Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)




Larry L. Jacoby


Conscious perception is substantially overestimated when standard measurement techniques are used. That overestimation has contributed to the controversial nature of studies of unconscious perception. I employed a process-dissociation procedure (Jacoby, 1991) for separately estimating the contribution of conscious and unconscious perception to performance of a stem-completion task. Unambiguous evidence for unconscious perception was obtained in seven experiments. Debner and Jacoby (1994, Experiment 1) showed that decreasing the duration of a briefly presented word diminished the contribution of both conscious and unconscious perception. In Experiments 2, 3 and 4, Debner and Jacoby found that dividing attention reduced the contribution of conscious perception while leaving that of unconscious perception unchanged. Debner (submitted) used the same stem-completion task to show that estimates of unconscious perception could also be affected. In one set of experiments (Experiments 1a and 1b), increasing the interstimulus interval between the briefly presented word and the test of stem completion decreased the contribution of unconscious perception to performance but left that of conscious perception intact. Experiment 2 revealed that a manipulation of visual similarity produced a similar process dissociation. Discussion focuses on the measurement of awareness, the relationship between perception and memory, and the possible episodic nature of conscious and unconscious perceptual processes.

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