to activate the mobile. Perception is an ongoing, active process. Methodology Gibson used experimental procedures while also attempting to retain ecological validity by simulating important features of the child's natural environment. In keeping with the idea of affordances, Gibson tried to provide multimodal stimulation for infants in these experiments (multiple kinds of objects, faces, or surfaces, for example) and ways of obtaining feedback through movement and exploration. One of Gibson's well-known perceptual experiments involved the construction of a "visual cliff," simulating a real cliff. Gibson and Walk placed infants near the cliff and placed mothers on the other side of the cliff. They found that infants perceived depth and were unwilling to crawl over the cliff at approximately 6–7 months. Later experiments showed that 12-month-old infants had learned to use their mothers' facial expressions as signals of potential affordances. If mothers smiled, infants were more likely to crawl over the "dangerous" cliff, but if mothers made a frightened face, infants avoided the cliff. Criticism Gibson's theory has been criticized for its "unclear account of cognition". Gibson's theory pertains to direct perception and does not take into account that behaviors may involve indirect, interpretive cognition. Gibson's methodology involves an expensive and complicated experimental set up, which may prove cost- and time-prohibitive for many researchers. Finally, Gibson's research was almost exclusively confined to infants and very young children, so it is difficult to make generalizations throughout the lifespan. Current State of Gibsonian Theory Aside from her own writings, Gibson's work is rarely described as a theory of development. When Gibson's primary area of research, affordances, is referenced, the citations typically refer only to James Gibson. Gibson is credited with popularizing affordances in perceptual research. However, unlike Gibson, researchers have studied affordances in all age groups, including adults. Affordances have been applied to a range of innovative topics, from automobile driving to text messaging. However, the concept of affordances is usually used in isolation rather than being integrated into Gibson's ecological framework. Some researchers are even attempting to create their own theories of affordances instead of revising Gibson's theory to accommodate new findings. References Human development