utricle

n. A fluid-filled sac in the vestibule of the inner ear which is part of the sense of bodily position. It contains mechanoreceptors called hair cells which respond to acceleration and deceleration and which are used to detect both bodily motion and body position. The nerves serving the mechanoreceptors do not adapt over time, so that if a person is standing up, the person does not lose over time the ability to know he/she is standing up, as a person will cease hearing a continuing sound over time.

A relatively brief amount of time, without explicit instruction, and from impoverished input that vastly under-represents what they eventually know about their language. Proponents of UG have proposed that children are able to learn such a complex system because most of it is available to them a priori, from birth.