Kari S. Kretch

Cliff or step? Posture-specific learning at the edge of a drop-off.

Infants require locomotor experience to behave adaptively at a drop-off. However, different experimental paradigms (visual cliff and actual gaps and slopes) have generated conflicting findings regarding what infants learn and the specificity of their learning. An actual, adjustable drop-off apparatus was used to investigate whether learning to distinguish a step from a cliff transfers from crawling to walking. Experienced 12-month-old crawlers (n = 16) refused to crawl over risky drop-offs but novice 12-month-old walkers (n = 17) stepped repeatedly over the edge. Experienced 18-month-old walkers (n = 18) refused to walk over risky drop-offs but descended using alternative methods. These findings suggest that infants do not acquire generalized responses like fear or wariness of heights. Rather, infants learn to perceive affordances for the experienced action.

Understanding the development of motion processing by characterizing optic flow experienced by infants and their mothers

Understanding the development of mature motion processing may require knowledge about the statistics of the visual input that infants are exposed to, how these change across development, and how they influence the maturation of motion-sensitive brain networks. Here we develop a set of techniques to study the optic flow experienced by infants and mothers during locomotion as a first step toward a broader analysis of the statistics of the natural visual environment during development.

No bridge too high: Infants decide whether to cross based on the probability of falling not the severity of the potential fall

Do infants, like adults, consider both the probability of falling and the severity of a potential fall when deciding whether to cross a bridge? Crawling and walking infants were encouraged to cross bridges varying in width over a small drop-off, a large drop-off, or no drop-off. Bridge width affects the probability of falling, whereas drop-off height affects the severity of the potential fall. For both crawlers and walkers, decisions about crossing bridges depended only on the probability of falling: As bridge width decreased, attempts to cross decreased, and gait modifications and exploration increased, but behaviors did not differ between small and large drop-off conditions. Similarly, decisions about descent depended on the probability of falling: Infants backed or crawled into the small drop-off, but avoided the large drop-off. With no drop-off, infants ran straight across. Results indicate that experienced crawlers and walkers accurately perceive affordances for locomotion, but they do not yet consider the severity of a potential fall when making decisions for action.

Active vision in passive locomotion: Real-world free viewing in infants and adults

Visual exploration in infants and adults has been studied using two very different paradigms: free viewing of flat screen displays in desk-mounted eye-tracking studies and real-world visual guidance of action in head-mounted eye-tracking studies. To test whether classic findings from screen-based studies generalize to real-world visual exploration and to compare natural visual exploration in infants and adults, we tested observers in a new paradigm that combines critical aspects of both previous techniques: free viewing during real-world visual exploration. Mothers and their 9-month-old infants wore head-mounted eye trackers while mothers carried their infants in a forward-facing infant carrier through a series of indoor hallways. Demands for visual guidance of action were minimal in mothers and absent for infants, so both engaged in free viewing while moving through the environment. Similar to screen-based studies, during free viewing in the real world low-level saliency was related to gaze direction. In contrast to screen-based studies, only infants - not adults - were biased to look at people, participants of both ages did not show a classic center bias, and mothers and infants did not display high levels of inter-observer consistency. Results indicate that several aspects of visual exploration of a flat screen display do not generalize to visual exploration in the real world.

Fear of Heights in Infants

Based largely on the famous “visual cliff” paradigm, conventional wisdom is that crawling infants avoid crossing the brink of a dangerous drop-off because they are afraid of heights. However, recent research suggests that the conventional wisdom is wrong. Avoidance and fear are conflated, and there is no compelling evidence to support fear of heights in human infants. Infants avoid crawling or walking over an impossibly high drop-off because they perceive affordances for locomotion—the relations between their own bodies and skills and the relevant properties of the environment that make an action such as descent possible or impossible.