This page remains for archival purposes as a supplement to our first paper about using GCA to analyze VWP data. The methods and code here are now substantially outdated and not recommended.
Growth curve analysis (GCA) is a multilevel orthogonal polynomial curve-fitting approach designed for analysis of time-course data. This method can be applied to visual world paradigm (VWP) data to analyze effects of experimental manipulations (e.g., word frequency) and to analyze individual differences.
Mirman, D. Dixon, J.A., & Magnuson, J.S. (2008). Statistical and computational models of the visual world paradigm: Growth curves and individual differences. Journal of Memory and Language, 59(4), 475-494.
Abstract: Time course estimates from eye tracking during spoken language processing (the "visual world paradigm", or VWP) have enabled progress on debates regarding fine-grained details of activation and competition over time. There are, however, three gaps in current analyses of VWP data: consideration of time in a statistically rigorous manner, quantification of individual differences, and distinguishing linguistic effects from non-linguistic effects. To address these gaps, we have developed an approach combining statistical and computational modeling. The statistical approach (growth curve analysis, a technique explicitly designed to assess change over time at group and individual levels) provides a rigorous means of analyzing time course data. We introduce the method and its application to VWP data. We also demonstrate the potential for assessing whether differences in group or individual data are best explained by linguistic processing or decisional aspects of VWP tasks through comparison of growth curve analyses and computational modeling, and discuss the potential benefits for studying typical and atypical language processing.
Examples
Data and analysis code (R and SAS): Download zip file
Here are materials from my workshops on using multilevel models (growth curve analysis) to analyze eye tracking data. (Both workshops were in Feb. 2010, one at MRRI and one sponsored by the Cognitive Science Program at Northwestern University).
A good place to start is Part 1: Conceptual Foundations. This presentation lays out the motivation and basic principles of growth curve analysis.
Part 2 is a step-by-step walk through an example of a growth curve analysis of data from a typical "visual world" eye tracking experiment (Mirman & Magnuson, 2009b). The presentation describes the experiment, analysis procedure, and results. The zipped archive contains the data file (SemanticCompetitionExample.txt) and the analysis script (gca_script.r) to go with that example.
How to use residual (aka "random") effects to quantify individual differences is described in Part 3: Individual Differences. That presentation gives one example (Mirman, Yee, Blumstein, & Magnuson, 2011) and the zip archive contains a script (gca_indivDiffs.r) for running a similar individual differences analysis on the walkthrough example data.
LCDL TR2011.01: Choosing between lme and lmer for Growth Curve Analysis
*** This list has not been updated since 2012. If you are very interested in papers that directly reference this method, try Google Scholar ***