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Many works have shown colorimetric additivity failures in colour-matching experiments. Thus, in the present work, using the colour-matching functions (CMF) of three real observers, we have conducted five experiments in isomeric and metameric matching. The stimuli matched, using two modified Donaldson colorimeters, were two achromatic, one blue, one orange and one green. Afterwards, we determined both the isomeric and the metameric discrimination ellipsoids for all the matches and for each observer. The results reflected differences in chromaticity and luminance with respect to the results of the CIE-1931 Standard Observer. When we compared our results (of each observer with his CMF) for the isomeric and metameric matches, we found that, according to the differential colour thresholds, the prediction was acceptable for chromaticity but not for luminance. The experimental results revealed the need to revise some aspects of the CIE-1931 Standard Observer.

The experimental determination of differential chromaticity thresholds from metameric matches show discrepancies in colorimetric prediction using the standard observers established by the CIE (Hita et al., J Opt Soc Am A 1986; 3: 1203-09; Jimenez del Barco et al., J Optics 17, 1986; 247-54). In this work we have determined whether the discrepancies of colorimetric prediction are contained in the differential color thresholds. To study the possibility of generalizing prior results to a wider range of experimental conditions we have carried out new experiments determining the differential color thresholds of an achromatic stimulus from metameric matches, using direct vision and a foveal field of 1.5 degrees . The results are expressed in terms of the color-matching functions of CIE-2 degrees standard observer, as well as those proposed by 2 degrees -Stiles and Burch and Nayatani et al. The discussion of the results is made taking into account different causes which may explain the failures of colorimetric prediction detected: rod intrusion, interactions of the responses of cones sensitive to short-wavelengths, errors and matching imprecision. Results show that the failures of colorimetric prediction obtained under our experimental conditions exceed the color differential threshold. These discrepancies increase with the relative difference of the S-cone excitation level for the matched stimuli.

The solution of the differential Eq. Delta g omega =rho 2 (where Delta g is the Laplace operator with respect to the metric g and rho is the scalar curvature) can provide some information in order to obtain an isotropic color space, i.e. a system in which the differential chromaticity thresholds are circles of different sizes. In three dimensions Weyls' theorem offers a geometric criterion to analyze new line elements from a practical viewpoint.

In order to study the mathematical reconstruction of diffuse spectral reflectance functions, the authors have generated an eigenvectors basis obtained after realizing a singular value analysis over Munsell chips, clustered by a hue classification.

Visual reaction time (VRT) has been measured for the detection of an achromatic stimulus on a CRT colour monitor. The adapting backgrounds were blue, cyan, green, yellow and red and the spatial and temporal presentation of the stimulus was computer-controlled. Comparisons of VRT have also been made between various retinal zones. The results are compared with those in the literature, obtained through conventional optical methods and are explained in terms of the opponent-colour theory.

New results of chromatic discrimination have been obtained for light transmitted by coloured filters and with a method which guarantees their reproducibility. These results are compared with others obtained for surface-colour presentation through the predictions of several colour-difference formulae: those recommended by CIE (CIELUV and CIELAB), the LABNHU formula, and the cdf-G, cdf-G* formulae, recently proposed by the authors' laboratory.

An experimental study of Weber's law is proposed using two different methods: by means of a bipartite field or by using the Masson rotating disc. Simple devices are shown with which university students can perform the experiments. Differences between the two methods are analysed in order to verify the above mentioned law.

The relationship between reaction time and visual latency relative to a fixed stimulus has been measured in haploscopic vision by means of the flicker effect produced by two stimuli of different luminance levels. The fields of foveal vision were of 50', the retinal illuminance was from 8 to 100 td and three observers were used. The results show in all cases that the motor component in the nervous system is not constant, and that the evolution of this factor according to the luminance of the stimulus conforms to a function of the same kind as Pieron's law.

Chromaticity differential thresholds for five colour stimuli and three observers have been measured from metameric matching. For each of the stimuli four differential thresholds were obtained, each of them corresponding to a different value of the degree of metamerism of the matching. Results obtained show failures in chromaticity predictions of the stimuli evaluated in the metameric matchings which are discussed with regard to the degree of metamerism, evaluated by different indexes proposed in the literature. These metamerism indexes lead to different results which are also discussed.

The visual reaction time has been analyzed as a function of two experimental parameters : size of the field and chromaticity of the stimulus. With regard to the first one, field sizes of 0.72, 1.25, 2, 3.5, 5 and 7.5 degrees were studied. The results show that reaction time decreases when the field size increases, also for values above the limits of Ricco's law. On the other hand, the reaction time was measured for chromatic stimuli with dominant wavelengths at 472, 500, 547, 571, 602 and 634 nm. In this case, no correlation between reaction time and chromaticity was found. The fact that these results were in agreement with those obtained for achromatic stimuli at the same luminance was analyzed in terms of color vision models, especially the opponent-colors theory.

Colour differential thresholds have been measured for three reference colours (red, green and blue) under five adaptation conditions (red, green, blue, achromatic and darkness) by a process of successive presentation. The resulting discrimination ellipsoids have been analysed both in terms of chromaticity and luminance. An overall worsening of discrimination capacity occurs under red-adaptation conditions, while all the adaptation conditions produce alterations in discrimination capacity along specific lines in the CIE1931 chromaticity diagram. The results conform to an opponent-colour model for colour vision.