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.协调着陆需要预判碰撞的时机与强度，而这一过程依赖于感觉输入。为深入探究以协调着陆能力著称的蔗蟾（cane toads）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（electromyographic, EMG）数据——这两种条件均会迫使受试动物的一侧前肢远早于另一侧完成着陆。在第一种条件中，着陆不对称源于起飞平台不稳定导致的空中翻滚，此时视觉、前庭与本体感觉信息均可用于预判不对称着陆的发生。在第二种条件中，受试动物起跳姿态正常，但由于着陆坡面倾斜，着陆姿态呈现不对称。此时感觉反馈存在冲突，仅视觉反馈能够准确预判不对称着陆的情况。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，先着陆一侧前肢的着陆前肌肉活动与肢体运动启动更早。然而，在仅依靠视觉信息即可预判不对称着陆的坡面着陆实验中，前肢准备动作并未出现此类不对称性差异。上述实验结果表明，蔗蟾在协调着陆过程中，相较于视觉反馈，会优先处理前庭或本体感觉信息。