Lexical access in the face of degraded speech: The effects of cognitive adaptation

Abstract

Hearing impaired listeners use cognitive adaptations to cope with degraded input. Here, we ask if they adapt processes that normal hearing listeners use to cope with the fact that speech unfolds over time, creating brief periods of ambiguity. Normal listeners cope with this ambiguity by activating multiple lexical candidates which compete for recognition (McClelland & Elman, 1986). These competition dynamics change when processing degraded input (Brouwer & Bradlow, 2016; McMurray, Farris-Trimble, & Rigler, 2017; McQueen & Huettig, 2012), but it is unclear whether this reflects the degraded input itself or cognitive adaptation. In two visual world paradigm experiments, listeners heard different levels of degraded (noise-vocoded) speech. Experiment 1 manipulated the level of degradation either in blocks or randomly interleaved across trials. Interleaving led to processing delays beyond that of the level of degradation: we found switch-costs when degradation levels differed between trials. This suggests differences in lexical dynamics are not solely due to degradation in the input. In Experiment 2, a visual cue indicated the level of degradation before each trial. This reduced the processing delays and switch costs, suggesting participants adapted before the auditory input. These experiments support a role for central processing in dealing with degraded speech input.