Some musings on the "sameness" of standardized experimental stimuli

The traditional approach to experimental research in psychology involves the creation of experimental settings with standardized stimuli and measures of response. Significant care is taken to eliminate differences in the stimuli presented to participants, except insofar as this constitutes manipulation of the independent variable. For example, a study investigating the effect of the color of light on mood might expose participants to environments that vary in color, but in no other way. It is assumed that participants exposed to the same color environment are being exposed to the same stimulus.

It's not hard to see how this can become problematic. In a psychological context, different qualities (e.g., color) are not readily manipulated independently of other qualities For example, changing a heart from yellow to purple is hardly just a change in color, since the latter color evokes the U.S. military service award the purple heart. Consequently, the variable color is confounded with presence or absence of whatever associations a particular participant may or may not have with the military medal.

There are two issues here. The first is the way that variables that are analytically distinct may be conflated empirically (color with connotations of military service). The second is that the fact that this conflation is not solely a result of the stimulus itself, but also of a particular participant's interpretation of that stimulus. In other words, the "same" stimulus can be interpreted in different ways by different participants (or the same participant on different occasions). In the color research example, this means that some participants exposed to the purple heart would perceive the connotation to military service honor and others would not. In effect, participants ostensibly exposed to the same stimulus have actually been exposed to different percepts.

This second issue--which has been raised by a number of critical commentators--is hardly hidden. It's fairly obvious that different stimuli could have different meanings for different participants. Still, the fact that researchers go on as if stimuli can be treated as "the same" for different participants is hardly just an error.

In acting as if the same stimulus will be "the same" for different participants, researchers are making an assumption that underlies human social interactions in general. The foundation of human cultural life is intersubjectivity, i.e., the assumption of a shared world of objects which exist for me as they do for you. If we were to replace wholesale the assumption of intersubjectivity with the skepticism that things as they appear to me are not necessarily as they appear to you, language would be impossible.

While accepting the basic reasonableness of the critique of standardized stimuli, it's worth considering whether the intersubjective basis of human cultural life entails some important role for standardized stimuli. In other words, what does the centrality of the assumption of a shared environment in human life in general mean for research contexts where this assumption may be made?