Stroop and Garner effects in comparative judgment of numerals: The role of attention

In 7 experiments, participants selected the larger member of pairs of digits that differed in numerical magnitude as well as in physical size. Selective attention to the relevant dimension (number or size) was gauged by Garner and Stroop interference, both of which varied considerably as a function of the number and relative discriminability of values along the constituent dimensions. When the to-be-ignored dimension was more discriminable, sizable Garner and Stroop effects affected performance on the relevant dimension. When it was less discriminable, Garner and Stroop effects were considerably smaller regardless of whether the relevant dimension was numerical or physical size. The sensitivity of Stroop interference to manipulations of discriminability is accounted for by the allocation of attention to the constituent dimensions. The demonstrated malleability of the Stroop effect is incompatible with claims of strong automaticity in numerical processing.