PsychoPro 2.0: using multidimensional scaling to examine the perceptual categorization of race.

Recently, researchers examining cognitive mechanisms involved in the detection of racial markers have been using psychophysics to examine perceptual thresholds delineating race using a program called PsychoPro (MacLin, MacLin, Peterson, Chowdhry, & Joshi, 2009). PsychoPro allows researchers to collect data using facial stimuli morphed along a racial continuum with psychophysical methodology. PsychoPro 2.0 was updated so researchers could collect paired-comparison data that can then be analyzed using multidimensional scaling (MDS). MDS allows researchers to examine the perceptions of racial boundaries along perceptual dimensions not bounded by the stimulus continuum, by having the observer make paired comparisons to racial stimuli based on their perceived similarity. Results indicate that ratings were made on the basis of at least six different racial dimensions that suggest the emergence of a third race not represented by the original morph starting images. Details of the software, the new paired-comparison feature and its relevance in psychophysical studies in general and racial categorization in particular are presented.