Subliminal self-help auditory tapes: an empirical test of perceptual consequences (Appraisal of claims of subliminal effects of commercially available tapes)

Canadian Journal of Behavioural Science, Jan 1995 by Moore, Timothy E

While subliminal perception is a valid phenomenon, recent research has shown that it occurs only under certain carefully controlled conditions. These include the establishment of individual thresholds for each participant, a controlled viewing environment, focussed attention on the display area, and exclusion of extraneous sources of stimulation. Most important, for the present purposes, is the finding that subliminal perception is most appropriately defined as a situation in which there is a discrepancy between the viewers' phenomenal experience, and their ability to discriminate between different stimulus states. Participants are often sensitive to stimuli they claim not to have seen. When required to distinguish between two or more stimuli, subjects can do so with some success, even while professing to be guessing (Holender, 1986). On the other hand, there is little reliable evidence of semantic processing of stimuli which cannot be discriminated (Cheesman & Merikle, 1984; 1986).

According to Merikle and Reingold (1992) the available evidence suggests that subliminal perception is not perception in the absence of stimulus sensitivity. Rather, it occurs when subjective experience is at odds with objective measures of signal detection. Such a perspective makes it possible to interpret and understand many previous studies. In the past, investigators did not typically distinguish very carefully between subjective and objective indicators of perception. Consequently somewhat mystical notions of supersensitive unconscious perceptual processes abounded. Today there is consensus that subliminal perception consists of a dissociation between an objective measure of perception and concurrent subjective awareness (Fowler, 1986; Greenwald, 1992a; Kihlstrom, 1987; Merikle, 1988).

This approach is an improvement over previous procedures that defined awareness exclusively in terms of observers' (or listeners') self reports of awareness. Dixon (1981), for example, in an extensive review of subliminal perception research, was content to accept introspective self reports as the defining criterion for 'awareness'. Critics have noted (e.g., Glucksberg, 1982; Merikle, 1983), that without the additional precision afforded by signal detection methods, it is impossible to make much sense of the countless studies that have relied on observers' self reports of their conscious experiences. Subjects may sometimes report a stimulus' absence because of response bias or demand characteristics. Alternatively, some stimuli may be so weak that they fall outside the range of subjects' sensory capabilities. The latter would, perforce, be "not consciously seen", nor would they initiate any perceptual activity at all. In short, studies that define awareness only in terms of self reports generate findings that shed little light on the topic of unconscious perception (Merikle, 1984). For the most part, research on subliminal auditory stimulation has not been sensitive to the distinction between objective and subjective thresholds (e.g., Borgeat, Elie, & Chabot, 1985; Henley, 1975).