The effects of intelligibility and variability on cognitive performance and acoustic comfort

Open-plan offices are very popular due to some assumed economic and organizational advantages. These benefits are confronted with typical drawbacks, i.e. office noise and lack of speech privacy. Ambient speech caused by conversations of colleagues is assumed to impair office workers' individual task performance at silent, concentrated work. The Speech Transmission Index (STI) is proposed to be a predictor of how much performance is reduced due to ambient speech in dependency of its intelligibility (Hongisto, 2005). Target values for the acoustic quality of open-plan offices were defined which account for the special importance of speech intelligibility (e.g. Virjonen et al., 2009). Fluctuation Strength, a hearing impression due to slow modulations of amplitude or frequency, has also been shown to predict the loss of individual task performance (Schlittmeier et al., 2012). The relevance of both variables is systematically explored with regard to cognitive performance and acoustic comfort. Based on these results target values are discussed.