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.协同着陆需要预判撞击的时机与幅度，而这一过程依赖于感觉输入。为明晰以协同着陆能力见长的蔗蟾在跳跃过程中如何权衡视觉与前庭反馈的优先级，我们记录了5只受试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；这两种条件均旨在迫使动物以一侧前肢显著早于另一侧的方式完成着陆。其中一种实验条件下，着陆不对称源于空中翻滚——该翻滚由不稳定的起飞表面诱发。在此场景中，受试动物可借助视觉、前庭与本体感觉信息预判不对称着陆的发生。另一种实验条件下，受试动物起跳过程正常，但因着陆表面存在坡度而出现不对称着陆。该条件下，感觉反馈存在冲突，仅视觉反馈可准确预判不对称着陆场景。在翻滚实验组中，当所有类型的感觉反馈均可用于预判不对称着陆时，先着陆一侧前肢的着陆前肌肉活动与运动启动时间更早。然而，在倾斜着陆表面的实验组中，当仅可凭借视觉信息预判着陆不对称时，前肢准备过程并未出现此类不对称特征。上述实验数据表明，蔗蟾在协同着陆过程中，优先采用前庭或本体感觉反馈，而非视觉反馈。