Time course and robustness of ERP object and face differences

Conflicting results have been reported about the earliest “true” ERP differences related to face processing, with the bulk of the literature focusing on the signal in the first 200 ms after stimulus onset. Part of the discrepancy might be explained by uncontrolled low-level differences between images used to assess the timing of face processing. In the present experiment, we used a set of faces, houses, and noise textures with identical amplitude spectra to equate energy in each spatial frequency band. The timing of face processing was evaluated using face–house and face–noise contrasts, as well as upright-inverted stimulus contrasts. ERP differences were evaluated systematically at all electrodes, across subjects, and in each subject individually, using trimmed means and bootstrap tests. Different strategies were employed to assess the robustness of ERP differential activities in individual subjects and group comparisons. We report results showing that the most conspicuous and reliable effects were systematically observed in the N170 latency range, starting at about 130–150 ms after stimulus onset

Spatial scaling factors explain eccentricity effects on face ERPs.

Event-related potential (ERP) studies consistently have described a strong, face-sensitive response termed the N170. This component is maximal at the fovea and decreases strongly with eccentricity, a result that could suggest a foveal bias in the cortical generators responsible for face processing. Here we demonstrate that scaling stimulus size according to V1 cortical magnification factor can virtually eliminate face-related eccentricity effects, indicating that eccentricity effects on face ERPs are largely due to low-level visual factors rather than high-level cortical specialization for foveal stimuli.\r\n\r\nThe article can be downloaded here:\r\nhttp://journalofvision.org/5/10/1/\r\