Pop-out of orientation but no pop-out of motion at isoluminance

Line textures in which one line was orthogonally oriented to the rest were briefly presented at various colour and luminance contrasts to the background. Subjects were able to detect the single line element pre-attentively even when the texture pattern was defined only by colour, indicating that "pop-out" of orientation is achieved at isoluminance. To exclude the possibility that this result was caused by luminance artefacts, especially by chromatic aberration, we carried out two control experiments. First, we showed that subjects could not detect a single moving line in a stationary texture under comparable conditions. Secondly, we repeated the experiments with a deuteranope who was unable to detect the differently oriented target under conditions under which the normal subject still could see it.