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.
Highlights
An unresolved question is how the reported clarity of degraded speech is enhanced when listeners have prior knowledge of speech content
The results from Experiment 1 demonstrate that prior knowledge of speech content from written text has a measurable effect on the rated clarity of vocoded speech, which replicates previous findings from studies that used a similar paradigm to the one employed here (Goldinger et al, 1999; Jacoby et al, 1988; Sohoglu et al, 2012; Wild et al, 2012)
With a lag of ϳ100 ms, the current results suggest that written text was less effective in enhancing speech perception when processed ϳ220 ms after speech onset, well within the 200 –300 ms range estimated to be the duration of auditory echoic memory
Summary
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. 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. Whether ms (Chandrasekaran, Trubanova, Stillittano, Caplier, & Ghazanfar, listening to a speaker with a foreign accent or in a noisy room, we 2009), improve speech intelligibility in noise One explanation for this considerable feat is that listeners are highly adept at exploiting prior knowledge of the environment to aid speech perception.
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