A method comprises: i) presenting to a subject a training stimulus, the training stimulus eliciting from the subject a desired response; ii) presenting to the subject a diffuse visual stimulus along with the training stimulus; and iii) repeating the presenting to the subject of the training stimulus along with the diffuse visual stimulus sufficiently many times so that subsequent presentation of the diffuse visual stimulus to the subject without the training stimulus elicits from the subject the desired response. The diffuse visual stimulus is arranged so as to be perceived by the subject only at a subliminal or near-subliminal level. Another method comprises presenting to the subject the diffuse visual stimulus in order to elicit the desired response, the subject having been conditioned according to the previous method.