EXPRESS: Measuring Individual Differences in Word-Meaning Disambiguation.

Theories of the mental lexicon must explain how people use context to interpret ambiguous words (e.g., "internal organ" vs. "musical organ") and why people vary on this core aspect of comprehension. Theoretical development has been hampered by the lack of reliable tests of disambiguation skill. We introduce a task in which participants hear three-sentence narratives with an ambiguous final word (e.g., "organ") and select the appropriate picture from two alternatives. Experiment 1 (N=197) confirmed the viability of this task using a repeated-measures design optimized for detecting group-level ambiguity effects: participants were slower and less accurate for ambiguous compared with closely matched control items in which the final word was replaced with a similar but unambiguous word, e.g., "piano"). We replicated this ambiguity disadvantage using a less closely matched control condition that was developed for Experiment 2 (N=242) which was optimised to measure variation in disambiguation skill. Experiment 2 confirmed robust variability in accuracy and response time, but measurement reliability ranged from r=.41 to .65, below the conventional r=.70 threshold, and correlations with other cognitive tasks were inconsistent. These results highlight the challenges of adapting complex, repeated-measures experimental paradigms to detect individual differences, and provide a framework for developing and assessing such measures.