Smooth Pursuit Eye Movements to Isoluminant Targets

Abstract

Braun DI, Mennie N, Rasche C, Schü tz AC, Hawken MJ, Gegenfurtner KR. Smooth pursuit eye movements to isoluminant targets. J Neurophysiol 100: 1287-1300, 2008. First published July 9, 2008 doi:10.1152/jn.00747.2007. At slow speeds, chromatic isoluminant stimuli are perceived to move much slower than comparable luminance stimuli. We investigated whether smooth pursuit eye movements to isoluminant stimuli show an analogous slowing. Beside pursuit speed and latency, we studied speed judgments to the same stimuli during fixation and pursuit. Stimuli were either large sine wave gratings or small Gaussians blobs moving horizontally at speeds between 1 and 11°/s. Targets were defined by luminance contrast or color. Confirming prior studies, we found that speed judgments of isoluminant stimuli during fixation showed a substantial slowing when compared with luminance stimuli. A similarly strong and significant effect of isoluminance was found for pursuit initiation: compared with luminance targets of matched contrasts, latencies of pursuit initiation were delayed by 50 ms at all speeds and eye accelerations were reduced for isoluminant targets. A small difference was found between steady-state eye velocities of luminance and isoluminant targets. For comparison, we measured latencies of saccades to luminance and isoluminant stimuli under similar conditions, but the effect of isoluminance was only found for pursuit. Parallel psychophysical experiments revealed that different from speed judgments of moving isoluminant stimuli made during fixation, judgments during pursuit are veridical for the same stimuli at all speeds. Therefore information about target speed seems to be available for pursuit eye movements and speed judgments during pursuit but is degraded for perceptual speed judgments during fixation and for pursuit initiation.

Dynamics of Smooth Pursuit Maintenance

“…These findings are in general agreement with the effect of contrast reported by Mulligan (2002). In comparison, latencies in the step-ramp task measured under varying contrast levels range widely between 100 and 300 ms (Braun et al 2008;Ilg 1997;Spering et al 2005), pointing to further differences between the dynamics of pursuit measured during its maintenance and initiation phases.…”

“…For an appropriate size of the initial step, this stimulus evokes smooth pursuit initiation without the occurrence of early saccades, facilitating the estimation of latency (Carl and Gellman 1987;Rashbass 1961;Robinson 1965). Using a variety of visual targets, pure delays during the initiation of smooth pursuit in human subjects are found to be broadly distributed between 100 and 300 ms (Braun et al 2008;Knox 1998;Lindner and Ilg 2000;Rashbass 1961;Robinson 1965;Spering et al 2005). The shortest latencies of pursuit initiation have been obtained in a "gapparadigm," where the fixation is extinguished 100 -200 ms before the onset of the target, yielding delays of ϳ90 ms (Krauzlis and Miles 1996b).…”

Competition between color and luminance for target selection in smooth pursuit and saccadic eye movements

“…Eye movement studies support these assumptions. Pursuit latency to isoluminant targets is delayed by about 50 ms in comparison with luminance targets (Braun et al, 2008). No such impairment for color processing was found for saccades (White, Kerzel, & Gegenfurtner, 2006).…”

“…However, these latency differences alone cannot explain the results. If visual signals of color and luminance stimuli were processed at different speeds to drive pursuit eye movements, as reported in Braun et al (2008), pursuit direction changes to the luminance stimulus should have occurred earlier than direction changes to color. However, across all contrast conditions, pursuit choices to luminance and color did not occur at significantly different times (F(1,5) = 0.65, n.s.).…”

Vision for Motor Performance in Virtual Environments Across the Lifespan

“…The specific role of luminance contrast for such processes has not been clearly identified, and previous study of this topic is sparse. Recently Braun et al (2008) investigated whether initiation of eye movements differed when tracking two types of targets, one with luminance contrast compared to the background and one isoluminant with the background (i.e. defined by color only).…”