Changes in the 'conspicuity' of coloured objects caused by coloured lenses and/or pre-receptor filters in the eye

When the visual world surrounding us is imaged on the retina by the optics of the eye, all available information is encoded in this image as spatial and temporal variations in intensity and / or spectral content. Of particular interest are edges and boundaries which help define objects and areas of interest. The perceived 'conspicuity' of coloured objects, a quantity that relates directly to visual performance, is often determined by a combination of colour and luminance contrast signals1 2. When coloured objects are involved, the wavelength composition of the ambient light, the spectral absorption of any coloured filters external to the eye and / or pre-receptor filters within the eye can cause significant changes to luminance and colour contrast signals and hence to the visual appearance of the objects we see. The expression of variant cone-pigment genes in some subjects, large differences in L/M cone ratio or the absence of either L or M cones in red / green dichromats can produce large deviations in both luminance and colour contrast signals with inevitable consequences on visual performance3. The purpose of this study is to explore how changes in these parameters can enhance or diminish colour appearance and the conspicuity of coloured objects.