Sensation and Perception

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Gestalt approach

we perceive objects as whole rather than as a sum of the individual parts

figure-ground perception

we inherently distinguish between objects and background

What is an organizational principal?

Proximality, Similarity, continuity, closure

Proximity

We tend to group together objects that are close to one another

Similartiy

we tend to group together objects that are similar to one another

Continuity

brain organizes stimuli into continuous lines or patters

Closure

we tend to perceive incomplete figures as complete

Depth Perseption

Perception of depthq or distance

What are the two kinds of visual information for depth

Binocular cues and monocular cues

Binocular cues

Each eye has a slightly different view of same scene

Retinal (binocular) disparity

images produce different image on each retina

Convergence

turning inward of eyes towards nearby objects

If someone is looking at a closer object is there a higher or lower convergence?

closer object —> greater convergence

When object are far way using monocular cues..

• relative size

• relative clarity

• linear perspective

percepual constancy

interpretation of changing sensations as perception that is relativity consistent

color constancy

consistent perception of color of objects although the amount of light changes

lightness constancy

consistent perception of shade of objects although the amount of light changes

shape constancy

perception that object’s shape remains constant despite changing shape of retinal image

size constancy

Perception that the size of object’s remains constant despite sizes of images on retina

Sensation

process by which sensory organs obtain information about the environment and transmit it to the brain

perception

the organization of sensation

How do sensations and perceptions work together?

Bottom-up processing and Top-down processing

Bottom-up processing

starts with raw sensory data that gets communicated to the brain

top-down processing

starts with observers expectations and knowledge

absoulte threshold

minimal amount of stimulation that can be detected half of the time

Difference threshold/just noticeable difference (jnd)

smallest difference in intensity between 2 stimuli that a person can detect

weber’s law (fraction)

for 2 stimuli to be perceived as difference in intensity, the second must differ from the first by a constant proportion

Sensory adaptation

the decreasing response of sensory receptors to constant unchanging stimuli

What is the evolutionary benefit of sensory adaptation

constant sensory input provides no new information

Signal detection theory

perception results from both sensory information and making a judgment

what does detection (perception of stimulus) depend on?

• sensitivity of sensory systems

• response bias

Response bias

person’s readiness to report detecting a stimulus

Possible outcomes for signal detection

Hits, misses, false alarms, correction rejection

Factors affecting response bias

• expectations

• motivations

  • history of signal detection errors may affect future response bias