On the tolerance of spectral blur in the perception of spoken words

Abstract

How does a listener resolve linguistic properties conveyed by speech? Many descriptions of perception attribute a causal role to brief spectral details in narrow frequency ranges. Perceptual standards allow far more variety, revealed by the robustness of perception of many kinds of distorted speech. The present study considered the effects of spectral blur on the recognition of spoken words. Listeners heard successive presentations of noise-vocoded easy and hard words. The number of spectral channels composing the word increased with each presentation, reducing blur within a trial. Four conditions counterbalanced the number of presentations of each word in a trial, 3 or 5, and the severity of initial blur, either 1 or 5 channels. In all conditions, the final presentation had 9 bands, yielding a net blur reduction of 4 or 8 bands. These conditions were also tested with the instruction that the words would become clearer during each trial. A control used two repetitions of each word at 9 spectral bands. Across the tests, exposure to spectral blur impaired the recognition of easy and hard words alike regardless of the listener’s belief during presentation. However, intelligibility of hard words declined sharply when subjects were instructed to attend to the continuity and successive decrease in blur within a trial. The pattern of results exposes the role of attention, uncertainty, and spectral resolution in the phonetic contribution to word identification.