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Sensation and Perception

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  1. Psych 120General PsychologyChristopher GadeOffice: 1030AOffice hours: MW 4:30-5:30Email: gadecj@gmail.comClass MW 1:30-4:30 Room 2240

  2. Sensation and Perception • Sensation: the conversion of energy from the environment into a pattern of responses by that nervous system. • Perception: the interpretation of that information. • In order to understand our perception of information, we first need to understand how we are sensing that information.

  3. Why Study Vision First? • Vision is the most widely studied topic in neurobiology and cognitive psychology. • Vision is critical to the human being’s experience. In fact, approximately 25% of our cognitive resources are reserved for that sense alone. • We know a lot more about the eye than any other sense organ, and we are significantly closer to understanding vision that we are to understanding any other sensation.

  4. What Exactly Do We See? • Light is composed of pulses of electromagnetic energy that vary in both wavelength and amplitude. • The wavelength (i.e. frequency) of the light pulse is what determines the hue (color) of the light wave.

  5. Humans are able to see light on a range of 400 to 700 nanometers (nm). Other animals have sensitivity at different wavelength ranges.

  6. What Exactly Do We See (cont.)? • The amplitude of the electromagnetic wave is what determines the intensity (brightness) of the light.

  7. The Structure of the Eye • The Pupil: a small adjustable opening in the eye, through which light enters.

  8. The Structure of the Eye • The Iris: a colored adjustable muscle on the surface of the eye that is responsible for controlling the amount of light that enters the eye through the pupil.

  9. The Structure of the Eye • The Cornea: A rigid, protective surface on the outer surface of the eye that focuses light toward the fovea.

  10. The Structure of the Eye • The Lens: A clear, flexible structure located behind the cornea that can vary in thickness (to help us focus on information at different depths), and focuses the incoming light rays into an image on the back of our eyes.

  11. Interesting Fact • The lens of our eyes actually flips the image that we are viewing. Our brains have to eventually take that flipped information and transform it in order for it to make sense.

  12. The Structure of the Eye • The Vitreous Humor: a clear jelly-like substance that light passes through on its way to the retina.

  13. The Structure of the Eye • The Retina: The multilayered tissue located on the back of the eye that is responsible for the transference of light rays into neural information.

  14. The Structure of the Eye • The Fovea: the central area of the retina that is highly adapted for detailed vision.

  15. The Structure of the Eye • Rods and Cones: Specialized visual receptors located along the retina. These neurons transfer the sensory information into neural impulses that are sent along the optic nerve.

  16. Rods and Cones (cont.) • Rods: receptors that are adapted for vision in dim light. Their primary purpose is to detect motion. • Cones: receptors adapted for color vision, daytime vision, and detailed vision. The fovea contains only cones. • Rod and Cone Example

  17. The Structure of the Eye • The Optic Nerve: a collection of cells that is responsible for carrying the information processed by your eye to the brain.

  18. The Path of Vision (After the Eye)

  19. Visual Sensation • Color: • wavelength and amplitude characteristics of emr correspond to different colors and brightness of light (and sound…).

  20. Color Sensation • The Young-Helmholtz/trichromatic theory. • Proposes that our receptors respond to three primary colors: blue, green and red. • “Color vision depends on the relative rate of response by the three types of cones.”, I.e. the combination of different levels of firing in each type of cone gives rise to the broad spectrum of colors perceived.

  21. Visual Sensation • Color: • What about yellow, white, and black? • What about negative afterimages? • The Opponent Process Theory: • We sense color not in terms of separate categories but rather in a system of paired opposites: red vs. green, blue vs. yellow and black vs. white. “ON” “OFF” redgreen greenred blueyellow yellowblue black white white black

  22. The Interpretation of Colors and Patterns • The Brightness Contrast • Method of determining the colors of objects (going beyond just the frequency of the electromagnetic waves). • The brightness of surrounding objects influences our perception of the color and brightness of an object.

  23. Visual Sensation • The Retinex Theory: • The Cerebral Cortex also plays a role in how we experience color, I.e. color constancy, by comparing different patterns of light from different areas of the retina.

  24. Perception and Gestalt Psychology • Knowing the visual system is great if we want to know about the basics of vision. • But what about interpretation? How do we make sense of ambiguous stimuli? • Gestalt and perception psychology address this problem.

  25. Gestalt Psychology (cont.) • Gestalt psychology is a field that focuses on our ability to perceive overall patterns. • “The whole is different (and often greater) than the sum of its parts”. • Our perception is based on our attempts to create semblance out of the mess of stimuli that we are presented with.

  26. Tricks to Determining Distance/Depth • Binocular Cues (two eyes) • Retinal disparity: the position of an object is determined by the different signals received by the two eyes. • Convergence: the distance of an object is determined by the amount of eye movement required to focus on an object.

  27. Monocular Cues (two eyes are not required) • Object size (relative size): nearer objects look bigger. • Accommodation: Our brains can detect how much the lens of the eye needed to shift in order to focus on an object. • Detail (relative clarity): more detail signifies a closer object.

  28. Visual Illusions • So we interpret stimuli in our world to make sense of it… great. Is there any situations where this comes at a cost? • Most of the time, this translation of information is very useful for our interaction with the real world. • But sometimes, there are situations that trick the mind.

  29. The Muller-Lyer Illusion

  30. Depth Perception Illusions

  31. The Ponso Illusion

  32. The Moon Illusion

  33. The Ames Room

  34. The Other Senses: Hearing The properties of sound and the basics of the ear.

  35. Listening Exercise Put your books, pens, pencils, phones, and all other items down. Close your eyes. Listen! What is it that you’re hearing?

  36. Life Without Hearing What are some of the things that we would miss out on if we couldn’t hear? What are some of the things that we would miss out on if we couldn’t see? Which would you rather lose, hearing or vision? Why?

  37. Is Hearing Physical or Perceptual? • Physical Definition of Sound: A change in pressure of the air or other physical medium. • Perceptual Definition of Sound: An experience of “sound waves” by the ear or other perceptual medium. • Sound Properties • Sound Wave: A sudden change in MOLECULE pressure • Boat Example

  38. More Properties of Sound • Amplitude: The concentration of the air pressure. Determines the “loudness” of the sound. • Decibel = 20log(p/po) (po= pressure medium for air, it = 20)

  39. More Properties of Sound • Frequency: The rate of sound wave occurrences. Determines the “pitch” of the sound. • Sound frequency is measured by Hertz (Hz). 1 Hz =1 cycle per second.

  40. The Equal Loudness Curve and Audibility Curve What’s the loudness button on your stereo doing?

  41. The Ear, Our Sound Wave Detector