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Pictures of line-drawn animals and objects were subliminally presented to each visual hemi-field of an experimental group consisting of forty healthy subjects.
Sixty-three control subjects received blanks. Next, both groups were shown progressively less fragmented versions of the same line drawings. Whereas subjects and controls performed at the same level when both groups had been presented subliminal blanks, the experimental group was able to identify the pictures in a far more fragmented form if they had had prior exposure subliminally to the complete picture. But this was true only after subliminal presentation to the left visual field, the right hemisphere. The authors conclude that pictures presented below the threshold of awareness can be perceived and that only the right hemisphere can perceive and utilize such perceptions. They then raise the question: Is the left hemisphere unable to gain access to such nonconscious percepts, or does the right hemisphere dominate such subliminal perceptions?
The experimenters might have avoided a serious flaw in the experiment as it stands now by adding one condition. Currently the test task itself—identifying pictures from fragments—is very possibly a right-hemisphere-dominated task. Suppose, though, in the test phase, another two groups of subjects after subliminal presentations of pictures (each group receiving the presentations to one of the hemi-fields), were provided with a different test task. Using the picture of a fish, for example, each of these groups would be asked, after subliminal picture presentation, to complete an ambiguous stem like “ish.” Would those with right hemisphere exposure complete the verbal fragment with “fish” rather than with the equally common “wish” or “dish” more or less frequently than the left hemisphere exposed group? And how would both groups compare with a control group subliminally exposed to blanks?