Speed encoding in human visual cortex revealed by fMRI adaptation
Speed encoding in human visual cortex revealed by fMRI adaptation
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DOI：
10.1167/9.13.3
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发表时间：
2009-01-01
影响因子：
1.8
通讯作者：
Smith, Andrew T.
中科院分区：
文献类型：
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作者：
Lingnau, Angelika;Ashida, Hiroshi;Smith, Andrew T.
在猕猴视觉皮层中，传统观点认为图像运动最初是由方向敏感神经元检测到的，这些神经元根据局部空间和时间频率（TF）进行调谐，随后对速度进行编码。我们使用功能性磁共振成像（fMRI）的适应，以寻求证据的速度或TF调谐在人类视觉皮层。成对呈现漂移正弦波光栅（S1：适配器，100%对比度; S2：探头，15、40或80%对比度）。在每次试验中，S1和S2的速度或TF是相同的，而另一个维度发生了变化。我们研究了响应是否对于相同速度的重复（指示速度编码）或对于TF的重复（指示TF编码）较弱（适应）。对于高对比度（80%）的探头，我们观察到清晰的速度编码MT和MST类似，但较弱的趋势，在几个较早的视觉领域。对于中等和低对比度探头，我们的数据表明，在大多数视觉领域的时间频率编码的趋势研究。在第二个实验中，我们调整刺激的感知速度，而不是物理速度，发现速度编码的趋势，即使是低对比度探头。我们的研究结果表明，速度编码占主导地位的MT/MST高对比度的刺激，也可能在其他视觉领域和/或在较低的对比度。
In macaque visual cortex, the conventional view is that image motion is initially detected by direction-sensitive neurons that are tuned in terms of local spatial and temporal frequency (TF), from which speed is encoded later. We used functional magnetic resonance imaging (fMRI) adaptation to seek evidence for speed or TF tuning in human visual cortex. Drifting sine-wave gratings were presented in pairs (S1: adapter, 100% contrast; S2: probe, 15, 40 or 80% contrast). In each trial, either speed or TF was the same for S1 and S2, whereas the other dimension changed. We investigated whether the response was weaker (adapted) for repetitions of the same speed, indicating speed coding, or for repetitions of TF, indicating TF coding. For high-contrast (80%) probes, we observed clear speed coding in MT and MST with similar but weaker trends in several earlier visual areas. For medium-and low contrast probes, our data indicated a trend towards temporal frequency coding in most visual areas studied. In a second experiment, we adjusted stimuli in terms of perceived rather than physical speed and found a trend for speed coding even for low-contrast probes. Our results suggest that speed coding dominates in MT/MST for high contrast stimuli, and possibly also in other visual areas and/or at lower contrasts.