Object permanence is the understanding that object continue to exist even when they cannot be seen, heard or touch. To investigate whether infants have objection permanence, Baillargeon, Spelke & Wasserman (1985) introduce a method call violation of expectation which can be used to test infants’ object permanence.

Violation expectation is a method which was focused on whether infants’ understand the principle of that a solid object cannot move through the space which is occupied by the other solid object. To test the understanding of this principle of infants, Baillargeon, Spelke & Wasserman used a situation involving a visible and occluded object. If infants were surprised when the visible object pass through the space which is occupied by the occluded object, it would mean that infants have some kind of knowledge about the existence and location of the occluded object and it also provided evidence that suggest they have object permanence.

In the experiment, authors used a box which was placed behind a wooden screen. At first, the screen lay flat and the box was clearly visible. Then the box started to raise, in the manner of drawbridge and hidden the box from view. Infants were shown two different events. One is possible event and the other is impossible. In the possible event, the box moved until it touched the box and then returned to the initial position. In the impossible event, the screen passed through the space which was occupied by the box as if it was nothing there. Then the screen completed a 180 degree arc so the box behind the screen was fully visible. After that, the screen returned to its initial position, revealing the box standing intact in the same location as before. To adults, the possible event is consistent with the solidity principle: the screen stop when it touches the box. However, in the impossible event, in contrast, violates the principle: the screen show free to move through the solid box.

In the experiment, authors also used a technique called habituation paradigm. Habituation is a psychological process in humans in which there is a decrease in both psychological and behavioral response to a stimulus after repeated exposure to that stimulus over a period of time, in the other word, they get bored. Before showing the test events to infants, infants were shown the screen moving back and forth through a 180-degree arc, with no box present until they reached habituation. After, infants were shown the possible and impossible event. Authors suggest a reason for doing this. They said if infants understood that the box continued to exist, in its same location, after it was occluded by the screen, and the screen could not move through the space occupied by the box, then they should think the impossible event to be novel and surprising. Base on the commonly-held assumption which suggests that infants will play more attention to the novel things. So they predicted that infants would look longer at the impossible than the possible event. However, the movement in the impossible event and habituation is the same; so, they also predicted than infant would look longer in the possible event because infants may perceive shorter screen movement was more interesting. To test the possibility that infants would perceive 120 degree movement was more interesting than 180 degree, the authors also set up a control experiment.

In the experiment, authors used two identical alleys containing identical screens and separated by a mirror to set up their event environment. The mirror divided the box to form a front alley and side alley. Both alleys had placed a wooden screen. There are also a wooden box but only placed in the front alleys. Only one alley was visible at any one time. During the experiment, each infant was sat on a parent’s lap in front of the opening end of the front alley. The parent has worn a glasses to prevent their vision and have been instructed not to prevent the interaction to the infant when the experiment was in process. The infant’s looking behaviour was monitored by two observers and the observers could not see the test events and also haven’t told the order which event was presenting. Inter-observer agreement for each infant was calculated on the basis of the number of seconds for which observer agreed on the direction of the infant’s gaze, out of the total number of seconds the habituation and test lasted. Agreement was calculated for 18 of the infants. The looking time of the primary observer were also recorded on a clock. By monitoring this clock, the recorder was able to notice the ending of each trial and to determine when the habituation criterion was met. Habituation event was shown repeatedly to the infant following an infant-control procedure. Each habituation event ended when the infant look away from the event for 2 seconds after looking at it for 4 seconds, or when the infant looked at the event for 120 seconds. Habituation event lasted until infant met the criteria above. After the habituation, the box was placed in to the front alley. During the trials, possible and impossible event was shown to the infant. Infants were given 3 pairs of these trails. Eleven infants were shown the impossible event and ten were shown the possible event. In the control experiment, as in the principal experiment, infants were given the habituation trail until they met the habituation criterion. After this, infants were given 3 pairs of test trails, with the 180 and 120 degree events. Twelve infants saw the 180 degree and ten saw the 120 degree.

In the principal experiment, authors found that infants showed a strong preference for the impossible over the possible event. The mean looking time of impossible event was obviously higher than the possible event. On the other hand, in the control experiment, infants showed no overall preference between the 180 and 120 degree movement event. In this experiment, authors used the SAS GLM procedure the analysis the result.

From the results of these experiments, these provide evidence that infants in the principal experiment looking longer at the impossible event than the possible not because they preferred the 180 degree screen movement, but because infants expected the screen would stop when it touch the occluded box and were surprised when it failed to do it. This result suggested that 5 months old infants understand that an object continues to exist when occluded. Also this result challenge Piaget’s theory which suggested that infants would not develop object permanence until they were about 9 months old. However, like Piajet, authors believe that a notion of object is not an isolated conceptual knowledge but an inseparable aspect of the infants’ knowledge of how objects behave in time and space. The experiment also provide evidence that infants understand object continue to exist when occlude and object can move only through space not occupied by other object.