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Perception

Perception. Thresholds . Absolute threshold – the point at which a stimulus can be detected 50% of the time wristwatch on a table - move to where you cannot hear it most of the time

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Perception

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  1. Perception

  2. Thresholds • Absolute threshold– the point at which a stimulus can be detected 50% of the time • wristwatch on a table - move to where you cannot hear it most of the time • Difference thresholds or Just Noticeable Difference(JND) – the minimal difference a person can detect between any two stimuli.

  3. Absolute Thresholds • See a flame 3 miles away on a clear dark night • Hear the tick of a watch under quiet conditions at 20 feet • Taste 1 teaspoon of sugar in 2 gallons of water • Smell one drop of perfume diffused in a three bedroom apt. • Feel the wing of a bee falling on your cheek at a distance of 1 cm

  4. Weber’s Law • Difference Threshold (or "Just Noticeable Difference") is the minimum amount by which stimulus intensity must be changed in order to produce a noticeable variation in sensory experience • This is a constant proportion

  5. Fechner’s Law • developed by Gustav Fechner • generalization of WEBER’S LAW • explain the relationship between the physical intensity of a stimulus, and the sensory experience that it causes • sensation increases as the logarithm of stimulus intensity

  6. Law & Disorder Gustav Fechner (1801-1887), was professor of physics at Leipzig. His fame owes to his discovery of the psychophysical law which states that the strength of a sensation is proportional to the logarithm of stimulus intensity. Fechner was most likely mad: He developed a philosophy that endowed consciousness to all matter; as an experiment, he stared at the sun and consequently damaged his retinas; he wore bandages over his eyes for three years, even though there was no hope of treating his ruined eyes. He is alleged to have shouted “Eureka" when he awoke one morning and suddenly became aware of the psychological law that bears his name.

  7. Vision / Hearing / Touch / Smell • Hermann Grid – retinal ganglion cells help form the optic nerve which carries information to the brain. • ON region responds to an increase in light while the OFF region responds to a decrease in light • Clapping for sound effect • Touching with Toothpicks • Orange you glad your not Orange

  8. Young-Helmholtz Trichromatic / Opponent-Process Theory • YHT: three color theory – the retina has three types of color receptors; Red, Green, Blue and when we stimulate this combination we see other colors. • OPT: after leaving the receptor cells, visual information is analyzed in terms of opponent colors red/green, blue/yellow, and black/white this is processed in the thalamus

  9. Seeing is Believing

  10. Perception at its Finest • Selective Attention – when we focus our awareness on only limited aspects of all that we are capable of experiencing. • Ex. someone watching football and can’t hear YOU • Perceptual Organization • Gestalt – meaning whole psychology, how we organize our sensations into perceptions

  11. Form Perception • Figure/Ground – figure are words and the ground is the white paper • Grouping – stimuli together, perceived whole differs from the sum of its parts • Proximity – groups nearby figure together • Similarity – similar objects we group • Continuity – smooth, continuous pattern • Connectedness – uniform and linked, spots, lines are a single unit • Closure – fill in the gaps to create a whole

  12. Form Perception: Binocular Cues • Retinal disparity - retinas receive slightly different image of the world, when the brain compares the two images. Ex: 3-D movies • It’s a toss-up: • 10 feet apart toss and catch with left then right hand • Count the number of times you catch the ball • Convergence – neuromuscular cue caused by the eye’s inward turn when they view a near object • Ex. Brain is focusing on the PowerPoint

  13. Form Perception:Monocular Cues • Interposition – object partially blocks our view of another, we believe it closer • Relative Size – objects similar in size, the smaller the picture the farther away • Relative Clarity – light from distances passes through the atmosphere = hazy objects are farther away • Texture Clarity – coarse, distinct texture to fine indistinct texture signals increase in distance, far away smaller • Relative height - increase the object the farther away • Relative Motion – as we move, objects that are stable may appear to move • Linear Perspective – parallel lines, RR tracks appear to converge w/distance • Light & Shadow – close objects reflect more light; 2 objects but one is dim = it appears to be farther away.

  14. Motion Perception • Phi Phenomenon – an illusion of movement created when 2 or more adjacent lights blink on and off • Perceptual Constancy – Helps us to perceive an object as unchanging even if the object changes size, shape, color, or brightness. For example, recognizing a friend from far away.

  15. Fun Web Sites • http://www.exploratorium.edu/exhibits/depth_spinner/index.html • http://dragon.uml.edu/psych/illusion.html • http://www.sandlotscience.com/Impossible/impos_frm.htm

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