Science B44 FINAL EXAM FALL 2005

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1 Science B44 Vision and Brain Fall 2005 Final Page 1 Science B44 FINAL EXAM FALL 2005 BOOK 1 MULTIPLE CHOICE QUESTIONS 1. Which of the following cues to depth require two eyes? a. Accomodation b. Convergence c. Motion parallax d. Linear perspective 2. Which of the following is true about the impossible triangle? a. It can be one view of a physically realizable object. b. It shows the importance of T-junctions. c. Globally, everything seems reasonable. d. Locally, the scene seems contradictory. 3. Choose the strategy for representing features that is NOT correctly matched with its description. a. Adaptive : adjacent cells inhibit each other b. Distribution : overall pattern of activity counts, not individual cells c. Ordered : adjacent cells represent adjacent values d. Sampled : only some values are represented. 4. Text with absent inner letters can sometimes be perceived as complete words (see picture). What method of recognition is this indicative of? a. Recognition by components b. Distinctive features c. Template matching d. Structural recognition

2 Science B44 Vision and Brain Fall 2005 Final Page 2 5. Which of the following is NOT true? a. We can see faster speeds with high-level motion than with low-level. b. A dynamic model of an action can increase the number of items we can track c. Finding a point-light walker among scrambled point-light walkers in a visual search task requires attention. d. The color and shape of objects in quartets can determine the direction of apparent motion. 6. Pick the FALSE statement: Random dot stereograms a. Were the first use of computers in perception research. b. Show that stereopsis doesn t depend on shape perception. c. Do not rely on disparity to produce depth. d. Could be used as a strong test of photographic memory. 7. Which of the following statements about the neural organization of color perception is correct? a. Cones can be divided into 3 opponent types. b. Trichromacy is present at all levels of the visual system. c. Trichomacy precedes opponency. d. Color opponency first occurs in the striate cortex. 8. Which of the following is NOT true? a. Based on correlation studies, the causality cannot be established b. Risks and goals of experiments need to be included in a consent form c. Subject expectancy affects principally the reliability of experiments d. Standard error is a measure of the reliability of the data 9. Which of the following visual memories has the most limited capacity? a. Iconic memory b. Long-term memory c. Short-term memory d. Photographic memory 10. Which of the following is not a visual memory a. Afterimage b. Persistence c. Iconic memory d. Echoic memory 11. Binocular disparity a. results from convergence and accommodation of the eyes b. occurs only if the images in the two eyes are identical c. occurs when an object falls on non-corresponding points in the two eyes d. only occurs for objects at fixation

3 Science B44 Vision and Brain Fall 2005 Final Page Which of the following is NOT true? a. Shadows tell us about the relative placement of objects b. Distant surfaces have less contrast because of atmospheric perspective c. Object knowledge can be overruled by other cues d. T-junctions can indicate how much one object is in front of the other BOOK 1 SHORT ANSWER QUESTIONS In your first book, write the answers to each of these questions. 1. What is a geon? Describe the four requirements for a shape to qualify as a geon. Geons are basic components to define objects. A Geon needs to be (1) recognizable in the 2D image from most viewpoints (view invariance), (2) sufficiently discriminable from others, (3) resistant to noise, and (4) sufficient to describe all the objects we can identify. 2. Below are two search displays. Describe the results of searching through these displays and the significance of these results to surface perception. Search for the backwards L is easy/parallel, whereas search for the differentlyoriented squares is hard/non-parallel. Since the searched-for shape is essentially the same in both cases, the difficulty in searching in the left-hand search array must mean that the perceived shape differs. In the left-hand search array, the black boxes act as occluders, causing the Ls to amodally complete and become the same square-shaped items. Since this affects the rate of search, we can conclude that amodal completion occurs preattentively. [ ½ credit for correct description of results, ½ for inference that amodal completion occurs pre-attentively].

4 Science B44 Vision and Brain Fall 2005 Final Page 4 3. Tihs qeutsoin semes mseesd up but sltil rabaedle. Berilfy disercbe the prlnipice of vuisal riecgontion taht it domnesrattes. It demonstrates that the whole object is not necessary to recognize it. A few cues are enough if there is redundancy. We can make good guesses based on context, continuity, stored object knowledge or distinctive features. 4. In the Ames room, we look through a small peephole into an apparently ordinary room. However when a person in that room walks from one corner to the other, something very unexpected happens. What does the Ames Room tell us about pictorial cues? The Ames room, viewed from above, is actually an irregular polygon. The back wall slants away from the viewer so that one of the back corners is actually much farther than the other. However, the shape of the two windows in the back wall is corrected for the slanting such that they look perfectly rectangular, and therefore the room looks perfectly rectangular, when viewed from straight ahead. A person walking from one corner of the other will appear smaller in the corner that (unbeknownst to the viewer) is further away. This suggests a hierarchy among pictorial cues, namely that linear perspective cues override information about known size. 5. Describe three main types of explicit visual memory and explain how information is transferred from one visual memory system to another. Three main types of visual memory are sensory memory (iconic), short-term memory and long-term memory. Sensory memory can hold the entire visual scene in details, but only lasts 100 to 250 ms. Only attended visual items enter short-term visual memory. The capacity of visual short term memory is limited to 4 items. Short term memory lasts a few seconds unless rehearsed. When rehearsed several times, items can enter from short term to long term memory. Long term memory has unlimited capacity, unlimited duration but can be lost. 6. Name 2 causes of low vision that are not correctable with lenses, and give a brief description of each. Macular degeneration- Degeneration of the macula characterized by spots of pigmentation and causing a reduction or loss of central vision. Glaucoma- A disease of the eye marked by increased pressure within the eyeball that can result in damage to the optic disk and gradual loss of vision Cataracts- Opacity of the lens or capsule of the eye, causing impairment of vision or blindness.

5 Science B44 Vision and Brain Fall 2005 Final Page 5 BOOK 2 MULTIPLE CHOICE QUESTIONS 1. There are few relative to in the fovea. a. Cones; Rods. b. Rods; Cones. c. Ganglion cells; Bipolar cells. d. Bipolar cells; Ganglion cells. 2. Why do folded pictures distort as we tilt them? a. Because our visual system compensates for the tilt of each surface. b. Because our internal representation of space is 3D. c. Because our internal representation of space is not really 3D. d. Because our visual system does not compensate for the tilt of pictures. 3. What are metamers? a. The colors that are seen after adapting to their opposites (e.g., red and green are metamers because red is seen after adapting to green and vice-versa). b. Two wavelength distributions that appear as the same color due to our trichromatic color perception. c. Colors whose names are different even though they only differ in brightness. d. Colors that are adjacent on the color wheel. 4. Which of the following is NOT true? a. Short-term memory can last up to a few seconds. b. Sensory memory can store about 4 items at a time. c. Long-term memory has capacity of about 1 million pictures. d. Short-term memory can store fewer than 4 very complex items. 5. Why do line drawings work (succeed at conveying depth and spatial layout)? a. Because we have learned the meaning of drawings from repeated exposures. b. Because neurons that respond to edges also respond to lines. c. Because objects in the real world often have lines at their borders. d. Because there are no shadows in line drawings. 6. The McGurk effect (demonstrated in lecture with a video of a man repeating a single syllable) is evidence that a. Our perception of events has a built-in delay that can be corrected in the case of predictable motion. b. Our visual perception can influence our auditory perception. c. We can voluntarily switch among multiple models for the same event. d. High level motion signals can override low level motion detectors.

6 Science B44 Vision and Brain Fall 2005 Final Page 6 7. Which of the following is a TRUE statement about our shadow perception? a. Shadow analysis is preattentive. b. Shadows are not always darker than the unshadowed areas of the surface they are seen on. c. Shadows make T junctions with surface contours. d. A shadow s source must be seen in order to be perceived as a shadow. e. A shadow should have its own texture. f. When shadows cross other shadows, they make T juctions. 8. Which of the following is true for a structural description of objects a. Relationship between parts matters b. Overall shape matters c. Shape of parts matters d. Angle of view of the object matters 9. Which of the following is NOT true? a. Motion is directly measured not inferred b. Directionally selective cells are best driven by color input c. Reverse motion shows the two motion systems d. MT & MST are specialized for motion 10. Which of the following is NOT true of social perception? a. We can evaluate whether an image has positive or negative valence before we can identify the event in the scene. b. The meaning of distinct, conscious gestures differs across cultures. c. The interpretation of facial expressions is quite similar across cultures. d. It is just as easy to extract the emotion from an inverted face as it is from an upright face. 11 Only one of the following search displays would be easy for normal subjects, but hard for those with visual agnosia. Which one is it? a. b. c. d. 12. Which of following is true about spatial resolution of attention? a. Spatial resolution of attention is coarser than visual resolution b. We cannot shrink the region of selection. c. As long as we can see them, we can individuate closely presented bars. d. Visual resolution is coarser than spatial resolution.

7 Science B44 Vision and Brain Fall 2005 Final Page 7 BOOK 2 SHORT ANSWER QUESTIONS In your second book, write the answers to each of these questions. 1. Describe two pieces of evidence that myopia may be caused in part by experience. How can myopia as a result of experience be avoided? Evidence 1. Inuit school kids were nearsighted though their illiterate parents were far sighted. 2. Same effect in Hong Kong vs. Rural Chinese 3. Experiments in chickens show that image focus on retina drives eye ball growth Read in bright light 2. What is the illusion seen below? Describe the illusion (what is illusory in this image). Explain why this illusion exists in terms of human contrast detection mechanisms. This is the Cornsweet-Craik illusion. The centers of all 6 squares are the same shade of grey, but 3 look darker than the other 3. The illusion is caused by the the sharp transition at each edge that is flanked by gradual transitions to the mid-gray values. This profile of luminance is very close to the response that center-surround cells would give to squares that actually were uniform light and uniform dark because these cells do not respond in the uniform areas. They only respond at the edges. In order to see the squares of uniform brightness as they really are, the visual system must fill in based on the activity profile near the edges. This filling in, triggered as well by the profile shape in the

8 Science B44 Vision and Brain Fall 2005 Final Page 8 illusion,leads to a percept that each square has uniform luminance, either light or dark depending on the direction of the transition at each edge.[1/3 for naming, 1/3 for describing illusion correctly, 1/3 for coherent explanation]. 3. What is a hypercolumn? Draw and label Hubel and Wiesel s model. A hypercolumn is the smallest region of V1 cortex that contains cells with preferences covering the full range of orientations, sizes and eyes. Show a drawing. 4. Our retina is crossed by thousands of blood vessels. Why do we not see them under normal circumstances? Under what circumstances do we see them? We do not see the blood vessels because they, and the shadows they cast on the receptors, are always in the same location. The receptors can therefore adapt to the pattern of shadows, increasing their sensitivity to compensate for the lower level of light behind the vessels. The shadows are therefore cancelled out and not seen. In order to see the vessels, light has to reach the retina at an oblique angle (flashlight off to the side or shining on the white of the eye) so that the vessels shadows are shifted to new locations where there is no adaptation. Without their compensation, the shadows are now visible. 5. Describe an experiment which shows location-based attention effects. Either just the Helmholtz example of instructing subjects to pay attention on the left and they can then report more of the items on the left in a briefly flashed array, or a cued experiment. An arrow point to the left or right and subject attend to that side. Performance is then better on the cued side than on the uncured side (tested on a few invalid cue trials). 6. On its wing, the fulgorida (peanut bug) has patterns that appear to be eyes. On each eye is a white spot that seems to be a reflection. What does this insect mimicry tell us about bird (the bug s predators) brains? The insect must have evolved these patterns in order to fool predators. The white spot is an artificial specular highlight. Unlike real specular highlights, it does not change with the position of the observer (or bird). However, since the highlight evolved it must enhance the illusion of an eye relative to a simple black dot. So, we can conclude that bird visual systems do not notice the discrepancy between real highlights and fake highlights.

9 Science B44 Vision and Brain Fall 2005 Final Page 9 BOOK 3 MULTIPLE CHOICE QUESTIONS 1. An array of squares viewed after adaptation to an array of triangles usually doesn t look any different than it normally does. Which of the following inferences is most likely? a. Triangles and squares are detected/coded/perceived in different areas of cortex. b. Polygon shape is determined on the basis of a distributed code in the same sense as facial characteristics, color, and orientation. c. Polygon shape is NOT determined on the basis of a distributed code. d. There are probably neurons that code shape as a dimension. That is, there are neurons that fire more when something is more like a triangle, or more like a square, etc. 2. Which is the proper sequence from earliest to latest in terms of the order of processing of information in the visual system? a. Temporal cortex; Bipolar Cells; LGN; Area MT. b. Rods, Ganglion Cells; LGN; V1; Area MT. c. Bipolar Cells, Cones; LGN; V1; Temporal cortex. d. LGN; Bipolar Cells; Temporal cortex; V1. 3. Which of the following is NOT one of the Gestalt laws of grouping? a. Closure b. Proximity c. Good continuation d. Valence e. Similarity f. Good form 4. Standard shape templates are able to match stored patterns against a. Patterns in different variants b. Patterns with different sizes c. Patterns with different orientations d. Patterns with different locations 5. What kind of patient would be likely to leave the food on one side of his dinner plate untouched? a. motion blind b. prosopagnosic c. agnosic d. neglect e. MIT student 6. Which of the following are the correct opponent color combinations found in the human retina? a. red/yellow, green/blue b. magenta/cyan, yellow/green

10 Science B44 Vision and Brain Fall 2005 Final Page 10 c. green/magenta, yellow/cyan d. red/green, blue/yellow 7. Which of the following is not a rule for perceived reflections by a human observer? a. Must be lighter than the surface they are seen on. b. Must follow the curves of the surface. c. Must be consistent with objects that are reflected. d. Objects and their reflections must be vertically aligned if the reflecting surface is horizontal. 8. Which of the following is not a pictorial cue to depth? a. Occlusion b. Shadows c. Disparity d. Texture gradients e. Known size 9. Select the anatomical structure that is not correctly paired with its function or one of its functions. a. Corpus callosum connecting the two hemispheres of the brain b. Temporal lobes analyzing auditory input c. Retina computing disparity d. V8 constructing the perceptual experience of color e. Thalamus conveying sensory information to the cortex 10. Which of the following is a cue that favors grouping a. T-junction b. X-junction c. Amodal completion d. Border ownership e. Proximity 11. Which is an error in the depiction of shadows which is not typically noticed? a. Shadows that are opaque. b. Shadows that have the wrong color (w/ respect to illumination) c. Shadows with volume. d. Shadows that are lighter than their surround. 12. A patient draws a clock with numbers confined to the right side. Most likely his brain damage is to: a. temporal cortex on the left side b. temporal cortex on the right side c. parietal cortex on the left side d. parietal cortex on the right side

11 Science B44 Vision and Brain Fall 2005 Final Page 11 BOOK 3 SHORT ANSWER QUESTIONS In your third book, write the answers to each of these questions. 1. What is the aperture problem in motion and what are the most effective cues to resolve it. The aperture problem arises because receptive fields measure only a small portion of a moving stimulus. If the receptive field picks up just a straight contour that is moving, it is not possible to know the actual direction of motion from just that one receptive field as many directions of motion (at different speeds) will produce the same displacement of the contour within the receptive field. The most effective cue to resolve the problem is any 2D feature like a corner or a line ending. The motions of these features are unambiguous and they are small enough to fit within a receptive field. 2. Explain the relationship between stereopsis and shape analysis. Describe one example to demonstrate their relationship. Stereopsis, which is the use of disparity between images from the two eyes to generate perceptions of depth, occurs earlier in processing than shape analysis. Bela Julesz s experiments using random-dot stereograms are an elegant demonstration. He used two images of randomly distributed dots. One of the images had a region of dots laterally displaced by a fixed amount from corresponding dots in the other image. No shape could be perceived in each image alone, but when fused, a perception of depth arose and a shape was perceived. Since depth was perceived despite no shape being present in the original images, we can conclude that depth perception does not rely on shape perception. And since a shape was perceived once depth was introduced, we can conclude that stereopsis can influence shape perception. 3. Draw a neuron and label 4 parts Needs dendrites, cell body, axon, and synapse 4. Pick any one of the lab exercises or your observation papers from this year. Identify the method you used (observation, correlation, experiment), justify your answer with some details of what you did. Describe how you followed (or not) the rules of informed consent. OK 5. Describe two pieces of evidence encountered in class about the existence of grandmother cells for coding face identity. One piece of evidence should support the grandmother cells existence, and the other should call it into question.

12 Science B44 Vision and Brain Fall 2005 Final Page 12 Face cells have been reported that are specific to particular people: the Clinton cell and the Halle Berry cell, for example. However, face adaptation suggests that the various features of faces are represented across populations of cells as this is an essential requirement for distorting a test face following adaptation to a different face. 6. Describe the locations of the modal contours in this image and make a rough sketch of just these regions of the image with the modal contours shown as dashed lines. The modal contours occur on the woman s skirt and the man s shirt, such that they both appear to be in front of the fence. [ ½ for woman s skirt, ½ for man s shirt full credit requires that shortest edge is drawn ] BOOK 4 MULTIPLE CHOICE QUESTIONS 1. What is NOT a theory of object recognition? a. Geons b. Size constancy c. Templates d. Distinctive Features 2. Patients with damage to the hippocampus a. Can acquire skills but not facts b. Have no short term memory c. Cannot form any new long term memories d. Cannot recognize faces 3. Which of the following is the most common? a. Female carriers of genes for red/green color blindness. b. Males with red/green color blindness. c. People, male or female, with rods but no cones. d. People, male or female, with cortical color blindness (result of injury to brain).

13 Science B44 Vision and Brain Fall 2005 Final Page Pianists were asked to play a short piece, which was recorded. For some players, the keyboard was silent, so they couldn t hear themselves. Later, all the recordings were played back to all the pianists, and they were asked to identify their own recording. The pianists were able to pick out their own recordings, but this ability was not affected by whether or not they could hear themselves play during the recording. What are the independent variable (IV) and dependent variable (DV) in this experiment? a. IV: recorded or not recorded, DV: ability to pick out their own performance b. IV: ability to pick out their own performance, DV: recorded or not recorded c. IV: ability to pick out their own performance, DV: silent keyboard or audible keyboard d. IV: silent keyboard or audible keyboard, DV: ability to pick out their own performance 5. Which of the following aspects of vision was relatively spared in formerly blind skier Mike May, who had a corneal transplant at age 53? a. Motion processing b. Illusory contours c. 3D Structure d. Face processing 6. Which of the following information does not vary within one of Hubel & Wiesel s hypercolumns? a. orientation b. retinal location c. eye of origin d. spatial frequency (size) 7. In class, we learned about epileptic patients who have had their corpus callosum severed surgically. Which of the following is NOT true about such people? a. They are sometimes better at certain visual tasks than people with an intact corpus callosum. b. A major conduit for communication between the two hemispheres of the brain has been destroyed in these patients. c. If you give them an object that they only see in their left visual field, they can usually name it. d. They showed reduced symptoms of epilepsy. 8. Which of the following cues to depth is not very useful for objects farther than 1-2 meters away from the viewer? a. Convergence b. Motion parallax c. Texture gradients d. Binocular disparity

14 Science B44 Vision and Brain Fall 2005 Final Page Which of the following is a principle about human vision that can be derived from examples of art presented in lecture? a. Humans have specialized face-processing mechanisms b. Shadows are not important to human vision c. Our internal representation of the world is not fully three dimensional d. Humans have separate what and where systems 10. Visual search experiments typically a. measure how many targets a subject can find b. ask subjects to look for a change between two displays c. measure the time it takes subjects to find a target d. measure how many targets a subject can track 11. The pac men of the Kanizsa subjective square (seen below) a. are seen at the same depth as the subjective figure. b. each amodally complete behind the square. c. own the borders between the pacmen and the square. d. are seen in front of the square. 12. Perceived size is a. Proportional to size on the retina times the perceived distance b. Visual angle times physical distance c. Given by Emmert s Law d. Size on retina divided by perceived distance

15 Science B44 Vision and Brain Fall 2005 Final Page 15 BOOK 4 SHORT ANSWER QUESTIONS In your fourth book, write the answers to each of these questions. 1. What s wrong with the depictions of shadows in this image? What does it tell us about the perception of shadows? The shadows in the back room are drawn in strange angles with respect to the other shadows in the scene (it is as if there is a second light source in the image). Some of the characters in the image do not actually have shadows. This shows us that shadows need not be consistent with actual light sources in order to be perceived as consistent. In other words, we do not construct a detailed model of the world that includes the locations of multiple light sources (or detects conflicts in light sources evident from shadows). [ ½ credit for identification of a major flaw in shadows, ½ credit for implication.]

16 Science B44 Vision and Brain Fall 2005 Final Page Describe the implications of the below picture for emotional face processing. Most people see the face on the left as sadder than the face on the right, but they are simply mirror images of one another. The face on the right appears happier than the one on the left. Given that these pictures are identical except for being mirror images, we can draw conclusions about which hemisphere of the brain is dominant in emotional face processing. Since the left half of the faces seems to determine their perceived emotion, and since the right half of the brain sees the left half of the face, the right hemisphere of the brain, and the right amygdala more specifically, must be more sensitive to emotions than the left hemisphere. 3. If your mother is color-blind and your father is normal, what are the chances that your sisters are born color-blind? Your brothers? Why? Answer: Color-blind mother and normal father can never have a color blind daughter. A woman has to have two defective red-green genes (on the X chromosome) to be color blind. The color blind mother has defective alleles on both Xs and so necessarily passes a defective copy to the daughter but the other (from the father) is always normal (father has only one X to give). On the other hand, all brothers are color-blind, since their X chromosomes come only from their mother and both of hers are defective. [ ¼ credit to # of sister color-blind, ¼ credit to brothers, ¼ credit to sister explanation, ¼ credit to brother]. 4. Describe an experiment that indicates that we extrapolate the position of a moving object to compensate for the innate delays in the visual system. Processing delays in the visual system create a lag of roughly 100 ms between arrival of light at the retina and our perception of it. For an object moving along a predictable path, we compensate for this delay extrapolating its location ahead along its motion path to the position it will have in an additional 100 ms. In the flash-lag experiment, a bar rotates around a central point. During the rotation, when the bar is horizontal, a second bar is briefly flashed so that it is perfectly aligned with the rotating bar. However, what we actually see is that the smoothly rotating bar is slightly ahead of the flashed bar. This is because the delay in perception of the rotating bar is compensated for, whereas the delay in perceiving the flashed bar is not.

17 Science B44 Vision and Brain Fall 2005 Final Page Describe two experimental techniques to evaluate unconscious visual processing. Adaptation to unseen patterns (unseen because of crowding or binocular rivalry). Priming by unseen presentations (unseen because of brief, masked presentation or diverted attention inattentional blindness). 6. What is a double dissociation? Give an example from material presented in class. Double dissociation indicates that two deficits are lost independently, showing two functions are processed separately and in parallel. For example, Pauelette (prosopagnosia) can recognize objects but cannot recognize familiar faces. However, CK can recognize familiar faces but can t identify objects BOOK 5 MULTIPLE CHOICE QUESTIONS 1. Emmert s law states that a. Two equally-sized lines will appear to differ in length if depth cues appear to place one farther in the background that another. b. Apparent size of an afterimage changes depending on the size of the surface it is seen on. c. Two objects of the same size appear to be different sizes if placed nearer or farther from the horizon. d. The apparent size of an afterimage is proportional to the perceived distance of the surface on which you see it. 2. Which of these is NOT a feature of neglect syndrome: a. Good prognosis for recovery b. Lost ability to attend to one half of visual space c. Results from damage to ventral pathway d. Impairment of imagery to one half of visual space 3. In class, we demonstrated a failure of lightness constancy where one white disc appeared black and the other white. The reason for the failure was a. There was a black hole in the field of illumination. b. The internal assumptions for light cannot manage a black hole in the middle. c. There is no memory for pattern of illumination. d. We did not know there was a black hole in the illumination.

18 Science B44 Vision and Brain Fall 2005 Final Page Which direction is the face moving? Which of the following areas would probably be LEAST involved in computing the answer to such a question? a. V8 b. FFA c. V1 d. MT/MST 5. Which of the following is NOT true? a. Capgras syndome is due to the lack of input to amygdala from face area in vision b. Reciprocal gestures are more frequent among friends c. Averageness is a good indicator to determine face attractiveness d. Unconscious gestures are often culture-specific 6. Which of the following images induces modal completion? a. b. c. d. 7. Which of the following is NOT true about the focus of expansion (FOE): a. The FOE specifies where you are heading. b. The FOE specifies what you will hit. c. The FOE tells you when you will hit an object d. There is an FOE for every object moving toward you on a collision path. 8. What can we NOT conclude from experiments on change blindness and inattentional blindness? a. Our internal representation of visual scenes is not that detailed. b. We often notice changes by relying on sudden changes in luminance. c. The types of change blindness evident from laboratory experiments using computer-edited photos cannot be demonstrated in the real world. d. Large background changes can be difficult to detect.. 9. Which of the following is NOT true? a. Restored sight depends on only age of loss but not the age of recovery b. Touch uses visual cortex in the blind c. Neglect is due to damage to V1 d. Neglect is typically temporary

19 Science B44 Vision and Brain Fall 2005 Final Page The room with walls that move independently of the floors was used to show that a. balance is maintained in part on the basis of optic flow. b. the balance of adults, but not children, is affected, showing that the association between balance and visible motion is learned. c. balance is dependent solely on non-visual stimulation. d. only movements of the wall toward observers affects balance. 11. In forming an image, tubes, pinholes, and lenses all solve a common problem. Which of the following best describes that problem? a. Light is scattered off surfaces in all directions from every point. b. Light loses strength as it reflects off objects. c. Light reflected off a surface contains many wavelengths. d. Light bends as it travels through substances, including the air, and this transformation must be corrected. 12. Extensive use of multi-target video games leads to all of the following EXCEPT a. Better, faster responses in memory tests b. Faster surgery with fewer errors c. Better resolution of attention (less crowding) d. Track more objects in multiple object tracking BOOK 5 SHORT ANSWER QUESTIONS In your fifth book, write the answers to each of these questions. 1. Does our visual system construct models of objects? Give at least two examples in support of your answer (drawings might be a good idea). Yes, we do construct object models. For example, we do not perceive a dog hidden behind a box as a disjointed collection of dog-tail and dog-snout; rather, we see a whole dog partially occluded by a box. In fact, these object models are sometimes dependent on cues to occlusion. For instance, a disjointed array of parts of letter B s will not be identifiable as a bunch of letters B unless the occluder is actually visible. 2. Describe the behavior of a patient (as seen on a video) that demonstrates that while visual agnosia limits conscious object recognition, objects are nevertheless processed to some extent in their brains. Patient can see details but cannot name objects or describe their function but makes appropriate gestures with his hands for a combination lock

20 Science B44 Vision and Brain Fall 2005 Final Page Describe the physiological mechanism of stereopsis. Where is this mechanism located in the brain? Binocular cells are present in V1. They collect and respond to information from both eyes. Binocular cells are responsive to stimuli of a particular orientation at different eccentricities in both eyes. A given binocular cell collects information from points at a given difference in eccentricity and prefers a particular edge orientation at those points. Some cells respond to stimuli that are present at uncrossed disparities, while others respond to stimuli that is present at crossed disparities (this last was not mentioned in lecture). From the distribution of responses across such cells, the depth of the stimulus can be determined. 4. How accurate is visual memory in the case of eyewitness testimony? Describe an experiment that suggested visual memory could be easily manipulated by wily questioning. Eyewitness testimony is not so accurate. Mistaken eyewitness is #1 cause of known false convictions. After subjects view the film of two-car accident, they were asked to estimate the speed of the cars at the time of the incident. Depending on which verb -- smashed, hit or contacted -- was used in the question, subjects estimated the speed differently. When subjects were questioned again a week later whether they saw broke glasses, subjects in the smashed condition gave more false positive responses than the other two groups. 5. Describe an experiment showing that infants pay attention to eye gaze. What were the independent and dependent variables? In the experiment, infants were shown a picture of a real human face. The person looked straight ahead, and then without moving her head, moved her eyes off to one side. Then the face disappeared, and two identical objects were displayed on either side of where the face used to be. Looking times to each object were measured. The experiment showed that infants looked first and longer at the object on the side of the screen to which the person had directed her eyes. The infants must have attended the person s eye gaze for this preference to occur. The independent variable was the direction in which the person looked, and the dependent variable was how much time each infant spent looking at the same side of the display as the eye gaze. 6. What does the Mach card (that reversed its motion when we reversed its depth and moved it or our heads) tell us about vision? The Mach card is a folded white index card which, when viewed with one eye, it can be seen with two different depth interpretations. When it s seen with the true-to-life interpretation, there is no difficulty. But when it s seen with reversed depth, and it is moved slightly, the visual system fights to keep the

21 Science B44 Vision and Brain Fall 2005 Final Page 21 depth interpretation consistent by changing our perception of its motion. In order to keep the depth interpretation the same, the card must move in the same direction as the viewer (and the opposite direction that it s actually moving in). The important lesson is that depth is not perceived directly, but inferred on the basis of multiple cues, and moreover that this inference can have dramatic consequences for other perceptual conclusions (motion in this case). Thus, depth perception is similar to many other instances in visual perception in which what we see is inferred rather than measured directly (e.g. action models).