The Various Psychological Phenomenon
The Various Psychological Phenomenon
ZAPS is a set of interactive online experiments and demonstrations that will allow you to experience the various psychological phenomenon, as well as, serve as an additional tool to reinforce the theoretical basis behind each experiment and demonstration. All of the experiments will also be discussed in a real-world context. Your grade will be based on these summaries, NOT the grade provided by the ZAPS website when you finish the experiment
Please answer the ZAPS question below: The Various Psychological Phenomenon
ZAPS 2: Visual Search—The goal of this ZAPS is to help you understand the importance of features in object recognition.
What is a feature search? What is a conjunctive search? Why does the number of distractors influence reaction time in the conjunctive search condition, but not the feature search condition? Describe your results for the feature search and conjunctive search conditions. Were your results similar to the referenceresults? Why or why not?
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ZAPS 3: Face Perception—The goal of this ZAPS is to help you understand how we processes faces in the environment.
In your summary please compare your results to the reference results. Were your results similar to the reference results, or different? Why? According to the ZAPS and textbook, how do we typically recognize a face? Why is it often difficult to recognize an inverted face?
ZAPS 4: Stroop Effect—The goal of the current ZAPS is to examine how we deal with conflicting/competing information.
In your summary please compare your results to the reference results. Were your results similar to the reference results, or different? Why? Discuss why individuals generally respond slower to incongruent trials while completing the Stroop task.
The rubric: The Various Psychological Phenomenon
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| 3 | Visual Perception |
The Visual System You receive information about the world through various sensory modalities: You hear the sound of the approaching train, you smell the freshly baked bread, you feel the tap on your shoulder. Researchers have made impressive progress in studying all of these modalities, and students interested in, say, hearing or the sense of smell will find a course in (or a book about) sensation and perception to be fascinating.
There’s no question, though, that for humans vision is the dominant sense. This is reflected in how much brain area is devoted to vision compared to any of the other senses. It’s also reflected in many aspects of our behavior. For example, if visual from other senses, you usually place your trust in vision. This is the basis for ventriloquism, in which ation conflicts with information received fo you see the dummy’s mouth moving while the sounds themselves are coming from the dummy’s master. Vision wins out in this contest, and so you experience the illusion that the voice is coming from the dummy. The Photoreceptors The Various Psychological Phenomenon
How does vision operate? The process begins, of course, with light. Light is produced by many objects in our surroundings-the sun, lamps, candles-and then reflects off other objects. In most cases, it’s this reflected light-reflected from this book page or from a friend’s face-that launches the processes of visual perception. Some of this light hits the front surface of the eyeball, passes through the cornea and the lens, and then hits the retina, the light-sensitive tissue that lines the back of the eyeball (see Figure 3.1). The cornea and lens focus the incoming light, just as a camera lens might, so that a sharp image is cast onto the retina. Adjustments in this process can take place because the lens is surrounded by a band of muscle. When the muscle tightens, the lens bulges somewhat, creating the proper shape for focusing the images cast by nearby objects. When the muscle relaxes, the lens returns to a flatter shape, allowing the proper focus for objects farther away. On the retina, there are two types of photoreceptors-specialized neural cells that respond directly to the incoming light. One type, the rods, are sensitive to very low levels of light and so play an essential role whenever you’re moving around in semidarkness or trying to view a fairly dim stimulus. But the rods are also color-blind: They can distinguish different intensities of light (and in that way contribute to your perception of brightness), but they provide no means of discriminating one hue from another (see Figure 3.2). Cones, in contrast, are less sensitive than rods and so need more incoming light to operate at all. But cones are sensitive to color differences. More precisely, there are three different types of cones each having its own pattern of sensitivities to different wavelengths (see Figure 3.3). You perceive color, therefore, by comparing the outputs from these three cone types. Strong firing from only the cones that prefer short wavelengths, for example, accompanied by weak (or no) firing from the other cone types, signals purple. Blue is signaled by equally strong firing from the cones that prefer short wavelengths and those that prefer medium wavelengths, with only modest firing by cones that across the three cone types, prefer long wavelengths. And so on, with other patterns of firing, corresponding to different perceived hues. Cones have another function: They enable you to discern fine detail. The ability to see fine detail is referred to as acuity, and acuity is much higher for the cones than it is for the rods. This explains why you point your eyes toward a target whenever you want to perceive it in detail. What you’re actually doing is positioning your eyes so that the image of the target falls onto the fovea, the very center of the retina. Here, cones far outnumber rods (and, in fact, the center of the fovea has no rods at all). As a result, this is the region of the retina with the greatest acuity The Various Psychological Phenomenon.
In portions of the retina more distant from the fovea (i.e., portions of the retina in the so-called visual periphery), the rods predominate; well out into the periphery, there are no cones at all. This distribution of photoreceptors explains why you’re better able to see very dim lights out of the corner of your eyes. Psychologists have understood this point for at least a century, but the key observation here has a much longer history. Sailors and astronomers have known for hundreds of years that when looking looking slightly away from the star, they ensured that the star’s image would fall outside of the fovea at a barely visible star, it’s best not to look directly at the star’s location. By and onto a region of the retina dense with the more light-sensitive rods. Lateral Inhibition Rods and cones do not report directly to the cortex. Instead, the photoreceptors stimulate bipolar cells, which in turn excite ganglion cells. The ganglion cells are spread uniformly across the entire retina, but all of their axons converge to form the bundle of nerve fibers that we call the optic nerve. This is the nerve tract that leaves the eyeball and carries information to various sites in the brain. The information is sent first to a way station in the thalamus called the lateral geniculate nucleus (LGN); from there, information is transmitted to the primary projection area for vision, in the occipital lobe.
Let’s be clear, though, that the optic nerve is not just a cable that conducts signals from one site to another. Instead, the cells that link retina to brain are already analyzing the visual input. One example lies in the phenomenon of lateral inhibition, a pattern in which cells, when stimulated, inhibit the activity of neighboring cells. To see why this is important, consider two cells, each receiving stimulation from a brightly lit area (see Figure 3.4). One cell (Cell B in the figure) is receiving its stimulation from the middle of the lit area. It is intensely stimulated, but so are its neighbors (including Cell A and Cell C). As a result, all of these cells are active, and therefore each one is trying to inhibit its neighbors. The upshot is that the activity level of Cell B is increased by the stimulation but decreased by the lateral inhibition it’s receiving from Cells A and C. This combination leads to only a moderate level of activity in Cell B. In contrast, another cell (Cell C in the figure) is receiving its stimulation from the edge of the lit area. It is intensely stimulated, and so are its neighbors on one side. Therefore, this cell will receive inhibition from one side but not from the other (in the figure: inhibition from Cell B but not from Cell D), so it will be less inhibited than Cell B (which is receiving inhibition from both sides). Thus, Cells B and C initially receive the same input, but C is less inhibited than B and so will end up firing more strongly than B.
Notice that the pattern of lateral inhibition highlights a surface’s edges, because the response of cells detecting the edge of the surface (such as Cell C) will be stronger than that of cells detecting the middle of the surface (such as Cell B). For that matter, by increasing the response by Cell C and decreasing the response by Cell D, lateral inhibition actually exaggerates the contrast at the edge-a importance, because it’s obviously object’s shape-information essential for figuring what the object is. And let’s emphasize that this edge enhancement occurs at a very early stage of process called edge enhancement. This process is of enormous highlighting the information that defines an out the visual processing. In other words, the information sent to the brain isn’t a mere copy of the incoming stimulation; instead, the steps of interpretation and analysis begin immediately, in the eyeball. (For a demonstration of an illusion caused by this edge enhancement- the so-called Mach bands-see Figure 3.5.) e. Demonstration 3.1: Foveation The Various Psychological Phenomenon
The chapter describes the basic anatomy of the eyeball, including the fact that the retina (the light- sensitive surface at the back of the eye) has, at its center, a specialized region called the fovea. The cells in the fovea are distinctive in several ways, but, perhaps most important, they are much better at discerning visual detail than cells elsewhere on the retina.
In fact, cells away from the fovea are not just worse at seeing detail in comparison to foveal cells, they are actually quite bad at seeing detail. As a result, if you want to see an object’s details, you need to look straight at it; this movement positions your eyes so that the object’s image falls on the fovea. If you want to see detail in other regions, then you need to reposition your eyes so that new inputs will be in “foveal view.”
Putting this more broadly, if you want to scrutinize an entire scene, you need to move your eyes a lot, and this point leads to another limitation, because eye movements are surprisingly slow: For the eye movements we use to explore the world- eye movements called “saccades“-you need almost 200 msec to change your eye position. Most of that time is spent in “planning” and “programming” each movement, but, even so, you’re only able to move your eyes four or five times each second; it’s just not possible to move your eyes more quickly than this. This combination-the inability to see detail outside of the fovea, and the slowness of eye movements-places severe limits on your pickup of information from the world, and these limits, in turn, influence how the nervous system must use and interpret the information actually received. How severe are these limits? And just how distinctive is the fovea? Position yourself about 12 inches from these words. Point your eyes at the black dot in the middle of the display, and try not to move them. Stare at the dot for a moment, to make sure you’ve got your eye position appropriately “locked” in place, and then, without moving your eyes, try to read the letters one row up or down to the left or right. You should be able to do this, but you will probably find that your impression of the letters is indistinct. Now-still without moving your eyes- from the dot, or a couple of positions try reading the letters further from the dot. This should be more difficult. What’s going on? When you point your eyes at the dot, you’re positioning each eyeball relative to the input so that the dot falls on the fovea; therefore, the other letters fall on retinal positions away from the fovea. The other letters are therefore falling on areas of the retina that are literally less able to see sharply.
Notice, however, that in the ordinary circumstances of day-to-day life, the entire visual world seems sharp and clear to you. You don’t have an impression of only being able to see a small region clearly, with everything else being blurry. Your sense of the world, though, is produced in large part by the “construction” and “filling in” that you do unconsciously-relying on inference and to supplement the surprisingly sparse input that is actually provided by your eyes. e. Demonstration 3.2: Eye Movements
The previous demonstration was designed to remind you that only a small portion of the retina (the fovea) is sensitive to fine detail. This is, of course, one of the reasons why you constantly move your eyes: Every shift in position points the eyes at a new portion of the visual world, allowing you to pick up detail from that portion of the world. Eventually, with enough time and enough changes in eye position, you can inspect an entire scene.
To explore the world, you rely on eye movements called “saccades.” These eye movements (mentioned in Demonstration 3.1) are abrupt and “jerky,” as your eyes hop from position to position, and, in fact, the word saccade is taken from the French for “jerk” or “twitch” To see just how jerky these eye movements are, sit (or stand) close to a friend (within 2 feet or so), but just off to the side. (There’s no need in this demonstration for you and your friend to be nose-to-nose.) Have your friend look off to the left, and then, when you say “go,” have your friend move his or her eyes smoothly to the right. You’ll easily see that-despite this instruction- the eye movements aren’t smooth at all. Instead, your friend’s eyes move left-to-right in a series of small jumps; these are the saccades. (Now, reverse roles, so that your friend can see your saccades.)
Next, try a variation of this procedure: Again, position yourself to watch your friend’s eye movements. This time, hold up a pen, positioning it off to your friend’s left. Now, smoothly move the pen from your friend’s left to your friend’s right, and have your friend watch the pen’s tip as it moves across his or her view. This time, you won’t see jerky eye movements. Instead, when someone is tracking a moving object (such as the pen’s tip), the person relies on a different type of eye movement called “smooth pursuit movements.” (And, once more, reverse roles so that your friend can watch your smooth pursuit.) The Various Psychological Phenomenon
Obviously, therefore, people which type do you use in your ordinary examination of the world? One last time, position yourself to watch your friend’s eye movements. This time, have your friend look around, counting the circular objects that are in view. (If there are no circular objects around, choose some other target. In truth, capable of producing smooth (not jerky) eye movements. But are want some chore that will force your friend to the nature of the target doesn’t matter; you just inspect the immediate environment.) Which type of eye movements does your friend use-the jerky saccades, or smooth movements? Finally, internal state. Consider, for example, one last comment: A person’s pattern of eye movements is also influenced by his or her one of the tests that police officers rely on when they suspect a driver is intoxicated. The police routinely conduct what’s called a “field sobriety test,” and one part of the test involves a close examination of the driver’s eye movements. The test can yield several indications of drunkenness-including a disruption of smooth pursuit, and also an inability to hold the eyes still when looking at a stationary target. Plainly, then, an understanding of eye movements has practical implications-and is one of the ways in which we promote safety by keeping drunk drivers off the road! e. Demonstration 3.3: The Blind Spot and the Active Nature of Vision The Various Psychological Phenomenon
Axons from the retina’s ganglion cells gather together to form the optic eyeball and carries information first to the thalamus and then to the visual cortex. Notice, therefore, nerve. This nerve leaves the that there has to be a location at the back of each eyeball that can serve as the “exit” for the ganglion cells’ axons, and the axons fill this “exit” entirely, leaving no room for rods or cones. As a result, this photoreceptors at all and, therefore, is completely insensitive to light. region contains no Appropriately enough, this region is called the “blind spot”.
Ordinarily, people aren’t aware of the blind spot-but we can make them aware with a simple procedure. L0ok at the following picture, with your face about 18 inches from the screen. Close your left eye. Stare at the center of the author’s picture on the left. Gradually lean toward or away from the screen. At most distances, you’ll still be able to see the brain (on the right) out of the corner of your eye. You should be able to find a distance, though, at which the brain picture drops from view- it just seems not to be there. What is going on? You’ve positioned the screen, relative to your eye, in a way that places the author’s picture on your fovea but the picture of the brain on your blind spot, and so the brain simply became invisible to you.
Even when the brain “disappeared,” however, you didn’t perceive a “hole” in the visual world. Instead, the brain picture disappeared, but you could still perceive the continuous grid pattern with interruption in the lines. Why is this? Your visual system detected the pattern in the grid no (continuous vertical lines plus continuous horizontals) and used this pattern to “fill in” the information that was missing because of the blind spot. But, of course, the picture of the brain isn’t part of this overall pattern, so it wasn’t included when you did the filling in. Therefore, the picture of the brain vanished, but the pattern was not disrupted. Visual Coding In Chapter 2, we introduced the idea of coding in the nervous system. This term refers to the relationship between activity in the nervous system and the stimulus (or idea or operation) that is somehow represented by that activity. In the study of perception, through which neurons (or groups of neurons) manage to represent the shapes, colors, sizes, and movements that you perceive? we can ask: What’s the code Single Neurons and Single-Cell Recording Part of what we know about the visual system-actually, part of what we know about the entire brain -comes from a technique called single-cell recording. As the name implies, this is a procedure through which investigators can record, moment by moment, the pattern of electrical changes within a single neuron The Various Psychological Phenomenon.
