Lexical Bias During Speech Perception Increases Under Signal Degradation but Not Cognitive Load

Lexical information shapes the interpretation of ambiguous speech sounds, often biasing perception toward real words rather than nonwords-a phenomenon known as lexical bias. This study examined the extent to which signal degradation and cognitive load modulate this bias.

Younger adults with normal hearing categorized stimuli along two word-nonword continua (Bap/Gap and Back/Gack), which differed primarily in the formant transitions of the initial consonant. Stimuli were either unprocessed or vocoded to introduce signal degradation, simulating cochlear implant listening. Cognitive load was manipulated via a dual-task paradigm: Participants memorized digits (Experiment A) or images (Experiment B) under low- and high-cognitive-load conditions while performing the categorization task.

Across both experiments, participants demonstrated robust lexical bias and reported more "Gap" (word) responses for the Bap/Gap continuum and more "Back" (word) responses for the Back/Gack continuum. Vocoded stimuli elicited stronger lexical bias than unprocessed stimuli. In Experiment A, the digit memory task produced a significant interaction: The increase in lexical bias for vocoded stimuli was attenuated under high cognitive load relative to low cognitive load. In Experiment B, the image memory task yielded no significant effect of cognitive load on lexical bias.

Signal degradation amplifies lexical bias during speech perception, whereas cognitive load appears to exert only limited influence. These findings have implications for understanding how individuals relying on spectrally degraded signals may draw on lexical knowledge to support speech perception in challenging conditions.