Pragmatic Inferences and ERP Components

The ERP components that have received the most attention in the investigation of pragmatic inference making are the N400 and the P600. While the N400 has historically been an index of semantic/world knowledge violations which occur at the sentence level (as shown in the well-known example, “He spread the warm bread with socks” [14]), it has also been shown that it more generally reflects inconsistencies between the linguistic code and the provided context (e.g., [15]–[17]). For example, Nieuwland and van Berkum [15] employed fictional contexts as they showed how an expression that is inconsistent with its immediate discourse context – even if it fits with one’s general knowledge – can elicit an enhancement of the N400. To give one specific example, they presented a story in which a peanut was as an animated character and, within this context, the utterance “The peanut was salted” elicited an enhancement of the N400 with respect to the utterance “The peanut was in love.”

The P600 was originally considered to be an index of syntactic violations (e.g., a violation of phrase structure, [18]) but it has since become associated with a broad range of linguistic expressions. For example, P600’s have been reported with respect to sentences that have semantic (reversal) anomalies (e.g., “The cat that fled from the mice”, [19]) and semantic (illusory) anomalies in a discourse context (e.g., “How many animals of each sort did Moses put on the Ark?” (e.g., [20]). The P600/Late positivity effect is also one of the most recurring outcomes from studies on pragmatic phenomena. For example, indirect requests (see for example, [21]), metaphors (see e.g., [9]) and ironies (see e.g., [11]) elicit an increase of the P600 component. However, considering the broad range of linguistic phenomena that can prompt a P600, it is hard to come up with a functional interpretation of the P600, even in the pragmatic domain, other than to say that these phenomena usually involve a mismatch between the literal meaning of an utterance and the message it conveys (e.g., when one says “John is a shark” it does not mean that John is a real shark; likewise, when (1) is used ironically it is meant to indicate that the day was very unproductive). A role for inconsistency is coherent with one of the major interpretations of the P600 effect, viz. an increase in the P600 correlates with an increase in sentence integration processes (for reviews see, for example, [22], [23]).

Given recent methodological advances, viz. the development of Time Frequency Analysis (TFA), it is clear that electrophysiological studies of language can now go beyond identifying ERP components and determining what may characterize them. Investigating the oscillatory dynamics of the brain with respect to language comprehension has the potential to identify, and in a fine-grained manner, how different streams of information are integrated in language comprehension and how different cognitive resources contribute to this process. In the current work, we follow a proposal from Bastiaansen (e.g., [24]) who assumes that two different cognitive processes, namely memory retrieval operations and unification operations, are among the most central to language comprehension (see Hagoort’s work e.g., [25] for a more detailed elaboration of this assumption) and that these link to oscillation dynamics. More specifically, memory operations – which refer to activities related to the retrieval and encoding of information – can be revealed through the theta and alpha bands while unification operations – which refer to the integration of two or more cognitive processes necessitated by a stimulus – can be detected through the oscillations in the beta and gamma bands. As will become clear, we will eventually focus on unification operations. However, before describing the link between brain oscillations and language processing in more detail, let us introduce a couple of crucial notions about Time Frequency Analysis.

Brain Oscillations

TFA allows one to investigate the patterns of synchronization and desynchronization of neuronal activity related to the coupling and uncoupling of functional networks in the brain (see e.g., [26]–[29]). Elements pertaining to the same functional network are identifiable as such by virtue of the fact that they fire synchronously at a given frequency. One of the main features of the oscillations is that they are ongoing phenomena that occur even in the absence of any experimental task. As a result, the phase of the oscillation at the time of occurrence of the event is variable. Therefore, one can say that any change in oscillatory activity that is related to an experimental event is time-locked to this event, but not necessarily phase-locked to the event (on the contrary, ERPs are phase-locked responses). However, the experimental stimuli modulate the oscillatory activity and so event-related but non-phase-related responses may be meaningfully related to an event such as language comprehension. Considering that synchronization/desynchronization reflects the coupling/decoupling of neural networks, it can be argued that these oscillatory EEG responses provide a window into the functional network dynamics of the brain (see for example [24]).

The Present Study

Both theoretical accounts (e.g., [43]–[45]) and experimental studies (e.g., [7], [11]) assume that irony is a prototypical case of pragmatic inference making in which the processing of the linguistic code does not itself guarantee the comprehension of the utterance. Listeners need to integrate the linguistic code with the context in a manner that ultimately reveals the speaker’s intention. The electrophysiology literature on pragmatic processing, briefly summarized above, indicates that the most reliable cue of such integration processes (or unification operations) are the P600 and the gamma band. Therefore, in the present paper we will concentrate our attention of these markers. However, it is likely that the unification operations also require an extensive engagement of cognitive resources and so we will take a closer look at the increase or decrease of power in the alpha band in the likely event that these become evident.

It is relevant to point out that current debates on irony processing are dominated by three accounts that are, for the most part, focused on the (presumed) impact that literal meanings have on the figurative interpretation of an ironic utterance. The earliest comes from what is often called the Standard Pragmatic Model (SPM), which represents psychology’s best effort to create a processing model based on Paul Grice’s theoretical account of communication [1], [43]), according to which figurative utterances are departures from a norm of literal truthfulness. Irony is said to be understood because the speaker is blatantly violating a maxim of quality (“Do not say what you believe to be false”) which then triggers implicatures that can be calculated from the literal meaning of the sentence. Implicitly, according to these SPM accounts, figurative readings of an utterance ought to come with extra processing costs because readers need to detect violations and come up with richer interpretations, which would not be the case for literal readings of the same utterances.In reaction to the so-called SPM, Raymond Gibbs pointed to a host of figurative cases, including irony (and especially sarcasm), that provide readers with an enriched pragmatic reading without requiring extra processing (time) when compared to literal readings of the same utterances. Central to Gibbs’s account is the assumption that a figurative interpretation is constructed “directly” by the early integration of lexical and contextual information. In his own words, ‘‘People need not first analyze the literal, pragmatic-free meaning of an utterance before determining its figurative, implicated interpretation” ([46], 421).

One of the most influential accounts, Giora’s Graded Salience Hypothesis ([47], [48]), seeks to find an equilibrium between these two extremes. This hypothesis emphasizes that the most salient meaning of an ironic utterance is the one that is accessed first regardless of whether it is literal or figurative (e.g., ironic) and that, furthermore, the salient meaning of a figurative remark is the one that is encoded in the mental lexicon of the audience. Salience is defined as a function of different features such as familiarity, conventionality, frequency and prototypicality. Therefore, if the figurative meaning of an ironic utterance is encoded in the lexicon it will be processed first; in cases where less familiar (and then less salient) ironies are used, more inferential steps – and thus more cognitive effort – will be necessary for arriving at the intended interpretation. Much recent work presents supporting evidence for the Graded Salience Hypothesis [47]–[50] which sets itself up as being in opposition to the Direct Access view.

As far as we know there are five EEG studies on irony [10], [11], [51]–[53] and the most recurrent finding is that ironical sentences elicit P600/late positivity components that are larger than those prompted by control (literal) sentences. As reported above, this result is in line with a general tendency reported in the ERP literature with respect to pragmatic phenomena. Nevertheless, it is difficult to come up with a functional interpretation of the P600 because a wide range of linguistic phenomena elicit enhancement of this component. Another limitation of ERP studies on irony is that they are focused on the three psycholinguistic accounts of irony described above. In the most recent study [11], for example, the authors aimed to determine the extent to which their results verify the predictions of the Standard Pragmatic Model, the Direct Access View and the Graded Salience Hypothesis. The data revealed just a partial match with both the Standard Pragmatic Model and the Graded Salience Hypothesis. This led Regel et al. to call for a revision of the psycholinguistic models of figurative language comprehension. By considering a wider array of theoretical approaches, one could be in a better position to understand the multiple processes that are generated by irony.

Rather than focus on the features of irony processing from the point of view of pragmatic theories, the present EEG study focuses on the integration of different streams of information while paying particular attention to those that can be described as uniquely pragmatic. Through both ERP analysis and TFA, it is our goal to have a clearer picture of critical moments of information integration in irony comprehension. By applying TFA to irony processing this approach promises to highlight how two critical aspects of comprehension – the linguistic code and context – combine.

Participants

Twenty healthy participants, who were students from the Université de Lyon, participated in the study. All participants (whose mean age was 23; no minors have participated to the study) were native French speakers, were right-handed and reported to have normal vision and no history of mental illness. In accordance with the principles of the Declaration of Helsinki, the study was approved by the Ethical Committee CPP Sud-Est II in Lyon. All participants gave their written informed consent prior to the beginning of the experimental session.

Materials

Sixty story-frameworks were created (in French) that led to a target sentence that could be interpreted either as ironic or as literal as a function of a minor modification made to prior context. For example, a story about two opera singers could describe a negative event (e.g., a terrible performance) or a positive context (e.g., an impressive performance) and thus give the utterance in (4) an Ironic or Literal interpretation, respectively:

1. “Tonight, we gave a superb performance.”

Otherwise, the introductory sentences and the wrap-up sentences of any given framework were the same for both conditions. The structure of the stories was the same as the one employed in Spotorno et al. [7] and thus contained the following six features:

First, all stories were seven lines long, each having a maximum length of 91 characters (spaces included) in order to fit into one line on a screen. Second, the stories described an everyday situation and an exchange between two characters who knew each other only casually (i.e., we avoided situations that presumed close relationships among interlocutors). Third, the first three sentences introduced the two characters and the situation. Fourth, the fourth and fifth sentences described the development of the situation that can be either positive (in the literal version) or negative (in the ironic version). These were the only two lines that could potentially change with respect to condition. Changes were designed to be as minimal as possible while keeping the stories sensible. Fifth, the sixth line was designed to be the target sentence. The length of all target sentences was between 10 and 12 syllables. Crucially, the target sentence (line 6) was exactly the same in both Ironic and Literal conditions and just the last word (e.g., “productive” in 1) allowed one to determine whether the sentence was ironic or not. Finally, the seventh line was an ordinary wrap-up conclusion of the story that makes sense for both the Ironic and Literal conditions (for an example see Table 1 and the Table S1).

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Table 1. Examples of the four kinds of stimuli (translated from French).

https://doi.org/10.1371/journal.pone.0066839.t001

We aimed to prevent negative contexts from being cues to the presence of ironic remarks by introducing other stories in which a negative context (e.g., a bad performance) led to a plain, non-ironic utterance (e.g., “We will do better the next time.”). We refer to these stories as decoys. We created 30 decoys having the same structure as the ironic stories (a negative event that occurs early on in a 7-sentence story), except that the target sentence was banal. For example, the decoy story in Table 1 describes how one character drops a mirror, which leads the other character to remark “We have made a big mistake.” Like in the Ironic and Literal conditions, the target sentence in decoy stories is between 10 and 12 syllables (see also the Table S2 for further examples). We also designed 30 positive fillers in which a positive context was followed by a positive remark (for examples, see the Table S3).

Each participant read 30 ironic stories, 30 literal stories, 30 decoys and 30 positive fillers. For each participant, the 60 critical (non-decoy) stimuli were extracted randomly from a pool of 60 frameworks that could each be the basis of either an ironic or literal target sentence. The 30 decoys and the 30 positive fillers remained the same for each participant.

To verify that the stimuli used here were perceived as intended, a rating study was conducted on the 90 stories (2 from each of the frameworks plus the 30 decoys) with 42 participants (22 women) whose ages ranged from 19 to 38 (with a mean of 26) and who did not participate in the EEG study. Participants were asked to read each story and rate the extent to which the target sentence was ironic on a scale from 1 (not at all ironic) to 5 (very ironic). Ironic target sentences were rated as highly ironic (mean of 4.3), while literal sentences and the banal lines from the decoy stories were rated as low on the ironic scale (1.3 both of them). Repeated measure ANOVAs showed significant differences between (i) the Ironic and Literal conditions and (ii) the Ironic condition and Decoys (both at p<.001, corrected for multiple comparisons using the Tukey method). The comparison between the Literal condition and the Decoys was not significant (p = .1).

A yes/no comprehension question followed one third of the items (regardless of whether it was a critical or filler item). The question was about a detail in the story that made no reference to the target sentence. The purpose of the comprehension question was to ensure that the participants were paying attention to the stories. (See Table 1 for an example of all conditions and questions and the Appendix for further examples.).

Procedure

Stimuli were prepared with Presentation 11.0 software (Neurobehavioral Systems, www.neurobs.com) and presented on a computer screen. Participants performed the experiment in four runs of 30 stories each. Each trial started with the presentation of a visual fixation mark (a white central cross). The participant read the stories line by line (i.e., sentence by sentence) in a self-paced manner (i.e., each sentence remained on the screen until the participant pressed a key) The interval between the disappearance of a sentence and the presentation of the next one was 500 ms. One line of each story was presented word-by-word in the center of the screen and each word appeared for 800 ms. In both the Ironic and Literal conditions the target line was always presented word-by-word. On the contrary, in the other 60 stories the line presented word-by-word was chosen randomly (see Figure 1) in order to prevent word-by-word presentation from being a cue about the experiment’s purpose. After the last sentence (line 7) disappeared, the question was presented in one third of the trials and the participants pressed one of two buttons on a mouse (yes/no response) to answer it (see Figure 1). Variable periods of visual fixation (1000 ms.+between 1 and 1000 ms.) were added at the end of each trial. The presentation order of the stories was pseudo-randomized. This means that the number of ironic and literal stories, decoys and fillers was balanced among the sessions. Fifteen ironic stories, 15 literal stories, 15 decoys and 15 positive fillers were presented in each half of the experiment. Each stimulus was displayed in a left-justified manner. Participants were instructed to read at a normal rate and to respond as accurately as possible to the questions. The experimental session began with 2 training trials, which did not include ironies. All told, a typical session lasted an hour (including breaks).

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Figure 1. Experimental procedure.

https://doi.org/10.1371/journal.pone.0066839.g001

Electroencephalogram (EEG) Recording

EEG data were recorded using BrainAmp amplifiers (Brain Vision recorder software, Brain Products GmbH, Munich, Germany). EEG was recorded from 32 scalp sites using the international 10–20 system [54], with a forehead ground. Impedance was 10 kΩ or less at the start of the recording. All scalp sites were referenced to the left mastoid. Horizontal and vertical eye movements were monitored using electro-oculograms (EOG) with a bipolar recording from electrodes placed around the left eye. The signal was sampled at 500 Hz.

Analysis

Both the ERP and TFA were conducted using ELAN-Pack software developed at INSERM U821 (Lyon, France) [55]. Trials contaminated by eye blinks or eye movements (threshold: ±75 µV) were not included in the analyses nor were trials that were affected by drifts (range value 150 µV and latency: 500 ms.). Data from 3 subjects were excluded from the analyses because noise and eye movements contaminated more than half of the trials in the target condition.

ERP Results

Figure 2 shows the time-course of the ERPs elicited by the Ironic and the Literal conditions at Cz. A repeated measures ANOVA on the 300–500 ms. time window showed a main effect for Laterality [F(2, 32) = 4.43, p<.05], Anterior-Posterior [F(2, 32) = 3.91, p<.05] as well as a significant interaction between the two variables [F(4, 64) = 2.62, p<.05]. However, the statistical analysis showed no significant difference between the Ironic and the Literal conditions [F(1, 16) = .03, p>.8] nor any interaction between the variable Intended-interpretation (Ironic/Literal) and the other variables. Therefore, our results do not reveal an N400 effect linked to Irony (see Appendix S1 and Figure S1 for a further analysis on a time window compatible with the N400). With respect to the 500–800 ms. time window, a repeated measure ANOVA revealed a main effect of Laterality [F(2, 32) = 11.23, p<.001], a marginally significant effect of the variable Intended-interpretation [F(1, 16) = 3.61, p = .075] and a significant interaction between Intended-interpretation and Anterior-Posterior [F(2, 32) = 5.84, p<.01]. A Tukey HSD test revealed that the difference between the Ironic and Literal conditions was due to a positive enhancement of the ERPs wave in the Ironic condition which were superior in the frontal sites. Considering the polarity and the shape of the ERP wave for the Ironic condition, we consider this difference in enhancement a P600 effect (see Figure 2).

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Figure 2. ERP waves for theIronic (red line) and the Literal (blue line) conditions at Fz.

The gray rectangle highlights the interval at which point the difference between the Ironic and the Literal condition is significant. On the right are the scalp distributions for both conditions at the peak of the P600 effect.

https://doi.org/10.1371/journal.pone.0066839.g002

TFA Results

Visual inspection of the spectrum of frequencies suggested the presence of an increase of power both in the theta band (4–7 Hz) and in the gamma band (30–90 Hz) during the Ironic condition. In addition, the power in the alpha band (8–12 Hz) seemed to increase in the frontal areas and to decrease in the parietal regions in this condition. The statistical analysis revealed that the difference of power in the theta band between the Ironic and the Literal conditions is significant between 500 and 700 ms., especially in the right frontal regions of the scalp (Z = 2.4; p<.05). In the alpha band, comparisons between the Ironic and Literal conditions were significantly different between (a) 400 and 700 ms. in the right frontal part of the scalp (Z = 2.6; p<.05) and between (b) 550 and 700 ms. in the left parietal areas (Z = − 1.7; p<.05). However, the variation (a) indicates an increase of power in the alpha band while the variation (b) reveals a decrease of power in the same band. The statistical analysis also showed a significant increase of power in the early range (31–35 Hz) of the gamma band between 280 and 400 ms. in the frontal areas of the scalp (Z = 2.4; p<.05) (see Figure 3 and 4). In the next section, we describe what these effects mean in cognitive terms.

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Figure 3. Time frequencies analysis.

From the left: Z value for the contrast Ironic/Literal in the theta band at F4; Z value for the contrast Ironic/Literal in the alpha band at F4; Z value for the contrast Ironic/Literal in the alpha band at P3 and Z value for the contrast Ironic/Literal in the gamma band at Fz.

https://doi.org/10.1371/journal.pone.0066839.g003

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Figure 4. Scalp distribution of the different frequency bands at the significant time-windows.

From the left: scalp distribution of theta waves (Z value for the contrast Ironic/Literal); scalp distribution of alpha waves (Z value for the contrast Ironic/Literal) and scalp distribution of gamma waves (Z value for the contrast Ironic/Literal).

https://doi.org/10.1371/journal.pone.0066839.g004

Contributions to the Debate on Irony Processing

A majority of studies on irony processing are focused on ongoing debates that pivot around the Standard Pragmatic Model, the Direct Access View and the Graded Salience Hypothesis. These theories are arguably focused on the alleged priority of a literal interpretation in an ironic remark while ignoring the cognitive mechanisms that are behind the comprehension of ironies; nevertheless, those accounts propose interesting predictions on irony processing and any researcher needs to face up to them.

The present work clearly supports accounts of irony understanding that reveal its complex and effortful nature; it extensively engages cognitive resources and it is demanding in terms of integration operations, as is reflected by both the P600 effect and the increase of power in the gamma band. Therefore, the data do not support the Direct Access View and they seem to be more compatible with either the SPM or the Graded Salience Hypothesis. However, the synchronization in the gamma band between 280 and 400 ms. seems to reveal that integration operations take place early in the comprehension process; this result cannot be easily accounted for by either of these two accounts because both assume that the integration between lexical aspects and contextual information occurs as part of a later-occurring second step. Therefore, the present study as well as Regel et al.’s [11] call for a revision of the dominant psycholinguistic models of irony processing.

A more recently developed position, called the Constraint-Satisfaction Approach [51], [72]–[74], seems to fit well with the present data. Following this proposal, all available information – such as lexical entries and contextual cues – are integrated as soon as they are relevant in order to derive a coherent representation of the speaker’s intent. Therefore, an ironic interpretation of the utterance is considered as soon as there is sufficient evidence that it might be supported. The constraint-satisfaction approach is compatible with results revealing extra effort in irony processing, (the increase of the P600) as well as those showing that integration operations take place early on, e.g., the increase of power in the gamma band between 280 and 400 ms. However, further studies are necessary to determine which constraints are being satisfied.

Conclusion

The results we presented support the hypothesis that pragmatic inferences basically require the addressee to integrate the linguistic stimulus with the information that she can extract from the context. The increase in magnitude of the P600 during the Ironic condition when compared to the Literal one reflects effort as one integrates the ironic utterance with the preceding context, while the increase of power in the gamma band for the contrast Ironic>Literal reveals that the integration between different streams of information takes place early in the comprehension process. While our reading of the TFA data is generally in line with the interpretation provided by Bastiaansen and colleagues [24] these results are newsworthy because we have extended the analysis so that it considers a pragmatic dimension. We have focused our investigation on irony because it is a prototypical pragmatic case that encourages a listener to go beyond the linguistic code in order to grasp the utterance’s intended meaning. We anticipate that the reported findings, coming from several angles (i.e., P600, the pattern of oscillations in the gamma band), as well as the interpretation that we provide for them can eventually be applied to pragmatic inference-making more generally.