# Intelligibility and Listening Effort of Spanish Oesophageal Speech +
Footnote †: _Applied_  
[PERSON]  
injected and is introduced into the oesophagus, after which it is expelled with control, thereby producing vibration [2]. This generation mechanism introduces acoustic artefacts and makes OS difficult and effortful to understand [3; 4], which greatly affects communication, social activities, and hence, quality of life [5]. Moreover, these less intelligible voices are not well received by machines that are operated by speech input. An increase in the popularity of devices with voice-based interaction means that machine intelligibility is gaining importance too. Therefore, we quantify intelligibility in both Human Speech Recognition (HSR) and Automatic Speech Recognition (ASR) contexts. We know that machine recognition, or ASR performance, is lower compared to HSR performance [6], although better ASR systems are being built increasingly, aiming towards humanlike recognition abilities. However, this is for HS and not for impaired speech, like OS. The difference in ASR-HSR intelligibility for OS and also HS is also something that we have investigated. Listening to OS is a challenging task, and it demands a lot of attention and effort. While intelligibility can reveal what percentage of the message has been correctly understood, it cannot quantify how much effort was required to understand the message. There is growing interest in research measuring these processing load aspects of speech as it gives another dimension for understanding challenges in speech perception in adverse listening conditions. Listening Effort (LE) has been defined as \"the mental exertion required to attend to, and understand, an auditory message\" [7]. Therefore, in this study, we have attempted to explore LE in addition to the ASR and HSR intelligibility measurements. The idea of intelligibility differences between experienced and inexperienced listeners of OS was explored in [8]. The findings were that OS was ranked similarly for intelligibility by both experienced and inexperienced listeners. This was intriguing, and led us to investigate the effect of familiarity on the intelligibility of OS. In addition, as we were collecting LE ratings too, we were interested in seeing if the same was observed for LE ratings, or if they would tell a different story. We consider friends, family (spouse, siblings, children), and caretakers of OS speakers as familiar listeners. This study contains two experiments. The first experiment was web-based, and was focused on getting preliminary intelligibility and LE metrics for our data. We investigated how intelligibility (both ASR and HSR) and LE differs for the two speech types (OS and HS) and the effect of familiarity. We also investigated to what extent intelligibility and LE are correlated. The second experiment (an extension of Experiment 1) was conducted in a laboratory setting, which allowed us better control of the experiment environment. The aim of this experiment was to find out if more LE is reported for OS even if the intelligibility of OS is close to HS. Additionally, in this experiment, we also investigated if the participants' performance in the speech perception tasks depended on their cognitive abilities. To sum up, our preliminary evidences from Experiment 1 are:  
* Word Error Rate (WER) is positively correlated with self-reported LE ratings. * HS is more intelligible and less effortful, compared to OS. Our hypotheses of Experiment 1 are:
* Listeners familiar with OS find it less effortful to process OS, compared to listeners that are not. * ASR performs worse for OS than for HS. Our hypotheses of Experiment 2 are:
* For the case that intelligibility of OS is similar to that of HS, there is still more effort in understanding OS. * Listeners with better cognitive abilities have better intelligibility scores and report lesser effort. We begin by describing some background on the research that has been conducted in both intelligibility and LE with a focus on OS.