Unit Three – Sensation & Perception

[Chapter 4]

S &P: Your Ticket to the Outside World• Sensation: stimulation of sensory receptors

& transmission of sensory info to CNS– Receptors in sensory organs (eyes, ears, skin, etc.)– Sensation is automatic (involuntary) process

• Perception: process in which sensations are organized into an inner representation of outside world (not automatic, not uniform)– Influenced by strength of stimuli, human factors

• Our sensitivity to stimuli is not perfect…– Absolute threshold: the minimum amount of

stimuli that can be distinguish from nothing at all• Only requires 50% accuracy (see chart to the right)• Under ideal conditions, we are amazingly sharp

– Difference threshold: the minimum difference in magnitude of 2 stimuli required to tell them apart• Again, only requires 50% accuracy to count• See Weber’s constants for differences (see textbook

– p. 144)

Absolute Thresholds for Humans:

• vision: a candle flame viewed from 30 miles on a clear night

• hearing: a watch ticking from 20 feet away in a quiet room

• taste: 1 teaspoon of sugar dissolved in 2 gallons of water

• smell: one drop of perfume diffused throughout a small house

• touch: the pressure of a wing of a fly falling on a cheek from 0.4 inches

How old is the woman in the picture?

(Click to continue)

On Tuning In or Tuning Out• Signal-Detection Theory: physical, biological,

psychological factors shape our perceptions– Sensory information often creates uncertainties – Many factors influence how we interpret them

• Amount of unrelated sensory information (“noise”)• Individual differences in sharpness of senses• Our prior experiences shape our expectations• Level of focus, motivation, mood also play a role

– Different people can be exposed to the same stimuli and have very different perceptions

– Selective Attention: our ability to distinguish desired stimuli for unwanted info is pretty keen• “Cocktail Party Effect”: to hear one voice out of many

• Sensory Adaptation: Our individual sensitivity can increase or decrease based on situation– Sensitization: becoming more sensitive to stimuli

that are low in magnitude (positive adaptation)– Desensitization: becoming less sensitive to constant

stimuli (negative adaptation)

Visual Sensation• Vision is the strongest of the human senses

– The collection of a small portion of the spectrum of electromagnetic energy: visible light (Roy G. Biv)• Length of visible light wave determines hue (color)

– Sharp vision allows humans to collect information about their surroundings without close or direct contact.• Compare to touch, taste, smell. Advantages?

• The World of Color– Color is a byproduct of the visible spectrum of light,

as surfaces emit, absorb, or reflect waves.• Adult humans can detect 1000s of colors; newborns: 0

– Detected by photoreceptors on the retina of the eye• Cones sense colors; Rods sense brightness & motion• Scientists debate the role different types of cones we

possess and how exactly they function (see text, p153)– Color Blindness: A World Without (a) Color

• Trichromat: possess all three types of cones• Monochromat: cannot detect color, only light & dark• Dichromat:can’t tell between red/green or blue/yellow

Visual Perception• Gestalt Psychology: studying the tendency to

organize individual bits of sensory information into meaningful wholes– Gestalt Rules for perceptual organization

• Figure-Ground: seeing geometric forms on background• Proximity: grouping together objects near each other • Similarity: grouping together objects like each other• Continuity: seeing separate lines or points as unified• Closure: seeing completed figure even when gaps exist

• Top-down vs. Bottom-up Processing– Analogous to putting together a jig-saw puzzle– Top-down processing: use of contextual information

or knowledge of pattern in order to organize pattern• Using picture on box to help piece together puzzle• When expectations or assumptions guide perception

– Bottom-up processing: organization of the parts of a pattern to recognize, or form an image of, the pattern• Putting a puzzle together without the picture on the box• When sensory data guides perception

– We function best when we are able to use both

Proximity

Similarity

Continuity

Closure

Ambiguous Figure/Ground Relationship

Ghostly Dots

• Notice that a strange effect is taking place on the white dots of this design. Strange black dots appear to be appearing over all the dots accept the one you are looking at!!! Then when you try to look at these dots they disappear!

• Still not fully under-stood, this is called the Hermann effect. The theory relates to the rods in center and periphery of your retina sending contradictory signals to your brain.

• Try looking at one of the black boxes…

Afterimage

• Fix your eyes on the center of the image for a minimum of 30 seconds & try not to move your gaze.

• Now quickly look at one of the white boards on the side of the room. You’ll see a circle of light and an astonishing image.

• Results from rod fatigue on your retina. Bright lights will have a similar effect, leaving a polarized trace image after you look away or close your eyes.

Moving Squares

• This illusion has two aspects: depth segregation and illusory motion

• Although this is a flat image, its components trick our brains into detecting a 3-D image. Much of this has to do with the difference in the edges of the shapes.

• Although this a still image, its creates a sense of movement to the brain. It is able to point out that the brain tries to make assumptions about depth and movement based on experience.

Spirals or Circles?

• This illusion shows the Gestalt rule of closure, as the mind naturally tries to close the shapes of this image into a single form. Much of this “perceptual reflex” has to do with the angles of the squares.

• Upon closer study, we are able to recognize that the squares form concentric circles that do not touch.

• In that we have to “realize” what is going on, this illusion shows that perceiving is not the same as understanding.

Sienna Brick Illusion

• This illusion shows a couple of the perceptual phenomenon we have discussed, most notably an ambiguous figure-ground relationship.

• Do you see stacked boxes with red tops?

• Or stacked boxes with black tops?

• Not many people will automatically see strings of white, red, and black diamonds at different angles. This would be a 2-D interpretation.

• This demonstrates the mind’s preference to create a 3-D representation.

Auditory Sensation & Perception• Sounds are created by changes in air pressure

– Expansion & contraction creates sound waves, emanating from the source like ripples in a pond• Length of wave sets frequency, measured in hertz (Hz)• Amplitude sets loudness, measured in decibels (db)

– Structures of ear funnel and amplify these changes in pressure and convert them into vibration of fluid• Tiny, hair-like receptors sense vibrations, signal to brain

– Having two ears provides clues to source of sounds• Stereo effect causes sounds to arrive in each ear at

slightly different times and intensities.

• Perception: Loudness, Pitch, and Language– Loudness is perceived through number of receptor

cells in the organ of Corti that fire impulses to brain– Scientists debate nature of precise pitch perception

• Some think that receptor cells in cochlea are arranged in order of pitch like a keyboard (Place Theory)

• Others believe that receptor cells fire at same frequency as that of sound wave (Frequency Theory)

– Speech perception crucial for human communication

The Chemical Senses: Taste & Smell• Both smell and taste function by collecting

molecular (chemical) samples of surroundings• Our ability to smell has many purposes

– Airborne molecules (odorants) are collected by breath of nostrils and stimulate the olfactory receptors• creates patterns of electrical activity perceived as smells

– Helps us enjoy delicious foods & avoid rotten ones– Olfactory bulb part of limbic system; smell closely tied

to emotions and memories (examples?)– Our sense of smell desensitizes very rapidly– Pheromones: is smell linked to physical attraction

• Tastes allows us to gain nutrients, avoid poison– The tongue has over 10,000 taste buds, each with 50

receptors that send signals to the brain– Both genetic & cultural influences on taste perception– Different basic tastes: sweet, salty, sour, bitter, others– Taste is merely one component of what is flavor

• Also odor, texture, and temperature• With a nose plug & blindfold it is difficult to tell an apple

from an onion

Skin Senses: More Than Touch• Skins protects & coats our bodies, collects a

variety of sensory information for our brains– Can discriminate touch, pressure, temperature, pain– Each sensation has unique receptors on, below skin

• Touch & Pressure– Receptors fire when skin is touched, tissue is moved– Active touching: continuous movement upon skin to

receive constant sensory information about an object– Different parts of body have different sensitivities

due to an unequal distribution of receptors• Homunculus: drawing of human where size of body

part is proportional to distribution of neurons

• Temperature: Everything is Relative– Receptors located just beneath skin’s surface– Sensation of temperature is relative for the most part

• Like smell, we desensitize to temperature info quickly• Extreme hot /cold often involve pain receptors instead

The Skin Senses: Pain & Perception• Pain sensation serves a vital protective purpose

– Awareness of injury guides decision-making regarding seeking care, resting injured area, and recovery

– Signals body’s natural healing process to initiate• Increased blood flow to area encourages healing

– Those who lack pain sensation at serious risk of harm

• Pain sensation uses unique neurological circuit– Receptors exclusive to pain located in skin, tissue– Travel along own pathways to specific regions of the

brain including the medulla, amygdala, hippocampus• Gate Theory: firing of other sensory receptors may block

out pain signals before they reach brain (examples?)– Endorphins quiet pain, create “high”

• Strong cognitive/emotional component to pain– Perception of pain signals seems to be greatly affected

by individuals expectations of pain and potential rewards, as well as their emotional state

– This does not mean that pain is “all in your head”, but that the level of pain each of us experience can be manipulated by cognitive and emotional factors

ESP: Perception Without Sensation• Its existence has been debated & studied by

psychologists, parapsychologists, society– Research has yet to yield reliable evidence it exists– Still, 60% of Americans believe in psychic powers

• Types of Extra-Sensory Perception:– Precognition: being able to perceive the future– Psychokinesis: mentally manipulating physical objects– Telepathy: transmissions of thoughts (mind-reading)– Clairvoyance: perception of objects without sensation

• Many in psychological community reject the study of parapsychology as inappropriate– To be considered scientific study, what do we need?– Joseph Rhine’s work with Zener cards in the 1930s

• Some subjects showed remarkable abilities in lab• These subjects had great difficulty replicating skills

– Selective reporting of data (“file-drawer problem”)• Failed hypotheses less likely to be reported or published• Causal observed more likely to remember a correct

predication than one that was incorrect