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Background on Subliminal Perception, Related Literature

Much research has been published in this domain in the past decades. There are two main streams of results: One group provided evidence that subliminal stimulation works (at least in specific, restricted settings), the other group found that it does not, or even cannot, work. Many psychological experiments have attempted to prove the existence of subliminal perceptual processes by demonstrating that stimuli are registered when subjects are not consciously aware of the stimuli [2]. The evidence offered in support of subliminal perception comes from a variety of experimental sources. For example, there is evidence that subliminally flashed pictures displaying emotionally positive or negative scenes affect the judgments of presumably neutral pictures of people [3]. Moreover, evidence exists that these subliminally presented emotional stimuli activate cortical areas that mediate emotional experience [4]. Thanks to the improvement of neuroimaging techniques, this type of validation could be more fruitful. Similar results can be found in the semantic meaning of the word. To illustrate, Fowler et al. performed a priming study in which words were flashed on a screen so rapidly that observers were not aware of what was presented. This was followed by above-threshold presentation of two words. When participants were asked to choose which of the two above-threshold words was most like the subliminally flashed word, they were significantly more likely to choose the related over the unrelated word. The most crucial factor in the success of such studies is the method used for assessing whether the non-consciously experienced stimulus is indeed unconsciously perceived. A facility to distinguish between consciously and non-consciously perceived information has been demonstrated in several experiments focusing on the type of reaction. Studies found that consciously perceived stimuli allow subjects to follow instructions, whereas unconsciously perceived stimuli lead to much more automatic reactions [1]. Furthermore, it was particularized that conscious perception of a stimulus is constrained by its context but that unconscious perception of the same stimulus leads to automatic reactions that are relatively unconstrained by the context. Regarding the relations between automaticity and the level of attention, similar theories can be found in vision and audition. These pre-attentive processes principles could be, for example, applied to display design in HCI [5]. Merikle and Daneman reviewed the history of unconscious perception from a psychological point of view [2] and summarized the status of experimental research in this area of investigation. They concluded that „[..] unconscious perception has been shown to have a firm empirical basis, future experimental studies can concentrate on exploring other characteristics of unconscious perception''. As one potential challenge they specified is to establish whether or not individuals differ in their sensitivity to the effects of unconsciously perceived information – this is an issue to be discussed at this workshop.