Rousselet Guillaume A, Pernet Cyril R, Bennett Patrick J, Sekuler Allison B
Centre for Cognitive Neuroimaging (CCNi) and Department of Psychology, University of Glasgow, Glasgow, UK.
BMC Neurosci. 2008 Oct 3;9:98. doi: 10.1186/1471-2202-9-98.
The present paper examines the visual processing speed of complex objects, here faces, by mapping the relationship between object physical properties and single-trial brain responses. Measuring visual processing speed is challenging because uncontrolled physical differences that co-vary with object categories might affect brain measurements, thus biasing our speed estimates. Recently, we demonstrated that early event-related potential (ERP) differences between faces and objects are preserved even when images differ only in phase information, and amplitude spectra are equated across image categories. Here, we use a parametric design to study how early ERP to faces are shaped by phase information. Subjects performed a two-alternative force choice discrimination between two faces (Experiment 1) or textures (two control experiments). All stimuli had the same amplitude spectrum and were presented at 11 phase noise levels, varying from 0% to 100% in 10% increments, using a linear phase interpolation technique. Single-trial ERP data from each subject were analysed using a multiple linear regression model.
Our results show that sensitivity to phase noise in faces emerges progressively in a short time window between the P1 and the N170 ERP visual components. The sensitivity to phase noise starts at about 120-130 ms after stimulus onset and continues for another 25-40 ms. This result was robust both within and across subjects. A control experiment using pink noise textures, which had the same second-order statistics as the faces used in Experiment 1, demonstrated that the sensitivity to phase noise observed for faces cannot be explained by the presence of global image structure alone. A second control experiment used wavelet textures that were matched to the face stimuli in terms of second- and higher-order image statistics. Results from this experiment suggest that higher-order statistics of faces are necessary but not sufficient to obtain the sensitivity to phase noise function observed in response to faces.
Our results constitute the first quantitative assessment of the time course of phase information processing by the human visual brain. We interpret our results in a framework that focuses on image statistics and single-trial analyses.
本文通过描绘物体物理属性与单次试验脑反应之间的关系，研究复杂物体（此处为面孔）的视觉处理速度。测量视觉处理速度具有挑战性，因为与物体类别共同变化的未控制物理差异可能会影响脑测量，从而使我们的速度估计产生偏差。最近，我们证明即使图像仅在相位信息上不同，且图像类别间的振幅谱相等，面孔与物体之间早期事件相关电位（ERP）的差异依然存在。在此，我们使用参数设计来研究面孔的早期ERP如何受相位信息影响。受试者在两张面孔（实验1）或纹理（两个对照实验）之间进行二选一的强制选择辨别。所有刺激具有相同的振幅谱，并使用线性相位插值技术，以10%的增量在11个相位噪声水平下呈现，范围从0%到100%。使用多元线性回归模型分析每个受试者的单次试验ERP数据。
我们的结果表明，面孔对相位噪声的敏感性在ERP视觉成分P1和N170之间的短时间窗口内逐渐显现。对相位噪声的敏感性在刺激开始后约120 - 130毫秒开始，并持续另外25 - 40毫秒。这一结果在受试者内部和受试者之间都很稳健。一个使用粉红噪声纹理的对照实验，其具有与实验1中使用的面孔相同的二阶统计特性，表明仅靠全局图像结构的存在无法解释观察到的面孔对相位噪声的敏感性。第二个对照实验使用了在二阶及更高阶图像统计方面与面孔刺激相匹配的小波纹理。该实验结果表明，面孔的高阶统计特性对于获得观察到的对面孔的相位噪声敏感性函数是必要的，但并不充分。
我们的结果构成了对人类视觉脑处理相位信息时间进程的首次定量评估。我们在一个专注于图像统计和单次试验分析的框架内解释我们的结果。
