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Harry S. Orbach, Ross M. Henderson, Mark R. Baker; Signal detection theory and implicit representation. Journal of Vision 2002;2(7):18. doi: https://doi.org/10.1167/2.7.18.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: This theoretical study gives a signal detection theory framework for evaluating claims that there are implicit representations of information not available for standard psychophysical tasks. Claims of subliminal perception as evidence for unconscious processing have been criticised on SDT grounds as merely indicating criterion effects or as simply reflecting “below threshold but above chance” performance. Physiological evidence from fMRI and ERP studies may be critiqued on the same grounds.
Methods: However using orthodox signal detection theory, one can make claims for evidence in favor of a more surprising type of implicit perception. If a “neurometric observer” (using physiological measures, such as single unit recordings or evoked potentials) had a higher sensitivity than that demonstrated psychophysically by the subject, information, unavailable for subject's psychophysical performance is represented in the brain. Interestingly, in such a case, even a forced choice psychophysics experiment (e.g. demonstrating blindsight), would give very low performance. Analysis is straightforward in the case of direct brain recording, but indirect analysis must be used in the case of scalp ERP measurements. We will present the framework for such analyses and how it may be applied to experiments on change perception where performance improves dramatically when a cue is given.
Results: For change blindness, the derived physiological and psychophysical “sensitivities” for uncued and cued trials can be used to give evidence for implicit representation (consistent with information in a visual pathway not available for the psychophysical task). Although an analysis giving the contrary result cannot be used to rule out implicit change perception (brain areas may be involved that do not generate measurable signals), it can be used to show that purported evidence of implicit perception is unconvincing.
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