This slideshow was created with images from the web. I claim no copyright or ownership of any images. If a copyright owner of any image objects to the use in this slideshow, contact me to remove it. This is for a course in Introductory Psychology using Wayne Weiten's "Psychology: Themes and Variations" 8th ed. Published by Cengage. Images from the text are copyrighted by Cengage.

1. Introduction to Sensation and Perception Chapter 4

2. How Psychology developed as a field. The ways Psychologists conduct research. The basic building blocks. Genes, Nervous System, Hormones Bringing the world into your brain. Sensation and Perception Chapter 1 – Chapter 2 – Chapter 3 – Chapter 4 –

3. Why Study Sensation and Perception? “I’ll believe it when I see it” “I know what I saw (heard)” “How can you eat that!!” “What do you mean, you like getting spanked?”

4. Each of these, at least at the most basic level, involves sensation and perception.

5. Two Main Points Human sense organs are not like electronic equipment Eyes are not cameras, Ears are not microphones… There is variability in sensation For different stimuli – sensation is relative Perception is SUBJECTIVE, not absolute

6. Sensation Definition: stimulation of the sense organs

7. Thresholds Intuitive definition The “threshold” of your house is your doorway. You’re outside until you pass through the threshold; then you are inside. This happens exactly at the door frame… every time… always the same… Do your eyes work like that?

8. Thought Experiment You have a two-mile long garage with no windows (pretend this isn’t ridiculous)

9. Thought Experiment Inside, you put a remote-controlled truck at one end. On top of the truck is an extremely tiny, faint light bulb. It has no other lights.

10. Thought Experiment You sit at the other end and turn off the lights. It’s pitch black. You hold the remote stick to start the truck moving toward you, slowly. Release the control to stop the truck as soon as you see the light bulb. Truck You

11. Thought Experiment Turn on the lights. Go to the truck and mark a chalk line on the floor where it stopped. Set up the truck again, turn off the lights. Start the truck. Stop it when you see the light. Mark the floor with chalk. Repeat this 100 times

12. Thought Experiment If your vision had a threshold like a doorway in a house, you would draw a chalk line in the same spot on the floor every time – 100 lines all on top of each other. That’s not what you get.

13. Thought Experiment Here is what the chalk lines on the floor would look like, approximately: So where is the “threshold”? Note: this is a simplification. The lines wouldn’t be symmetrical as drawn above, but explaining why needs physics and math. The example is valid despite this simplification.

14. Thresholds Operational definition of Threshold for light The minimum amount of light at which you detect it 50% of the time. In the thought experiment, it would be the point on the floor where 50% of the lines are in front of it, and 50% are beyond it. So about right here

15. If you graphed this, you would get the red curve. Note: the intuitive definition of a threshold is the blue curve

16. Truck getting closer The horizontal axis is the distance of the truck from you. When the light on the truck is far away, it is a very low intensity. As the truck gets closer, the intensity of the light increases (This is physics. Google the Inverse Square Law if you’re curious why this happens.)

17. Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

18. None Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

19. None Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

20. Couple Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

21. More Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

22. 50% Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

23. Most Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

24. All Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

25. So…

26. Thresholds – Review and Main Points Your eyes are not like cameras. There is variability in how you sense light. The intuitive idea of a “Threshold” simply does not fit. We use an operational definition of “absolute threshold” to describe how you really notice a stimulus.

27. Main Point 1. First Part There is variability in sensation

28. Just Noticeable Differences (JNDs) Now that you see a light, how much does it have to change in intensity for you to notice it? This is the JND The size of the JND depends on how intense the first light is.

29. Just Noticeable Differences (JNDs) Example: You have a bulb that lets you go from 5 Watts to 10 Watts. You would see this difference. 10 W 5 W

30. Just Noticeable Differences (JNDs) But if you went from a 100 Watt bulb to a 105 Watt bulb, you would see no difference. A difference of 5 Watts is only noticeable if you start with dim bulbs. 100 W 105 W

31. Have you ever purchased a three-way bulb that goes from 50 Watts to 100 Watts to 150 Watts? You see a big change from dark to 50W, then a large increase in brightness when you click to 100W….but there’s only a tiny change after the third click to 150W. 150 W 100 W 50 W

32. This is a similar idea to JNDs. The key point is that your eyes are not on an absolute scale. What you notice is relative to stimulus intensity!

33. Main Point 1. Complete There is variability in sensation For different stimuli – sensation is relative

34. Perception Definition: The selection, organization, and interpretation of sensory input

35. Playing with a truck in a fictional building was fun, but that isn’t the real world. The idea of an “absolute threshold” applies best to laboratories, or to silly situations like a two-mile long garage with no windows… In the real world, it is more complicated.

36. What if the survival of a plane full of people relies on you noticing this light as you look at this display

37. Signal Detection Theory Signal Detection Theory has direct applications in the design of many products. In the case of cockpits, it is essential.

38. Signal Detection Theory Whether or not a pilot detects a warning light depends on: Stimulus Intensity the idea of absolute threshold still applies If a light is too dim, the pilot doesn’t see it Noise in the environment “Noise” refers to stimuli competing for the same sense In a cockpit, other lights, dials, flashes, and reflected lights are “noise” More noise  more intense warning light is needed for detection Your Criterion for Deciding if you detect the stimulus

39. Signal Detection Theory Here is where detecting a little warning light becomes a question of perception. You select, organize, and interpret sensory information. You matter.

40. Signal Detection Theory Good situation: The pilot is vigilant, attentive, and motivated. He or she is concerned about doing the job well. Bad situation: The pilot feels comfortable flying, sees him or herself as a seasoned pro, and has the routine flight checklists so well learned that he or she can “do it in their sleep.”

41. Signal Detection Theory Good situation: The pilot is vigilant, attentive, and motivated. He or she is concerned about doing the job well. This is a very sensitive criterion Bad situation: The pilot feels comfortable flying, sees him or herself as a seasoned pro, and has the routine flight checklists so well learned that he or she can “do it in their sleep.” This is not a sensitive criterion

42. Main Point 2. Perception is SUBJECTIVE, not absolute.

43. Signal Detection Theory Review – Detecting a stimulus depends on: Stimulus Intensity If a light is too dim, the pilot doesn’t see it Noise in the environment More noise  more intense warning light is needed for detection The person’s criterion for deciding if they detect the stimulus

44. Four Possible Outcomes In a signal detection situation, there are four possible outcomes as you try to detect the stimulus. Columns represent reality Rows are the person’s decision.

45. Example: You order a pizza during a party. As you enjoy yourself, there is background noise. You are listening for the doorbell for the pizza person.

46. Right after placing the order, your Criterion is very low. You expect a “Correct Rejection,” where you don’t hear anything and nothing is at the door. This criterion increases risks of “Misses,” though. If they miraculously try to deliver a pizza 5 minutes after you call, you might not hear them ringing your doorbell!

47. However, 40 minutes later, your Criterion changes to high sensitivity. You want pizza! You want a “Hit,” but that also risks “False Alarms,” or thinking you hear a doorbell when there really was none.

48. What you expect, what you are doing, and how much you care about detecting the stimulus matters! Perception is subjective.

49. Main Point 2. Perception is SUBJECTIVE, not absolute. Different people can select, organize, and interpret the same stimulus differently. The same person can select, organize, or interpret the same stimulus differently on different occasions.

50. These ideas can be implemented and controlled in cockpit design, pilot training, and FAA regulations. Human Factors Engineering is an Applied field where Psychologists and other professionals use these ideas. Other situations do not have such extreme oversight, but lives are still at stake…

51. Example in Nursing Alarm Fatigue Nurses constantly hear alarms going off during their jobs. Low battery alerts, I/V alerts, monitor alerts… The beeps, buzzes, and alarms each day can number in the 100s. The problem is that some of these are trivial and others are life threatening.

52. Example in Nursing Situation: a nurse needs to hear a life threatening alarm Signal Detection Theory The loudness, pitch, and timbre of the alarm matters The “noise” in this case is all of the other beeps, blips, buzzes, and low priority alarms going off The decision criterion is the nurse’s attentiveness and focus on the alarms

53. Example in Nursing Situation: a nurse needs to hear a life threatening alarm Possible Outcomes Hit– Nurse hears alarm, emergency response started Correct Rejection – Nurse hears no alarm, nothing is wrong False Alarm – Nurse “hears” alarm, emergency response started unnecessarily: wastes resources, time, and money. Is embarrassing… Miss– Nurse hears no alarm, a person suffers, or worse…

54. Example in Nursing The problem is that the diverse cacophony of alarms can lead to a criterion that looks like this:

55. Example in Nursing Getting used to not reacting to alarms (Correct Rejections) leads to an increase risk of Misses.

56. Example in Nursing Unfortunately, there are many manufacturers of equipment. Each hospital may have various models of equipment, all with different alarms. Different departments in the same hospitals have different systems… There is no equivalent to the airline manufacturer who designs everything in a cockpit to work together, with FAA oversight. Finding a solution needs applied research. Psychology is essential.

57. Summary In this slideshow, we used several topics from your text to introduce sensation and perception. Psychologists who study sensation and perception can be basic researchers or applied researchers. Sometimes basic research (spending years studying how people notice differences between sounds) can become essential for applied research.

58. Summary You read examples of Thresholds and Just Noticeable Differences From this, we illustrated the first main point: There is variability in sensation. For different stimuli, sensation is relative. Then you read a descriptions of examples of using Signal Detection Theory From this, we illustrated the second main point: Perception is subjective, not absolute