Development and evaluation of a linguistically and audiologically controlled sentence intelligibility test

To allow for a systematic variation of linguistic complexity of sentences while acoustically controlling for intelligibility of sentence fragments, a German corpus, Oldenburg linguistically and audiologically controlled sentences (OLACS), was designed, implemented, and evaluated. Sentences were controlled for plausibility with a questionnaire survey. Verification of the speech material was performed in three listening conditions (quiet, stationary, and fluctuating noise) by collecting speech reception thresholds (SRTs) and response latencies as well as individual cognitive measures for 20 young listeners with normal hearing. Consistent differences in response latencies across sentence types verified the effect of linguistic complexity on processing speed. The addition of noise decreased response latencies, giving evidence for different response strategies for measurements in noise. Linguistic complexity had a significant effect on SRT. In fluctuating noise, this effect was more pronounced, indicating that fluctuating noise correlates with stronger cognitive contributions. SRTs in quiet correlated with hearing thresholds, whereas cognitive measures explained up to 40% of the variance in SRTs in noise. In conclusion, OLACS appears to be a suitable tool for assessing the interaction between aspects of speech understanding (including cognitive processing) and speech intelligibility in German.