sensation n.
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  1. Sensation Chapter 5

  2. Sensation • The process by which our sensory systems (eyes, ears, and other sensory organs) and nervous system receive stimuli from the environment • A person’s awareness of the world

  3. Bottom-Up Processing • Information processing that focuses on the raw material entering through the eyes, ears, and other organs of sensation

  4. Perception • The process of organizing and interpreting sensory information

  5. Top-Down Processing • Information processing that focuses on expectations and experiences in interpreting incoming sensory information

  6. Thresholds

  7. Threshold • An edge or a boundary

  8. Absolute Threshold • The minimum difference that a person can detect between two stimuli 50% of the time • Also called just noticeable difference

  9. Absolute Threshold

  10. Thresholds: Signal Detection Theory

  11. Signal Detection Theory • Set of formulas and principles that predict when we will detect the presence of a faint stimulus (signal) amid background stimulation (noise) • Developed out of the Cold War

  12. Signal Detection Theory • Three kinds of variables • Stimulus variables • Environmental variables • Organismic variables

  13. Sensory Adaptation

  14. Sensory Adaptation • Diminished sensitivity as a result of constant stimulation • If a stimulus is constant and unchanging, eventually a person may fail to respond to it

  15. Selective Attention

  16. Selective Attention • Focusing conscious awareness on a particular stimulus to the exclusion of others • The ability to focus on one stimulus at a time • Allows a person to function in a world filled with many stimuli

  17. The Visual System: The Nature of Light

  18. Electromagnetic Energy • An energy spectrum that includes X-rays, radar, and radio waves • A small portion of the spectrum includes light visible to the human eye

  19. The Electromagnetic Spectrum

  20. Hue • The color of light as determined by the wavelength of the light energy • Includes: red, orange, yellow, green, blue, indigo and violet (ROY G BIV) • The eye can detect 7 million separate hues

  21. Wavelength

  22. Amplitude • The brightness of light as determined by height of the wave • The taller the wave, the brighter the color

  23. Amplitude

  24. The Visual System: The Structure of the Visual System

  25. Cornea • The clear bulge on the front of the eyeball • Begins to focus the light by bending it toward a central focal point • Protects the eye

  26. Parts of the Eye – Cornea

  27. Iris • A ring of muscle tissue that forms the colored portion of the eye; creates a hole in the center of the iris (pupil) • Regulates the size of the pupil by changing its size--allowing more or less light to enter the eye

  28. Parts of the Eye - Iris

  29. Pupil • The adjustable opening in the center of the eye that controls the amount of light entering the eye (surrounded by the iris) • In bright conditions the iris expands, making the pupil smaller. • In dark conditions the iris contracts, making the pupil larger.

  30. Parts of the Eye - Pupil

  31. Lens • A transparent structure behind the pupil; focuses the image on the back of the eye (retina) • Muscles that change the thickness of the lens change how the light is bent thereby focusing the image • Glasses or contacts correct problems in the lens’ ability to focus.

  32. Parts of the Eye - Lens

  33. Retina • Light-sensitive surface with cells that convert light energy to nerve impulses • At the back of the eyeball • Made up of three layers of cells • Receptor cells • Bipolar cells • Ganglion cells

  34. Parts of the Eye - Retina

  35. Receptor Cells • These cells are present in every sensory system to change (transduce) some other form of energy into neural impulses. • In sight they change light into neural impulses the brain can understand. • Visual system has two types of receptor cells – rods and cones

  36. Rods • Visual receptor cells located in the retina • Can only detect black and white • Respond to less light than do cones

  37. Cones • Visual receptor cells located in the retina • Can detect sharp images and color • Need more light than the rods • Many cones are clustered in the fovea.

  38. Fovea • The central focal point of the retina • The spot where vision is best (most detailed)

  39. Parts of the Eye - Fovea

  40. Bipolar Cells • Gather information from the rods and cones and pass it on to the ganglion cells • Cells that form the middle layer in the retina

  41. Ganglion Cells • Pass the information from the bipolar cells through their axons • Together these cells form the optic nerve. • The top layer of the cells in the retina

  42. Visual Processing in the Retina

  43. Visual Processing in the Retina

  44. Visual Processing in the Retina

  45. Visual Processing in the Retina

  46. Optic Nerve • The nerve that carries visual information from the eye to the occipital lobes of the brain