Skilled readers form connections among a text’s semantically related ideas as they read

They found that reading the final sentence of expository texts relative to narrative texts elicited a greater increase in N400 amplitude, and they concluded that expository texts required more demanding semantic processing. Eason et al. also reported differences between genres, showing that expository texts placed higher demands on executive function than narrative texts, particularly inferencing and planning/organizing information. EF is thought to be essential to the process of building a coherent text representation because it enables readers to store previously read text ideas as they simultaneously read new ideas and integrate them into their mental representation . While behavioral data certainly support the theoretical significance of EF to reading comprehension in general , Eason et al.’s findings of higher demands on EF for expository text suggest that for this particular text genre, which is critical for acquiring new information, EF is particularly salient.One hallmark of successful reading comprehension is that the reader can distinguish between ideas that are important, or central, to the overall meaning of the text, and those that are less important, or peripheral.The ideas and their connections form a network in the reader’s mind . Some ideas are causally or logically connected to a great number of other ideas and as a result emerge as being important, or central, to the overall meaning of the text, while others have relatively few connections and fall out as being peripheral, or unimportant . A robust finding in the comprehension literature is that skilled readers are more likely to recognize and recall an idea the more central it is to the overall meaning of the text . This finding holds for both narrative and expository texts . van den Broek et al. propose that a reader’s ability to distinguish a text’s central and peripheral ideas, or their sensitivity to structural centrality,hydroponic fodder system is an important indicator of their comprehension ability.

For example, adults show greater sensitivity to structural centrality than do children ; typically developing children show greater sensitivity to centrality than do children with reading disability as well as those with Attention Deficit Hyperactivity Disorder ; and readers show greater sensitivity to centrality when reading in their native compared to foreign language . Importantly, studies suggest that centrality tends to emerge as a feature of the developing text representation. van den Broek used eye-tracking equipment to show that skilled readers fixate more frequently and spend more time reading central ideas than they do peripheral ones. This suggests that centrality is a dynamic construct that emerges as the reader processes a text, consistent with the idea that readers form connections among semantically related text ideas as they read. In theory, the ideas that are most important stand out because they are the ones that have the most connections and are consequently the ones most likely to be recalled. To date, although sensitivity to centrality has been investigated behaviorally, the neural mechanisms remain unknown. Understanding the neural mechanisms underlying sensitivity to centrality may allow for a more specific understanding of normal and disrupted comprehension processes.The current study sought first to identify the neural correlates specific to expository text comprehension, looking both at regions which overlap with single word processing and those which are specific to discourse-level processing. Once the systems for expository text comprehension were identified, we employed temporal analysis techniques to examine how these systems change over the course of building and maintaining a coherent mental representation of the text. We hypothesized that when isolating discourse-level comprehension from word-level comprehension, we would see regions that have previously been implicated by sentence and narrative comprehension, particularly those associated with discourse-level language processing separate from social cognition [bilateral TP, angular gyrus , and PCC] . We predicted that the other traditional language regions, such as left-lateralized inferior frontal gyrus , middle temporal gyrus , and anterior superior temporal sulcus , would most likely be shared by both word and passage tasks, but that these multi-functional regions would behave differently over the temporal course of passage comprehension compared to single-word comprehension .

Additionally, due to prevalence of information organization in expository comprehension, we expected to see activations in the dorsal attention network [dorsolateral prefrontal cortex , intraparietal sulcus , inferior parietal lobule ], which has been associated with the kind of updating, integrating, and immediate planning of information that has been behaviorally described in previous studies on expository comprehension . We consequently hypothesized that over the course of passages alone, semantic control areas shared by words and passages at the mean-level would become increasingly responsive over time in passage comprehension alone due to the increased semantic demands associated with integrating and maintaining new information in a global text representation. Given Yarkoni et al.’s study showing that the parietal visuospatial attention regions are involved in the construction of text , while classic language areas are reflective of the maintenance of readers’ mental models, we hypothesized that along with the emergence of a greater reliance on perisylvian regions over time, in passages we would see a decrease over time of posterior parietal regions. The second goal of the current study was to examine the patterns of neural activation that are uniquely associated with processing central vs. peripheral ideas. While behavioral measures clearly indicate that readers distinguish central from peripheral ideas, both online and when recalling the text, the neurobiological processes that support this fundamental aspect of text comprehension have yet to be explored. Gaining insight into processes that promote a reader’s sensitivity to centrality advances current comprehension models. More focally, it allows for isolating the underlying neural mechanisms supporting processes that may be disrupted in individuals with poor sensitivity to centrality. Such knowledge may eventually inform ways to individualize intervention for problematic reading comprehension. Given previous behavioral findings, we expected there to be unique semantic and integrative regions that differentiate central ideas from peripheral ideas. Finally, we predicted that with the temporal progression of the text, there are changes in the cognitive demands required in differentiating central and peripheral information and integrating those units into the mental model, resulting in temporally dynamic neural systems for different types of textual information.

To accomplish the goals of the study, an fMRI passage comprehension task was designed in which participants viewed three types of stimuli: coherent expository passages and scrambled words and nonalphanumeric symbols . Within the Passages condition, we delineated the text’s central and peripheral ideas. To examine differences between central vs. peripheral ideas, as well as overall patterns of activation associated with text, we employed a typical general linear model . To examine the emergence of a mental representation of the text, or dynamic changes taking place over time, an approach sensitive to temporal features was taken , whereby examination of neural activation that emerged or diminished over time for various conditions was revealed.Seventeen adults participated in the study. All participants met the following inclusion criteria: native English speakers; normal hearing and vision; no history of major psychiatric illness; no traumatic brain injury/epilepsy; no history of a developmental disability; and no contraindication to MRI. Each participant gave written consent at the beginning of the study, with procedures carried out in accordance with Vanderbilt University’s Institutional Review Board. All participants had a standard score within the average range on a composite of standardized reading tests or had no history of difficulty with reading. Participants received $25 as compensation for a 2-h testing session.Coh-Metrix 2.0 was used to create 8 passages that were equivalent across measures of word concreteness, syntactic simplicity, referential cohesion, causal cohesion, and narrativity. Passages were matched on descriptive factors, including: number of words, average sentence length, and all passages measured a Flesch-Kincaid grade-level between 4.0 and 4.9. To insure that passages were equivalent in difficulty, each of the 8 passages was isolated and compared to the mean of the remaining 7 passages. Passages were considered equivalent when measures were within a 90% confidence interval of the mean of the group of remaining passages. At the end of this process, fodder system the passages were equal across 23 measures of descriptive statistics, vocabulary frequency, word concreteness, syntactic simplicity, referential cohesion, causal cohesion, and narrativity . Four of these passages were used for the Passages condition and four were used for the Words condition , which included words from the passages in randomized order. All passages were 150 words in length. Each sentence was no longer than 13 words. The passages were all expository and included the following topics: Hang Gliding, Wrasses, Velvet Worms, and Hydroponics. Each passage consisted of two paragraphs, the first of which served to introduce the topic while the second elaborated on a particular detail of the subject matter.Using imaging technology to explore the neural correlates of reading comprehension is a challenging task due to the temporal nature of discourse processing. Previous studies have presented the entire paragraph on one screen , but this procedure prohibits comparing how readers process specific aspects of the passage, such as central vs. peripheral ideas, because the block contains both types of information.The most temporally precise presentation method is to present the story one word at a time, and several studies have employed this procedure . When piloting passages using this approach, participants reported that it created an uncomfortable, artificial reading experience, likely in part because readers typically process words up to 14–15 letters to the right of their fixation , and using a single word-by-word presentation prevents this.

The moving window procedure is an alternative method that allows examination of the processing associated with single words. The advantage of this procedure is that the word immediately preceding and following the word under fixation are also visible. Although this allows for a more naturalistic reading experience, the approach was undesirable for this study because it requires a self-paced design, and temporal consistency in the presentation of stimuli is required for group comparisons. To avoid both the above confounds, we presented our passages one meaningful phrase at a time. This procedure enabled us to compare activation related to processing central and peripheral ideas, yet decreased the artificial demands imposed by a word-byword presentation. Each phrase was presented on a separate trial. The phrases included noun phrases, verb phrases, and prepositional phrases, and they ranged from 1 to 6 words in length. The number and type of words presented together determined the phrases’ presentation duration. We allowed 550 ms for each content word and 275 ms for each function word. For timing purposes, we presented no more than three content words per slide and randomized the time between phrases to allow comparison across phrases. The Words condition followed the same presentation format as the Passages condition. The baseline condition was presented between paragraph 1 and paragraph 2 of both the Passages and Words conditions. The purpose of this design was to allow participants’ activation to return to baseline after reading each block . The presentation sequence was: Passage condition, Paragraph 1; Baseline condition; Passage condition, Paragraph 2; Baseline condition; Words condition; Baseline condition. The mean time for the passages block was 78.54 ; Baseline mean = 47.69 ; and Words mean = 82.45 . In all three conditions, 8% of the stimuli were repeated on two consecutive screens. To monitor whether participants attended to the stimuli, participants pressed a button with their right thumb when they detected a phrase repetition or a symbol configuration repetition. Mean percentage correct response was very high .Imaging was performed on a research-dedicated Philips Achieva 3T MR scanner with a 32-channel head coil. Functional images were acquired using a gradient echo planar imaging sequence with 40 slices with no gap and consisted of 4 runs, each 7 min . Other relevant imaging parameters for the functional images are TE = 30 ms , FOV 240 × 240 mm, slice thickness = 3 mm with 0 mm gaps, 75◦ flip angle, TR = 2200 ms, and a matrix size 80 × 80 , implying 3 mm3 isotropic voxels. All functional data were analyzed using MATLAB and SPM8 . The functional data for each participant were slice-timing corrected, aligned to the mean functional image, normalized to MNI space, and spatially smoothed with a 8 mm FWHM Gaussian filter.