The cost of simplifying complex developmental phenomena: A new perspective on learning to walk

Researchers can study complex developmental phenomena with all the inherent noise and complexity or simplify behaviors to hone in on the essential aspects of a phenomenon. We used the development of walking as a model system to compare the costs and benefits of simplifying a complex, noisy behavior. Traditionally, researchers simplify infant walking by recording gait measures as infants take continuous, forward steps along straight paths. Here, we compared the traditional straight-path task with spontaneous walking during 20 minutes of free play in 97 infants (10.75–19.82 months of age). We recorded infants’ footfalls on an instrumented floor to calculate gait measures in the straight-path and free-play tasks. In addition, we scored videos for other critical aspects of spontaneous walking—steps per bout, shape of walking path, and step direction. Studying infant walking during free play incurred no cost compared with the straight-path task, but considerable benefits. Straight-path gait was highly correlated with spontaneous gait and both sets of measures improved with walking age, validating use of the straight-path task as an index of development. However, a large proportion of free-play bouts were too short to permit standard gait measures, and most bouts were curved with omnidirectional steps. The high prevalence of these “non-canonical” bouts was constant over development. We propose that focus on spontaneous walking, the phenomenon we ostensibly wish to explain, yields important insights into the problems infants solve while learning to walk. Other areas of developmental research may also benefit from retaining the complexity of complex phenomena.

研究者既可以在包含所有固有噪声与复杂性的状态下研究复杂的发育现象，也可以简化行为表现，聚焦于某一现象的核心本质。本研究以行走发育作为模型系统，对比简化复杂且带噪声的行为所带来的利弊。传统上，研究者通过记录婴儿沿直线路径连续向前行走时的步态参数（gait measures），来简化对婴儿行走行为的分析。本研究针对97名年龄介于10.75至19.82个月的婴儿，对比了传统直线路径任务与20分钟自由玩耍（free play）期间的自发行走（spontaneous walking）行为。我们通过测力地板（instrumented floor）记录婴儿的足部触地数据，以此计算直线路径任务与自由玩耍任务中的步态参数。此外，我们通过视频编码分析自发行走的其他关键指标：每轮行走的步数、行走路径形状以及步向。相较于直线路径任务，对自由玩耍中婴儿行走行为的研究并未增加额外工作量，却能带来显著收益。直线路径步态与自发步态（spontaneous gait）具有高度相关性，且两类步态参数均随行走发育年龄的增长而改善，这验证了直线路径任务可作为发育水平的评估指标。但值得注意的是，绝大多数自由玩耍的行走回合（bout）时长过短，无法获取标准步态参数，且多数行走回合呈曲线形态，步向为全向性。这类“非典型”行走回合的高发生率在整个发育阶段中保持稳定。我们认为，聚焦于我们本欲阐释的自发行走这一真实现象，能够为理解婴儿在学习行走过程中所面临的各类问题提供重要洞见。其他发育研究领域或许也能从保留复杂现象的原始复杂性中获益。