On the importance of information-bearing acoustic changes for understanding speech in simulated electrical-acoustic stimulation

Abstract

Listeners utilize information-bearing acoustic changes in the speech signal to understand sentences. This has been demonstrated in full-spectrum speech using cochlea-scaled entropy (CSE; Stilp & Kluender, 2010 PNAS) and in vocoded speech (CSECI; Stilp et al., 2013 JASA). In simulations of electrical-acoustic stimulation (EAS), vocoded speech intelligibility is aided by the preservation of low-frequency acoustic cues. The extent to which listeners rely on information-bearing acoustic changes to understand EAS speech is unclear. Here, normal-hearing listeners were presented noise-vocoded sentences with 3–6 spectral channels in two conditions: 1) vocoder-only (80–8000 Hz, filtered using third-order elliptical filters), and 2) simulated hybrid EAS (vocoded >500 Hz; original acoustic <500 Hz). In each sentence, four 80-ms intervals containing high-CSECI or low-CSECI acoustic changes were replaced with speech-shaped noise. As expected, performance improved with more channels and the preservation of low-frequency fine-structure cues (EAS). Relative to control vocoded sentences with no noise replacement, performance was impaired more when high-CSECI intervals were replaced by noise than when low-CSECI intervals were replaced in 5- and 6-channel sentences, but not at lower spectral resolutions. This effect maintained across vocoder-only and EAS sentences. Findings support the conclusion that EAS users make use of information-bearing acoustic changes to understand speech.