一侧性(laterality)，亦称半球不对称性（hemispheric asymmetry）。
人类脑部一侧半球或在该半球控制下的身体的一侧发展出特化功能（如语言理解功能）的特性。最明显的例子是偏手性（总是用某只手从事活动的倾向），由於左或右脑半球各别控制人体的右或左侧，因此右利人主要以左半球来控制各种的活动功能，也包括看（用右眼）和语言理解能力。布罗卡首次提出大脑的言语中枢位於现称为布罗卡氏区的地方。後来的研究者发现涉及逻辑和序列分析功能的区域通常位於左半球内，同时在右半球控制处理空间－视觉和音乐的功能。更多的左利人比右利人显示出相反的半球特化功能，或是在两半球间更平均的功能分布。对於一侧性是经由基因遗传、妊娠期中形成或是学习而来，至今仍未普遍达成共识。
English version：
laterality
Characteristic of the human brain in which certain functions (such as language comprehension) are localized on one side in preference to the other. One example is handedness (the tendency to use one hand or the other to perform activities): Since the left and right cerebral hemispheres control the right and left sides of the body, respectively, right-handed people are left-dominant in terms of hemispheric control of various motor functions and ordinarily also with respect to seeing (right-eyed) and language comprehension as well. Paul Broca first identified the brain center for articulate speech in what is now called Broca's area. Later researchers discovered that functions involving logical or sequential analysis generally reside in the left hemisphere, while the right hemisphere seems to control processing of spatio-visual information and musical relations. More left-handers than right-handers display a reversal of hemispheric specialization or a more even distribution of functions between the two hemispheres. There is no general agreement about whether laterality is genetically transmitted, developed during gestation, or learned.