Can haptic feedback reduce the intermittency of slow hand movement velocities?

The velocity traces of slow movements are notable for their intermittency: they reveal continuous fluctuations between acceleration and deceleration. We investigate whether this intermittency can be overcome by analyzing haptic feedback's contribution to any reduction in intermittency. We report an experiment in which blindfolded participants tracked the preferred index finger right- and leftward along raised lines of 8 cm or 16 cm extent at one of three driving frequencies, resulting in movements that ranged from the very slow (mean: 1 cm/s) to the moderately rapid (mean: 32 cm/s). The raised line was punctuated by orthogonal marker lines at 1 cm intervals. We reasoned that if haptic feedback generated by crossing these tangible lines can be used to modulate finger velocity, then requirements to always move “at as smooth and constant a velocity as possible” would be more achievable as practice proceeds. While we found that practice resulted in statistically significant reductions in intermittency, the absolute reductions were only modest. It appears more likely, therefore, that the intermittency in slow movements is not easily obviated by haptic feedback. The precise origin of this intermittency remains uncertain.