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PSYC*2650 Ch 11.doc

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PSYC 2650
Anneke Olthof

Chapter 11: Visual Language Visual Imagery - when remembering the image of something you call a “picture” of it to your mind - visual images are used as a basis for making decisions and as an aid to remembering Introspections About Images - Galton asked his research participants to introspect (look within) and report on their own mental contest - the self-report data he obtained fit well with common sense: that participants reported that they could “inspect” their images much as they would inspect a picture - they could “read off” from the image details of colour and texture - all of this implies a mode of representation that is picture-like - participants also differed widely from each other - many described images of photo- graphic clarity, rich in detail as if they were seeing the image, other participants reported very sketchy images or none at all - perhaps we shouldn’t take these self-reports at face value, perhaps they all had the same imagery skill but some were cautious how they chose to describe it, may be a dif- ference in how they talk about it rather than the imagery itself Chronometric Studies of Imagery - chronometric (time-measuring) studies give us a more accurate portrait of mental im- agery than self-report data - examine how accurate and how fast people are in their responses for reading informa- tion off of their imagers or manipulating them - allow us to ask what sorts of information are prominent in a mental image and what sorts are not - the pattern of what information is included as well as what is prominent depends on the mode of presentations - for a description of a cat, the features that are prominent will be those that are distinc- tive and strongly associated with the object being described - for a depiction, distinctiveness and association won’t matter, size and position deter- mine what is prominent - in a study, participants were asked to form a series of mental images and to answer yes/no questions about each - e.g. asked to form a mental image of a cat and asked if they cat has a head, claws - participants responded to these questions quickly, the responses to the head ques- tions were quicker than the claws question - this suggests that information quickly available in the image follows the rules for pic- tures, not paragraphs - a different group was asked to think about cats with no mental imagery and the re- verse pattern showed - in a different experiment, participants were asked to memorize a fictional map and the locations of landmarks - they were asked to form a mental image and when a landmark was mentioned they were asked to imagine a black speck moving in a straight line from one landmark to the next, when it reached the target participants pressed a button, stopping a clock - the data from this Image-Scanning Procedure suggests that participants scan across their images at a constant rate, so that doubling the scanning “distance” doubles the time required for the scan - similar results are obtained if participants are given a task that requires them to “zoom in” or “zoom out” on their images - response times are directly proportional to the amount of zoom required - travel in the imaged world resembles travel in the actual world - in another study, participants were asked to imagine a mouse beside an elephant and asked if the mouse had whiskers, their response time was slow because they had to zoom in to see it, response times were faster if the mouse was beside a paper clip - these mental imagery data are telling us a great deal about the nature of mental im- ages - according to these results, images represent a scene in a fashion that preserves all of the distance relationships within that scene - the image preserves the spatial layout of the represented scene - images directly represent the geometry of the scene, and it is in that way images de- pict the scene rather than describing it Mental Rotation - participants were asked to decide whether images should 2 different shapes or just one shape viewed from two different perspective - to perform this mental rotation task, participants seem first to imagine one of the forms rotating into alignment with the other - then once the forms are oriented the same way, participants can make their judgment - this takes some time, the amount of time depends on how much rotation is needed - imagined movement resembles actual movement: the farther one has to imagine 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 resemble those obtained with picture-plane rotation - there is a clear relation between angle of rotation and response times, and the speed of rotation seems similar for both - visual images are not mental pictures, they are more like mental sculptures Avoiding Concerns About Demand Character - perhaps participants simply control the timing of their responses in order to recreate this normal pattern - participants may do this because they want to be helpful and give the researcher good data - they are sensitive to the demand character of the experiment (cues that signal how they are supposed to behave - we can set aside these concerns and maintain the claims we’ve already sketched that the scanning and rotation data are as they are because of how images represent spatial layout - in studies attempting to reduce demand character, experimenters never ask the partici- pants to use mental imagery - participants spontaneously form images and scan across them, and their responses show the standard pattern Interactions Between Imagery and Perception - in a study, participants were asked to detect very faint signals (dim visual stimuli or soft tones) - on each trial, participants task was to indicate whether a signal had been present or not - participants did this either while forming a visual image or an auditory image - forming a visual image interferes with seeing and forming an auditory image interferes with hearing - another study had participants visual a form (H or T) and a moment later either an H or a T was presented, although at a very low contrast and difficult to perceive - perception was facilitated if participants had just been visualizing the target form - confirms the claim that visualizing and perceiving draw on similar mechanisms, so that one of these activities can serve to prime the other - neuroimaging techniques reveal that visual perception relies heavily on tissue located in the occipital lobe - activity levels are also high in these areas when participants are visualizing a stimulus - different areas of the occipital cortex are involved in different aspects of visual percep- tion - here there are parallels between brain activity during perception and brain activity during imagery - areas V1 and V2 in the visual cortex are involved in the earliest stages of visual per- ception, responding to the specific low-level features of the input - the same areas are particularly active whenever participants are maintaining highly de- tailed images - the amount of brain tissue showing activation increases as participants imagine larger objects - areas MT/MST in the brain is highly sensitive to motion in ordinary visual perception and the same brain area is activated when participants are asked to imagine movement patterns - studies of brain damage also shows parallels between visual perception and visual im- agery - lose the ability to perceive colour and imagine colour - in one case, a patient had suffered a stroke, and developed neglect syndrome, if he were shown a picture he only saw the right side of it, if he was asked to imagine some- thing, he only described the right side of the image - more evidence comes from transcranial magnetic simulation (TMS) which creates strong magnetic pulses at a specific location, this causes a temporary disruption in the brain region - using TMS causes problems in vision and parallel problems in visual imagery Sensory Effects in Imagery - the neural machinery needed for imagery overlaps with that needed for perception - if the machinery is occupied with one of these functions, it is not available for the other - if the machinery is disrupted, both activities are compromised - there is an intimate relationship between imagery and perception - this sharing of neural mechanisms functions in similar ways - research indicates a functional equivalence - consider visual acuity (the ability to see fine detail), acuity is much greater at the center of the visual field than in the periphery - in measurements of “two-point acuity” observers are shown 2 dots, if they are far apart enough the observer can see that they are separate but if they are close they cannot - we can assess acuity by measuring how far apart the dots have to be before the ob- server can see that they are separate - two-point acuity is greatest when people are looking directly at the dots - if we position the dots 10 degree away from someone’s line of vision, acuity is worse - the data show a remarkable correspondence between participants’ performance with a actually perceived dots and their performance with imagined dots - in both cases, acuity fell off abruptly if the dots were not in the center of vision Spatial Images and Visual Images - a number of studies have examined imagery in people blind since birth - stimuli to be imaged are presented initially as sculptures to be explored with hands - blind individuals yield data quite similar to those obtained with sighted research partici- pants - response times are proportionate to distance traveled - people blind since birth must be using something different than what things look like - they are probably thinking about spatial layout and relations - we need to distinguish between visual and spatial imagery - visual imagery represents spatial layout in terms of how things look - spatial imagery can represent spatial layout in terms of movements or body feelings - this is also suggested by other evidence - when looking at brain damage, there are cases in which brain damage causes prob- lems in imagery but not perception or vice versa - in one case a patient’s lesions produced blindness but did well on many imagery tasks - other patients show neglect syndrome in vision but not imagery - visual imagery relies on brian areas needed for vision so damage to these areas dis- rupts both imagery and vision - spatial imagery relies on different brain areas, so damage to visual areas won’t inter- fere with this form of imagery Individual Differences - when do people use one type of imagery and when do they use the other? - some tasks require one form of imagery or the other - choices between visual and spatial imagery will also depend on your preferences and the exact instructions you receive - the choic
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