Abstract
Treadmill running produces several locomotor aftereffects (e.g., Anstis, 1995) that seem to derive from the novel (un)coupling of perception and action (Durgin and Pelah, 1999; Rieser et al., 1994). We have recently demonstrated overshoot in closed-loop walking tasks following closed-eye treadmill running (Durgin et al., 2000). That is, Anstis's adaptation produces Rieser's aftereffect. Here we show (Expt 1) that Rieser's counter-adaptation can reduce Anstis' aftereffect. We also show (Expt 2) that hopping aftereffects are similarly modulated by vision. EXPT 1: Subjects attempted to run in place for 20 s (eyes closed) before and after three forms of adaptation. Inadvertent forward drift was measured. Adaptation consisted of 60 s of travelling on a cart pulled at 16 kmph along an outdoor road (C), jogging on a treadmill at 6.7 kmph (T), or both simultaneously (CT). Results: After running without optic flow (T), inadvertent drift during the running in place task (3.2 m) was greater than (CT) when optic flow information had been available (2.4 m), t(11) = 2.96, p < .05. However, there was also a difference between the unadapted pretest (1.8 m) and adaptation to passive (C) travel (1.4 m), t(11) = 2.34, p < .05. Vision and action both mattered. EXPT 2: Subjects attempted to hop in place for 20 s, on each leg, following two forms of adaptation. They were adapted to forward hopping for 30 s with eyes either open or closed. Results: As predicted, forward drift was greater following eyes closed (86 cm) than eyes open (58 cm) adaptation, F(1,9) = 5.46, p < .05. In both adaptation conditions, however, there was greater drift on the adapted leg (93 cm) than on the unadapted leg (50 cm), F(1, 9) = 10.6, p < . 01. There was no reliable interaction between the two factors, F(1,9) < 1. Conclusions: Both of these experiments indicate strong contributions of vision to locomotor recalibration. Other perceptual information (e.g., kinesthetic, vestibular) may be involved as well.
Supported by HHMI and a Swarthmore College Faculty Research Grant.