Separable effects of inversion and contrast-reversal on face detection thresholds and response functions: a sweep VEP study

J. Liu-Shuang, J. Ales, B. Rossion, A.M. Norcia

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

The human brain rapidly detects faces in the visual environment. We recently presented a sweep visual evoked potential approach to objectively define face detection thresholds as well as suprathreshold response functions (Ales, Farzin, Rossion, & Norcia, 2012). Here we determined these parameters are affected by orientation (upright vs. inverted) and contrast polarity (positive vs. negative), two manipulations that disproportionately disrupt the perception of faces relative to other object categories. Face stimuli parametrically increased in visibility through phase - descrambling while alternating with scrambled images at a fixed presentation rate of 3 Hz (6 images/s). The power spectrum and mean luminance of all stimuli were equalized. As a face gradually emerged during a stimulation sequence, EEG responses at 3 Hz appeared at ≈ 35% phase coherence over right occipito-temporal channels, replicating previous observations. With inversion and contrast-reversal, the 3-Hz amplitude decreased by ≈ 20%-50% and the face detection threshold increased by ≈ 30%-60% coherence. Furthermore, while the 3-Hz response emerged abruptly and saturated quickly for normal faces, suggesting a categorical neural response, the response profile for inverted and negative polarity faces was shallower and more linear, indicating gradual and continuously increasing activation of the underlying neural population. These findings demonstrate that inversion and contrast-reversal increase the threshold and modulate the suprathreshold response function of face detection.
Original languageEnglish
Article number11
JournalJournal of Vision
Volume15
Issue number2
DOIs
Publication statusPublished - 10 Feb 2015

Keywords

  • Face detection
  • Sweep SSVEP
  • Parametric image variation
  • Face inversion
  • Contrast polarity reversal

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