Sensation and Perception Part 1 Psychophysics AP Psychology

Sensation and Perception Part 1: Psychophysics AP Psychology Zahuta

Sensation and Perception l Sensation – the stimulation of sense organs - absorption of energy (light/sound waves) by sensory organs (eyes/ears) Perception – the selection, organization, and interpretation of sensory output -translating sensory input into something meaningful.

Example Sensation = hearing the voice Perception = recognizing/associating it as your friend.

Psychophysics Study of how physical stimuli are translated into the psychological experience. How do we process/ understand the things we see and hear around us? Gustav Fechner 1860 University of Leipzig

The Threshold l l Fechner – “For any given sense, what is the weakest detectable stimulus? ” Ex. What is the minimum amount of light for someone to recognize they see light? The Threshold Absolute Threshold= Minimum amount to be detectable Gradual response as stimuli increases Nothing absolute about it l *dividing point between energy levels that do or do not have a detectable effect

JND (Just Noticeable Difference) The just noticeable difference in stimulus intensity that a specific sense can detect. very similar to absolute threshold Easiest example is weight. JND=greater for heavy objects than for light ones. vs. Proportional to the original objects weight

Weber’s Law Fechner’s bro-in-law Weber’s law- the size of the JND is a constant proportion of the size of the initial stimulus - Applies to all senses *matches Fechner’s idea of threshold to the concept of detectability and probability.

Signal Detection Theory (SDT) -How stimulus are detected. Needs a decision process AND a sensory process –susceptible to influence from a variety of factors besides stimulus intensity. Ex. Trying to detect a knock at the door in the middle of a huge party

4 possible outcomes in SDT 1. 2. 3. 4. Hit- Detecting signals that are present Miss- failing to detect signals when they are present False Alarm – detecting signals when they are not present Correct Rejections – not detecting signals that are absent

How does decision making affect stimulus detection? l Must decide if stimulus is present l Criterion – expectations and consequences l Awareness of outside “noise” that can make detection more difficult.

Perception without Awareness l Subliminal Perception below the threshold sensory input without conscious awareness James Vicary (1957) Subliminal messages throughout Movie “Eat popcorn!” Sales by 58%!?

Subliminal Advertising KFC Coca-Cola

Subliminal Messages in Music The Beatles Led Zeppelin Britney Spears? !

Subliminal Messages in Disney Movies? ! Are people defenseless against subliminal messages? ? Operating below threshold awareness

Perception without Awareness l l CAN TAKE PLACE? ? Jon Krosnick (1992) Sensory Adaptation gradual decline of sensitivity to prolonged stimulation ex. Jumping into a cold pool “come on in, the water’s fine!” - Automatic/built-in process - Focus on Changes instead of Constants - Evolutionary Psych

In Conclusion Important to Remember. There is no one-to-one correspondence between sensory input and sensory experience. Next we will look at the Visual System…How do we draw in visual sensations?