Saccadic distractor effect and S-cone processing in normal observers and two cases of hemianopia

When observers have to make saccades to a target with a distractor presented at a non-target location, saccadic latencies are significantly slower than to targets presented in isolation. This is termed the saccadic distractor effect (SDE) and is thought to be explained by the competitive interactions between target and distractor and activity at the superior colliculus. We have measured the SDE in a group of normal participants and two hemianopic patients for luminance-defined and chromatic signals in the presence and absence of dynamic visual noise. Similar to previous reports, we found some evidence of a SDE for luminance-defined stimuli embedded in random noise. In the absence of luminance noise, a significant SDE was found for both luminance defined stimuli and S-cone contrast targets. Both hemianopic patients showed evidence of SDE for luminance-defined targets. Surprisingly, one patient showed a significant SDE for S-cone stimuli. These findings are significant as S-cone afferent signals reportedly, do not project to midbrain structures such as superior colliculus, a structure implicated in both SDE and blindsight. [Supported by James Mearns Charitable Trust.]