Figure 153

The correct response (a) and incorrect responses (b-d) for the aeroplane problem. Reproduced from Mental models (edited by D.Gentner & A. Stevens) published by Lawrence Erlbaum Associates Inc., © 1983 Lawrence Erlbaum Associates Inc.

However, few subjects appear to think about the problem in this way. Only 40% of subjects drew diagrams with parabolic arcs and not all of these placed the plane above the ball as it hit the ground. The remaining 60% produced the other variants shown in Figure 15.3. According to McCloskey (1983) these responses arise from a simple model of motion that he calls impetus theory. In deference to classical physics, impetus theory proposes that (i) the act of setting an object in motion imparts to the object an internal force or "impetus" that serves to maintain the motion, and (ii) that a moving object's impetus gradually dissipates. McCloskey argued that this mental model was useful in predicting object motions in everyday life. However, the model is not true in general and leads to incorrect predictions in many contexts.

Many of these experiments were carried out on university-level subjects and so illustrate surprising misconceptions in educated people. More recently, several investigators have questioned the generality of these findings and their explanation. It now seems that the results found are, in part, due to the use of paper-and-pencil tests. Kaiser, Jonides, and Alexander (1986) asked subjects to reason about similar problems in familiar contexts and found that the majority of people produced correct predictions. Cooke and Breedin (1994) have also shown that aspects of the display and response instructions also affect the results found (but see Ranney, 1994). Furthermore, if subjects are asked to make judgements about object motions as part of a dynamic simulation of ongoing events, then they rarely make errors (see Kaiser, Proffitt, & Anderson,

1985). It has also been shown that when people have made erroneous predictions on a picture-based task, they frequently view simulations of their predictions as being anomalous. So, people are not as poor at predicting particle motions as the McCloskey studies suggested. However, it does appear that people are quite poor at judgements of more complex events, like the dynamics of wheels, under many testing contexts (see Kaiser, Proffitt, Whelan, & Hecht, 1992; Proffitt, Kaiser, & Whelan, 1990).

Yates et al. (1988) have challenged the theoretical basis of McCloskey's work. They have argued that people do not have abstract theories about motion, but rather rely on imagery-based, prototypical motion events to construct specific "enactments" of the motions of objects. This theory predicts that the more "realistic" or familiar the testing scenario, the greater the likelihood that such prototypes would be cued and used to generate appropriate predictions. Ironically, the conception of mental models is wide enough to include both intuitive theories or prototypic motion events as instances of mental models. In conclusion, it should be noted that whatever mental model we do use, may be entirely appropriate for making predictions about the motions of everyday objects, even though it may be at variance with the predictions of classical physics (see Hecht, 1996; Springer, 1990; Yates, 1990).

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