Mean speech effort (EFF), speech naturalness (NA), and stutterfree syllables per minute (SFSPM) for the persistent stuttering (PS) group (left) and the control group (right), with percent syllables stuttered (%SS) for the PS group only, for the five 1-min oral reading trials in each phase (A1-B-A2), for each of four fluency-inducing conditions. Note that on the NA and EFF ordinate axis “1 = highly natural sounding speech”(NA) and “1 = highly effortless speech”.