Effect of Contrast on the Active Control of a Moving Line

Abstract

Li, Li, Barbara T. Sweet, and Leland S. Stone. Effect of contrast on the active control of a moving line. J Neurophysiol 93: 2873-2886, 2005. First published December 22, 2004 doi:10.1152/jn.00200.2004. In many passive visual tasks, human perceptual judgments are contrast dependent. To explore whether these contrast dependencies of visual perception also affect closed-loop manual control tasks, we examined visuomotor performance as humans actively controlled a moving luminance-defined line over a range of contrasts. Four subjects were asked to use a joystick to keep a horizontal line centered on a display as its vertical position was perturbed by a sum of sinusoids under two control regimes. The total root mean square (RMS) position error decreased quasi-linearly with increasing log contrast across the tested range (mean slope across subjects: Ϫ8.0 and Ϫ7.7% per log 2 contrast, for the two control regimes, respectively). Frequency-response (Bode) plots showed a systematic increase in openloop gain (mean slope: 1.44 and 1.30 dB per log 2 contrast, respectively), and decrease in phase lag with increasing contrast, which can be accounted for by a decrease in response time delay (mean slope: 32 and 40 ms per log 2 contrast, respectively). The performance data are well fit by a Crossover Model proposed by McRuer and Krendel, which allowed us to identify both visual position and motion cues driving performance. This analysis revealed that the position and motion cues used to support manual control under both control regimes appear equally sensitive to changes in stimulus contrast. In conclusion, our data show that active control of a moving visual stimulus is as dependent on contrast as passive perception and suggest that this effect is attributed to a shared contrast sensitivity early in the visual pathway, before any specialization for motion processing.

Influence of Hemianopic Visual Field Loss on Visual Motor Control

“…Figure 7 plots the response gains and phases as a function of input perturbation frequency for the HH and the control groups for both target motion conditions. The decreasing response gain and the steady phase roll-off at high frequencies are consistent with the low-pass gain control with a time delay typically observed in previous active control studies [35], [36], [55].…”

“…It has also been shown that human operators can perform such a closed-loop visual motor control task under various controller dynamics [32], [33], [34]. Based on these findings, Li et al have developed a simple closed-loop visual motor control task that involves controlling a randomly moving visual target on the screen to evaluate how the visual system uses different sources of visual information for the control of target motion [35], [36], and how the recruitment of new visual information for visual motor control is affected by controller dynamics [37].…”

“…In the current study, we used a simple closed-loop visual motor control task similar to that developed by Li et al [35], [36], [37] to evaluate the visual motor control abilities of HH patients. The goal was to compare the control performance of HH patients to that of a group of age-matched normally sighted participants to determine the extent to which the visual impairment in HH patients affects their ability to effectively use visual information for online control of a moving target.…”

Impact of simulated visual impairment on the cognitive test performance of young adults

“…For instance, the opaque strips used by Gumenik and Glass (1970) reduce words to small visible line segments that may not form an effective Gestalt of a word. By comparison, the effects of contrast which are manifested in early stages of visual processing (Harley, Dillon, & Loftus, 2004;Li, Sweet, & Stone, 2005) appear to slow but not qualitatively alter the outcome of the word recognition process and consequently may not eliminate the Stroop effect.…”

Influence of optic flow on the control of heading and target egocentric direction during steering toward a goal

“…4. The duration of each trial was 95 s. Following previous studies on manual control (Li et al 2005(Li et al , 2006aLi WO et al 2009), all chosen frequencies for the vehicular heading and orientation perturbations went through an integer number of cycles in 90 s, and we added 5 s in each trial, such that we could skip the initial transient response at the beginning of the trial.…”