Lecture #1 – Sensation
Chapter 5 – Sensation * How do we perceive the world around us? * Gain information from a variety of sources * Psychophysics and Psychophysiology
What do Weber fractions tell you about sensation?
Psychophysics is a relation between physical stimulus and psychological response * Fechner: Father of Psychophysics * Can determine a just noticeable difference * JND – Just Noticeable Difference * Can be light, hearing – tells us how sensory systems are taking information in
Threshold * Value of a stimulus characteristic required to produce some response * Absolute: Lower Limit * Sensory systems kick in
Vision: Candle flame at 50 km on a clear dark night
Hearing: Tick of a watch at 6 metres
Taste: Tsp. of sugar in 8 L. of water in order of most sensitive
Smell: 1 drop of perfume in a 6 room apt.
Touch: Wing of a fly falling on cheek from 1 cm * Difference: Amount of change for JND * What’s the relation between psychological stimulation and actual stimulation * Example: Brightness & Perceived Brightness * Not a 1 to 1 relation
Weber’s Law * Size of difference threshold relative to physical intensity of test is constant * If I = 50db and JND is reported at 55db. Therefore delta I is 5 and I is 50 * Therefore C = 5/50 = 1/10 * Note: Can we predict other JNDS * Example: What a JND at 10db * 10 I = therefore delta I is 10. This tells us that the JND would occur at 110db, or the test bends – 90db. Allows to make prediction * As you calculate these constants of JNDS, the value of JND is NOT constant * The relative difference is constant * Vision (Brightness) = 1/60 * Kinesthesis (Weights) = 1/50 * Pain (Thermal) = 1/30 * Audition (Mid. Pitch; Mod. Loud) = 1/10 * Pressure (Skin) = 1/7 * Smell (India Rubber) = 1/4 * Taste (Salt) = 1/3
Fechner’s Law * Sensation increases with the logarithm of intensity * S = k log I * More general and cognitively economic
Steven’s Power Law * S = k log I to the power of N * More predictive across a variety of sensation
Can we perceive subliminal messages? * James Vicary (1957) * Claimed 50% increase in popcorn sales * Concern about the use of subliminal “cuts”
Can we perceive stimuli that are below threshold? * Fitzsimons et al. (2008) * 30 msec exposure to two pictures * Task involves identifying which side of the screen the target appears on (right or left) * Creativity Tasks – creative way of using a brick * Apple logo is associated with a highly creative company as opposed to IBM * Your response in using a brick will be more creative
Is our behaviour affected by subliminal stimuli? * In general, there is no evidence that subliminal cuts influence consumer behaviour * But consider Bruce & Valentine (1986) * Priming – used in memory experiments * Semantic Priming – show you a word very quickly and determine whether it is a real word or fake * Before I show you this word, I would show you the word doctor (priming you) to associate doctor with hospital
Sensory Systems 1. Accessory Structures * Example: Outer Ear 2. Transduction * Receptors 3. Coding * Example: Frequency 4. Interaction * Physiological & Psychological
How does the visual system work?
Iris is the coloured portion of the eye * Muscle that can constrict and expand which controls the pupil – the amount of light that enters the pupil
Pupil is the structure that permits light
Cornea protects the eye, it is an outside coding; lens cover. * Most important thing in bending light waves to focus on the back of the eye
Lens is a large structure,