As discussed in the introduction, early studies relating complex span measures like reading span to sentence processing assumed that these measures reflected a single capacity that could be flexibly allocated to storage or processing (Daneman and Carpenter, 1980; Just and Carpenter, 1992). However, recent studies argue against the assumption that WM capacity reflects a unitary capacity. Both Shipstead et al. (2014) and Unsworth et al. (2014) concluded, on the basis of large scale individual differences studies, that WM capacity can be divided into three components reflecting primary memory capacity (i.e., the capacity for maintaining information in the focus of attention), attentional control, and the ability to retrieve information from outside the focus of attention (i.e., from secondary memory). Secondary memory retrieval ability was not assessed in the present study and thus we cannot comment on its potential contribution to interactions of WM capacity with sensitivity to syntactic and semantic interference. Although, digit span may not be an ideal measure of primary memory capacity, it is highly correlated with other measures that have been argued to reflect this capacity (e.g., running span; Cowan et al., 2005). Thus, the significant interaction of WM capacity with syntactic interference even with digit span in the model suggests that the influence of WM capacity does not reflect the influence of primary memory capacity. An obvious candidate for explaining the relevant shared variance between WM capacity and interference resolution that would be consistent within the cue-based retrieval framework is attentional control. This hypothesis could also explain the link observed between WM capacity as measured by the complex WM tasks and the efficiency of controlled memory retrieval in previous memory studies (Öztekin and McElree, 2010; Mızrak and Öztekin, 2016). Öztekin and McElree found that low-WM span subjects took longer for the controlled retrieval of episodic information as compared to high-WM span subjects. As they suggested that there should be no differences in subjects' primary memory capacity (or the limit of focus of attention) assuming both groups could only maintain 1-item, such a relation might reflect better attentional control for high WM span subjects.