Myers EXPLORING PSYCHOLOGY

Module 14

Introduction to Sensation and

Perception: Vision

James A. McCubbin, PhDClemson University

Worth Publishers

Sensation

Sensation the process by which our sensory

receptors and nervous system receive and represent stimulus energy

Perception the process of organizing and

interpreting sensory information, enabling us to recognize meaningful objects and events

Sensation Our

sensory and perceptual processes work together to help us sort out complex images

Sensation

Bottom-Up Processing analysis that begins with the sense

receptors and works up to the brain’s integration of sensory information

Top-Down Processing information processing guided by

higher-level mental processes as when we construct perceptions

drawing on our experience and expectations

Sensation: Basic Principles

Psychophysics study of the relationship between

physical characteristics of stimuli and our psychological experience of them

Light- brightness Sound- volume Pressure- weight Taste- sweetness

Sensation: Thresholds

Absolute Threshold minimum stimulation needed to detect

a particular stimulus 50% of the time Difference Threshold

minimum difference between two stimuli required for detection 50% of the time

just noticeable difference (JND)

Sensation: Thresholds

Subliminal when stimuli

are below one’s absolute threshold for conscious awareness

0

25

50

75

100

Low Absolutethreshold

Medium

Intensity of stimulus

Percentageof correctdetections

Subliminal stimuli

Sensation: Thresholds

Weber’s Law to be perceived as different, two

stimuli must differ by a constant minimum percentage (rather than a constant amount) light intensity- 8% weight- 2% tone frequency- 0.3%

Now you see it, now you don’t!

Sensory Adaptation- diminished sensitivity as a consequence of constant stimulation

Vision

Transduction conversion of one form of energy

to another in sensation, transforming of

stimulus energies into neural impulses

Wavelength the distance from the peak of one

wave to the peak of the next

Vision

Hue dimension of color determined by

wavelength of light Intensity

amount of energy in a wave determined by amplitude brightness loudness

The spectrum of electromagnetic energy

Vision: Physical Properties of Waves

Short wavelength=high frequency(bluish colors, high-pitched sounds)

Long wavelength=low frequency(reddish colors, low-pitched sounds)

Great amplitude(bright colors, loud sounds)

Small amplitude(dull colors, soft sounds)

Vision

Vision

Accommodation- the process by which the eye’s lens changes shape to help focus near or far objects on the retina

Retina- the light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of neurons that begin the processing of visual information

Retina’s Reaction to Light- Receptors

Rods peripheral retina receptors detect black, white and gray for peripheral or twilight

conditions Cones

receptors near center of retina fine detail and color vision for daylight or well-lit conditions

Retina’s Reaction to Light

Optic nerve nerve that carries neural impulses

from the eye to the brain Blind Spot

point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there

Vision: Receptors

Receptors in the Human Eye

Cones Rods

Number

Location in retina

Sensitivity in dim light

Color sensitive? Yes

Low

Center

6 million

No

High

Periphery

120 million

Pathways from the Eyes to the Visual Cortex

Visual Information Processing

Feature Detectors nerve cells in the

brain that respond to specific features

shape angle movement

Stimulus

Cell’s responses

Visual Information Processing

Parallel Processing simultaneous processing of several

aspects of a problem simultaneously

Visual Information Processing

Trichromatic (three color) Theory Young and Helmholtz three different retinal color receptors

red green blue

Visual Information Processing

Opponent-Process Theory- opposing retinal processes enable color vision“ON” “OFF”red greengreen red blue yellow yellow blue black whitewhite black

Visual Information Processing

Color Constancy Perceiving familiar objects as

having consistent color, even if changing illumination alters the wavelengths reflected by the object

Color-Deficient Vision

People who suffer red-green dificiency have trouble perceiving the number within the design

Opponent Process: Afterimage Effect