Figure 1

PSE/POE. The PSE is the “point of subjective equality”, when the two stimuli (Test and Standard) look subjectively the same, and thus, an observer would choose randomly between them. As such, the PSE is the 0.5 probability point. The POE refers to “point of objective equality” which corresponds to the ‘Standard’ stimulus saturation. The POE values are the median of the 11 saturation levels on the x-axis of the PSE graph. If exogenous covert attention (cue) has an effect on saturation perception, the PSE value would be significantly apart from POE. We expected that exogenous covert attention would enhance the saturation perception, hence, the test cue line would move towards the left, while standard cue line moves towards the right side. This change would indicate that due to the cue presented at the same side as the test stimuli, lower saturation level of the actual test stimuli would appear to have the same saturation level as the neutral stimuli.