Asia-Pacific Forum on Science Learning and Teaching, Volume 11, Issue 1, Foreword (Jun., 2010) John K. GILBERT The role of visual representations in the learning and teaching of science: An introduction Previous Contents Next

The scope of the concrete/material mode of representation

The major characteristic of this mode is that it retains the three dimensions of that which is being represented. A vast array of sub-modes or forms has come into existence. They can be separated into those than are derived by a simplification and highlighting of perceived aspects of the original macro representation, what Harré calls homomorphs, for example cross-sections of a the human body,  and those having different source, what Harré calls paramorphs, for example the ‘ball-and-stick’ representation form used in chemistry (Harre 1970).

The ball-and-stick representation uses spheres (the ‘balls’, often polystyrene) to depict atoms and ions, and thin slithers of wood (the ‘sticks’) to separate them so spatial distributions can be readily perceived. The scope of this form is determined by the sum of Hessé’s positive aspects: for the ‘balls’, their spherical shape and the availability of a range of sizes and colours with which to differentiate between entities; for the ‘sticks’, the angles between them  and their length, to  produce clear angular relationships. The negative aspects are of no representational value but, despite that, of equal importance: for the ‘balls’, their homogeneous nature, capacity for compression, possible solubility and flammability; for the ‘sticks’, their thickness. The only neutral aspect of the ‘balls’ is their rough surface, there are none for the ‘sticks’. The sum of these aspects constitutes the code of representation for the form (Gilbert 1993).

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