CHAPTER 7 Perception SENSATION VS. PERCEPTION Sensation involves receiving the stimulus Perception is the brains interpretation of the stimuli PERCEPTION Psychophysics The study of the interaction between the sensation we receive and our experience of them Bah, Bah, Bah PERCEPTION: THRESHOLDS Absolute Threshold The smallest amount of stimulus we can detect (50% of the time) Subliminal Stimulus below our absolute threshold SOME COMPANIES CLAIM TO PRODUCE MESSAGE MEDIA THAT CAN CHANGE OUR UNWANTED BEHAVIORLOSE WEIGHT PSYCHOLOGICAL RESARCH DISPUTES THESE CLAIMS SUBLIMINAL MESSAGES IF IT IS SUBLIMINAL, WE CANT PERCEIVE IT! RESEARCH SUGGESTS IF CLAIMS WORK IT IS SIMPLE DUE TO PLACEBO EFFECT IF IT IS TRULY SUBLIMINAL THEN WE WOULDNT HEAR IT BACKMASKING supposed hidden messages put into music records, media coverage peaked in the in 1980s. Many States called for legislation to ban use of backmasking Musicians accused of planting hidden messages on their records. If you played them backwards you could hear them. BACKMASKING Accused of hiding sadistic, dangerous messages, in some case bands were accused of fans suicides. Most bands claimed they never planted hidden messages. Reality, if you expect to hear something sadisticchances are, you will! Many groups led record-burning protests and proposed anti-backmasking legislation by state and federal governments. Popular Rock bands like Led Zeppelin, Electric Light Orchestra, and StyxLed ZeppelinElectric Light OrchestraStyx BACKMASKING Here is to my sweet Satan Stairway to Heaven by Led Zeppelin "Warning: This record contains backward masking which may be perceptible at a subliminal level when the record is played forward." THRESHOLDS Difference Thresholds - Smallest amount of change needed in a stimulus before we can detect the change WEBERS LAW or WEBERS-FECHNER LAW States the change needed is proportional to the original intensity The more intense the original stimulus, the more needed for us to notice a difference WEBERS LAW CONTINUED Adding a dash of pepper to a plain dish youll notice But adding a dash to an already spicy dish you wont Each Sense varies according to a constant, but constant are different per sense hearing 5% & vision 8% Example: 8 candles would need to be added to 100 candles before it looked brighter PERCEPTUAL THEORIES These are NOT in competition with one another. Each Theory describes different examples or parts of perception. At times, it takes all the theories to explain our interpretation of our sensations Signal Detection Theory Investigates the effects of distractions and interference we experience while perceiving the world Tries to predict what we will perceive among competing stimuli PERCEPTUAL THEORIES: SIGNAL DETECTION Response criteria or receiving operating characteristics- Determines how motivated we are to detect certain stimuli Ex. Will the quarterback see the one open receiver in the end zone? PERCEPTUAL THEORIES: SIGNAL DETECTION CONTINUED False Positive When we think we perceive a stimulus that is not present Walking down the crowed hall and think you see a friend you wave, turns out you are waving to a stranger (real cool!) False Negative Not perceiving a stimulus when it is present For example - you dont notice the directions at the top of your test to transpose the booklet number on your answer document LETS PRACTICE FALSE + & FALSE - Both false positives and false negatives can have grave ramifications Example: A brain surgeon looking at a CAT scan may not see a tumor that is present =__________ Example: A brain surgeon sees a tumor that is not really there = ____________________ MORE TERMS TO KNOW Empirical Perception: A perception strongly influenced by prior experience Figure-Ground: Part of a stimulus stands out as a figure (object) against a plainer background (ground) *only the figure is seen* Reversible Figure: Figure and ground that can be reversed FIG. 7.2 SO WHAT IS THIS? The first step in perceiving an image is determining the figure and ground. Gestalt principles shape our day to day perceptions GESTALT PRINICPLES We perceive images as groups, not as isolated elements Started with Max Wertheimer in early 1900, grew out of structuralism to become its own school of thought The whole is greater the sum of its parts. GESTALT PRINCIPLES OF ORGANIZATION MAX WERTHEIMER Nearness: Stimuli that are near each other tend to be grouped together Similarity: Stimuli that are similar in size, shape, color, or form tend to be grouped together Continuation, or Continuity: Perceptions tend toward simplicity and continuity BOOK PAGE 206 GESTALT PRINCIPLES OF ORGANIZATION MAX WERTHEIMER Closure: Tendency to complete a figure so that it has a consistent overall form Contiguity: Nearness in time and space; perception that one thing has caused another Common Region: Stimuli that are found within a common area tend to be seen as a group OUR PERCEPTION SIJwJUFy88aAJmrGZmlXaSH-QMJB&index=2SIJwJUFy88aAJmrGZmlXaSH-QMJB&index=2 Bottom Down & Top Up Processing Top Down We perceive information by filling in the gaps based on our prior experiences I h_ _ e y _ u g _ t a 5 on t_ _ A _ e_ am Bottom Up Processing Opposite of top-down We use only features to build a complete perception THESE ARE A VERY AUTOMATIC PROCESS! HARD TO PERCEIVE WE EVEN USE BOTH TOP-DOWN OR BOTTOM - UP