EP Chapter 05-m

8/3/2019 EP Chapter 05-m

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Sensation and Perception

Chapter 5


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Sensation and Perception

DefinitionsSensing the World: Thresholds

Sensory Adaptation

Vision

The Stimulus Input: LightEnergy

The Eye

Visual InformationProcessing

Color Vision

Perceptual Organization

Form Perception

Depth Perception

Perceptual Constancy

Perceptual Interpretation

Sensory Deprivation

and Restored Vision

Perceptual Adaptation

Perceptual Set


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Sensation & Perception

How do we construct our representations of the external

world?

To represent the world, we must detect physical energy

(a stimulus) from the environment and convert it into

neural signals. This is a process called sensation.

When we select, organize, and interpret our sensations,

the process is calledperception.


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Bottom-up Processing

Analysis of the stimulus begins with the sense receptors

and works up to the level of the brain and mind.

Letter A is really a black blotch broken down into features

by the brain that we perceive as an A.


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Top-Down Processing

Information processing guided by higher-level

mental processes as we construct perceptions,

drawing on our experience and expectations.

THE CHT


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Our sensory and perceptual processes work together

to help us sort out complex images.

Making Sense of Complexity

The Forest Has Eyes, Bev Doolittle


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Psychophysics

A study of the relationship between physicalcharacteristics of stimuli and our psychological

experience with them.

Physical WorldPsychological

World

Light Brightness

Sound Volume

Pressure Weight

Sugar Sweet


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Exploring the Senses

What stimuli cross our threshold for

conscious awareness?


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Thresholds

AbsoluteThreshold: Minimum stimulation needed to

detect a particular stimulus 50% of the time.

Proportionof

YesResponses

0.00

0.50

1.0

0

0 5 10 15 20 25

Stimulus Intensity (lumens)


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Sensing the World Around Us

Absolute threshold

The smallest intensity of

a stimulus that must bepresent for it to be

detected


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Subliminal Threshold

Subliminal Threshold: When

stimuli are below ones

absolute threshold for

conscious awareness.

KurtScholz/Superstock


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Puzzles of Perception

Can we ever perceive what is happening

below our usual sensory threshold?

Can we pick up signals from world or fromother people without using our usual

sensory channels at all?


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Perceiving without Awareness

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Priming

A method used to insure unconscious processes, inwhich a person is exposed to information and is

later tested to see whether the information affectsbehavior or performance on another task or inanother situation

Findings suggest simple primes influence perception, memory, thinking,

and decision-making.


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Perception vs. persuasion

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Although subliminal priming can influencejudgments and preferences, research doesntsupport its success in major levels ofpersuasion.


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Extrasensory perception

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ESP

The ability to perceive something without ordinary sensory information

Has not been scientifically demonstrated


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Difference threshold

The smallest difference in stimulation thatcan be reliably detected by an observer whentwo stimuli are compared

Also called the Just Noticeable Difference(JND)

Also known as Webers Law

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Sensory Adaptation

Diminished sensitivity as a consequence of constant

stimulation.

Put a band aid on your arm and after awhile

you dont sense it.


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Vision


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Transduction

In sensation, the transformation of stimulus energy

(sights, sounds, smells) into neural impulses.


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Visible

Spectrum

The Stimulus Input: Light Energy

BothPhotos:ThomasEisner


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Physical Characteristics of Light

1. Wavelength (hue/color)

2. Intensity (brightness)


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Wavelength (Hue)

Different wavelengths of light result

in different colors.

400 nm 700 nm

Long wavelengthsShort wavelengths

Violet Indigo Blue Green Yellow Orange Red


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Intensity (Brightness)

Blue color with varying levels of intensity.

As intensity increases or decreases, blue color

looks more washed out or darkened.


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The Eye


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Parts of the eye

1. Cornea: Transparent tissue where light enters the

eye.

2. Iris: Muscle that expands and contracts to change

the size of the opening (pupil) for light.

3. Lens: Focuses the light rays on the retina.

4. Retina: Contains sensory receptors that process

visual information and sends it to the brain.


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The Lens

Lens: Transparentstructure behind the pupil

that changes shape to focus

images on the retina.

Accommodation: The

process by which the eyes

lens changes shape to helpfocus near or far objects on

the retina.


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Retina

Retina: The light-sensitive inner

surface of the eye,

containing receptorrods and cones inaddition to layers of

other neurons(bipolar, ganglion

cells) that processvisual information.


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Optic Nerve, Blind Spot & Fovea

http://www.bergen.org

Optic nerve: Carries neural impulses from the eye to the brain.

Blind Spot: Point where the optic nerve leaves the eye because

there are no receptor cells located there. Fovea: Central point in

the retina around which the eyes cones cluster.


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Photoreceptors

E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969


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Visual Information Processing

Optic nerves connect to the thalamus in the middle of

the brain, and the thalamus connects to the visual

cortex.


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Feature Detection

Nerve cells in the visual cortex respond to specific

features, such as edges, angles, and movement.

RossKinnaird/Allsport/Get

tyImages


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Shape Detection

Specific combinations of temporal lobe activity occur

as people look at shoes, faces, chairs and houses.

Ishai,Ungerleider,MartinandHaxby/NIMH


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Trichromatic theory

Young (1802) and vonHelmholtz (1852) bothproposed that the eye

detects 3 primarycolorsRed, blue, and green

All other colorsderived bycombination

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ColorBlindness

Ishihara Test

Genetic disorder in which people are blind to green orred colors. This supports the Trichromatic theory.

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Afterimages

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