Human visual cortical gamma reflects natural image structure

Many studies have reported visual cortical gamma-band activity related to stimulus processing and cognition. Most respective studies used artificial stimuli, and the few studies that used natural stimuli disagree. Electrocorticographic (ECoG) recordings from awake macaque areas V1 and V4 found gamma to be abundant during free viewing of natural images. In contrast, a study using ECoG recordings from V1 of human patients reported that many natural images induce no gamma and concluded that it is not necessary for seeing. To reconcile these apparently disparate findings, we reanalyzed those same human ECoG data recorded during presentation of natural images. We find that the strength of gamma is positively correlated with different image-computable metrics of image structure. This holds independently of the precise metric used to quantify gamma. In fact, an average of previously used gamma metrics reflects image structure most robustly. Gamma was sufficiently diagnostic of image structure to differentiate between any possible pair of images with >70% accuracy. Thus, while gamma might be weak for some natural images, the graded strength of gamma reflects the graded degree of image structure, and thereby conveys functionally relevant stimulus properties.

许多研究报道了与刺激处理和认知相关的视觉皮层伽马波段活动。大多数相关研究使用人工刺激，而少数使用自然刺激的研究结果不一致。从清醒猕猴的V1和V4区域进行的皮质脑电图（ECoG）记录发现，在自然图像自由观看期间伽马波很丰富。相比之下，一项对人类患者V1进行皮质脑电图记录的研究报告称，许多自然图像不会诱发伽马波，并得出结论认为伽马波对于视觉不是必需的。为了调和这些明显不同的发现，我们重新分析了在呈现自然图像期间记录的相同的人类皮质脑电图数据。我们发现伽马波的强度与不同的可计算图像结构指标呈正相关。这与用于量化伽马波的具体指标无关。事实上，先前使用的伽马波指标的平均值最能稳健地反映图像结构。伽马波对图像结构具有足够的诊断性，能够以>70%的准确率区分任意一对可能的图像。因此，虽然对于某些自然图像伽马波可能较弱，但伽马波的分级强度反映了图像结构的分级程度，从而传达了功能相关的刺激特性。