Week 6Perception

Sensation & Perception

Sensation Light bounces off people Light forms image on retina Image generates electrical

signals in receptors Signals travel along nerve

fibers to the brain...

PerceptionSignals are processed and you “perceive” people

(Kohn & Kohn, 1998)

How Do We Study Sensation?

Psychophysics• Study of the

relationship between a physical stimulus and your perception of it.

• Concerned mostly with physical attributes of the stimulus (e.g., amp & loudness).Gustav FechnerGustav Fechner

Father of Psychophysics(Richarson, 1999)

Absolute Thresholds

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

Intensity

Crossover Values

YYYYYYN

YYNNNN

YYYYYYN

YNNNNN

YYYYYYN

105104103102101100 99 98 97 96

99.5 99.5 98.5100.5 99.5

orHow Low Can We Go?

VisionOn a clear, dark

night you cansee a candlefrom 30 miles

away(Richarson, 1999)

Signal Detection

Detecting a weak signal Detecting a weak signal dependsdepends on:on:

1. Signal’s strengthSignal’s strength2. Our internal psychological Our internal psychological states states (experience, motivation & fatigue)

Do “absolute” thresholds really exist?Do “absolute” thresholds really exist?(Richarson, 1999)

(Kohn & Kohn, 1998)

(Kohn & Kohn, 1998)

Subliminal Stimulation

Can we process informationwithout being aware of it?

(Richardson, 1999)

Subliminal StimulationSelf-Help Tape

Memory Self-Esteem

SubjectRequest

Memory

Self-Esteem

M-M M-SE

SE-M SE-SE

Result? No Differences!No Differences!(Richardson, 1999)

What is the minimumdifference between two

stimuli that a person candetect 50% of the time?

What is the minimumdifference between two

stimuli that a person candetect 50% of the time?

Difference Thresholds (JND)

(Richardson, 1999)

What is the minimumdifference between two

stimuli that a person candetect 50% of the time?

What is the minimumdifference between two

stimuli that a person candetect 50% of the time?

Difference Thresholds (JND)

(Ernst) Weber’s Law“Regardless of magnitude, two stimuli must

differ by a constant proportion for thedifference to be noticeable.”

(Ernst) Weber’s Law“Regardless of magnitude, two stimuli must

differ by a constant proportion for thedifference to be noticeable.”

(Richardson, 1999)

VisionTransduction - the process by which

stimulus energy (e.g., light) is convertedinto neural energy.

ElectromagneticElectromagneticSpectrumSpectrum

(Kohn & Kohn, 1998)

LongerWavelength

LowerFrequency

LongerWavelength

LowerFrequency

ShorterWavelength

HigherFrequency

ShorterWavelength

HigherFrequency

Properties of...LIGHT

(Richardson, 1999)

SmallerAmplitude

DullColors

SmallerAmplitude

DullColors

HigherAmplitude

BrightColors

HigherAmplitude

BrightColors

Properties of...LIGHT

(Richardson, 1999)

The Eye

Lens

(Kohn & Kohn, 1998)

Retina (Rods & Cones)

Cones RodsNumber 6 million 125 millionLocation in Retina Center PeripherySensitivity to Light Low HighColor Sensitive Yes No

RetinaRetina

(Richardson, 1999)

Dark & Light Adaptation

Adaptation - process by which the eye becomesmore or less sensitive to light

(Kohn & Kohn, 1998)

Processing Info in the Visual Cortex

Three Major Types ofThree Major Types ofVisual Cells in CortexVisual Cells in Cortex

Simple CellsSimple Cells - line of correct width & angle, in the right position in receptive field

Complex CellsComplex Cells - same as Simple, plus line must be moving in a particular direction

Hypercomplex CellsHypercomplex Cells - same as Complex but line must be a certain length

(Richardson, 1999)

(Kohn & Kohn, 1998)

Visual Information ProcessingRetinal Processing

Rods & Cones Bipolar Cells Ganglion Cells

Feature DetectionDetector cells respond to elementary features

AbstractionHigh-level cells respond to combined info

from feature-detector cells

RecognitionBrain matches the constructed image with stored images

(Richardson, 1999)

Trichromatic Theory of Color Vision

Helmholtz 1852

Human eye has 3 types of coneHuman eye has 3 types of conereceptors sensitive to differentreceptors sensitive to different

wavelengths of lightwavelengths of light.

Short Medium Long

People see colors because thePeople see colors because theeye does its own “color mixing”eye does its own “color mixing”

by varying ratio of coneby varying ratio of coneneural activityneural activity (Richardson, 1999)

(Kohn & Kohn, 1998)

Cones and Color

(Kohn & Kohn, 1998)

Opponent Process Theory

Ewald HeringEwald Hering - Eye contains 3 - Eye contains 3 mechanisms that produce antagonisticmechanisms that produce antagonistic

responses to three pairs of colorsresponses to three pairs of colors

R

G

B

Y

B

W

Why?Why?Afterimages & Color DeficiencyAfterimages & Color Deficiency (Richardson, 1999)

Hearing

What is Sound?What is Sound?Compression & Rarefaction

of air molecules. (Richardson, 1999)

Sound WavesAmplitude (Loudness)

Strength or height of thewave

Frequency (Pitch)Distance twixt consecutive

peaks

Mix (Timbre)Interaction of different

waves

1 Hertz = 1 Cycle/Sec1 Hertz = 1 Cycle/Sec Human HearingHuman Hearing20 - 20k Hz20 - 20k Hz

(Richardson, 1999)

(Kohn & Kohn, 1998)

(Kohn & Kohn, 1998)

(Kohn & Kohn, 1998)

(Kohn & Kohn, 1998)

(Kohn & Kohn, 1998)

Auditory Pathway

(Kohn & Kohn, 1998)

Perceiving Pitch

Georg von Békésy1899-1972

Place Theory - pitch determined bypoint of maximal vibration on

basilar membraneTraveling Wave Theory 1957Traveling Wave Theory 1957

Frequency Theory - pitch determined by the rateat which the hair cells fire (i.e., 1KHz tone cause

hair cells to fire 1k times/sec) Volley PrincipleVolley Principle

(Richardson, 1999)

(Kohn & Kohn, 1998)

Smell

(Kohn & Kohn, 1998)

Taste

(Kohn & Kohn, 1998)

References

• Feldman, M. (1999). McGraw Hill Company. Retrieved May 2002 from World Wide Web at: http://www.mcgrawhill.com.

• Kohn, A. J. & Kohn, W. (1998). The Integrator 2.0. CD-Rom. Brooks/Cole Thomson Learning.

• Richardson, K. (1999). Retrieved May 2002 from the World Wide Web at:

http://www.monmouth.edu.