Psychology 100 Chapter 4 Sensation & Perception

Psychology 100 Chapter 4 Sensation & Perception

Chapter 4.1 October 6, 2014 Outline • How do we sense our world? • - Areas of investigation • - Sensory coding • >Quantitative and Qualitative coding • - Psychophysics • > Weber’s and Fechner’s Laws • > Signal detection theory Study Question: • What is sensory transduction? Compare and contrast how quantitative and qualitative aspects of the sensory input get encoded.

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

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 • Common elements of the various senses

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, brightness. • 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. • E.g., Red, Green, and Blue receptors in the retina

Sensation • Quantitative and qualitative aspects

Approximate absolute thresholds Taste 1 tsp sugar in 4 liters of water Smell 1 drop perfume diffused in 6 rooms Touch A fly’s wing falling on your cheek from 1cm Hearing Clock tick at 6 meters Vision Candle flame at 50 kms on a dark clear night Sensation • Psychophysics • Absolute Threshold:The critical level of intensity that gives rise to sensation. • The faintest stimulus that can be detected 50% of the time

Gustav Fechner (1801-1887 ) Ernst Weber (1795-1878) Sensation • Psychophysics • 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 • The Weber fraction

Ernst Weber (1795-1878) Sensation • Psychophysics • 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? • If 50 people hum, how many more? Answer: 1 Answer: 5

Ernst Weber (1795-1878) Other Weber fractions Vision 1/60 Kinesthesia 1/50 Pain 1/30 Pressure 1/7 Smell 1/4 (in dogs -> 1/33) Taste 1/3 Sensation • Psychophysics • The Weber fraction

Gustav Fechner (1801-1887 ) Sensation • Psychophysics • Fechner’s law:Sensation strength grows as a function of the Log of stimulus intensity S = k log(I) Where S = magnitude of sensory experience K = a constant I = stimulus intensity • E.g., Loudness • S =decibels (dB) • I = sound pressure units • K = 20

Fechner’s law and sound: Decibels 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 Sensation • Psychophysics • Loudest Band (130 - 140)? • 1976 The Who 126 dB (measured at 32 meters) • 1984 Manawar 129.5 dB • 1994 Manawar 139 dB(during sound check, Guiness record terminated) • 2007 Gallows 132.5 dB (in studio, not live) • 2009 KISS 136 (measured by Ottawa bylaw officers)

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 (nay-sayer) criterion • E.g., • Hits and false alarms on a True/False test

Response True False Hit Miss True Test Item False alarm Correct rejection False Sensation • Signal detection theory • Payoff matrices

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

Response True False 60 % 40 % True Test Item 10 % 90 % False Sensation • Signal detection theory • Payoff matrices • 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

Psychology 100 Chapter 4 Sensation & Perception