title: Top-down influences of written text on perceived clarity of degraded speech.
abstract: An unresolved question is how the reported clarity of degraded speech is enhanced when listeners have prior knowledge of speech content. One account of this phenomenon proposes top-down modulation of early acoustic processing by higher-level linguistic knowledge. Alternative, strictly bottom-up accounts argue that acoustic information and higher-level knowledge are combined at a late decision stage without modulating early acoustic processing. Here we tested top-down and bottom-up accounts using written text to manipulate listeners' knowledge of speech content. The effect of written text on the reported clarity of noise-vocoded speech was most pronounced when text was presented before (rather than after) speech (Experiment 1). Fine-grained manipulation of the onset asynchrony between text and speech revealed that this effect declined when text was presented more than 120 ms after speech onset (Experiment 2). Finally, the influence of written text was found to arise from phonological (rather than lexical) correspondence between text and speech (Experiment 3). These results suggest that prior knowledge effects are time-limited by the duration of auditory echoic memory for degraded speech, consistent with top-down modulation of early acoustic processing by linguistic knowledge.
authors.affiliation: MRC Cognition and Brain Sciences Unit.
authors.forename: Ediz
authors.initials: E
authors.lastname: Sohoglu
authors.affiliation: MRC Cognition and Brain Sciences Unit.
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Peelle
authors.affiliation: MRC Cognition and Brain Sciences Unit.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Carlyon
authors.affiliation: MRC Cognition and Brain Sciences Unit.
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Davis
mesh_terms: D000293:Adolescent; D000328:Adult; D006801:Humans; D019359:Knowledge; D008570:Memory, Short-Term / Q000502:physiology*; D011932:Reading; D013065:Speech Intelligibility / Q000502:physiology*; D013067:Speech Perception / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult