The response of face-selective cortex with single face parts and part combinations

Abstract

A critical issue in object recognition research is how the parts of an object are analyzed by the visual system and combined into a perceptual whole. However, most of the previous research has examined how changes to object parts influence recognition of the whole, rather than recognition of the parts themselves. This is particularly true of the research on face recognition, and especially with questions related to the neural substrates. Here, we investigated patterns of BOLD fMRI brain activation with internal face parts (features) presented singly and in different combinations. A preference for single features over combinations was found in the occipital face area (OFA) as well as a preference for the two-eyes combination stimulus over other combination stimulus types. The fusiform face area (FFA) and lateral occipital cortex (LO) showed no preferences among the single feature and combination stimulus types. The results are consistent with a growing view that the OFA represents processes involved in early, feature-based analysis.

Figure 1

Single feature and combination stimuli. The top row shows the twelve different faces from which the stimuli were drawn. In the bottom two rows, from left to right, the stimuli are single features of nose, mouth, left eye, and right eye; and combinations of two-eyes, eyes-mouth, and eyes-nose-mouth. Stimuli in the second from bottom row are shown at a contrast level equal to the mean threshold contrast across subjects for the eyes-nose-mouth stimulus, which was the highest contrast level used in the scanner. Stimuli in the bottom row are shown at 10 times that contrast level too make the stimuli easier for the reader to view.

Figure 2

Accuracy as a function of stimulus type. 2E-M = eyes-mouth, 2E-N-M = eyes-nose-mouth. Error bars are 95% confidence intervals.

Figure 3

Locations of object- and face-selective regions of interest. The object – noise contrast is shown with a threshold of t=16. The face – object contrasts is shown with the FDR threshold (q=.05; voxel-wise t=3.51). Z-values are from the Talairach reference. FFA = fusiform face area, LO = lateral occipital area, OFA = occipital face area.

Figure 4

BOLD signal change as a function of stimulus type for the left and right OFA and for the average across hemispheres. Significant differences (p<.05) between selected stimulus types are shown with an *. 2E-M = eyes-mouth, 2E-N-M = eyes-nose-mouth. Error bars are 95% confidence intervals.

Figure 5

BOLD signal change as a function of stimulus type and hemisphere for the FFA and LO. 2E-M = eyes-mouth, 2E-N-M = eyes-nose-mouth. Error bars are 95% confidence intervals.