Abstract
What is the information mediating race categorization? Mangini & Biederman (2004; see also Konsevitch & Tyler, 2004) have recently proposed an original application of the reverse-correlation technique in which the base stimulus (i.e. the stimulus on which the decision is done) is ambiguous with respect to the task at hand (e.g. in a task where the subject had to identify John Travolta and Tom Cruise, the stimulus was a morph of both). This methodology permits to reveal the information mediating face classification and the combination of the noise classification image with the base stimulus explicitly shows the prototype used by the subject for the decision process in the task. We selected 6 faces of White and Black men. Each pair of black/white faces (36 possible combinations) was morphed by incorporating different amount of the black and white faces (e.g. 10% white, 90% Black; 16% white, 84% Black and so on) to find the combination that led observers to categorize the stimulus as Black (or White), 50% of the time. We then asked 5 subjects to categorize 10,000 times the resulting 36 ambiguous stimuli embedded in white Gaussian noise. The subjects were unaware that each base face was ambiguous with respect to race, with only the noise tipping one way or the other. We then computed the classification image by subtracting the average noise fields for which the subjects responded “White”, from the average noise fields for which they responded “Black”. The resulting classification images, computed on an individual basis, reveal what information mediates race categorization as well as the prototype used by each subject to respond. These results will be discussed in relation to the racial prejudices shown by each individual subject.