The irrelevant sound effect is a well-replicated finding in cognitive psychology. People asked to memorise a sequence, such as digits or words shown on a screen, recall the order less accurately when sound plays in the background, even though they are told to ignore it. Speech is a particularly disruptive kind of sound, and studies suggest it can interfere even when it is not intelligible, which is why it is sometimes called the irrelevant speech effect.
Reviews of noise and cognition report disruption not only of serial recall but also of reading, while noting that real-world effects are usually modest and that studies vary in quality. The finding helps explain why many people find vocal music or nearby conversation harder to work with than instrumental tracks or silence.
For jazz lo-fi listeners the practical lesson is simple: when a task depends on words or on keeping things in order, wordless music at a low volume is the safer companion, and switching it off is always an option.