This article presents a cognitive model that reconciles a surprising observation in the picture-word interference (PWI) paradigm with the general notion that PWI is a form of Stroop interference. Dell'Acqua, Job, Peressotti, and Pascali (2007) assessed PWI using a psychological refractory period (PRP) paradigm, and concluded that the locus of interference in PWI is during the perceptual encoding stage. Stroop interference, on the other hand, is generally attributed to response selection. Based on these findings it was argued that PWI is not a Stroop effect. The present article discusses an alternative interpretation of these results. We assume that both effects are caused by the same interference mechanism, but that the processing speed associated with the different stimuli (colors vs. words) accounts for the previously reported differences. We support this argument by presenting a single computational model that accounts for both PWI and Stroop phenomena in single task and PRP settings.
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Over the years, the idea that the picture-word interference (PWI) effect and the Stroop effect are two manifestations of the same process has gained wide support. For instance, MacLeod's influential review on the Stroop effect (MacLeod, 1991) also discusses PWI, and even lists the PWI task in his list of "eighteen major empirical results that must be explained by any successful account of the Stroop effect" (MacLeod, 1991, Appendix B, p. 203). Recently, Dell'Acqua, Job, Peressotti, and Pascali (2007) have argued that the underlying processes of the PWI and Stroop effects are different, challenging the assumption of a single underlying process. In this article, we will present a computational model that, on the basis of a single process, can explain both the traditional phenomena discussed by MacLeod (1991) and the data of Dell'Acqua et al. (2007).
In the Stroop paradigm, participants are presented with a word written in a specific color and are instructed to either read the word or name the color the word is printed in (MacLeod, 1991; Stroop, 1935). A typical Stroop experiment consists of three conditions: a congruent condition, in which the word and the color refer to the same color concept (e.g., the word "red" written in red ink); an incongruent condition, in which the word and the color refer to different color concepts (e.g., the word "red" written in green ink); and a neutral condition, in which only the text or the color is displayed. This is usually operationalized by presenting a set of Xs in red ink (for color naming) or the word red printed in black ink (for word reading).
Three experimental findings in a Stroop study are extremely robust. First, color naming in the incongruent condition is slower than color naming in the neutral condition. That is, participants required to name the color of the ink are slower if the word describes a different color than if they have to name the color of a row of Xs. This is often referred to as semantic interference, since many accounts of this effect assume that the relation in meaning between the color of the ink and the word itself causes the interference (e.g., Cohen, Dunbar, & McClelland, 1990; W. R. Glaser & Glaser, 1989; Klein, 1964). A second finding in the Stroop literature is that naming the color of the ink of a word that describes the same color (congruent condition) is faster than in the neutral condition. This will be referred to as semantic facilitation (but see MacLeod & MacDonald, 2000, for an alternative explanation of semantic facilitation based on accidental reading of the word). A third important observation is that both semantic interference and semantic facilitation disappear when participants are not instructed to name the color of the stimulus but instead are asked to pronounce the word, regardless of the color the word is printed in. This so-called Stroop asynchrony is often explained by the difference in processing speed between colors and words (e. …