Effect of viewing background on turbidity perception thresholds

摘要

Colloidal-size synthetic-polymer microspheres of three sizes (0.15, 0.31 and 0.70-mu m diameter) were each suspended in liquids of three different colors (clear, tan and dark brown) at a range of concentrations. The samples were presented to panelists in a viewing box. Visual-threshold determinations were made for each of the nine sample sets using the ascending method of limits (AMLs) and bright illumination (1,192 lux) with each of the three viewing backgrounds: black velvet, white cotton and white taffeta. The thresholds were much more similarly expressed as turbidimeter observations than as either weight or number concentration. With the black-velvet background, the thresholds ranged from 0.206 to 2.190 nephelometric turbidity units (NTU). With white cotton and white taffeta, they were considerably higher (P < 0.001), ranging from 1.97 to 41.00 and 2.97 to 34.40 NTU, respectively. This large difference appears to be a matter of contrast - scattered white light is much easier to perceive against a dark background.