Distinctiveness, not dual coding, explains the picture-superiority effect

The picture-superiority effect is the finding that memory for pictures exceeds memory for words on many tasks. According to dual-coding theory, the pictures' mnemonic advantage stems from their greater likelihood to be labelled relative to words being imaged. In contrast, distinctiveness accounts hold that the greater variability of pictures compared to words leads to their mnemonic advantage. Ensor, Surprenant, et al. tested these accounts in old/new and forced-choice recognition by increasing the physical distinctiveness of words and decreasing the physical distinctiveness of pictures. Half of the words were presented in standard black font, and half were presented in varying font styles, font sizes, font colours, and capitalisation patterns. Half of the pictures were presented in black and white and half in colour. Consistent with the physical-distinctiveness account but contrary to the dual-coding account, the picture-superiority effect was eliminated when comparing the black-and-white pictures to distinctive words. In the present study, we extend Ensor, Surprenant, et al.'s results to associative recognition and free recall. Results were consistent with physical distinctiveness. We argue that dual-coding theory is no longer a viable explanation of the picture-superiority effect.