I stutter when I read aloud alone. A little less, but I still stutter. And I stutter when I speak to Alexa and other non-human devices. Stuttering is a mix of neurological \*and\* psychological issues. A physical ailment triggers a prevalence of stuttering, this develops into psychological anxiety and social stresses that exacerbate the stutter. So, it's \*not\* purely psychological, the psychology is a big part of the stutter, but the stutter is initially caused by physical issues within our brains. This has been scientifically proven over and over. If you want to challenge that science, please feel free to conduct your experiments and publish your findings in scientific journals for peer review and, in this case, ridicule.