On the salience of the inducer's displacement in induced rotary movement

It has been reported that an annulus patterned with two equally-spaced radial lines elicits slower induced rotary movement than an annulus patterned with sixteen equally-spaced radial lines. This has been attributed to the quantity of inducing stimulation. However, the number of pattern elements also affects the time course of induced rotary movement: it can be intermittent with two-radii inducers, but persistent with sixteen-radii inducers. Displacement of a two-radii inducer may be more salient to the subject than displacement of a sixteen-radii inducer: from time to time the displacement of the former may come to dominate perception, suppressing induced movement. Hypotheses invoking quantity of stimulation and salience of inducer displacement were tested by way of inducers with different numbers and spacings of pattern elements. Subjects timed induced rotary movement (experiment 1) and a subsequent aftereffect (experiment 2). The results were consistent with both the quantity of stimulation (experiments 1 and 2) and the salience of inducer displacement (experiment 2) having an effect. This suggests that at least two mechanisms may be involved in induced rotary movement.