Labov's (1966) attention-to-speech model suggested both social and cognitive elements in style-shifting: social awareness of prestige norms and cognitive defaulting to an easier style when attention is diverted. A focus on social motivations in later work has left the cognitive dimension under-explored. As the contexts elicited in sociolinguistic interviews vary in both attention and register, new methods are needed to tease these apart. In this study, we investigate the cognitive prediction: Does an increase in attentional load cause individuals to struggle to maintain a later-learned style? The novel experimental design eliminates contextual differences by requiring a formal news report style throughout. Twelve speakers of vernacular British English completed two speech production tasks (reading and recall), each with varying attentional load conditions. Higher load conditions included a cross-modal distractor task requiring simultaneous arithmetical calculations. Both of the variables examined—glottal replacement of /t/ and th-fronting—exhibited a consistent but mild trend towards an increase in vernacular forms under higher load. Speakers seem slightly less able to maintain a formal style when their attention is diverted, as suggested in Labov's original description of the vernacular as a default. However, the low level of the effect also suggests that sharp formality shifts cannot be purely due to a reduction in monitoring, but must also involve social awareness of the stylistic norms of a given register. Processing and cognitive ease should therefore be factored in alongside social motivations in the study of style variation.