Timing of responses to gradual and abrupt visuo-proprioceptive cue conflict with and without feedback.

When people observe conflicting visual and proprioceptive cues about their static hand position, visuo-proprioceptive recalibration results: The proprioceptive estimate of hand position shifts toward the visual estimate, and vice versa. Recalibration also occurs during gradual or abrupt visuomotor adaptation, in response to both cue conflict and sensory prediction errors experienced as the hand reaches to a target. Here we asked whether creating a cue conflict gradually vs. abruptly, or providing error feedback, affects recalibration in a static hand. We examined participants' responses to a 70 mm conflict imposed by shifting the visual cue forward from the proprioceptive cue (static left hand). Participants pointed with their unseen right hand to indicate perceived bimodal and unimodal cue positions. Conflict was introduced gradually (groups 1 and 2) or abruptly (groups 3 and 4), with performance feedback present (groups 2 and 4) or absent (groups 1 and 3). For abrupt groups, most behavioral change occurred immediately after the conflict began. No-feedback groups (1 and 3) showed comparable magnitudes of overall recalibration, indicating that abrupt and gradual conflicts result in similar recalibration but with different timings. Proprioceptive recalibration occurred in the presence of error feedback (groups 2 and 4); however, recalibration was not increased by the addition of error-based processes. Control groups confirmed accurate performance on the pointing task despite the visual cue shift. These findings highlight the distinct timing of recalibration mechanisms for gradual versus abrupt cue conflicts and potential smaller contribution of error mechanisms for a cue conflict in a stationary hand.