Through his work, Piaget enabled further research in this area and gave others the opportunity to conduct similar studies to correlate with his findings. However, his work has been criticized for being too ambitious and for overestimating the difference between the phases, while also underestimating the process of developmental transition between them. It assumes that cognitive development is strategic and set independently of environmental factors, but is unable to support this point with evidence. Another criticism is that of Piaget's sensorimotor stage theory, which has been challenged on the grounds that an eight-month-old infant can very well understand object permanence but is physically incapable of reaching and searching for it and has even lost interest in try to find it.