# Influence of TTS Systems Performance on Reaction Times in People with Aphasia
## 4 Discussion and Conclusions  
This study aimed to answer the following research questions: (i) Are the significant results in reaction times in Ogmios TTS caused by one or more acoustic voice characteristics? (ii) If so, which one? After conducting a system-level automatic assessment of the intelligibility and naturalness, the sample voices were analysed using jitter and shimmer parameters. Ogmios, in general, performed worse than the other voices in these measurements; therefore, there are indeed acoustic voice characteristics that contributed to the longer RTs in Ogmios: intelligibility, jitter, and shimmer. The exception was with the naturalness measure in relation to Festival TTS. However, this result was expected due to the better naturalness usually recognised in the statistical TTS (Festival TTS). To conclude, when considering a TTS for PWA and acquired reading impairments, it should be kept in mind that there is no one-fits-all solution. From our experiment, it appeared that for the Spanish language, the concatenative speech synthesis available is not suitable for the target population considered. These results are not generalisable to all concatenative speech systems for every language, and we realise it is TTS-specific. However, our results would suggest that an initial analysis of jitter, shimmer, and WER and TER intelligibility measures could give initial information about whether a synthetic voice could be used with PWA with acquired reading impairments. Nonetheless, repeating the experiment with another TTS for another language with a larger sample size could complete the results gathered in this analysis. For further investigations, the results obtained from the acoustic analysis and automatic investigation of intelligibility and naturalness could be paired and further investigated based on [PERSON] and [PERSON]'s [28] results. [PERSON] and [PERSON] [28] reported that in a noisy environment, neural network TTS systems (such as Bluemix in the current study) have lower intelligibility in a healthy population than concatenative systems. This is due to the fact that neural networks have more coarticulated and human-like speech than concate  
Figure 2: Box plot illustrating the RT distribution of the single items per participant, divided by the four voices. The circles correspond to outliers and the asterisk to extreme outliers. native systems, which have a more hyper articulated voice. As a result, the concatenative system is more understandable than neural networks in a noisy, competing environment. A further extension of the current study could investigate which acoustic characteristics are not detrimental for PWA and acquired reading impairments in a functional, realistic situation such as a noisy environment and do not cause longer RTs. Conceptualization, G.C. ([PERSON]), A.P.-L. and M.F. ; methodology, G.C. ([PERSON]), I.v.d.M., A.P.-L. and G.C. ([PERSON]); software, A.P.-L. and G.C. ([PERSON]); validation, M.F. ; formal analysis, A.P.-L., G.C. ([PERSON]) and G.C. ; investigation, G.C. ([PERSON]), A.P.-L. and G.C. ([PERSON]); resources, G.C. ([PERSON]), A.P.-L. and G.C. ([PERSON]); data curation, A.P.-L., G.C. ([PERSON]) and G.C. ([PERSON]); writing--original draft preparation, G.C. ([PERSON]), A.P.-L. and G.C. ([PERSON]); writing--review and editing, G.C. ([PERSON]), A.P.-L. and M.F. ; visualization, G.C. ([PERSON]); supervision, M.F. ; project administration, M.F. and I.v.d.M. All authors have read and agreed to the published version of the manuscript. The last author has been funded by the Agencia Estatal de Investigacion (AEI), Ministerio de Ciencia, Innovacion y Universidades and the Fondo Social Europeo (FSE) under grant RYC-2015-17239 (AEI/FSE, UE). The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Committee for Ethical Review of Projects (CIREP) of Universitat Pompeu Fabra (Approval Nr. 0118, 06.06.2019).