sensation outline
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Unit IV. Sensation and Perception
Unit 4. Sensation and Perception
College Board - “Acorn Book”
Course Description
6-8% (7-9% in past)
Unit IV. Sensation and Perception
Overview
A. Thresholds B. Sensory Mechanisms C. Attention D. Perceptual Processes
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
A. Thresholds
Threshold Absolute threshold Just-noticeable-difference (jnd) Weber’s Law Fechner’s Law (Psychophysical scaling) Subliminal perception
Unit IV. Sensation and Perception
Signal Detection TheoryChart
Response
Yes
Response
No
Signal
Present
Signal
Absent
Unit IV. Sensation and Perception
Signal Detection Theory Correctly identifies stimulus present
Response
Yes
Response
No
Signal
PresentHIT
Signal
Absent
Unit IV. Sensation and Perception
Signal Detection Theory Fails to identify stimulus present
Response
Yes
Response
No
Signal
Present
Hit MISS
Signal
Absent
Unit IV. Sensation and Perception
Signal Detection Theory Incorrectly identifies stimulus as present when absent
Response
Yes
Response
No
Signal
Present
Hit Miss
Signal
AbsentFALSE ALARM
Unit IV. Sensation and Perception
Signal Detection Theory Correctly identifies stimulus as absent
Response
Yes
Response
No
Signal
Present
Hit Miss
Signal
Absent
False Alarm Correct Negative
Unit IV. Sensation and Perception
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
Figure 6.7 The eyeMyers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers
Figure 6.8 The retina’s reaction to lightMyers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers
Table 6.1Myers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
Source:http://en.wikipedia.org/wiki/Color_mixing
A simulated example of additive color mixing
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
Source:http://en.wikipedia.org/wiki/Color_mixing
A simulated example of subtractive color mixing
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
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)
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
The Inner Ear From Coren, Ward, & Enns Sensation and Perception 6th ed. John Wiley &
Sons, Inc. 2004
Figure 6.16 Hear here: How we transform sound waves into nerve impulses that our brain interprets Myers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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.
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
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.
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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.
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
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.
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
D. Perceptual Processes
Feature analysis Bottom-up processing Top-down processing
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
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)
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
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.
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
Brightness Contrast
Unit IV. Sensation and Perception
Principles of Perceptual Organization:
Figure-Ground
Grouping (Gestalt Principles) Proximity (Nearness) Similarity Continuity Closure
Unit IV. Sensation and Perception
Closure
Unit IV. Sensation and Perception
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”
Unit IV. Sensation and Perception
Unit IV. Sensation and Perception
Necker cube (1)
Unit IV. Sensation and Perception
Necker cube (2)
Unit IV. Sensation and Perception
Necker cube (3)
Unit IV. Sensation and Perception
Necker cube (4)
Unit IV. Sensation and Perception
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)
Unit IV. Sensation and Perception
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)
Unit IV. Sensation and Perception
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
Unit IV. Sensation and Perception
The Janus Mask
Example of the Ames Room
Unit IV. Sensation and Perception
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.)
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