Advances in the Modularity of Vision Selections From a Symposium on Frontiers of Visual Science (1990) / Chapter Skim
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Visual Coding of Features and Objects: Some Evidence from Behavioral Studies
Visual Coding of Features and Objects: Some Evidence from Behavioral Studies
Pages 39-61
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From page 39... ...
That makes sense, since what we need to react to are tigers, footballs, or motor cars, not color patches. If there are extensive preprocessing operations, we need to probe them through indirect behavioral evidence; we cannot expect people to 39
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From page 40... ...
But, maybe we could say a little more about what kinds of similarity are important in mediating grouping. Here we find a fairly sharp dichotomy: differences in simple aspects of shapes, like curved or straight lines and edges, will produce a good boundary between groups of elements; so will differences in colors and in brightness.
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From page 41... ...
For the earlier preattentive level of processing, however, grouping is based on different principles from those that mediate consciously judged similarity for single attended figures. Segregation and boundary formation offer one possible diagnostic for what happens early in visual processing.
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From page 43... ...
The idea is that there may be a number of relatively independent modules, each of which computes its own property, one specializing in color, one in orientation, one in stereoscopic depth, one in motion, and so on. These modules need not necessarily be anatomically separate, although some specialization into different anatomical channels has been described (Livingstone and Hubel, 1988; Van Essen, 1985~; but I am suggesting they may be functionally separate.
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From page 44... ...
The results suggest that checking several different properties takes longer than checking a single property. Although search remains spatially parallel, the latency to detect the target was greater when its nature was not specified in advance, as if subjects checked separately within each of the different modules until they found it.
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From page 45... ...
As Figure 6 illustrates, the search time for this type of conjunction target increases linearly as a function of the number of the distracters in the display. This pattern of performance suggests that each item was serially checked, adding about 60 milliseconds for each extra nontarget item that had to be rejected.
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From page 46... ...
·~FIGURE 5 (a) A locally unique item is hard to find when items elsewhere share its locally unique property.
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From page 47... ...
is about half the slope for the negative teals (target absent)
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From page 48... ...
For · · Conjunction 1B ~ 9 16 present __ rant FIGURE 7 Search times for each conjunction of color, size, motion, and orientation and for each feature on its own. M = motion; C = color; S = size; 0 = orientation.
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From page 49... ...
In further experiments, we obtained similar illusory recombinations with parts of shapes (lieisman and Paterson, 1984~. For example, when we showed displays like those in Figure 9 and asked subjects to look for a dollar sign, they frequently reported illusory dollar signs in displays in which none was present.
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From page 50... ...
The evidence suggests at least a functional separation between a set of color maps, a set of orientation maps, a set of directions of motion, and so on. When we are involved in a visual search task with a target defined by a single feature, we can simply check: Is there activity in the red map?
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From page 51... ...
. that attention selects particular stimuli through a kind of master map of locations to which the different feature maps in separate modules are all connected.
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From page 52... ...
When presented with brief displays of multiple objects, subjects should be able to check the map for "red" and to see whether there is activity there, without necessarily linking it to any particular location in the master map of locations. In the other experiment, we tested the prediction that the presence of a feature could be detected when its absence could not.
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From page 53... ...
In another condition (Figure lib) we replaced the "orange or H" feature targets by two conjunction targets.
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From page 54... ...
We can know, "Yes, there is orange there, but I do not know where." Obviously, if the display remains present for long, the subject will home in on the target very quickly; but our results suggest that it is possible to cut off processing at a time at which the subject knows what the target is but not where it is. THE ABSENCE OF A FEATURE If the story is correct, then there should also be other tasks besides search for conjunction targets, that require attention.
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From page 55... ...
ss o c J %~ c ~ J o c - ~ 1 ~ o o o c' % % c D o % %% % %% %% % % %~ % %% % \ \ \ O ~ ~ %' I ~ ~ I ~ ~ \]
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From page 56... ...
We can ask subjects to look for a tilted line amongst vertical lines or a vertical line amongst tilted lines. Again, we found a large asymmetry: this time it was the tilted line that was easy to find against a background of vertical lines, and gave hat functions relating latency of search to number of distracter lines.
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From page 57... ...
57 oo o o o ° oo o o o o° ~ oo o o \l _ 1,,, -.7 u ~a V)
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From page 58... ...
The coding language used by the visual system seems to be quite general across these different channels or media. PERCEPTION OF OBJECTS My speculations at present are that vision initially forms spatially parallel maps in functionally separate specialized modules.
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From page 59... ...
In some recent experiments with Daniel Kahneman and Brian Gibbs, we have found evidence that new stimulus information gets integrated with the previously perceived object that is best linked to it by spatio-temporal continuity. For example, a letter is named faster if the same letter was previously presented within the same outline shape, even when the shape has moved to a new location in the interval between the two letters (Figure 14~.
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From page 60... ...
. [a I, FIGURE 14 Example of displays used to demonstrate the integration of information in object-specific representations.
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From page 61... ...
Joumal of EN Psych~f~y:General 114:285-310. Van Essen, D.C 1985 Functional organization of primate visual cortex.
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