Gray R, Regan D
Department of Psychology, York University, Ontario, Canada.
Vision Res. 1998 Feb;38(4):499-512. doi: 10.1016/s0042-6989(97)00230-7.
We measured both the just-noticeable difference in time to collision (TTC) with an approaching object, and the absolute accuracy in estimating TTC in the following cases: only binocular information available; only monocular information available; both binocular and monocular information available as in the everyday situation. Observers could discriminate trial-to-trial variations in TTC on the basis of binocular information alone: the just-noticeable difference in TTC (5.1-9.8%) was the same for a small (0.03 deg) target and for a large (0.7 deg) target. In line with previous reports, when only monocular information was available, the just-noticeable difference in TTC was 5.8-12% for the large target. However, observers could not reliably discriminate trial-to-trial variations in TTC with the small target when only monocular information was available. When both binocular and monocular information was available, the just-noticeable difference in TTC for the large target was not significantly different from when only binocular or only monocular information was available. Observers could make reliable estimates of absolute TTC using binocular information only. Errors ranged from 2.5 to 10% for the large target, and 2.6 to 3.0% for the small target, all being overestimates. Errors for the small target were the same or lower than errors for the large target. Observers could make reliable estimates of TTC with the large target using monocular information only. Errors ranged from 2.0 to 12%, all being underestimates. Since monocular information did not provide a basis for reliable estimates of absolute TTC with the small target we conclude that, in everyday conditions, accurate estimates of TTC with small targets are based on binocular information when the object is small and is no more than a few metres away. Errors in estimating absolute TTC were lower in the case where both binocular and monocular information were available (as in the everyday situation) than when only binocular information or only monocular information was available. Errors ranged from 1.3 to 2.7%. An error of 1.3% approaches the accuracy required to explain the +/- 2.0-2.5 msec accuracy with which top sports players can estimate the instant of impact between bat and ball.
我们测量了与接近物体碰撞时间（TTC）的刚可察觉差异，以及在以下几种情况下估计TTC的绝对准确度：仅提供双眼信息；仅提供单眼信息；以及像日常情况那样同时提供双眼和单眼信息。观察者仅基于双眼信息就能辨别TTC的逐次试验变化：对于小目标（0.03度）和大目标（0.7度），TTC的刚可察觉差异（5.1 - 9.8%）是相同的。与之前的报告一致，当仅提供单眼信息时，大目标的TTC刚可察觉差异为5.8 - 12%。然而，当仅提供单眼信息时，观察者无法可靠地辨别小目标TTC的逐次试验变化。当同时提供双眼和单眼信息时，大目标的TTC刚可察觉差异与仅提供双眼信息或仅提供单眼信息时相比无显著差异。观察者仅使用双眼信息就能对绝对TTC做出可靠估计。大目标的误差范围为2.5%至10%，小目标的误差范围为2.6%至3.0%，均为高估。小目标的误差与大目标的误差相同或更低。观察者仅使用单眼信息就能对大目标的TTC做出可靠估计。误差范围为2.0%至12%，均为低估。由于单眼信息无法为小目标的绝对TTC提供可靠估计的基础，我们得出结论，在日常情况下，当物体较小且距离不超过几米时，对小目标TTC的准确估计基于双眼信息。与仅提供双眼信息或仅提供单眼信息的情况相比，同时提供双眼和单眼信息（如日常情况）时，绝对TTC估计的误差更低。误差范围为1.3%至2.7%。1.3%的误差接近顶级运动员估计球棒与球撞击瞬间所需的±2.0 - 2.5毫秒准确度所要求的精度。
