Fitting objects into holes 

When we drop a letter in the mailbox we do it almost automatically, without reflecting on how the action is done. Since we have been exposed to similar situations before, we do not consider the task to be particularly tricky. Before performing the physical action, we form a plan of how to mentally rotate the letter on the way to the box, the intended goal. When our hand holding the letter finally arrives at the box, we do an always perfect insertion (Munakata 1998; Atkinson 2000; 2006). If we have a letter that is much too large for the slot, we do not even try to insert it. In our minds we have already compared the slot to the letter, deciding that the letter’s circumference is too large to fit in the slot. While adults insert objects into apertures without so much as reflecting, the difficulties and repeated failures young children face when they manipulate objects can be striking. Researchers have long proposed a mismatch between children’s and adults’ representations of objects (Piaget 1952). Looking at the matter more closely, the task of inserting an object into an aperture is not so easy after all. It requires processes that cause difficulties for adults as well as children that will be discussed below. 

 Although some animals use simple tools, the human is unique in utilizing complex tools to expand manipulation possibilities (Shmuelof and Zohary 2005). Inserting a letter into a mailbox, or doing other similar everyday activities, provides a good example of the sort of new situations human children are exposed to when acting on the environment that surrounds them. The ability to solve such problems reflects infants’ development of spatial perception and mechanical cognition. By encouraging children to insert objects into apertures in different ways, we are able to study their development of motor competence as well as their perceptual and cognitive capabilities. This achievement is the end point of several important developments that include motor competence, perception of the spatial relationship between object and aperture, mental rotation, anticipation of goal states, and an understanding of means-end relationships. These abilities are not independent of each other in a task like this and cannot be totally separated. Motor competence is expressed in actions, and actions rely on spatial perception and anticipations of goal states. 


The problem with fitting objects into holes


At the end of the first year, infants start to think about how different objects are related to one another (Hayashi and Matsuzawa 2003). They love to pile blocks, put lids on cans and insert objects into apertures. Through these activities, the child learns to plan actions that involve more than one item. The ability to solve such problems reflects the child’s spatial, perceptual and motor development. When children can imagine objects in different positions and orientations, we know that their ability to act improves drastically. Still, the underlying representational abilities impelling this development, and the cognitive problems children must overcome, are poorly understood. The present thesis aims to contribute to this understanding through studies of children’s developing abilities to fit blocks into apertures. 

Fitting experiments are more complicated than grasping experiments. To succeed with a grasping experiment the hand must pre-adjust to the physical aspects and orientation of the object, and then close around it (von Hofsten and Rönnqvist 1988; McCarty and Ashmead 1999; McCarty,

Clifton et al. 2001; Oztop, Bradley et al. 2004). In fitting objects into holes, the object must be used as an instrument on another object (Connolly and Dalgleish 1989; McCarty, Keen et al. 2001). In addition to perceiving and manipulating the object, one must know what the object shall be used for and how it will be used, that is, the affordance of the object (Gibson 1977). The goal of the action must be clear. In a box-aperture experiment, children must comprehend how the three-dimensional (3D) object is related to the two-dimensional (2D) aperture. Further, they must mentally rotate the object in an appropriate way so that it fits. This demands careful planning (CaseSmith 1995). At the age of about one, children begin to be interested in the problem of how to get an object into an aperture (Gesell and Thompson 1934; Bayley 1969; Hayashi and Matsuzawa 2003; Hayashi 2007). However, they do not yet know how to do it (Meyer 1940; Piaget and Inhelder 1956; McKenzie, Slater et al. 1993; McCarty, Clifton et al. 1999). Piaget and Inhelder (1956) claim that children do not develop an understanding of the relationship between objects until three years of age, but act more instinctively. If the children must choose between two objects, the problem is possibly even greater. Not only do they have to mentally rotate and predict the position of the object, but they must also exclude one object in favor of another.