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sensation and perception

3. sensation and perception.

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sensation and perception

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  1. 3 sensation and perception

  2. why study sensation and perception?Without sensations to tell us what is outside our own mental world, we would live entirely in our own minds, separate from one another and unable to find food or any other basics that sustain life. Sensations are the mind’s window to the world that exists around us. Without perception, we would be unable to understand what all those sensations mean—perception is the process of interpreting the sensations we experience so that we can act upon them.

  3. Learning Objectives • LO 3.1 Sensation and how it enters central nervous system • LO 3.2 What is Light? • LO 3.3 How eyes see and how eyes see color • LO 3.4 What is sound? • LO 3.5 Hearing impairment and improvement • LO 3.6 How senses of taste and smell work • LO 3.7 Sense of touch, pain, motion and balance • LO 3.8 Perception and perceptual constancies • LO 3.9 Gestalt principles of perception • LO 3.10 What is depth perception? • LO 3.11 How visual illusions work and other factors influence perception

  4. What is Sensation? LO 3.1 Sensation and the central nervous system • Process where various forms of outside stimuli become neural signals in the brain • Transduction: • Converting outside stimuli into neural activity • Sensory receptors • Specialized neurons • Stimulated by energy

  5. Sensory Thresholds LO 3.1 Sensation and the central nervous system • Weber’s Law: Difference Threshold • Just noticeable difference (jnd) • Smallest difference between two stimuli detectable 50 percent of the time • Absolute Threshold • Lowest level of stimulation energy needed to detect a stimulus 50 percent of the time

  6. Table 3.1 Examples of Absolute Thresholds

  7. Subliminal Sensation LO 3.1 Sensation and the central nervous system • Subliminal stimuli • Stimuli below the level of conscious awareness • Strong enough to activate the sensory receptors but not strong enough for conscious awareness

  8. Subliminal Sensation LO 3.1 Sensation and the central nervous system • Subliminal perception • Subliminal stimuli act upon the unconscious mind, influencing behavior • Scientific evidence suggests subliminal perception does not work in advertising • We do, however, process stimuli unconsciously

  9. Habituation and Sensory Adaptation LO 3.1 Sensation and the central nervous system • Habituation • Lower centers of the brain filter sensory stimulation • "Ignores" or prevents conscious attention to unchanging stimuli

  10. Habituation and Sensory Adaptation LO 3.1 Sensation and the central nervous system • Sensory adaptation • Sensory receptor cells become less responsive unchanging stimulus • Microsaccades • Constant movement of eyes • Prevents sensory adaptation

  11. Perceptual Aspects to Light LO 3.2 What is light • Three aspects of the perception of light • Brightness • Determined by amplitude of wave – height of wave • Higher waves are bright, low waves dimmer

  12. Perceptual Aspects to Light LO 3.2 What is light • Three aspects of the perception of light • Color (hue) • Determined by wavelength • Visible spectrum • Portion of spectrum visible to the human eye • Long wavelengths in red end, shorter wavelengths found at blue end

  13. Perceptual Aspects to Light LO 3.2 What is light • Three aspects of the perception of light • Saturation • Purity of color • Less saturated contains larger variety of wavelengths

  14. Figure 3.1 The Visible SpectrumThe wavelengths that people can see are only a small part of the whole electromagnetic spectrum.

  15. Structure of the Eye LO 3.3 How eyes see and see color • Cornea • Clear membrane, covers eye’s surface • Protects eye • Focuses most light coming into the eye • Photoreactive Keratectomy (PRK)/ Laser-Assisted keratomileusis (LASIK) • Vision-improving techniques • Small incisions in the cornea change focus

  16. Structure of the Eye LO 3.3 How eyes see and see color • Aqueous humor • Clear, watery fluid • Continually replenished • Supplies nourishment to the eye • Pupil • Hole where light from visual image enters interior of the eye

  17. Structure of the Eye LO 3.3 How eyes see and see color • Iris • Colored, round muscle • Controls light via pupil size

  18. Structure of the Eye LO 3.3 How eyes see and see color • Lens • Located behind the iris • Suspended by muscles • Finishes focusing process begun by the cornea

  19. Structure of the Eye LO 3.3 How eyes see and see color • Lens • Visual accommodation • Change in the thickness of lens • Eye focuses on objects that are far away or close • Vitreous humor • Jelly-like fluid • Nourishes the eye and gives it shape

  20. Figure 3.2 Structure of the EyeLight enters the eye through the cornea and pupil. The iris controls the size of the pupil. From the pupil, light passes through the lens to the retina, where it is transformed into nerve impulses. The nerve impulses travel to the brain along the optic nerve.

  21. Structure of the Eye LO 3.3 How eyes see and see color • Retina • Final stop for light in the eye • Contains 3 layers: • Ganglion cells • Bipolar cells

  22. Structure of the Eye LO 3.3 How eyes see and see color • Retina • Contains 3 layers: • Photoreceptors • Respond to various light waves • Rods • Sensitivity to low levels of light • Cones • Color vision, sharpness of vision

  23. The Blind Spot LO 3.3 How eyes see and see color • “Hole” in retina • Axons of three layers of retinal cells exit the eye • Form the optic nerve • Insensitive to light

  24. Figure 3.3 The Parts of the Retina(a) Light passes through ganglion and bipolar cells until it reaches and stimulates the rods and cones. Nerve impulses from the rods and cones travel along a nerve pathway to the brain. (b) On the right of the figure is a photomicrograph of the long, thin rods and the shorter, thicker cones; the rods outnumber the cones by a ratio of about 20 to 1.

  25. Figure 3.3 (continued) The Parts of the Retina (c) The blind spot demonstration. Hold the book in front of you. Close your right eye and stare at the picture of the dog with your left eye. Slowly bring the book closer to your face. The picture of the cat will disappear at some point because the light from the picture of the cat is falling on your blind spot.

  26. Figure 3.4 Crossing of the Optic NerveLight falling on the left side of each eye’s retina (from the right visual field, shown in yellow) will stimulate a neural message that will travel along the optic nerve to the visual cortex in the occipital lobe of the left hemisphere. Notice that the message from the temporal half of the left retina goes directly to the left occipital lobe, while the message from the nasal half of the right retina crosses over to the left hemisphere (the optic chiasm is the point of crossover). The optic nerve tissue from both eyes joins together to form the left optic tract before going on to the left occipital lobe. For theleft visual field (shown in blue), the messages from both right sides of the retinas will travel along the right optic tract to the right visual cortex in the same manner.

  27. How the Eyes Work LO 3.3 How eyes see and see color • Retina is divided into halves • Temporal retinas • Halves toward the temples of the head • Nasal retinas • Halves toward nose

  28. How the Eyes Work LO 3.3 How eyes see and see color • Axons from temporal halves project to visual cortex on the same side of brain • Axons from the nasal halves cross over to the visual cortex on opposite side of brain

  29. How the Eyes Work LO 3.3 How eyes see and see color • Dark adaptation • Rods work best in low light • Eyes adapt to low light after exposure to bright light • Light adaptation • Cones adapt to increase in light rapidly • 6 million cones in each eye

  30. While this deer may see quite well when using its rods at night, the bright headlights of a car will activate the cones. The cones will adapt rather quickly, but it takes time for the deer’s pupil to contract, leaving the deer blinded by the light until then.

  31. Theories of Color Vision LO 3.3 How eyes see and see color • Trichromatic theory • Proposes three types of cones: • Red, blue, and green • Mixing of direct light is additive; painting is subtractive • Afterimage • Visual sensation persists for a brief time after original stimulus is removed • Colors contrast to those initially seen

  32. In trichromatic theory, the three types of cones combine to form different colors much as these three colored lights combine.

  33. Theories of Color Vision LO 3.3 How eyes see and see color • Opponent-process theory • Proposes four primary colors with cones paired: • Red and green, blue and yellow • Theory explains colors in afterimage • Opponent-process cells are located in Lateral geniculate nucleus (LGN) of thalamus

  34. Figure 3.5 Color AfterimageStare at the white dot in the center of this oddly colored flag for about 30 seconds. Now look at a white piece of paper or a white wall. Notice that the colors are now the normal, expected colors of the American flag. They are also the primary colors that are opposites of the colors in the picture and provide evidence for the opponent-process theory of color vision.

  35. Color Blindness LO 3.3 How eyes see and see color • Caused by defective cones in the retina • Color deficient more accurate description

  36. Color Blindness LO 3.3 How eyes see and see color • Three types: • Monochrome colorblindness • Either have no cones or cones not working • Red-green colorblindness • Either red or the green cones are not working • Sex-linked inheritance • Recessive inheritance pattern

  37. Figure 3.6 The Ishihara Color TestTwo facsimiles of the Ishihara Color Test. In the circle on the left, the number 5 should be easier to see for those with normal color vision, and on the right, the number 96. In both circles, individuals with color-deficient vision will have difficulty identifying the numbers or may see nothing but a circle of dots.

  38. Sound LO 3.4 What is sound? • Sound waves are vibrations of the molecules of air that surround us. • Hertz (Hz): measurement of frequency • Has the same properties as light waves: wavelength, amplitude, and purity

  39. Sound LO 3.4 What is sound? • Wavelength • Frequency or pitch (high, medium, or low) • Amplitude • Volume (how soft or loud a sound is) • Purity • Timbre (richness in the tone of the sound)

  40. Figure 3.7 Sound Waves and Decibels(a) A typical sound wave. The higher the wave, the louder the sound; the lower the wave, the softer the sound. If the waves are close together in time (high frequency), the pitch will be perceived as a high pitch. Waves that are farther apart (low frequency) will be perceived as having a lower pitch.

  41. Figure 3.7 (continued) Sound Waves and Decibels(b) Decibels of various stimuli. A decibel is a unit of measure for loudness. Psychologists study the effects that noise has on stress, learning, performance, aggression, and psychological and physical well-being.

  42. Structure of the Ear LO 3.4 What is sound? • Pinna • Visible, external part of the ear • Funnels sound waves • Auditory canal • Short tunnel runs to the eardrum (tympanic membrane)

  43. Structure of the Ear LO 3.4 What is sound? • Eardrum • Tightly covers opening into the middle part of the ear • Sound waves cause eardrum to vibrate • In turn, three tiny bones in the middle ear vibrate • Hammer, Anvil, Stirrup

  44. Structure of the Ear LO 3.4 What is sound? • Cochlea • Snail-shaped structure of the inner ear • Filled with fluid • Organ of Corti • Rests in the basilar membrane • Contains receptor cells for hearing

  45. Structure of the Ear LO 3.4 What is sound? • Auditory nerve • Bundle of axons from hair cells of inner ear • Receives neural message from organ of Corti

  46. Figure 3.8 The Structure of the Ear(a) This drawing shows the entire ear, beginning with the outer ear (pinna, ear canal, and eardrum). The vestibular organ includes the semicircular canals and the otolith organs (inside the round structures just above the cochlea). (b) The middle ear. Sound waves entering through the ear canal cause the eardrum to vibrate, which causes each of the three bones of the middle ear to vibrate, amplifying the sound. The stirrup rests on the oval window, which transmits its vibration to the fluid in the inner ear.

  47. Figure 3.8 (continued) The Structure of the Ear(c) The inner ear. Large spaces are filled with fluid (shown in purple) that vibrates as the oval window vibrates. A thin membrane suspended in this fluid is called the basilar membrane, which contains the organ of Corti, the structure composed of the hairlike cells that send signals to the auditory cortex of the brain by way of the auditory nerve. (d) A close-up view of the basilar membrane (in dark pink) with the hair cells of the organ of Corti (in lighter pink). Notice the axons (small green lines) leaving the hair cells to form the auditory nerve.

  48. Theories of Pitch LO 3.4 What is sound? • Pitch • How high or low a sound is • Corresponds to frequency of sound waves • Higher frequencies are perceived as higher pitches

  49. Theories of Pitch LO 3.4 What is sound? • Place theory • Pitch is determined by location of stimulation on the organ of Corti. • Hair cells near oval window are stimulated with high sound • Lower pitch located further out on organ

  50. Theories of Pitch LO 3.4 What is sound? • Frequency theory • Pitch is related to how fast basilar membrane vibrates • Faster the vibration, the higher the pitch • Volley principle • Frequencies between 400Hz and 4000Hz cause hair cells (auditory neurons) to fire in a volley pattern • Cells take turns in firing

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