The Psychoacoustics Of The Irrelevant Sound Effect

The decrement in memory performance observed while listeners are being exposed to acoustically structured stimuli is called the irrelevant sound effect (ISE). The present review summarizes the research identifying physical features of the irrelevant background that reliably induce performance decrements. It shows that speech, or speech analogues, produce the largest effects by far, suggesting that speech-specific features may contribute to auditory distraction. When an attempt is made to isolate psychoacoustical parameters contributing to the effect, it turns out that noticeable spectral change over time is a necessary condition to observe an ISE, while level change by itself is not. New empirical evidence is presented determining the rate of frequency modulation at which maximal effects are obtained. Results of a further study employing noise-vocoded speech show the importance of spectral detail in producing an ISE. At present, the wealth of empirical findings on the effects of irrelevant sound is not well accounted for by the available theoretical models. Cognitive models make only qualitative predictions, and psychoacoustical models (e.g., those based on fluctuation strength or the speech transmission index) account for subsets of the available data, but have thus far failed to capture the combined effects of temporal structure and spectral change in generating the interference.