Testing the viability of webDMDX for masked priming experiments

The DMDX software package (Forster & Forster, 2003) is a Windows-based application that displays stimuli and records responses. Recent developments in this program have made it possible to deploy DMDX experiments over the Internet. This study evaluates the viability of the web-deployable implementation of DMDX, or webDMDX, for masked priming experiments. A lexical decision task (LDT) with masked repetition priming on high- and low-frequency words and an e/a letter detection task were conducted with both lab-based DMDX (labDMDX; Experiment 1) and webDMDX. The webDMDX experiments were run on lab computers (Experiments 2) and on different (unknown) hardware (Experiment 3). The labDMDX and webDMDX experiments yielded comparable results on the LDT. In the e/a-detection task, the only important difference observed among the tests was between the lab-based experiment (Experiment 1) and the first webDMDX experiment (Experiment 2), at the 50 ms display duration. However, after a minor change in keyword coding (Experiment 2 follow-up) and an adjustment to the millisecond-to-retrace conversion process (Experiment 3), the detection rates at all display durations were similar in both labDMDX and webDMDX. Taken together, these results indicate the utility of webDMDX for masked priming experiments as well as for other time-sensitive methodologies.