Initial visual information determines endpoint precision for rapid pointing.

We investigated how visual noise in the initial estimate of target location affects precision for rapid pointing. Visual localization thresholds (an error measure) rise systematically with eccentricity, doubling at eccentricities of a degree or less. Previous work, which we confirmed, has shown that the precision of pointing, measured by the standard deviation, to a single isolated target is relatively constant over small lateral extents near the midline, and that pointing error is substantially larger than visual error. We used target uncertainty (randomly chosen locations) to greatly increase visual noise so that we could explore the influence of visual noise on pointing error. We compared precision for comparable visual and pointing tasks as a function of target eccentricity. The target was presented for 110 ms at one of eight isoeccentric locations, chosen at random. Under these conditions, pointing error increased significantly with increasing target eccentricity. Beyond 4 degrees eccentricity, visual thresholds and pointing error were identical. Even when the target remained visible until the movement was completed, initial target eccentricity affected pointing error. The quality of visual information varies with task demands, and therefore so does its influence on endpoint precision. Our results demonstrate that the initial visual information about target location can limit endpoint precision, even over as small a range as 12 degrees in the central visual field (a lateral extent of +/-8.5 cm at the midline).