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.
2. The follow series of slides is intended to demonstrate some of the phenomena that you read about in Chapter 4 Sensation and Perception
3. The eye: A Living Optical Instrument Sensory organ for vision: The eye Main sensory component: The retina
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5. The eye: A Living Optical Instrument Characteristics of the Retina The retina is an extension of your central nervous system. It is only a couple neurons away from your occipital cortex.
6. The eye: A Living Optical Instrument Characteristics of the Retina Functions of the retina Absorb light – the obvious function Process light information – yes, the retina processes light information. Some of what hits the retina never makes it to your brain! Send information to the brain – this has a fun consequence
7. Functions of the Retina Function 1: Absorbing Light Humans have two main types of receptor cells When photons hit chemicals inside of these cells, the cell changes its electrical charge. This leads to action potentials in connected neurons. Two types: Rods – sensitive to low light. Only shades of black, gray, white Cones – sensitive to color. Most sensitive in daylight vision
8. Fun Time Cones are more sensitive. There is a cluster of cones directly in the back of the eye at a location called your fovea. Fovea
9. Fun Time When you “look at” something, you are angling your eyes so that light from the object hits your fovea. If you force yourself to stare at something and not move your eyes, you also can see off to the sides. This is peripheral vision.
10. Fun Time Your peripheral vision is mostly due to rods detecting light. Rods are not sensitive to color. There are far fewer cones on the retina outside of the fovea. Yes, this means that your amazing brain constantly lies to you. Look around the room, now.
11. Fun Time You do not see a round spot of color moving around a mostly black and white room as you scan your eyes, do you? Your brain fills it in, keeping your experience of the room constant, despite your retina.
12. Fun Time I don’t have a test to show you this with color, but you can see your peripheral vision’s limitations in the next demonstration.
13. On the next screen, stare at the cross, and don’t let your eyes move. As you keep your eyes staring at the cross, see if you can count the number of vertical lines in your peripheral vision. Don’t cheat! You should struggle trying.
14. Stare at the Cross Try to count these lines Click to see just the figure.
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16. Why do you struggle to make out individual lines in your peripheral vision? Rods aren’t as sensitive as cones, so you cannot see as crisply as you can when you orient your eyes to make an object fall on your fovea, where cones are plentiful.
17. Functions of the Retina Function 1: Absorbing Light The retina does not absorb light on an absolute scale. If there is a drastic change in the level of light hitting your rods and cones, the chemicals inside the cells change and become more or less sensitive. This leads to Adaptation
18. Examples Light Adaptation You experience this when you leave a movie theater and walk into noon-day sun. Your eyes don’t seem to work. Dark Adaptation You experience this when you walk into a pitch black room from outside. Slowly…you see more and more.
19. Fun with Adaptation Adaptation is awesome. Without adaptation, we couldn’t have pig farms.
20. Fun with Adaptation Normally functioning people experience adaptation with each sense.
21. Fun with Adaptation Touch When you put on your clothes, you feel how they fall on your skin. You may be able to tell, just by the feel on your skin, just how good or bad you look in those new clothes…
22. Fun with Adaptation Touch A few minutes later, you no longer feel your clothes. They no longer capture your attention. All of those sensations fall into the background. Can you imagine if you felt your clothes, constantly, with every motion you make…
23. Fun with Adaptation Smell If you light a scented candle, you smell the scent pretty quickly. An hour later, you’re surprised to notice that it is still burning, but you smell nothing! Now you may regret buying a crappy candle.
24. Fun with Adaptation Smell This is sensory adaptation for smell. You notice changes. With prolonged, continuous exposure, you stop noticing a smell. This is why friends comment on your cologne, which you no longer smell. This is why people can live beside pig farms, and not smell them.
25. Several companies have realized that people experience smell adaptation for room fresheners. Have you noticed the new products that pulse smells periodically instead of releasing them continuously? If a candle smells good constantly, you don’t notice it! If it only smells good occasionally, you notice it and like it!
27. Review The first function of the retina: Absorb light Rods and Cones react to light They are located in different numbers in the fovea and periphery They do not absorb light on an absolute scale. They are sensitive to changes in light levels. We experience this as Adaptation.
28. Functions of the Retina Function 2: Processing Information Key point: Each neuron leaving the eye through the optic nerve contains information from around 100 rods and/or cones. The retina processes the information and only sends the most important parts to the brain.
29. The apparent flashing on this picture is due to the processing of information on your retina
30. Functions of the Retina Function 3: Sending Information to the Brain Because of this…you have a blind spot.
31. Example: Your Blindspot The cells that process light are actually in front of your retina. Rods and cones only get photons after they pass through all of that cellular circuitry. To exit the eye, there is a hole in the retina for the optic nerve to leave. This is your blind spot. Rod Light Cone Light Optic Nerve Light
32. Want to see your blind spot? Close your right eye. With your left eye, stare at the circle. Start sitting back in your chair, and move your head closer to the screen, staring at the dot. The cross will disappear at about 12 – 15 inches from the screen.
33. Functions of the Retina Function 3: Sending Information to the Brain Optic nerve – a bundle of myelinated axons leaving your eye.
34. From the Retina to the Brain The optic nerves from each eye send information to the left and right occipital cortex. This is a brain, viewed from the back. The red is your primary visual cortex. Yellow is visual association cortex.
35. From the Retina to the Brain The following screens show how each side of your visual field goes to the opposite hemisphere. Click through quickly.
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74. Information Processing in the Visual Cortex From the primary visual cortex, action potentials radiate out into neighboring brain regions, like the lights below.
75. Information Processing in the Visual Cortex Different brain areas are sensitive to different information. The following image shows how brain cells in your parietal lobe begin to fire, or not fire, based on details of space, orientation, distance, etc. Brain cells in your temporal lobes begin to fire, or not, based on details of shapes, colors, features, etc.
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77. Information Processing in the Visual Cortex Think of the connected neurons in your cerebral cortex as groups of gossiping coworkers. Dorsal Stream – is like a group of people who only spread a rumor if that rumor is about “where” people are, where they are going, or how they are moving. Other rumors don’t spark their interest. Ventral Stream – is like a group of people who only spread rumors about “what” people are like, how they look, what group they belong to, or what they do. Other rumors don’t spark their interest.
78. Review Functions of the retina Absorb light Process light information Send information to the brain From the Retina, neural activity goes to the primary visual cortex From there, visual information is processed in two streams
80. Do you see numbers in these circles? If not, you might want to get an eye exam.
81. Stare at the white circle below. Don’t move your eyes. Hold for 20 – 60 seconds. Then go to the next slide. What do you see?
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83. Summary We pointed out parts of the eye Then we looked at characteristics and functions of the retina Specifically, the retina Absorbs light Processes light information Sends information to the brain We traced this path from retina to occipital cortex, then to the parietal and temporal lobes
84. Let’s explore some more visual stimuli. The following are used to demonstrate how perceptions can vary.
94. Most of us are extremely sensitive to details of faces. Bottom-up processing is pretty easy for us. To actually feel what it is like to process differently, look at the next few slides.
95. Briefly flip past the next slide. Ask yourself what is different between the two faces?
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98. Now look at the same image, turned right side up. Isn’t it MUCH more noticeable what they did to poor Britney?
100. Top-down Processing I cdnuolt blveiee taht I cluod aulaclty uesdnatnrd waht I was rdanieg. The phaonmneal pweor of the hmuan mnid. Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be in the rghit pclae. The rset can be a taotl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe. Amzanig huh? yaeh and I awlyas thought slpeling was ipmorantt.
102. For people who are skilled readers, we typically do not read every word on the page. As you read, you begin to predict what is coming next. That allows you to skip a lot of bottom-up processing (looking at every letter is not necessary). If you were able to read the sentences with letters missing, this shows that you were using top-down processing.
104. Could you read “Love” and “Hate” on the two shirts fairly easily? This is top-down processing. When you tried to confirm if it was a real reflection, did you have to pay careful attention to each angle and twist of the text? This is more bottom-up in its approach.
105. Now let’s mess with your depth perception The following slide is NOT animated. Nothing is moving.
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107. Click the back arrow to try it again, and this time focus on only one football. It isn’t moving. If you do not move your eyes, it seems to stop moving. If you move your eyes around, it writhes like snakes. This happens because your brain interprets the light and dark edges as depth cues, but they are purposefully arranged in an impossible way. As your eyes move, your brain tries to figure out the shading. What you get is a wonderfully headache-inducing illusion.
108. Summary Vision is Complex! Psychologists study how light is registered by your retina and then sent to your brain (sensation). Psychologists also study how your brain processes this information (perception). Perception is subjective. Top-down processing is a great example of this. See your text for more details.
