Earlier quoted context omitted.
From the article: > Yet we know that language can also be present in the absence of sound, when we read... or when we use words while thinking — in technical terms, when we engage in endophasic activity. > This simple fact immediately raises the following crucial question: What happens to the electric waves in our brain when we generate a linguistic expression without emitting any sound? "Endophasic activity" is our…
I think you misinterpreted the use of "endophasic activity" here, it just means that the speech is not real, that it is inner, or the brain not producing any real efferent output, just internal-bounded output. So, the study considers what happens when using linguistic thought without uttering words (aka inner speech), but it does not investigate the properties of the mind of people who do not experience inner speech.…
> Being or pertaining to endophasia (internal, unvocalized speech).
I only mentioned it so people didn't have to look it up like I had to; I don't think our interpretation differs.
I quoted the first couple of sentences from the last three paragraphs of the article. Those paragraphs emphasize the exciting questions raised by this small study, including the important question you raised.
To be fair I only read the article and I didn't search for the study but I look forward to reading the book:
> This article is adapted from Andrea Moro’s book “Impossible Languages.”