Local gender biases in face appearance across the visual field.
Seyed-Reza Afraz, Maryam Vaziri-Pashkam, Patrick Cavanagh
While testing stimuli in another experiment, we had noticed that the
perceived gender of a neutral face could change from male to female
at different locations in the visual field. To investigate this
effect systematically, we asked subjects to discriminate face gender
for briefly presented faces at 8 different loci around the fixation.
The stimuli were faces morphed at various levels between the female
prototype to the male prototype. The faces were about 2 degrees in
diameter, presented at 3 degrees eccentricity for 50 milliseconds.
The point of subjective equality (PSE) for male/female discrimination
was determined from the psychometric curves for tested locations.
Results from all individual subjects showed hot spots in which faces
look significantly more masculine or feminine (in comparison to the
average PSE of the individual). The configuration of these hot spots
was distinctive for each individual. To investigate stability of this
hot spot configuration, subjects were tested again after about three
weeks (19 to 24 days) from the initial test. All subjects showed the
same pattern and the PSE values for the tested locations were highly
and significantly correlated for each individual across the three
weeks interval. Using the same paradigm in a separate experiment, we
asked subjects to discriminate slightly horizontally vs. vertically
elongated ellipses at different loci. There again we found some
degree of heterogeneity across space, although the effect magnitude
was smaller and the pattern was less stable in time. Our results suggest
localized, independent biases in the tuning of face selective units, at least
in the gender dimension, that support recent findings of crude retinotopy in
face analysis areas in the brain.