sensation outline

Unit IV. Sensation and Perception

Unit 4. Sensation and Perception

College Board - “Acorn Book”

Course Description

6-8% (7-9% in past)


Overview

A. Thresholds B. Sensory Mechanisms C. Attention D. Perceptual Processes


A. Thresholds

Threshold Absolute threshold Just-noticeable-difference (jnd) Weber’s Law Fechner’s Law (Psychophysical scaling) Subliminal perception


Signal Detection TheoryChart

Response

Yes

Response

No

Signal

Present

Signal

Absent


Signal Detection Theory Correctly identifies stimulus present

Response

Yes

Response

No

Signal

PresentHIT

Signal

Absent


Signal Detection Theory Fails to identify stimulus present

Response

Yes

Response

No

Signal

Present

Hit MISS

Signal

Absent


Signal Detection Theory Incorrectly identifies stimulus as present when absent

Response

Yes

Response

No

Signal

Present

Hit Miss

Signal

AbsentFALSE ALARM


Signal Detection Theory Correctly identifies stimulus as absent

Response

Yes

Response

No

Signal

Present

Hit Miss

Signal

Absent

False Alarm Correct Negative


B. Sensory Mechanisms

Vision The Stimulus – Light

Amplitude, wavelength, purity, saturation Structure of the Eye

Lens, retina, rods & cones, fovea Bipolar cells and ganglion cells Optic nerve and blind spot


Color - Color - Color Chromatic vs. achromatic (Colors vs. black &

white) Hue, brightness, saturation (Color, light-dark,

purity of color) Subtractive mixture vs. additive mixture

(filters vs. paints) Good Web Site on Color Mixing

http://home.att.net/~RTRUSCIO/COLORSYS.htm

Additive

New colors are made by the combination of different colored lights

The three colors used are Red, Green, and Blue

This is used for television screens, video, and computer monitors


Source:http://en.wikipedia.org/wiki/Color_mixing

A simulated example of additive color mixing


Subtractive

New colors can be made when paints, inks, markers, and other coloring media are combined

The three colors used are Magenta, Yellow, and Cyan

This is used in color printers


Source:http://en.wikipedia.org/wiki/Color_mixing

A simulated example of subtractive color mixing


http://home.att.net/~RTRUSCIO/COLORSYS.htm

The above site provides an informative explanation and description of color mixing Color Vision Mixing Light Mixing Dyes – Paints – Ink The Basic Three - The physics and biology

of color mixing Painting Photography Printing Other Considerations



Color Vision Trichromatic theory – Young-Helmholtz (three color receptors –

different wavelengths) Color blindness (dichromats, etc.) Processing at receptor level

Opponent-process theory – Hering, Jameson, Hurvich (three pairs of color-

sensitive neurons) Negative afterimage Processing at receptive field level (thalamus)


Color Vision:From Weiten. Themes and Variations. 4th ed. Brooks/Cole. 1998

Colors of the Rainbow

R O Y G B I V Color is determined by wave length Red is the longest wavelength of

visible light. Violet is the shortest Water (mist) refracts light into

different wavelengths



Hearing

The Stimulus – Sound waves Amplitude (Loudness), Wavelength or

frequency (Pitch), Wave purity or mixture (Timbre))

Structure of the Ear Outer ear – Auditory canal Middle ear – Eardrum, Hammer, Anvil,

Stirrup Inner ear – Cochlea, Basilar Membrane

The Ear From Coren, Ward, & Enns. Sensation and Perception 6th ed. John Wiley & Sons, Inc. 2004

Outer Ear•Auditory Canal•Eardrum

Middle Ear•Hammer, anvil, stirrup

Inner Ear•Cochlea



The Inner Ear From Coren, Ward, & Enns Sensation and Perception 6th ed. John Wiley &

Sons, Inc. 2004


Taste and Smell

Taste (Gustatory Sense) Stimulus – Chemicals Four taste receptors

Smell (Olfactory Sense) Stimulus – Chemicals Olfactory bulbs, olfactory cilia Pheromones Taste and Smell

Demonstrations Raw Apple, Raw Potato, Raw Onion Jelly Bellies


Skin Senses

PressureHotColdPain

Gate control theory in pain perception

See Reading: WHAT IS PAIN? Messages about tissue damage are picked up

by nociceptors and transmitted to the spinal cord via small myelinated fibers and very small un-myelinated fibers.

From the spinal cord, the impulses are carried to the brainstem, thalamus and cerebral cortex, and ultimately perceived as pain.

These messages are suppressed by a system of neurons that originate in the gray matter of the midbrain.


This descending pathway sends messages to the spinal cord where it suppresses the transmission of tissue-damage signals to the higher brain centers.

Some of these descending pathways utilize naturally-occurring chemicals called opioids.


HOW PAIN KILLERS WORK. At the site of injury, the body produces

prostaglandins which increase pain sensitivity. Some analgesics, such as aspirin, prevent the

production of prostaglandins. Acetaminophen is believed to block pain

impulses in the brain itself. Local anesthetics intercept pain signals

traveling up the nerve. Opiate drugs prevent the transfer of pain

signals from the spinal cord to the brain.Unit IV. Sensation and Perception


Internal Senses

Kinesthesis Internal body position Muscle position

Vestibular sense Balance Semi-circular canals in ear

C. Sensory Adaptation

Sensory adaptation is a change in sensitivity to a stimulus that results from exposure to the stimulus.

Examples include adapting to darkness, adapting to bright conditions, adapting to hot or cold conditions, adapting to the presence of odors, and many more.



Sensory Adaptation Light and Dark Adaptation

Entering / Exiting a movie theatre One eye covered demonstration

The eye has two types of photoreceptors Cones (for color) Rods (for night vision)

Dark Adaptation Move into a darkened theater and two

changes occur to increase sensitivity to light: The pupils enlarge. This admits more

light onto the retina of the eye. Light-sensitive chemicals in the

photoreceptors increase their concentration. This makes each photoreceptor more sensitive to light.


Light Adaptation

Leaving the theater, you encounter bright light Your pupils constrict immediately,

reducing the light reaching the retina The light-sensitive chemicals in the

photoreceptors quickly bleach out, reducing the photoreceptors’ sensitivity to light


Preserving Dark Adaptation

It takes 20-30 minutes to become fully dark adapted

This is destroyed by exposure to light in a few seconds

Rods are blind to red light Cover light source with red lens

Read map with conesRods remain dark adapted


Sound Adaptation

Adaptation to loud noise Very loud sound

small muscle in the inner ear contracts dampens sound vibrations being

conducted by the ossicles (bones) to the chochlea

Adaptation does not work well for sudden loud sounds, such as gun shots


Odor / Smell

The sense of smell is probably the quickest sense - as a whole - to adapt

We can detect amazingly low concentrations of some chemicals in the air (e.g., perfumes) but although the perfume is still in the air about us, we quickly cease to detect it


Taste

Certain tastes may cause rather surprising (and unexpected) anomalies in other taste stimuli Eating artichoke makes sour substances

taste sweet briefly Jujuba temporarily abolishes sweet

sensitivity Spicy foods will also stimulate pain

receptors


Touch – Heat – Cold

Skin temperature receptors respond more to rate of change in temperature than to steady temperature

This explains why hot bath feels hot at first, then cooler

This explains why pool/ocean feels freezing at first, then comfortable cool

Demonstration One Hand in Cold Water, the other in

Warm WaterUnit IV. Sensation and Perception

Pain Adaptation

Acute pain – tells us to get away from the painful stimulus

Chronic pain – tells us not to move something while it heals



C. Attention Selective Attention Bottleneck Theories of Selective Attention

We have a limited capacity to attend to stimuli There is no limit to how much stimulation can

be present Selective Attention allows us to select what

to attend to Sometimes we seem to do it Other times it seems to happen to us

Selective Attention and the Cocktail Party Phenomenon

Cocktail Party Phenomenon the ability to focus one's listening attention

on a single talker among a mixture of conversations and background noises, ignoring other conversations

then if someone over the other side of the party room calls out our name suddenly, we also notice that sound and respond to it immediately


Selective Attention and the Stroop Test

Stroop Test Why is this task so difficult to do reading is an automatic process color naming is a controlled process automatic process of reading interferes

with our ability to selectively attend to ink color


Bottleneck or Filter Models of Selective Attention

Early selection David Broadbent (1958) proposed that physical

characteristics of messages are used to select one message for further processing and all others are lost

Attenuation Treisman (1964) proposed that physical characteristics

are used to select one message for full processing and other messages are given partial processing

Late Selection Deutsch & Deutsch (1963) proposed that all messages

get through, but that only one response can be madUnit IV. Sensation and Perception


D. Perceptual Processes

Feature analysis Bottom-up processing Top-down processing


Is it a circus act?

Or a couple dancing?

Ambiguous or Reversible figure

Feature analysis Detecting specific

elements Assembling them in a

more complex form


Bottom-up Processing

A progression from Individual elements to the

whole

Also called data-driven processing

Detect Specific Features

Combine features

Recognize Stimulus

Bottom-Up Processing

Perception must be largely data-driven because it must accurately reflect events in the outside world

The information is determined mainly be information from the senses (not from your expectations)



Top-Down Processing

A progression from The whole to the elements

Also known as schema-driven processing

Form perceptual hypothesis about the nature of the

stimulus as a whole

Select and examine features to

Check hypothesis

Recognize Stimulus

Top-Down Processing

In many situations your knowledge or expectations (or schemas) will influence your perception

In this case a schema is a pattern formed earlier in your experiences.


Abstract concepts tend to be referred to as higher level

Concrete details are referred to as lower level

Top-down occurs when a higher level concept influences your interpretation of lower level data

Set or expectancy demonstrate top-down processing

Ambiguous figures often demonstrate top-down processing



Visual Contrast Brightness contrast (gray on white

appears darker than gray on black) Mach Bands (Series of bands of

increasing darkness - each strip affected by the neighboring strips)

Lateral inhibition


Brightness Contrast


Principles of Perceptual Organization:

Figure-Ground

Grouping (Gestalt Principles) Proximity (Nearness) Similarity Continuity Closure


Closure


Perception of Depth and Distance Perception of Motion Perceptual Constancy (Size, Shape,

Brightness) Perceptual Illusions Perceptual Set Perceptual Adaptation

Depth Perception “I could have

sworn that mesa was a whole lot farther away”


Necker cube (1)


Necker cube (2)


Necker cube (3)


Necker cube (4)


Necker cube (5)

Handouts

DISTRIBUTION OF RODS AND CONES – Bernstein (Colored pencils)

Light-Dark Sensory Adaptation Demonstration (Eye patch)

Simple Compelling Demonstrations of Retinal Disparity (“Hole in hand” etc.)

DEMONSTRATING THAT SMELL IS AS IMPORTANT – Beins (Jelly Bellies)


Monocular Depth Perception Student Assignment

Chart - Depth Perception Cues (Study Guide / May be used in a variety of assignments)

Color Vision – Roygbiv (Demonstration) Pulfrich effect (Reading from Wikipedia)


Moon Illusion (Reading from Bad Astronomy by Philip Plait)

The Big Picture - Gestalt applied The Neuroscience of Yorick's Ghost and

Other Afterimages Mindsights Tables (Drawing by Shepard) Various Visual Illusions


The Janus Mask

Example of the Ames Room


The Magic of the Wundt-Jastrow Illusion

From: Gregory, R. I., Eye and Brain (2nd ed.) New York: World University Library, 1973. (pp. 78-80.)

sensation outline

Health & Medicine

pain perception unit

absent unit iv

color color

color printers unit

considerations unit

past unit iv

stimulus present unit

different wavelengths