Investigating the Disturbance Impact of Background Speech on Verbal and Visual-Spatial Short-Term Memory: On the Differential Contributions of Changing-State and Phonology to the Irrelevant Sound Effect

The empirically robust phenomenon of impaired verbal short-term memory due to task-irrelevant background speech is known as the Irrelevant Sound Effect (ISE). Yet, the underlying cognitive mechanisms are still not fully resolved, like whether phonology-based interference contributes to the disruptive effect of speech on verbal serial recall. Thus, we tested the ISE for such a speech-specific aspect by varying the phonological content of the irrelevant speech and the verbal nature of the task. Furthermore, we also varied the changing-state characteristic of irrelevant speech. Therefore, visual-verbal and visual-spatial serial recall of 70 participants each was measured during silence and syllable series varying in phonological (unaltered speech vs. sinewave speech) and in changing-state content (one repeatedly presented vs. successively changing syllables). Both phonology and changing-state characteristic had significant and independent impacts on each of the two serial recall tasks, and both effects were unrelated to participants’ working memory capacity. Changing-state sequences were more disturbing than steady-state sounds for both serial recall tasks, but the effect of phonological content was not in the same direction for the two tasks. Whereas unaltered speech sounds impaired verbal serial recall more than their phonologically reduced sinewave versions, this was the opposite for visual-spatial serial recall. In the latter task, however, only changing-state sinewave speech reduced performance significantly compared to silence condition. In summary, our results indicate that there is a speech-specific, disruptive effect of phonological content, which is an attention-independent interference effect and presumably restricted to verbal short-term memory.