Gil-da-Costa Ricardo, Hauser Marc D
Cognitive Evolution Laboratory, Department of Psychology, Harvard University, Cambridge, MA 02138, USA.
Proc Biol Sci. 2006 Sep 22;273(1599):2313-8. doi: 10.1098/rspb.2006.3580.
A robust finding in the human neurosciences is the observation of a left hemisphere specialization for processing spoken language. Previous studies suggest that this auditory specialization and brain asymmetry derive from a primate ancestor. Most of these studies focus on the genus Macaca and all demonstrate a left hemisphere bias. Due to the narrow taxonomic scope, however, we lack a sense of the distribution of this asymmetry among primates. Further, although the left hemisphere bias appears mediated by conspecific calls, other possibilities exist including familiarity, emotional relevance and more general acoustic properties of the signal. To broaden the taxonomic scope and test the specificity of the apparent hemisphere bias, we conducted an experiment on vervets (Cercopithecus aethiops)-a different genus of old world monkeys and implemented the relevant acoustic controls. Using the same head orienting procedure tested with macaques, results show a strong left ear/right hemisphere bias for conspecific vocalizations (both familiar and unfamiliar), but no asymmetry for other primate vocalizations or non-biological sounds. These results suggest that although auditory asymmetries for processing species-specific vocalizations are a common feature of the primate brain, the direction of this asymmetry may be relatively plastic. This finding raises significant questions for how ontogenetic and evolutionary forces have impacted on primate brain evolution.
人类神经科学领域一个确凿的发现是观察到左半球在处理口语方面具有特异性。以往的研究表明，这种听觉特异性和大脑不对称性源自灵长类祖先。这些研究大多聚焦于猕猴属，并且均显示出左半球偏向性。然而，由于分类学范围狭窄，我们并不清楚这种不对称性在灵长类动物中的分布情况。此外，尽管左半球偏向性似乎是由同种叫声介导的，但还存在其他可能性，包括熟悉度、情感相关性以及信号更一般的声学特性。为了拓宽分类学范围并检验明显的半球偏向性的特异性，我们对绿猴（猕猴属的另一个物种）进行了一项实验，并实施了相关的声学控制。采用与猕猴相同的头部定向程序进行测试，结果显示，对于同种叫声（熟悉的和不熟悉的），存在强烈的左耳/右半球偏向性，但对于其他灵长类动物的叫声或非生物声音则不存在不对称性。这些结果表明，尽管处理物种特异性叫声的听觉不对称性是灵长类大脑的一个共同特征，但这种不对称性的方向可能具有相对可塑性。这一发现对个体发育和进化力量如何影响灵长类大脑进化提出了重大问题。
