The faces were created using FACES™ 4.0 by IQBiometrix Inc and
eye-removal was done in Adobe™ Photoshop CS5. Forty different face
identities were created (20 males, 20 females) by choosing a combination
of different internal features displayed at the exact same location
within the same bald face outline. This ensured features remained in
constant relative positions in every face. This also ensured that the overall
luminance across pictures was identical within a category, with only
tiny local variations seen as a result of using different features
(e.g. a larger mouth, smaller eyes, thinner eye brows etc.). A simple
180° rotation created the inverted stimuli and all images were presented
over a white background. Stimuli subtended 9.5° horizontally and
13.6° vertically of visual angles. Angular distances between fixation
locations were as follows: forehead-nasion: 2.1°; nasion-nose tip:
2.1°; nose tip-mouth: 2.1°; nasion-left/right eye: 1.9°. The positioning
of the face to obtain the desired feature fixated resulted in opposite
face positions for upright and inverted faces for two fixation locations.
When upright, faces were situated almost entirely in the upper visual
field when fixation was on the mouth and almost entirely in the
lower visual field when fixation was on the forehead. The opposite
pattern was seen when faces were inverted (Fig. 1).
Root Mean Square Contrast andmean luminance (pixel intensity) of
the pictures were calculated using custom Matlab (Mathworks, Inc.)
scripts (see Table 1). Houses and intact faceswere compared using independent
t-tests (two-tailed, equal variance not assumed) and intact andeyeless faces were compared using paired sample t-tests (two-tailed).
Compared to house stimuli, mean luminance was greater (t(39.2) =
−11.09, p b 0.001) and contrast was lower (t(43.9) = 44.02, p
b 0.001) for face stimuli. Luminance was also greater (t(39) = −25.5,
p b 0.001) and contrast was lower (t(39) = 32.9, p b 0.001) for eyeless
compared to intact faces, as expected given the removal of the high contrast
zone that eyes represent.
Design
Participants sat 70 cm in front of a computer monitor in a dimly-lit
sound-attenuated Faraday-cage protected booth and performed an
orientation-detection task using a game-controller, pressing one button
for upright and another for inverted stimuli. Button order was counterbalanced
across participants. Participants were asked not to move their