Presentations

Abstract

The ability to use linguistic representations to refer to the world is a vital mechanism that gives human language its communicative power. In particular, the anaphoric use of words to refer to previously mentioned concepts (antecedents) is what allows dialogue to be coherent and meaningful. Psycholinguistic theory posits that anaphor comprehension involves reactivating an episodic memory representation of the antecedent [1-2]. Whereas this implies the involvement of memory structures, the neural processes for reference resolution are largely unknown. Here, we report time-frequency analysis of four EEG experiments [3-6], revealing the increased coupling of functional neural systems associated with coherent referring expressions compared to referentially ambiguous expressions. We performed time-frequency analysis on data from four experiments in which referentially ambiguous expressions elicited a sustained negativity in the ERP waveform compared to coherent expressions. In Experiment 1, 32 participants read 120 correct Dutch sentences with coherent or ambiguous pronouns. In Experiment 2, 31 participants listened to 90 naturally spoken Dutch mini-stories containing coherent or ambiguous NP anaphora. In Experiment 3, 22 participants each read 60 Spanish sentences with a coherent or ambiguous ellipsis determiner. In Experiment 4, 19 participants each read 180 grammatically correct English sentences containing coherent or ambiguous pronouns. Analysis was performed with Fieldtrip [7], separately for low frequency (2-30 Hz) and high frequency (25-90 Hz) activity. Power-changes per trial were computed as a relative change from a pre-CW baseline interval, average power changes were computed per subject for coherent and ambiguous conditions separately. Statistical tests used cluster-based random permutation [8]. Despite varying in modality, language and type of expression, all experiments showed larger gamma-band power around 80 Hz for coherence compared to ambiguity, within a similar time range. No differences were observed in low frequencies. In high-density EEG Experiment 4, an additional short-duration gamma-increase was observed around 40 Hz, around 300-500 ms after pronoun-onset, which was localised using Beamformer analysis [9] to left posterior parietal cortex (PPC). The 80 Hz power increase around 600-1200 ms after word onset was localised to left inferior frontal-temporal cortex. We argue that the observed gamma-band power increases reflect successful referential binding and resolution, linking incoming information to previously encountered concepts and integrates that information into the unfolding discourse representation. Specifically, we argue that this involves antecedent reactivation in the PPC episodic memory network [10-11], interacting with unification processes in the frontal-temporal language network [12]. Based on these results, and on results of patient [13] and fMRI [14] research on pronoun comprehension, we propose an initial neurobiological account of reference, by bridging the psycholinguistics of anaphora with the neurobiology of language and of episodic memory. [1] Dell et al., 1983 [2] Gerrig & McKoon, 1998 [3] Nieuwland & Van Berkum, 2006 [4] Nieuwland et al., 2007a [5] Martin et al., 2012 [6] Nieuwland, 2014 [7] Oostenveld et al., 2011 [8] Maris & Oostenveld, 2007 [9] Gross et al., 2001 [10] Shannon & Buckner, 2004 [11] Wager et al., 2005 [12] Hagoort & Indefrey, 2014 [13] Kurczek et al., 2013 [14] Nieuwland et al., 2007b

Abstract

The ability to use words to refer to the world is a vital mechanism that gives human language its communicative power. In particular, the use of words to refer to previously mentioned concepts (anaphora) is what allows dialogue to be coherent and meaningful. Psycholinguistic theory posits that anaphor comprehension involves reactivating a memory representation of the antecedent. Whereas this implies the involvement of episodic memory, the neural processes for reference resolution are largely unknown. Here, we report time-frequency analysis of four EEG experiments to reveal the increased coupling of functional neural systems associated with referring expressions that can be straightforwardly understood compared to those that cannot (referential coherence or ambiguity). Despite varying in modality, language and type of referential expression, all experiments showed larger gamma-band power for coherence compared to ambiguity. In high-density EEG Experiment 4, Beamformer analysis localised this increase to the posterior parietal cortex around 300-500 ms after onset of the anaphor and to frontal-temporal cortex around 500-1000 ms. We argue that the observed gamma-band power increases reflect successful referential binding and resolution, which links incoming information to previously encountered concepts through an interaction between the episodic memory network and the frontal-temporal language network.

Abstract

Current accounts of sentence comprehension invoke the notion of retrieval interference as a primary determinant of difficulty during processing [1-2]. Specifically, similarity between constituents (e.g., NP feature-overlap) has been argued to interfere when people resolve subject-verb or anaphoric dependencies [3-7]. We ask whether similarity-based interference effects arise as a function of multiple NPs in the discourse that overlap in gender and/or number. We take a novel approach by examining interference effects at the second NP rather than downstream after “maintaining” multiple NPs [6- 8], using ERPs to establish quantitative and qualitative processing consequences. We used the empty category PRO to introduce two NPs, only the second NP could be PRO controller (e.g., “While [PRO] talking to the waitresses, the man/men/woman/women inspected the menu”). If feature overlap affects processing of the second NP, most interference should occur under gender- and number-matching NPs. Because this interference crosses the subject-object distinction, we predicted that interference would elicit a P600 effect, the effect most reliably associated with syntactic processing difficulties [9]. Methods: During EEG recording, 24 participants read 160 grammatical sentences (40 per condition) in a 2(gender: match, mismatch) x 2(number: match, mismatch) factorial design where the first clause introduced the object-NP and had PRO as subject, and the matrix clause introduced the controller of PRO. Subject and object NPs could overlap in gender and/ or number. We fully counterbalanced 160 male/female singular/plural gender-definitional nouns as object NPs, and as critical NP always ‘woman/man/girl/boy’ (or plural form). Sentences were mixed with 156 fillers and presented word by word (300 ms duration, 200 ms blank), followed by intermittent comprehension questions (85% response accuracy). Results: Across all electrodes, a significant gender by number interaction was observed (500-800 ms window [9]; F(1,23)=6.02, p<.05), due to a robust P600 effect of number-mismatch in the gender- match conditions (M=-1.18, F(1,23)=8.04, p=.01), that did not occur in the gender-mismatch conditions (M=-.17, F(1,23)=.18, ns). No distributional effects were observed. Conclusions: The P600 effect for double-match NPs suggests that interference was driven by similarity contingent upon matching gender and number. Our results testify to the strength of gender-cues during incremental processing, consistent with memory-based accounts of discourse comprehension [2-7]. The results suggest that when features maximally overlap, the subject NP may be momentarily considered as an anaphor for the more distinctive (i.e., first-mentioned and semantically richer) object NP. Alternatively, the P600 may reflect increased discourse complexity stemming from similar NPs [10]. Our results imply a central role for interference during comprehension, even of simple grammatical sentences. References: [1] Lewis, Vasishth, Van Dyke, 2006; [2] McElree, Foraker, & Dyer, 2003; [3] Gerrig & O’Brien, 2005; [4] Gordon, Hendrick, & Johnson, 2004; [5] McKoon & Ratcliff, 1998; [6] Van Dyke & McElree, 2006; [7] Gordon, Hendrick, Johnson, & Lee, 2006; [8] Wager & Phillips, 2013; [9] Osterhout & Holcomb, 1992; [10] Kaan & Swaab, 2003

Abstract

Current accounts of sentence comprehension invoke the notion of retrieval interference as a primary determinant of difficulty during processing [1-2]. Specifically, similarity between constituents (e.g., NP feature-overlap) has been argued to interfere when people resolve subject-verb or anaphoric dependencies [3-7]. We ask whether similarity-based interference effects arise as a function of multiple NPs in the discourse that overlap in gender and/or number. We take a novel approach by examining interference effects at the second NP rather than downstream after “maintaining” multiple NPs [6-8], using ERPs to establish quantitative and qualitative processing consequences. We used the empty category PRO to introduce two NPs, only the second NP could be PRO controller (e.g., “While [PRO] talking to the waitresses, the man/men/woman/women inspected the menu”). If feature overlap affects processing of the second NP, most interference should occur under gender- and number-matching NPs. Because this interference crosses the subject-object distinction, we predicted that interference would elicit a P600 effect, the effect most reliably associated with syntactic processing difficulties [9]. Methods: During EEG recording, 24 participants read 160 grammatical sentences (40 per condition) in a 2(gender: match, mismatch) x 2(number: match, mismatch) factorial design where the first clause introduced the object-NP and had PRO as subject, and the matrix clause introduced the controller of PRO. Subject and object NPs could overlap in gender and/or number. We fully counterbalanced 160 male/female singular/plural gender-definitional nouns as object NPs, and as critical NP always ‘woman/man/girl/boy’ (or plural form). Sentences were mixed with 156 fillers and presented word by word (300 ms duration, 200 ms blank), followed by intermittent comprehension questions (85% response accuracy). Results: Across all electrodes, a significant gender by number interaction was observed (500-800 ms window [9]; F(1,23)=6.02, p<.05), due to a robust P600 effect of number-mismatch in the gender-match conditions (M=-1.18, F(1,23)=8.04, p=.01), that did not occur in the gender-mismatch conditions (M=-.17, F(1,23)=.18, ns). No distributional effects were observed. Conclusions: The P600 effect for double-match NPs suggests that interference was driven by similarity contingent upon matching gender and number. Our results testify to the strength of gender-cues during incremental processing, consistent with memory-based accounts of discourse comprehension [2-7]. The results suggest that when features maximally overlap, the subject NP may be momentarily considered as an anaphor for the more distinctive (i.e., first-mentioned and semantically richer) object NP. Alternatively, the P600 may reflect increased discourse complexity stemming from similar NPs [10]. Our results imply a central role for interference during comprehension, even of simple grammatical sentences. References: [1] Lewis, Vasishth, Van Dyke, 2006; [2] McElree, Foraker, & Dyer, 2003; [3] Gerrig & O’Brien, 2005; [4] Gordon, Hendrick, & Johnson, 2004; [5] McKoon & Ratcliff, 1998; [6] Van Dyke & McElree, 2006; [7] Gordon, Hendrick, Johnson, & Lee, 2006; [8] Wager & Phillips, 2013; [9] Osterhout & Holcomb, 1992; [10] Kaan & Swaab, 2003

Abstract

Research on subject-verb agreement during comprehension suggests a ‘grammaticality asymmetry’ in similarity-based retrieval interference. Whereas processing costs incurred by ungrammatical subject- verb agreement are reduced in the presence of a grammatically illicit attractor noun that matches the verb in number, attractor nouns have not been found to affect the processing of grammatical sentences [1]. However, most existing studies have only included singular verbs in the grammatical conditions, and the lack of retrieval interference in such cases could be a result of the fact that singular is an unmarked feature [2]. In the current study, we tested for similarity-based interference for both singular and plural verbs in fully grammatical sentences. If plural is a marked feature, we expect to find evidence of retrieval interference for plural verbs but not singular verbs when multiple items in memory match the number of the verb. We predicted that retrieval interference would elicit a P600 effect [3-4], the effect commonly associated with syntactic processing difficulties. Methods: Participants read 120 grammatical sentences (30 per condition) belonging to a 2(subject noun: plural, singular) x 2(attractor noun: plural, singular) factorial design in which the critical verb (have/had/were/was) always agreed in number with the subject noun. PS: “The keys to the cabinet were getting very rusty”, PP: “The keys to the cabinets were getting very rusty”, SS: “The key to the cabinet was getting very rusty”, SP: “The key to the cabinets was getting very rusty”. Sentences were mixed with 280 fillers and presented word by word (300 ms duration, 200 ms blank). Intermittent yes/no comprehension questions were answered with 92% accuracy. EEG data was recorded from sixty-four channels and segmented into epochs from 200 ms before to 1000 ms verb onset. Data was baselined to 0-200 ms post-stimulus to eliminate spurious effects from pre-critical word differences (see also [3-4]). Results: Using average amplitude per condition across 16 centrally distributed EEG electrodes, repeated measures ANOVAs in the 500-700 ms time window showed an effect of attractor that was reliably different for plural and singular verbs (F(1,35)=4.8, p<.05), with a robust P600 effect elicited by plural verbs (PP minus PS voltage difference, M=.64, F(1,35) = 5.7, p < .05) but none for singular verbs (SS minus SP, M= -.22, F(1,35)=.44, ns). Conclusions: The observed P600 effect for grammatically correct, plural verbs in context of a plural attractor noun suggests that retrieval interference arises as a by-product of grammatical processing, and constitutes evidence against a grammaticality asymmetry in interference effects. References: [1] Wagers, M. W., Lau, E. F., & Phillips, C. (2009). Journal of Memory and Language [2] Bock, K., & Eberhard, K. M. (1993). Language and Cognitive Processes [3] Kaan, E. (2002). Journal of Psycholinguistic Research [4] Tanner, D., Nicol, J., Herschensohn, J., & Osterhout, L. (2012). Proceedings of the 36th Annual Boston University Conference on Language Development (pp. 594-606).