Smith Matthew A, Kelly Ryan C, Lee Tai Sing
Center for the Neural Basis of Cognition, Carnegie Mellon University, Mellon Institute, Pittsburgh, PA 15213, USA.
J Neurophysiol. 2007 Dec;98(6):3436-49. doi: 10.1152/jn.00441.2007. Epub 2007 Sep 26.
Contextual modulation due to feature contrast between the receptive field and surrounding region has been reported for numerous stimuli in primary visual cortex. One type of this modulation, iso-orientation surround suppression, has been studied extensively. The degree to which surround suppression is related to other forms of contextual modulation remains unknown. We used shape-from-shading stimuli in a field of distractors to test the latency and magnitude of contextual modulation to a stimulus that cannot be distinguished with an orientation-selective mechanism. This stimulus configuration readily elicits perceptual pop-out in human observers and induces a long-latency contextual modulation response in neurons in macaque early visual cortex. We found that animals trained to detect the location of a pop-out stimulus were better at finding a sphere that appeared to be lit from below in the presence of distractors that were lit from above. Furthermore, neuronal responses were stronger and had shorter latency in the condition where behavioral performance was best. This asymmetry is compatible with earlier psychophysical findings in human observers. In the population of V1 neurons, the latency of the contextual modulation response is 145 ms on average (ranging from 70 to 230 ms). This is much longer than the latency for iso-orientation surround suppression, indicating that the underlying circuitry is distinct. Our results support the idea that a feature-specific feedback signal generates the pop-out responses we observe and suggest that V1 neurons actively participate in the computation of perceptual salience.
据报道，初级视觉皮层中，由于感受野与周围区域之间的特征对比度而产生的上下文调制适用于多种刺激。这种调制的一种类型，即等方向环绕抑制，已经得到了广泛研究。环绕抑制与其他形式的上下文调制之间的关联程度仍然未知。我们在一个干扰物场中使用由明暗恢复形状的刺激，来测试对一种无法通过方向选择机制区分的刺激的上下文调制的潜伏期和幅度。这种刺激配置很容易在人类观察者中引发感知突显，并在猕猴早期视觉皮层的神经元中诱导出长潜伏期的上下文调制反应。我们发现，经过训练以检测突显刺激位置的动物，在存在从上方照亮的干扰物的情况下，更善于找到似乎从下方照亮的球体。此外，在行为表现最佳的条件下，神经元反应更强且潜伏期更短。这种不对称与人类观察者早期的心理物理学发现一致。在V1神经元群体中，上下文调制反应的潜伏期平均为145毫秒（范围从70到230毫秒）。这比等方向环绕抑制的潜伏期长得多，表明其潜在的神经回路是不同的。我们的结果支持这样一种观点，即特定特征的反馈信号产生了我们观察到的突显反应，并表明V1神经元积极参与感知显著性的计算。
