2. Week 6 Perception

3. Sensation & Perception Sensation  Light bounces off people ‚ Light forms image on retina  Image generates electrical signals in receptors „ Signals travel along nerve fibers to the brain... Perception Signals are processed and you “perceive” people

4. How Do We Study Sensation? Psychophysics Study of the relationship between a physical stimulus and your perception of it. Concerned mostly with physical attributes of the stimulus (e.g., amp & loudness). Gustav Fechner Father of Psychophysics (Richarson, 1999)

5. Absolute Thresholds What is the minimum stimulation necessary to detect a stimulus 50% of the time? Intensity  Crossover Values YYYYYYNYYYYYYN YYNNNNYYNNNN YYYYYYNYYYYYYN YNNNNNYNNNNN YYYYYYNYYYYYYN 105 104 103 102 101 100 99 98 97 96 99.5 98.5100.599.5 or How Low Can We Go? Vision On a clear, dark night you can see a candle from 30 miles away (Richarson, 1999)

6. Absolute Thresholds Method of Limits Stimuli are presented in ascending or descending order Some stimuli above and some below threshold Ave crossover from Yes to No = absolute threshold Intensity  Crossover Values YYYYYYNYYYYYYN YYNNNNYYNNNN YYYYYYNYYYYYYN YNNNNNYNNNNN YYYYYYNYYYYYYN 105 104 103 102 101 100 99 98 97 96 99.5 98.5100.599.5 (Measurements) (Richarson, 1999)

7. Signal Detection Detecting a weak signal dependson: Detecting a weak signal depends on: Signal’s strength 1. Signal’s strength Our internal psychological states 2. Our internal psychological states (experience, motivation & fatigue) Do “absolute” thresholds really exist? (Richarson, 1999)

8. (Kohn & Kohn, 1998)

10. Subliminal Stimulation Can we process information without being aware of it? (Richardson, 1999)

11. Subliminal Stimulation Self-Help Tape MemorySelf-Esteem Subject Request Memory Self-Esteem M-MM-SE SE-MSE-SE No Differences! Result? No Differences! (Richardson, 1999)

12. What is the minimum difference between two stimuli that a person can detect 50% of the time? What is the minimum difference between two stimuli that a person can detect 50% of the time? Difference Thresholds (JND) (Richardson, 1999)

13. What is the minimum difference between two stimuli that a person can detect 50% of the time? What is the minimum difference between two stimuli that a person can detect 50% of the time? Difference Thresholds (JND) (Ernst) Weber’s Law “Regardless of magnitude, two stimuli must differ by a constant proportion for the difference to be noticeable.” (Ernst) Weber’s Law “Regardless of magnitude, two stimuli must differ by a constant proportion for the difference to be noticeable.” (Richardson, 1999)

14. Vision Transduction - the process by which stimulus energy (e.g., light) is converted into neural energy. ElectromagneticSpectrum (Kohn & Kohn, 1998)

15. Longer Wavelength Lower Frequency Longer Wavelength Lower Frequency Shorter Wavelength Higher Frequency Shorter Wavelength Higher Frequency Properties of...LIGHT (Richardson, 1999)

16. Smaller Amplitude Dull Colors Smaller Amplitude Dull Colors Higher Amplitude Bright Colors Higher Amplitude Bright Colors Properties of...LIGHT (Richardson, 1999)

17. The Eye Lens (Kohn & Kohn, 1998)

18. Retina (Rods & Cones) Cones Rods Number6 million125 million Location in RetinaCenterPeriphery Sensitivity to Light LowHigh Color SensitiveYesNo Retina (Richardson, 1999)

19. Dark & Light Adaptation Adaptation - process by which the eye becomes more or less sensitive to light (Kohn & Kohn, 1998)

20. Visual Receptive Fields (+)(-) Lateral Inhibition Neural activity in a cell that opposes activity in surrounding cells Receptive Field Retinal area that, when stimulated, affects the firing of that cell (Richardson, 1999)

21. Lateral Inhibition in Action (Richardson, 1999)

22. Visual Pathway Left Visual Field Right Visual Field Retina Optic Chiasm Thalamus Right Visual Cortex Corpus Callosum Left Visual Cortex Optic Nerve Optic Chiasm LGN Visual Cortex Superior Colliculus (Midbrain) localization of objects general perception (Richardson, 1999)

23. Processing Info in the Visual Cortex Three Major Types of Visual Cells in Cortex Simple Cells Simple Cells - line of correct width & angle, in the right position in receptive field Complex Cells Complex Cells - same as Simple, plus line must be moving in a particular direction Hypercomplex Cells Hypercomplex Cells - same as Complex but line must be a certain length (Richardson, 1999)

24. (Kohn & Kohn, 1998)

25. Visual Information Processing Retinal Processing Rods & Cones  Bipolar Cells  Ganglion Cells Feature Detection Detector cells respond to elementary features Abstraction High-level cells respond to combined info from feature-detector cells Recognition Brain matches the constructed image with stored images (Richardson, 1999)

26. Trichromatic Theory of Color Vision Helmholtz 1852 Human eye has 3 types of cone receptors sensitive to different wavelengths of light wavelengths of light. ShortMediumLong People see colors because the eye does its own “color mixing” by varying ratio of cone neural activity (Richardson, 1999)

27. (Kohn & Kohn, 1998)

28. Cones and Color (Kohn & Kohn, 1998)

29. Opponent Process Theory Ewald Hering - Eye contains 3 mechanisms that produce antagonistic responses to three pairs of colors RGRG BYBY BWBW Why? Afterimages & Color Deficiency (Richardson, 1999)

30. Form Perception & Feature Analysis Bottom-Up Processing Based upon properties of the stimulus (e.g., patterns of light & dark areas Top-Down Processing Based upon higher-order information (e.g., prior knowledge & context) (Richardson, 1999)

31. Subjective Contours Perception of contours where there really are none. SubjectiveNeckerCube (Kohn & Kohn, 1998)

32. Hearing What is Sound? Compression & Rarefaction of air molecules. (Richardson, 1999)

33. Sound Waves Amplitude (Loudness) Strength or height of the wave Frequency (Pitch) Distance twixt consecutive peaks Mix (Timbre) Interaction of different waves 1 Hertz = 1 Cycle/Sec Human Hearing 20 - 20k Hz (Richardson, 1999)

34. (Kohn & Kohn, 1998)

39. Auditory Pathway (Kohn & Kohn, 1998)

40. Perceiving Pitch Georg von Békésy 1899-1972 Place Theory - pitch determined by point of maximal vibration on basilar membrane Traveling Wave Theory 1957 Frequency Theory - pitch determined by the rate at which the hair cells fire (i.e., 1KHz tone cause hair cells to fire 1k times/sec) Volley Principle Volley Principle (Richardson, 1999)

41. (Kohn & Kohn, 1998)

42. Smell (Kohn & Kohn, 1998)

43. Taste (Kohn & Kohn, 1998)

44. References Feldman, M. (1999). McGraw Hill Company. Retrieved May 2002 from World Wide Web at: http://www.mcgrawhill.com.http://www.mcgrawhill.com Kohn, A. J. & Kohn, W. (1998). The Integrator 2.0. CD-Rom. Brooks/Cole Thomson Learning. Richardson, K. (1999). Retrieved May 2002 from the World Wide Web at: http://www.monmouth.eduhttp://www.monmouth.edu.