Effect of focus on verbal working memory: Critical role of the focus word in reading

The effect of focus on working memory was investigated with the reading span test (RST). In two experiments, the span scores and the number of intrusion errors were compared between the focused RST the and the nonfocused RST. Focus word was defined as the most important word for comprehending a sentence. For the focused RST, the target word to be maintained was the focus word for the sentence. In the nonfocused RST, however, the target word was not the focus word for the sentence. The results of both experiments showed that RST span scores were higher for the focused RST than for the nonfocused RST, and intrusion errors were found to increase for the nonfocused RST. In Experiment 2, the effect of focus was compared between high-span and low-span subjects. An effect of sentence length was also investigated. The result showed that low-span subjects were more affected than were high-span subjects by whether the word to be remembered was the focus word. The effect of sentence length was not confirmed. These findings suggest that the low-span subjects had deficits in their ability to establish and/or inhibit mental focus when faced with conflict situations in reading.     

Perceptual attenuation of nonfocused auditory streams

The aim of this study was to measure the perceptual attenuation, measured in decibels, resulting from the focusing of attention on one stream within a multistream auditory sequence. The intensity of a nonfocused stream was increased until the accuracy of detecting a temporal irregularity in this stream was the same as in a focused stream. Eight subjects were required to detect a temporal irregularity created by delaying or advancing one tone which could be situated in one of three temporally regular streams played simultaneously to create a multistream sequence. The three streams differed in tempo and frequency. Subjects’ attention was focused on one of the streams by preceding the multistream sequence with one of the single streams (a cue). We first established the size of temporal irregularity detected at a 90% level in cued streams, confirming that subjects were able to focus on one particular stream. Second, an irregularity of this size was not detected above chance level in noncued streams, demonstrating that listeners focus only on the cued stream. Third, for 5 subjects, a 15-dB increase in the level of one of the noncued streams was necessary to bring detection up to that found in the cued streams. This gain provides an equivalent measure of the perceptual attenuation of nonfocused streams. For 3 other subjects, detection in the noncued stream remained at chance performance whatever the level. For all subjects, detection in the cued stream decreased slightly as the level of the noncued stream increased. We conclude that the attenuation of nonfocused auditory streams can attain as much as 15 dB, at least for some subjects.     

Dissociating semantic and phonological maintenance using fMRI

Functional magnetic resonance imaging (fMRI) distinguished regions of neural activity associated with active maintenance of semantic and phonological information. Subjects saw a single word for 2 sec, and following a 10-sec delay, made a judgment about that word. In the semantic task, subjects focused on the meaning of the word and decided whether a second word was synonymous with it. In the phonological task, subjects repeated the word silently and decided whether it shared a vowel sound with a nonsense word. Analyses allowed for isolation of neural activity during the maintenance delay. Semantic maintenance elicited greater activity in bilateral inferior frontal gyrus and left middle temporal gyrus regions of interest (ROI). In contrast, there was greater activity for phonological maintenance in the left superior parietal ROI. These results show a frontal-temporal network involved in actively maintaining the meanings of words, and they indicate that semantic and phonological maintenance processes are dissociable within working memory.     

Focus as a contextual priming mechanism in reading

In two experiments, we found that readers are sensitive to manipulations of syntactically marked focus and that focus is an effective message level contextual priming mechanism. Changes in focus resulted in changes in sentence context effects on subsequent target word processing. This was demonstrated in latency to name the target word (Experiment 1) and in initial looking time on the target in silent reading (Experiment 2). Experiment 2 also revealed direct effects on the focused items, as readers made fewer regressions and spent less total time on a word that was focused than when it was not focused. However, no initial processing time effects were found on the focused word.     

Perceptual representation as a mechanism of lexical ambiguity resolution: An investigation of span and processing time

In 2 experiments, the authors investigated the ability of high- and low-span comprehenders to construe subtle shades of meaning through perceptual representation. High- and low-span comprehenders responded to pictures that either matched or mismatched a target object's shape as implied by the preceding sentence context. At 750 ms after hearing the sentence describing the target object, both high- and low-span comprehenders had activated a contextually appropriate perceptual representation of the target object. However, only high-span comprehenders had perceptually represented the contextually appropriate meaning immediately upon hearing the sentence, whereas low-span comprehenders required more processing time before the perceptual representation was activated. The results are interpreted in a framework of co-occurring lexical representations and perceptual-motor representations.     

多目标追踪的神经机制

多目标追踪任务是研究动态场景中视觉注意加工机制常用的范式。自1998年开始对多目标追踪神经机制的影像学研究以来, 研究者采用ERP和fMRI等技术对多目标注意追踪所涉及的神经电生理活动和脑功能区激活方面开展了大量研究。ERP研究发现, 追踪过程持续的ERP脑电成分如N2pc、CDA的波幅与注意追踪负荷有关, 并且出现在目标与非目标上的探测刺激诱发的脑电成分如N1、P1波幅的差异可反映注意资源的分配, 具体为目标在追踪过程中得到了激活, 而非目标受到了抑制。fMRI研究比较一致地发现了顶叶(包括前顶内沟、后顶内沟、顶上小叶)、背外侧额叶皮层等在注意追踪中的强烈激活。其中顶内沟主要与注意负荷有关, 顶内沟的活动水平直接决定了观察者注意追踪的行为表现。而顶上小叶可能更多的负责注意转移。背外侧额叶皮层可能负责追踪时的感觉运动预测过程。     

Differential cognitive processing of Kanji and Kana words: do orthographic and semantic codes function in parallel in word matching task.

Relative engagements of the orthographic and semantic codes in Kanji and Hiragana word recognition were investigated. In Exp. 1, subjects judged whether the pairs of Kanji words (prime and target) presented sequentially were physically identical to each other in the word condition. In the sentence condition, subjects decided whether the target word was valid for the prime sentence presented in advance. The results showed that the response times to the target swords orthographically similar (to the prime) were significantly slower than to semantically related target words in the word condition and that this was also the case in the sentence condition. In Exp. 2, subjects judged whether the target word written in Hiragana was physically identical to the prime word in the word condition. In the sentence condition, subjects decided if the target word was valid for the previously presented prime sentence. Analysis indicated that response times to orthographically similar words were slower than to semantically related words in the word condition but not in the sentence condition wherein the response times to the semantically and orthographically similar words were largely the same. Based on these results, differential contributions of orthographic and semantic codes in cognitive processing of Japanese Kanji and Hiragana words was discussed.     

Neural basis for sentence comprehension deficits in frontotemporal dementia

Many patients with frontotemporal dementia (FTD) have impaired sentence comprehension. However, the pattern of comprehension difficulty appears to vary depending on the clinical subgroup. The purpose of this study was to elucidate the neural basis for these deficits in FTD. We studied patients with two different presentations: Three patients with Progressive Non-Fluent Ahasia (PNFA), and five non-aphasic patients with a dysexecutive and social impairment (EXEC). The FTD patient subgroups were compared to a cohort of 11 healthy seniors with intact sentence comprehension. We monitored regional cerebral activity with blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) while subjects read sentences featuring both a grammatically complex object-relative center-embedded clause and a long linkage between the head noun phrase (NP) and the gap where the NP is interpreted in the center-embedded clause. Subjects decided whether the agent of the action is a male or a female. Healthy seniors activated both ventral portions of inferior frontal cortex (vIFC) and dorsal portions of IFC (dIFC) in the left hemisphere, often associated with grammatical and working memory components of these sentences, respectively. PNFA patients differed from healthy controls since they have reduced activation of left vIFC, while EXEC patients have less recruitment of left dIFC. We conclude that FTD subgroups have distinct patterns of sentence comprehension difficulty in part because of selective interruptions of a large-scale neural network for sentence processing.     

Focused and Nonfocused Attention in Verbal and Emotional Dichotic Listening: An FMRI Study

Functional magnetic resonance imaging (fMRI) was used to identify cortical regions which are involved in two dichotic listening tasks. During one task the subjects were required to allocate attention to both ears and to detect a specific target word (phonetic task), while during a second task the subjects were required to detect a specific emotional tone (emotional task). During three attentional conditions of each task, the subjects were required to focus attention to the right (FR) or left ear (FL), while during a third condition subjects were required to allocate attention to both ears simultaneously. In 11 right-handed male subjects, these dichotic listening tasks evoked strong activations in a temporofrontal network involving auditory cortices located in the temporal lobe and prefrontal brain regions. Hemodynamic responses were measured in the following regions of interest: Heschl's gyrus (HG), the planum polare (PP), the planum temporale (PT), the anterior superior temporal sulcus (aSTS), the posterior superior temporal sulcus (pSTS), and the inferior frontal gyrus region (IFG) of both hemispheres. The following findings were obtained: (1) the degree of activation in HG and PP depends on the direction of attention. In particular it was found that selectively attending to right-ear input led to increased activity specifically in the left HG and PP and attention to left ear input increased right-sided activity in these structures; (2) hemodynamic responses in the PT, aSTS, pSTS, and IFG were not modulated by the different focused-attention conditions; (3) hemodynamic responses in HG and PP in the nonforced conditions were the sum activation of the forced conditions; (4) there was no general difference between the phonetic and emotion tasks in terms of hemodynamic responses; (5) hemodynamic responses in the PT and pSTS were strongly left-lateralized, reflecting the specialization of these brain regions for language processing. These findings are discussed in the context of current theories of hemispheric specialization.     

Working memory and inferences: evidence from eye fixations during reading

Eye fixations during reading were monitored to examine the relationship between individual differences in working memory capacity-as assessed by the reading span task-and inferences about predictable events. Context sentences predicting likely events, or non-predicting control sentences, were presented. They were followed by continuation sentences in which a target word represented an event to be inferred (inferential word) or an unlikely event (non-predictable word). A main effect of reading span showed that high working memory capacity was related to shorter gaze durations across sentence regions. More specific findings involved an interaction between context, target, and reading span on late processing measures and regions. Thus, for high- but not for low-span readers, the predicting condition, relative to the control condition, facilitated reanalysis of the continuation sentence that represented the inference concept. This effect was revealed by a reduction in regression-path reading time in the last region of the sentence, involving less time reading that region and fewer regressions from it. These results indicate that working memory facilitates elaborative inferences during reading, but that this occurs at late text-integration processes, rather than at early lexical-access processes.     

Prominence vs. aboutness in sequencing: A functional distinction within the left inferior frontal gyrus

Prior research on the neural bases of syntactic comprehension suggests that activation in the left inferior frontal gyrus (lIFG) correlates with the processing of word order variations. However, there are inconsistencies with respect to the specific subregion within the IFG that is implicated by these findings: the pars opercularis or the pars triangularis. Here, we examined the hypothesis that the dissociation between pars opercularis and pars triangularis activation may reflect functional differences between clause-medial and clause-initial word order permutations, respectively. To this end, we directly compared clause-medial and clause-initial object-before-subject orders in German in a within-participants, event-related fMRI design. Our results showed increased activation for object-initial sentences in a bilateral network of frontal, temporal and subcortical regions. Within the lIFG, posterior and inferior subregions showed only a main effect of word order, whereas more anterior and superior subregions showed effects of word order and sentence type, with higher activation for sentences with an argument in the clause-initial position. These findings are interpreted as evidence for a functional gradation of sequence processing within the left IFG: posterior subportions correlate with argument prominence-based (local) aspects of sequencing, while anterior subportions correlate with aboutness-based aspects of sequencing, which are crucial in linking the current sentence to the wider discourse. This proposal appears compatible with more general hypotheses about information processing gradients in prefrontal cortex (Koechlin & Summerfield, 2007).     

The anatomy of auditory word processing: individual variability

This study used functional magnetic resonance imaging (fMRI) to investigate the neural substrate underlying the processing of single words, comparing activation patterns across subjects and within individuals. In a word repetition task, subjects repeated single words aloud with instructions not to move their jaws. In a control condition involving reverse speech, subjects heard a digitally reversed speech token and said aloud the word "crime." The averaged fMRI results showed activation in the left posterior temporal and inferior frontal regions and in the supplementary motor area, similar to previous PET studies. However, the individual subject data revealed variability in the location of the temporal and frontal activation. Although these results support previous imaging studies, demonstrating an averaged localization of auditory word processing in the posterior superior temporal gyrus (STG), they are more consistent with traditional neuropsychological data, which suggest both a typical posterior STG localization and substantial individual variability. By using careful head restraint and movement analysis and correction methods, the present study further demonstrates the feasibility of using overt articulation in fMRI experiments.     

Attention and semantic processing during speech: an fMRI study

This fMRI study was conducted to investigate whether language semantics is processed even when attention is not explicitly directed to word meanings. In the “unattended” condition, the subjects performed a visual detection task while hearing semantically related and unrelated word pairs. In the “phoneme” condition, the subjects made phoneme judgements between prime and target words, and in the “word” condition, they indicated whether the words in each word pair were semantically related or unrelated. In the word condition, stronger activity was obtained for unrelated than related words in the superior temporal gyrus/sulcus (STG/STS), lingual/fusiform gyri and cuneus, whereas in the phoneme condition no such effect was observed. However, during the unattended condition, stronger activity was found in the right STG. Our results suggest that both semantic judgement of word pairs and their passive hearing activate the same neural networks but this activation is more restricted in the passive hearing.     

Working memory capacity and time course of predictive inferences

A naming task assessed activation of inference concepts during reading. A predicting, or a control, context sentence was followed by a target word to be named, which represented the predicted event or an inconsistent event. The interval between the end of the context and the onset of the target word varied between 50 and 1050 msec. Individual differences in working memory capacity were assessed by the reading span task. As reflected by facilitation in naming latencies in the predicting condition, relative to the control condition, (a) inferences were not made within the first 50 msec after the context, regardless of reading span; (b) only the high-span participants drew inferences within a 550-msec interval; and, (c) both the high- and the low-span participants generated them within a 1050-msec interval. These results indicate that high working memory capacity accelerates the time course of predictive inferences, although they do not become automatic. We propose that this effect occurs because these inferences involve time-consuming elaborations that place demands on the effortful and limited resources of working memory. Deficiencies in word knowledge, speed of lexical access, or comprehension of explicit information do not account for low-span readers' difficulties in generating predictive inferences.     

Working Memory Capacity and Time Course of Predictive Inferences

A naming task assessed activation of inference concepts during reading. A predicting, or a control, context sentence was followed by a target word to be named, which represented the predicted event or an inconsistent event. The interval between the end of the context and the onset of the target word varied between 50 and 1050-msec. Individual differences in working memory capacity were assessed by the reading span task. As reflected by facilitation in naming latencies in the predicting condition, relative to the control condition, (a) inferences were not made within the first 50-msec after the context, regardless of reading span; (b) only the high-span participants drew inferences within a 550-msec interval; and, (c) both the high-and the low-span participants generated them within a 1050-msec interval. These results indicate that high working memory capacity accelerates the time course of predictive inferences, although they do not become automatic. We propose that this effect occurs because these inferences involve time-consuming elaborations that place demands on the effortful and limited resources of working memory. Deficiencies in word knowledge, speed of lexical access, or comprehension of explicit information do not account for low-span readers' difficulties in generating predictive inferences.     

Dissociable patterns of brain activity during comprehension of rapid and syntactically complex speech: evidence from fMRI

Sentence comprehension is a complex task that involves both language-specific processing components and general cognitive resources. Comprehension can be made more difficult by increasing the syntactic complexity or the presentation rate of a sentence, but it is unclear whether the same neural mechanism underlies both of these effects. In the current study, we used event-related functional magnetic resonance imaging (fMRI) to monitor neural activity while participants heard sentences containing a subject-relative or object-relative center-embedded clause presented at three different speech rates. Syntactically complex object-relative sentences activated left inferior frontal cortex across presentation rates, whereas sentences presented at a rapid rate recruited frontal brain regions such as anterior cingulate and premotor cortex, regardless of syntactic complexity. These results suggest that dissociable components of a large-scale neural network support the processing of syntactic complexity and speech presented at a rapid rate during auditory sentence processing.     

Neural correlates of feigned memory impairment are distinguishable from answering randomly and answering incorrectly: an fMRI and behavioral study

Previous functional magnetic resonance imaging (fMRI) studies have identified activation in the prefrontal-parietal-sub-cortical circuit during feigned memory impairment when comparing with truthful telling. Here, we used fMRI to determine whether neural activity can differentiate between answering correctly, answering randomly, answering incorrectly, and feigned memory impairment. In this study, 12 healthy subjects underwent block-design fMRI while they performed digit task of forced-choice format under four conditions: answering correctly, answering randomly, answering incorrectly, and simulated feigned memory impairment. There were three main results. First, six areas, including the left prefrontal cortex, the left superior temporal lobe, the right postcentral gyrus, the right superior parietal cortex, the right superior occipital cortex, and the right putamen, were significantly modulated by condition type. Second, for some areas, including the right superior parietal cortex, the right postcentral gyrus, the right superior occipital cortex, and the right putamen, brain activity was significantly greater in feigned memory impairment than answering randomly. Third, for the areas including the left prefrontal cortex and the right putamen, brain activity was significantly greater in feigned memory impairment than answering incorrectly. In contrast, for the left superior temporal lobe, brain activity was significantly greater in answering incorrectly than feigned memory impairment. The results suggest that neural correlates of feigned memory impairment are distinguishable from answering randomly and answering incorrectly in healthy subjects.     

Sentence processing strategies in healthy seniors with poor comprehension: an fMRI study

We used fMRI to examine patterns of brain recruitment in 22 healthy seniors, half of whom had selective comprehension difficulty for grammatically complex sentences. We found significantly reduced recruitment of left posterolateral temporal [Brodmann area (BA) 22/21] and left inferior frontal (BA 44/6) cortex in poor comprehenders compared to the healthy seniors with good sentence comprehension, cortical regions previously associated with language comprehension and verbal working memory, respectively. The poor comprehenders demonstrated increased activation of left prefrontal (BA 9/46), right dorsal inferior frontal (BA 44/6), and left posterior cingulate (BA 31/23) cortices for the grammatically simpler sentences that they understood. We hypothesize that these brain regions support an alternate, nongrammatical strategy for processing complex configurations of symbolic information. Moreover, these observations emphasize the crucial role of the left perisylvian network for grammatically guided sentence processing in subjects with good comprehension.     

Neural correlates of Dutch Verb Second in speech production

Dutch speakers with agrammatic Broca's aphasia are known to have problems with the production of finite verbs in main clauses. This performance pattern has been accounted for in terms of the specific syntactic complexity of the Dutch main clause structure, which requires an extra syntactic operation (Verb Second), relative to the basic Subject-Object-Verb order surfacing in Dutch subordinate clauses. We report an fMRI study into the question whether this syntactic complexity is reflected in increased brain activation correlated with the production of Dutch main clause word order, in speakers without language impairment. Nineteen healthy subjects performed a covert sentence completion task, during which main and subordinate clauses were alternately elicited in a block design. Results show a left middle to superior frontal cluster of activation correlated to production of Verb-Second over Verb-Final clauses, with no activation in the opposite contrast. This activation pattern is counter to what might be expected from the frequency distribution of main and subordinate clauses. We conclude that the Verb-Second deviation from the basic Dutch SOV word order costs extra neural resources and that this also underlies the agrammatic problems with the production of finite verbs in Dutch main clauses.     

熟悉主题说明文阅读推理加工的认知神经机制

采用功能磁共振成像(Functional Magnetic Resonance Imaging, fMRI)技术对熟悉主题说明文阅读过程因果推理加工进行研究, 探讨说明文阅读过程中读者是否能够自发进行因果推理加工, 以及阅读焦点的存在是否会对说明文阅读过程中的因果推理加工产生影响。结果表明, 读者在熟悉主题说明文阅读过程中能够自动进行推理加工, 负责推理加工的主要脑区为额叶(尤其是额下回)、顶叶下部及双侧楔前叶等区域。在熟悉主题说明文阅读过程中, 阅读焦点的存在一定程度上使读者的认知加工资源集中在对与焦点相关的推理关系的加工上。