Memory disruption by irrelevant noise-vocoded speech: Effects of native language and the number of frequency bands

Abstract

To investigate the mechanisms by which unattended speech impairs short-term memory performance, speech samples were systematically degraded by means of a noise vocoder. For experiment 1, recordings of German and Japanese sentences were passed through a filter bank dividing the spectrum between 50 and 7000 Hz into 20 critical-band channels or combinations of those, yielding 20, 4, 2, or just 1 channel(s) of noise-vocoded speech. Listening tests conducted with native speakers of both languages showed a monotonic decrease in speech intelligibility as the number of frequency channels was reduced. For experiment 2, 40 native German and 40 native Japanese participants were exposed to speech processed in the same manner while trying to memorize visually presented sequences of digits in the correct order. Half of each sample received the German, the other half received the Japanese speech samples. The results show large irrelevant-speech effects increasing in magnitude with the number of frequency channels. The effects are slightly larger when subjects are exposed to their own native language. The results are neither predicted very well by the speech transmission index, nor by psychoacoustical fluctuation strength, most likely, since both metrics fail to disentangle amplitude and frequency modulations in the signals.

Acoustic Detail But Not Predictability of Task-Irrelevant Speech Disrupts Working Memory

“…This is in agreement with one previous study by Ellermeier et al (2015), which also used noise-vocoded speech in an irrelevant-speech task. Going beyond noise-vocoding, several studies using other auditory signal processing techniques have demonstrated higher distraction by acoustically more intact task-irrelevant speech (e.g., Tremblay et al, 2000; Little et al, 2010; Viswanathan et al, 2014).…”

English phonology and an acoustic language universal

“…The crossings of these factor-loading curves separated four frequency bands that were similar across these languages/dialects. These four bands were used by our research group to generate noise-vocoded speech in Japanese and German when the present analysis was on the way, and the generated signals indicated high intelligibility of up to 95%3. These results were consistent with representative past data on noise-vocoded speech45.…”

Suppression of irrelevant sounds during auditory working memory

“…However, evidence from ERP (Berti and Schroger, 2003; Muller-Gass and Schroger, 2007) and behavioral (Dalton et al, 2009) studies that utilized purely auditory paradigms supports an alternative view that distracter suppression occurs at a later stage and requires active control (Berti and Schroger, 2003; Dalton et al, 2009). At the same time, recent behavioral studies also suggest that during auditory WM, irrelevant speech sounds are suppressed only after initial feature processing (Ellermeier et al, 2015; Wöstmann and Obleser, 2016). The present results seem to be more consistent with the latter group of ERP and behavioral studies: The aspect of left AC time course that was statistically significantly modulated by the contextual WM maintenance load was relatively late, clearly after the P50/N1/P2 pattern that is thought to reflect the emergence of conscious sound percept and the initiation of stimulus encoding in ACs (Parasuraman and Beatty, 1980).…”