Lower-Level Stimulus Features Strongly Influence Responses in the Fusiform Face Area

Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA.
Cerebral Cortex (Impact Factor: 8.67). 04/2010; 21(1):35-47. DOI: 10.1093/cercor/bhq050
Source: PubMed


An intriguing region of human visual cortex (the fusiform face area; FFA) responds selectively to faces as a general higher-order stimulus category. However, the potential role of lower-order stimulus properties in FFA remains incompletely understood. To clarify those lower-level influences, we measured FFA responses to independent variation in 4 lower-level stimulus dimensions using standardized face stimuli and functional Magnetic Resonance Imaging (fMRI). These dimensions were size, position, contrast, and rotation in depth (viewpoint). We found that FFA responses were strongly influenced by variations in each of these image dimensions; that is, FFA responses were not "invariant" to any of them. Moreover, all FFA response functions were highly correlated with V1 responses (r = 0.95-0.99). As in V1, FFA responses could be accurately modeled as a combination of responses to 1) local contrast plus 2) the cortical magnification factor. In some measurements (e.g., face size or a combinations of multiple cues), the lower-level variations dominated the range of FFA responses. Manipulation of lower-level stimulus parameters could even change the category preference of FFA from "face selective" to "object selective." Altogether, these results emphasize that a significant portion of the FFA response reflects lower-level visual responses.

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    • "The stimuli had equivalent mean luminance values in the present study, but to achieve sufficient image quality, the contrast and spatial frequency information were not explicitly controlled. This may raise the argument that we created systematic differences in the low-level visual properties of the stimuli based on spatial frequency information differences between faces and non-face objects since several fMRI studies showed that VTC areas (including the fusiform gyrus) were sensitive to spatial frequency information (e.g., Eger et al., 2005; Rotshtein et al., 2007; Gauthier et al., 2005; Yue et al., 2011). However, our P1 analysis indicated that low-level image differences are unlikely to account for the difference in N170s for faces and others. "
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    ABSTRACT: Scalp event-related potential (ERP) studies have demonstrated larger N170 amplitudes when subjects view faces compared to items from object categories. Extensive attempts have been made to clarify face selectivity and hemispheric dominance for face processing. The purpose of this study was to investigate hemispheric differences in N170s activated by human faces and non-face objects, as well as the extent of overlap of their sources. ERP was recorded from 20 subjects while they viewed human face and non-face images. N170s obtained during the presentation of human faces appeared earlier and with larger amplitude than for other category images. Further source analysis with a two-dipole model revealed that the locations of face and object processing largely overlapped in the left hemisphere. Conversely, the source for face processing in the right hemisphere located more anterior than the source for object processing. The results suggest that the neuronal circuits for face and object processing are largely shared in the left hemisphere, with more distinct circuits in the right hemisphere. Copyright © 2015. Published by Elsevier B.V.
    International journal of psychophysiology: official journal of the International Organization of Psychophysiology 07/2015; 98(1). DOI:10.1016/j.ijpsycho.2015.07.008 · 2.88 Impact Factor
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    • "Four images of human faces (see Figure 1A) were generated using FaceGen 3.4 (Singular Inversions, Canada), as described previously (Yue et al., 2011, 2013; Holt et al., 2014). All four faces (A, B, C and D) were male and caucasian, and achromatic (i.e., all color parameters were set to 0). "
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    ABSTRACT: Fear generalization is the production of fear responses to a stimulus that is similar – but not identical - to a threatening stimulus. Although prior studies have found that fear generalization magnitudes are qualitatively related to the degree of perceptual similarity to the threatening stimulus, the precise relationship between these two functions has not been measured systematically. Also, it remains unknown whether fear generalization mechanisms differ for social and non-social information. To examine these questions, we measured perceptual discrimination and fear generalization in the same subjects, using images of human faces and non-face control stimuli (“blobs”) that were perceptually matched to the faces. First, each subject’s ability to discriminate between pairs of faces or blobs was measured. Each subject then underwent a Pavlovian fear conditioning procedure, in which each of the paired stimuli were either followed (CS+) or not followed (CS-) by a shock. Skin conductance responses (SCRs) were also measured. Subjects were then presented with the CS+, CS- and five levels of a CS+-to-CS- morph continuum between the paired stimuli, based on individual discrimination thresholds. Finally, subjects rated the likelihood that each stimulus had been followed by a shock. Subjects showed both autonomic (SCR-based) and conscious (ratings-based) fear responses to morphs that they could not discriminate from the CS+ (generalization). For both faces and non-face objects, fear generalization was not found above discrimination thresholds. However, subjects exhibited greater fear generalization in the shock likelihood ratings compared to the SCRs, particularly for faces. These findings reveal that autonomic threat detection mechanisms in humans are highly sensitive to small perceptual differences between stimuli. Also, the conscious evaluation of threat shows broader generalization than autonomic responses, biased towards labeling a stimulus as threatening.
    Frontiers in Human Neuroscience 09/2014; 8:624. DOI:10.3389/fnhum.2014.00624 · 3.63 Impact Factor
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    • "In contrast, Yue and his colleagues reported that FFA produces neural activities that fit well with the model based on V1 function [26]. They analyzed neural responses along 4 meridians, including the ipsilateral horizontal positions. "
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    ABSTRACT: In human visual cortex, the primary visual cortex (V1) is considered to be essential for visual information processing; the fusiform face area (FFA) and parahippocampal place area (PPA) are considered as face-selective region and places-selective region, respectively. Recently, a functional magnetic resonance imaging (fMRI) study showed that the neural activity ratios between V1 and FFA were constant as eccentricities increasing in central visual field. However, in wide visual field, the neural activity relationships between V1 and FFA or V1 and PPA are still unclear. In this work, using fMRI and wide-view present system, we tried to address this issue by measuring neural activities in V1, FFA and PPA for the images of faces and houses aligning in 4 eccentricities and 4 meridians. Then, we further calculated ratio relative to V1 (RRV1) as comparing the neural responses amplitudes in FFA or PPA with those in V1. We found V1, FFA, and PPA showed significant different neural activities to faces and houses in 3 dimensions of eccentricity, meridian, and region. Most importantly, the RRV1s in FFA and PPA also exhibited significant differences in 3 dimensions. In the dimension of eccentricity, both FFA and PPA showed smaller RRV1s at central position than those at peripheral positions. In meridian dimension, both FFA and PPA showed larger RRV1s at upper vertical positions than those at lower vertical positions. In the dimension of region, FFA had larger RRV1s than PPA. We proposed that these differential RRV1s indicated FFA and PPA might have different processing strategies for encoding the wide field visual information from V1. These different processing strategies might depend on the retinal position at which faces or houses are typically observed in daily life. We posited a role of experience in shaping the information processing strategies in the ventral visual cortex.
    PLoS ONE 08/2013; 8(8):e72728. DOI:10.1371/journal.pone.0072728 · 3.23 Impact Factor
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