Sensorimotor adaptation maintains movement accuracy by counteracting perturbations
or miscalibrations. It can operate explicitly, by consciously adjusting motor plans to
correct errors, or implicitly, by automatically recalibrating sensorimotor mappings without
altering the motor plan. While explicit adaptation is known to reduce sensorimotor
confidence—the perceived likelihood of successful action—it is unclear whether implicit
adaptation similarly affects confidence in sensorimotor judgments or motor awareness
(knowledge of one’s own limb position). To investigate this, participants made reaching
movements to visual targets without seeing their hand. Cursor feedback followed an
“error-clamped” trajectory: its radial position matched the hand, but its angular direction
was fixed and independent of actual hand direction, a manipulation participants were
told to ignore. The clamp direction varied sinusoidally over trials (±10°; 12 cycles per
session). Participants reported confidence by adjusting the size of an arc centered on
the target or, in another task, centered on reported reach direction; larger arcs indicated
lower confidence. Points were awarded when the arc encompassed the true reach
direction, with fewer points for larger arcs, encouraging accurate and meaningful
confidence reports. Fourier analysis of reach and report time series revealed a strong
12-cycle component in both, demonstrating robust implicit adaptation and
corresponding changes in motor awareness. These findings indicate that although
implicit adaptation operates unconsciously, the resulting mismatch between motor plans
and proprioceptive signals can bias judgments of reach outcomes. However, confidence
judgments were not consistently affected, suggesting that sensorimotor confidence and
confidence in proprioceptive awareness may rely on partially distinct mechanisms.