Abstract
PurposeShifting the region-of-interest within the input image to compensate for gaze shifts (“gaze compensation”) may improve hand–eye coordination in visual prostheses that incorporate an external camera. The present study investigated the effects of eye movement on hand-eye coordination under simulated prosthetic vision (SPV), and measured the coordination benefits of gaze compensation.MethodsSeven healthy-sighted subjects performed a target localization-pointing task under SPV. Three conditions were tested, modeling: retinally stabilized phosphenes (uncompensated); gaze compensation; and no phosphene movement (center-fixed). The error in pointing was quantified for each condition.ResultsGaze compensation yielded a significantly smaller pointing error than the uncompensated condition for six of seven subjects, and a similar or smaller pointing error than the center-fixed condition for all subjects (two-way ANOVA, P < 0.05). Pointing error eccentricity and gaze eccentricity were moderately correlated in the uncompensated condition (azimuth: R2 = 0.47; elevation: R2 = 0.51) but not in the gaze-compensated condition (azimuth: R2 = 0.01; elevation: R2 = 0.00). Increased variability in gaze at the time of pointing was correlated with greater reduction in pointing error in the center-fixed condition compared with the uncompensated condition (R2 = 0.64).ConclusionsEccentric eye position impedes hand–eye coordination in SPV. While limiting eye eccentricity in uncompensated viewing can reduce errors, gaze compensation is effective in improving coordination for subjects unable to maintain fixation.Translational RelevanceThe results highlight the present necessity for suppressing eye movement and support the use of gaze compensation to improve hand–eye coordination and localization performance in prosthetic vision.
Highlights
Visual prostheses aim to provide artificial vision to blind patients by using implanted electrodes to electrically stimulate the retina,[1,2,3,4] optic nerve,[5] thalamus,[6] or visual cortex,[7] evoking localized visual percepts
In a previous study on suprachoroidal retinal implant recipients, we showed that gaze compensation improved performance in a static image localization task but we did not assess hand–eye coordination
Our second hypothesis stated that the larger pointing error in the uncompensated condition was attributed to noncentral gaze. We investigated this by testing correlation between pointing error and response gaze for the gaze-compensated and uncompensated conditions using least-squares linear regression analysis (Fig. 7)
Summary
Visual prostheses aim to provide artificial vision to blind patients by using implanted electrodes to electrically stimulate the retina,[1,2,3,4] optic nerve,[5] thalamus,[6] or visual cortex,[7] evoking localized visual percepts. The location of the percept within the patient’s egocentric spatial map is known to move in parity with the orientation of the eyes.[1,7,8] This apparent movement is because eye position plays an important role in the integration of retinotopic visual signals into a consistent spatial map,[9] even after blindness.[10]. For tasks of coordination it is important that the percept location properly reflects the real world. This requires the orientation of the image sensor to be directly coupled with eye position; most present devices use an external camera of fixed orientation, divorcing the camera axis from the pupillary axis.[1,2,3] Recipients of these devices must rely exclusively on head movements to direct their field of view. While retinal implants have been shown to assist in hand–eye coordination tasks[2,11,12,13] it is TVST j 2018 j Vol 7 j No 1 j Article 2
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