Figure 1.

Tactile length contraction (A–E) and time dilation (F) illusions. Actual stimulus sequences (plotted points) evoke illusory perceived sequences (positions on forearms in A–E; clock times in F). Colored arrows in panels A, B, E, and F indicate direction of perceptual effect (arrow at right) caused by adjustment to corresponding stimulus location or time (arrow at left). (A) Rabbit illusion [12]. The two intermediate taps, separated by short temporal interval (rapid movement), are perceptually displaced towards one another. (B) Classic tau effect [15], [16]. The more rapidly traversed of two equal distances is perceived as shorter. (C) Tau effect with two-arm comparison [17]. Stimulus parameters were adjusted to reach the point of subjective equality, at which the greater distance (faster movement) is perceived equal to the shorter distance (slower movement). (D) Perceptual merging [18]. At very rapid velocities, the perceived locations of the two taps merge to a single point. The velocity required to accomplish perceptual merging increases with tap separation. (E) Two-stimulus distance estimation [19]. When inter-stimulus distance is increased at fixed inter-stimulus time, perceived distance both underestimates, and grows with, actual distance. (F) Kappa effect [21]. When inter-stimulus distance is increased at fixed inter-stimulus time, perceived inter-stimulus time overestimates actual time. Stimulus parameters were adjusted to reach the point of subjective equality, at which perception dilates the temporal interval defined by the greater distance (faster movement) to equal the slightly longer temporal interval defined by the smaller distance (slower movement).