Memory for linguistic features and the focus of attention: evidence from the dynamics of agreement inside DP.

The amount of information that can be concurrently maintained in the focus of attention is strongly restricted (Broadbent, 1958). The goal of this study was to test whether this restriction was functionally significant for language comprehension. We examined the time course dynamics of processing determiner-head agreement in English demonstrative phrases. We found evidence that agreement processing was slowed when determiner and head were no longer adjacent, but separated by modifiers. We argue that some information is shunted nearly immediately from the focus of attention, necessitating its later retrieval. Plural, the marked feature value for number, exhibits better preservation in the focus of attention, however, than the unmarked value, singular.

Retrieval cues and syntactic ambiguity resolution: Speed-accuracy tradeoff evidence.

Successful language comprehension often involves coping with lexical and syntactic ambiguity, and sometimes, recovering from misanalysis of the input. Syntactic ambiguity resolution has been shown throughout the literature to result in increases reaction time compared to unambiguous sentences, a fact which has shaped debates about architectures and mechanisms in sentence processing. However, increased reaction time can be caused either by a decrease in true processing speed, or by a decrease in the quality or quantity of information needed to reach criterion when making a response. Thus, increased reaction time to syntactic ambiguity could reflect differences in representational quality or multiple reanalysis attempts, or both. Current cue-based accounts of sentence processing predict that cues at the point where misanalysis becomes apparent (e.g., onset of second verb) may aid in reanalysis (e.g., retrieval of the correct subject). We used the speed-accuracy tradeoff procedure (SAT) to orthogonally derive estimates of processing speed and accuracy. We manipulated ambiguity and the semantic similarity between a disambiguating verb and the nouns already present in the sentence. Estimates of processing speed (SAT rate) indicated that, on average, ambiguous conditions took 250ms longer to interpret than unambiguous controls, demonstrating that reanalysis does increase veridical processing time. No interaction between cue diagnosticity and ambiguity was observed on speed or accuracy, but verbs more strongly related to the correct subject increased accuracy, regardless of ambiguity. These findings are consistent with a language processing architecture where cue-driven retrieval operations give rise to interpretation, and wherein diagnostic cues aid retrieval, regardless of parsing difficulty or structural uncertainty.

Filling Predictable and Unpredictable Gaps, with and without Similarity-Based Interference: Evidence for LIFG Effects of Dependency Processing.

One of the most replicated findings in neurolinguistic literature on syntax is the increase of hemodynamic activity in the left inferior frontal gyrus (LIFG) in response to object relative (OR) clauses compared to subject relative clauses. However, behavioral studies have shown that ORs are primarily only costly when similarity-based interference is involved and recently, Leiken and Pylkkänen (2014) showed with magnetoencephalography (MEG) that an LIFG increase at an OR gap is also dependent on such interference. However, since ORs always involve a cue indicating an upcoming dependency formation, OR dependencies could be processed already prior to the gap-site and thus show no sheer dependency effects at the gap itself. To investigate the role of gap predictability in LIFG dependency effects, this MEG study compared ORs to verb phrase ellipsis (VPE), which was used as an example of a non-predictable dependency. Additionally, we explored LIFG sensitivity to filler-gap order by including right node raising structures, in which the order of filler and gap is reverse to that of ORs and VPE. Half of the stimuli invoked similarity-based interference and half did not. Our results demonstrate that LIFG effects of dependency can be elicited regardless of whether the dependency is predictable, the stimulus materials evoke similarity-based interference, or the filler precedes the gap. Thus, contrary to our own prior data, the current findings suggest a highly general role for the LIFG in dependency interpretation that is not limited to environments involving similarity-based interference. Additionally, the millisecond time-resolution of MEG allowed for a detailed characterization of the temporal profiles of LIFG dependency effects across our three constructions, revealing that the timing of these effects is somewhat construction-specific.

The difficult mountain: enriched composition in adjective-noun phrases.

When readers need to go beyond the straightforward compositional meaning of a sentence (i.e., when enriched composition is required), costly additional processing is the norm. However, this conclusion is based entirely on research that has looked at enriched composition between two phrases or within the verb phrase (e.g., the verb and its complement in . . . started the book . . .) where there is a discrepancy between the semantic expectations of the verb and the semantics of the noun. We carried out an eye-tracking experiment investigating enriched composition within a single noun phrase, as in the difficult mountain. As compared with adjective-noun phrases that allow a straightforward compositional interpretation (the difficult exercise), the coerced phrases were more difficult to process. These results indicate that coercion effects can be found in the absence of a typing violation and within a single noun phrase.

Direct-access retrieval during sentence comprehension: Evidence from Sluicing.

Language comprehension requires recovering meaning from linguistic form, even when the mapping between the two is indirect. A canonical example is ellipsis, the omission of information that is subsequently understood without being overtly pronounced. Comprehension of ellipsis requires retrieval of an antecedent from memory, without prior prediction, a property which enables the study of retrieval in situ (Martin & McElree, 2008, 2009). Sluicing, or inflectional phrase ellipsis, in the presence of a conjunction, presents a test case where a competing antecedent position is syntactically licensed, in contrast with most cases of nonadjacent dependency, including verb phrase ellipsis. We present speed-accuracy tradeoff and eye-movement data inconsistent with the hypothesis that retrieval is accomplished via a syntactically guided search, a particular variant of search not examined in past research. The observed timecourse profiles are consistent with the hypothesis that antecedents are retrieved via a cue-dependent direct-access mechanism susceptible to general memory variables.

Comprehension of Linguistic Dependencies: Speed-Accuracy Tradeoff Evidence for Direct-Access Retrieval From Memory.

Comprehenders can rapidly and efficiently interpret expressions with various types of non-adjacent dependencies. In the sentence The boy that the teacher warned fell, boy is readily interpreted as the subject of the verb fall despite the fact that a relative clause, that the teacher warned, intervenes between the two dependent elements. We review research investigating three memory operations proposed for resolving this and other types of non-adjacent dependencies: serial search retrieval, in which the dependent constituent is recovered by a search process through representations in memory, direct-access retrieval in which the dependent constituent is recovered directly by retrieval cue operations without search, and active maintenance of the dependent constituent in focal attention. Studies using speed-accuracy tradeoff methodology to examine the full timecourse of interpreting a wide range of non-adjacent dependencies indicate that comprehenders retrieve dependent constituents with a direct-access operation, consistent with the claim that representations formed during comprehension are accessed with a cue-driven, content-addressable retrieval process. The observed timecourse profiles are inconsistent with a broad class of models based on several search operations for retrieval. The profiles are also inconsistent with active maintenance of a constituent while concurrently processing subsequent material, and suggest that, with few exceptions, direct-access retrieval is required to process non-adjacent dependencies.

Are representations in working memory distinct from representations in long-term memory? Neural evidence in support of a single store.

Neural activation in a 12-item probe-recognition task was examined to investigate the contribution of the hippocampus to long-term memory (LTM) retrieval and working memory (WM) retrieval. Results indicated a dissociation between the last item that participants studied and other items of the study list: Compared with all other serial positions, activation was reduced for the item in the most recent position (for which no items intervened between study and test). This finding suggests that this last item was in focal attention at test time, and, therefore, no retrieval operation was required to access it. However, contra the assertion that the hippocampus should selectively support LTM, activation of the medial temporal lobe was observed for all serial positions other than the last position, and activation level could be predicted from the underlying memory strength. Collectively, these findings support single-store accounts that assume there are similar operating principles across WM and LTM representations, and the focus of attention is limited.

Relationship between measures of working memory capacity and the time course of short-term memory retrieval and interference resolution.

The response-signal speed-accuracy trade-off (SAT) procedure was used to investigate the relationship between measures of working memory capacity and the time course of short-term item recognition. High- and low-span participants studied sequentially presented 6-item lists, immediately followed by a recognition probe. Analyses of composite list and serial position SAT functions found no differences in retrieval speed between the 2 span groups. Overall accuracy was higher for high spans than low spans, with more pronounced differences for earlier serial positions. Analysis of false alarms to recent negatives (lures from the previous study list) revealed no differences in the timing or magnitude of early false alarms, thought to reflect familiarity-based judgments. However, analyses of false alarms later in retrieval indicated that recollective information accrues more slowly for low spans, which suggests that recollective information may also contribute less to judgments concerning studied items for low-span participants. These findings can provide an explanation for the greater susceptibility of low spans to interference.

On the automaticity and flexibility of covert attention: a speed-accuracy trade-off analysis.

Exogenous covert attention improves discriminability and accelerates the rate of visual information processing (M. Carrasco & B. McElree, 2001). Here we investigated and compared the effects of both endogenous (sustained) and exogenous (transient) covert attention. Specifically, we directed attention via spatial cues and evaluated the automaticity and flexibility of exogenous and endogenous attention by manipulating cue validity in conjunction with a response-signal speed-accuracy trade-off (SAT) procedure, which provides conjoint measures of discriminability and information accrual. To investigate whether discriminability and rate of information processing differ as a function of cue validity (chance to 100%), we compared how both types of attention affect performance while keeping experimental conditions constant. With endogenous attention, both the observed benefits (valid-cue) and the costs (invalid-cue) increased with cue validity. However, with exogenous attention, the benefits and costs in both discriminability and processing speed were similar across cue validity conditions. These results provide compelling time-course evidence that whereas endogenous attention can be flexibly allocated according to cue validity, exogenous attention is automatic and unaffected by cue validity.

Memory operations that support language comprehension: evidence from verb-phrase ellipsis.

Comprehension of verb-phrase ellipsis (VPE) requires reevaluation of recently processed constituents, which often necessitates retrieval of information about the elided constituent from memory. A. E. Martin and B. McElree (2008) argued that representations formed during comprehension are content addressable and that VPE antecedents are retrieved from memory via a cue-dependent direct-access pointer rather than via a search process. This hypothesis was further tested by manipulating the location of interfering material-either before the onset of the antecedent (proactive interference; PI) or intervening between antecedent and ellipsis site (retroactive interference; RI). The speed-accuracy tradeoff procedure was used to measure the time course of VPE processing. The location of the interfering material affected VPE comprehension accuracy: RI conditions engendered lower accuracy than PI conditions. Crucially, location did not affect the speed of processing VPE, which is inconsistent with both forward and backward search mechanisms. The observed time-course profiles are consistent with the hypothesis that VPE antecedents are retrieved via a cue-dependent direct-access operation.

The medial temporal lobe and the left inferior prefrontal cortex jointly support interference resolution in verbal working memory.

During working memory retrieval, proactive interference (PI) can be induced by semantic similarity and episodic familiarity. Here, we used fMRI to test hypotheses about the role of the left inferior frontal gyrus (LIFG) and the medial temporal lobe (MTL) regions in successful resolution of PI. Participants studied six-word lists and responded to a recognition probe after a short distracter period. We induced semantic PI by using study lists containing words within the same semantic category (e.g., animals). We also measured PI induced by recent study, which should increase episodic familiarity, by comparing recent negative probes (lures studied in previous trial) to distant negative probes (lures that had not been presented within a block). Resolving both types of PI resulted in enhanced activation in LIFG and MTL regions. We propose that the LIFG and the MTL support successful resolution of interference via controlled retrieval processes that serve to recover detailed episodic (e.g., list-specific or source) information: Specifically, the data suggest that BOLD activation in the LIFG reflects the deployment of controlled retrieval operations, regardless of whether the retrieval attempt succeeds in recovering the target information, whereas MTL activation specifically reflects access to relevant episodic information that serves to successfully resolve PI.

The Anterior Midline Field: coercion or decision making?

To study the neural bases of semantic composition in language processing without confounds from syntactic composition, recent magnetoencephalography (MEG) studies have investigated the processing of constructions that exhibit some type of syntax-semantics mismatch. The most studied case of such a mismatch is complement coercion; expressions such as the author began the book, where an entity-denoting noun phrase is coerced into an eventive meaning in order to match the semantic properties of the event-selecting verb (e.g., 'the author began reading/writing the book'). These expressions have been found to elicit increased activity in the Anterior Midline Field (AMF), an MEG component elicited at frontomedial sensors at approximately 400 ms after the onset of the coercing noun [Pylkkänen, L., & McElree, B. (2007). An MEG study of silent meaning. Journal of Cognitive Neuroscience, 19, 11]. Thus, the AMF constitutes a potential neural correlate of coercion. However, the AMF was generated in ventromedial prefrontal regions, which are heavily associated with decision-making. This raises the possibility that, instead of semantic processing, the AMF effect may have been related to the experimental task, which was a sensicality judgment. We tested this hypothesis by assessing the effect of coercion when subjects were simply reading for comprehension, without a decision-task. Additionally, we investigated coercion in an adjectival rather than a verbal environment to further generalize the findings. Our results show that an AMF effect of coercion is elicited without a decision-task and that the effect also extends to this novel syntactic environment. We conclude that in addition to its role in non-linguistic higher cognition, ventromedial prefrontal regions contribute to the resolution of syntax-semantics mismatches in language processing.

Working memory retrieval: contributions of the left prefrontal cortex, the left posterior parietal cortex, and the hippocampus.

Functional magnetic resonance was used to identify regions involved in the working memory (WM) retrieval. Neural activation was examined in two WM tasks: an item recognition task, which can be mediated by a direct- access retrieval process, and a judgement of recency task that require a serial search. Dissociations were found in the activation patterns in the hippocampus and in the left inferior frontal gyrus (LIFG) when the probe contained the most recently studied serial position (where a test probe can be matched to the contents of focal attention)compared to when it contained all other positions (where retrieval is required). The data implicate the hippocampus and the LIFG in retrieval from WM, complementing their established role in long-term memory. Results further suggest that the left posterior parietal cortex (LPPC) support serial retrieval processes that are often required to recover temporal order information. Together this data suggest that the LPPC, the LIFG, and the hippocampus collectively support WM retrieval. Critically, the reported findings support accounts that posit a distinction between representations maintained in and outside of focal attention, but are at odds with traditional dual-store models that assume distinct mechanisms for short- and long-term memory representation.

Complement coercion is not modulated by competition: evidence from eye movements.

An eye-movement study examined the processing of expressions requiring complement coercion (J. Pustejovsky, 1995), in which a noun phrase that does not denote an event (e.g., the book) appears as the complement of an event-selecting verb (e.g., began the book). Previous studies demonstrated that these expressions are more costly to process than are control expressions that can be processed with basic compositional operations (L. Pylkkanen & B. McElree, 2006). Complement coercion is thought to be costly because comprehenders need to construct an event sense of the complement to satisfy the semantic restrictions of the verb (e.g., began writing the book). The reported experiment tests the alternative hypotheses that the cost arises from the need to select 1 interpretation from several or from competition between alternative interpretations. Expressions with weakly constrained interpretations (no dominant interpretation and several alternative interpretations) were not more costly to process than expressions with a strongly constrained interpretation (1 dominant interpretation and few alternative interpretations). These results are consistent with the hypothesis that the cost reflects the on-line construction of an event sense for the complement.

The Effect of Negative Polarity Items on Inference Verification.

The scalar approach to negative polarity item (NPI) licensing assumes that NPIs are allowable in contexts in which the introduction of the NPI leads to proposition strengthening (e.g. Kadmon & Landman 1993; Krifka 1995; Lahiri 1997; Chierchia 2006). A straightforward processing prediction from such a theory is that NPIs facilitate inference verification from sets to subsets. Three experiments are reported that test this proposal. In each experiment, participants evaluated whether inferences from sets to subsets were valid. Crucially, we manipulated whether the premises contained an NPI. In Experiment 1, participants completed a metalinguistic reasoning task and Experiments 2 and 3 tested reading times using a self-paced reading task. Contrary to expectations, no facilitation was observed when the NPI was present in the premise compared to when it was absent. In fact, the NPI significantly slowed down reading times in the inference region. Our results therefore favour those scalar theories that predict that the NPI is costly to process (Chierchia 2006), or other, non-scalar theories (Ladusaw 1992; Giannakidou 1998; Szabolcsi 2004; Postal 2005) that likewise predict NPI processing cost but, unlike Chierchia (2006), expect the magnitude of the processing cost to vary with the actual pragmatics of the NPI.

The cost of question concealment: eye-tracking and MEG evidence.

Although natural language appears to be largely compositional, the meanings of certain expressions cannot be straightforwardly recovered from the meanings of their parts. This study examined the online processing of one such class of expressions: concealed questions, in which the meaning of a complex noun phrase (the proof of the theorem) shifts to a covert question (what the proof of the theorem is) when mandated by a sub-class of question-selecting verbs (e.g., guess). Previous behavioral and magnetoencephalographic (MEG) studies have reported a cost associated with converting an entity denotation to an event. Our study tested whether both types of meaning-shift affect the same computational resources by examining the effects elicited by concealed questions in eye-tracking and MEG. Experiment 1 found evidence from eye-movements that verbs requiring the concealed question interpretation require more processing time than verbs that do not support a shift in meaning. Experiment 2 localized the cost of the concealed question interpretation in the left posterior temporal region, an area distinct from that affected by complement coercion. Experiment 3 presented the critical verbs in isolation and found no posterior temporal effect, confirming that the effect of Experiment 2 reflected sentential, and not lexical-level, processing.

An MEG study of silent meaning.

Although research on the neural bases of language has made significant progress on how the brain accesses the meanings of words, our understanding of sentence-level semantic composition remains limited. We studied the magnetoencephalography (MEG) responses elicited by expressions whose meanings involved an element not expressed in the syntax, which enabled us to investigate the brain correlates of semantic composition without confounds from syntactic composition. Sentences such as the author began the book, which asserts that an activity was begun although no activity is mentioned in the syntax, were contrasted with control sentences such as the author wrote the book, which involved no implicit meaning. These conditions were further compared with a semantically anomalous condition (the author disgusted the book). MEG responses to the object noun showed that silent meaning and anomaly are associated with distinct effects, silent meaning, but not anomaly, eliciting increased amplitudes in the anterior midline field (AMF) at 350-450 msec. The AMF was generated in ventromedial prefrontal areas, usually implicated for social cognition and theory of mind. Our results raise the possibility that silent meaning interpretation may share mechanisms with these neighboring domains of cognition.

A time course analysis of enriched composition.

Linguistic analyses suggest that common and seemingly simple expressions, such as began the book, cannot be interpreted with simple compositional processes; rather, they require enriched composition to provide an interpretation, such as began reading the book (Jackendoff, 1997; Pustejovsky, 1995). Recent reading time studies have supported these accounts by providing evidence that these expressions are more costly to process than are minimally contrasting controls (e.g., McElree, Traxler, Pickering, Seely, and Jackendoff, 2001). We report a response signal speed-accuracy trade-off (SAT) study in which two types of expressions that are thought to require enriched composition were examined. Analyses of the full time course SAT data indicate that these expressions were interpreted less accurately and, most importantly, more slowly than control sentences. The latter finding suggests that enriched composition requires the online deployment of complex compositional operations.

Attention speeds processing across eccentricity: feature and conjunction searches.

We investigated whether the effect of covert attention on information accrual varies with eccentricity (4 degrees vs 9 degrees) and the complexity of the visual search task (feature vs conjunction). We used speed-accuracy tradeoff procedures to derive conjoint measures of the speed of information processing and accuracy in each search task. Information processing was slower with more complex conjunction searches than with simpler feature searches, and overall it was faster at peripheral (9 degrees) than parafoveal (4 degrees) locations in both search types. Covert attention increased discriminability and accelerated information accrual at both eccentricities, and the magnitude of this attentional effect was the same for both feature (simple) and conjunction (complex) searches. Interestingly, in contrast to the compensatory effect of covert attention on information processing at iso-eccentric locations (temporal performance fields), covert attention did not eliminate speed differences across eccentricity.

Retrieval interference in sentence comprehension.

The role of interference effects in sentence processing has recently begun to receive attention, however whether these effects arise during encoding or retrieval remains unclear. This paper draws on basic memory research to help distinguish these explanations and reports data from an experiment that manipulates the possibility for retrieval interference while holding encoding conditions constant. We found clear support for the principle of cue-overload, wherein cues available at retrieval cannot uniquely distinguish among competitors, thus giving rise to interference effects. We discuss the data in relation to a cue-based parsing framework (Van Dyke & Lewis, 2003) and other interference effects observed in sentence processing (e.g., Gordon, Hendrick, & Johnson, 2001, 2004). We conclude from the available data that the memory system that subserves language comprehension operates according to similar principles as memory in other domains.