Sensation & Perception Don’t Just Happen

1
Sensation Perception DontJust Happen

• Sensation
• Light bounces off Dilbert
• Light forms image on retina
• Image generates electrical signals in
  receptors
• Signals travel along nerve fibers to the brain...

Perception Signals are processed and you
perceive Dilbert
2
How Do We Study Sensation?

• Psychophysics
• Study of the relationship twixt a physical
  stimulus and your perception of it.
• Concerned mostly with physical attributes of the
  stimulus (e.g., amp loudness).

Gustav Fechner Father of Psychophysics (and a lot
of fun at parties)
3
Absolute Thresholds
or How Low Can We Go?

• What is the minimum stimulation necessary to
  detect a stimulus 50 of the time?

Vision On a clear, dark night you can see a
candle from 30 miles away
4
Absolute Thresholds
(Measurements)

• Method of Limits
• Stimuli are presented in ascending or descending
  order
• Some stimuli above and some below threshold
• Ave crossover from Yes to No absolute threshold

5
Signal Detection
Detecting a weak signal depends on 1.
Signals strength 2. Our internal Y state
(experience, motivation fatigue)
Do absolute thresholds really exist?
6
Signal Detection
Signal
Present
Absent
Yes
Hit
Miss
Ss Response
False Alarm
Correct Rejection
No
7
Subliminal Stimulation
Can we process information without being aware of
it?
8
Subliminal Stimulation
Self-Help Tape
Memory
Self-Esteem
M-M
M-SE
Memory
Subject Request
SE-M
SE-SE
Self-Esteem
Result? ZILCH! No Differences!
9
Difference Thresholds (JND)
What is the minimum difference between
two stimuli that a person can detect 50 of the
time?
10
Difference Thresholds (JND)
What is the minimum difference between
two stimuli that a person can detect 50 of the
time?
(Ernst) Webers Law Regardless of magnitude, two
stimuli must differ by a constant proportion for
the difference to be noticeable.
11
Sensory Adaptation
The most important aspect of our environment is...
CHANGE
CHANGE
Our senses are designed to notice
changes Visual Auditory Olfactory Touch
CHANGE
CHANGE
CHANGE
CHANGE
CHANGE
CHANGE
CHANGE
Sensory Adaptation
12
(No Transcript)
13
Vision
Transduction - the process by which stimulus
energy (e.g., light) is converted into neural
energy.
Electromagnetic Spectrum
Violet 360nm Indigo Blue Green 500nm Yellow Orange
600nm Red 700nm
14
Properties of...LIGHT
15
Properties of...LIGHT
16
The Eye
Cornea
Iris
Lens
Blind Spot
Fovea
Retina
Optic Nerve
17
Retina (Rods Cones)
Retina
Cones Rods Number 6 million 125
million Location in Retina Center Periphery Sensi
tivity to Light Low High Color Sensitive Yes No
18
Dark Light Adaptation
Adaptation - process by which the eye
becomes more or less sensitive to light
19
Visual Receptive Fields
Receptive Field Retinal area that,
when stimulated, affects the firing of that cell
Lateral Inhibition Neural activity in a cell that
opposes activity in surrounding cells
20
Lateral Inhibition in Action
21
Visual Pathway
Left Visual Field
Right Visual Field
Optic Nerve
general perception
localization of objects
Optic Chiasm
Retina
Optic Chiasm
Superior Colliculus (Midbrain)
LGN
Thalamus
Visual Cortex
Right Visual Cortex
Left Visual Cortex
Corpus Callosum
22
Processing Info in the Visual Cortex
Hubel Wiesel
Three Major Types of Visual Cells in Cortex
Simple Cells - line of correct width angle, in
the right position in receptive field Complex
Cells - same as Simple, plus line must be moving
in a particular direction Hypercomplex Cells -
same as Complex but line must be a certain length
23
Visual Information Processing
Retinal Processing Rods Cones èBipolar Cells
èGanglion Cells
Feature Detection Detector cells respond to
elementary features
Abstraction High-level cells respond to combined
info from feature-detector cells
Recognition Brain matches the constructed image
with stored images
24
Color Vision
Do objects possess color?
25
Trichromatic Theory of Color Vision
Human eye has 3 types of cone receptors sensitive
to different wavelengths of light.
Short
Medium
Long
People see colors because the eye does its own
color mixing by varying ratio of cone neural
activity
26
Cones and Color
27
Opponent Process Theory
Ewald Hering - Eye contains 3 mechanisms that
produce antagonistic responses to three pairs of
colors
Why? Afterimages Color Deficiency
28
Form Perception Feature Analysis
Bottom-Up Processing Based upon properties of the
stimulus (e.g., patterns of light dark areas
Top-Down Processing Based upon higher-order inform
ation (e.g., prior knowledge context)
What is this picture?
29
Subjective Contours
Subjective Necker Cube
Is it really there?
Perception of contours where there really are
none.
30
If a tree falls
NOSound (like color) is all in your head!
31
Hearing
What is Sound? Compression Rarefaction of air
molecules.
32
Sound Waves
Amplitude (Loudness) Strength or height of
the wave
Frequency (Pitch) Distance twixt consecutive peaks
Mix (Timbre) Interaction of different waves
1 Hertz 1 Cycle/Sec
Human Hearing 20 - 20k Hz
33
Outer Ear
auditory/8th nerve
pinna
malleus
cochlea
auditory canal
incus
tympanic membrane
Pinna - collect and direct sound into auditory
canal
Auditory Canal - amplify funnel sound
to tympanic membrane
Tympanic Membrane - collect sound vibrate
ossicles
34
Middle Ear
Malleus - vibrate move the Incus Incus -
vibrate move the Stapes Stapes - vibrate
against Oval Window of Cochlea
35
Inner Ear
Cochlea - filled with fluid contains
receptors for hearing (Hair Cells)
Basilar Membrane - divides length of cochlea
holds the hair cells
36
Auditory Pathway
37
Perceiving Pitch
Place Theory - pitch determined by point of
maximal vibration on basilar membrane Traveling
Wave Theory 1957
Frequency Theory - pitch determined by the
rate at which the hair cells fire (i.e., 1KHz
tone cause hair cells to fire 1k times/sec)
Volley Principle