Signal Detection Theory and Psychophysics - Andrei Gorea

HIGH-THRESHOLD THEORY*The HTT proposes that sensitivity (q) be measured by the adjustedHit rate:q = (H F) / (1 F) H = (1 q)F + q [High Thresh ROC: H is linear with F]The statistic q, "corrects" the hit rate for "guessing“. It adjusts thisindex so that it ranges from 0 to 1 (rather than from 0 to 1 – F). Theequation deflates H to take account of the tendency to make falsealarms. The correction for guessing lowers the hit rate more when thefalse-alarm rate is higher.The essential tenet of high-threshold theory is that “Yes" responsesto Noise stimuli must be guesses based on no information. Astate diagram incorporating this idea is shown next.*From McMillan & Creelman (2005; pp 82-84).