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Sensation and Perception

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  1. Sensation and Perception Chapter 6

  2. Our Sensational Senses • Defining sensation and perception • The riddle of separate senses • Measuring the senses • Sensory adaptation • Sensory overload

  3. Defining Sensation and Perception • Sensation • The detection of physical energy emitted or reflected by physical objects. • It 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.

  4. Ambiguous Figure • Colored surface can be either the outside front surface or the inside back surface • Cannot simultaneously be both • Brain can interpret the ambiguous cues two different ways

  5. The Riddle of Separate Sensations • Sense receptors • Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain.

  6. Sensation & Perception Processes

  7. Doctrine of 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. • Synthesia • A condition in which stimulation of one sense also evokes another.

  8. Measuring Senses • Absolute threshold • Difference threshold • Signal-detection theory

  9. Absolute Threshold • The smallest quantity of physical energy that can be reliably detected by an observer.

  10. Absolute Sensory Thresholds • Vision: • A single candle flame from 30 miles on a dark, clear night • Hearing: • The tick of a watch from 20 feet in total quiet • Smell: • 1 drop of perfume in a 6-room apartment • Touch: • The wing of a bee on your cheek, dropped from 1 cm • Taste: • 1 tsp. Sugar in 2 gal. water

  11. Difference Threshold • The smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared; • Also called Just Noticeable Difference (JND).

  12. Signal-Detection Theory • A psychophysical theory that divides the detection of a sensory signal into a sensory process and a decision process.

  13. Sensory Adaptation and Deprivation • Adaptation • The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious. • Prevents us from having to continuously respond to unimportant information. • Deprivation • The absence of normal levels of sensory stimulation.

  14. Sensory Overload • Overstimulation of the senses. • Can use selective attention to reduce sensory overload. • Selective attention • The focusing of attention on selected aspects of the environment and the blocking out of others.

  15. Vision • What we see • An eye on the world • Why the visual system is not a camera • How we see colours • Constructing the visual world

  16. What We See • Hue • Visual experience specified by colour names and related to the wavelength of light. • Brightness • Lightness and luminance; the visual experience related to the amount of light emitted from or reflected by an object. • Saturation • Vividness or purity of colour; the visual experience related to the complexity of light waves.

  17. What We See • Hue • Brightness • Saturation

  18. 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 • Widens or dilates to let in more light.

  19. An Eye on the World • Retina • Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision. • Rods • Visual receptors that respond to dim light. • Cones • Visual receptors involved in colour vision. Most humans have 3 types of cones.

  20. The Structures of the Retina

  21. Why 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 cells in the cortex 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.

  22. Hubel & Wiesel’s Experiment

  23. How We See Colours • Trichromatic theory • Opponent process theory

  24. Trichromatic Theory • Young (1802) & von Helmholtz (1852) both proposed that the eye detects 3 primary colours: • red, blue, & green • All other colours can be derived by combining these three.

  25. Opponent-Process Theory • A competing theory of colour vision, which assumes that the visual system treats pairs of colours as opposing or antagonistic. • Opponent-Process cells are inhibited by a colour, and have a burst of activity when it is removed.

  26. Afterimages

  27. Test of Colour Deficiency

  28. Constructing the Visual World • Form perception • Depth and distance perception • Visual constancies: When seeing is believing • Visual illusions: When seeing is misleading

  29. Form Perception • Gestalt principles describe the brain’s organization of sensory building blocks into meaningful units and patterns.

  30. Figure and Ground • Proximity • Seeing 3 pair of lines in A. • Similarity • Seeing columns of orange and red dots in B. • Continuity • Seeing lines that connect 1 to 2 and 3 to 4 in C. • Closure • Seeing a horse in D.

  31. Depth and Distance Perception • Binocular Cues: • Visual cues to depth or distance 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 left eye and the right eye.

  32. Depth and Distance Perception • Monocular Cues: • Visual cues to depth or distance that can be used by one eye alone.

  33. 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 using binocular depth cues

  34. Visual Constancies • The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce. • Shape constancy • Location constancy • Size constancy • Brightness constancy • Colour constancy

  35. Shape Constancy • Even though these images cast shadows of different shapes, we still see the quarter as round

  36. Visual Illusions • Illusions are valuable in understanding perception because they are systematic errors. • Illusions provide hints about perceptual strategies. • In the Muller-Lyer illusion (above) we tend to perceive the line on the right as slightly longer than the one on the left.

  37. The Ponzo Illusion • Linear perspective provides context • Side lines seem to converge • Top line seems farther away • But the retinal images of the red lines are equal!

  38. Fooling the 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” in front of face.

  39. Hearing • What we hear • An ear on the world • Constructing the auditory world

  40. What We Hear • Loudness • The dimension of auditory experience related to the intensity of a pressure wave. • Pitch • The dimension of auditory experience related to the frequency of a pressure wave. • Timbre (pronounced “TAM-bur”) • The distinguishing quality of sound; the dimension of auditory experience related to the complexity of the pressure wave.

  41. An Ear on the World

  42. Auditory Localization • Sounds from different directions are not identical as they arrive at left and right ears • Loudness • Timing • Phase • The brain calculates a sound’s location by using these differences.

  43. Other Senses • Taste: savoury sensations • Smell: The sense of scents • Senses of the skin • The mystery of pain • The environment within

  44. Taste: Savoury Sensations • Papillae • Knoblike elevations on the tongue, containing the taste buds (Singular: papilla). • Taste buds • Nests of taste-receptor cells.

  45. Taste Buds • Photograph of tongue surface (top), magnified 75 times. • 10,000 taste buds line the tongue and mouth. • Taste receptors are down inside the “bud” • Children have more taste buds than adults.

  46. Four Tastes • Four basic tastes • Salty, sour, bitter and sweet. • Different people have different tastes based on: • Genetics • Culture • Learning • Food attractiveness

  47. Smell: The Sense of Scents • Airborne chemical molecules enter the nose and circulate through the nasal cavity. • Vapors can also enter through the mouth and pass into nasal cavity. • Receptors on the roof of the nasal cavity detect these molecules.

  48. Olfactory System

  49. Sensitivity to Touch

  50. Gate-Control Theory of Pain • Experience of pain depends (in part) on whether the pain impulse gets past neurological “gate” in the spinal cord and thus reaches the brain.