Subliminal influence

Subliminal influence ¹
A lot of the research on (behavioural) priming is conducted by exposing test subjects to subliminal stimuli. In this procedure, a word or picture is briefly flashed on the computer screen. The exposure time of the stimulus on the screen is at a level that ensures that the participant is not conscious of the stimulus being presented. ‘Subliminal’ literally means `below a threshold’, and researchers often draw a distinction between what they call the objective and the subjective threshold value. The former is a threshold value of exposure below which nothing is observed. This can be tested using a so-called forced choice procedure: participants are given a few choices and have to answer which stimulus they saw being flashed on the screen. When participants answer at chance level, this means that the exposure time was so short that no one was able to see anything (e.g., Cheesman & Merikle, 1984). Interestingly, when the presentation length is increased, participants slowly start to perform better than chance levels, even if they say they didn’t see anything. This illustrates the subjective  threshold, where people are not consciously aware they saw something, but the presented stimulus has an effect on memory processes nonetheless. It is in this time frame that subliminal perception takes place. It is difficult to give an exact estimate of the exposure time needed to present a stimulus subliminally, but can differ from anywhere between 10 to 100 milliseconds. This depends on the size and complexity of the stimulus presented, on the illumination and background contrast, where on the screen the stimulus is presented, as well as individual differences. Research on subliminal priming investigates what influence, if any, such subliminally presented information has on people’s thoughts and behaviour.

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