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Current perspectives in primate laterality. Review of Primate Laterality Current Behavioral Evidence of Primate Asymmetries edited by Jeannette P. Ward and William D. Hopkins. New York Springer Verlag 1993 xii + 356 pp $49

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American Journal of Primatology 35327430 (1995)
Current Perspectives in Primate Laterality
Review of Primate Laterality: Current Behavioral Evidence of Primate Asymmetries, edited
by Jeannette P. Ward and William D. Hopkins. New York, Springer Verlag, 1993, xii + 356
pp, $49.00.
Traditionally, it has been assumed that cerebral functional asymmetry was
unique to humans. Although scientists found behavioral and neurological asymmetries in nonhuman primates, the prevailing view was that these cases were
isolated and not relevant to our own species. This perspective has changed in
recent years as new ideas and findings have emerged. The current acceptance that
nonhuman primate asymmetries have implications for human evolution, behavior,
and neurofunctioning has created a need for collation of theory and empirical data.
The current volume represents a significant effort t o fulfill this need.
The contributors to this volume represent an impressive array of internationally-known researchers. They are primarily psychologists, and many have published seminal papers on primate laterality in the scientific literature. Contributions report findings across a broad range of species, and review major historical
and theoretical perspectives. Data graphs comprise the majority of figures.
Harris (Chapter 1) begins the volume with an historical review of primate
handedness. A long-standing question in laterality research is whether biased
limb use in animals approximates that in humans. Harris discusses the views of
Plato, Aristotle, and several 17th through 19th century scholars, and then examines more recent treatments of this issue. The modern era of laterality research
began with Finch’s 1941 study published in Science. Publication frequency in this
area has steadily increased over the last 50 years, and has matched the growth in
interest in human cortical lateralization. Harris demonstrates that primate handedness has held interest across several generations, and that the early work has
facilitated advances which have been made in recent years.
Ward, Harris, and Milliken (Chapter 2) describe lateralized behavior in prosimians. Prosimians represent a primate group which is much less studied than
anthropoids. The authors distinguish between manual preference, viewed as bias
in lateral response, and manual performance, viewed as differences in efficiency.
Ward, Harris, and Milliken report several interesting findings, including a disproportionate percentage of left-preferent subjects, and a left-hand reaching advantage in galagos. One of the greatest difficulties in examining manual performance
is to induce subjects to use their nonpreferred hand. The authors describe innovative procedures which they have used to overcome this difficulty without resorting
to forced physical constraint.
Fragaszy and Adams-Curtis (Chapter 3) report findings on manual preference
and performance in crab-eating macaques. The purposes of these studies were to
develop a manipulative ethogram, evaluate hand preference during spontaneous
manipulations, and examine performance in unimanual and bimanual tasks. Fragaszy and Adams-Curtis found that performance measures in bimanual tasks and
choice measures in fine manipulation were most promising for revealing lateral
0 1995 Wiley-Liss, Inc.
328 I Westergaard
bias, and recommend a broad research agenda in the realm of lateral bias in
manual activity. This contribution is noteworthy because it emphasizes the importance of bimanual coordination in primate laterality assessment.
King and Landau (Chapter 4) describe hand preference for reaching in squirrel
monkeys. The authors present an enlightening review of methodological and statistical considerations for studies of nonhuman primate handedness. Their observations support two generalizations for squirrel monkey handedness. First, manual preferences are modifiable by the context of reaching, and second, there is little
support for the idea of a symmetrical reaching preference distribution. The authors
hypothesize that visually guided reaching for stationary incentives evokes a system with right hand predominance contingent on postural instability and urgency
for rapid responding, and that visually guided ballistic reaching for moving incentives evokes a system with left hand predominance contingent on similar postural
and response demands.
Preilowski (Chapter 5 ) discusses factors which have inhibited progress in primate laterality research. The author describes problems associated with Scala
Naturae thinking, and compromises which have led to inadequate assessment of
lateralized cerebral control. Preilowski presents a theory which provides for lateralized learning in subjects with intact neocortical commissures, and an active
role of the corpus collosum in preventing interhemispheric transfer. The author
then reports data on handedness and intermanual transfer in rhesus monkeys.
Preilowski concludes that the main difference in handedness between men and
monkeys is that monkeys lack awareness of behavioral asymmetries and expectancies concerning the use of a particular hand. It is therefore possible that monkeys could have handedness if they were able know or think that they were
handed, or if they could develop an efficient mechanism for generalizing hand-use
between different tasks.
Lehman (Chapter 6) reviews hand preference in prosimians, monkeys, and
apes. The author addresses symmetry as opposed to duplication of hand use, individual hand preference, population hand preference, and hand preference in relation to other lateralized functions. Lehman draws three main conclusions from this
review. First, voluntary hand use is usually asymmetric, with one hand playing a
leading role and the other a subordinate one. Second, hand preference is reproducible a t the individual level, but not at the population level. Third, there is little
similarity between cerebral organization responsible for hand preference in monkeys and hemispheric specialization in the human population. Lehman suggests
that there is a weak population trend toward left-handedness among prosimians,
but no population bias toward either hand among monkeys and apes.
Wantabe and Kawai (Chapter 7) provide data on hand preference for wheat
and sweet potato washing among Japanese macaques. The authors report a population-level trend toward use of the left hand for carrying wheat grains and sweet
potatoes, and for reaching to pick up wheat grains. Several subjects exhibit consistent hand preference across tasks. Age does not appear to influence the distribution of hand preference and there is no evidence of heritability of hand preference in these subjects. These data are unique and should be of great interest to
researchers who study processes associated with innovative behavior in primates.
Vauclair and Fagot (Chapter 8) compare manual specialization in gorillas and
baboons. They distinguish between handedness, defined as consistent hand-use in
familiar tasks, and manual specialization, defined as hand-use on novel and relatively complex tasks. The authors present data on gorillas and baboons performing
reaching and panel displacement tasks. Both species exhibit asymmetrical distributions of hand preference for simple reaching, and increased left-hand preference
Primate Laterality I 329
for displacement. This study reinforces the relevance of task demands to assessments of primate laterality. Vauclair and Fagot conclude that investigators should
focus their research efforts on complex manual specialization tasks rather than
simple tasks of primate handedness.
Morris, Hopkins, Bolser Gilmore, and Washburn (Chapter 9) review lateralization in chimpanzees. The authors provide evidence which indicates that nonhuman primates have anatomical asymmetries which are similar to those of humans. They argue that nonhuman primate handedness is not robust, but caution
that more research is needed before firm conclusions can be drawn. The authors
then examine laterality in language-trained apes. The chimpanzees Austin and
Sherman exhibit consistent findings across tasks which examine the same processes from different perspectives. Data from Lana indicate that similarities and
contrasts between subjects may be due to subject sex and experience. The authors
interpret ape laterality research in view of recent theoretical advances in the areas
of language, cognition, and development, and conclude that understanding the
neurological systems which underlie basic cognitive processes will depend upon
application of emerging models and techniques to a wide variety of species.
Fagot (Chapter 10) presents a study on the development of manual lateralization in Guinea baboons. The author argues that the ontogeny of asymmetrical
hand usage should be studied because it helps to explain lateral preferences in
adults, reveals insights into underlying brain maturation, and raises questions of
resemblance and dissimilarities across species. Fagot notes that few studies have
examined primate laterality from an ontogenetic perspective. The author videotaped the manipulations of four infant baboons and then used a detailed coding
system to score these acts. Three baboons expressed lateral tendencies before two
weeks of age. The fourth expressed lateral tendencies between the ages of two and
four weeks. Hand preference occurred mainly at the onset of behavioral patterns,
and these biases were mostly right-sided. Fagot argues that novelty is fundamental to primate manual laterality and that this factor should be considered in future
Hopkins and Bard (Chapter 11) review the development of lateralized behavior
in nonhuman primates with special reference to chimpanzees. The authors propose
that the most common explanations for hand preference variability are genetic,
maturational, and environmental. Hopkins and Bard argue that the environmental model is inadequate to account for recent findings. To support this claim they
cite age-related similarities and discrepancies which have been noted across several investigations. The authors then present their own data on laterality in nursery-reared chimpanzees. They note sex and age effects for the strength and direction of lateralized hand-to-mouth actions. The authors conclude that arousal is
related to infant chimpanzee laterality, and that the right hand may contrast with
the left hand because of cerebral hemisphere activation processes.
Shafer (Chapter 12) compares handedness in nursery school children and gorillas. Comparative data on behavioral laterality in humans and apes are rare and
this contribution is a welcome addition to the literature. Shafer notes a right-hand
preference for both gorillas and children (this bias was stronger among humans).
A sex difference was noted as males showed a greater percentage of right-handed
actions than did females. Shafer provides a strong argument for comparing laterality in humans and apes and reports a straight-forward and well-designed investigation.
Harris and Carlson (Chapter 13) compare human infant and adult hand preference for visually-guided reaching. Infants were tested between 24 and 52 weeks
of age. Adult subjects were college students. Infants underwent considerable
330 I Westergaard
changes in hand preference and a clear population-level lateral bias did not
emerge. Adults were consistent in their preferences. Object positioning influenced
hand preference in both subject groups. Object size was not related to hand preference in infants but did influence the extent of dominant hand-use in adults.
These results suggest that visually guided reaching tasks are appropriate for comparative primate laterality research and underscore the necessity for controlling
for object position and size.
Glick (Chapter 14) describes lateralized rotational behavior in children and
adults. Research with rats has linked turning behavior to unilateral lesions of the
nigrostriatal pathways. Extension of this model to humans has led to research
examining the relation between turning and brain function. The author notes that
the functional significance of lateralized rotation in humans is not yet known, but
in rats it appears to serve as a proprioceptive reference. Glick notes a sex difference
in the rotational behavior of adult humans such that females rotate more than
males. Parkinson’s patients exhibit spontaneous rotation toward the hemisphere
that presumably has less dopaminergic activity. The strength of their rotation was
greater than that of normal controls. Glick concludes that rotational behavior has
similar characteristics in humans and other animals and that continued research
in this area will contribute to our understanding of neural lateralization in normal
and pathological behavior.
MacNeilage (Chapter 15) concludes the volume by discussing implications of
primate functional asymmetries for the evolution of cerebral hemispheric specializations. The author argues that our anthropocentric tendencies have led us to
reject evidence of nonhuman primate asymmetries. MacNeilage’s postural origins
theory represents a significant step in overcoming this bias. This theory proposes
that population-level handedness evolved in primates as a result of selection pressures which favored asymmetrical use of the limbs for feeding and postural support. Questions remain concerning the role of human language in this process.
Research addressing aspects of behavioral laterality, including the relationship
between footedness and cerebral dominance, should help to resolve these issues.
This book represents a substantial contribution to the scientific literature. It is
the first volume of its kind and would be a valuable addition to the collection of
those interested in primate behavioral laterality. The models presented will stimulate research in this area for years to come. I commend Ward and Hopkins for
assembling this work.
The author was supported by an Intramural Research Training Award from
the National Institute of Child Health and Human Development. I thank Clara
Menuhin-Hauser for editorial assistance and insightful comments on this review.
Gregory Charles Westergaard
Laboratory of Comparative Ethology
National Institute of Child Health and Human Development
Poolesville, Maryland
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xii, current, asymmetric, 356, hopkins, laterality, new, 1993, york, springer, behavior, william, primate, evidence, jeannette, edited, verlag, perspectives, review, ward
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