In exemplary implementations of this invention, stimuli are intermittently presented to the left or right side of a user. For example, this invention may comprise a method of presenting stimuli to a bilateral organism, which organism has a left side and a right side, wherein: (a) the stimuli are produced by at least one transducer, (b) the stimuli include an intermittent beat train, and (c) the beat train has a beat frequency that is substantially equal to 7.8×(1.618)n Hz, where n is an even integer, which even integer may be negative, zero or positive.