Inhibition of feature extraction with multiple instances of the target feature in different orientations

Analyses of alphabetic confusion matrices have produced feature lists defined in terms of confusability of characters thought to contain them. Identical shapes of low confusability (e.g., b, d, p, q) therefore share few or no features. Several researchers have observed mutual inhibition of feature extraction with simultaneously presented confusable shapes. Mutual inhibition observed in the current experiments provides a basis for a definition of features in terms of orientation-independent structural relationships. In the first experiment, four alphanumeric characters were each confused with one other character in this same set; however, when another set was formed by reorienting some of these same shapes to become different characters (e.g., 6 to 9), these confusions disappeared. In the second experiment, characters within each set were exposed parafoveally in pairs to different groups of subjects. If members of a pair were similar in shape (disregarding orientation), identification accuracy was poorer than if they were not. Similar shapes in the same orientation were not signficantly more mutually inhibiting than similar shapes in different orientations.