How different effectors and action effects modulate the formation of separate motor memories

Abstract

Humans can operate a variety of modern tools, which are often associated with different visuomotor transformations. Studies investigating this ability have shown that separate motor memories can be acquired implicitly when different sensorimotor transformations are associated with distinct (intended) postures or explicitly when abstract contextual cues are leveraged by aiming strategies. It still remains unclear how different transformations are remembered implicitly when postures are similar. We investigated whether features of planning to manipulate a visual tool, such as its visual identity or the environmental effect intended by its use (i.e. action effect) would enable implicit learning of opposing visuomotor rotations. Results show that neither contextual cue led to distinct implicit motor memories, but that cues only affected implicit adaptation indirectly through generalization around explicit strategies. In contrast, a control experiment where participants practiced opposing transformations with different hands did result in contextualized aftereffects differing between hands across generalization targets. It appears that different (intended) body states are necessary for separate aftereffects to emerge, suggesting that the role of sensory prediction error-based adaptation may be limited to the recalibration of a body model, whereas establishing separate tool models may proceed along a different route.

Direct and indirect cues can enable dual-adaptation, but through different learning processes

“…Here we find that the adaptation induced by the visual separation of workspace is primarily implicit. In contrast, visuomotor adaptation in similar conditions was almost entirely explicit (11–13). While it is unclear why this difference exists, we propose a few different hypotheses.…”

“…One class of cues including visual workspace location enables dual-adaptation directly via state-dependent implicit learning. Another class of cues, including color cues, does not do so, though dual-adaptation with these cues may occur via different routes, such as explicit learning (13, 16, 83). Attempting to categorize cues previously found effective versus ineffective (or inconclusive), the emerging picture is that effective cues like separate locations can be considered directly representative of the dynamic or neural state, thus allocating adaptation to different regions in the state space (40, 84), whereas ineffective cues like arbitrary peripheral movement (31) or temporal sequence (4, 85) are not directly related to dynamic state.…”

“…One class of cues including visual workspace location enables dual-adaptation directly via state-dependent implicit learning. Another class of cues, including color cues, does not do so, though dualadaptation with these cues may occur via different routes, such as explicit learning (13,16,83).…”

“…Here, we hypothesize that the effectiveness of direct versus indirect cues may map onto implicit and explicit motor learning processes (45,72,80) , which have gained recent attention in visuomotor adaptation studies (28,74) . Indeed, recent work suggests that dual-adaptation to opposing cursor rotations can arise from implicit motor adaptation as well as explicit cognitive strategies, with implicit dual-adaptation enabled only by cues that can be considered immediately relevant to the dynamic state of the body, such as the use of separate hands or movement directions (27,67,69,77,82) . Given that explicit cognitive strategies have been suggested to contribute to force field learning under some circumstances (39,49,53,68,76) , differential contributions of explicit and implicit learnings under specific task conditions could then potentially explain the conflicting findings regarding the effectiveness of color cues outlined above.…”

“…These adjustments are associated with the formation and selection of appropriate motor memories (1). In order to investigate the formation and recall of these independent motor memories, dual-adaptation studies expose participants to opposing dynamics (2)(3)(4)(5)(6)(7)(8)(9) or opposing visuomotor transformations (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20).…”