FMRI analysis of contrast polarity in face-selective cortex in humans and monkeys

• Published in: NeuroImage (Orlando, Fla.) Vol. 76; pp. 57 - 69
• Main Authors: Yue, Xiaomin, Nasr, Shahin, Devaney, Kathryn J., Holt, Daphne J., Tootell, Roger B.H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.08.2013; Elsevier; Elsevier Limited
• Subjects: Absorbance; Adult; Animals; Bias; Biological and medical sciences; Brain Mapping; Contrast polarity; Contrast Sensitivity - physiology; Experiments; Face; Face inversion; Face patches; Face recognition; Female; FFA; Fundamental and applied biological sciences. Psychology; Humans; Image Processing, Computer-Assisted; Macaca; Magnetic Resonance Imaging; Male; Monkey fMRI; Monkeys & apes; Photic Stimulation; Recognition (Psychology) - physiology; Vertebrates: nervous system and sense organs; Visual Cortex - physiology; FFA; Monkey fMRI; Contrast polarity; Face patches; Face recognition; Face inversion; Human; Monkey; Nuclear magnetic resonance imaging; Vertebrata; Mammalia; Primates; Polarity; Face; Functional imaging
• ISSN: 1053-8119; 1095-9572
• DOI: 10.1016/j.neuroimage.2013.02.068

Recognition is strongly impaired when the normal contrast polarity of faces is reversed. For instance, otherwise-familiar faces become very difficult to recognize when viewed as photographic negatives. Here, we used fMRI to demonstrate related properties in visual cortex: 1) fMRI responses in the human Fusiform Face Area (FFA) decreased strongly (26%) to contrast-reversed faces across a wide range of contrast levels (5.3–100% RMS contrast), in all subjects tested. In a whole brain analysis, this contrast polarity bias was largely confined to the Fusiform Face Area (FFA; p<0.0001), with possible involvement of a left occipital face-selective region. 2) It is known that reversing facial contrast affects three image properties in parallel (absorbance, shading, and specular reflection). Here, comparison of FFA responses to those in V1 suggests that the contrast polarity bias is produced in FFA only when all three component properties were reversed simultaneously, which suggests a prominent non-linearity in FFA processing. 3) Across a wide range (180°) of illumination source angles, 3D face shapes without texture produced response constancy in FFA, without a contrast polarity bias. 4) Consistent with psychophysics, analogous fMRI biases for normal contrast polarity were not produced by non-face objects, with image statistics similar to the face stimuli. 5) Using fMRI, we also demonstrated a contrast polarity bias in awake behaving macaque monkeys, in the cortical region considered homologous to human FFA. Thus common cortical mechanisms may underlie facial contrast processing across ~25million years of primate evolution.