Article Abstract:
Experimental evidence exists that when people are presented with a series of letters, they process the information differently, depending on whether the letters are actual words, pseudowords (sequences of letters that obey English spelling rules, such as 'polt'), or nonwords (such as 'NLPFZ'). Thus, activation of different areas of the cortex (the outer layer of brain cells) is known to occur, depending on the semantic content of the visual stimuli. To study this issue in more detail, experiments were carried out using PET (positron emission tomography), an approach that allows cortical activation to be measured. Subjects (eight volunteers) were presented with four sets of stimuli: common nouns that are real words; pseudowords formed according to the rules of English; consonant strings; and strings of shapes that looked like letters, but were not. Seven PET scans were performed for each subject during the presentation of stimuli. Results showed that, while one region (the lateral extrastriate cortex) was activated for all four stimulus sets, the presentation of real words or pseudowords activated another processing area (left medial extrastriate area). This could be the result of the fact that pseudowords 'look like' real words, and, hence, are seen as a legitimate word, or because both stimuli are pronounceable, whereas consonant strings and shapes are not. A rationale for preferring the first explanation is presented. The fact that a region in the visual cortex responds similarly to real words and to pseudowords suggests that information specific to the English language is presented early in the visual processing process. Additional experiments showed that left frontal cortex is activated for real-word presentation, but not for pseudowords. This implies that the left frontal cortex has a role in processing semantic information. Overall, the data show that stimuli requiring semantic versus visual processing are, in fact, apparently processed in different brain regions. (Consumer Summary produced by Reliance Medical Information, Inc.)
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Article Abstract:
We are all bombarded by sensory information (sight, sound, touch, smell and taste) all of the time, and it is impossible for our brains to assimilate all that data at once. People usually respond to only a small portion of sensory information received. In this study of how people look for key visual information, researchers used positron emission tomography (PET) to measure changes in certain regions of the brain in response to visual stimuli. (PET is a sophisticated imaging technique that allows study of biochemical activity in the body.) Attributes such as the shape, color, or velocity of objects influences the behavioral and physiological measures of how visual processing occurs. Different parts of the brain seem to be involved in responses to shape, color, and velocity. Focusing attention on one attribute rather than among several increases the chance for seeing subtle changes, and changes the way different parts of the brain responsible for seeing (the visual cortex) processes information. (Consumer Summary produced by Reliance Medical Information, Inc.)
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Article Abstract:
Research indicates that visual imagery activates the primary visual cortex and that visual perception and visual imagery share a common neural substrate. Recent advances in the understanding of how the brain generates, stores and maintains visual imagery are discussed.
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