Second Language Acquisition and Second ... - Stephen Krashen
Second Language Acquisition and Second ... - Stephen Krashen
Second Language Acquisition and Second ... - Stephen Krashen
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(e.g. the pair "2" (right ear) <strong>and</strong> "9" (left ear) would be presented, followed one halfsecond<br />
later by "6" (right ear) <strong>and</strong> "4" (left ear), followed by "1" (right ear) <strong>and</strong> "3"<br />
(left ear). The subject is asked to recall as many digits as possible out of the six<br />
presented.) In most other studies, one single pair of syllables (e.g. "ba" <strong>and</strong> "ga") or<br />
words were used, a lower short-term memory load. This raises the possibility that<br />
there might be two different developmental courses for two different kinds of<br />
language processing, one complete lateralized to the left hemisphere by puberty <strong>and</strong><br />
the other much earlier in life.<br />
2. Motor skills. Early completion of the development of cerebral dominance is also<br />
indicated by studies examining the development of unimanual motor skills. Caplan<br />
<strong>and</strong> Kinsbourne (1976), in a paper appropriately titled "Baby drops the rattle",<br />
provide an interesting example. The experimenters gave rattles to twenty-one<br />
infants (average age 21 months, 21 days) <strong>and</strong> found that the babies tended to hold<br />
the rattles longer when they were placed in their right h<strong>and</strong>s (average duration of<br />
grasp = 62 seconds for the right h<strong>and</strong> <strong>and</strong> 41 seconds for the left h<strong>and</strong>), suggesting<br />
early lateral specialization of the central nervous system. Witelson (1977) has<br />
reviewed many studies of this sort using children age 7 <strong>and</strong> younger <strong>and</strong> concludes<br />
that "right-h<strong>and</strong> or right-sided superiority was observed in the large majority of the<br />
34 studies" (p. 236). This supports the hypothesis that there is an early propensity<br />
for unimanual performance in motor tasks, which is consistent with the hypothesis<br />
that cerebral dominance is established early in life.<br />
3. Brain damage. Studies examining the effects of unilateral brain damage on<br />
language in children also imply that lateralization is complete earlier than puberty.<br />
In later childhood (age 5 <strong>and</strong> older), just as in adults, aphasia is primarily the result<br />
of left hemisphere lesions. It appears to be the case, however, that before age 5<br />
aphasia may result from right hemisphere lesions somewhat more frequently (about<br />
30 per cent of the time, as compared with 3 per cent in adults <strong>and</strong> older children).<br />
Still, even for very young children, aphasia is associated more often with left lesions<br />
than with right lesions (for reviews, see Witelson, 1977; <strong>Krashen</strong>, 1973a; Hecean,<br />
1976).<br />
4. Hemispherectomy. The removal of an entire hemisphere, hemispherectomy, is<br />
perhaps the ultimate test of laterality. If the left<br />
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