Port N L, Lee D, Dassonville P, Georgopoulos A P
Brain Sciences Center (11B), Veterans Affairs Medical Center, Minneapolis, MN 55417, USA.
Exp Brain Res. 1997 Oct;116(3):406-20. doi: 10.1007/pl00005769.
We investigated the capacities of human subjects to intercept moving targets in a two-dimensional (2D) space. Subjects were instructed to intercept moving targets on a computer screen using a cursor controlled by an articulated 2D manipulandum. A target was presented in 1 of 18 combinations of three acceleration types (constant acceleration, constant deceleration, and constant velocity) and six target motion times, from 0.5 to 2.0 s. First, subjects held the cursor in a start zone located at the bottom of the screen along the vertical meridian. After a pseudorandom hold period, the target appeared in the lower left or right corner of the screen and traveled at 45 degrees toward an interception zone located on the vertical meridian 12.5 cm above the start zone. For a trial to be considered successful, the subject's cursor had to enter the interception zone within 100 ms of the target's arrival at the center of the interception zone and stay inside a slightly larger hold zone. Trials in which the cursor arrived more than 100 ms before the target were classified as "early errors," whereas trials in which the cursor arrived more than 100 ms after the target were classified as "late errors." Given the criteria above, the task proved to be difficult for the subjects. Only 41.3% (1080 out of 2614) of the movements were successful, whereas the remaining 58.7% were temporal (i.e., early or late) errors. A large majority of the early errors occurred in trials with decelerating targets, and their percentage tended to increase with longer target motion times. In contrast, late errors occurred in relation to all three target acceleration types, and their percentage tended to decrease with longer target motion times. Three models of movement initiation were investigated. First, the threshold-distance model, originally proposed for optokinetic eye movements to constant-velocity visual stimuli, maintains that response time is composed of two parts, a constant processing time and the time required for the stimulus to travel a threshold distance. This model only partially fit our data. Second, the threshold-tau model, originally proposed as a strategy for movement initiation, assumes that the subject uses the first-order estimate of time-to-contact (tau) to determine when to initiate the interception movement. Similar to the threshold distance model, the threshold-tau model only partially fit the data. Finally, a dual-strategy model was developed which allowed for the adoption of either of the two strategies for movement initiation; namely, a strategy based on the threshold-distance model ("reactive" strategy) and another based on the threshold-tau model ("predictive" strategy). This model provided a good fit to the data. In fact, individual subjects preferred to use one or the other strategy. This preference was allowed to be manifested at long target motion times, whereas shorter target motion times (i.e., 0.5 s and 0.8 s) forced the subjects to use only the reactive strategy.
我们研究了人类受试者在二维（2D）空间中拦截移动目标的能力。受试者被要求使用由关节式二维操作器控制的光标在电脑屏幕上拦截移动目标。目标以三种加速度类型（匀加速、匀减速和匀速）与六个目标运动时间（从0.5秒到2.0秒）的18种组合中的一种呈现。首先，受试者将光标保持在屏幕底部沿垂直子午线的起始区域。在一段伪随机的保持时间后，目标出现在屏幕的左下角或右下角，并以45度角朝着位于起始区域上方12.5厘米处垂直子午线上的拦截区域移动。要使一次试验被视为成功，受试者的光标必须在目标到达拦截区域中心的100毫秒内进入拦截区域，并停留在一个稍大的保持区域内。光标在目标之前超过100毫秒到达的试验被归类为“早期错误”，而光标在目标之后超过100毫秒到达的试验被归类为“晚期错误”。基于上述标准，该任务对受试者来说被证明是困难的。只有41.3%（2614次运动中的1080次）的运动是成功的，而其余58.7%是时间上的（即早期或晚期）错误。大多数早期错误发生在目标减速的试验中，并且它们的百分比倾向于随着目标运动时间的延长而增加。相比之下，晚期错误与所有三种目标加速度类型都有关，并且它们的百分比倾向于随着目标运动时间的延长而降低。研究了三种运动起始模型。首先，阈值距离模型最初是为对匀速视觉刺激的视动眼运动提出的，它认为反应时间由两部分组成，一个恒定的处理时间和刺激移动阈值距离所需的时间。该模型仅部分拟合了我们的数据。其次，阈值τ模型最初是作为一种运动起始策略提出的，它假设受试者使用接触时间（τ）的一阶估计来确定何时开始拦截运动。与阈值距离模型类似，阈值τ模型也仅部分拟合了数据。最后，开发了一种双策略模型，该模型允许采用两种运动起始策略中的任何一种；即，一种基于阈值距离模型的策略（“反应性”策略）和另一种基于阈值τ模型的策略（“预测性”策略）。该模型对数据拟合良好。事实上，个体受试者更喜欢使用其中一种策略。这种偏好允许在较长的目标运动时间表现出来，而较短的目标运动时间（即0.5秒和0.8秒）迫使受试者仅使用反应性策略。
