A set of neurolinguistic experiments which are aimed at obtaining evidence of how persuasion through implicitness is furthered by neural and processing mechanisms which are distinct from those at play during the processing of explicitly encoded meanings.
The assumption that implicit strategies are more efficient than straightforward explicit communication, though already experimentally inquired through behavioral lines of research, still awaits full neurological description. Three experiments will be carried out. Brain activity will be captured thorough a high temporal resolution electroencephalograph and the acquired encephalographic signal (EEG) will be analyzed using spatio-temporal techniques in order to shed light on the “brain signatures” of linguistic implicits. They will be aimed at measuring the differences in processing effort and brain localization between the assertion of certain content and its implicitation (within the same context) through presupposition and topicalization.
The neurophysiological bases of implicit information processing: inquiring the brain
The experiments will inquire the brain signatures for better understanding of the neurophysiological bases of persuasion through implicits. The project will provide some experimental evidence for the different resources devoted by the brain respectively to the processing of explicit and implicit information. This will represent a progress in our attempts to understand why professional persuaders can have recourse to the implicit encoding of some content as an effective means to persuade people of doubtful or false contents, which the same people would reject if overtly stated.
In order to explain the persuasive effectiveness of implicits, the project will inquire the neurophysiological correlates of their brain processing. It will contribute neurolinguistic evidence of how persuasion through implicitness exploits neural responses different from those at play when processing explicitly encoded meanings.
2. State of the art
The interplay of discourse strategies and attention has been the plank of much experimental work. The first behavioral studies (Hornby 1974, Loftus 1975, Birch & Rayner 1997, Ward & Sturt 2007, among others) on the psychological underpinnings of presupposition, topicalisation and implicature showed, through reading time or eye movement techniques, that the mental representation of presupposed and topicalised information involved reduced processing demands, as compared to assertive and focal counterparts. On the contrary, implicatures are reported to require extra mental work (Cory et al. 2014, Romoli & Schwarz 2015).
Most early behavioral paradigms used poorly contextualized or isolated sentences, which may have led subjects to interpret utterances by following linguistic cues only (Masia 2017), whereby topic and presupposition instructed to less attentive processing than asserted or focal information. Subsequent neuroimaging studies (Burkhardt 2006, Cowles et al. 2007, Burmester et al. 2014, La Rocca et al. 2016, Masia et al. 2017) have highlighted the crucial role of context in the decoding of presuppositional/assertive and topical/focal units. The processing cost of presupposed and topical information seemed to be more strongly conditional on discourse-driven expectations than on surface properties of content presentation: presupposition and topic cost more when they convey new information (Wang & Schumacher 2013, Masia et al. 2017, La Rocca et al. 2016) or are realized with less expected accentuation patterns (Hruska & Alter 2004, Baumann & Schumacher 2011).
3. Research questions
Despite some initial insights on the brain correlates of implicit communication, evidence is still scant and not always convergent on systematic patterns. Among other things, this can be put down to the adoption of diversified experimental paradigms as well as to the manifold functional interpretations still given to electrophysiological components, such N400 or P600 (Luck & Kappenman 2012), and to the oscillatory activity in given frequency bands (Pfurtscheller & Lopes da Silva 1999). Therefore, with particular regard to the processing of presuppositions and topicalisations, the project will address the following lines of research:
a. develop neurobiologically and cognitively plausible accounts of the way the brain deals with implicit contents in a message;
b. isolate the brain signatures of different implicit communication strategies;
c. unravel the relation that different kinds of cognitive costs bear on the efficiency of critical judgment and truth evaluation of a sentence.
4. Electrophysiological methodologies adopted
In line with recent practices in electroencephalographic research on language processing (Bastiaansen & Hagoort 2006, Bastiaansen et al. 2012), both event-related potential recordings and data from oscillatory brain rhythms will be elicited. Differently from the Event Related Potential (ERP) technique, the measurement of brain oscillations has only recently been re-applied extensively, also due to its utility in clarifying the functional significance of N400 and P600 (Roehm et al. 2007). To the best of our knowledge, brain oscillations have never been considered for investigating the neurophysiological underpinnings of presuppositions, and little is known on the activity of different frequency bands in response to topic-focus processing, except for some first studies carried out by ourselves (La Rocca et al. 2016, Masia et al. in prep.). So, this part of the project may also provide a pioneering groundwork to fine-tune new experimental methodologies.
5. Experimental designs
In order to comply as strictly as possible with parameters of ecological validity, experimental materials will be created out of authentic occurrences of transcribed speech taken from the political corpus. Slight modifications will ensure the normalization of the stimuli for experimental purposes. So, instead of using context-isolated sentences, all target presuppositions and topicalisations will be preceded by a natural amount of contextual information. The three experiments will inquire the brain processing of, respectively: presuppositions vs assertions; accommodated vs satisfied presuppositions; and topicalized vs focalized contents. Different presupposition triggers will be tested in each of the two first experiments. With a view to isolating linguistic packaging effects from contextual ones, all critical contents will be New information in the provided contexts (Chafe 1976).