Centre for Cognitive Neuroimaging, Institute of Neuroscience and Psychology, University of Glasgow Glasgow, UK.
Front Psychol. 2011 Jun 23;2:137. doi: 10.3389/fpsyg.2011.00137. eCollection 2011.
We studied how task constraints modulate the relationship between single-trial event-related potentials (ERPs) and image noise. Thirteen subjects performed two interleaved tasks: on different blocks, they saw the same stimuli, but they discriminated either between two faces or between two colors. Stimuli were two pictures of red or green faces that contained from 10 to 80% of phase noise, with 10% increments. Behavioral accuracy followed a noise dependent sigmoid in the identity task but was high and independent of noise level in the color task. EEG data recorded concurrently were analyzed using a single-trial ANCOVA: we assessed how changes in task constraints modulated ERP noise sensitivity while regressing out the main ERP differences due to identity, color, and task. Single-trial ERP sensitivity to image phase noise started at about 95-110 ms post-stimulus onset. Group analyses showed a significant reduction in noise sensitivity in the color task compared to the identity task from about 140 ms to 300 ms post-stimulus onset. However, statistical analyses in every subject revealed different results: significant task modulation occurred in 8/13 subjects, one showing an increase and seven showing a decrease in noise sensitivity in the color task. Onsets and durations of effects also differed between group and single-trial analyses: at any time point only a maximum of four subjects (31%) showed results consistent with group analyses. We provide detailed results for all 13 subjects, including a shift function analysis that revealed asymmetric task modulations of single-trial ERP distributions. We conclude that, during face processing, bottom-up sensitivity to phase noise can be modulated by top-down task constraints, in a broad window around the P2, at least in some subjects.
我们研究了任务约束如何调节单次事件相关电位 (ERP) 与图像噪声之间的关系。13 名受试者执行了两个交替任务：在不同的块中，他们看到了相同的刺激，但他们要么区分两张脸，要么区分两种颜色。刺激是两张包含 10%至 80%相位噪声的红色或绿色面孔的图片，噪声递增 10%。在身份任务中，行为准确性遵循依赖噪声的 sigmoid 曲线，但在颜色任务中，准确性高且与噪声水平无关。同时记录的 EEG 数据使用单试 ANCOVA 进行分析：我们评估了任务约束的变化如何调节 ERP 对噪声的敏感性，同时回归由于身份、颜色和任务引起的主要 ERP 差异。单次 ERP 对图像相位噪声的敏感性始于刺激后约 95-110 毫秒。组分析显示，与身份任务相比，颜色任务的噪声敏感性从刺激后约 140 毫秒到 300 毫秒显著降低。然而，对每个受试者的统计分析显示出不同的结果：在 8/13 名受试者中，颜色任务的显著任务调制发生，一名受试者表现出噪声敏感性增加，七名受试者表现出噪声敏感性降低。在组和单试分析中，效应的起始和持续时间也不同：在任何时间点，只有最多四名受试者（31%）的结果与组分析一致。我们为所有 13 名受试者提供了详细的结果，包括移位函数分析，该分析揭示了单次 ERP 分布的任务不对称调制。我们的结论是，在面孔处理过程中，自上而下的任务约束可以在 P2 周围的宽窗口内调节对相位噪声的下传敏感性，至少在一些受试者中是这样。
