Efficiently Measuring Magnocellular and Parvocellular Function in Human Clinical Studies.

PURPOSE Pokorny and Smith (J Opt Soc Am A Opt Image Sci Vis. 1997;14:2477-2486) described a laboratory method to behaviorally measure magnocellular and parvocellular pathway sensitivity. We investigated whether their method may be more efficiently applied to clinical populations by reducing adaptation times. METHODS We measured contrast detection thresholds to a 30-ms increment on a 30 cd/m2 background every 2 seconds after a 1-minute preadaptation to either a bright (90 cd/m2) or dim (3 cd/m2) luminance, in four observers. We also measured increment thresholds atop a steady 60 cd/m2 luminous pedestal (30 cd/m2 above the background) that remained on for 80 seconds, and tracked thresholds for 60 seconds after pedestal offset. We also assessed the minimum number of stimulus presentations required to reliably estimate thresholds using our four alternative forced choice (4-AFC) zippy estimation by sequential testing (ZEST) procedure. RESULTS Detection thresholds between the bright and dim preadaptation conditions were identical within seconds after the offset of the preadaptation luminance. Thresholds on the steady luminance pedestal reached stable values within approximately 10 seconds from pedestal onset, and recovered within 2 seconds of pedestal offset. Analysis of the 4-AFC ZEST procedure found little decrease in threshold variability after approximately 14 stimulus presentations. CONCLUSIONS Preadaptation and stimulus adaptation times may be reduced dramatically from those described by Pokorny and Smith, without altering thresholds. TRANSLATIONAL RELEVANCE Experimental time with clinical populations often is limited. Increasing the efficiency of the method of Pokorny and Smith allows for either shorter test sessions, or for a more extensive range of experimental parameters to be explored in disease.