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