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Chapter 10

PSYB57 - Cognition ch.10

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Pare, Dwayne

PSYB57 – Chapter 10: Visual Knowledge Visual Imagery  Everyday use of visual images = a basis for making decisions, as an aid to remembering Introspections About Images  Galton asked participants to describe their images and to rate them for vividness; he asked them to introspect or look within and to report on their own mental contents  The self-report data he obtained fit well with common sense: participants reported that they could inspect their images much as they would inspect a picture. Their descriptions made it clear that they were viewing their images from a certain position and a certain distance; they also reported that they could read off the image details of color and texture  Galton’s participants differed from each other in their self-reports; many described images of photographic clarity, rich in detail while others reported very sketchy images or none at all  Perhaps all of the participants had the same imagery skill but some were cautious in how they chose to describe their imagery while others were more extravagant; some chose to keep their descriptions brief while other took pleasure in providing elaborate and flowery descriptions  In this way, Galton’s data might reveal differences in how people talk about their imagery rather than differences in imagery per se Chronometric Studies of Imagery  Imagery researchers have been sensitive to these concerns about self-reports and this is why imagery experiments usually don’t ask participants to describe their images  To gain more objective fata, these experiments ask people to do something with their images, to make a judgment based on the image and then examine how fast people are in the judgments and use the measurements as a basis for testing hypotheses about imagery  The data are generally chronometric (time measuring) and give much more accurate portrait of imagery than could ever be obtained with self-report  Chronometric studies allow us to ask what sorts of info are prominent in a mental image and what sorts aren’t  The pattern of what info is included as well as what info is prominent depends on the mode of presentation o For a description, the features that are prominent will be those that are distinctive and strongly associated with the object being described o For a depiction, distinctiveness and association won’t matter, instead, size and position will determine what’s prominent and what’s not  In a study by Kosslyn, participants were asked to form a series of mental images and to answer yes/no questions about each o Ex. They were asked to form a mental image of a cat and asked if the cat has a head/claws. The participants responded faster to the head question than the claws question o The difference suggests that info quickly available in the image follows the rules for pictures, not paragraphs o Another group of participants were just asked to think about cats with no mention of imagery; these people showed the reverse pattern (gave quicker response to claws than to head) o People have the option of thinking about cats via imagery and also the option of thinking about cats without imagery; as a mode of representation changes, so does the pattern of indo availability  In an image scanning procedure, participants had to scan from one point on their mental image to another point; they pressed a button to indicate when their mind’s eye had arrived at its destination. Response times were closely related to the distance participants had to scan across on the image, implying that mental images are similar to actual pictures in how they represent position and distance o Doubling the scanning distance doubles the time required for the scan  Similar results are seen if participants are given a task that requires them to zoom in on their images or zoom out. o In these studies, response times are directly proportional to the amount of zoom required, suggesting once again that travel in the imaged world resembles travel in the actual world, at least with regard to timing  Ex. Participants in one study were asked to imagine a mouse standing next to an elephant and then asked to confirm by inspecting their image that the mouse had whiskers o Participants were relatively slow in responding because they first needed time to zoom in on the image in order to see the whiskers o Response times were faster if they were asked to imagine the mouse next to a paper clip (no zooming is required)  There’s a clear relationship between “travel time” (scanning done in the mind) and travel distance o The same relationship would be observed if participants are asked to move their eyes across an actual map or literally to zoom in on a real picture  All this points to the similarity between mental images and actual out-in-the-world pictures  According to these results, images represent a scene in a fashion that preserves all of the distance relationships within that scene o Points closer to each other in the scene are somehow close to each other in the image and vice versa o In a very real sense, the image preserves the spatial layout of the represented scene  In this fashion, images directly represent a geometry of the scene and depict the scene rather than describing it, and are much more similar to pictures/maps than they are to descriptions Mental Rotations  In experiments done by Shepard, participants were asked to decide whether displays showed 2 different shapes or just one shape viewed from 2 different perspectives  To perform this mental rotation task, participants seem first to imagine of the forms rotating into alignment with other. Once the forms are oriented in the same way, participants can make their judgment  The amount of time it takes depends on how much rotation is needed  The farther you have to image a form rotating, the longer the evaluation takes  People have no trouble with mental rotation in depth. They make very few errors and the data resembles those obtained with picture-plane rotation  Participants can represent 3D forms in their images, and they can imagine these forms moving in depth  In some circumstances, visual images are not mental pictures; they are more like mental sculptures Avoiding Concerns About Demand Character  In both mental rotation and metal scanning, the farther the imagined travel the longer it takes  Participants in these studies obviously know that movement through the world takes time and that moving a longer distance takes more time. Perhaps, therefore, the participants simply control the timing of their responses in order to re-create this normal pattern  Participants in these studies are not imagining rotations or scanning across an image at all. Instead, they might be thinking “the experimenter just asked me to scan a long way, and I’d like to make it look like I’m obeying  One reason is that participants in experiments usually want to be helpful, so they do all they can to give the experimenter good data. As a result, they are very sensitive to the demand character of the experiment  A different possibility is that this sort of simulation is what imagery is really all about, perhaps whenever someone tries to imagine something, he draws on his knowledge about how an event in the world would actually unfold, and then he does his best to simulate this event o in this case, longer scan or a greater rotation requires more time, not because there really is some travel involved, but because people know that these manipulations should take more time and do their best to simulate the process  the scanning and rotation data are as they are, but indeed because of how images represent spatial layout  in several studies, the experimenters have asked participants to make judgments about spatial layout but have taken care never to mention to participants that imagery was relevant to the task o this should diminish the demand character  even without imagery instructions, the participants in these procedures spontaneously form images and scan across them and their responses show the standard pattern: longer response times observed with longer scans  this result really does emerge whenever participants are using visual imagery – whether the result is encouraged by the experimenters’ instructions or not Interactions Between Imagery and Perception  What is the relation between imaging and perceiving? (Segal & Fusella) o Participants were asked to detect very faint signals either dim visual stimuli or soft tones o On each trial, the task was merely to indicate whether a signal had been presented or not o Participants did this is one of 2 conditions: either while forming a visual image before their mind’s eye or while forming an auditory image before their mind’s ear o 2X2 design: 2 types of signals to be detected, and 2 types of imagery  Hypothesis: there is some overlap between imaging and perceiving o There are some mental processes that are used by both activities therefore if these processes are occupied with imaging, they’re not available for perceiving and vice versa o We should expect competition if participants try to do both activities at once  Segal & Fusella results indicate that forming a visual image interferes with seeing and that forming an auditory image interferes with hearing o Participants were less successful in detecting a weak visual signal if they were simultaneously maintaining a visual image than if they were maintaining an auditory image o The reverse is true with weak auditory signals: participants were less successful in this detection if maintaining an auditory image than if visualizing o Visual images often led to dales alarms for participants trying to detect visual signals; auditory images led to false alarms for auditory signals  What happens if participants are contemplating a mental image related to the stimulus they’re trying to perceive? o Farah (1985) had participants visualize a form (either H or T) o A moment later, either an H or a T was presented but at a very low contrast, making the letter difficult to perceive o Perception was facilitated if participants had just been visualizing the target form, and the effect was quite specific: visualizing an H made it easier to perceive an H; visualizing a T made it easier to perceive T o This confirms the claim that visualizing and perceiving draw on similar mechanisms, so that one of these activities can serve to prime the other  Specific brain structures required for vision and many of the same structures are required for imagery  Neuroimaging techniques confirm that vision relies heavily on tissue located in the occipital cortex  Activity levels are also high in these areas when participants are visualizing a stimulus before their mind’s eye  Different areas of the occipital cortex are involved in different aspects of visual perception o Areas V1 and V2 in the cortex are active when whenever participants are maintaining highly detailed images, and that the amount of brain tissue showing activation increases as participants imagine larger and larger objects o Area MT/MST in the brain is highly sensitive to motion in ordinary visual perception, and it turns out that same brain area is particularly activated when participants are asked to imagine movement patterns o Brain areas that are especially active during the perception of faces are also highly activated when people are imagining faces  Using TMS, it’s possible to disrupt Area V1 temporarily in an otherwise normal brain; Area V1 is the brain area where axons from the visual system first reach the occipital cortex  Using TMS in this way causes problems in vision, but it also causes parallel problems in visual imagery, providing a powerful argument that Area V1 is crucial for both processing of visual info and for the creation and maintenance of visual images  Patients who, because of brain damage, have lost the ability to perceive fine detail seem also to lose the ability to visualize fine detail  Brain damage also causes parallels in how people pay attention to visual inputs and to visual images Sensory Effects in Imagery  Because of these shared neural mechanisms, we might expect imagery and perception to function in similar ways and research indicates that they do  The research indicates a functional equivalence between many aspects of visual imagery and aspects of visual perception  In vision, acuity is much greater at the center of the visual field that in the visual periphery  In measurements of two-point acuity, observers are shown 2 dots. If the dots are very close together, the observer had trouble seeing the gap between then and so the dots seem to fuse together  We can assess acuity by measuring how far apart the dots have to be before the observer can see that they are separate; this tells us how well the observer can perceive fine detail  Two-point acuity is greatest when people are looking directly at the dots  If we position the dots 10 degrees away from someone’s line of vision, acuity is far worse  In one study, participants were first shown 2 dots of appropriate size. The dots were then removed but the participants were asked to imagine as if they are still present o The participants moved their eyes away from the imagined dots’ position, and as they looked farther and farther away, thy had to judge whether they could still see that the dots were separate o In this way, two-point acuity was measured with imaginary stimuli  In both cases, acuity fell off abruptly if the dots were not in the center of vision; the pattern of falloff was virtually the same in perception and in imagery  Acuity falls off more rapidly if participants look above or below the 2 dots, rather than to the left or right o This pattern was also observed in the imagery condition.  Qualitatively and quantitatively, the imagery data match the perceptual data Spatial Images and Visual Images  Studies have examined imagery in blind people o The stimuli to be imaged are presented initially as sculptures to be explored with the hands rather than as pictures to be examined visually o In tests involving mental rotation or image scanning, blind individuals yield data quite similar to those obtained with sighted research participants, with response times being proportionate to the distance traveled, and so on o They have some other means of thinking about spatial layout and spatial relations. This spatial imagery might be represented in the mind terms of a series of imagined movements so that it is body imagery or motion imagery rather than visual imagery o Perhaps, spatial imagery is not tied to any sensory modality but is instead part of our broader cognition about spatial arrangements and layout  visual imagery represents an arrangement or a shape in terms of how things look  spatial imagery might represent arrangements or shapes in terms of movements, or body feelings, or perhaps some more abstract format  blind individuals presumably use spatial imagery to carry out tasks and sighted people can use either visual or spatial imagery to carry out tasks  fMRI data tells us that the brain areas activated for visual tasks are different from those activated by spatial tasks  brain damage seems to produce similar patterns of disruption in seeing and imaging o patients who have lost their color vision also seem to lose the ability to imagine scenes in color o patients who have lost their ability to perceive motion also lose the ability to imagine movement  There are exceptions to this however… o A patient whose bilateral occipital lobe lesions have produced blindness but despite this deficit, the patient does well on many imagery tasks o Other patients show the pattern of neglect syndrome in their vision but not in their imagery  Visual imagery relies on brain areas also needed for vision and spatial imagery relies on different brain areas and so damage to visual areas won’t interfere with this form of imagery and damage to brain sites needed for this imagery wont interfere with vision  A patient known has L.H. suffered brain damage and now has enormous difficulty in tasks requiring judgments about visual appearance o L.H. performs well on tasks like image scanning or mental rotation o He shows little disruption on tasks requiring spatial manipulations or memory for spatial positions Indivi
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