How many faces do you see?

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Chapter 8 Perception

Yvaral

Sensation vs. Perception Sensation involves receiving the stimulus Perception is the brain’s interpretation of the stimuli

Perception: Thresholds Absolute Threshold – The smallest amount of stimulus we can detect (50% of the time) 1 gram table salt in 500 liters of water 1 drop of perfume diffused throughout a 3 bedroom apartment Subliminal – Stimulus below our absolute threshold SOME COMPANIES CLAIM TO PRODUCE MESSAGE MEDIA THAT CAN CHANGE OUR UNWANTED BEHAVIOR…”LOOSE WEIGHT” PSYCHOLOGICAL RESARCH DISPUTES THESE CLAIMS

SUBLIMINAL MESSAGES IF IT IS SUBLIMINAL, WE CAN’T PERCEIVE IT! RESEARCH SUGGESTS IF CLAIMS “WORK” IT IS SIMPLE DUE TO PLACEBO EFFECT http://www.youtube.com/watch?v=1QYYOuQGEp0 IF IT IS TRULY “SUBLIMINAL” THEN WE WOULDN’T HEAR IT

THRESHOLDS Difference Thresholds - Smallest amount of change needed in a stimulus before we can detect the change

Just Noticeable Difference or “JND” The just noticeable difference (JND), also known as the difference threshold, is the minimum level of stimulation that a person can detect 50-percent of the time. 

Weber-Fechner Law WEBER’S LAW or “WEBER’S-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 Girl is wearing a lot of perfume, it will take _________ to notice an increase. Your eating plain rice, it will take __________to notice an increase.

Weber’s Law Continued Adding a dash of pepper to a plain dish you’ll notice But adding a dash to an already spicy dish you won’t 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

Time for Just Noticeable doughnuts Volunteer, anyone?

Signal Detection Theory – Perceptual THEOries These are NOT in competition with one another. 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 What makes this different from traditional threshold theories is that the subject makes a decision, a cognitive act, as to whether the signal is present or not and what signal to pay attention to or not 

Perceptual Theories: Signal Detection Response Criteria - 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 – We perceive a stimulus that isn’t present Walking down the crowed hall and think you see a friend you wave, turns out you are waving to a stranger (real cool!)

Is that a False + or False – ? False Negative – Not perceiving a stimulus when it is present

Perceptual Constancies Size Constancy: Perceived size of an object remains constant, DESPITE changes in its retinal image size As a car drives away we know it is not really shrinking! Shape Constancy: The perceived shape of an object unaffected by changes in its retinal image As a door opens, we don’t think a magic spell morphed it onto a different shape

Perceptual Constancies Brightness Constancy: Apparent brightness of an object stays the same under changing lighting conditions As the sun sets and the usual red brick on your house appears a brown. We know that it is still red

Fig. 7.1 Shape constancy. (a) When a door is open its image actually forms a trapezoid. Shape constancy is indicated by the fact that it is still perceived as a rectangle. (b) With great effort you may be able to see this design as a collection of flat shapes. However, if you maintain shape constancy the distorted squares strongly suggest the surface of a sphere. (From Spherescapes-1 by Scott Walter and Kevin McMahon, 1983.)

What Constancy is this?

Perceptual Terms Empirical Perception: Visual Capture: A perception strongly influenced by prior experience Common explanation for false positives Visual Capture: Where we perceive a conflict among senses, vision usually dominates = McGurk Effect http://www.youtube.com/watch?v=G-lN8vWm3m0

Figure-Ground Organization: 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.

Max wertheimer & Wolfgang Kohler Gestalt Principles shape our day to day perceptions

Gestalt Principles of Organization – Max Wertheimer Summarize them in your notes as we view them, you need to know them for the test http://psychology.about.com/od/sensationandper ception/ss/gestaltlaws_2.htm

Monocular cues vs. Binocular cues

Monocular Cues- clues about distant based on use image of one eye ACCOMODATION - THE BENDING OF THE LENS THAT OCCURS WHEN THE EYE FOCUASES ON A NEARBY OBJECTS PICTORAL DEPTH CUES – creating Depth IN TWO-DIMENSIONAL SURFACES (PG 213) texture Changes Overlap light and shadow linear perspective Relative size height in the picture plane ARIELA PERSPECTIVE

Binocular Cues Depth Perception- THE ABILITY TO SEE 3 DIMENSIONAL SPACE AND JUDGE DISTANCE Visual Cliff Apparatus- (Gibson & Walk) SEE pg 209 Binocular Cues – clues about distance requiring use of two eyes Convergence – your eyes converge to see objects less than 50 feet away (muscle turn your eyes in) Retinal Disparity – seeing depth perception from the discrepancy between the right and left eye

ames room - lopsided space that appears square when viewed from certain point

Ponzo Illusion

Müller-Lyer illusion

Processing Principles Top Down Processing - we form our perceptions starting with a larger object, concept, or idea before working our way toward more detailed information Overview 1st, then notice smaller pieces / “Big Picture Processing” Bottom Up Processing -"small chunk” processing and suggests that we attend to or perceive elements by starting with the smaller, more fine details of that element and then building upward until we have a solid representation of it in our minds. Stimuli to concept http://www.youtube.com/watch?v=TLHlfPTRekA

Got it…? For example, imagine that you are driving down an unfamiliar street and you see a sign for a convenience store. The sign has several missing letters, but you are still able to read it. Why? you use __________ processing and rely on your existing knowledge to make an educated guess about what the sign says.

What processing is this a Visual representation of?

Part of Your Homework! You need to research the internet or your book to find one example of each of the perceptual principles below. You either need a printed picture for each example or you could draw and replicate the image. Be sure to label each of your 6 examples. Gestalt-Closure Gestalt-Proximity Gestalt-Continuity Gestalt-Similarity _______________ Size constancy Shape constancy