In most situations where people understand everything but speak of increased listening effort, the speech volume is higher than the volume of the surrounding sounds. Although a high level of individual speech intelligibility can be achieved, hearing impaired people in particular report that a great deal of effort is required to achieve this speech intelligibility. But how can this subjectively perceived so-called hearing effort be measured individually?
A new scaling method - "ACALES: Adaptive CAtegorical Listening Effort Scaling - has now been developed for laboratory measurements at the Hörzentrum Oldenburg.
ACALES is a measurement method in which the subjectively perceived listening Effort is evaluated using a scale (Figure 1). The 14-step scale contains eight labelled categories (from "effortless" to "extremely strenuous" and "noise only") and six intermediate categories.
During the measurement, the listener is presented with three sets of the Oldenburg sentence test in succession in a background noise. Sentences of the form name - verb - number - adjective - noun (e.g. Peter buys seven red knives) are used as language material. The sequence of words is a random combination of an inventory of 50 words.
The level of background noise remains constant during the measurement and the level of speech changes adaptively, based on the previous evaluation. By varying the ratio of speech volume to ambient noise volume - the so-called signal-to-noise ratio (SNR) - different listening situations are created.
In previous procedures, the SNR values to be tested had to be selected beforehand and, in the optimum case, would then cover the entire auditory effort range from "effortless" to "extremely strenuous". These pre-tests are not necessary with ACALES. As an adaptive measurement method, ACALES optimally determines the SNR values to be individually tested during the measurement.
In addition to differences in the perceived hearing effort of different people, changes caused by a hearing aid fitting and the influence of a fine adjustment can also be individually determined and demonstrated to the hearing aid user.
During the measurement, the speech level is changed adaptively and based on the previous assessment of the hearing effort, whereby an individual SNR range can be determined for each test person. The task of the subjects is to evaluate how strenuous it was to follow the speaker. For laboratory measurements the speech material as well as the background noise can be freely selected and adapted to any test situation. Adaptive scaling of listening effort is particularly sensitive in the test area where speech intelligibility measurements can no longer detect differences in speech intelligibility, i.e. in the area where everything can be understood, but effort is required to understand everything.
Krueger, M., Schulte, M., Brand, T., & Holube, I. (2017a). Development of an adaptive scaling method for subjective listening effort. The Journal of the Acoustical Society of America, 141(6), 4680-4693.
Krueger, M., Schulte, M., Zokoll, M. A., Wagener, K. C., Meis, M., Brand, T., & Holube, I. (2017b). Relation between listening effort and speech intelligibility in noise. American journal of audiology, 26(3S), 378-392.