Perceptual difficulty differences predict asymmetry in redundant modification with color and material adjectives

When referring to objects, speakers are often more specific than necessary for the purpose of establishing unique reference, e.g., by producing redundant modifiers. A computational model of referring expression production that accounts for many of the key patterns in redundant adjectival modification assumes that adjectives differ in how noisy (reliable), and consequently, how useful they are for reference. Here we investigate one hypothesis about the source of the assumed adjectival noise: that it reflects the perceptual difficulty of establishing whether the property denoted by the adjective holds of the contextually relevant objects. In Exp.1, we collect perceptual difficulty norms for items that vary in color and material. In Exp. 2, we test the highest (material) and lowest (color) perceptual difficulty items in a reference game and find that material is indeed less likely to be mentioned redundantly, replicating previous work. In Exp. 3, we obtain norms for the tested items in a second perceptual difficulty measure with the aim of testing the effect of perceptual difficulty within property type. The overall results provide preliminary support for the hypothesis that the propensity to redundantly use color over material adjectives may be driven by the relative ease of assessing an object’s color, compared to the relative difficulty of assessing its material.