Active Control With an Isoluminant Display

Humans perceive isoluminant visual stimuli (i.e., stimuli that show little or no luminance variation across space) to move more slowly than their luminance-defined counterparts. To explore whether impaired motion perception at isoluminance also affects visuomotor control tasks, the authors examined the performance as humans actively controlled a moving line. They tested two types of displays matched for an overall salience: a luminant display composed of a luminance-defined Gaussian-blurred horizontal line and an isoluminant display composed of a color-defined line with the same spatial characteristics, but near-zero luminance information. Six subjects were asked to use a joystick to keep the line centered on a cathode ray tube display as its vertical position was perturbed pseudorandomly by a sum of ten sinusoids under two control regimes (velocity and acceleration control). The mean root mean square position error was larger for the isoluminant than for the luminant line (mean across subjects: 22% and 29% larger, for the two regimes, respectively). The describing functions (Bode plots) showed that, compared to the luminant line, the isoluminant line showed a lower open-loop gain (mean decrease: 3.4 and 2.9 dB, respectively) and an increase in phase lag, which can be accounted for by an increase in reaction time (mean increase: 103 and 155 ms, respectively). The performance data are generally well fit by McRuer´s classical crossover model. In conclusion, both our model-independent and model-dependent analyses show that the selective loss of luminance information impairs human active control performance, which is consistent with the preferential loss of information from cortical visual motion processing pathways. Display engineers must therefore be mindful of the importance of luminance-contrast per se (not just total stimulus salience) in the design of effective visual displays for closed-loop active control tasks