Figure 9. Metameric matching of spectral stimuli.

In the right half of the field, the observer is presented with a yellow stimulus of 589 nm from an external monochromator (H20-VIS, Jobin-Ivon), and in the right half with red and green stimuli of 671 and 546 nm from the two internal holographic diffraction gratings of the visual colorimeter. The bandwidth of the three monochromatic stimuli was 10 nm. The stimuli are presented for more than 30 seconds in each exposure to ensure a stable level of photopigment bleaching. The luminance of the yellow stimulus is kept constant at 21 cd/m2. The luminance of the stimuli in the right half is regulated independently by adjusting the voltages of the power supplies to each lamp. This was done using the aforementioned digital power supplies and chromatic characterization system. The experiment was carried out in a dark room. Each observer adapted to the darkness for several minutes before beginning to match the stimuli. The stimuli were matched in hue and luminosity using a stepping method in which the observer was asked to express judgements on the relative hue and luminosity of the two halves of the field.

C. SAMPLE

The subjects were chosen randomly from teaching and administration staff and students of the Science Faculty, and from passers-by who were on the university campus. Initially, 65 people – 32 men and 33 women – were selected. Of these, two were rejected on the basis of a prior personal interview – a woman suffering the first stages of cataracts, and a man who had recently received medication that made his participation inadvisable. The remaining 63 were between 18 and 55 years old. The mean age of both populations was very similar – 31.5 years the men, 28.0 years the women (29.7 years for the overall sample), although in this experiment the age was not an important factor since the spectral stimuli used are far from the visible zone which is affected by the preretinal absorption as an individual ages [27].

The observers participated in the test with their vision compensated by eyeglasses or contact lenses when necessary, and having previously passed the Ishihara 38 plates edition and Farnsworth D-15 colour vision tests. The aim of the psychophysical test was simply to study the possible differences between the average male observer and the average female observer, without attempting to identify the various subgroups within the two populations which would have required a larger number of observers.