Testing the limits of intentional linguistic control in bilinguals

Researchers have investigated the psychological processes (and their neural underpinnings) that enable bilinguals to speak the desired language with little/no intrusion from the other language(s). One popular laboratory paradigm that asks bilinguals to switch languages on demand, has shown switches to result in delayed and less accurate spoken responses - the "switch cost". A likely source of the "switch cost" is that communication in the required language can be subject to interference from the other language(s). How bilinguals resolve such interference to select the intended language is a fundamental question still awaiting a satisfactory answer. The project proposes to test and evaluate two intriguing, yet contentious, hypotheses put forward recently.

Can bilinguals "switch off" the unwanted language?
One established theory argues that when looking for a lexical item (word) in the desired language, bilinguals inhibit the word(s) with the same meaning in the other language(s). More recently, this "inhibitory control" framework has been extended by the suggestion that bilinguals may be able to intentionally suppress not only specific words, but an unwanted language - referred to as "global inhibition". Evidence for this hypothesis comes from the "reverse language dominance" effect: when bilinguals use two languages intermittently, performance in their dominant/strong language (henceforth L1) is worse than in the non-dominant/weak language (henceforth L2), presumably as a result of having to inhibit L1 more strongly while communicating in L2, and subsequently having to overcome that inhibition to use L1 again. However, a recent meta-analysis concluded that the available data do not unequivocally indicate the existence of reverse dominance. Thus the evidence for global inhibition is limited and indirect.
To address this state of affairs, the project will:
- employ a within-participants design (to maximise power) and develop conditions which will encourage global inhibition (should it exist) to contrast with other conditions requiring little/no global inhibition. For instance, participants would first be asked to generate words in L2 which they more commonly use in L1. Presumably, this should engage global inhibition of L1 to prevent interference from it, subsequently impairing performance in L1, relative to a control condition where the initial L2 block contains items that are easy to generate in L2 (hence less need to inhibit a less interfering L1).
- employ novel multivariate decoding of brain potentials (EEG) to derive and temporally track latent EEG "signatures" of the activation of L1 and L2 to look for any signs of global inhibition.

Can language switches be "cost-free"?
As mentioned previously, there is ample evidence that when bilinguals are required to switch languages (e.g. by presenting a visual cue specifying the language to use for the following stimulus), there is invariably a performance "switch cost". However, recently it has been proposed that when bilinguals have the opportunity to switch freely they can adopt a "mixed-language processing mode" wherein the word most available for retrieval is spoken irrespective of the language it comes from, which should eliminate the switch cost. Indeed, two recent studies claimed to provide evidence of such cost-free voluntary switching. However, these studies had relatively low power, relied on very limited stimulus sets and instructed participants to remember to use the same language for any given stimulus throughout the experiment. The latter encourages participants to approach this as a memory (associative retrieval) task. To address the aforementioned concerns, the project will examine the possibility of cost-free language switching using large sets of stimuli, avoiding stimulus repetitions, and removing any language requirement for specific stimuli, to rule out the interpretation in terms of cued associative retrieval and ensure free choice of language.