Sensory feedback and coordinating asymmetrical landing in toads

Coordinated landing requires anticipating the timing and magnitude of impact, which in turn requires sensory input. To better understand how cane toads, well known for coordinated landing, prioritize visual versus vestibular feedback during hopping, we recorded forelimb joint angle patterns and electromyographic data from five animals hopping under two conditions that were designed to force animals to land with one forelimb well before the other. In one condition, landing asymmetry was due to mid-air rolling, created by an unstable takeoff surface. In this condition, visual, vestibular and proprioceptive information could be used to predict asymmetric landing. In the other, animals took off normally, but landed asymmetrically because of a sloped landing surface. In this condition, sensory feedback provided conflicting information, and only visual feedback could appropriately predict the asymmetrical landing. During the roll treatment, when all sensory feedback could be used to predict an asymmetrical landing, pre-landing forelimb muscle activity and movement began earlier in the limb that landed first. However, no such asymmetries in forelimb preparation were apparent during hops onto sloped landings when only visual information could be used to predict landing asymmetry. These data suggest that toads prioritize vestibular or proprioceptive information over visual feedback to coordinate landing.

协调着陆需要预判撞击的时机与强度，而这一过程依赖于感觉输入。为了明确以协调着陆能力著称的蔗蟾在跳跃过程中如何优先处理视觉与前庭反馈，我们记录了5只蔗蟾在两种实验条件下跳跃时的前肢关节角度模式与肌电图数据，这两种条件旨在迫使动物以一侧前肢先于另一侧着陆的方式落地。在第一种条件中，着陆不对称由不稳定的起飞平台导致的空中翻滚引起，此时视觉、前庭与本体感觉信息均可用于预判不对称着陆。在另一种条件下，动物正常起飞，但因着陆平台倾斜而出现不对称着陆，此时感觉反馈存在冲突，仅视觉反馈可准确预判不对称着陆。在翻滚处理组中，当所有感觉反馈均可用于预判不对称着陆时，先着陆侧前肢的着陆前肌肉活动与运动启动更早。但在仅依靠视觉信息预判不对称着陆的倾斜平台着陆实验中，前肢准备活动并未出现此类不对称差异。上述实验数据表明，蔗蟾在协调着陆时，会优先使用前庭或本体感觉反馈而非视觉反馈。