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Some type of physical energy, such as sound or light, to which we can respond.


The direct effect of stimulation of receptor cells by a stimulus

Basic, immediate experiences that a stimulus such as a sound elicits in a sense organ such as the ear


Our organization and interpretation of sensory experience

Process of interpreting, organizing, and often elaborating on sensations

Skin senses

Pressure, temperature, and change


Body senses that allow us to detect movement and the position of our bodies.


The process by which sensory information reaches our brain.

Process by which sensory organs transform mechanical, chemical, or light energy into the electrochemical energy that is generated by neurons firing

mechanical energy

hearing and skin senses

chemical energy

smelling and tasting

light energy



Chemicals contained in our eyes that change their shape when they are hit by light

Stimulate occipital cortex at back of brain

creates sensations of flashing light

Stimulate auditory region on side of the brain

Causes patients to hear tones


Ability to hear flavors or see sounds

Most important factors that determine whether or not we perceive things happening around us

Sensory thresholds, attention, and adaptation


part of psychology that focuses on relationship between physical aspects of external stimuli and our perceptions of these stimuli

perception of sensory inputs occurs only when?

the strength of stimulus reaches minimal or threshold level of intensity sufficient to activate a sensory process


minimum level of intensity or strength of a stimulus that is sufficient to activate a sensory process

Most important reason we do not respond to many stimuli?

Biological limitation of our senses

2 kinds of sensory thresholds that operate to limit our perception of sensation?

Absolute threshold and difference threshold

Absolute threshold

The minimum physical intensity of a stimulus that can be perceived by an observer 50% of the time

Differ from person to person

Difference threshold

Minimum increase in intensity of a stimulus necessary to notice a change 50% of the time

Just noticeable difference


Perception of a stimulus

always relative to its background level or its context.

The degree of increase or decrease in intensity that is necessary to produce a jnd (just noticeable difference) depends on?

the original strength of the stimulus

Weber's law


major principle of sensation

describes relationship between stimulus intensity and our perception of stimulus change

difference threshold tends to be a constant fraction of the original stimulus intensity

as the strength of the original stimulus increases, the magnitude of the change must also increase in order for a jnd to be perceived

^I = kI


change in stimulus intensity neccessary for a jnd


initial stimulus intensity


Weber's constant


selective psychological process in that we are aware of certain stimuli and not others at any moment

refers to the control of our behavior by specific stimuli or stimulus situations

psychological selection mechanism that determines which stimuli an organism responds to or perceives

does not block physical and biological response of our sense organs to stimuli; increases or decreases our perception

sensory adaptation

the decrease in the response of sensory receptors to stimuli when they are exposed to continual, unchanging stimulation

Perception is dependent on?

Stimulus change

If stimuli remain constant, we adapt to them and they are no longer perceivable

Which sense adapts most quickly?


saccadic movements

the rapid scanning movements of an eye

eyes continually move, rapidly changing the location of the stimulus within the eye

which sense modality is slowest to adapt?


signal detection theory

variables that influence what we do or do not perceive

our ability to detect a sensory stimulus (signal) depends not only on the intensity of the signal but also on variables such as distractions and motivation

no such thing as an absolute threshold for a given stimulus modality because detecting a signal depends not only on stimulus strength but also on background noise and psychological variables such as expectation and response bias


any kind of distracting and irrelevant stimuli

external noise

distracting factors in the outside environment

internal noise

ongoing, variable, random firing of neurons

sensory inputs

occur against a variable background of external and internal noise, the level of which affects our ability to detect signals

response bias

inclination or tendency to respond in a certain way

created by positive and negative consequences associated with hits, misses, and false alarms

ROC curve

receiver operating characteristic curve

illustrates trying harder to avoid false alarms and thus raise response criterion by requiring a stronger stimulus before reporting a sighting

points falling above the diagonal line represent stimulus intensities above the threshold

points below the diagonal line represent stimulus intensities below threshold

response criterion

the particular criterion you set for how sure you must be before reporting a signal has been detected

perceptual organization

the process by which we structure elementary sensations into the objects we perceive

Who identified major principles of perceptual organization?

Gestalt psychologists

Max Wertheimer

Kurt Koffka

Wolfgang Kohler


The whole patterns that develop after people organize sensations


the part of an image on which we focus our attention


the background against which the figure that we focus on stands

feature of perceptual organization

tendency to differentiate between figure and ground

perceptual grouping

tendency to organize patterns of stimuli into larger units according to proximity, similarity, and good continuation

how we organize sensory input into meaningful wholes

3 major ways patterns of stimuli grouped into larger units



good continuation


perceptual grouping principle that says we tend to organize perceptions by grouping elements that are the nearest to each other


tend to group elements that are similar to each other.

good continuation

perceptual grouping principle that we are more likely to perceive stimuli as a whole or single group if they flow smoothly into one another than if they are discontinuous


perceptual organizing principle that we tend to perceive incomplete figures as complete

selective attention

basic principle of perceptual processing

process of focusing on one or a few stimuli of particular significance while ignoring others and enhances our perceptual ability

Inverse hypothesis

related to selective attention

the more complex the stimulus, the less attention we can focus on any particular aspect of it

sudden change

a sudden change in either the quality or quantity of a background stimulus generally causes a shift in attention


diverts our attention because it contrasts with its surroundings


things that are novel or unusual tend to attract our attention

stimulus intensity

vary the intensity of a stimulus


another way to attract attention to stimuli

key stimuli

captures attention by activating motivational mechanisms such as fear, hunger, or sexual arousal

played important role in guiding and directing behavior throughout evolution

the major function of vision

to represent the spatial arrangement of objects in our environment

what perceptual cues allow us to judge accurately the distance of objects?

binocular cues and monocular cues

binocular cues

visual cues for depth or distance, such as binocular disparity and convergence, that depend on both eyes working together

monocular cues

distance cues such as linear perspective, interposition, relative size, texture gradients, aerial perspective, relative motion, and height on a plane that can be used with just one eye

binocular (retinal) disparity

difference in the retinal image of an object as seen from each eye, due to the difference in viewing angles, that provides an important binocular cue for depth

when is there greater binocular disparity?

when objects are close to our eyes

important depth cues for perception

binocular (retinal) disparity and convergence

the minimum disparity required to detect a depth difference

1 micron (1 millionth of a meter)


binocular distance cue based on the fact that two eyes must converge or rotate toward the inside to perceive objects closer than about 25 feet

the closer the object, the more rotation is necessary and the more muscle tension created

If objects that are far away create little retinal disparity and no convergence, how can we judge their distance?

Monocular cues

height on a plane


important monocular depth cue based on the fact that objects that are highest on one's plane of view appear to be farthest away



monocular distance cue based on the fact that objects close to us tend to block out parts of objects that are farther away

linear perspective

monocular distance cue based on the fact that parallel lines converge when stretched into the distance

relative size

monocular distance cue based on the fact that objects of the same size appear to be smaller the farther they are from the viewer

texture gradient

monocular distance cue based on the fact that textured surfaces (such as a grassy lawn) appear to be smoother, denser, and less textured when they are far from the viewer than when they are close

aerial (atmospheric) perspective

monocular distance cue based on the fact that distant objects tend to appear more fuzzy and less clear than those close to the viewer due to dust and haze

relative motion (motion parallax)

monocular distance cue based on the fact that moving objects appear to move a greater distance when they are close to the viewer than when they are far away

spacial perception

perceptual processing is necessary

spatial cues draw upon both past experience (memory) and cognitive processing for spatial representation such as depth

Gibson's theory of direct perception

all of the visual information necessary for spatial representation is available from the environment
in the form of environmental invariances

spatial representation is a process of direct perception, not a process of cognition

all information necessary for perception is available to the sensory system and no cognitive processing is necessary to complete the perceptual process

direct perception

the interpretation of sensory information directly by the brain as opposed to perceptual interpretation resulting from cognitive processing


sensory information from the environment that is constant from one experience to the next

sufficient to represent depth or distance without additional cognitive processing.

Examples are texture and motion parallax

Eleanor Gibson and Richard Walk (1960)

provided evidence that some aspects of depth perception are inborn or innate

visual cliff

created by Gibson and Walk.

elevated glass surface that produces the illusion of a cliff, allowing researchers to test the ability of animals to perceive and respond to depth cues

suggested that depth perception is based on the monocular cue motion parallax

Is depth perception an innate ability or learned?

depth perception is either innate or learned very early in life. infants are not living in a visual world as stated by William James in 1890. Rather, their world is perceived

size constancy

1 form of perceptual constancy

although the retinal image of an object becomes smaller as the object recedes into the distance (or larger as it approaches), the viewer adjusts for this change and perceives the object to be constant in size

perceptual constancy

allows us to adjust for varying conditions and changing patterns as we perceive the world

objects that are normally perceived to be constant in size, color, or brightness, and shape, despite the fact that their retinal images change according to different conditions

A.H Holway and Edwin Boring (1941)

performed classic study of size constancy that found that subjects were able to make extremely accurate judgments of the size of a circle located at varying distances under conditions filled with distance cues

As distance cues were eliminated, judgment of size became dependent on the size of the retinal image

conclusion was that that an important cue for size constancy is retinal size

brightness constancy

element of perceptual constancy

we perceive objects that we see at night or in poor lighting to be the same brightness as they appear during the day

color constancy

element of perceptual constancy

we perceive objects that we see in the dark to be the same color as they appear during the day even though their retinal images change

shape constancy

element of perceptual constancy

we perceive objects as maintaining the same shape even though their retinal images change when we view them from different angles

we perceive our dynamic environment as stable and containing constant stimulus properties

Factors of object constancy

object familiarity


perception of physical stimuli not the same as properties of physical stimulus

some of this discrepancy produced by our nervous system during the process of transducing the physical sensation

other discrepancies more related to the perceptual organization of stimuli


false or inaccurate perception that differs from the actual physical state of the perceived object

provides insights into normal perception

ames illusion

when people walk across room, they appear to grow or shrink

illusion produced by conflicting environmental cues

our perceptual constancy processes cause us to perceive the room as rectangular and the windows as equal in size and rectangular in shape

Muller-lyer illusion

result of size constancy according to R.L. Gregory

the angled lines provide linear perspective cues

R.L. Gregory

theory that Muller-lyer illusion is result of size constancy.

supported by research demonstrating that muller-lyer is weak or absent in cultures in which people have little exposure to angles.

moon illusion

when moon is low on the horizon,it appears larger than when it is overhead, yet the actual size of the moon's image on the retina is the same regardless of position in sky.illusion result of size constancy.

when moon is low, it appears to be farther away than when it is overhead. this effect results from visual cues for distance. compared to trees and other objects on the horizon, we perceive moon to be far away. when we look at the moon overhead, we have no visual cues for distance

ponzo illusion

two horizontal lines are equal in length although we perceive the distant line as longer

illusion of perspective

poggendorf illusion

appears that if the diagonal line were continued toward each other, the one on the right would pass above the left line. in reality, they would join. results from our inclination to maintain shape constancy


optical illusions of depth created from flat 2-D images

depend on binocular vision and the inhibition of ocular convergence

binocular disparity produces 3-D image


produces 3-D illusions

similar to stereograms

present a 2-D image of the same object from slightly different perspectives to each eye. brain interprets the retinal display as depth and thus creates 3-D.

perceptual set

tendency to see, hear, smell, feel, or taste what we expect or what is consistent with our preconceived notion

motivational state can also have an impact

selective perception

a form of perceptual set

tendency to perceive stimuli that are consistent with our expectations and to ignore those that are inconsistent

ability to distinguish sensations

does not depend on differences between sense organs but rather on what part of brain activated by sensory messages

3 important principles that influence how people organize sensations into whole patterns called Gestalts

Figure and ground

perceptual grouping


characteristics of stimuli that tend to capture attention almost automatically

sudden change

contrast and novelty



stimulus difficulty

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