Additivity of segregation cues in simulated cocktail-party listening

An approach is borrowed from Measurement Theory [Krantz et al. (1971). Foundations of Measurement (Academic, New York), Vol. 1] to evaluate the interaction of voice fundamental frequency and spatial cues in the segregation of talkers in simulated cocktail-party listening. The goal is to find a mathematical expression whereby the combined effect of cues can be simply related to their individual effects. On each trial, the listener judged whether an interleaved sequence of four vowel triplets (heard over headphones) were spoken by the same (MMM) or different (FMF) talkers. The talkers had nominally different fundamental frequencies and spoke from nominally different locations (simulated using head-related transfer functions). Natural variation in these cues was simulated by adding a small, random perturbation to the nominal values independently for each vowel on each trial. Psychometric functions (PFs) relating d' performance to the difference in nominal values were obtained for the cues presented individually and in combination. The results revealed a synergistic interaction of cues wherein the PFs for cues presented in combination exceeded the simple vector sum of the PFs for the cues presented individually. The results are discussed in terms of their implications for possible emergent properties of cues affecting performance in simulated cocktail-party listening.