Asymmetry in Stroop interference arising from naming practice: shape beats color

Stroop interference is characterized by strong asymmetry between word and color naming such that the former is faster and interferes with the latter but not vice versa. This asymmetry is attributed to differential experience with naming in the two dimensions, i.e., words and colors. Here we show that training on a visual-verbal paired associate task equivalent to color and shape naming leads to strongly asymmetric interference patterns. 28 adults practiced naming colors and novel shapes, one dimension more extensively (10 days) than the other (2 days), using nonsense syllables. Despite equal training, color naming was strongly affected by shape even after extensive practice, whereas shape naming was more resistant to interference. To reconcile these findings with theoretical accounts of interference, reading may be conceptualized as involving visual-verbal associations akin to “shape naming.” An inherent advantage for naming shapes may provide an evolutionary substrate for the invention and development of reading.