Some experiments give subjects a "distractor" task to ensure that subjects are not consciously paying attention to the experimental stimuli; this may be done to test whether a certain computation in the brain is carried out automatically, regardless of whether the subject devotes attentional resources to it. For example, one study had subjects listen to non-linguistic tones (long beeps and buzzes) in one ear and speech in the other ear, and instructed subjects to press a button when they perceived a change in the tone; this supposedly caused subjects not to pay explicit attention to grammatical violations in the speech stimuli. The subjects showed a mismatch response (MMN) anyway, suggesting that the processing of the grammatical errors was happening automatically, regardless of attention—or at least that subjects were unable to consciously separate their attention from the speech stimuli.