Department of Psychology and Program in Cognitive Neuroscience, The City College and Graduate Center of the City University of New York, NY 10031, USA.
Neuropsychologia. 2013 Jul;51(8):1497-503. doi: 10.1016/j.neuropsychologia.2013.04.013. Epub 2013 Apr 30.
Early visual cortex activity is influenced by both bottom-up and top-down factors. To investigate the influences of bottom-up (saliency) and top-down (task) factors on different stages of visual processing, we used transcranial magnetic stimulation (TMS) of areas V1/V2 to induce visual suppression at varying temporal intervals. Subjects were asked to detect and discriminate the color or the orientation of briefly-presented small lines that varied on color saliency based on color contrast with the surround. Regardless of task, color saliency modulated the magnitude of TMS-induced visual suppression, especially at earlier temporal processing intervals that reflect the feedforward stage of visual processing in V1/V2. In a second experiment we found that our color saliency effects were also influenced by an inherent advantage of the color red relative to other hues and that color discrimination difficulty did not affect visual suppression. These results support the notion that early visual processing is stimulus driven and that feedforward and feedback processing encode different types of information about visual scenes. They further suggest that certain hues can be prioritized over others within our visual systems by being more robustly represented during early temporal processing intervals.
早期视觉皮层的活动受到自上而下和自下而上因素的影响。为了研究自下而上（显著度）和自上而下（任务）因素对视觉加工不同阶段的影响，我们使用经颅磁刺激（TMS）刺激 V1/V2 区，在不同的时间间隔内诱导视觉抑制。要求受试者检测和辨别短暂呈现的小线的颜色或方向，这些小线的颜色显著度基于与周围环境的颜色对比度而变化。无论任务如何，颜色显著度都调节了 TMS 诱导的视觉抑制的幅度，尤其是在反映 V1/V2 中视觉加工前馈阶段的更早的时间处理间隔内。在第二个实验中，我们发现我们的颜色显著度效应也受到颜色红色相对于其他色调的固有优势的影响，并且颜色辨别难度并不影响视觉抑制。这些结果支持了早期视觉加工是由刺激驱动的观点，并且前馈和反馈加工对视觉场景的不同类型的信息进行编码。它们进一步表明，在早期时间处理间隔内，某些色调可以通过更稳健地表示而在我们的视觉系统中优先于其他色调。
