CHAPTER 4

Sensation & Perception

Lecture Overview• Introduction to

Sensation & Perception

• Understanding Sensation

• How We See and Hear

• Our Other Senses

• Understanding Perception

Sensation and Perception

• Sensation – process of receiving, converting, and transmitting

raw sensory information from the external and internal environments to the brain

• Perception – process of selecting, organizing, and interpreting

sensory information

Sensation Versus Perception

• When you stare at the cube on the left, which area is the top, bottom, or back?

• In the figure on the right, is this a young woman looking to the right, or an older woman with her chin buried in her jacket?

Sensation Vs. Perception

SENSATION

Processing

• Processing– sensory organs contain

receptors that receive sensory information from the environment

Processing

• Three Types of Processing: – Transduction:• Converts sensory stimuli into neural impulses

– Sensory reduction:• Filters/analyzes incoming sensations before sending to

the brain– Coding:• Converts sensory input into a specific sensation sent to

the brain

Processing

• All processing occurs at the sensory level and messages are then sent on to the brain.

Thresholds

• Psychophysics: Testing limits and changes– Absolute Threshold: • smallest amount of a stimulus we can detect

– Difference Threshold: • Min. difference needed to detect a stimulus change;

also called the just noticeable difference (JND)

Sensory ThresholdsVision A candle flame seen at 30

mi. on a clear, dark night

Hearing The tick of a watch under quiet conditions at 20 ft.

Taste One teaspoon of sugar in 2 gallons of water

Smell 1 drop of perfume diffused into the entire volume of a 3 room apartment

Touch The wing of a bee falling on your cheek from a height of 1 cm

Sensory 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%

Thresholds

• Sensory Adaptation: – decreased sensory response to continuous

stimulation

How We See: Vision

• Light is a form of electromagnetic energy that moves in waves

• Many types of electromagnetic waves form the electromagnetic spectrum

Electromagnetic Spectrum

Electromagnetic Spectrum

• The flower on the left looks normal to us, whereas the one on the right was photographed under ultraviolet light

How We See: Light Waves

• Light waves vary in: – length (wavelength), which determines frequency

(hue or color)– height (amplitude), which determines brightness

or intensity

Anatomy of the Eye

• The function of the eye is to capture light waves and focus them on receptors at the back of the eyeball.

Structures of the Retina

• Receptors for vision are the rods and cones located in the retina.

Are You Nearsighted or Farsighted?

• Myopia:– Near sightedness– Focused in front of retina

• Hyperopia:– Far sightedness– Focused behind retina

Optic Nerve, Blind Spot & Fovea

• 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 eye’s cones cluster.

Photoreceptors

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

Visual Information Processing

Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual

cortex.

Feature Detection

• Feature Detection:– Nerve cells in the visual cortex respond to specific

features, such as edges, angles, and movement.

Shape Detection

Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses.

How We Hear: Audition• Sound results from movement of air molecules in a

particular wave pattern.

• Sound waves vary in:• Length which determines pitch (highness or

lowness).• Height which determines loudness

How We Hear: Audition

• The loudness of a sound is measured in decibels. Constant noise above 90 decibels can cause permanent nerve damage to the ear.

How We Hear: Anatomy of the Ear

Receptors forhearing are hair cells located in the cochlea.

Our Other Senses• Our sense of

smell is called olfaction.

• Receptors for smell are embedded in a nasal membrane, the olfactory epithelium.

Gustation (Sense of Taste)

• Receptors for gustation are taste buds, located in the papillae on the surface of the tongue.

Three Body Senses

• Skin senses involve three basic skin sensations

– Touch (or pressure)– Temperature– Pain

• Receptors for these sensations occur in various concentrations and depths in the skin.

Three Body Senses

• Vestibular sense (or sense of balance) involves the vestibular sacs and semicircular canals located in the inner ear.

Three Body Senses

• Kinesthesia provides the brain with information about bodily posture and bodily movement

• Kinesthetic receptors are found throughout the muscles, joints, and tendons of the body.

UNDERSTANDING PERCEPTION

Chapter 4

Understanding Perception

• Illusions: – false or misleading

perceptions help scientists study the processes of perception (e.g., the horizontal-vertical illusion)

The Muller-Lyer Illusion

Which vertical line is longer?

Understanding Perception

Do You See the Cow?

Understanding Perception

Now Can You See the Cow?

Understanding Perception

• Perception’s three basic processes:– Selection– Organization– Interpretation

Selection

• Selection (choosing where to direct attention) involves these factors:– Selective Attention• filtering out and attending only to

important sensory messages (cocktail party conversations)

– Habituation • brain’s tendency to ignore environmental

factors that remain constant

Selection

• Kittens raised with only vertical visual stimuli fail to develop the ability to detect horizontal lines. Can you explain why?

Organization

• Organization: assembling of information into patterns that help us understand the world

• We organize sensory information in terms of:– Form– Consistency – Depth– Color

Form Perception

• Gestalt psychologists developed laws explaining how people perceive form according to:– Figure and ground• Ground is always seen as farther away than the figure

– Proximity• Objects that are physically close together are grouped

together

Form Perception

• Gestalt laws cont’d– Continuity• Objects that continue a pattern

are grouped together– Closure• The tendency to see a finished

unit from an incomplete stimulus– Similarity• Similar objects are grouped

together

Grouping Principles

The Gestalt Grouping Principles are in use here

Form Perception: Can You Explain These Impossible Figures?

Form Perception

Organization

• Perceptual Constancy: – Tendency to perceive the environment as

remaining the same even with changes in sensory input.

• Four best-known constancies: – Size– Shape– Color– Brightness

Can You Identify the Size, Shape, Color, and Brightness

Constancies?

Organization

The Ames Room Illusion

Interpretation

• Depth Perception:– ability to perceive three

dimensional space and accurately judge distance

Depth Perception

Depth Perception

The Visual Cliff

Depth Perception

• Depth Perception involves both binocular (two eyes) and monocular (one eye) cues.

• Two Binocular Cues for Depth:– Retinal disparity • separation of the eyes causes different images to fall

on each retina– Convergence • the closer the object the more the eyes turn inward

Binocular Cues Retinal Disparity

(left) Convergence

(right)

Depth Perception

Depth Perception

• Monocular Cues– relative size• smaller image is more distant

– interposition• closer object blocks distant object

– relative clarity• hazy object seen as more distant

– texture • coarse = close• fine = distant

Depth Perception

Relative Size

Depth Perception

Interposition

Depth Perception

• Monocular Cues (cont.)– relative height• higher objects seen as more distant

– relative motion• closer objects seem to move faster

– linear perspective• parallel lines converge with distance

– relative brightness• closer objects appear brighter

Depth Perception

Relative Height

Six Monocular Depth Cues: Can You Find Them?

1. linear perspective 2. interposition3. relative size4. texture gradient5. aerial perspective6. light and shadow

Depth Perception

Two main theories:• 1. Trichromatic: – color perception

results from mixing three distinct color systems (red, green, and blue)

Colour Perception

Colour Perception

2. Opponent-process: • color perception results from three systems of color

opposites (blue-yellow, red-green, and black-white) “ON” “OFF”red greengreen red blue yellow yellow blue black whitewhite black

Colour Perception

• After-Image effect– Complimentary colours don’t exist together (no

bluish-yellow or reddish-green)– After images appear in complimentary colours

Interpretation

• Interpretation– How we explain perception– 4 factors• Perceptual adaptation• Perceptual set• Frame of reference• Bottom-Up or Top-Down Processing

Four Factors in Interpretation

• 1. Perceptual adaptation– Brain adapts to

changed environments

• 2. Perceptual set– Readiness to perceive in a

particular manner, based on expectations

– Past experiences, motives, contexts, or suggestions

Four Factors in Interpretation

Perceptual Set

Flying saucers or clouds

• Another example of perceptual set.

• Do you notice anything wrong with these photos?

Four Factors in Interpretation

Four Factors in Interpretation

• 3. Frame of reference:– based on the context of the situation– Internal standards for judging stimuli

Four Factors in Interpretation

• 4. Bottom-Up Processing:– Analyzing information starting at the bottom

(small units) and going up to form a complete perception

• 4. Top-Down Processing:– Pre-existing knowledge that is used to rapidly

organize features into a meaningful whole• drawing on our experience and expectations

Perception & Memory

• The ability to accurately perceive stimuli in the environment is highly correlated with the ability to correctly remember that same stimuli– i.e. the better you are at perceiving, the more

accurate you will be at remembering

Extrasensory Perception

• Extrasensory perception (ESP): – supposed ability to perceive things that go beyond the 5

normal senses– ESP research is criticized due to lack of experimental

control and replicability.

Extrasensory Perception (ESP)

• Parapsychology: Study of ESP and other psi phenomena (events that seem to defy accepted scientific laws)– Clairvoyance: Purported ability to perceive events

unaffected by distance or physical barriers– Telepathy: Purported ability to read minds– Precognition: Purported ability to accurately predict the

future (“Minority Report” and the “Pre-Cogs,” like Agatha)– Psychokinesis (Mind Over Matter): Purported ability to

influence physical objects by willpower

ESP continued

• Run of Luck: Statistically unusual outcome that could occur by chance alone (e.g., getting five heads in a row, two jackpots within six pulls of a slot machine)

• Stage ESP: Simulation of ESP for entertainment purposes

• Conclusion: Existence of ESP has NOT been scientifically demonstrated; positive results are usually inconclusive and easily criticized

• In sum: Be skeptical! If it seems too good to be true, it probably is!

Problems with Believing in Subliminal Perception and ESP

• Subliminal perception may occur, but there is little or no evidence of subliminal persuasion