About the unidirectionality of interference: Insight from the musical Stroop effect

Abstract

The asymmetry of interference in a Stroop task usually refers to the well-documented result that incongruent colour words slow colour naming (Stroop effect) but incongruent colours do not slow colour word reading (no reverse Stroop effect). A few other studies have suggested that, more generally, a reverse Stroop effect can be occasionally observed but at the expense of the Stroop effect itself, as if interference was inherently unidirectional, from the stronger to the weaker of the two competing processes. We describe here a situation conducive to a pervasive mutual interference effect. Musicians were exposed to congruent and incongruent note name/note position patterns, and they were asked either to read the word while ignoring the location of the note within the staff, or to name the note while ignoring the note name written inside the note picture. Most of the participants exhibited interference in the two tasks. Overall, this result pattern runs against the still prevalent model of the Stroop phenomenon [Cohen, J. D., Dunbar, K., & McClelland, J. L. (1990). On the control of automatic processes: A parallel distributed processing account of the Stroop effect. Psychological Review, 97(3), 332–361]. However, further analyses lend support to one of the key tenets of the model, namely that the pattern of interference depends on the relative strength of the two competing pathways. The reasons for the impressive differences between the results collected in the present study and in the standard colour–word (or picture–word) paradigms are also examined. We suggest that these differences reveal the importance of stimulus–response contingency in the formation of automatisms.

Keywords:

• Stroop
• Interference
• Automatism
• Musical expertise
• Contingency

This research was supported by the Agence Nationale de la Recherche [grant number ANR-09-JCJC-0129]; the Conseil Régional de Bourgogne [grant number 2012-9201AAO05S01353].

Notes

¹For the sake of simplicity, except when specified otherwise, the difference between incongruent and congruent conditions is coined here as interference, even though a part of the effect may arguably be due to facilitation in the congruent condition.

²This terminology is conventional (e.g., MacLeod, 1991), but not without its own shortcomings, notably because it applies only to situations in which reading is one of the two competing processes. Given that an overwhelming proportion of the Stroop literature involves reading, however, this is not a strong limit, and this definition is used throughout this paper.

³Using two logographic scripts, Japanese and Chinese, Verdonschot, La Heij, and Schiller (2010) reported standard Stroop effects in a picture–word interference task. However, when investigating the RSE, they observed that reading Japanese kanji was shortened by the incongruent pictures compared to unrelated pictures. No effect at all was observed with Chinese hànzì. Irrespective of the interpretation of these findings, they concur to generalize the asymmetry of the Stroop effect to nonalphabetic writing systems.

⁴In addition, Zakay and Glickson (1985) used similar conditions as a part of a more general paradigm, and verbal responses showed no reliable evidence for an MSE. However, methodological limitations are probably responsible for this failure, as analysed in Grégoire et al. (2013).

⁵Given that the MSE is an instance of RSE as defined above, the RMSE, in which reading is the interfering process, has the status of a Stroop-like effect. This terminological quibble is unfortunate, but seems unavoidable, because it is difficult to revisit a terminology forged through eight decades of tradition during which reading has been the almost exclusive target in Stroop studies.

⁶Some proportionality between the size of a difference and the raw values on which this difference is computed is a common observation. In addition, the effect may be strengthened by the fact that slow responses may be less automatized and, hence, following Cohen et al.'s (1990) model, more receptive to interference than fast responses.