Sensation and Perception Part 1: Psychophysics AP Psychology Zahuta
Sensation and Perception 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 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? Absolute Threshold= Minimum amount to be detectable Gradual response as stimuli increases Nothing absolute about it The Threshold *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. Hit- Detecting signals that are present 2. Miss- failing to detect signals when they are present 3. False Alarm – detecting signals when they are not present 4. Correct Rejections – not detecting signals that are absent
How does decision making affect stimulus detection? Must decide if stimulus is present Criterion – expectations and consequences Awareness of outside “noise” that can make detection more difficult.
Perception without Awareness 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 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?