1. A method comprising: repeatedly presenting to a subject a training stimulus, the training stimulus eliciting from the subject a selected physiological, psychological, emotional, or mechanical response; presenting to the subject a diffuse, non-imaged visual stimulus along with each presentation of the training stimulus; and after repeatedly presenting the training stimulus, presenting the diffuse, non-imaged visual stimulus to the subject without the training stimulus so as to elicit from the subject the selected response, wherein: the diffuse, non-imaged visual stimulus is presented via a visual display and comprises a selected spatial pattern or arrangement of deviation of a selected parameter of the visual display from a reference level of that selected parameter; and the diffuse, non-imaged visual stimulus is arranged so as to be perceived by the subject only at a subliminal or near-subliminal level.