Peltola et al. (2012) showed that there are two types of bilinguals.
Balanced bilinguals mix their two languages and are effected by linguistic categories from both.
Dominant bilinguals seem to switch on the categories of the language they are using, and suppress the categories of the language not in use.
The task Peltola et al. (2012) studied was phoneme categories. The boundaries between vowels are arbitrary and set by the language of the user. The researchers focused on two sounds that are categorised as different vowels in Finnish, but are the same vowel in Swedish. When dominant bilingual participants were briefed about the study in Finnish, they distinguished the sounds quickly. When the same participants were briefed about the same experiment a week later in Swedish, their ability to distinguish the sounds slowed significantly. The balanced bilinguals were equally slow under both briefings.
A similar arbitrary language-dependent categorization exists in colour perception (Regier & Kay, 2009). In fact, the effect of this arbitrary categorization is even lateralized: the Whorf hypothesis is supported in the right visual field but not the left (Gilbert et al., 2006)! So the basics of linguistic relativity seem to be cross-modal.
Do dominant bilinguals switch linguistic categories on and off in the visual domain? Is the result of Peltola et al. (2012) cross-modal?