Disruptive effect of unattended noise-vocoded speech on recall of visually presented digits: Interaction between the number of frequency bands and languages

To assess the effects of degraded irrelevant speech on the serial recall of visually presented digits, noise-vocoded speech was generated in Japanese and German. Effects of the participants' native language were also examined by studying 40 Japanese and 40 German listeners. The number of frequency bands used in vocoding and the language (native or not) the irrelevant sound was derived from affected performance significantly. The participants' native language had a greater disruptive effect than the non-native language, particularly in conditions in which intelligibility was moderate. Speech sounds appear to have been processed automatically although the participant was instructed to neglect them. This must have required some amount of cognitive resources, which could have been used for the recall task otherwise. This automatic interference was stronger when the native language was used, probably because it contained perceptual cues that were more difficult to degrade.