Chapter 8- Sensation and Perception

Perceptual Illusions Illusions provide good examples in understanding how perception is organized. Studying faulty perception is as important as studying other perceptual phenomena. OBJECTIVE 2| Explain how illusions help us understand some of the ways we organize stimuli into meaningful perceptions. Line AB is longer than line BC.

Perception The brain receives information from the senses and unconsciously organizes into meaningful experiences Makes whole structures out of bits and pieces of info in the environment Gestalt- this meaningful whole (German for pattern). The study of how parts are organized into whole perceptions

Gestalt Grouping Principles group nearby figures together proximity group figures that are similar similarity perceive continuous patterns continuity fill in gaps closure spots, lines and areas are seen as unit when connected connectedness 5

Gestalt Grouping Principle 1 How are perceptions constructed? Proximity: occurs when elements are placed close together. They tend to be perceived as a group.

Gestalt Grouping Principle 2 How are perceptions constructed? Similarity: occurs when objects look similar to one another. People often perceive them as a group or pattern.

Gestalt Grouping Principle 3 How are perceptions constructed? Continuity: occurs when the eye is compelled to move through one object and continue to another object.

Gestalt Grouping Principle 4 How are perceptions constructed? Closure: occurs when an object is incomplete or a space is not completely enclosed. If enough of the shape is indicated, people perceive the whole by filling in the missing information

Figure Ground Perception: The ability to discriminate properly between a figure and its background

Perceptual Inference: Filling in the gaps in what our senses tell us Assuming the sound of barking is a dog Assuming a chair will hold us even in a dark theater Depends on experience

Learning to Perceive In large part, something we learn to do Infants under one month will smile at a nodding image the size of a human face At about 20 weeks, a blank oval will not, but a mask will At 30 weeks, will smile more readily at a familiar face Will not be able to recognize different people until 7 or 8 months Learning to perceive is influenced by environment interaction, needs, beliefs, and experiences

Subliminal Perception Brief auditory or visual messages present below the absolute threshold so that there is a less than 50% chance that they will be perceived False claim that the words “Eat popcorn” and “Drink Coke” had flashed briefly on a movie screen once every 4 seconds for 1/3000 of a second and that sales had risen Hysterical reaction- Congress called for FCC, admitted data was false. But still banned in 1974, regardless of efficacy Even if it is possible for people to perceive info at low levels of intensity, no clear evidence that they influence people. But many believe it is a powerful advertising tool

Depth Perception: The ability to recognize distances and three dimensionality Present in infancy Testing infants 6-14 months: most have depth perception

Binocular Fusion The process of combining the images received from the two eyes into a single, fused image Retinal disparity- the difference between the images stimulating each eye Essential to depth perception- a large retinal disparity means an object is nearby

Visual Cliff The Visual Cliff is a test given to infants to see if they have developed depth perception. Then, a piece of glass or other clear material is placed on top of the platform and extends well off of the platform, creating a sort of bridge. An infant is then placed on the platform, and the infant's mother stands on the other side of the clear bridge. The mother calls for the child who, if it crawls off the platform and onto the clear bridge, it does not yet have depth perception. If it stops when it gets to the edge of the platform, looks down, and either is reluctant to cross or refuses to cross, then the child has depth perception.

Monocular Depth Cues: Perceive distance and depth with a single eye Relative size: bigger = nearer Relative clarity: closer objects appear clearer than distant objects Interposition: closer objects block distant objects

Monocular Depth Clues: Motion Parallax- the apparent movement of objects when you move from side to side or walk around; Near objects seem to move more Linear Perspective- parallel lines will converge in the distance Relative motion- objects nearby are moving in the opposite direction objects far away are moving in the same direction

Binocular Depth Cues: Convergence- turning eyes inward to look at near objects Retinal Disparity- larger the difference = closer

Constancy: The tendency to perceive certain objects in the same way regardless of changing angle, distance, or lighting

Illusions Perceptions that misrepresent physical stimuli; cues are distorted Converging lines = distance

Extrasensory Perception An ability to gain information by some other means other than the ordinary senses Clairvoyance- perceiving objects or information Telepathy- reading someone's mind or transferring thoughts Psychokinesis- moving objects through purely mental effort Precognition- ability to foretell events

Extrasensory Perception James Randi has campaigned against people who say they have ESP Many are convinced because of an intense personal experience that cannot be scientifically validated Successes and failures must be taken into account Findings are unstable and contradictory