It has been argued that the relationship between "F 2 locus" and "F 2 target", expressed in terms of the so-called locus equation, provides a context-independent measure of place of articulation in stop consonants. In this experiment, however, data from three Swedish speakers suggest that a variable other than place of articulation, namely aspiration (quantified in terms if voice onset time,
... [Show full abstract] VOT), can affect locus equation parameters substantially. This is accounted for in terms of aerodynamic constraints on the production of aspirated stop releases. The result of this experiment complicates the definition of an invariant measure of place of articulation and suggests that an acoustic separation of stop categories can only be achieved by introducing additional dimensions, e.g., VOT.