Subliminal stimuli

Subliminal stimuli (/sʌbˈlɪmᵻnəl/; literally "below threshold"), contrary to stimuli or "above threshold", are any sensory stimuli below an individual's threshold for conscious perception. A recent review of functional magnetic resonance imaging (fMRI) studies shows that subliminal stimuli activate specific regions of the brain despite participants being unaware. Visual stimuli may be quickly flashed before an individual can process them, or flashed and then masked, thereby interrupting the processing. Audio stimuli may be played below audible volumes or masked by other stimuli.

Applications of subliminal stimuli often base themselves on the persuasiveness of the message. Importantly, research on action priming has shown that subliminal stimuli can trigger only actions a receiver of the message plans to perform anyway; however, consensus of this finding remains unsubstantiated by other research. Most actions can be triggered subliminally only if the person already has the potential to perform a specific action. The following sections have more information on specific studies which investigate the effectiveness of subliminal stimuli.

The threshold in subliminal stimuli research is the level at which the participant is not aware of the stimulus being presented. Researchers determine a threshold for the stimulus that will be used as the subliminal stimulus. That subliminal stimulus is then presented during the study at some point and measures are taken to determine the effects of the stimulus. The way in which studies operationally define thresholds depends on the methods of the particular article. The methodology of the research also varies by the type of subliminal stimulus (auditory or visual) and the dependent variables they measure.

The objective threshold is found using a forced choice procedure, in which participants must choose which stimulus they saw from options given to them. Participants are flashed a stimulus (e.g. the word "orange") and then given a few choices and asked which one they saw. Participants must choose an answer in this design. The objective threshold is obtained when participants are at chance level of performance in this task. The length of presentation that causes chance performance on the forced choice task is used later in the study for the subliminal stimuli.

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