flock, in which the birds are flying in synchrony with each other.
Biological movement
When a person or animal moves, movement of individual units - arms, legs, and body - become coordinated with each other.
Event
Segment of time at a particular location that is perceived by observers to have a beginning and an end.
Event boundary
The point in time when each of these events ends and the next one begins. Perception of movement plays an important role in separating activities into meaningful events. More likely to occur when there is change in speed or acceleration of movement.
Social perception
Social cues are often linked to movement. Point-light walkers:
1) Social interaction: the people were near interacting in various ways.
2) Non-social interaction: the people were near each other but were acting independently. The observers were able to indicate whether the two people were interacting with each other or were acting independently.
Taking action
Navigating through the environment (safely). Watching and playing sports. Pouring drinks etc.
The Ecological Approach to Motion Perception
Looking for information in the environment that is useful for perception. According to Gibson, information is located not on the retina but “out there” in the environment. Optic Array.
