“HOW DO WE SENSE and

PERCEIVE THE WORLD?”

CHAPTER 5:

SENSATION and PERCEPTION

SENSATIONthe process of receiving stimulus energies from

the external environment.sensory organs: eyes (visual system)

ears (auditory)

nose (olfactory)

tongue (gustatory)

skin (tactile)

TRANSDUCTION the process of transforming physical energy into electrochemical energy.

PE ECE

PERCEPTIONthe process of organizing and interpreting sensory information to give it meaning.

Prior experiencesExpectationsMemoryBiases

BOTTOM-UP PROCESSING

Processing that begins with sensory receptors registering environmental information and sending it to the brain for cognitive processing and integration.

TOP-DOWN PROCESSING

Processing of perpetual information that starts out with cognitive processing at the higher levels of the brain.

JIGSAW PUZZLE

Why is it important to study sensation and perception?

The purpose of perception is:1) to represent information from the

outside world internally;2) adaptation that improves a species’

chances for survival; and3) to help in designing devices to restore

perception to those who have lost some (or all) and also to devise treatments for other perceptual problems.

SENSORY RECEPTORS

All sensation begins with sensory receptors.

Sensory receptors are specialized cells that detect and transmit stimulus information to sensory nerves and the brain.

3 Classes of SENSORY RECEPTORS1.Photo reception(detection of

light, perceived as sight.)2.Mechanoreception

(detection of pressure, vibration, and movement perceived as touch, hearing and equilibrium.)

3.Chemoreception (detection of chemical stimuli detected as smell and taste.

How close does an approaching bumblebee have to be before you can here its buzzing?

Difference between a ‘Coke’and a ‘Coke Zero’?The percentage of fat in a ‘low fat’ and a regular milk?

THRESHOLDA level or point at which something starts or ceases to happen or come in to effect.

SENSORY THRESHOLDSAbsolute Threshold

-Orange juice

-One tablespoon?

-Two tablespoon?

-Three tablespoon!-Watching TV while your roommate is sleeping.

-Volume?

SENSORY THRESHOLDSAbsolute threshold

Difference threshold

- Minimum amount of energy that a person can detect.

- just noticeable difference (jnd)- the degree of difference that must

exist between two stimuli before the difference is detected.

30 25 20 15 10 5 00

20

40

60

80

100

120

Perc

ent

of

yes

resp

onse

s

Distance in feet from an alarm clock.

Approximate Absolute Thresholds

Vision

- A candle flame at 30 miles on a dark, clear night.Hearing

- A ticking watch at 20 feet under quiet conditions.Smell

- One drop of perfume diffused throughout 3 rooms

Taste

- A teaspoon of sugar in 2 gallons of waterTouch

- The wing of a fly falling on your cheek from a distance of one centimeter.

Difference Threshold

-Watching TV while your roommate is sleeping.

-Your roommate, suddenly wakes-up.

-Also wants to watch the TV!

-Volume?

2 4 6 9 12

13

No JND!

JND!

A student late for his class.10: 03 – late?10:05 – late?10: 10 – late?10:15 – late!!!It takes 15 minutes for a student

to be detected as late.Absolute or difference threshold?*Depends on the individual who

perceives and the condition of the environment.

WEBER’S LAWThe principle that two stimuli must differ by a constant minimum percentage to be perceived as different.

Subliminal Perception-the ability to detect information below the level of conscious awareness.

SIGNAL DETECTION THEORY

The theory that focuses on decision making about stimuli in the presence of uncertainty; detection depends on a variety of factors beside the physical intensity of the stimulus and the sensory abilities of the observer.

PERCEIVING SENSORY STIMULIA.Attention

Selective Attention—focusing on a specific aspect of experience while ignoring others.

B. Perceptual Seta predisposition, or

readiness, to perceive something in a particular way.

Sensory AdaptationA change in the

responsiveness of the sensory system based on the average level of surrounding stimulation.

THE VISUAL SYSYTEM

THE EYE!LIGHT

form of electromagnetic energy that can be described in terms of wavelength; travels through space in waves.

CHARACTERISTICS of LIGHT1.Wavelength- distance

from the peak of one wave to the next.

2. Hue- color3. Amplitude- the height of

a wave.4.Purity- the mixture of

wavelengths in light.

COLOR TREE

PARTS OF THE EYESCELERA

the white outer part of the eye that helps maintain the shape and protects from injury.

IRISthe colored part of the eye, contains muscle that control the size of the pupil, hence, the amount of light that enters.

PUPILappears black, and is the opening in the center of the iris.

A clear membrane just in front of the eye.

A transparent, flexible, disklike gelatinous material. Use to bend light on the eye.

The light sensitive surface in the back of the eye that houses light receptors.

A minute area in the center of the retina which vision is at its best.

It’s the place on the retina where the optic nerve leaves the on its way to the brain.

VISUAL CORTEXlocated in the occipital lobe of the brain. Visual information processing involves feature detection, parallel processing and binding.

A.Feature Detectors(David Hubel&Torsten Wiesel)

neurons of the brain’s visual system that respond to particular lines or other features of a stimulus.

PARALLEL PROCESSING1.What Pathway

processes information about what the object is, its color, form and its texture; temporal lobe.

2.Where Pathwayprocesses information on an

object’s location, movement, depth of the object; parietal lobe.

BINDINGThe bringing together and integration of what is processed by different pathways or cells.

TRICHROMATIC THEORY(THOMAS YOUNG 1802)(ex: HERMANN von HELMONTZ 1852)Color perception is

based on the existence of three of color receptors that are maximally sensitive to different, but overlapping ranges wavelengths.

COLOR VISION1.Trichromatic

theoryColor perception is based on the existence of three color receptors that are maximally sensitive to different, but overlapping, ranges of wavelengths.

A.Dichromatspeople with only two kinds of cones.

B.Trichromatshave three kinds of cone receptors

and normal vision.

C.Afterimages- sensations that remain after a stimulus is removed.

OPPONENT-PROCESS TheoryCells in the visual sys. respond to green and blue-yellow colors; a given cell might be excited be red and inhibited by green, whereas another might be excited by yellow and inhibited by blue.

Sensory adaptation

- The sensory receptor cells become less responsive to an unchanging stimulus.

- The receptors are no longer sending signals to the brain.

Habituation- The sensory receptor cells are still

responding to the stimulus, but the lower centers of the brain are not sending the signals from those receptors in the cortex.

QUESTIONS?