The Similarity Differential Rate Hypothesis

After Contrastive Analysis was called into question because it could not predict areas of difficulty, it was modified into the so‐called moderate version, claiming that similar phenomena are more difficult to acquire than dissimilar phenomena (see Oller & Ziahosseiny, 1970). Eckman (1977) added a very significant modification to further salvage Contrastive Analysis by incorporating markedness. In addition, the prolific work of Flege on similarity,including his Speech Learning Model (1995), has provided us with extensive data on degree of difficulty in second language acquisition. Although the bulk of his and his collaborators' work supports his claim that similar sounds are harder to learn than dissimilar sounds, there are important exceptions (e.g., Bohn & Flege, 1992). Furthermore, other researchers have presented conflicting claims and results. The importance of this chapter is that it ties together similarity and markedness in a claim concerning rate of acquisition, rather than “degree of difficulty”—a vaguely defined term. The Similarity Differential Rate Hypothesis (SDRH) quite simply claims that similar phenomena are acquired at faster rates than dissimilar phenomena and that markedness is a mediating factor that slows rate. In making its claims, it calls into question some widespread time‐honored concepts in L1 and L2 studies that are poorly defined or mean different things to different researchers. Specifically, what criterion level or percent accuracy is needed for a phenomenon to be “acquired”? What does it mean for x to be acquired before y? If at Stage I, x = 40% accuracy and y = 20% accuracy, we could say x is acquired before y and is less difficult; but if at Stage II, x = 50% and y = 80%, we could say y is acquired before x and is more difficult. In light of this, the SDRH claims that we have been asking the wrong questions, and that rate is the significant factor. In the example above, what is consistent is rate: The rate of acquisition of y is faster than x. In L1 acquisition research, although order of acquisition has been a perennial concern (e.g., Jakobson, 1941, 1968, and current research on the minimal word involving morae), according to David Ingram (personal communication, 1998), rate has not been a major topic in L1 phonology. (Although Ingram himself [1991] has talked about gradual and abrupt rates, he says there is no explanation why these variable patterns exist.) However, because rates have predictive implications (with the ca