Verghese P, Stone L S
NASA Ames Research Center, Moffett Field, CA 94035-1000, USA.
Vision Res. 1995 Oct;35(20):2811-23. doi: 10.1016/0042-6989(95)00038-2.
We used speed discrimination tasks to measure the ability of observers to combine speed information from multiple stimuli distributed across space. We compared speed discrimination thresholds in a classical discrimination paradigm to those in an uncertainty/search paradigm. Thresholds were measured using a temporal two-interval forced-choice design. In the discrimination paradigm, the n gratings in each interval all moved at the same speed and observers were asked to choose the interval with the faster gratings. Discrimination thresholds for this paradigm decreased as the number of gratings increased. This decrease was not due to increasing the effective stimulus area as a control experiment that increased the area of a single grating did not show a similar improvement in thresholds. Adding independent speed noise to each of the n gratings caused thresholds to decrease at a rate similar to the original no-noise case, consistent with observers combining an independent sample of speed from each grating in both the added- and no-noise cases. In the search paradigm, observers were asked to choose the interval in which one of the n gratings moved faster. Thresholds in this case increased with the number of gratings, behavior traditionally attributed to an input bottleneck. However, results from the discrimination paradigm showed that the increase was not due to observers' inability to process these gratings. We have also shown that the opposite trends of the data in the two paradigms can be predicted by a decision theory model that combines independent samples of speed information across space. This demonstrates that models typically used in classical detection and discrimination paradigms are also applicable to search paradigms. As our model does not distinguish between samples in space and time, it predicts that discrimination performance should be the same regardless of whether the gratings are presented in two spatial intervals or two temporal intervals. Our last experiment largely confirmed this prediction.
我们使用速度辨别任务来测量观察者整合来自分布于空间中的多个刺激的速度信息的能力。我们将经典辨别范式中的速度辨别阈值与不确定性/搜索范式中的阈值进行了比较。阈值采用时间双间隔强制选择设计进行测量。在辨别范式中，每个间隔内的n个光栅均以相同速度移动，观察者被要求选择光栅速度更快的间隔。该范式的辨别阈值随着光栅数量的增加而降低。这种降低并非由于有效刺激面积的增加，因为一项增加单个光栅面积的对照实验并未显示出阈值有类似的改善。给n个光栅中的每一个添加独立的速度噪声会导致阈值以与原始无噪声情况相似的速率降低，这与观察者在添加噪声和无噪声情况下都对每个光栅的速度进行独立采样并整合的情况一致。在搜索范式中，观察者被要求选择n个光栅中其中一个移动速度更快的间隔。在这种情况下，阈值随着光栅数量的增加而升高，这种行为传统上归因于输入瓶颈。然而，辨别范式的结果表明，这种升高并非由于观察者无法处理这些光栅。我们还表明，这两种范式中数据的相反趋势可以通过一个决策理论模型来预测，该模型整合了空间中速度信息的独立样本。这表明经典检测和辨别范式中通常使用的模型也适用于搜索范式。由于我们的模型不区分空间和时间上的样本，它预测无论光栅是呈现在两个空间间隔还是两个时间间隔中，辨别性能都应该是相同的。我们的最后一个实验在很大程度上证实了这一预测。
