Recognising faces: effects of lighting direction, inversion, and brightness reversal

Area of Science:

• Psychology
• Cognitive Science
• Neuroscience

Background:

• The human visual system often interprets ambiguous 3D shape from shading and shadows with an assumption of top-down illumination.
• Rotating images can invert their perceived orientation and alter perceived lighting direction.

Purpose of the Study:

• To investigate whether the effects of figural inversion and lighting orientation on face recognition are independent or interactive.
• To determine how illumination direction influences the face inversion effect.

Main Methods:

• Participants viewed images of faces under different lighting conditions (top-lit vs. bottom-lit) and orientations (upright vs. inverted).
• The effect of figural inversion on face recognition was assessed for each lighting condition.
• The impact of lighting direction on photographic negatives was also examined.

Main Results:

• A significant face inversion effect was observed for faces illuminated from above.
• This inversion effect was substantially reduced or eliminated for faces illuminated from below.
• A strong inversion effect was found for photographic negatives, independent of illumination direction.

Conclusions:

• The findings suggest that illumination from below interferes with the visual system's ability to form surface-based representations of facial shape.
• The results support the hypothesis that lighting orientation and figural inversion interact in face recognition.
• Bottom lighting may disrupt the typical processing of facial geometry and identity.