1. A method for authenticating a user, comprising the steps of: receiving a claim from an individual claiming to be an enrolled user; retrieving a stored electroencephalographic response profile associated with the enrolled user, the electroencephalographic response profile being generated as a result of a supervised enrollment process based on a shared secret, wherein the shared secret comprises a sequence of visual elements which follows an explicit rule known by the enrolled user during the supervised enrollment process, wherein the explicit rule specifies at least one of a relationship between the visual elements and an allowed sequence of the visual elements; presenting perceptory stimuli to the individual, the perceptory stimuli comprising the shared secret; obtaining at least one electroencephalographic response from the individual in response to the perceptory stimuli comprising said shared secret presented to the individual; and authenticating the individual's claim as being the enrolled user based on the obtained electroencephalographic response, wherein authenticating comprises; detecting a pattern of P300 event-related potentials in the obtained electroencephalographic response; comparing the detected pattern of P300 event-related potentials with an expected pattern of P300 event-related potentials as provided by the stored electroencephalographic response profile associated with the enrolled user, wherein an unexpectedly produced P300 event-related potential in the detected pattern is indicative of an imposter; determining an authentication score based on results of said comparing; and comparing the determined authentication score to a predetermined authentication threshold value to positively authenticate the individual as being the claimed enrolled user when the authentication score meets or exceeds the predetermined authentication threshold or to reject the individual as an imposter when the authentication score does not meet or exceed the predetermined authentication threshold.