The main development during the sensorimotor stage is the understanding that objects exist and events occur in the world independently of one’s own actions (“the object concept”, or “object permanence”).
Object permanence means knowing that an object still exists, even if it is hidden. It requires the ability to form a mental representation (i.e. a schema) of the object.
For example, if you place a toy under a blanket, the child who has achieved object permanence knows it is there and can actively seek it. At the beginning of this stage, the child behaves as if the toy had simply disappeared.
The attainment of object permanence generally signals the transition from the sensorimotor stage to the preoperational stage of development.
Blanket and Ball Study
Aim: Piaget (1963) wanted to investigate at what age children acquire object permanence.
Method: Piaget hid a toy under a blanket, while the child was watching, and observed whether or not the child searched for the hidden toy.
Searching for the hidden toy was evidence of object permanence. Piaget assumed that the child could only search for a hidden toy if s/he had a mental representation of it.
Results: Piaget found that infants searched for the hidden toy when they were around 8-months-old.
Conclusion: Children around 8 months have object permanence because they can form a mental representation of the object in their minds.
Evaluation: Piaget assumed the results of his study occurred because the children under 8 months did not understand that the object still existed underneath the blanket (and therefore did not reach for it).
However, there are alternative reasons why a child may not search for an object rather than a lack of understanding of the situation.
The child could become distracted or lose interest in the object and therefore lack the motivation to search for it, or simply may not have the physical coordination to carry out the motor movements necessary for the retrieval of the object (Mehler & Dupoux, 1994).
The A-not-B Error
When presented with two possible locations, the A-not-B error occurs when infants search for a hidden toy at the incorrect location (Piaget, 1954).
The toy is repeatedly hidden at location A. After a short delay, infants are then allowed to reach for and retrieve the toy.
After a few trials, the toy is then clearly hidden in location B. After a short delay, they are then allowed to reach for the toy.
Infants 8 to 10 months of age consistently reach location A despite clearly seeing the toy hidden at location B.
There is evidence that object permanence occurs earlier than Piaget claimed. Bower and Wishart (1972) used a lab experiment to study infants between 1 – 4 months old.
Instead of using Piaget’s blanket technique, they waited for the infant to reach for an object, then turned out the lights so that the object was no longer visible. They then filmed the infant using an infrared camera. They found that the infant continued to reach for the object for up to 90 seconds after it became invisible.
Again, just like Piaget’s study, there are also criticisms of Bower’s “reaching in the dark” findings. Each child had up to 3 minutes to complete the task and reach for the object. Within this time period, it is plausible they may have successfully completed the task by accident.
For example, randomly reaching out and finding the object or even reaching out due to the distress of the lights going out (rather than reaching out with the intention of searching for an object).
Violation of Expectation Research
A further challenge to Piaget’s claims comes from a series of studies designed by Renee Baillargeon. She used a technique that has come to be known as the violation of expectation (VOE) paradigm.
It exploits the fact that infants tend to look for longer at things they have not encountered
In a VOE experiment, an infant is first introduced to a novel situation. They are repeatedly shown this stimulus until they indicate, by looking away, that it is no longer new to them. In Baillargeon et al.’s (1985, 1987) study, the habituation stimulus was a ‘drawbridge’ that moved through 180 degrees.
The infants are then shown two new stimuli, each variation on the habituation stimulus.
In Baillargeon’s experiments, one of these test stimuli is a possible event (i.e., one which could physically happen), and the other is an impossible event (i.e., one that could not physically happen in the way it appears).
In the ‘drawbridge’ study, a colored box was placed in the path of the drawbridge. In the possible event, the drawbridge stopped at the point where its path would be blocked by the box. In the impossible event, the drawbridge appeared to pass through the box and ended up lying flat, and the box apparently disappeared.
Baillargeon found that infants spent much longer looking at the impossible event. She concluded that this indicated surprise on the infants’ part and that the infants were surprised because they had expectations about the behavior of physical objects that the impossible event had violated.
In other words, the infants knew that the box still existed behind the drawbridge and, furthermore, that they knew that one solid object could not just pass through another. The infants in this study were five months old, at which Piaget would say that such knowledge is beyond them.
Baillargeon, R. (1987). Object permanence in 3½-and 4½-month-old infants . Developmental psychology, 23(5), 655.
Baillargeon, R., Spelke, E. S. & Wasserman, S. (1985). Object Permanence in Five-Month-Old Infants. Cognition, 20,
Bower, T. G. R., & Wishart, J. G. (1972). The effects of motor skill on object permanence. Cognition, 1, 165–172.
Mehler, J., & Dupoux, E. (1994). What Infants Know: The New Cognitive Science of Early Development. Blackwell Publishers.
Piaget, J. (1954). The construction of reality in the child. New York: Basic Books.
Piaget, J. (1963). The Psychology of Intelligence. Totowa, New Jersey: Littlefield Adams.