Piaget's developmental stages of object concept in infancy has undoubtedly been at the root of numerous investigations, over the last twenty years or so. Some researchers have been concerned with trying to find alternative explanations for the basic Paigetian phenomena, especially the stage iv search errors. Whilst other researchers have used a number of new techniques, in order to test the reliability of his theory of object permanence. For instance a number of authors (e.g Bower 1974; Baillargeon,Spelke, & Wasserman 1985;), have suggested that the reason why young infants fail Piaget's search tasks before the age of 9 months, is because they lack the motor and coordination skills required to perform such actions. As a result of his own studies on the development of action in infants, Piaget (1952) acknowledged that an infants ability to act in a coordinated manner develops slowly over time, and that it's not until the infant reaches about 9 months of age that he/she can begin to combine these coordination skills to achieve their goal. The concern over young infants poor performance on Piaget's manual search tasks has prompted investigators to devise several different means of testing young infants understanding of occlusion events.
Bower (1974), reported that infants as young as 20 days old showed surprise, (measured by change in heart rate) when a stationary object failed to reappear after it had been occluded by a screen. An explanation of Bower's findings, is that infants possess a perceptual mechanism which detects violations in the way an object disappears. Such a rule is said to be governed by the laws of object permanence.
Baillargeon (1985) devised several tests which focused on the infants understanding that a solid object can not move through the space occupied by another solid object. Baillargeon suggested, that if the infant showed they were surprised when one solid object moved through the space occupied by the occluded solid object then this would indicate that they took into account the existence of the occluded object, demonstrating that they possessed the concept of objects being permanent.
To test this theory Baillargeon, Spelke, and Wasserman (1985) devised an experiment whereby 5 month old infants were habituated to a wooden screen that rotated back and forth in 180 degree arc. After habituation had occurred a wooden box was placed behind the screen, two test events were measured. The (possible event), where the screen was raised until it reached the occluded box, stopped, and then returned to its start position. In the (impossible event) the screen was raised until it reached the occluded box but then kept on going through 180 degree arc, as if the box no longer existed, after which the screen was rotated back to its original position, revealing the box still intact and standing in the same position. Baillargeon found that infants looked reliably longer at the impossible event, which he took to indicate that they were aware that objects continued to exist even when occluded. These results have further been confirmed by (e.g Baillargeon, DeVos, & Graber, 1989; Baillargeon & Graber 1988) who have all conducted experiments using the same principle as the above experiment, but different techniques.
It would appear from the evidence presented so far that infants seem to possess knowledge of object permanence at a far earlier age than Piaget had reported. Further studies were conducted to investigate whether infants can extend these beliefs about permanence to moving objects.
Bower (1974), along with several other colleagues (e.g Bower, Broughton & Moore 1971; Moore, Borton & Darby 1979) conducted a series of experiments using visual tracking techniques. These provided evidence to suggest that quantitative changes in tracking behaviour occur between the ages of 4 & 5 months. Bower asserts, younger infants seemed to be insensitive to the changes that occurred to the moving object whilst it was occluded behind a screen. Whereas, 5 month olds showed signs of surprise and looked back at the screen for the missing object. Bower et al (1974) interpreted these findings to mean that young infants understand permanence, but do not understand object dynamics. Therefore infants perceive a moving object and a stationary object as not being the same object.
The evidence presented so far seems to suggest that infants possess an understanding of object permanence from a very early age and that it may even be an innate perception. If this is the case why then do infants below the age of 8 months fail to search for a hidden object? Can it just be attributed to their lack of motor skills or could there be some other explanation as to why the infant does not search?
For instance, Bower and Wishart (1972), found most 6 month old infants would pick up a transparent cup, that was covering an object, but that none of the infants would pick up an opaque cup to retrieve the object that was hidden beneath it. Further more, on average it took infants twice as long to pick up the transparent cup, when it was covering an object than it did when it was not. From their results they suggest that infants of this age not only have a problem with inviable objects, but also their mental representation of an object becomes confused, or disturbed by the presence of another object, even when the object was visible.
Bower and Wishart (1972), conducted a study which produced further findings to support their view. They first tested a group of 5 month olds using Piaget's standard search task, and found that none of the infants could perform this task successfully. They then presented the infant with an object that was suspended on a piece of string in front of them and within their reach. After a while the lights in the room were extinguished, making the object invisible to the infant. Bower and Wishart reported, that all of the infants reached out to grasp the object despite it being hidden by the darkened room. They interpreted these findings to mean, infants do possess some understanding of object permanence, but that the methods used to investigate this concept can disrupt the infants perception of object permanence. Therefore, the reason why infants fail Piaget's search task is not because they fail to recall the objects existence but because the object loses its identity once it is combined with another object. In the case of Piaget's search task the object is transformed into something new when it is covered by the cloth.
Other studies have suggested that part of the problem can be associated to the infants inadequate motor skills, for example. Rader (1979), found that 5 month olds retrieved an object that was hidden beneath a small rigid cover but were unsuccessful when a larger cloth was used. Others have suggested that it is the manner in which the object is occluded,which plays a important factor in infants search behaviour. For example, Brown (1973) reported that 5 month olds successfully retrieved an object which was occluded by a screen, but did not search for an object when it was hidden beneath a cup. Dunst, Brooks and Doxsey (1982) reported that some types of search tasks are more difficult than others. For example, 6 to 8 month olds found it easier to search under a cover than they did to search in a box or behind a screen. Neilson (1977) suggests that the depth between the occluded object and the screen was an important factor in 6 month olds search behaviour. These results have suggested that failure to search for an object is not entirely due to the infants lack of motor coordination.
Willatts (1984) suggested that infants use different ways of searching depending on their age. From his own study Willatts concluded that 6 month olds used, what he termed a 'transitional' form of search behaviour, whereby they removed a cover without any intention of it revealing an hidden object. Whereas, 7 and 8 month olds indicated by their behaviour that removal of the cover was 'intentional', in order to retrieve the object hidden beneath it. Therefore, the type of 'transitional' behaviour described by Willatts could be accounted for in the stage iii behaviour described by Piaget, as a result of his own observations.
With regard to Piaget's stage iv error theory, there has been a mass of research conducted to try and find an alternative explanation as to why this phenomenon should occur. Bjork & Cummings (1984) suggest that the reason why infants keep returning to the A location on B trials is because they forget the precise location of the object, therefore they search for the object where they had previously found it. Diamond (1985), says that the stage iv search errors can not be attributed to either a lack of object concept or memory limitation but our as a result of poor neurological control which means they are unable to inhibit the conditioned response of reaching for A. The enormous amount of research conducted in this area of Piaget's theory has certainly cast doubt upon his own explanations for these stage iv errors.
Returning to the visual tracking studies. Bower and his associates proposed a completely different account from the Piagetian one. They concluded from their data that very young infants understand object permanence, only if the object is stationary, moving objects lose their identity and cease to exist. By the age of 6 months the infant has overcome this problem and perceive space in much the same way as adults do. This account suggests that infants are aware of object being permanent in space and time at a far earlier age than Piaget had suggested. However questions have been raised as to whether tracking data can be taken as evidence of an infants understanding of object permanence.
Moore and Meltzoff (1978), argue that infants need to obtain a notion of object identity before they acquire an understanding of object permanence. They proposed three higher levels of object identity which would account for Bower's findings. Firstly, infants in Bower's study who were under 6 months of age were said to be operating at the fist level, whereby, the object stays the same as long as it is stationary or moves in the same trajectory. Six month olds in Bower's study were said to be at the second level. At both of the above levels the infant is said to have the ability to identify objects, but still does not understand permanence. Therefore, it's not until they reach the third level where the object maintains its identity even when out of sight that they are said to have gained an understanding of object permanence.
Moore, Borton and Darby (1978), supported Moore and Meltzoff view and concluded from their own studies that infants do not gain a knowledge of object permanence until around 9 months of age. These finding give support to Piaget's own theory of the age at which understanding of object permanence emerges.
Many other researchers, such as (Goldberg 1976; Muller and Aslin 1978; and Meicler and Gratch 1980) have also suggested alternative accounts for Bowers findings, or have failed to replicate them. However, Wishart (1979) found that the more experience infants had of visual tracking trials the earlier they became competent at Piaget's search tasks. Suggesting a link between tracking behaviour and object permanence. Although Simoneau and Decarie (1979) failed to replicate these findings.
In view of the vast amount of research, which often appears to be very contradictory, some of the findings call into question certain aspects of Piaget's theory on the development of object permanence. Firstly, it has been suggested that Piaget may have overestimated the age at which an infant understands the permanence of an objects existence. The results from studies such as Bower's (1974) and also Baillargeon (1985), indicate that very young infants possess the concept of objects being permanent.
Secondly, many researchers were concerned by the methods Piaget used to measure an infants understanding of object permanence. Piaget claimed that infants below the age of 9 months failed to search for a hidden object because once it was out of sight it failed to exist. Many researchers claimed that the reason why infants failed to search before the age of 9 months was because they lacked the motor coordination skills to do so. However there seems sufficient evidence to rule out the possibility that failure to search before 9 months of age is not entirely due to a motor deficiency. On the other hand, considering the amount of conflicting views as to the possible cause of search failure, it is difficult to determine what factors contribute to successful search behaviour. This lack of consistency in infants search behaviour calls into question Piaget's own interpretation as to why infants did not search for a hidden object.
Finally, with respect to all the more recent evidence, Piaget's account for this particular aspect of infant behaviour seem to come out fairly unscathed; except that he probably underestimated the age at which an infants understand object permanence. That is however, only if you believe the notion that the infants knowledge of objects is constructed through his/her action. As soon as you begin to question this notion and consider perhaps that knowledge of permanence could be either innate or develop independently of action, then Piaget's account seems less adequate.
BIBLIOGRAPHY
Bremner, J.G. (1988) Infancy, Oxford Blackwell.
Baillargeon, R. Spelke, E.S & Wasserman, S. (1985) Object Permanence in 5 month old infants, Cognition, 20. pp191-208.
Baillargeon, R. (1986) Representing the existence and the location of hidden objects: Object permanence in six- and eight month old infants. Cognition, 23 pp 21-41.
Baillargeon, R. & DeVos, J. (1991) Object permanence in young infants: further evidence. Child Development, 62 pp 1227-1246.
Flavell, J.H. (1977) Cognitive Development. Englewwod Cliff, New Jersey.
Goldberg, S. (1976) Visual tracking and existence constancy in 5-month-old infants, Journal of Experimental Child Psychology, 22 pp 478-491.
Gratch, G. (1980) Responses to hidden persons and things by 5-,9- and 16-month-old infants in a visual tracking situation. Development Psychology, 18 pp 232-237.
Hood, B. & Willatts, P. (1986) Reaching in the dark to an object's remembered position: evidence for object permanence in 5- month-old infants, British Journal of Development Psychology, 4 pp 57-65.
Meicler, M. & Gratch, G. (1980) Do 5-month-olds show object conception in Piaget's sense? Infant Behavior & Development, 3 pp265-282.
Moore, M.K. Borton, R. & Darby, B.L. (1978) Visual tracking in young infants: evidence for object identity or object permanence? Journal of Experimental Child Psychology, 25. pp 183-198.
Muller, A.A. & Aslin, R.N. (1978) Visual tracking as an index of the object concept. Infant Behavior & Development, 1, pp309-319.
Slater, A. Morison, V. Somers, M. Matlock, A. Brown, E. & Taylor, D. (1990) Newborn and older infants' perception of partly occluded objects, Infants Behavior & Development, 13, pp33-49.