Physiological and psychological evaluation for visual display colour readability: a visual evoked potential study and a subjective evaluation study

This study was conducted, by subjective and objective evaluation, to clarify the complex relationships among VDT (visual display terminal) display colour readability and the related physical and physiological factors. Readability was defined as participants being able to read sentences easily on a VDT screen irrespective of their meanings. In the subjective evaluation, paired comparison tests and a colour impression test using the semantic differential (SD) method with factor analysis were carried out for 30 colour stimuli with different dominant wavelengths and stimulus purity values. The former test yielded identification of the most readable stimulus purity, which was in the range of 0.2 to 0.55 for any dominant wavelength. From the latter test, a 'conspicuousness factor' and a 'comfort factor' were extracted for evaluating readability. In the objective evaluation, three kinds of dominant wavelengths and three levels of stimulus purity were used. This evaluation showed that P100 peak latencies of colour-VEPs (visual evoked potentials) evoked by the subjectively optimal stimulus purity colours fully displayed on the screen were significantly shorter than those evoked by any other stimulus purity colours. Moreover, VEP P100 peak latencies evoked by the text colours that had the most readable stimulus purities were also shorter than those evoked by any other stimulus purity colours. Consequently, it was concluded that the optimum VDT display colour was that which had the most readable stimulus purity for each dominant wavelength, and that colour-VEP peak latency could serve as an indicator for quantification of VDT display colour readability.