Empirical psychologists frequently rely on deception and error in order to infer how cognitive processes work. When intersubjective agreement is total regarding some phenomenon, then it’s impossible to distinguish between the nature of that phenomenon and the way in which the human subject perceives that phenomenon. The research psychologist tries to open up a split. Optical illusions are common enough examples. In one well-known example, two perfectly parallel lines appear to bow apart from each other in the middle. The lines are constructed in such a way as to deceive the human perceptual system. Or researchers can construct deceptive problems for subjects to solve. If subjects tend to make particular kinds of errors on tasks for which the right solutions are well-defined a priori, then the errors can be attributed to quirks of human subjectivity that caused the subjects to misapprehend the nature of the problem.
In one study, the researcher displays four brands of a particular product on a table, arrayed from left to right. The researcher asks the subjects to choose which brand they regard as best and why. Subjects make their choices and offer their rationales. In fact, all four displayed products are identical. Empirically, it turns out that, on average, subjects prefer objects on the right side of the display to those on the left. In explaining the basis for their choices, the subjects describe (nonexistent) differences in quality without ever showing any conscious awareness of what must actually have motivated their choices. The subject perceives differences in the individual objects, but these differences are illusory. They’re actually responding to an unconscious subjective preference for arraying objects that tends to be a characteristic bias of human subjectivity.
From the researcher’s point of view, subject’s errors in task performance and misattributions in accounting for their own behaviors are real enough. Errors and self-deceptions are counted, categorized, analyzed statistically, interpreted theoretically. Again, though, what motivates this sort of work is to use these errors as a means of distinguishing perceptual-cognitive processes from the external phenomena they’re processing. The errors are real in the paradoxical sense that they present real evidence of human limitations in discerning external reality accurately.
The physical sciences make progress by identifying and controlling for observational error caused by limitations and biases in human perceptual-cognitive capabilities. To the human eye, the moon and the sun appear to be just about the same size. But it turns out this is an illusion resulting from intrinsic human limitations in judging distance between the eye and the observed object, especially when the distances are enormous. The apparent size-equivalence of sun and moon to the naked eye is real enough, in the sense that it’s a real illusion pointing to real limitations in humans’ ability to perceive the external world accurately. What interests the astronomer, though, are the actual sizes and distances of the sun and moon.
I grasp the “object-oriented” contention that my perception of the size of the sun is just as real as the sun itself. Call me old-fashioned, but I can’t help finding this ontological equivalence rather dissatisfying when trying to distinguish illusion from fact, subjective from objective, the apparently real from the really real.