We administered GVS (or sham stimulation) to healthy individuals engaged in an attentional task. The attentional task (AT) was a spatial cueing paradigm: lateralized targets were presented following a cue which could appear on the same side of the screen (congruent condition) or on the opposite side (incongruent condition). Behavioral differences between congruent and incongruent conditions provide indications about the distribution of spatial attention. Furthermore, the cue could also inform participants about the amount of (monetary) reward at stake. Thus, the AT was designed to measure: 1) performance improvements for cues signaling high rewards; 2) the differential distribution of attention as a function of the value at stake. We have found no evidence for GVS to affect how attention is distributed in space according to the value at stake. However, we have found that GVS reduces sensitivity to rewards. Overall, high rewards at stake boosted participants’ performance; however, this effect was reduced while they were receiving GVS. Results are described in Blini, Tilikete, Farné, and Hadj-Bouziane, (2018, Cortex).
Results have been discussed as originating from visuo-vestibular mismatches, a fundamental, yet overlooked, bodily signal. Visual and vestibular information are usually tightly linked, hence their uncoupling raises several flags. For example, visuo-vestibular mismatches can be subtle, but informative, warning signals which follow the ingestion of noxious neurotoxins, hence the association with nausea, disgust, and vomiting (an attempt to expel them), and the proposed role in aversive conditioning. Thus, results echoed an embodied mechanism to evaluate the desirability of rewards, which seems to extend to secondary-abstract ones (i.e. monetary rewards), and may largely depend on interoception, namely the ability to perceive our innermost physiological states.
With this new evidence, we decided to amend our second objective. As GVS does not affect the interplay between attention and motivation, and additionally reduces performance improvements associated to rewards, we worried that patients with USN would not gain additional benefit from this technique. Instead, we reasoned that GVS may benefit clinical populations in which sensitivity to rewards is extreme, e.g. Addiction Disorders (AD). We have thus designed a task supposedly closer to the clinical picture of AD patients. Specifically, we designed a task capable to measure both motivation and executive functions, i.e. the ability to inhibit irrelevant and conflicting information. In addition, we evaluated the impact of GVS on negative reinforcers (i.e. monetary losses). We have found, indeed, evidence for GVS to increase sensitivity to losses, causing overall increased distraction when losses are at stake. These results suggest that, when the value of one stimulus must be computed, the information arising from bodily processes is taken into account. GVS, through a perturbation of the vestibular system, may bias the desirability of stimuli toward a more negative valence attribution. Positive reinforcers would be, in the context of visuo-vestibular mismatches, devalued; negative ones – whose intrinsic valence matches the current physiological state, meant to arise in perturbed physiological states, e.g. motion sickness – would instead gain in salience. In summary, interoceptive signals drive human motivation, and GVS may be a useful tool to probe this link experimentally. Results are described in a pre-print (Blini, Tilikete, Chelazzi, Farné, and Hadj-Bouziane, submitted,
https://osf.io/b9ezq/(odnośnik otworzy się w nowym oknie)).
During the course of this action, we strived to adhere to the golden standards of Open Science. Results have been published with the Open Access formula, and are thus public. Raw data, materials, and annotated scripts are public as well. The studies have been pre-registered and preliminarily submitted for publication as registered reports. This new format enables full transparency of the experimental protocol and pipeline, enhancing the credibility of reported findings and mitigating publication bias (as findings are published regardless of the final results). Dissemination has been performed through social media (e.g. Kudos, ResearchGate, Twitter, Facebook, Linkedin) and traditional venues; all the materials are publicly available as well (
https://osf.io/5rqy3(odnośnik otworzy się w nowym oknie)). Outreach to a broader audience occurred on social media (e.g. Twitter, Facebook), through individual debriefing for participants to the studies, ad hoc events (e.g. la fête de la science – researchers’ night France, the Web Conf), or initiatives promoted by the Lyon Neuroscience Center (such as Open days for high-school students).
