# Influence of TTS Systems Performance on Reaction Times in People with Aphasia
## 2 Materials and Methods
### Experimental Design
#### 2.1.2 Clinical Experiment Stimuli and Procedure  
The experiment was carried out in Spanish and was divided into two parts. The first part was a picture-point auditory comprehension test composed of 48 sentences. Each sentence was associated with four images: one target image and three foils. The foil images displayed the object, the location, or the action described in the target sentence. The sentences pertained to four different grammatical categories: (a) transitive, (b) transitive plus adjunct, (c) intransitive plus adjunct, and (d) complex subject + verb \"be\". Twelve sentences were assigned to every grammatical category.  
Moreover, the sentences were spoken by four different voices: [PERSON] TTS, Ogmios TTS, Bluemix TTS, and a digitised human voice (DHV). Each of the four output voices produced 12 sentences. The 48 sentences were presented in random order for each participant. At the beginning of the experiment, the participants went through a short calibration phase to check the audio volume, decide the speech rate to execute the experiment and check that they understood the researcher's instructions. The patients were asked which speech rate they preferred when carrying out the experiment: the original rate, mean (SD) = 210.86, 32.5 words per minute; 25% slower; or 50% slower. Four participants chose to perform the experiment with the 25% slower speech rate, while the remaining three chose the 50% slower rate. None of the patients selected the standard speech rate. The speech rate of the sentences was manipulated using Audacity(r) recording and editing software (Version 2.4.2, [[https://audacityteam.org](https://audacityteam.org)]([https://audacityteam.org](https://audacityteam.org)), retrieved on 29 November 2021). To slow down the speech rate without causing distortions, we used the \"change tempo\" option, as it does not affect pitch and frequency. After the calibration passage, the comprehension task started. The patients listened to a sentence while looking at the computer screen, where a four-image set appeared. Afterwards, the patients pointed at the computer screen to the image corresponding to the sentences they heard. A number from 1 to 4 was assigned to every image. Once the participant pointed at one of the four images on the screen, the researchers immediately pressed the number key corresponding to the picture chosen by the patient, and then the experiment automatically proceeded. The researcher pressed the number key on behalf of the participants because some could not press the keyboard keys by themselves. To keep the reaction time (RT) measurements controlled by the individual factors, we decided that the researcher would press the number keys for all participants. The answers and the reaction times in milliseconds were recorded.  
The experiment was carried out with a laptop and DMDX [10], a Windows-based software used primarily for language processing experiments, and designed to precisely record the time of the presentation of text, audio, graphical, and video material and record the measurements of RTs [10]. The control group received the experiment, designed using Google Forms, via email. The images, recording, and the general setup was the same as for the other participants, with the only difference being the software used. Since Google Forms does not allow the collection of RTs, the control group was used only to compare the comprehension accuracy, which resulted in a ceiling effect.