Definitions Sensation Sensation and perception Perception

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1 Definitions Sensation and perception Sensation The detection of physical energy emitted or reflected by physical objects Occurs when energy in the external environment or the body stimulates receptors in the sense organs Perception The process by which the brain organizes and interprets sensory information Sensation and perception Specific nerve energies Different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain. Synesthesia A condition in which stimulation of one sense also evokes another 1

2 Sensory adaptation and deprivation Sensory overload Adaptation The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious Prevents us from having to respond continuously to unimportant information Deprivation The absence of normal levels of sensory stimulation. To some degree, Our response depends on our expectations and our interpretations. Over-stimulation of the senses Can use selective attention to reduce sensory overload. The cocktail party phenomenon Selective attention: the focusing of attention on selected aspects of the environment and the blocking out of others. May also cause innattentional blindness Vision What we see What we see An eye on the world Why the visual system is not a camera How we see colors Constructing the visual world Hue Visual experience specified by color names and related to the wavelength of light Brightness Visual experience related to the amount of light emitted from or reflected by an object, more light is more bright. Saturation Visual experience related to the complexity of light waves, how wide or narrow the wavelengths. A single wavelength is pure and rare in nature. 2

3 What we see An eye on the world Cornea Protects eye and bends light toward lens Lens Focuses on objects by changing shape Iris Controls amount of light that gets into eye Pupil Aperture through which light reaches the retina An eye on the world Structures of the retina Retina Neural tissue lining the back of the eyeball s interior containing the receptors for vision Rods Visual receptors that respond to dim light Cones Visual receptors involved in color vision. Do not respond well in dim light. On reason it might be hard to find a red car in a dark parking lot. 3

4 The visual system is not a camera Much visual processing is done in the brain Some cortical cells respond to lines in specific orientations (e.g., horizontal). Other cortical cells respond to other shapes (e.g., bulls-eyes, spirals, faces). Feature detectors Cells in the visual cortex that are sensitive to specific features of the environment Huble and Wiesel s 1981 Nobel Prize How we see colors: Trichromatic theory Young (1802) and von Helmholtz (1852) both proposed that the eye detects 3 primary colors Red, blue, and green cones in the retina. Color in context The way you perceive a color depends on the color surrounds. All other colors derived by combination 4

5 Opponent-process theory A competing theory of color vision, which assumes that the visual system treats pairs of colors as opposing or antagonistic Opponent-process cells are inhibited by a color, and have a burst of activity when it is removed. Test of color deficiency 5

6 Form perception Gestalt principles Gestalt principles describe the brain s organization of sensory building blocks into meaningful units and patterns. Proximity Things close to one another are grouped together Closure The brain tends to fill in gaps to perceive complete forms Gestalt principles Your turn Similarity Things that are alike are perceived together Continuity Seeing continuity in lines that could be interpreted as either continuous or abruptly shifting in direction. Which Gestalt principle is illustrated by the fact that we see columns of dots rather than rows in this diagram? 1. Similarity 2. Proximity 3. Closure 4. Continuity

7 Your turn Depth and distance perception Which Gestalt principle is illustrated by the fact that we see columns of dots rather than rows in this diagram? 1. Similarity 2. Proximity 3. Closure 4. Continuity Binocular cues: visual cues that require the use of both eyes Convergence Turning inward of the eyes, which occurs when they focus on a nearby object Retinal disparity The slight difference in lateral separation between two objects as seen by the right and left eyes Depth and distance perception Fooling the eye Monocular cues: visual cues that can be used by one eye The cats in (a) are the same size. The diagonal lines in (b) are parallel. You can create a floating fingertip frankfurter by holding hands as shown, 5 10 inches in front of face. 7

8 The Müller-Lyer illusion The Ames room A specially-built room that makes people seem to change size as they move around in it. The room is not a rectangle, as viewers assume it is. A single peephole prevents use of binocular depth cues. Have you been to the Mystery Spot? SPOILER WARNING: :-) The phenomena that visitors to the attraction may experience result from the effects of forced perspective, optical adaptation, and certain optical illusions in combination with the steep gradient of the site. That is, the situation inside a Mystery Spot is arranged in some way so that the visitors don't feel that the site's gradient is actually steep (the site is actually tilted, that is), despite the fact that it is. Some of the effects are identical to those in an Ames Room. As visitors travel through the site, they habituate to this gradient. The effects of this adaptation are then exploited, especially within closed structures, so that visitors may feel as though gravity does not operate as it should in the Mystery Spot. OF COURSE, The guides tell you otherwise. Body Swap Illusion A person wears virtual reality goggles connected to a mannequin s or another person s point of view. This might help in marital therapy. NYT did an article last year. 8

9 Inborn abilities: The visual cliff Critical periods Glass surface, with checkerboard underneath at different heights Visual illusion of a cliff Baby can t fall Mom stands across the gap. Babies show increased attention over deep side at age 2 months, but aren t afraid until about the age they can crawl. If infants miss out on experiences during a crucial period of time, perception will be impaired. When adults who have been blind since birth have vision restored, they may not see well. Other senses such as hearing may be influenced similarly. Psych-socio-cultural influences Needs- We are more likely to perceive something when we need it. Hungry people are faster than others at seeing words related to hunger (stomach, food, dish, stove) Beliefs- What we believe can affect what we perceive. The image of Elvis, Jesus, or Mary in food items etc. Psych-socio-cultural influences Emotions- Fear and anxiety ear can influence perceptions. A small child who is afraid sees her beloved doll as a monster. Pain is particularly affected by anger, fear and sadness Expectations based on previous experiences can influence perception. Perceptual set: the tendency to perceive what you expect. Walter Cronkite (veteran newscaster) was sailing into port and kept smiling and waving as people shouted Shallow Water shallow water! He thought they were saying Hello Walter! Hello Walter! 9

10 Psych-socio-cultural influences All are influenced by culture and learning. In a classic 190 study, Rural Africans are less susceptible to the Muller-Lyer and other Geometric illusions illusion than are Westerners, probably because they live in a less in round huts carpentered world (round huts) and don t view as many 2-d images meant to represent the 3-d world. Japanese pay more attention to context than Americans When shown underwater scenes of brightly colored fish, Japanese reported more details about the background and small plants than Americans. Japanese scenes do tend to be more complex ESP or Extrasensory perception: The field of Parapsychology ESP - (telepathy, precognition) The ability to perceive something without ordinary sensory information. Has been studied extensively but studies have been poorly designed with inadequate precautions against fraud. After an exhaustive review, the National Research Council Concluded that there was No scientific justification.for the existence of parapsychological phenomena. BUT, the issue isn t gone is it? Many people really really WANT to believe in ESP. Consider the story of James Randi (The Amazing Randi), Dr. Andrew Weil, and Uri Geller in (or at the end of) Chapter. Amazing Randi- The Magician Dr. Andre Weil ESP or Extrasensory perception: The field of Parapsychology Dr. Andre Weil Psychology Today Dr. Weil's book Other sections that may be on the exam The mystery of pain 10