Sensation and PerceptionModules 5 & 6

What’s the difference?? Sensation: the process by which sensory

systems and the nervous system receive stimuli from our environment

Bottom-up processing: info processing that analyzes raw stimuli entering through the many sensory systems

Perception: process of organizing and interpreting incoming sensory info

Top-down processing: info processing that draws on expectations and experiences to interpret incoming info

• Weakest amount of a stimulus that can be sensed

• Has been found for vision, hearing, smell, touch

• Varies depending on psychological and biological factors

ABSOLUTE THRESHOLD

•AKA " just noticeable difference"•Minimum amount of difference that

can be detected between 2 stimuli(paint colors)

- How much do the laces on your shoes need to be loosen so that they feel less

tight?- How much does the volume have to increase before you can tell that your

stereo has gotten louder?

DIFFERENCE THRESHOLD

Are subliminal messages a real thing??Subliminal = “below threshold”

• Investigates the effects of the distractions and interferences we experience while perceiving the

world• Developed during the Cold War

• Attempts to explain & predict the different perceptual mistakes we

make• Variables to consider:• Stimulus variables

• Environmental variables • Organism variables

SIGNAL-DETECTION THEORY

• Process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli

• Ex: living in the city, odors, darkness at the movie theater, temperature

SENSORY ADAPTATION

Selective Attention

REVIEW

1.Define absolute threshold.2.Give 2 examples of sensory

adaptation.3.What is the difference between sensation and

perception?4.What is difference

threshold also known as?5.What is the signal

detection theory?

• Light is electromagnetic energy• Described in wavelengths

• Light visible to humans only makes up a small part of the spectrum• Wavelength = color

• Amplitude = brightness• Human photoreceptors in the eye are sensitive to wavelengths of light energy

called the visible spectrum. (photoreceptors --> brain)

• ROY G BIV

VISION

• Light enters the eye and then is projected onto a surface

• Cornea --> part of the sclera; bulge on front of eye: focuses light by bending

toward a central focal point; protects eye• Amount of light that enters is determined

by size of opening (pupil) in the • colored part of our eye --> iris• Opening --> pupil: size adjusts

automatically based on the amount of light entering eye; sensitive to emotions

THE EYE

• Once light enters the eye, it encounters the lens

• Lens adjusts to the distance of objects by changing its thickness

• As the light passes through the lens, images are flipped and inverted

• These changes project a clear image of the object onto the retina

(focuses image)

Cont…

So essentially….

Light travels through the pupil to the lens and is then reflected onto the retina. The optic nerve sends the visual information to

the brain.

Rods - located in retina's periphery; sensitive only to brightness of light; allow us to see in

black & whiteCones - located in the middle of retina; involved

in color perceptionBlind spot - where the optic nerve connects to

the eye and contains neither rods or conesActivity 2.2

RETINA CONTAINS THESE RECEPTOR CELLS...

DEMONSTRATION

1. For the first demonstration, hold the side of the paper with the X and Y at arm's

length while covering one eye with the other hand. If the left eye is covered, fixate on the X (assuming it is on the

left), and vice versa. Then slowly advance the paper toward the eye. Notice what happens to the Y: At some critical distance from the eye it disappears, but as the distance

from the eye is further decreased, it reappears. You should then be able to tune the Y in and out by adjusting the

distance of the paper from the eye.

2. The second demonstration involves using the side of the paper with the X, Y, and Z; holding it at arm's length; fixating on the Y with the left eye covered; and slowly advancing the paper toward the eye. At some critical

distance from the eye, the Z will disappear. If the paper is then held at this point, it is possible to observe an unusual

phenomenon: Shifting fixation to the X causes the Y to disappear and the Z to reappear. Thus, by shifting fixation back and forth between and Y and the X, you can make the

Z and the Y alternately pop in and out of view.

Young - Helmholtz trichromatic theory - retinas contain 3 types of cone cells, each responding best

to a particular wavelength: blue, green, redOpponent process theory - two-color processes,

red vs. green, yellow vs. blue, black vs. white (complementary colors)

OPT explains afterimage p. 84Color blindness - absence/ malfunction of cones

(monochromatic and dichromatic)The Stroop Effect/interference

COLOR VISION

Figure 4.19Demonstration of a complementary afterimage. Stare at the dot in the center of the flower for at least 60 seconds, then quickly shift your gaze to the dot in the white rectangle. You should see an afterimage of the flower—but in complementary colors.

REVIEW!!!

1. What are rods and cones?2. Where is the blindspot located?3. Provide one example of difference

threshold.4. What is the stimulus for light?5. You’re holding your dog’s leash as

he calmly lays down. Your friend comes up to talk to you…after several minutes you accidently drop the leash. What is this an example of???

VISION

HEARING

Sound is mechanical energy typically caused by vibrating objectsVibrations produce movement of air

molecules (sound waves)Moving one's head helps in

detecting the source of a soundLocating sound is automatic; in

front and behind is more difficult (uses other senses)

HEARING

Frequency - corresponds to pitch; measured in hertz (Hz) [vocal chords - more cycles = higher

pitch]; 20-20,000 HzAmplitude - corresponds to loudness; measured in decibels (dB); 0 dB threshold = ticking of a

watch 20 ft away in quiet room

CHARACTERISTICS OF SOUND

Outer/middle/innerPinna - visible skin/cartilage

Auditory canal --> eardrum (tympanic membrane)

Eardrum - gateway to the middle ear; thin membrane that vibrates when sound waves

strike it (damage)Ossicles - located in the back of the

eardrum; 3 small bones that pick up and transmit vibration

1. Hammer2. Anvil

3. Stirrup (smallest bone in the body)

THE EAR

Cochlea - inner ear; fluid-filled, snail-shaped bony tube

Vibrating fluid stimulates hair cells --> tiny projections in cochlea that are receptor

cells for hearingEnergy is converted to neural impulses that

are transmitted to the brain via auditory nerve --> projected to hearing areas of

cerebral cortex (temporal lobe)

Cont…

2 million people are deafConductive deafness - sound waves are

unable to be transferred from the outer ear to inner ear; damage to the ossicles (middle

ear) – unable to vibrate (hearing aids)Sensorineural deafness - damage to the

inner ear or hair cells in the cochlea (disease or trauma); people are unable to

hear certain frequenciesActivity 2.3

DEAFNESS

REVIEW1. What determines loudness? How is it measured?

2. How do we SEE? Describe the process, listing the parts involved.

3. How do we HEAR? Describe the process, listing the parts involved?

4. How do we see in color?

5. What is an afterimage? What theory describes this phenomenon?

6. What is the smallest bone in the body?

7. What takes information from the eye to the brain?

8. Where does auditory information go to in the brain? (What lobe???)

9. What is the stimulus for vision? For hearing?

10.Describe 2 types of deafness.

Starbursts!Molecules are given off by substances

Olfactory cells carry it to the olfactory bulb, which activates the prefrontal cortex amygdala/hippocampus

Olfactory nerve sends info to brainOdors can evoke highly emotional memories

Women detect odors more readily than men; brain responses to odors are stronger in women

Pheromones - same-species odors, form of chemical communication

Anosmia - loss of sense of smell

SMELL

Also known as gustationReceptor cells are located in the taste buds

Receptors are sensitive to 4 basic taste qualities:1. Salty2. Sweet3. Sour4. Bitter

5. UmamiReceptor cells reproduce rapidly enough to completely

renew in a week1/4 of population are "supertasters"

TASTE

Skin senses pressure, temperature, and painTouch is vitally important to infants and elderly

Pressure --> hairTemperature --> relative

Pain --> prostaglandins are chemicals that help body transmit pain messages to the brain (aspirin

curbs production); endorphins block release

TOUCH

Message sent to spinal cord to thalamus then projected to cerebral cortex which registers the

location and severityGate-control theory - only certain amount of info

can be processed by nervous system at a timePain messages travel on one set of nerve fibers in

spinal cord, and all other sensory messages travel along another set

Fibers carrying pain messages have pain gates that open

Non-pain fibers can close gates if there is a competing stimulation to larger nerve fibers

(rubbing/icing)

PAIN

Vestibular sense - located in your inner earProvides information about your overall

orientationRelies on fluid-filled semicircular canals in ear

Concerned with balance and body position Kinesthesis - communicates information about movement and location of body parts; relies on

receptors in muscles and joints (touch nose/"falling asleep")

Activity 3.1 – Sensory Interdependencies

BODY SENSES

Perception

http://www.youtube.com/watch?v=-yl0HGD7B20

“Maybe each human being lives in a unique world, a private world different from those

inhabited and experienced by all other humans. . If reality differs from person to

person, can we speak of reality singular, or shouldn't we really be talking about plural

realities? And if there are plural realities, are some more true (more real) than others? What about the world of a schizophrenic? Maybe it's as real as our world. Maybe we cannot say that we are in touch with reality and he is not, but should instead say, His reality is so different

from ours that he can't explain his to us, and we can't explain ours to him. The problem, then, is

that if subjective worlds are experienced too differently, there occurs a breakdown in

communication ... and there is the real illness.” ― Philip K. Dick

Gestalt (remember this???) - the whole experience is greater than the sum of the

individual parts; we don’t focus on individual stimuli in our environment – we group them into

more meaningful unitsClosure - tendency to perceive a whole figure

even if there are gapshttp://www.youtube.com/watch?v=nxKcpfFvuf8

PERCEPTION

Closure

A Gestalt

Figure-ground perception - perception of figures against a background

Grouping Principles: proximity, similarity, continuity, common fate

Perception of movement - relative; waiting at a light

Stroboscopic motion - drawing books, movies; law of continuity - prefer to see things as one

continuous image

PERCEPTION

Figure-ground Perception

Figure-Ground

Grouping Principles

Monocular cues - depth cues provided by one eye

Motion parallax

Texture gradient

Shadow

Overlapping/interposition

Clearness

Linear Perspective

Binocular cues - depth cues provided by both eyes

Retinal disparity

Convergence

DEPTH PERCEPTION - PERCEIVED BY USING A NUMBER OF CUES

Monocular cues Motion Parallax Texture Gradient

Monocular Cues Shadow Overlapping Interposition

Monocular Cues Linear Perspective

Binocular Depth Cues: Finger Sausage

Perceptual illusions occur when sensory stimuli are misinterpreted; reveal the strategies we use

to interpret sensations correctlyMuller-Lyer

PonzoThe Ames room

VISUAL ILLUSIONS

Muller-Lyer

Ponzo

Size Distance Relationship

Size Distance Relationship

Size Distance Relationship

SizeShape

Lightness

PERCEPTUAL CONSTANCY

Perceptual Constancies