Hernández A, Salinas E, García R, Romo R
Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510 México DF, México.
J Neurosci. 1997 Aug 15;17(16):6391-400. doi: 10.1523/JNEUROSCI.17-16-06391.1997.
Humans and monkeys have similar capacities to discriminate the frequencies of mechanical sinusoids delivered to their hands in the range that corresponds to the sense of flutter (10-50 Hz). Previous studies showed that monkeys can discriminate whether comparison stimuli are higher or lower in frequency than a base stimulus that does not vary from trial to trial during an experiment. We verified this result in two monkeys trained in this manner. To confirm that these animals were able to discriminate, we tested them in a variant of the task in which the frequency of the base stimulus changed randomly from trial to trial. The monkeys failed to discriminate in this new testing mode; instead they seemed to categorize the comparison stimuli, ignoring the base stimulus. After further training in the randomized base condition, the two monkeys learned to discriminate accurately. We then explored how the stimulation parameters affected performance. We found that animals could discriminate accurately with stimulus durations as short as 250 msec, with interstimulus intervals as long as 10 sec, with 50% differences between base and comparison stimulus amplitudes or when stimulated on a different finger. Performance did not degrade in these conditions, even though the monkeys had never been trained or tested under them. The results show that monkeys may try to categorize rather than discriminate when the task allows either strategy, although they are capable of performing true discriminations very robustly. These findings have important implications for investigating the neuronal processes underlying sensory discrimination.
人类和猴子在辨别传递到其手部的机械正弦波频率方面具有相似的能力，该频率范围与颤动感觉相对应（10 - 50赫兹）。先前的研究表明，猴子能够辨别比较刺激的频率高于还是低于在实验过程中每次试验都不变的基础刺激的频率。我们以这种方式对两只猴子进行训练，验证了这一结果。为了确认这些动物能够进行辨别，我们在基础刺激频率每次试验随机变化的任务变体中对它们进行测试。在这种新的测试模式下，猴子无法进行辨别；相反，它们似乎对比较刺激进行了分类，而忽略了基础刺激。在随机基础条件下进一步训练后，这两只猴子学会了准确辨别。然后，我们探究了刺激参数如何影响表现。我们发现，动物能够在刺激持续时间短至250毫秒、刺激间隔长达10秒、基础刺激与比较刺激幅度相差50%或在不同手指上进行刺激的情况下准确辨别。即使猴子从未在这些条件下接受过训练或测试，在这些条件下其表现也不会下降。结果表明，当任务允许两种策略时，猴子可能会尝试进行分类而非辨别，尽管它们能够非常稳健地进行真正的辨别。这些发现对于研究感觉辨别背后的神经元过程具有重要意义。
