Mental travel: some reservations.

Two experiments were conducted to assess the extent of potential experimental demand characteristics inherent in the image-scanning paradigm. The results of the first "mental travel" experiment that pitted verbal versus imagery coding showed that (a) the positive correlation between physical distance and reaction time was replicated, and (b) when given a choice, subjects' reaction times varied as a function of verbal codes rather than imagery. To isolate the effects due to demand constraints from those produced by mode dominance, a nonexperiment in which subjects received only a description of the image-scanning procedure was conducted. Results demonstrated that subjects were capable of predicting the reaction time results for both verbal and imagery codes. The presence of experimental demand in the image-scanning paradigm necessitates caution when structural interpretations of visual images are considered.