Numerosity-length interference: a Stroop experiment

The existence of a common mechanism for length and numerosity processing was tested with a Stroop task. Participants compared the length or the numerosity of arrays of dots, for which the two variables were manipulated independently to create congruent, incongruent, or neutral pairs. Results showed that the spatial cues strongly interfered with the processing of numerosity, whereas the numerical cues only moderately interfered with the processing of length. These findings reflect a different mandatory processing of numerosity and length.