Abstract: One aspect of the invention provides a method of measuring brain state. The method includes: receiving a first plurality of electrical signals from a contact lens placed on a surface of a subject's eye, the first plurality of electrical signals associated with a first plurality of electrodes lying adjacent to an iris dilator muscle of the subject's eye. Another aspect of the invention provides a contact lens including: an optically transparent or translucent substrate; and one or more pairs of electromyography electrodes arranged on or within the optically transparent or translucent substrate. At least one of the one or more pairs electromyography electrodes are arranged to lie adjacent to an iris dilator muscle of a subject's eye when the contact lens is placed on the eye.