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Perception

Perception. Meyers, Chapter 6. Selective Attention. The focusing of our conscious awareness on a particular stimulus. Cocktail Party Effect : the ability to tend to one voice among many. Inattentional Blindness: failing to see visible objects when our attention is directed elsewhere. .

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Perception

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  1. Perception Meyers, Chapter 6

  2. Selective Attention • The focusing of our conscious awareness on a particular stimulus. • Cocktail Party Effect: the ability to tend to one voice among many. • Inattentional Blindness: failing to see visible objects when our attention is directed elsewhere. While intent on counting basketball passes, about half the viewers fail to notice the gorilla passing through.

  3. Selective Attention (cont’d) • Change Blindness: the failure of an observer to notice large changes in a visual display. • Change Deafness: inability to detect the changes between two voices when allocating one’s attention to a specific task. • Choice Blindness: failure to detect conspicuous mismatches between intended (and expected) choice and the actual outcome.

  4. PERCEPTUAL ORGANIZATION • Visual Capture: the tendency for vision to dominate the other senses • gestalt: German psychologists in the early 20th century noted that when the mind organizes sensations into perceptions, it perceives the sensations as a meaningful WHOLE. • “the whole is greater than the sum of its parts” Necker Cube

  5. Form Perception • Figure-ground: the organization of the visual field into objects (the figures) that stand out from their surroundings (the ground) • The figure-ground relationship above continually reverses, but we always organize the stimulus into a figure seen against a ground and illustrates that the same stimulus can trigger more than one perception.

  6. Form Perception (cont’d) • Grouping: the perceptual tendency to organize stimuli into coherent groups. • Proximity: we see nearby figures together. We see 3 sets of two lines, not six separate lines.

  7. Form Perception (cont’d) • Similarity: we group together figures that are similar to each other than horizontal groups of triangles and circles or as individual shapes. • Continuity: We perceive smooth, continuous patterns rather than discontinuous ones. • Instead alternating semi-circles, we perceive the image above as one wavy and one straight line.

  8. Form Perception (cont’d) • Connectedness: because they are uniform and linked, we see nearby figures together. We see 3 sets of two lines, not six separate lines. • Closure:We fill in gaps to create a complete, whole object. • We assume the circles are complete but partially blocked by the illusionary triangle.

  9. Depth Perception • Depth Perception: the ability to see objects in three dimension although the images that strike the retina are two dimensional – allows us to judge distance. • Visual Cliff: a laboratory device for testing depth perception in infants and young animals.

  10. Depth Perception (cont’d) • Binocular Cues: depth cues that depend on the use of two eyes to judge the distance of nearby objects. • Retinal Disparity: since the eyes are about 2 ½ inches apart, our retinas receive slightly different images of the world. By comparing the images from both eyes, the brain computes distance. The greater the disparity (distance) between two images, the closer the object. • Convergence: a neuromuscular cue caused by the eyes’ greater inward turn when they view a near object. The greater the inward strain, the closer the object.

  11. Retinal Disparity • The Floating Finger Sausage:

  12. Depth Perception (cont’d) • Monocular Cues: Depth cues that are available to each eye separately. • Relative Size: if we assume that two objects are similar in size, we perceive the one that casts the smaller retinal image as farther away. • Interposition: If one object partially blocks our view of another, we perceive it as closer. • Relative Clarity: Because light rom distant objects passes through more atmosphere, we perceive hazy objects as father away than sharp clear objects.

  13. Depth Perception (cont’d) • Monocular Cues: • Texture Gradient: a gradual change from a coarse, distinct texture to a fine, indistinct signals increasing distance. Objects farther away appear smaller and more densely packed

  14. Depth Perception (cont’d) • Monocular Cues: • Relative Motion (motion parallax): when you are moving. Objects closer than a fixed point appear to move backward. The nearer the object is, the faster it moves. Objects beyond the fixation point appear to move with you. • Linear Perspective: the more two parallel lines converge, the farther away they are.

  15. Depth Perception (cont’d) • Monocular Cues: • Relative Height: We perceive objects higher in our field of vision as farther away. • Since we perceive the lower part of a figure ground illustration as closer, we perceive it as figure. St. Louis gateway Arch

  16. Relative Motion

  17. Depth Perception (cont’d) • Monocular Cues: • Light and Shadow: nearby objects reflect more light than faraway objects. Shading also produces a sense of depth consistent with the assumed light source.

  18. Motion Perception • As objects move across or toward our retinas, our basic assumption is that shrinking objects are retreating & enlarging objects are approaching. • Stroboscopic Movement: our brains perceive continuous movement in a rapid series of slightly varying images. • Phi Phenomenon: an illusion of movement created when two or more adjacent lights blink on and off in quick succession, as seen in a marquee sign or holiday lights.

  19. Perceptual Constancy • Perceptual Constancy is necessary in vision to recognize an object, regardless of its changing angle, distance or illumination. • Shape Consistency: our ability to perceive familiar objects as unchanging in shape despite the changing images cast on our retinas. • Size Consistency: our ability to perceive familiar objects as unchanging in size regardless of the changing images cast on our retinas. • There is a close relationship between perceived size and perceived distance.

  20. Perceptual Constancy (cont’d) • The monocular cues for distance (line perspective a& relative height) make the pursuing monster look larger than the pursued. • They are actually the same size.

  21. Ponzo Illusion • The two red bars cast the same size image on our retinas. • Experience tells us that the more distant object can create the same sized image as the nearer one only if it is actually larger. • Thus, we perceive the bar that seems farther away as lager.

  22. Muller-Lyer Illusion • Which vertical line is longer? • Richard Gregory (1968) suggested that the corners of our rectangular world teach us to interpret outward or inward pointing arrowheads at the end of lines as a cue to the line’s distance from us.

  23. The red line defined by the corner at the ticket booth looks shorter than the red line defined by the room corner, but are they really different lengths?

  24. Perceptual Constancy (cont’d) • Perception of the Muller-Lyer Illusion reflects cultural experience. • Rural Africans who did not live in environments of constructed rectangular buildings, such as the South African Zulu who live in round houses, were less vulnerable to this illusion. • Size-distance relationships also explain the illusion of the shrinking & growing girls. • When viewed through a peephole with one eye, the room appears to have a normal rectangular shape.

  25. The Shrinking & Growing Girls • Although the room is a trapezoidal shape, the brain, when receiving sensations from one eye, assumes that the room is normal and the girls are the same distance from the viewer.

  26. Perceptual Constancy (cont’d) • Lightness or Brightness Constancy: the ability to perceive an object as having constant lightness even when the light cast on it (illumination) changes. • Depends on Relative Luminance – the amount of light an object reflects relative to its surroundings. • Color Constancy: the perception that the color of an object stays the same even when the illumination changes. • In either case, the brain perceives the relative lightness or color relative to the surrounding objects.

  27. PERCEPTUAL INTERPRETATION • Are all aspects of visual perception innate? • The answer is no, based on the following sensory deprivation and restored vision research: • Patients who born blind but regained sight after cataract surgery, were able to distinguish figure-ground and to perceive colors but lacked the experience to recognize shapes, forms, & complete faces. • Research with infant kittens & monkeys reared with severely restricted visual input evidenced similar abilities to see color & brightness but remained functionally blind to shape when their vision was restored.

  28. Perceptual Interpretation (cont’d) • It appears that there is a critical period for some aspects of sensory & perceptual development. • Without the stimulation provided by early visual experiences, the brain’s neural organization does not develop normally. • Perceptual Adaptation: in vision, the ability to adjust to an artificially displaced or even inverted visual field. • Distorting Goggles: glasses that shift the apparent location of objects 40˚ to the left. • When wearing these glasses, there is an initial disorientation, but people, with practice, can move with ease.

  29. Perceptual Interpretation (cont’d) • Perceptual Set: a mental predisposition to perceive one thing & not the other. • Because our schemas prime us to organize & interpret ambiguous stimuli in certain ways, our perceptions reflect our version of reality. What do you see in the center picture?

  30. Perceptual Interpretation (cont’d) Perceptual Set (cont’d) • Context Effects: A given stimulus may trigger radically difference perceptions, partly due to different schema, but also because of immediate context. • Context creates immediate expectations that guide our perceptions. • Emotional contexts also color our perceptions of other people’s behavior • Perceptual set and context also interact to help construct our perceptions.

  31. Perceptual Interpretation (cont’d) • Human Factor Psychology: explores how people and machines interact and how machines and physical environments can be made safe and easy to use. • They encourage developers & designers to consider human perceptual abilities to avoid the “curse of knowledge” - assuming that others share in our expertise & will behave as they would). • They also suggest user testing of new technologies to discover perception-based problems before production & distribution. • Human Factor psychologists have contributed to the improved safety in air & space travel, better designed appliances, equipment, & workplaces, & easier to use assisted listening.

  32. Paranormal Phenomena • Parapsychology the study of paranormal phenomena, including ESP & psychokinesis (PK)

  33. PSI (cont’d) • Claims of paranormal phenomena (PSI) include: • Astrological predictions • Out of body experiences • Communication with the dead • Psychokinesis: mind over matter (moving of stationary objects) • Extrasensory Perception (ESP): the controversial claim that perception can occur apart from sensory input. Three testable forms of ESP include: • Telepathy: mind to mind communication • Clairvoyance: perceiving remote events • Precognition: perceiving future events

  34. PSI (cont’d) • Most researchers are skeptical about claims of PSI because: • To believe in ESP you must believe the brain is capable of perceiving without sensory input. • Parapsychologists have been unable to replicate ESP phenomena under controlled conditions.

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