Dwight Peterson

Social psychophysics: Using psychophysics to answer “social” questions with PsychoPro

Complex social stimuli (like faces) can be studied using a methodology typically reserved for studying lights, tones, and colors: psychophysics. Given that psychophysics examines how humans detect and respond to stimuli in their environment, we can extend that to the study of how humans detect social stimuli in the environment. Using psychophysical methodology to answer “social” questions provides another dimension of experimental manipulation and control to the diverse array of methodologies already used by social psychologists. In this article, we review psychophysical methodology, provide a rationale for social psychophysics, describe an easy-touse software program called PsychoPro, for collecting psychophysical data, and present data collected using this program to examine racial thresholds that provide evidence for a cognitive gating mechanism for racial information that impacts face processing (MacLin & MacLin, 2007, in press; MacLin, MacLin, & Peterson, 2008).

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.

The "Bookshelf Illusion" - A Real World Zöllner-type Illusion?

We discovered an interesting perceptual distortion in our office where an upright lamp in front of a bookshelf was noticeably curved to form several subtle S-shaped bends. We realized that the books in the bookshelf fell in a particular manner, leaning in alternative directions, which caused the straight lamp to appear bent, creating what may be a real-world example of the Zöllner illusion. Evidence for the production of the illusion diagrammatically and an explanation for the effect are provided.