Intuitive Physics: Across Tasks and Age

1. Introduction Methods Results References Conclusion Research Questions X ? Intuitive Physics: Across Tasks and Age Cedar Riener, Dennis Proffitt, Timothy Salthouse Department of Psychology University of Virginia Assessments Sample 1. Intuitive physics performance does reflect a unitary disposition. A number of tasks have been adopted to test people’s intuitive understanding of physics. These tasks have met with surprising results. Instead of demonstrating comprehension of basic physics, many studies in the field of intuitive physics have shown that a large percentage of adults display a systematic misunderstanding about the simple principles which govern physical events (Champagne, Klopfer, & Anderson, 1980; Caramazza, McCloskey, & Green, 1981). Much of the previous work in the field of intuitive physics has focused on two major approaches to explain these unexpected results. The first approach asserts that the systematic errors observed on intuitive physics tasks are due to systematically incorrect implicit theories of physics (McCloskey, 1983). Jean Piaget showed that young children were not simply failing at certain tasks, but instead showing systematic biases (Piaget & Inhelder, 1956). This led him to propose that children went through stages of theoretical development which reflected a non-incremental reorganization of knowledge. McCloskey observed that when adult participants were given the c-shaped tube task (see Intuitive Physics Items on right) they behaved as if they possessed something akin to medieval impetus theory (McCloskey & Kohl, 1983). Those participants that drew a curved path for a ball exiting a c-shaped tube seemed to hold a belief that the curvilinear “impetus” imparted to the ball by the tube gradually dissipates after the ball exits the tube. There are two sources of evidence against a theoretical explanation of intuitive physics performance. First of all, the surface characteristics of the problem can affect performance. For example, while many participants erroneously report that a ball exiting a c-shaped tube will continue to curve, very few also believe that water exiting a curved hose will also continue to curve (Kaiser, Jonides & Alexander, 1986). Secondly, while impetus beliefs may explain performance on the c-shaped tube task, they do not generalize well to other intuitive physics tasks. The beliefs that have been invoked to explain performance on intuitive physics tasks, while making precise claims and predictions, lack the scope that would allow them to explain performance across the range of intuitive physics tasks. The second approach has sought to analyze the specific problem or task and explain errors based on characteristics of each task. McAfee and Proffitt (1991) explained errors on the water level task by applying a universal perceptual bias. These authors pointed out that the water-level task is not necessarily a problem which tests one’s knowledge of whether water remains horizontal regardless of the orientation of the container. Performance on the water level task could reflect how one represents the problem; either based on an environment-centered coordinate frame or a container-centered coordinate frame. Representing the problem with a container-centered frame of reference induces a well-known perceptual bias; misperceiving the horizontal in the same direction of the container. While this explanation explains the errors in the water level task, it does not apply well to other tasks, such as the c-shaped tube problem. Proffit and Gilden (1989) explained errors in natural dynamics tasks as related to the complexity of the problem, not the principles tested. This approach is broad in its scope (it applies to many physical events) but it is limited in its precision, in that it makes a binary distinction between simple and complex problems. Our research is aimed at answering questions at a more fundamental level. If there are compelling explanations for individual physics tasks, but no generalized theory, do we still have reasons to believe that intuitive physics tasks belong to a single category? If we hope to choose between the accounts discussed above, it would be useful to know whether there were reliable individual differences in performance across the range of intuitive physics tasks. In search of evidence for or against the unity of intuitive physics task, our research addresses the question: Does intuitive physics performance reflect an underlying disposition? We also sought to elaborate on the nature of this hypothesized disposition by further investigation. We examined how this disposition relates to general mechanical reasoning ability. We used subjects from across the adult lifespan to test the persistence of intuitive physics ability. Finally, we compared our measure of intuitive physics ability to other well-known measures of cognitive ability to better understand the nature of this disposition. These results yield insights which are valuable not only to the study of intuitive physics, but also to the study of cognitive aging. b. Factor analysis a. Tests of Reliability • Intuitive Physics Items: • 5 pairs of standard intuitive physics tasks (see below) • Standardized battery of Mechanical Reasoning Items: • 6 items from the Woodcock Johnson Mechanical Reasoning subtest • Standardized Battery of Fluid Intelligence Items: • Average of the z-scores from the Woodcock Johnson Analysis-Synthesis and Wechsler Block Design • Standardized Battery of Crystallized Intelligence Items: • Average of the z-scores from the Wechsler Vocabulary subtest and the Woodcock Johnson Picture Vocabulary subtest • The intuitive physics items are strongly correlated with the mechanical reasoning items, suggesting that they reflect the same underlying ability. • Cronbach’s coefficient α = 0.74 • Nunnally (1978) sets criteria at 0.70 • 204 participants • Ages 20-91 • Broad cross section of healthy adults • only 7% in school • Mean years of education = 16 • Even if factors do exist, they are weak. • 5 factors with eigenvalues greater than 1. • Only the first factor accounts for more than 6% of variance (19.1%) • all five together only account for 36.2% of variance 2. This disposition is persistent across the adult lifespan. 3. Intuitive physics performance is strongly correlated with fluid intelligence. Intuitive Physics Items Pendulum Problem C- Shaped Tube Problem Water Level Problem Intuitive Physics Performance Intuitive Physics Performance The pendulum below is swinging from side to side. The string is cut when the pendulum reaches its highest point (indicated by the scissors). Draw the path of the pendulum bob as it falls to the ground. The c-shaped tube you see below is lying flat on a table (this is an aerial view). A ball is placed in one end and launched so that it proceeds through the tube and out the other side. Draw the path that the ball will take once it exits the tube, starting at the given point. On the left is a glass of water sitting on the table. On the right, the glass has been tilted. Assume that the glass and water are now stationery. Draw the line showing the top surface of the water, given that it ends at the indicated point. Fluid Intelligence Chronological Age The Paradox of Intuitive Physics and Aging Given that fluid intelligence decreases with age, and intuitive physics performance is highly correlated with fluid intelligence, one would expect that intuitive physics performance would also decrease with age. It does not. Archimedes Principle Problem Falling Object Problem Fluid Intelligence This airplane is carrying a canister of supplies as it flies over a field. The plane drops the canister. Draw the path that the canister will follow before it hits the ground. The picture on the left shows a styrofoam disc floating in a tub of water. A clay ball is attached to the top of the disc with glue. The water level on the tub is marked with an “X.” The disc and the ball are then removed from the tub and placed back into the tub, upside down (as shown). Where will the water level be relative to the case on the left? (above, the same, or below the X) (circle one) Chronological Age The performance of participants in our study offers compelling evidence that intuitive physics performance is indeed reflective of a general mechanical reasoning ability. Furthermore, this ability is stable across the adult lifespan, as well as highly correlated with measures of fluid cognitive ability. In asserting that intuitive physics performance is influenced by a mechanical reasoning ability, we seek to complement, rather than disprove, current theory approaches or individual problem explanations. The fact that individuals do differ in their ability to solve these intuitive physics problems does not preclude other reasons to explain errors on certain tasks. Future researchers can design intuitive physics studies knowing that a certain amount of the variance that they see in their performance data can be attributed to individual differences in a mechanical reasoning ability. By assessing this ability prior to administering the intuitive physics problems, this variance could be controlled for, allowing other patterns in the data to be more easily recognizable. Applying our findings to the two major approaches discussed in the introduction, the evidence for an underlying mechanical reasoning ability seems to lend support to the account discussed by Proffitt and Gilden (1989). Our evidence suggests an expansion on this account. Rather than splitting intuitive physics tasks between easy and hard categories along the lines of problem complexity, perhaps items can be placed on a continuum of difficulty. Just as certain people are more likely to get more intuitive physics problems wrong, there are certain problems which are harder than others. Finally, the paradox of intuitive physics and aging is important to the aging community. Despite its high level of correlation with fluid intelligence, intuitive physics ability seems to remain stable across the lifespan. This stability could indicate that rather than being considered a form of fluid intelligence, general mechanical reasoning ability is better conceived as a form of concrete knowledge, or crystallized intelligence. Mechanical Reasoning Items • Does intuitive physics performance reflect a unitary mechanical reasoning disposition? • Is this disposition persistent across the adult lifespan? • How is intuitive physics related to other cognitive abilities? The Mechanical Reasoning Items are made up of 6 multiple choice items which require mechanical reasoning using physical concepts such as center of mass, gravity, and collision dynamics. Fluid and Crystallized Intelligence Tests Fluid intelligence was measured by taking an average of the z-scores from the Woodcock Johnson Analysis-Synthesis and Wechsler Block Design subtests. These subtests provide an approximate measure of one’s facility with processing given information, regardless of experience or stored knowledge. Crystallized intelligence was measured by taking an average of the z-scores from the Woodcock Average of the z-scores from the Wechsler Vocabulary subtest and the Woodcock Johnson Picture Vocabulary subtest. These subtests provide an approximate measure of the level of stored knowledge that an individual has acquired by testing vocabulary and picture recognition. • Champagne, A. B., Klopfer, L. E. & Anderson, J. H. (1980). Factors influencing the learning of classical mechanics. American Journal of Physics. 48, 1074-1079 • Caramazza, A., McCloskey, M., & Green, B. (1981). Naive beliefs in "sophisticated" subjects: Misconceptions about trajectories of objects. Cognition, 9(2), 117-123. • McCloskey, M. (1983) Intuitive physics. Scientific American. 248(4), 122-130. • Piaget, J., & Inhelder, B. (1956). The child’s conception of space. London: Routledge and Kegan Paul. • McCloskey, M., & Kohl, D. (1983). Naive physics: The curvilinear impetus principle and its role in interactions with moving objects. Journal of Experimental Psychology: Learning, Memory, & Cognition, 9(1) 146-156. • Kaiser, M. K., Jonides, J., & Alexander, J. (1986). Intuitive reasoning about abstract and familiar physics problems. Memory & Cognition, 14(4), 308-312. • McAfee, E. A., & Proffitt, D. R. (1991). Understanding the surface orientation of liquids. Cognitive Psychology, 23(3) • Proffitt, D. R., & Gilden, D. L. (1989). Understanding natural dynamics. Journal of Experimental Psychology: Human Perception & Performance, 15(2), 384-393. * This research was supported by funds from the Virginia Aging Initiative directed by Timothy Salthouse