 Psychophysics (the study of the relationship between physical sensory input and consequent psychological state or response), where the introspective psychologists had found their greatest success, underwent a subtle shift in this period from a focus on subjective methods—methods that involve asking subjects to report on their experiences or percepts—to a focus on objective methods such as asking participants to report on states of the outside world, including insisting that participants guess even when they feel they don’t know or have no relevant conscious experience (especially with the rise of “signal detection theory” in psychophysics: Green and Swets 1966; Cheesman and Merikle 1986; Macmillan and Creelman 1991; Merikle, Smilek, and Eastwood 2001). Perhaps in accord with transparency views of introspection (Section 2.3.4 above), the two types of instruction seem very similar (compare the subjective “tell me if you visually experience a flash of light” with the objective “tell me if the light flashes”). On the other hand, perhaps in tension with transparency views, subjective and objective instructions seem sometimes to differ importantly, especially in cases of known illusion, Gestalt effects such as perceived grouping, stimuli near the limits of perceivability, and the experience of ambiguous figures (Boring 1921; Merikle, Smilek, and Eastwood 2001; Siewert 2004).