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PowerPoint® presentation by Jim Foley

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1 PowerPoint® presentation by Jim Foley
Chapter 6 Sensation and Perception PowerPoint® presentation by Jim Foley © 2013 Worth Publishers

2 Sensation vs. Perception
“The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.” “The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.” The brain receives input from the sensory organs. The brain makes sense out of the input from sensory organs. Sense: especially vision and hearing smell, taste, touch, pain, and awareness of body position How do the sense organs and nervous system handle incoming sensory information? How does the brain turn sensory information into perceptions? Why is our style of creating perceptions better at perceiving the real world than at decoding tricky optical illusions?

3 Making sense of the world
Top-down processing: using models, ideas, and expectations to interpret sensory information What am I seeing? Bottom-up processing: taking sensory information and then assembling and integrating it Click to reveal definitions for bottom-up and top-down processing. Is that something I’ve seen before?

4 Do you see a painting or a 3D bottle? What’s on the bottle?
Kids see eight to ten dolphins. Why do you think kids see something different than adults? Click to reveal answer and to circle the dolphins. Answer to the question: Top-down processing by children uses different experiences and different models; they are likely to have seen more images of dolphins than images of a nude embrace. Adults also do more top-down processing, and are more likely to “see” objects that aren’t fully there. This shows that “seeing” involves the process of perception, not just the process of our eyes taking in information.

5 Top-down Processing You may start to see something in this picture if we give your brain some concepts to apply: “tree” “sidewalk” “dog” “Dalmatian” Click to reveal sidebar and hints one by one.

6 From Sensory Organs to the Brain
The process of sensation can be seen as three steps: Reception-- the stimulation of sensory receptor cells by energy (sound, light, heat, etc) Transduction-- transforming this cell stimulation into neural impulses Transmission--delivering this neural information to the brain to be processed Automatic animation. Psychophysics refers to the study of the psychological effects of the forms of energy (heat, light, sound) that we can detect.

7 Anything below this threshold is considered “subliminal.”
Thresholds The absolute threshold refers to the minimum level of stimulus intensity needed to detect a stimulus half the time. Anything below this threshold is considered “subliminal.” No animation. Instructor: You could first present this question using a specific sense, such as “How loud does a sound have to be before you can detect it?”

8 below our threshold for being able to consciously detect a stimulus
Subliminal Detection Subliminal: below our threshold for being able to consciously detect a stimulus Although we cannot learn complex knowledge from subliminal stimuli, we can be primed, and this will affect our subsequent choices. We may look longer at the side of the paper which had just showed a nude image for an instant. Click to reveal bullets and example. Research seems to show that: 1) we can sense something without being aware of it. 2) we can be briefly primed, but not enduringly influenced, by subliminal stimuli.

9 When Absolute Thresholds are not Absolute
Signal detection theory refers to whether or not we detect a stimulus, especially amidst background noise. This depends not just on intensity of the stimulus but on psychological factors such as the person’s experience, expectations, motivations, and alertness. No animation. For example, parents of newborns can detect a faint baby’s cry that for others would not stand out from background noise.

10 Sensory Adaptation To detect novelty in our surroundings, our senses tune out a constant stimulus. The rock in your shoe or the ticking of a clock are more difficult to sense after a while. We don’t notice this visually because normally our eyes are constantly moving. However, if you concentrate on keeping your eyes in one spot, you’ll see the effects, as your eyes adjust to stimuli in the following slides. Click to reveal bullets. To prepare for this slide, at the beginning of class you could ask students to tuck a pen behind one ear, and by the time they get to this slide, ask if they feel it. Or ask whether they feel the cell phone in their pockets, and then ask them to switch to the opposite pocket and see if they notice it more.

11 Automatic animation. Instructor: you can tell students, “This will push your motion sensors into sensory adaptation. For this to work, you must stare at the white dot in the center and never move your gaze. When the motion stops, quickly stare at a nearby doorway, window, or a face next to you. Decide now what you will look at.” Explanation: The nerve cells for counter-clockwise rotation become fatigue and start firing slow – we have tired them out by staring. There are still a few cells that might fire off randomly in the clockwise signal. When you look at an unmoving object, the end result is your brain sees the spiral going in opposite direction, and aftereffect of sensory adaptation.

12 Perceptual Set Perceptual set is what we expect to see, which influences what we do see. Perceptual set is an example of top-down processing . Click to reveal second picture. Loch Ness monster or a tree branch? Flying saucers or clouds?

13 Perceptual set can be “primed.”
Old woman Ambiguous Young woman Click to reveal second picture. Instructor: if you used this extra example, you can ask one half the class to focus on the image on the left, the other to look right. Then click and the ambiguous image appears, and the class can raise hands about which of the two images they see, to see if priming influenced their perception.

14 Context Effect on Perception
In which picture does the center dot look larger? Perception of size depends on context. The text at the bottom of the screen will appear on click, and is mean to appear only AFTER you do the “spelling” test below. Instructor: The point of the test is to demonstrate how context, affected/primed by the previous word you stated, can affect which word they perceived. You can state to students, “Six word spelling test! You cannot ask questions; just take a guess and listen for the next word. Write these words down: Double. Pear. (Students may, if “double” gives them context, write “pair.”) Apple. Payor. (Students may, when primed by “apple”, write “pear.”) Payee. Pair. (Here, students might be confused, or some may write “payor.”) Spelling test answers: double pear apple payor payee pair Did context affect which word you wrote?

15 Effect of Emotion, Physical State, and Motivation on Perception
Experiments show that: destinations seem farther when you’re tired. a target looks farther when your crossbow is heavier. a hill looks steeper with a heavy backpack, or after sad music, or when walking alone. something you desire looks closer. Click to reveal bullets. After reading the last bullet, click again to zoom the banana split.

16 Vision: Energy, Sensation, and Perception
The Visible Spectrum We encounter waves of electromagnetic radiation. Our eyes respond to some of these waves. Our brain turns these energy wave sensations into colors. No animation.

17 Color/Hue and Brightness
We perceive the wavelength/frequency of the electromagnetic waves as color, or hue. Click to reveal two illustrations. We perceive the height/amplitude of these waves as intensity, or brightness.

18 The Eye Light from the candle passes through the cornea and the pupil, and gets focused and inverted by the lens. The light then lands on the retina, where it begins the process of transduction into neural impulses to be sent out through the optic nerve. The lens is not rigid; it can perform accommodation by changing shape to focus on near or far objects. Click to reveal bullets.

19 Turning Neural Signals into Images
Some ganglion cells in the eye send signals directly to the visual cortex in response to certain features such as visual patterns, certain edges, lines, or movements. In and around the visual cortex of the occipital lobe, supercells integrate these feature signals to recognize more complex forms such as faces. Faces Houses Chairs Houses and Chairs Click to reveal bullets and example. Instructor: damage to these areas of the brain appears to make it difficult to see certain kinds of objects; most striking is those who have face blindness. Those with these conditions can often see the features, but not integrate them into a whole. SUPERCELLS

20 Color Vision Young-Helmholtz Trichromatic (Three-Color) Theory According to this theory, there are three types of color receptor cones--red, green, and blue. All the colors we perceive are created by light waves stimulating combinations of these cones. No animation. Instructor: you could start by saying that we see the color of an orange because it absorbs all light except the wavelengths that our brain interprets as orange. You could note that the red, green and blue don’t actually refer to the appearance of the cones; they are the colors to which these three cones react.

21 Color Blindness People missing red cones or green cones have trouble differentiating red from green, and thus have trouble reading the numbers to the right. Opponent-process theory refers to the neural process of perceiving white as the opposite of perceiving black; similarly, yellow vs. blue, and red vs. green are opponent processes. Click to reveal text boxes. Instructor: you could add, “Some people say that dogs have “black and white” vision. In fact, they are lacking red receptors, so their vision has simpler color perception, dichromatic, not monochromatic.” Feeling superior to animals? Note that many birds and insects can sense ultraviolet and infrared that you can’t see.

22 Opponent-Process Theory Test
Instructor: Tell the students: “Stare at the center dot for 30 seconds; if you’re doing it well, the flag will start to disappear. If it does, keep staring at the dot.” Further narration as they stare at the dot: “If opponent-process theory is correct, then fatiguing our perception of one will make a blank slide look like the opposite color… and the opponent processes are white vs. black, red vs. green, and yellow vs. blue.” Click to make flag disappear. What do you see? Question for students: “Besides opponent-process theory, what else are we demonstrating here?”...(sensory adaptation). After our color receptors for green become fatigued, an empty white background will briefly seem red, just as plain water might taste salty or strange after eating a lot of intensely sweet candy to the point of fatiguing our tongue. There have been versions of this circulating online in which our receptors get fatigued just by some dots near the center dot, and a B&W picture turns to full color when we look at a blank space. The dot, the dot, keep staring at the dot in the center…

23 Turning light waves into mental images/movies... Perceptual Organization
We have perceptual processes for enabling us to organize perceived colors and lines into objects: grouping incomplete parts into gestalt wholes seeing figures standing out against background perceiving form, motion, and depth keeping a sense of shape and color constancy despite changes in visual information using experience to guide visual interpretation Click to reveal bullets. This is a summary slide for this upcoming section, listing the major concepts and not the section headings.

24 The Role of Perception Our senses take in the blue information on the right. However, our perceptual processes turn this into: a white paper with blue circle dots, with a cube floating in front. a white paper with blue circle holes, through which you can see a cube. a cube sticking out to the top left, or bottom right. blue dots (what cube?) with angled lines inside. Click to reveal bullets, BUT before any bullets appear, see how many different visual perceptions students can come up with. To nudge the discussion, note the little ‘x’ near the center of the picture; ask if it looks like it’s inside a blue hole, or at the back and bottom of a cube that opens up and to the left…

25 Figure-Ground Perception
In most visual scenes, we pick out objects and figures, standing out against a background. Some art muddles this ability by giving us two equal choices about what is figure and what is “ground”: Click to reveal bullets and two examples. Goblet or two faces? Stepping man, or arrows?

26 Grouping: How We Make Gestalts
“Gestalt” refers to a meaningful pattern/configuration, forming a “whole” that is more than the sum of its parts. Three of the ways we group visual information into “wholes” are proximity, continuity, and closure. Click to show a different perspective on each image. Instructor: perhaps you can get students to bring out the definitions of the concepts in these pictures (as you click to reveal the animations). “Proximity” means we tend to see objects that are close together as being part of the same object.

27 Visual Cliff: A Test of Depth Perception
Babies seem to develop this ability at crawling age. No animation. Instructor: as a preview of figuring out how we perceive depth, note that the pattern on the floor looks more condensed (and thus farther away) to the infant than the identical pattern on the table. The infant can perceive this difference as depth/height and see a danger of falling. Note that the ability to perceive glass as solid does not appear to be as innate as the fear of the cliff. Even newborn animals fear the perceived cliff.

28 Perceiving Depth From a 2D Image: Binocular Methods
Binocular (using both eyes) cues exist because humans have two eyes in the front of our head. This gives us retinal disparity; the two eyes have slightly different views, and the more different the views are, the closer the object must be. In an extreme example, your nose is so close that each eye sees a completely opposite half-view of it. Click to reveal second text box. How do we perceive depth from a 2D image?... by using monocular (needing only one eye) cues

29 Monocular Cue: Interposition
Interposition: When one object appears to block the view of another, we assume that the blocking object is in a position between our eyes and the blocked object. No animation.

30 Monocular Cue: Relative Size
We intuitively know to interpret familiar objects (of known size) as farther away when they appear smaller. No animation.

31 Monocular Cues: Linear Perspective and Interposition
The flowers in the distance seem farther away because the rows converge. Our brain reads this as a sign of distance. No animation. Instructor: see if students can notice one other monocular cue for depth perception evident in this picture...interposition. The flowers in the very front (bottom of the frame) partially block the view of other flowers, and the whole hill of flowers appears to block the view of the hill in the background.

32 Tricks Using Linear Perspective
These two red lines meet the retina as being the same size However, our perception of distance affects our perception of length. Click to bring bottom line up. The way our brain changes the perception of length in this case is called the Ponzo illusion, first demonstrated by Italian psychologist Mario Ponzo in 1913. The two [rods/bars/logs] are the same size on screen, but our eyes tend to see one as larger because linear perspective makes its location on the train tracks seem farther away.

33 Monocular Cues: Shading Effects
Shading helps our perception of depth. Does the middle circle bulge out or curve inward? How about now? Click to invert the image and show the hollow as a hill.

34 Monocular Cues: Relative Motion
When we are moving, we can tell which objects are farther away because it takes longer to pass them. A picture of a moon on a sign would zip behind us, but the actual moon is too far for us to pass. No animation. A great animated example can be found at This depth perception cue is often referred to as motion parallax. It is used by many animals that don’t have the benefit of binocular cues because their eyes are on the sides of their heads. It is called “relative motion”; when we are moving, the objects we pass can appear to be moving in the opposite direction, and the farther objects don’t move as fast.

35 Perceptual Constancy Our ability to see objects as appearing the same even under different lighting conditions, at different distances and angles, is called perceptual constancy. Perceptual constancy is a top-down process. Examples: color and brightness constancy shape and size constancy No animation. Instructor: you can use this narrative to tie things together after the definition--“Because this means perceiving sameness even when receiving different sensory information, this means that we use this top-down process to change what colors, shapes, sizes and objects we think we see, depending on the context.”

36 Color Constancy This ability to see a consistent color in changing illumination helps us see the three sides as all being yellow, because our brain compensates for shading. As a result, we interpret three same-color blue dots, with shades that are not adjusted for shading, as being of three different colors. Click to reveal bullets and animate example.

37 Brightness Constancy On this screen, squares A and B are exactly the same shade of gray. You can see this when you connect them. So why does B look lighter? Click to show image with gray bars to demonstrate. Click to show image with gray bars connecting the A and B squares. Hopefully, your students can explain that our brains compensate for shadows and other context by perceiving a constant color shade/brightness even when things are in shadow. This means mentally erasing the shadow to see objects in a lighter shade. This process, plus the checkerboard context, makes B seem lighter to our brain than the images sensed by our eyes.

38 Shape Constancy Shape constancy refers to the ability to perceive objects as having a constant shape despite receiving different sensory images. This helps us see the door as a rectangle as it opens. Because of this, we may think the red shapes on screen are also rectangles. No animation. Instructor: you could ask students an intentionally ambiguous question...“What shapes do you see outlined in red?” If they say “rectangle,” ask again, no longer referring to the doors. “Tell us the names of the red shapes.” Then click to fade the doors and reveal that the second and third red shapes are trapezoids.

39 The Moon Illusion The moon appears larger on the horizon than overhead. Why do we perceive the moon as a different size depending on its location? One possible theory is that our ancestors assumed overhead objects were closer than objects on the horizon. The moon, like one of these monsters, seems larger because we see it as farther away. Click to reveal bullets. Note that there are several other theories about the moon illusion. One has to do with horizon reference objects; maybe on the horizon we compare the moon to a smaller section of sky than when it’s overhead (try looking at a moonset picture that is NOT zoomed in).

40 Size Constancy We have an ability to use distance-related context cues to help us see objects as the same size even if the image on the retina becomes smaller. The Ames room was invented by American ophthalmologist Adelbert Ames, Jr. in 1934. The Ames room was designed to manipulate distance cues to make two same-sized girls appear very different in size. Click to reveal bullets and to show explanation.

41 Hearing/Audition: Starting with Sound
Length of the sound wave; perceived as high and low sounds (pitch) Height or intensity of sound wave; perceived as loud and soft (volume) Click for Frequency sequence; click for Amplitude sequence. Amplitude, or loudness, is measured relative to the threshold for human hearing (set at zero decibels). The rustling of leaves you heard measures at about 20 decibels, my voice (and most conversation) measures at about 40 to 60 decibels. You’ll find out more about the decibels of common sounds a little later in this presentation, but here’s an important decibel tip: enough exposure to a sound above 85 decibels can cause hearing damage.   Click for Complexity sequence. We distinguish the same note played by a piano and any other instrument due to the complexity of the sound wave and our perception of timbre. Each human voice has its own complexity; for instance, can you describe what it is about the voice of a friend that allows you to recognize that person on the phone? Of these properties, frequency provides most of the information we need to identify sounds. It is measured in cycles per second, or hertz (Hz), and perceived by humans as pitch (high and low sound). Both amplitude and frequency will be demonstrated further in the next slide. Perceived as sound quality or resonance

42 Sound Waves Reach The Ear
The outer ear collects sound and funnels it to the eardrum. In the middle ear, the sound waves hit the eardrum and move the hammer, anvil, and stirrup in ways that amplify the vibrations. The stirrup then sends these vibrations to the oval window of the cochlea. In the inner ear, waves of fluid move from the oval window over the cochlea’s “hair” receptor cells. These cells send signals through the auditory nerves to the temporal lobe of the brain. Click to show details about outer, middle, and inner ear.

43 Preventing Hearing Loss
Exposure to sounds that are too loud to talk over can cause damage to the inner ear, especially the hair cells. Structures of the middle and inner ear can also be damaged by disease. Prevention methods include limiting exposure to noises over 85 decibels and treating ear infections. People with conduction hearing loss may be helped by hearing aids. These aids amplify sounds striking the eardrum, ideally amplifying only softer sounds or higher frequencies. People with sensorineural hearing loss can benefit from a cochlear implant. The implant does the work of the hair cells in translating sound waves into electrical signals to be sent to the brain.

44 Sound Perception: Loudness
Loudness refers to more intense sound vibrations. This causes a greater number of hair cells to send signals to the brain. Soft sounds only activate certain hair cells; louder sounds move those hair cells AND their neighbors. Click to reveal bullets.

45 Sound Perception: Pitch
How does the inner ear turn sound frequency into neural frequency? Frequency theory At low sound frequencies, hair cells send signals at whatever rate the sound is received. Place theory At high sound frequencies, signals are generated at different locations in the cochlea, depending on pitch. The brain reads pitch by reading the location where the signals are coming from. Click to reveal three text boxes. Volley Principle At ultra high frequencies, receptor cells fire in succession, combing signals to reach higher firing rates.

46 proteins to grow and repair tissue
Taste Our tongues have receptors for five different types of tastes, each of which may have had survival functions. Bitter: potential poisons Sweet: energy source Umami: (savoriness) proteins to grow and repair tissue Salty: sodium essential to physiological processes Click to show labels. Tastes may exist to attract humans to energy and protein-rich foods that are typically sweet or “umami,” and to avert them from potentially toxic or harmful substances that are often bitter or sour. Umami is a recently identified, savory taste that is associated with monosodium glutamate, meats, mushrooms, seaweed, and aged cheeses (such as Parmesan). Salty tastes also attract humans to replenish essential salts. Sour: potentially toxic acid

47 Neurochemistry of Taste
There are no regions of the tongue, just different types of taste receptor cells projecting hairs into each taste bud’s pore. These cells are easily triggered to send messages to the temporal lobe of the brain. Burn your tongue? Receptors reproduce every week or two. But with age, taste buds become less numerous and less sensitive. Top-down processes still can override the neurochemistry; expectations do influence taste. Click to reveal bullets.

48 Mixing the different senses together
456789 Sensory interaction occurs when different senses influence each other. For example: a burst of sound makes a dim light source more visible. flavor is an experience not only of taste, but also of smell and texture. seeing text or lip movement, or even feeling the puff of air from consonants, affects what words we hear. Synaesthesia is a condition when perception in one sense is triggered by a sensation in a DIFFERENT sense. Some people experience synaesthesia all the time, reporting that, “the number 7 gives me a salty taste” or “rock music seems purple.” Click to reveal bullets.

49 Sensing Body Position and Movement
Kinesthesis (“movement feeling”) refers to sensing the movement and position of individual body parts relative to each other. How it works: sensors in the joints and muscles send signals that coordinate with signals from the skin, eyes, and ears Without kinesthesis, we would need to watch our limbs constantly to coordinate movement. Click to reveal bullets.

50 Sensing Body Position and Movement
Vestibular sense refers to the ability to sense the position of the head and body relative to gravity, including the sense of balance. How it works: fluid-filled chambers in the inner ear (vestibular sacs and semicircular canals) have hairlike receptors that send messages about the head’s position to the cerebellum Vestibular sense serves as the human gyroscope, helping us to balance and stay upright. Click to reveal bullets.

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