Final answer:
The fifth substage of the sensorimotor stage, known as 'Tertiary Circular Reactions' from around 12-18 months of age, is where an infant begins to use trial and error to problem-solve. During this period, they experiment with new behavior to see the effects their actions produce.
Step-by-step explanation:
The sensorimotor stage is the first stage in Piaget's theory of cognitive development, wherein an infant learns about the world through their senses and motor behavior. This stage spans from birth to about 2 years old. Within this stage, there are several substages, including the trial and error problem-solving phase.
This occurs during the fifth substage, known as the 'Tertiary Circular Reactions' phase, which happens around 12-18 months of age.
During this period, infants begin to experiment with new behavior to see what effects their actions produce, effectively engaging in a primitive form of trial and error problem-solving.
Previously, younger infants do not demonstrate this level of problem-solving ability as indicated by their reactions to hidden objects.
For example, infants develop object permanence between 5 and 8 months old, where they understand that objects continue to exist even when out of sight.
As toddlers progress, they show more autonomy and tend to act more deliberately on their environment to get results. This increased complex behavior is a sign of cognitive milestones being reached, which includes the ability to engage in trial and error problem-solving.