ON THE APPARENT HEAVINESS OF COLOURS

The apparent heaviness of colours EARLY this century, E. Bullough l showed that some combinations of colours, one above the other, are chosen as more `natural' than other combinations, which tend to look top heavy. Various methods of measuring the apparent weight of colours were subsequently devised: Bullough's preference method, tests in which the weight of coloured blocks was judged either visually or directly by hand • , and the `weighing' of half-inch circles of coloured paper at either end of a simulated balance arm with an adjustable fulcrum s . There was general agreement that red and blue were the heaviest colours, yellow the lightest. But no statistical evaluation was used in the earlier work; and as the colours were surface-illuminated, the effect of colour was easily confounded with that of brightness. In fact, most investigators considered that brightness was probably a crucial factor. In the present study, an adaptation of Monroe's procedures, the effects of colour and brightness were investigated separately using larger transilluminated stimuli, with brightness carefully controlled. Our results show that the effect is independent of brightness. Coloured circles, equal in subjective brightness, differ considerably in apparent weight, while achromatic stimuli which differ in brightness are not consistently different in weight. The display as seen by the subjects is shown in Fig. 1. Two circular holes, 10 cm in diameter with 30 cm between centres, were cut in a matt black screen. The holes were covered by ground glass, on to which the stimuli were back-projected by two slide projectors. Between the circles was a horizontal slit along which the subject could move a small luminous pointer to the `balance point', by turning a knob below the board. The display was positioned vertically in front of the subject in a dark cubicle, so that his eyes were about level with the stimuli and the control knob was within easy reach. Movements of the pointer were recorded on an oscilloscope screen, unseen by the subject. We tested the effects of colour in the absence of brightness differences, and the effects of brightness in the absence of colour differences. In order to simplify the procedure, each of the test stimuli was individually `weighed' against a white stimulus of constant brightness. For the colour experiment five colours were used: Red, Orange, Yellow, Green, and Blue (Kodak