# Intelligibility and Listening Effort of Spanish Oesophageal Speech +
## 5 Discussion  
In Experiment 1, we were able to show that speaker type (OS or HS) had an effect on both LE and WER. OS speakers had poorer intelligibility compared to HS speakers and also a higher LE. The correlation between LE and WER suggests that more effort was reported as the intelligibility of the speaker worsened. Therefore, a drop in intelligibility caused an increase of LE. A further step in this direction would be to know what aspects of OS contribute to more LE: Its spectral characteristics, lack of fundamental frequency, or poor rhythm in speech, or a combination of these.  
Our findings about the effect of familiarity with the listener on intelligibility are in a similar vein to a study investigating the experience of the listener (speech expert vs. novice) on OS intelligibility [8]. However, in this study we were more interested in investigating the experience that comes from constant exposure as family members, close friends, and caretakers. We found that indeed the intelligibility scores were similar for familiar and unfamiliar listeners. However, interestingly, familiar listeners reported less LE. So LE was able to provide more information about listening to OS.  
As far as ASR is concerned, we found that ASR WER scores were higher for OS compared to HS. We compared WERs from our ASR system with HSR WERs. ASR WERs were higher compared to HSR WERs, but it could be because our ASR system was based on a unigram language model and focused only on acoustic models. The reason to choose such an ASR was to evaluate the drop in intelligibility owing to acoustic degradations, which is the case for OS.  
In Experiment 2, the goal was to measure LE when listening to OS and HS with similar intelligibility scores taken from Experiment 1. Although WER data in Experiment 2 indicate a higher intelligibility for HS than OS, the overall intelligibility for both OS and HS can be considered to be very high. Despite this  
Figure 4: WER and LE for oesophageal (OF1) and healthy (HF1) speakers. Error bars show 95% confidence intervals.  
high intelligibility for both speaker types, we observed a considerable gap in LE, and this suggests that LE is a relevant dimension to be considered in OS evaluation.  
The negative correlation of the digit span scores with WER suggests that participants with a poorer working memory (denoted by lower digit span scores) made more errors in recognition. This is understandable, as the ability to hold more information helps in correctly recalling and repeating the stimuli. The correlation with Flanker effect was not significant, suggesting that, in this case, selective inhibition plays a minor role to explain differences in LE. Flanker task is a measure of selective inhibition of distracting signals, such as noise added to the signals or signals with distracting speakers. However, the distraction in our stimuli are not of that nature. It is more in the form of undesired pauses and swallowing sounds that appear within and between words in the OS signal. The increase in LE was observed likely due to poorer quality of speech, rather than due to interfering information that has to be suppressed as is the case in noisy environments. On the whole, we cannot tell from these results alone whether better cognitive abilities mean better performance (low LE and low WER) in OS speech perception. Future studies using different cognitive test batteries are necessary to help us answer that question better.  
Finally, the familiarity effect on LE, as reported in Experiment 1, could mean that OS speakers might find it easier communicating with family and close friends as opposed to others. Although this was not investigated in this study, it would be interesting to know at what level of familiarisation does this effect show and also whether there is a ceiling effect to this familiarisation. That is, is there a point where, due to familiarity, they find OS as effortful as HS?