Test 2 Psy 2600 Sensation and Perception

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Computers + Object Perception

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Computers + Object Perception

-Poor object perception -stimulus on receptor is ambiguous -objects can be hidden or blurred

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Viewpoint invariance

-Object properties don't change when viewed from different angles -How humans recognize objects from different angles

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Perceptual Organization

Small objects become perceptually grouped into larger objects

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Gestalt psychology

-Principles of perceptual organization and figure-ground segregation -"Whole is different than the sum of its parts"

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-Wundt -Perception results from the summation of sensations

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Apparent movement

-Illusion of movement when two objects separated in space are presented rapidly, one after another, separated by a brief time interval -Perceptual organization creates movement (contradicts structuralism)

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Illusory contours

Contour that is perceived even though it is not present in the physical stimulus

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Principle of good continuation

Points, when connected, result in straight or smoothly curving lines seen as belonging together, following the smoothest path

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Principle of Pragnanz/Good Figure/Simplicity

Every stimulus pattern is seen in a way that the resulting structure is as simple as possible

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Principle of Similarity

Similar things appear to be grouped together

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Principle of Proximity/Nearness

Things that are near each other appear to be grouped together

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Principle of Common Fate

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

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Principle of Common Religion

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

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Principle of Uniform Connectedness

Connected regions of a visual stimulus are perceived as a single unit

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Figure-ground segregation

The perceptual separation of an object from its background

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Reversible figure-ground

-A figure-ground pattern that perceptually reverses as it is viewed (figure and ground switch) -Ex Rubin's vase-face pattern

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Border ownership

When two areas share a border (in figure-ground displays) the border is usually perceived as belonging to the figure

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Gibson and Peterson experiment

-Standing woman in a doorframe -Meaningfulness of stimulus matters

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-A view of real-world environments -contains background elements -contains objects organized in meaningful ways relative to each other and the background

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Gist of a scene

General description of a scene, can be perceived in 1/4 seconds

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Persistence of vision

-Perception of any stimulus persists for about 250ms after the stimulus is physically terminated -Can be disrupted by visual masking

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Visual masking stimulus

Visual pattern presented after a visual stimulus to decrease a person's ability to perceive the stimulus. Stops persistence of vision and effective duration of the stimulus

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Global image features

Degree of naturalness, openness, roughness, expansion, and colour

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Degree of naturalness

-Natural scenes have textured zones and undulating contours -Man-made scenes have horizontal and vertical straight lines

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Degree of openness

Open scenes typically have a visible horizon line and contain few objects (Ocean and streets)

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Degree of roughness

Smooth scenes (ocean) contain fewer small elements, whereas high roughness contain many small elements and are more complex

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Degree of expansion

Convergence of parallel lines (ex. railroad tracks that appear to vanish in distance) have high degree of expansion. Dependent on observers, viewpoint

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Physical regularities

-Regularly occurring physical properties of the environment -vertical + horizontal orientations more common than diagonals

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Observer's knowledge about what is contained in typical scenes

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Likelihood Principle

Helmholtz; we perceive the object that is most likely to have caused the pattern of stimuli we have received

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Unconscious Inference

Helmholtz; some perceptions are the result of unconscious assumptions that we make about the environment

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Bayesian inference

-Perception determined by accounting for probability -Probability based on past experiences in perceiving properties of objects and scenes

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Prior probability

In Bayesian inference, a person's initial estimate of the probability of an outcome

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In Bayesian inference, the extent to which the available evidence is consistent with a particular outcome

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Binocular Rivalry

-One image presented to OS, one image presented to OD, and perception alternates back and forth between the two images -Attention activates one brain area over another

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Brain areas and facial responses

Occipital cortex: initial processing of face information FFA: Face identification Amygdala: Emotional aspects of faces + reactions to facial expressions STS: Evaluate where a person is looking + mouth movements Frontal cortex: Evaluate a face's attractiveness

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Visual scanning

Moving the eyes to focus attention on different locations, on objects, or in scenes

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The brief pause of the eye that occurs between eye movements as a person scans a scene

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Saccadic eye movement

Rapid eye movement between fixations that occurs when scanning a scene

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Overt vs Covert attention

Overt: involves looking directly at attended object Covert: attention without looking

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Visual salience

Characteristics that cause stimuli to stand out and therefore attract attention

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Spatial attention

Attention to a specific location

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A cue stimulus is presented to direct an observer's attention to a specific location where a test stimulus is likely to be presented. Posner used this to show attention enhances processing of a stimulus presented at cued location

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Features (colour, form,motion, location) are combined to create our perception of a coherent object. Occurs across senses

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Binding problem

Problem of how neural activity in many separated areas in the brain is combined to create a perception of a coherent object

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Feature integration theory (FIT)

Anne Treisman; explains how an object is broken down into feature and how these features are recombined to result in a perception of the object

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Preattentive stage (FIT)

Automatic and rapid stage of processing, during which a stimulus is decomposed into individual features

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Focused attention stage (FIT)

Stage of processing in which features are combined (requires focused attention)

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Balint's Syndrome

Damage to parietal lobe, causing inability to focus attention on individual objects

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Inattentional blindness

A stimulus that is not attended is not perceived, even though the person is looking directly at it

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Change blindness

Difficulty detecting differences between two visual stimuli presented one after another. Also occurs when part of a stimulus is changed very slowly (Continuity errors)

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Load theory of attention

Lavie; the amount of perceptual capacity that remains as a person is carrying out a task determines how well the person can avoid being distracted by task-irrelevant stimuli

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Perceptual capacity

The resources a person has for carrying out perceptual tasks

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Perceptual load

The amount of a person's perceptual capacity needed to carry out a particular perceptual task

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Low-load vs high-load tasks

Low-load: uses small amount of person's perceptual capacity High-load: involve more processing and therefore use more of a person's perceptual capacity

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Perceptual completion

Perception of an object as extending behind occluding objects

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Habituation vs dishabituation

Habituation: Paying less attention when same stimulus is presented repeatedly Dishabituation: increase in responding that occurs when a stimulus is changed

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Task-irrelevant stimuli

A stimulus that does not provide information relevant to the task at hand

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Ecological validity

Gibson; An ecologically valid experiment matches its stimuli, conditions, and procedures to those present in the natural world

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Optic flow

Flow of stimuli in the environment that occurs when an observer moves relative to the environment (gradient of flow and FOE are important characteristics)

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Gradient of flow

Gradient created in optic flow by movement of an observer through the environment

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Focus of Expansion (FOE)

The point in the optic flow pattern caused by observer movement in which there is no expansion (Where you are looking towards)

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Invariant information

Environmental properties that do not change as the observer moves relative to an object or scene

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Self-produced information

Environmental information that is produced by actions of the observer. (Ex: somersaults by experts vs beginner)

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Swinging room experiment

Lee and Aronson; posture is corrected by vision

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Visual direction strategy

A strategy used by moving observers to reach a destination by keeping their body oriented toward the target

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Car Driving Experiment

Land and Lee; drivers don't look at FOE, instead look at the road where they are headed, and look at curves when turning

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Navigating through the environment by perceiving and remembering objects in the environment and their relation to the overall scene, knowing when to turn and in what direction (using landmarks)

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Objects on a route that serve as cues to indication where to turn (used in way finding)

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Topographical Agnosia

Patients unable to recognize landmarks in real-world environment due to parahippocampal gyrus damage

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Cognitive Map

Mental map of the spatial layout of an area of the environment (Tolman; rat experiment in maze with cheese)

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Information specified by a stimulus pattern that indicates how the stimulus can be used

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Parietal Reach Region (PRR)

In parietal cortex, involved in reaching behaviour

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Monkey grasp experiment

Fattori; visuomotor grip cells: responds when an object is scene and also when hand grasps same object

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Mirror neurons

Neuron in premotor area that respond when monkey grasps an object and when monkey observes someone else grasping the object

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Audiovisual mirror neurons

Respond to actions that produce sound

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Action-specific perception hypothesis

People perceive their environment in terms of their ability to act on it (perception changes based on skills and difficulty level)

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A segment of time at a particular location that is perceived by observers to have a beginning and an end

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Event boundary

The point in time when one event ends and another begins

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Damage to an area of the cortex involved in motion perception causes blindness to motion

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Real motion

The physical movement of a stimulus

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Illusory motion

Perception of motion when there actually is none

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Induced motion

The illusory movement of one object that is caused by the movement of another object that is nearby

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Motion aftereffects

Illusion that occurs after a person views a moving stimulus and then sees movement in the opposite direction when viewing a stationary stimulus immediately afterward (ex. waterfall illusion)

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Optic array

The structured pattern of light created by the presence of objects, surfaces, and textures in the environment

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Local disturbance in the optic array

Occurs when one object moves relative to the environment, so that the stationary background is covered/uncovered by the moving object. Indicates object is moving relative to the environment

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Global optic flow

Information for movement that occurs when all elements in a scene move. Indicates the observer is moving and not the scene

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Reichardt detector

Neural circuit in which signals caused by movement of a stimulus across the receptors are processed by a delay unit and an output unit so that signals are generated by movement in one direction but not the opposite direction

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Output unit

Component of Reichardt detector; compares signals received from 2+ neurons. Activity in this unit is necessary for motion perception

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Delay unit

Component of Reichardt detector; explains how neural firing occurs to different directions of movement. Delays transmission of nerve impulses as they travel from receptors towards brain

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Corollary discharge theory

Explains motion perception as being determined both by movement of the image on the retina and by signals that indicate movement of the eyes

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Image displacement signal (IDS)

In corollary discharge theory, the signal that occurs when an image moves across the visual receptors

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Motor signal (MS)

In corollary discharge theory, the signal that is sent to he eye muscles when the observer moves or tries to move their eyes

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Corollary discharge signal (CDS)

A copy of the motor signal that is sent to the eye muscles to cause movement of the eye. Copy is sent to the hypothetical comparator of corollary discharge theory

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Structure hypothesized by the corollary discharge theory. the CDS and IDS meet at the comparator to determine whether movement will be perceived

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Real-motion neuron

Neuron in monkey's cortex that responds when movement of an image across the retina is caused by movement of a stimulus, but does not respond when movement across the retina is caused by movement of the eyes

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In movement perception research when arrays of moving dots are used as stimuli, the degree of correlation between the direction of the moving dots

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Transcranial magnetic stimulation (TMS)

Presenting a strong magnetic field to the head that temporarily disrupts the functioning of a specific area of the brain

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Aperture problem

A portion of the moving stimulus is seen through a narrow aperture or "field of view" of a neurons' receptive field, causing misleading information about the direction the stimulus is moving

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Shorts path constraint

In apparent motion perception, the principle that apparent movement tends to occur along the shortest path between two stimuli (ex: women with hand infront vs behind head)

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