151
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Corballis MC, Bradshaw J, Rogers L. The Evolution of Lateral Asymmetries, Language, Tool Use, and Intellect. AMERICAN JOURNAL OF PSYCHOLOGY 1994. [DOI: 10.2307/1423294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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152
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Abstract
Subjects were timed as they judged whether a small bar perpendicular to one side of a clockhand would point left or right if the hand was pointing upward (i.e., at the 12:00 position). The clockhand was shown in two successive orientations 30 degrees apart, so that it was perceived to jump from one to the other, but the bar was included at only one of the two orientations. Analysis of reaction times as a function of angular orientation showed that the subjects "mentally rotated" the clockhand to the upright position before making their decisions. When the bar appeared on the second presentation, the jump had no significant influence on mental rotation but when it appeared on the first presentation, the estimated orientation from which the clockhand was mentally rotated was "dragged" in the direction of the jump.
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153
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Corballis MC. Taking different sides. Nature 1993. [DOI: 10.1038/363682b0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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154
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Corballis MC, Sidey S. Effects of concurrent memory load on visual-field differences in mental rotation. Neuropsychologia 1993; 31:183-97. [PMID: 8455787 DOI: 10.1016/0028-3932(93)90046-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Normal right-handers mentally rotated letters flashed in the left or right visual fields under different conditions of working-memory load. In Experiment 1, the subjects held patterns of eight dots or sequences of eight letters in working memory, and these conditions produced a progressively increasing right visual field (RVF) advantage in rate of mental rotation relative to a control condition in which there was no load. Experiment 2 confirmed the shift toward increasing RVF advantage with a load of eight digits relative to two control conditions, one in which there was no load and another in which the subjects recalled digits before carrying out the mental rotation on each trial. These results are discussed in terms of the priming of the hemispheres by the concurrent loading of working memory.
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155
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Abstract
Normal right-handed subjects performed a task requiring mental rotation of the letter R, presented in varying angular orientations in the left or right visual fields. They were told to attend to the side indicated prior to each trial by a centrally located arrow, while maintaining visual fixation on the arrow. On 75% of trials (compatible trials) the arrow pointed to the side of the letter, while on 25% (incompatible trials) it pointed to the other side. Although overall RT was shorter on compatible than on incompatible trials, there was no evidence that spatial attention affected mental-rotation rate. However, estimated rate was higher when attention was to the left side of space, consistent with right hemispheric specialization for mental rotation. This effect was especially marked when presentation of the letter was to the right.
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156
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Corballis MC, Trudel CI. Role of the forebrain commissures in interhemispheric integration. Neuropsychology 1993. [DOI: 10.1037/0894-4105.7.3.306] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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157
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Abstract
A commissurotomized subject, L.B., was shown asterisks flashed at random locations, up to four in each field, and attempted either to compare the numbers in the two fields or to report the total number. The main results were: (a) Report was more accurate with unilateral than with bilateral presentation, suggesting that the difficulty integrating across fields was partly attentional; (b) in integrating across fields, attention was focused on one field, with only crude 'one-or-many' information from the other; (c) in cross-field comparisons, the focus was on the LVF, but in reporting the number it was on the RVF when report was oral or right-handed, and on the LVF when report was left-handed; (d) cross-field comparisons were improved when the locations were mirrored across the midline.
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158
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Abstract
One of the properties that most conspicuously distinguishes human language from any other form of animal communication is generativity. Language with this property therefore presumably evolved with the Homo line somewhere between H. habilis and H. sapiens sapiens. Some have suggested that it emerged relatively suddenly and completely with H. sapiens sapiens, and this view is consistent with (a) linguistic estimates as to when vocal language emerged, (b) the relatively late "explosion" of manufacture and cultural artifacts such as body ornamentation and cave drawings, and (c) evidence on changes in the vocal apparatus. However, evidence on brain size and developmental patterns of growth suggests an earlier origin and a more continuous evolution. I propose that these scenarios can be reconciled if it is supposed that generative language evolved, perhaps from H. habilis on, as a system of manual gestures, but switched to a predominantly vocal system with H. sapiens sapiens. The subsequent "cultural explosion" can then be attributed to the freeing of the hands from primary involvement in language, so that they could be exploited, along with generativity, for manufacture, art, and other activities.
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159
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Corballis MC. Out on a limb. Nature 1992. [DOI: 10.1038/356637b0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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160
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Corballis MC. Left Brain, Right Brain:
The Decline and Fall of Hemispheric Specialization
. Robert Efron. Eribaum, Hillsdale, NJ, 1990. xvi, 117 pp., illus. $19.95. Science 1991. [DOI: 10.1126/science.251.4993.575-b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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161
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Corballis MC. Left Brain, Right Brain:
The Decline and Fall of Hemispheric Specialization
. Robert Efron. Eribaum, Hillsdale, NJ, 1990. xvi, 117 pp., illus. $19.95. Science 1991. [DOI: 10.1126/science.251.4993.575.b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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162
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163
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Abstract
Eleven subjects were timed as they judged whether a small bar perpendicular to one side of a clockhand would point left or right if the hand was pointing upward (i.e., at the "12 o'clock" position). The clockhand was shown in two successive orientations 30 degrees apart, so that it was perceived to jump from one to the other in either a clockwise or a counterclockwise direction. Reaction times were consistent with the interpretation that the subjects "mentally rotated" the clockhand from its perceived orientation back to the upright before making their decisions. The direction of the jump influenced perceived orientation but did not influence either the direction or rate of mental rotation itself.
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164
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Sergent J, Corballis MC. Categorization of disoriented faces in the cerebral hemispheres of normal and commissurotomized subjects. J Exp Psychol Hum Percept Perform 1989. [PMID: 2531205 DOI: 10.1037//0096-1523.15.4.701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We examined the capacity of the cerebral hemispheres to process faces that deviate from canonical perspective. In Experiment 1, normal Ss performed a gender categorization of faces presented at varying angular orientations in the left visual field (LVF) or right visual field (RVF). Orientation affected processing speed, more so in the RVF than in the LVF. The function relating reaction times to disorientation of the faces was approximately monotonic and reflected the increased difficulty in extracting relevant configurational information as the faces were rotated from canonical perspective. In Experiment 2, 3 commissurotomized Ss performed the same task. They responded above chance in the 2 visual fields, and the pattern of their results was similar to that obtained with the normal Ss, but the effect of disorientation was considerably more pronounced. It is suggested that the right hemisphere contribution becomes more critical the further the visual pattern departs from conventional view. Issues regarding the specification of processes correcting for disorientation and comparison of normal and commissurotomized Ss are discussed.
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165
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Abstract
The question of whether there is a fundamental discontinuity between humans and other primates is discussed in relation to the predominantly human pattern of right-handedness and the left-cerebral representation of language. Both phenomena may go back at least to Homo habilis, 2-3 million years ago. However, a distinctively human mode of cognitive representation may not have emerged until later, beginning with H. erectus and the Acheulean tool culture about 1.5 million years ago and culminating with H. sapiens sapiens and rapid, flexible speech in the last 200,000 years. It is suggested that this mode is characterized by generativity, with multipart representations formed from elementary canonical parts (e.g., phonemes in speech, geons in visual perception). Generativity may be uniquely human and associated with the left-cerebral hemisphere. An alternative, analogue mode of representation, shared with other species, is associated with the right hemisphere in humans.
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166
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Abstract
A sample of 133 normal subjects, and one commissurotomized subject, were given a "mental-rotation" task, in which they were timed as they decided whether rotated letters, flashed in the left or right visual hemifield, were normal or backward. The normal subjects showed a significant right-hemifield advantage in reaction time, while the commissurotomized subject showed a pronounced left-hemifield advantage in both accuracy and reaction time. We argue that mental-rotation is primarily a right-hemispheric specialization, but that this was offset in the normal subjects by a stronger left-hemispheric specialization for letter identification.
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167
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Abstract
The commissurotomized subject L.B. showed a strong right-hemispheric advantage on a task requiring him to judge rotated letters normal or backward, but a left-hemispheric advantage in a task requiring discrimination of the same letters, implying that the right-hemispheric advantage has to do with mental rotation. However, his right hemisphere proved unable to perform a task requiring mental rotation of a simple unfamiliar pattern to a designated "upright", and was inferior to the left on a task requiring two such patterns, at varying orientations relative to one another, to be judged same or different. We suggest that the deficiency of the right hemisphere on these tasks was unrelated to mental rotation per se, but reflected a failure to comprehend the tasks properly.
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168
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Sergent J, Corballis MC. Categorization of disoriented faces in the cerebral hemispheres of normal and commissurotomized subjects. ACTA ACUST UNITED AC 1989; 15:701-10. [PMID: 2531205 DOI: 10.1037/0096-1523.15.4.701] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We examined the capacity of the cerebral hemispheres to process faces that deviate from canonical perspective. In Experiment 1, normal Ss performed a gender categorization of faces presented at varying angular orientations in the left visual field (LVF) or right visual field (RVF). Orientation affected processing speed, more so in the RVF than in the LVF. The function relating reaction times to disorientation of the faces was approximately monotonic and reflected the increased difficulty in extracting relevant configurational information as the faces were rotated from canonical perspective. In Experiment 2, 3 commissurotomized Ss performed the same task. They responded above chance in the 2 visual fields, and the pattern of their results was similar to that obtained with the normal Ss, but the effect of disorientation was considerably more pronounced. It is suggested that the right hemisphere contribution becomes more critical the further the visual pattern departs from conventional view. Issues regarding the specification of processes correcting for disorientation and comparison of normal and commissurotomized Ss are discussed.
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169
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Corballis MC, Murray JE, Connolly G. Memory scanning: Are fixed and varied sets scanned concurrently or successively? J Exp Psychol Learn Mem Cogn 1989. [DOI: 10.1037/0278-7393.15.6.1175] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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170
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Corballis MC. Distinguishing clockwise from counterclockwise: does it require mental rotation? Mem Cognit 1988; 16:567-78. [PMID: 3193888 DOI: 10.3758/bf03197058] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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171
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Corballis MC, Ogden JA. Dichotic listening in commissurotomized and hemispherectomized subjects. Neuropsychologia 1988; 26:565-73. [PMID: 3405401 DOI: 10.1016/0028-3932(88)90113-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Three commissurotomized and two left-hemispherectomized subjects were tested on spoken report of sequences of three dichotic pairs of digits. With instruction to report only one digit from each pair, there was an overall advantage to the ear contralateral to the hemisphere mediating speech, but report of ipsilateral-ear digits ranged from 40 to 100%. In commissurotomized subjects, the more extreme ipsilateral suppression under instructions to report all digits may be due to failure to gain access to unattended information stored in the right hemisphere, rather than to suppression of the ipsilateral pathway. However one commissurotmized patient did appear to have access to right-hemisphere items, the result either of subcortical transfer or of external cross-cueing. The hemispherectomized subjects seemed able to store both attended and unattended information in the same hemisphere.
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172
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Abstract
A commissurotomized patient, L.B., was tested on several imagery tasks, in which the stimuli were flashed tachistoscopically in the left or right visual half-field. On tests requiring the generation of images of lowercase letters from their uppercase versions, or the generation of the positions of the hands on a clockface from digitally presented times, there was a strong right half-field (left-hemispheric) advantage in accuracy, but a left half-field (right-hemispheric) advantage in reaction time (RT). On tests requiring the mental rotation of letters or stickfigures to the upright, however, there was a strong left half-field (right-hemispheric) advantage in accuracy, RT, and conformity of RTs to an ideal "mental-rotation" function when plotted against angular orientation. These data provide strong evidence that the right hemisphere was capable of mental rotation comparable to that of normal subjects; the left hemisphere, by contrast, seemed virtually incapable of mental rotation in the early testing sessions, and never achieved the proficiency of the right.
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173
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174
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Beale IL, Matthew PJ, Oliver S, Corballis MC. Performance of disabled and normal readers on the Continuous Performance Test. JOURNAL OF ABNORMAL CHILD PSYCHOLOGY 1987; 15:229-38. [PMID: 3611521 DOI: 10.1007/bf00916351] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Twelve-year-old reading-disabled children of normal intelligence were compared on the Continuous Performance Test with two control groups of normal intelligence and reading ability either of the same age or of the same reading age as the reading-disabled group. Signal-detection analysis showed that the reading-disabled were more conservative than chronological-age controls in their willingness to identify the target letter sequence. Although this conservative performance was shared by the reading-age controls, the reading-disabled suffered an additional handicap of relatively frequent anticipatory errors. Groups also differed on a sensitivity measure, suggesting a deficit in working memory in the reading-disabled children.
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175
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Abstract
In two experiments, right-handed men and women were tested for ear differences in report of dichotically presented digits, with their heads straight ahead, turned 90 degrees to the left, and turned 90 degrees to the right. In Experiment 1, head turn was controlled simply by asking the subjects to fixate an appropriately located point; a right-ear advantage occurred under all conditions of head turn among the men, but only in the head-straight condition among the women. In Experiment 2, head turn was controlled by having the subjects direct a flashlight attached to their heads toward the fixation point. This eliminated the right-ear advantage under all head conditions for the men, but for the women the right-ear advantage was, if anything, more pronounced when their heads were turned than when straight. These results suggest that auditory asymmetry depends in part on whether space is perceived as divided into left and right sides, and in part of the balance between spatial and verbal requirements. Both factors, and the asymmetry itself, may interact with sex.
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176
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177
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Abstract
By their very nature, studies of visual hemifield differences in normals are biased toward the discovery of hemispheric asymmetries that occur early in visual processing, and may consequently give a narrow and distorted view of human laterality as a cultural and evolutionary phenomenon. One saving factor, however, is that hemifield differences may in some cases actually represent differences between the two sides of phenomenal space, and thus represent cerebral asymmetries at a relatively late stage in processing. It may therefore be important to develop techniques for distinguishing retinal effects from higher order spatial ones.
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178
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179
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Corballis MC. Brain Asymmetries:
Cerebral Lateralization in Nonhuman Species
. Stanley D. Glick, Ed. Academic Press, Orlando, FL, I985. xiv, 287 pp., illus. $49.50. Behavioral Biology. Science 1986. [DOI: 10.1126/science.231.4741.1022.b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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181
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182
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Dawe S, Corballis MC. The influence of gender, handedness and head-turn on auditory asymmetries. Neuropsychologia 1986; 24:857-62. [PMID: 3808293 DOI: 10.1016/0028-3932(86)90085-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Subjects performed dichotic tasks with their heads turned 90 degrees to the left, 90 degrees to the right, and straight ahead. In Experiment 1 the stimuli were digits and the subjects varied in both sex and handedness. Right-handedness males showed a significant right-ear advantage under the head-right and head-straight conditions, while left-handed males and both right- and left-handed females failed to show any consistent ear asymmetries. In Experiment 2 the stimuli were melodies and the subjects were all right-handed. Head-turn had no significant influence on the results, and only the males showed a significant left-ear advantage. Overall, the results confirm previous findings that sex and handedness may influence auditory asymmetries, but fail to reveal systematic effects of head turn.
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183
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Corballis MC, Macadie L, Crotty A, Beale IL. The naming of disoriented letters by normal and reading-disabled children. J Child Psychol Psychiatry 1985; 26:929-38. [PMID: 4066817 DOI: 10.1111/j.1469-7610.1985.tb00607.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Normal and reading-disabled children, 11-13 years old, named the letters F, G and R, presented in normal and backward versions, in varying angular orientations, in left and right visual fields. Both groups were faster at naming the normal than the backward letters, even though mental rotation was evidently not required. The results also offered no support for Orton's theory concerning the interrelations between mirror-image equivalence, hemispheric differences and reading disability. The only measures unrelated to reading itself that discriminated the groups were digit span and a special difficulty among the disabled readers in naming the letter G.
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184
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Corballis MC, Macadie L, Beale IL. Mental rotation and visual laterality in normal and reading disabled children. Cortex 1985; 21:225-36. [PMID: 4028739 DOI: 10.1016/s0010-9452(85)80028-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Normal and reading disabled children, aged from 11 to 13 years and matched for I.Q., were timed as they discriminated bs from ds. When the letters were presented only in their normal upright orientations, normal readers responded more quickly when they were presented in the right than in the left visual hemifield, while the disabled readers showed a slight but insignificant left hemifield advantage. When the letters were presented in varying angular orientations the reaction times indicated that both groups "mentally rotated" an internal representation of each letter to the upright in order to discriminate them. The two groups did not differ in the accuracy of discrimination or in the estimated rate of mental rotation, and there were no significant hemifield differences in this phase of the experiment. These data offer no support for the view that disabled readers are deficient in spatial ability, but confirm earlier evidence that they may suffer a lack of left-hemispheric specialization.
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185
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Corballis MC, McLaren R. Winding one's ps and qs: mental rotation and mirror-image discrimination. J Exp Psychol Hum Percept Perform 1984; 10:318-27. [PMID: 6232348 DOI: 10.1037/0096-1523.10.2.318] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Subjects were timed as they made judgments about ps and qs (also interpretable as ds and bs) in different angular orientations. Whether these judgments were left-right mirror-image discriminations (b vs. d or p vs. q) or up-down mirror-image discriminations (b vs. p or d vs. q), the subjects' reaction times increased sharply with the angular departure of each letter from its designated normal upright orientation, a fact implying mental rotation. This was so whether the subjects responded with the letter labels themselves (e.g., b vs. d) or with the labels left versus right or top versus bottom. It was again the case when the letters were replaced by nonletter forms, in which event there was also a left visual-field advantage in reaction time. This study is therefore the first to demonstrate a mental-rotation strategy when the canonical forms to be discriminated are up-down mirror images as well as when they are left-right mirror images. In both cases, however, the task requires the ability to tell left from right, and we suggest that this is the critical ingredient that induces mental rotation.
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186
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187
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188
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189
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190
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Corballis MC, Katz J, Schwartz M. Retrieval from memory sets that exceed the memory span. ACTA ACUST UNITED AC 1980. [DOI: 10.1037/h0081017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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191
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192
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Corballis MC, Nagourney BA, Shetzer LI, Stefanatos G. Mental rotation under head tilt: factors influencing the location of the subjective reference frame. PERCEPTION & PSYCHOPHYSICS 1978; 24:263-73. [PMID: 704287 DOI: 10.3758/bf03206098] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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193
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Corballis MC, Anuza T, Blake L. Tachistoscopic perception under head tilt. PERCEPTION & PSYCHOPHYSICS 1978; 24:274-84. [PMID: 704288 DOI: 10.3758/bf03206099] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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194
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Corballis MC, Zbrodoff NJ, Shetzer LI, Butler PB. Decisions about identity and orientation of rotated letters and digits. Mem Cognit 1978; 6:98-107. [PMID: 661562 DOI: 10.3758/bf03197434] [Citation(s) in RCA: 114] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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195
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Corballis MC, Nagourney BA. Latency to categorize disoriented alphanumeric characters as letters or digits. ACTA ACUST UNITED AC 1978. [DOI: 10.1037/h0081685] [Citation(s) in RCA: 43] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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196
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197
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198
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199
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200
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Corballis MC, Roldan CE. Detection of symmetry as a function of angular orientation. J Exp Psychol Hum Percept Perform 1975. [PMID: 1202144 DOI: 10.1037//0096-1523.1.3.221] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Subjects decided as quickly as possible whether dot patterns were or were not symmetrical about a line. Their decision times were shorter when the line was verticle and increased as the angle between the line and the verticle increased. This orientation function was essentially the same whether or not the subjects knew in advance what the orientation of the line would be. When the subjects tilted their heads, the function shifted in the direction of the head tilt, indicating that it was tied more closely to retinal than to gravitational coordinates. These data can be interpreted to mean that people mentally rotate patterns to a vertical orientation before judging their symmetry. This in turn suggests that the "template" for detecting symmetry may itself be embedded symmetrically in the brain.
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