Sensation & Perception, 4e

Chapter 7 Summary

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1.   Attention is a vital aspect of perception because we cannot process all of the input from our senses. The term attention refers to a large set of selective mechanisms that enable us to focus on some stimuli others. Though this chapter talked almost exclusively about visual attention, attentional mechanisms exist in all sensory domains.
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2.   In vision, it is possible to direct attention to one location or one object. If something happens at an attended location, we will be to respond to it. It can be useful to refer to the “spotlight” of attention, though deployments of attention differ in important ways from movements of a spotlight.
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3.   In visual tasks, observers typically look for a target item among a number of distractor items. If the target is defined by a salient basic feature, such as its color or orientation, search is very efficient and the number of distractors has on the reaction time (the time required to find the target). If no basic feature information can guide the deployment of attention, then search is inefficient, as if each item needed to be examined one after the other. Search can be of intermediate efficiency if some feature information is available (e.g., if we’re looking for a red car, we don’t need to examine the blue objects in the parking lot).
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4.   Search for objects in real scenes is guided by the known features of the objects, by the salient features in the scenes, and by a variety of scene-based forms of guidance. For example, if you’re looking for your can of soda, you will guide your attention to physically plausible locations (horizontal surfaces) and logically sensible places (the desk or counter, probably not the floor).

5.   Attention varies over time as well as space. In the attentional blink paradigm, observers search for two items in a rapid stream of stimuli that appear at fixation. Attention to the first target makes it to find the second if the second appears within 200–500 ms of the first. When two identical items appear in the stream of stimuli, a different phenomenon makes it hard to detect the second instance.
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6.   The effects of attention manifest themselves in several different ways in the brain. In some cases, attention is marked by a general in neural activity or by a greater correlation between activity in different brain areas. In other cases, attention to a particular attribute tunes cells more sharply for that attribute. And in still other cases, attention to a stimulus or location causes receptive fields to so as to exclude unattended stimuli. All of these effects might be the result of a single, underlying physiological mechanism of attention.
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7.   Damage to the parietal lobe of the brain produces deficits in visual attention. Damage to the parietal lobe can lead to neglect, a disorder in which it is hard to direct attention into the contralesional (in this case, the left) visual field. Neglect patients may ignore half of an object or half of their own body.
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8.   Scene perception involves both selective and nonselective processing. Tasks like visual search make extensive use of processing. processing allows observers to appreciate the mean and variance of features across many objects (or proto-objects). Thus, you know the average orientation of trees in the woods (vertical) before knowing whether any particular tree is oriented perfectly vertically. Using spatial-frequency information, even without segmenting the scene into regions and objects, the nonselective pathway can provide information about the nature of a scene (e.g., whether it’s natural or man-made).
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9.   Picture memory experiments show that people can remember thousands of images after only or two of exposure to each. In contrast, change experiments show that people can miss large changes in scenes if those changes do not markedly alter the meaning of the scene.
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10.   Our perceptual experience of scenes consists of processing of the layout and ensemble statistics of the scene, combined with processing of a very few objects at each moment. However, the final experience is an inference based on all of the preceding processing, not merely the sum of that processing. Usually this inference is adequate because we can rapidly check the world to determine whether the chair, the book, and the desk are still there. In the lab, however, we can use phenomena like inattentional blindness and change blindness to reveal the limits of our perception, and it is becoming increasingly clear that those limits can have real-world consequences.
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