Cross-dominance, also known as mixed dominance or mixed laterality, describes a pattern where an individual does not consistently favor one side of the body for all skill-based tasks. This means a person might use the right hand for certain actions and the left hand for others, or have a dominant hand on one side and a dominant eye or foot on the opposite side. This arrangement varies from the typical pattern where one side of the body is uniformly dominant across all motor and sensory functions.
Measuring and Defining Rarity
Determining the exact prevalence of cross-dominance is challenging because the definition is not uniformly applied across studies. When defined strictly as mixed-handedness—the use of different hands for different manual tasks—estimates typically range from 1% to 10% of the population. If the definition is broadened to mixed laterality, which includes the combination of hand, foot, and eye dominance, the reported frequency rises significantly. Some researchers suggest that up to 30% or more of people exhibit some form of mixed dominance, though this variability highlights the difficulty in consistent measurement.
The Neurodevelopmental Basis of Cross-Dominance
The foundation of cross-dominance lies in the brain’s organization, specifically a process called cerebral lateralization. In most people, the left cerebral hemisphere is specialized for fine motor control, making the right side of the body the dominant side. In individuals with cross-dominance, this specialization is not absolute or is variable across different motor and sensory systems. This suggests that the strong functional specialization of one hemisphere is either incomplete or distributed, resulting in an inconsistent preference for one side of the body.
Inherited factors play a role, as the preference for a dominant side is influenced by multiple genes, making it a polygenic trait. However, genetics do not fully determine the outcome; environmental and developmental factors also contribute. Early developmental events, such as prenatal or perinatal conditions, are thought to affect how lateralization progresses, potentially leading to a less distinct or more variable pattern of dominance.
Practical Manifestations of Mixed Dominance
Cross-dominance manifests when an individual uses different preferred sides for distinct, unrelated actions. This means the side of the body favored for a task requiring fine motor skill may be opposite to the side favored for a task requiring gross motor power or sensory input. The most common manifestation is mixed-handedness, such as a person writing with the right hand but preferring the left hand for throwing a ball or dealing cards. The pattern extends beyond the hands to include other paired body parts, creating mixed laterality. For instance, an individual might use their right hand for writing but prefer their left foot for kicking a ball, or have a dominant right hand paired with a dominant left eye for sighting.
Cross-Dominance vs. Ambidexterity
Cross-dominance is frequently confused with ambidexterity, but the two represent distinct functional organization patterns. Ambidexterity is the ability to perform a single task, such as writing, with equal skill using either the left or the right hand, suggesting a symmetrical motor capacity. In contrast, cross-dominance is characterized by the preferential use of one side for one task and the opposite side for a different task, or a mix of hand, foot, and eye preferences. True ambidexterity is exceptionally rare, occurring in less than 1% of the population. Cross-dominance, defined more broadly as mixed laterality, is significantly more common because it reflects a distribution of specialized preferences rather than an equal skill level across all tasks.