Topic 5: Object Perception Flashcards
Object Recognition
the ability to identify objects
Inverse Projection Problem
the idea that a particular image on the retina could have been caused by an infinite number of different objects
this means that the retinal image does not unambiguously specify a stimulus
Viewpoint Invariance
the condition in which object properties don’t change when viewed from different angles
responsible for our ability to recognize objects when viewed from different angles
Perceptual Organization
the process by which small elements become perceptually grouped into larger objects
Grouping
in perceptual organization, the process by which visual events are “put together” into units or objects
Segregation
the process of separating one area or object from another
Gestalt Psychologists
an approach to psychology that developed as a reaction to structuralism
the Gestalt approach proposes principles of perceptual organization and figure-ground segregation and states that “the whole is different than the sum of its parts”
Structuralism
the approach to psychology, prominent in the late 19th and early 20th centuries, that postulated that perceptions result from the summation of many elementary sensations
the Gestalt approach to perception was, in part, a reaction to structuralism
Apparent Movement
an illusion of movement that occurs when two objects separated in space are presented rapidly, one after another, separated by a brief time interval
Illusory Contours
contour that is perceived even though it is not present in the physical stimulus
Principles of Perceptual Organization
principles describe how elements in a scene become grouped together
many of these principles were originally proposed by the Gestalt psychologists, but new principles have also been proposed by recent researchers
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
Pragnaz
a Gestalt principle of perceptual organization that states that every stimulus pattern is seen in such a way that the resulting structure is as simple as possible
also called the principle of good figure or the principle of simplicity
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, such as lightness, color, texture, or motion, is perceived as a single unit
Figure-Ground Segregation
the perceptual separation of an object from its background
Figure
when an object is seen as separate from the background (the “ground”), it is called a figure
Ground
in object perception, the background is called the ground
Reversible Figure-Ground
a figure-ground pattern that perceptually reverses as it is viewed, so that the figure becomes the ground and the ground becomes the figire
the best known reversible figure-ground pattern is Rubin’s vase-face pattern
Border Ownership
when two areas share a border, as occurs in figure-ground displays, the border is usually perceived as belonging to the figure
Figural Cues
visual cues that determine how an image is segregated into figure and ground
Recognition By Components (RBC) Theory
theory that states that objects are comprised of individual geometric components called geons, and we recognize objects based on the arrangements of those geons
Geons
according to recognition by components (RBC) theory, individual geometric components that comprise objects
Scene
a view of a real-world environment that contains (a) background elements and (b) multiple objects that are organized in a meaningful way relative to each other and the background
Gist of a Scene
general description of a scene
people can identify most scenes after viewing them for only a fraction of a second, as when they flip rapidly from one TV channel to another
it takes longer to identify the details within a scene
Persistence of Vision
a phenomenon in which perception of any stimulus persists for about 250 ms after the stimulus is physically terminated
Visual Masking Stimulus
a visual pattern that, when presented immediately after a visual stimulus, decreases a person’s ability to perceive the stimulus
this stops the persistence of vision and therefore limits the effective duration of the stimulus
Global Image Features
information that may enable observers to rapidly perceive the gist of a scene
features associated with specific types of scenes include degree of naturalness, degree of openness, degree of roughness, degree of expansion, and color
Regularities of the Environment
characteristics of the environment that occur regularly and in many different situations
Physical Regularities
regularly occurring physical properties of the environment
for example, there are more vertical than horizontal orientations in the environment than oblique (angled) orientations
Light-From-Above Assumption
the assumption that light usually comes from above, which influences our perception of form in some situations
Semantic Assumptions
characteristics associated with the functions associated with different types of scenes
these characteristics are learned from experience
for example, most people are aware of the kinds of activities and objects that are usually associated with kitchens
Scene Schema
an observer’s knowledge about what is contained in typical scenes
an observer’s attention by knowledge of what is usually found in the scene
Likelihood Principle
the idea proposed by Helmholtz that we perceive the object that is most likely to have caused the pattern of stimuli we have received
Unconscious Principle
the idea proposed by Helmholtz that some of our perceptions are the result of unconscious assumptions that we make about the environment
Bayesian Influence
a statistical approach to perception in which perception is determined by taking probabilities into account
these probabilities are based on past experiences in perceiving properties of objects and scenes
Prior Probability
in Bayesian influence, a person’s initial estimate of the probability of an outcome
Likelihood
in Bayesian influence, the extent to which the available evidence is consistent with a particular outcome
Predictive Coding
a theory that describes how the brain uses our past experiences to predict what we will perceive
Lateral Occipital Complex (LOC) Area
area of the brain that is active when a person views any kind of object – such as an animal, face, house, or tool – but not when they view a texture, or an object with the parts scrambled
Fusiform Face Area (FFA)
an area in the human inferotemporal (IT) cortex that contains neurons that are specialized to respond to faces
Prosopagnosia
a form of visual agnosia in which the person can’t recognize faces
Extrastriate Body Area (EBA)
an area of the temporal lobe that is activated by pictures of bodies and parts of bodies
Parahippocampal Place Area (PPA)
an area in the temporal lobe that is activated by indoor and outdoor scenes
Spatial Layout Hypothesis
proposal that the parahippocampal cortex responds to the surface geometry or geometric layout of a scene
Binocular Rivalry
a situation in which one image is presented to the left eye, a different image is presented to the right eye, and perception alternates back and forth between the two images
Neural Mind Reading
using a neural response, usually brain activation measured by fMRI, to determine what a person is perceiving or thinking
Multivoxel Pattern Analysis
in neural mind reading, a technique in which the pattern of activated voxels is used to determine what a person is perceiving or thinking
Decoder
a computer program that can predict the most likely stimulus based on the voxel activation patterns that were previously observed in the calibration phase of neural mind reading
Expertise Hypothesis
the idea that human proficiency in perceiving certain things can be explained by changes in the brain caused by long exposure, practice, or training
What kind of information is required to identify a distal stimulus?
light sources: primary (sun, light bulbs), secondary (moon, walls)
reflectance of surfaces: proportion of light reflected; absorption spectra: surfaces absorb certain wavelengths
surface orientation: position of surface causes different amount of light to fall on it/reflect off it
viewing position: scene appears different from different viewing angles
What is the inverse projection problem?
how do you go from the proximal stimulus to identifying the distal stimulus?
“uncreate” the image, using reverse geometry?
retinal image is 2-D, real world is 3-D
any 2-D image may have many potential 3-D sources that created it (underdeterminism)
but the visual system selects the proper interpretation (most of the time)
how does it do this?
What is contour?
border between light and dark areas in an image
What is the Ganzfeld (“total field”) experiment on contour detection?
sort of sensory deprivation; developed to test for telepathic communication
translucent ping-pong ball halves placed over eyes; headphones deliver white noise
causes some observers to “blank out” or hallucinate
sharp luminance contours must be important to visual system
What are microsaccades?
minute, involuntary, almost imperceptible eye movements that occur during fixations; purpose seems to be to change the position of the image on the retina
What is the Pritchard (1961) experiment on dynamic stimuli?
observers wore contact lenses with attached device
projected constant image onto retina
image disappeared within ~3 seconds
eye responds best to changing stimuli; static pattern will quickly fade from view
What is the basis of Gestalt psychology?
movement could be produced by a succession of stationary stimuli
What is the motto of Gestalt psychology?
“the whole is different than the sum of its parts”
What are illusory contours?
contours not present on the retina, but still affect contour perception
end-stopped cell are activated by illusory contours
What are the general properties of figures as stated in figure-ground segregation?
appear to be in front
are smaller
have well-defined shape
are meaningful
have more detail
differ from background in lightness
What is the law of proximity/nearness?
things near to each other tend to be grouped together
What is the law of similarity?
similar things tend to be grouped together
What is the law of good continuation?
points that, if connected, would result in either straight or smoothly curving lines, tend to be seen as belonging together; and lines tend to follow the smoothest path
What is the law of closure?
a space enclosed by a contour (real or illusory) tends to appear as a figure
What is the law of common fate?
things that are moving in the same direction tend to be grouped together
What is the law of meaningfulness/familiarity?
things that are meaningful or familiar tend to form groups
What is the law of pragnanz?
“good figure” or “simplicity”
every stimulus pattern is seen in such a way that the resulting structure is as simple as possible
What are the pros and cons of Gestalt psychology?
pro: holistic approach
cons: operates post hoc (not good for predictions), not good at explanations, vague definitions (simplicity)
What is recognition?
perceiving something as previously known
What is identification?
naming or classifying an object
What are template theories of object perception?
compare input to a model or “template” stored in memory
stimulus categorized by exact match
What are the pros of template theories?
successfully used by machines
e.g., MICR numbers at the bottom of a cheque
What are the cons of template theories?
intolerant to variations in a stimulus
too many templates required
cannot handle novel stimuli
cannot handle context
What are feature-based theories of object perception?
Pandemonium (Selfridge, 1959)
stage 1: “image demon” gets sensory input (has a big eye)
stage 2: “feature demons” analyze input in terms of features (each have a t-shirt with symbol they’ll shout if they see their symbol)
stage 3: “cognitive demons” determine which groups of features are present (also have a t-shirt, listening to their features so they shout)
stage 4: “decision demon” identifies pattern by listening for cognitive demon shouting the loudest (listen to the loudest demon)
What are the pros of feature-based theories?
evidence: “feature-detectors” physiologically relate to cells in visual system
can identify wide range of stimuli – just specify component features
What are the cons of feature-based theories?
doesn’t define “feature”: single line segment? two lines forming an angle? curved line?
cannot handle Gestalt organizational principles: when is a row of dots a line?
cannot handle context
what about real-life/3-D objects?
What is the computational approach?
multi-stage approach that applies precise mathematical formulas
What is the primal sketch stage in the computational approach?
image analyzed to determine “primitives”: contours, object edges
based on natural constraints: consistent, universal properties of the world
e.g., changes in luminance at borders are abrupt; fuzzy border doesn’t delineate a different object – it’s a property of shading
What is the 2 1/2-D sketch stage in the computational approach?
primitives are grouped (e.g., via Gestalt principles), and processed using depth information
structured with reference to the observer’s point of view
What is the 3-D model representation stage in the computational approach?
3-D component parts and their relations are determined, and matched to stored knowledge to identify object
is independent of viewing angle/point of view
only this last stage is available to consciousness
What are the pros of the computational approach?
can be highly accurate
takes world knowledge into account, top-down processing
What are the cons of the computational approach?
difficult to identify neural circuits for this processing
What is recognition by components?
basis: visual scene can be decomposed into basic elements that are constant
components called “geons” (geometric icons): 36 basic volumetric shapes that can be modified (length, width, etc.), and yet remain identifiable (cylinder, brick, cone)
What is the principle of componential recovery?
if an object’s geons can be determined, then the object can be identified – even if the object is partially obsured
What are the pros of recognition by components?
has well-defined features
can handle variation, novel stimuli
What are the cons of recognition by components?
cannot handle context
may be too broad – objects also differ in their details
not all 3-D objects easily decompose into parts (e.g., puddle)
What is shape constancy?
perceived shape of an object remains constant despite variations in orientation
knowledge of depth is important (indicates orientation of object), as is assumption of rigidity
What is the objective view?
what is the real shape of the object?
distal stimulus
What is the projective view?
what is the shape of the image on the retina?
proximal stimulus
What was the Thouless (1931) experiment on shape constancy?
observers viewed a circle at different angles
task: match retinal images with given ellipses
observers never produced correct projective view; there was always some shape constancy at work
critical factor in shape constancy: knowing your viewing angle/orientation of the object
What is bottom-up processing?
data-driven, data-based
incoming sensory stimuli are gathered by receptors and combined into a whole
representation created via Gestalt laws
What is top-down processing?
conceptually driven, knowledge-based
higher-level cognitive processes like memories, beliefs, or expectations affect interpretations of (possibly ambiguous) stimulus input gathered by the senses
may tell us “where to look”
What is perceptual priming?
perceiving and identifying an object is affected by previous experience with that object (or another one similar in form)
e.g. seeing the word boat will subsequently enhance processing of the word goat
What is a perceptual set?
predisposition to interpret a stimulus in a particular way, based on past experience of knowledge
e.g., Stroop effect: you can’t help but read the words
What are schemas?
mental structures that help us organize the world into a coherent, meaningful whole
are learned, thus affected by context, culture, and experience
What is pareidolia?
illusion or misperception involving a vague or obscure stimulus being perceived as something clear and distinct
Why is a balance needed between top-down and bottom-up processing?
only top-down –> see only what you expect to see, even if it differs from reality
only bottom-up –> you can’t use anything you’ve learned about the (perceptual) world
What is telepathy?
direct mind-to-mind communication
What is clairvoyance?
perception of distant events, beyond the range of vision
What is precognition?
perception of future events (not just guessing)
What is telekinesis/psychokinesis?
acting upon objects directly with the mind
