Thatcher and the Cheshire cat: context and the processing of facial features.
As has been noted before, a face made gruesome by the inversion of its mouth will not be so perceived when the entire construction is inverted. Results are presented which suggest that this is because the mouth and eye features are evaluated individually (although each feature may influence the evaluation of the other) and the mouth, whether normal or inverted, tends to have its uppermost part assigned as 'top', providing for either a pleasant smiling-mouth expression or a gruesome 'biting-intention' expression. However, the gruesomeness of an inverted mouth is attenuated when eyes are shown below it (producing an inverted smiling face) which suggests that the location of other facial features can also influence the assignments of 'top'.
D005123:Eye; D005149:Facial Expression; D005556:Form Perception; D006801:Humans; D009055:Mouth; D010364:Pattern Recognition, Visual