Regular Minimality: A Fundamental Law of Discrimination: Ehtibar N. Dzhafarov & Hans Colonius
There is more to the notion of an observation area than the difference between spatiotemporallocations of stimuli, but this need not be discussed now. Formally, we refer to x in (x~ y) as belonging to the first observation area, and to y as belonging to the second observation area, the adjectives "first" and "second" designating the ordinal positions of the symbols in the pair rather than the chronological order of their presentation. The difference between the two observation areas, whatever their physical meaning, is always perceptually conspicuous, and the observer is supposed to ignore it: thus, when asked to determine whether the stimulus on the left (or presented first) is identical to the stimulus on the right (presented second), the observer would normally perceive two stimuli rather than a single one, and understand that the judgment must not take into account the difference between the two spatial (or temporal) positions. In the history of psychophysics, this aspect of discrimination has not received due attention, although G. T. Fechner did emphasize its importance in his insightful discussion of the "non-removable spatiotemporal non-coincidence" of two stimuli under comparison (1887, p. 217; see also the translation in Scheerer, 1987).