Using fuzzy logic in psychophysical experiments to separate hits, false positives and guesses in posturally perturbed standing subjects.

In a 2-Alternative Forced Choice Interval task (2AFCi), a standing subject is required to press a button once or twice to signal in which of two 4 s sequential intervals that (s)he thought that a short ≤ 16 mm postural perturbation had occurred. The perturbation might or might not result in transient changes of the subject's Anterior-Posterior Center of Pressure (APCOP) or in other measures. This paper used fuzzy inference to explore whether the correctness of a subject's stimulus detection can be gleaned from analyzing changes in one of more metrics related to changes in the APCOP. Also, distinguishing guesses from correct responses is a critical issue in any psychophysical detection paradigm. Biomechanical and psychophysical data are used to design a prediction model based on fuzzy inference that is able to discriminate correct responses from guesses.