Exploring Sensation and Perception in Psychology: An Overview

Psychology 100:11 Chapter 5.1 Sensation & Perception

Outline • Introduction • Syllabus & code of conduct • Sensation and Perception • Phantom Limb Pain • Coding • Psychophysics Study Question: • What are four common elements of our various senses? Use examples from two senses to clarify your answer.

Introduction • My Psych 100 web site • Power Point Lectures • Syllabus • Policies • Lab information • Interesting links Psych 100 Page

Ronald Melzack Sensation • 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”

Sensation Vilayanur Ramachandran From: A journey to the center of your mind

Sensation • Three classes of interest • Physical stimuli E.g, visible light, sound waves, odors, etc. • Physiological response Electrical activity in sense organs, nerves, and brain • Sensory experience Psychological sensations E.g., sound, sight, smell, taste, etc.

Sensory Physiology Physiological Response Physical Stimulus Sensory Physiological Psychology Psychophysics Sensory Experience Sensation Domains 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.

Gustav Fechner 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

Ernst Weber Sensation • The Weber fraction: • E.g, The Weber fraction for loudness c = 1/10 • If 10 people hum, how many more must be added to notice the difference? Answer: 1 If 50 people hum, how many more must be added to notice the difference? Answer: 5

Sensation • Other Weber Fractions: • Vision: 1/60 • Kinesthesia: 1/50 • Pain: 1/30 • Pressure 1/7 • Smell 1/4 • Taste 1/3

Gustav Fechner 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

Sensation • Loudness is measured using this relationship: • S =decibels (dB) • I = sound pressure units • K = 20 Example 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

Response Yes No Hit Miss On Stimulus False alarm Correct rejection Off Sensation • Signal detection theory - Payoff matrices

Response True False 90 % 10 % True Test Item 60 % 40 % False Sensation • Signal detection theory - Gullible student (Lax; yea-sayer)

Response True False 60 % 40 % True Test Item 10 % 90 % False Sensation • Signal detection theory - Skeptical student (strict; nea-sayer)

False Alarm Rate .5 1.0 1.0 Lax Hit Rate .5 Strict Sensation • Signal detection theory • Dissociates “Bias” from “Sensitivity • Receiver operator charactistics Bias vs. Sensitivity

Exploring Sensation and Perception in Psychology: An Overview