A reminder about procedures needed to reliably produce perfect timesharing: comment on Lien, McCann, Ruthruff, and Proctor (2005).

M.-C. Lien, R. S. McCann, E. Ruthruff, and R. W. Proctor (2005) argued that simultaneous ideomotor-compatible choice tasks cannot be perfectly timeshared. Their conclusion is limited in generalizability for 2 reasons: (a) Their experiments did not include procedures that previous research has shown to be necessary for obtaining perfect timesharing (motivating subjects to perform the 2 tasks rapidly and simultaneously; homogeneous blocks of simultaneous stimuli for the 2 tasks), and (b) their experiments included a procedure that previous research has shown to interfere with perfect timesharing of simultaneous tasks (within-block variation of task interstimulus intervals). Also discussed here are problems in M.-C. Lien et al.'s (2005) analysis of slopes relating Task 2 latency to Task 1 latency and their advocacy of a central bottleneck theory that may not be disconfirmable.