Celebrini S, Newsome W T
Department of Neurobiology, Stanford University School of Medicine, California 94305.
J Neurosci. 1994 Jul;14(7):4109-24. doi: 10.1523/JNEUROSCI.14-07-04109.1994.
We recorded the responses of single neurons in extrastriate area MST while rhesus monkeys discriminated the direction of motion in a set of stochastic visual displays. By varying systematically the strength of a coherent motion signal within the visual display, we were able to measure simultaneously the monkeys' psychophysical thresholds for direction discrimination and the responses of single neurons to the same motion signals. Neuronal thresholds for reliably signaling the direction of motion in the visual display were calculated from the measured responses using a method based in signal detection theory. Neurons in MST were exquisitely sensitive to motion signals in the display, having thresholds for discriminating the direction of coherent motion that were, on average, equal to the psychophysical thresholds of the monkeys. For many MST neurons, the intensity of the response was correlated with the monkey's psychophysical judgements for repeated presentations of a given near-threshold stimulus; the monkey tended to choose the preferred direction of the neuron under study when that neuron responded more strongly to the stimulus. In both of these respects, MST neurons were indistinguishable from neurons in extrastriate area MT, a major source of afferent input to MST. In a second set of experiments, we found that both of these results held true in the face of pronounced manipulations of the visual stimulus. Severe reductions in stimulus size and speed, for example, compromised neuronal and psychophysical sensitivities by similar amounts so that the average neuronal and psychophysical thresholds remained approximately equal. In addition, the trial-to-trial covariation of neuronal response and perceptual decision was unaffected by our stimulus manipulations. Thus, MST neurons carry signals appropriate for supporting psychophysical performance on our task over an impressively wide range of stimulus configurations.
我们记录了恒河猴在一组随机视觉显示中辨别运动方向时，纹外区域MST中单个神经元的反应。通过系统地改变视觉显示中连贯运动信号的强度，我们能够同时测量猴子辨别方向的心理物理学阈值以及单个神经元对相同运动信号的反应。利用基于信号检测理论的方法，根据测量到的反应计算出视觉显示中可靠地发出运动方向信号的神经元阈值。MST中的神经元对显示中的运动信号极为敏感，辨别连贯运动方向的阈值平均而言与猴子的心理物理学阈值相等。对于许多MST神经元，在重复呈现给定的接近阈值的刺激时，反应强度与猴子的心理物理学判断相关；当所研究的神经元对刺激反应更强时，猴子倾向于选择该神经元的偏好方向。在这两个方面，MST神经元与纹外区域MT中的神经元没有区别，MT是MST主要的传入输入源。在第二组实验中，我们发现面对视觉刺激的显著改变，这两个结果仍然成立。例如，刺激大小和速度的大幅降低，以相似的程度损害了神经元和心理物理学的敏感性，使得平均神经元阈值和心理物理学阈值大致保持相等。此外，我们的刺激操作并未影响神经元反应与知觉决策之间逐次试验的协变关系。因此，在令人印象深刻的广泛刺激配置范围内，MST神经元携带的信号适合支持我们任务中的心理物理学表现。
