Psychology 100:11

Chapter 5.1

Sensation &

Perception

Study Question:

• What are four common elements of our various senses? Use examples from two senses to clarify your answer.

Outline• Introduction

– Syllabus & code of conduct

• Sensation and Perception– Phantom Limb Pain– Coding– Psychophysics

Introduction• My Psych 100 web site

– Power Point Lectures

– Syllabus

– Policies

– Lab information

– Interesting links

Psych 100 Page

• Sensation: The experience of a physical stimulus.– The initial steps taken by sense organs and neural

pathways to organize information.

• Perception: Subsequent organization and meaningful interpretation of physical stimuli.– Later processing steps that lead to internal

representations of the stimulus

• Ronald Melzack - The “King of Pain?”“Pain is in the brain”

Ronald Melzack

Sensation

Sensation

From: A journey to the center of your mind

Vilayanur Ramachandran

Sensation• Three classes of interest

1. Physical stimuliE.g, visible light, sound waves, odors, etc.

2. Physiological response Electrical activity in sense organs, nerves, and

brain

3. Sensory experience Psychological sensations

E.g., sound, sight, smell, taste, etc.

Physical Stimulus

PhysiologicalResponse

Sensory Experience

SensoryPhysiology

SensoryPhysiologicalPsychology

Psychophysics

SensationDomains of questions

Sensation

• Sensory coding– Recording music

>Vinyl, tape, and digital codes

– Physical properties of stimuli -> neural code> nerve impulses

Sensation

• Common elements of the various senses– Receptors: Cells that respond to physical stimuli

by creating electrical impulses.

– Transduction: The process by which stimuli alter the balance of Na+ and K+ until a receptor reaches receptor potential.

– Sensory Neurons: Neurons that carry the impulses from the receptor to the CNS.

– Sensory Areas: Specific areas of the cerebral cortex designated for analyzing/organizing sensory information.

Sensation• Quantitative and qualitative aspects

– During transduction information concerning the quantitative and qualitative aspects of the stimulus are coded.>Quantitative information: The intensity of the

stimulus, e.g., sound volume. Coding quantity: Faster rate of responding

>Qualitative information: Type of energy contained in the stimulus, e.g., sound frequency, colour.

Coding quality: Different receptors respond to different forms of energy.

Sensation• Psychophysics

– Absolute Threshold: The critical level of intensity that gives rise to sensation.

– Fechner and the difference threshold>Just Noticeable Difference (JND). The smallest

difference between two similar stimuli that can be distinguished.

– Weber: The size of a JND depends on stimulus intensity

e.g., 3 people hum + 1 more -> noticeable 100 people hum + 1 more -> not noticeable

Gustav Fechner

II

= c

I10

1=10

I50

1=10

If 50 people hum, how many more must be added to notice the difference?

Answer: 1

E.g, The Weber fraction for loudness c = 1/10 If 10 people hum, how many more must be added to notice the difference?

• The Weber fraction:

Answer: 5

Sensation

Ernst Weber

Sensation• Other Weber Fractions:

– Vision: 1/60

– Kinesthesia: 1/50

– Pain: 1/30

– Pressure 1/7

– Smell 1/4

– Taste 1/3

Sensation• Fechner’s law: Sensation strength grows as a

function of the Log of stimulus intensity– E.g., 15 w, 30 w light bulbs vs. 30 w, 45 w

S = k log(I)

– Where> S = magnitude of sensory experience

> K = a constant

> I = stimulus intensity

Gustav Fechner

Sensation– Loudness is measured using this relationship:

> S =decibels (dB)> I = sound pressure units

> K = 20Example     Sound pressure units (I)  Log(I)  20Log(I)= dB

Softest detectable 1 (100) 0 0

Conversation 1000 (103) 3 60

Bar band 100000 (105) 5 100

Jet airplane 10000000 (107) 7 140

- Loudest Band (130 - 140)?

Sensation• Signal detection theory

– Human judgement and the absolute threshold

> E.g., A radar operator during 9/11/01 versus a radar operator today

> Sensation vs. decision> Discriminating a signal + noise from noise alone> Lax (yea-sayer) and strict (nea-sayer) criterion

E.g., Hits and false alarms on a true-false test

Sensation• Signal detection theory

- Payoff matrices

MissHit

Correctrejection

Falsealarm

Response

Yes No

Sti

mul

us

On

Off

Sensation• Signal detection theory

- Gullible student (Lax; yea-sayer)

10 %90 %

40 %60 %

Response

True False

Tes

t Ite

m True

False

Sensation• Signal detection theory

- Skeptical student (strict; nea-sayer)

40 %60 %

90 %10 %

Response

True False

Tes

t Ite

m True

False

Sensation• Signal detection theory

– Dissociates “Bias” from “Sensitivity> Receiver operator charactistics

Bias vs. Sensitivity

Hit

Rat

e

False Alarm Rate

1.0

.5

1.0.5

Strict

Lax