Chapters 6

1. Chapters 6 Sensation Chapter 6 - Sensation

2. Overview In this chapter we will be focusing on our “input systems”, the senses we use to perceive the world around us. We will focus primarily on vision, but will also discuss audition, touch and smell. Much of the information will attempt to explain how these systems work … though we will also discuss illusions that show us how our sensory systems can be tricked. Throughout, we will again emphasize the distinction between sensation, the information arriving through the sense organs, and perception, the subjective impression of the world that we end up with. Chapter 6 - Sensation

3. Sensation versus Perception The textbook actually defines sensation and perception slightly differently from how I have, though the flavour is the same. According to the text: Sensation is the detection of simple stimulus properties such as brightness, colour, sound frequency, sweetness. Perception is the detection of objects, their location, their movements, their background. Thus, seeing purple and blue in the picture is sensation, whereas seeing beautiful fireworks is perception Chapter 6 - Sensation

4. Transduction Transduction is the process by which sense organs convert energy from environmental events into neural activity … eventually ending up in the brain. Sense organs differ in terms of the kinds of environmental energies they are sensitive to, and in the manner they transduce that energy. Usually the transduction is accomplished via specialized receptor cells that release specialized neurotransmitters that stimulate other neurons. Steve, show table 6.1 here to show some of the variety across the sense organs Chapter 6 - Sensation

5. Sensory Coding As we discussed earlier, nerve cells can only send a message or not. The message does not vary in terms of what it says, or how it says it. So how then can the same nerve cells transmit the fact that bananas are yellow, but carrots are orange? The answer lies in the use of code … think of Morris Code for example. In Morris Code complex semantic messages were transmitted using simple clicks Chapter 6 - Sensation

6. How does the Brain Code Information? The first answer to this question is: We’re not absolutely sure yet … the puzzle still needs more unraveling. But, we do think the following two codes are involved. Anatomical Coding - Sensory organs located in different parts of the body send their signals to different locations in the brain … the brain uses this to interpret the signals correctly. Example, rubbing your eyes & phantom limbs Temporal Coding - Information can be coded according to time. The easiest way to do this is with respect to rate of neural firing. May be the main way to code the intensity of stimulation Chapter 6 - Sensation

7. Psychophysics - Physics of the Mind The systematic study of the relation between the physical characteristics of stimuli, and the sensations they produce. Example - JNDs Chapter 6 - Sensation

8. Psychophysics - Physics of the Mind The systematic study of the relation between the physical characteristics of stimuli, and the sensations they produce. Example - JNDs Chapter 6 - Sensation

9. Psychophysics - Physics of the Mind The systematic study of the relation between the physical characteristics of stimuli, and the sensations they produce. Example - JNDs Chapter 6 - Sensation

10. Psychophysics - Physics of the Mind The systematic study of the relation between the physical characteristics of stimuli, and the sensations they produce. Example - JNDs Chapter 6 - Sensation

11. Psychophysics - Physics of the Mind The systematic study of the relation between the physical characteristics of stimuli, and the sensations they produce. Example - JNDs Chapter 6 - Sensation

12. Psychophysics - Physics of the Mind The systematic study of the relation between the physical characteristics of stimuli, and the sensations they produce. Example - JNDs Chapter 6 - Sensation

13. Psychophysics - Physics of the Mind The systematic study of the relation between the physical characteristics of stimuli, and the sensations they produce. Example - JNDs Chapter 6 - Sensation

14. Just Noticeable Differences - JNDs Ernst Weber was the first to measure JNDs, the smallest change in the magnitude of a stimulus that can be detected. He found that the JND is directly related to the magnitude of the stimulus. For example, when examining people’s ability to detect differences in weights, he found that if the weights were within 1/40th of each other, no difference was detected. Weber examined all the senses in this respect. For example, to detect a difference in brightness, the difference must exceed 1/60 of the average brightness of the stimuli. These results are now called Weber Fractions. Chapter 6 - Sensation

15. Measuring Sensitivity via Thresholds The JND is a threshold is a difference threshold. It reflects how big a difference has to be before it is detected. There is a more simple thresholds as well, how intense does a stimulus have to be before the subject claims to see, hear, smell, taste, or feel it? These sorts of thresholds have been used to assess the sensitivity of our sensory apparatus … and have lead to areas of research such as subliminal perception. How do we know if a message is subliminal? > simple threshold approach - establish the “limon”, the point where it is noticed half the time, and go below Chapter 6 - Sensation

16. Vacation Anyone? Fly with us on Air Joordens! We’ll take you anywhere you want to go!! And our serving staff are all REALLY sexy!! Chapter 6 - Sensation

17. The Problem With Simple Thresholds Jastrow’s (1897) Subliminal Perception Experiment H 3 F 1 6 R B 5 The notion (and evidence) for perceptual defense CART SHIT Chapter 6 - Sensation

18. The Problem With Simple Thresholds Jastrow’s (1897) Subliminal Perception Experiment H 3 F 1 6 R B 5 The notion (and evidence) for perceptual defense CART SHIT Chapter 6 - Sensation

19. The Problem With Simple Thresholds Jastrow’s (1897) Subliminal Perception Experiment H 3 F 1 6 R B 5 The notion (and evidence) for perceptual defense CART SHIT Chapter 6 - Sensation

20. The Problem With Simple Thresholds Jastrow’s (1897) Subliminal Perception Experiment H 3 F 1 6 R B 5 The notion (and evidence) for perceptual defense CART SHIT Chapter 6 - Sensation

21. The Problem With Simple Thresholds Jastrow’s (1897) Subliminal Perception Experiment H 3 F 1 6 R B 5 The notion (and evidence) for perceptual defense CART SHIT Demand characteristics and response bias can prevent accurate measurements of a threshold Chapter 6 - Sensation

22. Separating Bias from Sensitivity In 1974 (1974!) Green & Swets came up with a way of measuring sensitivity free of response bias … it is an approach called signal detection theory. Signal detection theory involves presenting a stimulus on some trials, and not on others … then asking subjects on each trial to state (guess) whether or not a stimulus was presented. This leads to four possibilities: Hit - saying a stimulus is present when it is. Miss - saying a stimulus is not present when it is. False Alarm - Saying a stimulus is present when it is not. Correct Rejection - Saying a stimulus is not present when it is not. Chapter 6 - Sensation

23. Is there a word? CLOUD QUEEN TRUCK RADIO PAPER APPLE Chapter 6 - Sensation

24. Is there a word? CLOUD QUEEN TRUCK RADIO PAPER APPLE Chapter 6 - Sensation

25. In Reality, stimulus was Present Absent False Alarm “Present” “Absent” Hit Correct Negative Miss So far bias can still have an effect, but it effects both hits and false alarms. Chapter 6 - Sensation

26. How do we get rid of bias? The trick here is to use some manipulation that will vary response bias, and test a given subject under a number of levels of this manipulation .. E.g., payoffs Null Sensitivity Chapter 6 - Sensation

27. How do we get rid of bias? The trick here is to use some manipulation that will vary response bias, and test a given subject under a number of levels of this manipulation .. E.g., payoffs Hit / FA $1 / .00 $1 / -.50 .50 / -.50 .50 / -$1 .00 / -$1 Chapter 6 - Sensation

28. How do we get rid of bias? The trick here is to use some manipulation that will vary response bias, and test a given subject under a number of levels of this manipulation .. E.g., payoffs Maximum Sensitivity Free of Bias Null Sensitivity Chapter 6 - Sensation

29. Vision - Near vs. Far Some of our senses are primarily concerned with provide information about stimuli and events in our immediate environment (e.g. touch, perhaps smell). Others provide information about stimuli and events that are further away (e.g., vision, audition). Clearly, knowledge about things not in our immediate environment can be critical as actions can than be taken that either bring the stimulus close if it is desirable, or make sure it stays far away if it is undesirable. Of our “early warning” senses, vision is primary. So how does it work? Chapter 6 - Sensation

30. Vision - What you see and What you don’t First of all, we often believe that we see all there is to see in the world. That is simply false. As illustrated in the overhead Steve will soon show (see Figure 6.7 in the text) the light spectrum ranges from short wavelength signals like Gamma Rays, up to long wavelength like AC television and radio waves. We see only a small part of this called the visible spectrum. It ranges from light with wavelengths of between 380 nanometers (violet) up to 760 nanometers (red). This is really a tiny part of the light spectrum, other beasties can see more. Chapter 6 - Sensation

31. Vision - Basic Anatomy of Outer Eye Steve, put up overhead corresponding to Figure 6.8 in some way that also allows the students to see these overheads. Iris - The coloured part of your eye … it is actually a muscle that controls the size of the pupil. Pupil - The black part in the middle of the eye … simply is the opening that allows light into the eyeball. Sclera - The white part of the eye … a tough membrane that serves as protection for the eye itself. Cornea - The fluid filled outer coating of the eye … provides moisture and nutrients to the above parts. OK, so now the light is in the eye … what happens next? Chapter 6 - Sensation

32. Vision - Basic Anatomy of Inner Eye Lens - sits behind the pupil and focuses the incoming light onto the retina. This lens is flexible and slight alterations in it can alter the focus of it, a process called accommodation (as an example, squint). Aqueous Humor - The now focussed light passes through the eyeball proper which is filled with a liquid called aqueous humor (watery fluid). This fluid nourishes the front of the eye in a way that blood vessels normally would. Retina - If the eye is properly shaped, a nicely focussed image lands on the inner coating of the back of the eye. This inner coating is the retina, and it is the part that transmits the light signal (focussed or not) into a neural signal. Chapter 6 - Sensation

33. Vision - Transduction The process of transducing a light signal into a neural impulse comes about through several interim steps as illustrated in the overhead similar to Figure 6.12. Step 1 - Photoreceptors Light strikes the back of the eye stimulating photoreceptor cells which can be either rods or cones (show overhead). Rods are not responsive to colour, but they are very responsive to dim light … great for low light situations. Cones are sensitive to colour and provide a much more detailed image … great for high light, detailed imaging. The transduction is done via a bleaching process in which the photopigments are split, causing an action potential. Chapter 6 - Sensation

34. Vision - Photoreceptors Step 1 - Photoreceptors (Continued) There are actually three kinds of photoreceptors in the retina. Rods have one type, a type that is only sensitive to brightness (i.e., shades of grey) Cones come in three varieties, one roughly sensitive to the colour red, another to green, and a third to blue (approximately) The photoreceptors of the cones are sensitive to colour in the inverse way that a TV (or computer monitor) displays colour. Hue Lum Sat Chapter 6 - Sensation

35. Vision - Bipolar Cells Step 2 - Bipolar Cells The signal from the photoreceptors is then passed on to the bipolar cells which reprocess the signal in a way that tends to emphasize edges and contours. Essentially, when the photoreceptors associated with spatially close parts of the retina are sending very different signals, the bipolar cells accentuate these spots aiding us in our ability to perceive edges. Chapter 6 - Sensation

36. Vision - Ganglion Cells Step 3 - Ganglion Cells The third and final step in the retina pre-processing of visual information is the ganglion cells. Ganglion cells come in two types, red/green and blue/yellow Each cell represents an opponent process system. For example in red/green cells, the resting behaviour of the cell is to produce some mid-level rate of responding. This rate increases when red is present, and decreases when green is present. The yellow/blue increases when both red and green are present (yellow?) but decreases when blue is present Chapter 6 - Sensation

37. Demo of Ganglion Rebound STOP Chapter 6 - Sensation

38. Demo of Ganglion Rebound Chapter 6 - Sensation

39. Vision Conclusion The visual system is able to transform light waves into electro-chemical nerve impulses through the use of photoreceptors. The image is significantly pre-processed prior to leaving the eye in ways that allow us to see a rich palette of colours and that accentuate contours. This pre-processing is done via different types of nerve cells that perform slightly different operations on the signal prior to passing it along. Surely such an intricate system requires a creator, n’est pas? Chapter 6 - Sensation

40. The Other Senses Audition Like the eye, the ear is able to take a physical stimulus (sound waves) and convert it to a nerve impulse which is passed along to the brain. Also like the eyes, the ears pre-process the signal fairly extensively before passing it along. However, there differences in the way that auditory and visual information is pre-processed, and these differences lead to different benefits example: The synthesis of light versus the analysis of sounds Using Doppler effects to sense relative motion Chapter 6 - Sensation

41. The Other Senses Continued The text goes on to describe how some of our other senses work including touch, taste, and internal body senses. We simply do not have enough time to discuss all of these in class, so I leave it to you to read and learn. Given this, let me once again recite our new class motto: “We, the students of PsyA01, are responsible for all of the information in the lectures AND all of the information in the text” Chapter 6 - Sensation