Mechanisms underlying nonmonotonic Weber functions in forward‐masked intensity discrimination

Abstract

Nonmonotonic growth in threshold for intensity discrimination has been noted for pure tones preceded by intense sinusoidal maskers; thresholds are highest for 40–60 dB SPL standards, producing what has often been described as a ‘‘midlevel hump.’’ Both physiologic and cognitive factors have ben suggested as mechanisms underlying this phenomenon. Three subjects received four conditions designed to examine this issue. A 2IFC paradigm assessed intensity discrimination of 1000‐Hz, 100‐ms sinusoids. A no‐masker condition provided a baseline. Three forward‐masked conditions were implemented: An ipsilateral condition that typically produces a mid‐level hump; a contralateral condition in which the hump is typically absent or greatly reduced; and a binaural condition presenting these two maskers simultaneously (contralateral stimulation was 13 dB greater than ipsilateral stimulation; listeners perceived only the contralateral masker). It was argued that if this condition produced a hump despite a perceptually absen...