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Sensation and
Perception
Modules 18, 19 , 20
What we’ll sense and perceive…in this chapter: Sense:
especially vision and hearing smell, taste, touch, pain, and
awareness of body position How do the sense organs and
nervous system handle incoming sensory information?
How does the brain turn sensory information into perceptions?
Why is our style of creating perceptions better at perceiving the real world than at decoding tricky optical illusions?
Sensation vs. Perception
“The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.”
“The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.”
The brain receives input
from the sensory organs.
The brain makes sense out of the
input from sensory organs.
Sensation Perception
Making sense of the world
What am I seeing?
Is that something I’ve seen before?
Bottom-up processing:
taking sensory information and then assembling and integrating it
Top-down processing:
using models, ideas, and
expectations to interpret sensory
information
Do you see a painting or a 3D
bottle?
What’s on the bottle?
Kids see eight to ten dolphins.
Why do you think kids see
something different than
adults?
Top-down Processing You may start
to see something in this picture if we give your brain some concepts to
apply: “tree”
“sidewalk”“dog”
“Dalmatian”
From Sensory Organs to the Brain
The process of sensation can be seen as three steps:
Reception--the stimulation
of sensory receptor cells by energy (sound, light, heat, etc)
Transduction-- transforming
this cell stimulation into neural impulses
Transmission--delivering this
neural information to the brain to be
processed
Sensation-Perception
The strange case of Dr. PVisual Agnosia
seeing without "knowing"
Helen SellersProsopagnosia
face blindness
http://abcnews.go.com/GMA/Books/video/heather-sellers-battle-face-blindness-11906989
Fusiform areaFace recognition
Face blindness
ProsopagnosiaGreek:
“prosopon” ( face) “ag nosia” (not knowing)
What if face recognition ok, but emotion inputs are disconnected?
CAPRAS SYNDROME: My wife is an imposter!!
Oliver SacksProsopagnosia
face blindness
https://www.youtube.com/watch?v=k5bvnXYIQG8
Sensation-Perception Agnosias show both sides of “-”
Sensation transduction/assemblyPerception recognition/meaning
Importance of S-P research ancient philosophical riddle: What is reality? clinical and practical applications
Sensory disordersProblems of daily living (e.g. accidents)
3 Approaches to Sens-Percep
1. Psychophysical
2. Physiological
3. Cognitive
Psychophysics Quantifying sensation
How much energy needed before detection?What does "twice" as loud mean?
Gustav Fechner (1860)Absolute threshold (50% likelihood of being
detected)
Thresholds
The absolute threshold refers to the minimum level of stimulus intensity needed to detect a stimulus half the time.
Anything below this threshold is considered “subliminal.”
Psychophysics Gustav Fechner (1860)
JND= Just Noticable Difference Q: What is the JND for light?Q: What is the JND for sound?
Any general law for intensity scaling? Weber's Law: Intensity = constant proportion of initial stimulus
Weber Fraction e.g., JND for light = 1/60 watts
General scaling of "intensity“
Fechner: Use #JNDs above absoluteStevens (1960s): “Power Law”
Magnitude ratings Fit mathematical curves Best fitting exponent for each sense
When Absolute Thresholds are not Absolute
17
Signal detection theory refers to whether or not we detect a stimulus, especially amidst background noise. This depends not just on intensity of the stimulus but on psychological factors such as the person’s experience, expectations, motivations, and alertness.
Signal Detection Theory (SDT)
Detection is rarely absolute because Stimulus certainty varies (e.g., noise)Motivation varies (e.g., boredom)
Signal Detection Theory (SDT)Hits + / +Correct Rejections - / -Misses - / +False Alarms + / -
Signal Detection Theory (SDT)
Detection rate controlling response bias
Takes into account statistical nature of detection
Takes into account psychological factors affecting detection
Signal Detection Theory (SDT)
In medical diagnosis which signal detection outcome is most critical?
a) Hits
b) Misses
c) False Alarms
d) Correct rejections
Signal Detection Theory (SDT)
In the judicial system which signal detection outcome is most critical?
a) Hits
b) Misses
c) False Alarms
d) Correct rejections
Sensory Adaptation Entering movie theatre (vision) Visiting friend's apartment (smell) Change detection is evolutionarily critical
Why don't visual images fade? Saccades eye movements
Pritchard (1961) Martinez-Conde et al. (2006)
Sensory Adaptation
Even visual perception of emotional expressions show evidence of sensory adaptation….
Gaze at the angry face on the left for 20 to 30 seconds, then look at the center face (looks scared, yes?). Then gaze at the scared face on the right for 20 to 30 seconds, before returning to the center face (now looks angry, yes?). (From Butler et al., 2008.)
http://www.forbes.com/pictures/eimh45mfkh/mocha-cookie-crumble/
500 grams of fat.
2 Big Macs
=
Subliminal Perception Sub + Limen
Advertising: e.g., "Joe Camel"
Big Tobacco & Subliminal Percep.
Subliminal Perception
Silverman (1988)Use subliminal msg. to test Freudian ideas
“Dynamic Activation Method”
Tachistoscope
“Mommy and I Are One”
RESULT? Positive mood/wellbeing
“Beating Dad is OK” RESULT? Dart throwing accuracy
Begg et al (1993) Rock band Judas Priest, lawsuit: “Do it!” Experiment : backward song effect??
No comprehension. No effect on behavior.
Greenwald et al. (1991) Self-esteem; Memory enhancementGave wrong tape to half of sample.Measured actual self-steem, and memory
Believed it worked---even if wrong tape!!NO effect on self-esteem, or memory.
Subliminal Perception
Krosnick et al. (1992) subliminal prime (dead bodies vs flowers) rate persons in photographs Result? primes affected ratings
Yes, subliminal primes can work.
But very weak, very brief.
Unknown sensory systems?
TelepathyClairvoyancePrecognition
ESP
Does ESP exist?JB Rhine (Duke University): 1934 book
Zenner Cards Guess the symbols!
Telepathy (sender)Clairvoyance (face down)Precognition (predict)
Results:RESULT: Yes, > chance! (5 vs 7.2) Wow! Maybe ESP is real ???
ESP: Bem & Hornton (1994 )Gansfeld Procedure
Sensory maskingTalk aloud about what
floats through one’smind
Present 4 objectsWhich one correct?
Psych Bulletin (199432 correct rate! (> chance)
Bem (2011) “Feeling the Future”
Extrasensory PornceptionNeutral? Chance levels (no effect).Erotic images?
53% accuracy!!
Bem (2011) “Feeling the Future”
No one has been able to replicate Bem’s result. Maybe it was bad stats and overly awed reviewers.
Sensory Systems1) Sensory neurons: transduction
2) Nerves--> spinal cord--> brain
3) Thalamus (except smell)
4) Cortex association areas
… retrieval, comparison, categorization...recognition,
5) Recognition !
6) Do something.
Vision
Electromagnetic Radiation Spectrum(e.g., Newton, Faraday, Maxwell...)
The Eye“…To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems I freely confess, absurd in the highest degree. "
Darwin, 1859
The EyeCharles Darwin (Origin of Species)
So complex!! Challenge to evolution theory?
Basic anatomy of the eye
The Eye
iris
pupil
Anatomy of the Eye
A
B
Anatomy of the Eye
Visual System
Pupil
Accommodationciliary muscles changing thickness of lens
Which has no rods?
http://www.youtube.com/watch?v=a1Y73sPHKxw
A: OWL B: CHIPMUNK
Visual SystemRetina ("Duplex" vision).
1. RodsB&W
125 million
high convergence (many converge on 1 ganglion cell)
v. sensitive to low light (eg, Owls)
Visual SystemRetina ("Duplex" vision).
2. Cones
Color vision (3 cone types: RGB)
6 million (all in the Fovea)
low convergence (1 to 1 ganglion cell)
chipmunks (no Rods)
Retina (cont'd) Fovea
small spot, middle of retinacones only (no rods)
Bipolar cells
Ganglion cellsaxons --> "optic nerve"
Horizontal & Amacrine cells"preprocessor" Frog: "bug detector"
Retina layers
Receptive Fields (center-surround)
Lateral antagonism
firing of a cell inhibits firing of adjacent cells
permits coding of contrasts
Explains Hermann Grid Ilusion...
Dark/Light Adaptation
Rodsslow to adapt (30 minutes)10,000x more sensitive to light
Cones fast to adapt (10 minutes) focal vision back quickly
Visual PathwaysThalamus
LGN (lateral
geniculate nucleus)
MidbrainSuperior
Colliculus
ThalamusLGN (lateral
geniculate nucleus)
MidbrainSuperior
Colliculus
Visual Pathways to the Brain
LGN (Lateral Geniculate Nucleus) parvocellular layer (90%)
form, texture, color
magnocellular layer (10%)depth, brightness, motion
LateralGeniculateNucleus90% of retinal ganglion cells send axons to LGN
1
2
3
4
5
6
Magnocellular layers
Parvocellular layers
Extrastriate Cortex (green)
Faces
Houses
Chairs
Houses and Chairs