Subliminal perception and its cognates: theory, indeterminacy, and time.

Unconscious processes, by whatever name they may be known (e.g., "subliminal," "implicit"), are invariably operationalized by the dissociation paradigm, any situation involving the dissociation between two indicators (or sets of indicators), one of availability (epsilon) and the other, of accessibility (alpha), such that, epsilon>alpha. Subliminal perception has been traditionally defined by a special case of the dissociation paradigm in which availability exceeds accessibility when accessibility is null (epsilon>alpha/alpha=0). Construct validity issues bedevil all dissociation paradigms since it is not clear what might constitute appropriate indicators that, moreover, are pure and exhaustive. Semantic and theoretic drifts in the recent literature--e.g., the confusion of different versions of the dissociation paradigm, the equation of conscious-unconscious with direct-indirect tests, and the foisting of the criterion of qualitative differences--have tended to undermine emerging theoretic parsimony. On the other hand, a crucial factor has been left out of theory development: time. Both epsilon and alpha can rise and fall over time, often asynchronously, and so dissociations may wax and wane and, even, reverse over time. Some laboratory evidence suggests that accessibility measures (e.g., d'), as they approach chance, may actually dip below chance (subchance perception). If so, d'=0 (the chance-limen or objective threshold), could be an averaging artifact of positive and negative d's. Conscious accessibility is not either-or but more or less, and variable over time.