The organization of exploratory behaviors in infant locomotor planning

Abstract

How do infants plan and guide locomotion under challenging conditions? This experiment investigated the real-time process of visual and haptic exploration in 14-month-old infants as they decided whether and how to walk over challenging terrain - a series of bridges varying in width. Infants' direction of gaze was recorded with a head-mounted eye tracker and their haptic exploration and locomotor actions were captured on video. Infants' exploration was an organized, efficient sequence of visual, haptic, and locomotor behaviors. They used visual exploration from a distance as an initial assessment on nearly every bridge. Visual information subsequently prompted gait modifications while approaching narrow bridges and haptic exploration at the edge of the bridge. Results confirm predictions about the sequential, ramping-up process of exploration and the distinct roles of vision and touch. Exploration, however, was not a guarantee of adaptive decisions. With walking experience, exploratory behaviors became increasingly efficient and infants were better able to interpret the resulting perceptual information in terms of whether it was safe to walk.

Figure 1

(A) Infant wearing head-mounted eye tracker. (B) Bridge apparatus. Parents stood at the far end and encouraged infants to cross, and an experimenter followed beside infants to ensure their safety. (C) Areas of interest (AOIs) for frame-by-frame coding of gaze data. (D) Exemplar data from a trial on a 30-cm bridge. Each shade of gray in the top bar represents a different 15-cm section of the starting platform, with the black bar indicating time with the infant's feet past the platform edge.

Figure 2

Measures of looking and touching at each bridge width. (A) Average accumulated duration of looking at each AOI and touching the bridge. Overall height of the stacked bars represents the total time with valid gaze data. (B) Average proportion of trials in which infants looked at the bridge (white circles) and touched the bridge (gray squares). Error bars denote standard errors.

Figure 3

Infants' location on the starting platform. (A) Average accumulated time spent in each 15-cm section of the platform, pooled over all trials. (B) Average accumulated time spent in each third of the platform, for trials at each bridge width. The close section contains locations less than 45 cm from the edge; the middle section contains locations 45-90 cm from the edge, and the far section contains locations more than 90 cm from the edge. Overall height of stacked bars represents the total platform duration. Error bars denote standard errors.

Figure 4

Timing of exploration sequence components. (A) Latency from trial onset to first step. (B) Latency from trial onset to first look at the bridge. (C) Latency from trial onset to first touch. (D) Lag between first step and first look. Positive values indicate that the infant stepped before looking; negative values indicate that the infant looked before stepping. (E) Lag between first look and first touch. Positive values indicate that the infant looked before touching; negative values indicate that the infant touched before looking.

Figure 5

Properties of infants' gait before the first look (gray squares) and after the first look (white circles) at each bridge width. (A) Average walking speed (distance covered / time). (B) Average step length (distance covered / number of steps). Error bars denote standard errors.

Figure 6

(A) Average proportion of trials at each bridge width in which infants succeeded (dark green bars), failed (light green bars), or refused (gray bars). (B) Average accumulated duration of looking at each AOI while crossing the bridge (successful trials only). Error bars denote standard errors.

Figure 7

Relations with walking experience. (A) Relation between walking experience and the proportion of trials in which infants looked at the bridge. (B) Relation between walking experience and the proportion of trials on narrow (6-, 14-, and 22-cm) bridges in which infants touched the bridge. (C) Relation between walking experience and the proportion of trials on wide (30-, 38-, and 60-cm) bridges in which infants touched the bridge. (D) Relation between walking experience and the proportion of trials in which infants fell. (E) Distribution of walking experience and two experience groups. (F) Average proportion of trials at each bridge width in which inexperienced (white circles) and experienced (gray squares) infants touched the bridge. Error bars denote standard errors.