The Picture-Word Interference Effect is a Stroop Effect After All

The Picture-Word Interference Effect is a Stroop Effect After All Leendert van Maanen (leendert@ai.rug.nl) Hedderik van Rijn (D.H.van.Rijn@rug.nl) Artificial Intelligence, University of Groningen P.O. Box 407 9700 AK Groningen, The Netherlands color if it spells a different color word than if it does not spell a color word (e.g., M. O. Glaser & Glaser, 1982). That is, participants are slower in naming the color of a written word if that word is another color (e.g., saying “red” to a stimulus that is the word “green” written in red), as compared to naming a colored spot alone (that is, without the distractor “green”). This effect is usually referred to as Stroop interference. In picture-word interference tasks, a similar interference pattern can be observed (e.g., W. R. Glaser & Dungelhoff, 1984). Picture-naming latencies are increased for pictures that are accompanied by incongruent words relative to latencies of these pictures in isolation. For example, naming a picture of a cat together with the word “dog” takes longer than naming that same picture without the word. However, when target and distractor relate to the same concept, participants typically respond faster than to the target alone, an effect called facilitation. For example in the Stroop task, the word “red” written in red ink elicits a faster color naming response than a red spot. The PWI analog is that a picture of a cat accompanied by the word “cat” is responded to faster than a picture of a cat alone. Besides the interference and facilitation effects and their prototypical design, PWI and Stroop share many other characteristics. For instance, both interference and facilitation typically disappear if the task is changed to naming the written word. This effect is sometimes referred to as Stroop asynchrony (W. R. Glaser & Dungelhoff, 1984). Given all these similarities 1 , it has regularly been assumed that both tasks tap a similar set of underlying processes. Abstract The idea that picture-word interference (PWI) and the Stroop effect are two manifestations of the same process has been widely accepted. However, recently Dell’Acqua and colleagues (2007) have questioned the identical nature of the Stroop effect and picture-word interference, based on the observation that the loci of both effects in the mental processing stream differ. In this paper, we will present a dynamic computational model of semantic interference for both the Stroop effect and PWI. The model is based on competition between possible responses in both Stroop and PWI tasks. The differences between both tasks are solely explained by differences in processing speed of the stimuli. This way, our model does justice to the different loci of effects observed by Dell’Acqua et al, while at the same time supporting the long-held view that both Stroop and PWI are indeed similar in the underlying processes. Keywords: Stroop effect; picture-word cognitive model; ACT-R; RACE. interference; Introduction Through the years, the idea that the picture-word interference (PWI) effect and the Stroop effect are two manifestations of the same process has been widely accepted. For instance, MacLeod’s influential review on the Stroop effect (MacLeod, 1991) also discusses picture-word interference, and even lists the picture-word 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). In previous work, we have also taken for granted that picture-word interference is just an instance of the Stroop effect. Van Maanen and Van Rijn (2007b) described a computational model of picture-word interference, and when discussing related models, we actually focused on models of the Stroop task. The wide acceptance that PWI and the Stroop effect are one and the same effect probably stems from the (behavioral) similarities between the two. First, the prototypical paradigm for both tasks is that participants are requested to respond to one stimulus, while being presented with a second stimulus. In the case of the Stroop task, the to-respond-to stimulus (henceforth referred to as the target) is the color a word is printed in, and the to-be-ignored stimulus (the distractor) is a written word. Similarly, in picture-word interference tasks, the target is a picture, and the distractor is a word. Over the years, a wide range of variations of this paradigm have been presented (for an overview, see MacLeod, 1991). Second, both tasks display similar latency distributions. The typical Stroop effect is that it is harder to name the ink Difference between Stroop and PWI Recently it has been suggested that the Stroop effect and picture-word interference may not be caused by the same process (Dell'Acqua et al., 2007). In particular, it seems that the loci of the two effects in the mental processing stream differ. Many researchers now agree that the locus of the Stroop effect is on the level of response selection (e.g., Fagot & Pashler, 1992; Kuipers, La Heij, & Costa; MacLeod, 1991; Roelofs, 2003). That is, the Stroop interference comes about because an incorrect response possibility that is triggered by the distractor, interferes with the correct response that is triggered by the target stimulus. Fagot and Pashler (1992, Experiment 7) studied whether the Stroop effect would persist in a psychological refractory For a more extensive comparison between PWI and Stroop, see (Dell'Acqua, Job, Peressotti, & Pascali, 2007; MacLeod, 1991).