Perceiving the affordance of a tool requires the integration of several complementary relationships among actor, tool, and target. Highers order affordance structures are introduced to deal with these forms of complex action from an ecological-realist point of view. The complexity of the higher order affordance structure was used to predict the difficulty of perceiving the tool function. Predictions were tested in 3 experiments involving children between 9 months and 4 years old. In a classical tool use task dating back to W. Köhler, a desirable target was obtained by using a hook as a tool. The relative positions of the hook and the target were systematically varied to obtain structures differing in complexity. The observed difficulty of the task was found essentially in accordance with the theoretical complexity of the higher order affordance structures involved in perceiving the tool function.

This study investigated 4-, 6-, and 9-month-old infants' ability to perceive whether the width relation between a block and the opening of a box specified passing through or support. If infants could perceive which outcome was specified by the width relation, longer looking times would be expected for an outcome that violates this specification. Six-and 9-month-olds looked significantly longer when a block wider than a box opening passed through this opening and when a block with a width smaller than the opening seemed to become supported at the level of this opening. Results indicate that around 6 months of age, infants become able to perceive relations between objects that specify the outcomes of events.Events consisting of interacting objects are a daily part of infants' lives. Colliding, cutting, containing, and supporting are examples of such interactions. When objects interact, relations between properties of objects constrain the course and the outcome of such interactions. These relations, which we call dynamic object relations, are invariant properties of the event. That is, the course and outcome of an interaction covary with the dynamic relations between the objects involved. Perception of these relations allows for anticipation of the outcome of the event. The present study investigated infants' ability to perceive dynamic relations between objects.According to Gibsonian theory ( cf. J. J. Gibson, 1979), relations between objects can be perceived to the extent that information that specifies these relations is available for the perceptual system. For the visual system, information is contained within in variances in the flow of stimulation in the optic array (cf. J. J. Gibson, 1979). For example, a series of projective transformations in the visual field produces invariances that specify an object's shape, whereas its shape would remain ambiguous from any single projection (Ruff, 1982). Research on infant perception has shown that infants are able to perceive Margriet M. Sitskoorn and Ad W. Smitsman, University ofNijmegen,

Numerosity was defined as an invariant property of a collection of objects specifying its numerical size. Infants looked at displays of small numerosities that changed optic structure such that size was not tied to certain static or dynamic configurational properties of the display but remained constant across patterns of optic motion. The displayed figures moved continuously and at a constant speed. The trajectories were irregular and could produce occlusion of objects. The task used involved infant-controlled habituation of visual looking time. At ages 5 months, 8 months, and 13 months, 44 infants were tested for the numerosities 2, 3, and 4 in three randomly ordered sessions. The results demonstrated that infants from the age of at least 5 months perceive small numerosities. It appears that discrimination of units, rather than discrimination of characteristic patterns, underlies numerosity perception.

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001 use has evolved in humans at a scale that surpasses that of any T other species. It has reshaped and continues to reshape the environment in which children grow up, but it also alters the action potential of the human body. The potential of humans for perceiving and acting evolves with the evolution of implements for perceiving and acting. Both processes influence one another. This evolution concerns individuals and society as a whole, including the children who grow up in a particular society. In Western society implements are available for nearly every activity. These implements form an essential component of the skills and knowledge children obtain and should obtain with age. Tool use is the road for transmitting insights from older to younger generations and from experts to novices.The significant role tool use plays in the transmission of skills and knowledge among individuals makes the study of tool use highly relevant to anyone interested in development. Questions about how development takes place and what causes it warrant careful investigation of the fundamental role tool use plays in and among individuals. It is therefore remarkable that tool use was rarely studied by developmentalists. A major 301