Abstract
Last year we reported that the color information alone is sufficient to determine the sex of a human face and that observers rely on this information in sex judgments when shape information is degraded. Here we build on these findings by addressing two new questions. First, when shape information in a face is ambiguous with regards to sex can we manipulate sex judgments by altering the ratio of red to green? This was investigated by crossing several morphs between male and female faces (I. Bülthoff — MPIK Tübingen) with a continuum of different red to green ratios. This two-dimensional shape-color space is bounded by male-shaped, reddish faces and female-shaped, greenish faces. Subjects judged the sex of faces at many points in this space. At the boundaries of the space, shape information determines sex classification regardless of the red to green ratio. However, at intermediate points where shape information is ambiguous, observers appear to rely on color information in judging sex. This effect is enhanced by forcing observers to judge sex very quickly or by removing the most extreme male and female faces along the shape dimension (i.e., when shape is less diagnostic overall, observers weight it less).
Second, how early in the visual processing of information does color influence sex decisions? Using a go-no-go sex judgment task with Event Related Potentials (ERPs) as the dependent measure we explored whether a “visual decision marker” (Thorpe et al., 1996) would be modulated depending on whether color was present or not in faces. We found that the ERP signal difference between go and no-go trials occurring approximately 200 ms post stimulus was both larger and earlier for color faces as compared to grayscale faces. Critically, there was no difference between the color and grayscale conditions independent of the sex judgment. We conclude that early decisions about the sex of a face are facilitated by the presence of color.
This research was supported by Grant no. 1R01EY12691 from the NEI/NIH.