Chapter 4

1. Chapter 4 Sensation and Perception Schacter Gilbert Wegner PSYCHOLOGY • Slides prepared by: • Melissa S. Terlecki, Cabrini College

2. 4.1 The Doorway to Psychology PSYCHOLOGY Schacter Gilbert Wegner

3. Figure 4.1: Synesthesia (p. 90)

4. Questions • What role does the brain play in what we see and hear?

5. Sensation • Synesthesia: the perceptual experience of one sense that is evoked by another sense. • psychological and neurobiological evidence. • Sensation: simple awareness due to the stimulation of a sense organ. • Perception: the organization, identification, and interpretation of a sensation in order to form a mental representation. • Transduction: when sensors in the body covert physical signals from the environment into neural signals sent to the nervous system.

6. Culture and Community: Our Brain Interpret Messages… • Cultural differences (Japanese and American participants) in relative versus absolute tasks of sensation and perception. • experiment in line drawing.

7. Psychophysics • Scientific investigation requires objective measures, but behavior must be operationalized; quantify perception. • Psychophysics: methods that measure the strength of a stimulus and the observer’s sensitivity to that stimulus. • experiments involving making judgments.

8. Questions • Why is the perception of any event unique to yourself?

9. Measuring Thresholds • Absolute threshold: the minimal intensity needed to just barely detect a stimulus. • threshold: a boundary. • difference between “sensing” and “not sensing”. • detection on 50% of experimental trials. • Just noticeable difference (JND): the minimal change in a stimulus that can just barely be detected. • Weber’s Law: the just noticeable difference of a stimulus is a constant proportion despite variations in intensity.

10. Table 4.1: Approximate Sensory Thresholds (p. 92)

11. Signal Detection • Sensing is gradual, not all-or-none. • Noise: all other stimuli coming from the internal and external environment. • can compete and interfere. • Signal detection theory: an observation that the response to a stimulus depends both on a person’s sensitivity to the stimulus in the presence of noise and on a person’s response criterion. • errors: hits, misses, false alarms, and correct rejections.

12. Questions • How accurate and complete are our perceptions of the world?

13. Cluttered Environments (p. 93)

14. Sensory Adaptation • Sensory adaptation: sensitivity to prolonged stimulations tends to decline over time as an organism adapts to current conditions. • stimulus doesn’t change.

15. Questions • What conditions have you already adapted to today? • sounds? • smells?

16. The Real World: Multitasking • Selective attention impairs multitasking when sudden reaction is required. • driving and multitaksing: reaction time experiments. • more impaired for complex or novel tasks.

17. 4.2 Vision: More Than Meets the Eye PSYCHOLOGY Schacter Gilbert Wegner

18. Vision • Visual acuity: the ability to see fine detail. • smallest font readable from 20 feet away in humans (20/20 is perfect). The Snellen Eye Chart, p. 96

19. Sensing Light • Visible light is the portion of the electromagnetic spectrum that we can see. • light waves vary in wavelength. • length (hue), amplitude (brightness), number of wavelengths (purity).

20. Table 4.2: Properties of Light Waves (p. 96)

21. Figure 4.2: Electromagnetic Spectrum (p. 97)

22. The Human Eye • Parts of the eye include the cornea, pupil, iris, and retina. • retina: light-sensitive tissue lining the back of the eye that houses the receptors for detecting light. • Accommodation: the process by which the eye maintains a clear image on the retina. • myopia: nearsightedness. • hyperopia: farsightedness.

23. Figure 4.3: Anatomy of the Human Eye (p. 97)

24. Figure 4.4: Accommodation (p. 98)

25. Questions • How do eyeglasses actually correct vision?

26. Phototransduction in the Retina • Two types of photoreceptors in the retina. • cones: detect color, operate under normal daylight conditions, and allow us to focus on fine detail. • rods: become active only under low-light conditions for night vision. • Fovea: an area of the retina where vision is the clearest and there are no rods at all. • Peripheral vision: lower acuity. • Layers of retina include rod and cone layers, but also bipolar and retinal ganglion cells (RGCs). • Blind spot: an area of the retina that contains neither rods nor cones and therefore has no mechanism to sense light, connects with the optic nerve.

27. Figure 4.5: Close-up of the Retina (p. 99)

28. Figure 4.6: Blind Spot Demonstration (p. 100)

29. Receptive Fields • Receptive field: the region of the sensory surface that, when stimulated, causes a change in the firing rate of that neuron. • on-center cell: receptive field with a central excitatory zone surrounded by an inhibitory zone. • off-center cell: receptive field with a central inhibitory zone surrounded by an excitatory zone.

30. Figure 4.7: RGC Receptive Fields Viewed End-on (p. 100)

31. Perceiving Color • Visible spectrum; most sensitive to red (long), green (medium), and blue (short) wavelengths. • additive color mixing: increasing light to create color. • subtractive color mixing: removing light from the mix. • Color deficiency/color blindness: one or more cone types is missing. • Color afterimage: staring too long at one color can cause sensory adaptation, a type of color deficiency.

32. Figure 4.8: Seeing in Color (p. 101)

33. Figure 4.9: Color Mixing (p. 101)

34. Figure 4.10: Color Afterimage (p. 102)

35. The Visual Brain • Outside of the eye, visual information travels to the lateral geniculate nucleus (LGN) in the thalamus to area V1 in the occipital cortex. • area V1: the part of the occipital lobe that contains the primary visual cortex. • perceiving shapes, location, orientation, and edges.

36. Figure 4.11: Visual Pathway from Eye Through Brain (p. 103)

37. Figure 4.12: Single Neuron Feature Detectors (p. 103)

38. Representing Objects and Faces in the Brain • Modular view: specialized brain areas, or modules, detect and represent objects and faces. • Distributed representation: pattern of activity across multiple brain regions that identifies any viewed object (including faces). • Visual-Form agnosia: the inability to recognize objects by sight.

39. Questions • How do we recognize our friends, even when they’re hidden behind sunglasses?

40. Principles of Perceptual Organization • Perceptual constancy: a perceptual principle stating that even as aspects of sensory signals change, perception remains constant. • Gestalt perceptual grouping rules: simplicity, closure, continuity, similarity, proximity, common fate. • Figure versus ground perception. • size, movement, edge assignment.

41. Figure 4.13: Perceptual Grouping Rules (p. 105)

42. Figure 4.14: Ambiguous Edges (p. 106)

43. Perceiving Depth and Size • The visual world exists in length, width, and depth dimensions, but the retina only processes 2 dimensions (length and width) and thus must rely on depth cues. • Monocular depth cues: aspects of a scene that yield information about depth when viewed with only one eye. • linear perspective, texture gradient, interposition, relative height

44. Figure 4.15: Familiar Size and Relative Size (p. 106)

45. Figure 4.16: Pictorial Depth Cues (p. 107)

46. Perceiving Depth and Size • Binocular disparity: the difference in the retinal images of the two eyes that provides information about depth. • Illusions in depth perception • Ames room.

47. Figure 4.17: Binocular Disparity (p. 108)

48. Figure 4.18: The Amazing Ames Room (p. 109)

49. Questions • What does the Ames room tell us about how the brain can be fooled?

50. Perceiving Motion • The visual system encodes information regarding space and time. • MT region of temporal lobe. • Motion perception subject to illusions. • waterfall illusion, phi phenomenon. • apparent motion: the perception of movement as a result of alternating signals appearing in rapid succession in different locations.