Search PubMed⌕ Search

Biomedical subjects

M C Corballis

Publications and source records attributed to M C Corballis.

At least 19 recordsLinked to original sources
PubMed1992

On the evolution of language and generativity.

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.

Brain↗
PubMed1992

Judgements about numerosity by a commissurotomized subject.

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.

Adult↗
PubMed1990

The effect of apparent movement on mental rotation.

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.

Adult↗
PubMed1989

Mental rotation in a commissurotomized subject.

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.

Adult↗
PubMed1989

Hemispheric specialization for mental rotation.

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.

Adolescent↗
PubMed1989

Categorization of disoriented faces in the cerebral hemispheres of normal and commissurotomized subjects.

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.

Adult↗
PubMed1989

Laterality and human evolution.

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.

Animals↗
PubMed1988

Imagery in a commissurotomized patient.

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.

Adult↗
PubMed1988

Dichotic listening in commissurotomized and hemispherectomized subjects.

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.

Adult↗
PubMed1987

Performance of disabled and normal readers on the Continuous Performance Test.

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.

Attention↗
PubMed1987

The effect of head turn on auditory asymmetry.

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.

Adolescent↗
PubMed1986

The influence of gender, handedness and head-turn on auditory asymmetries.

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.

Adolescent↗
PubMed1986

Fresh fields and postures new: a discussion paper.

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.

Corpus Callosum↗