| Humans seem to be face experts. From a single glance of a face, we can extract a wealth of information about a person's identity, sex, age and mood. This thesis investigated whether specialized cognitive and neural mechanisms underlie our expertise for specific faces and faces as a general category. Visual search was used to investigate expertise for specific overlearned faces such as one's own. Observers showed consistently faster processing for their own face than a stranger's face irrespective of whether the face appeared in front or profile view, upright or upside-down, as target or distractor. Moreover, these effects persisted after several hundred presentations of the stranger's face. This suggests that extensive experience of a specific face may lead to the development of a robust representation that mediates rapid, flexible face processing.; Functional magnetic resonance imaging was used to investigate the Fusiform Face Area (FFA), a candidate region for the general processing of face stimuli. FFA responses were found to be: (i) equally strong for cat, cartoon and human faces, (ii) stronger for human faces with eyes occluded than eyes shown alone, (iii) stronger for front and profile than back views of human heads, and (iv) weakest for non-face objects. Generalization of the FFA response across very different face types could not be explained in terms of a response to a salient feature such as the eyes, or a general response to heads. Instead, the FFA seems to be optimally tuned to the broad category of faces.; The third study investigated whether FFA activity reflected the conscious perception of a face. Subjects viewed a bistable binocular rivalry display consisting of a face and house presented to different eyes. Perceptual alternations between face and house led to concomitant increases and decreases in FFA activity respectively. These responses during rivalry were as large as those evoked by actual alternations between a face and house stimulus, suggesting that FFA activity entirely reflects the conscious perception of a face and not the retinal stimulus.; In summary, these studies demonstrate that extensive experience of specific faces and faces as a general category may lead to the development of specialized representations or neural mechanisms. More generally, these studies may reveal how the visual system becomes tuned to important stimuli in our environment. |
