Stationary points embedded in the derivatives are often critical for a model to be interpretable and may be considered as key features of interest in many applications. We propose a semiparametric ...Bayesian model to efficiently infer the locations of stationary points of a nonparametric function, which also produces an estimate of the function. We use Gaussian processes as a flexible prior for the underlying function and impose derivative constraints to control the function's shape via conditioning. We develop an inferential strategy that intentionally restricts estimation to the case of at least one stationary point, bypassing possible mis‐specifications in the number of stationary points and avoiding the varying dimension problem that often brings in computational complexity. We illustrate the proposed methods using simulations and then apply the method to the estimation of event‐related potentials derived from electroencephalography (EEG) signals. We show how the proposed method automatically identifies characteristic components and their latencies at the individual level, which avoids the excessive averaging across subjects that is routinely done in the field to obtain smooth curves. By applying this approach to EEG data collected from younger and older adults during a speech perception task, we are able to demonstrate how the time course of speech perception processes changes with age.
Objective
Lexical retrieval deficits are characteristic of a variety of different neurological disorders. However, the exact substrates responsible for this are not known. We studied a large cohort ...of patients undergoing surgery in the dominant temporal lobe for medically intractable epilepsy (n = 95) to localize brain regions that were associated with anomia.
Methods
We performed a multivariate voxel‐based lesion–symptom mapping analysis to correlate surgical lesions within the temporal lobe with changes in naming ability. Additionally, we used a surface‐based mixed‐effects multilevel analysis to estimate group‐level broadband gamma activity during naming across a subset of patients with electrocorticographic recordings and integrated these results with lesion–deficit findings.
Results
We observed that ventral temporal regions, centered around the middle fusiform gyrus, were significantly associated with a decline in naming. Furthermore, we found that the ventral aspect of temporal lobectomies was linearly correlated to a decline in naming, with a clinically significant decline occurring once the resection extended 6 cm from the anterior tip of the temporal lobe on the ventral surface. On electrocorticography, the majority of these cortical regions were functionally active following visual processing. These loci coincide with the sites of susceptibility artifacts during echoplanar imaging, which may explain why this region has been previously underappreciated as the locus responsible for postoperative naming deficits.
Significance
Taken together, these data highlight the crucial contribution of the ventral temporal cortex in naming and its important role in the pathophysiology of anomia following temporal lobe resections. As such, surgical strategies should attempt to preserve this region to mitigate postoperative language deficits.
Contextual information influences how we perceive speech, but it remains unclear at which level of processing contextual information merges with acoustic information. Theories differ on whether early ...stages of speech processing, like sublexical processing during which articulatory features and portions of speech sounds are identified, are strictly feed-forward or are influenced by semantic and lexical context. In the current study, we investigate the time-course of lexical context effects on judgments about the individual sounds we perceive by recording electroencephalography as an online measure of speech processing while subjects engage in a lexically biasing phoneme categorization task. We find that lexical context modulates the amplitude of the N100, an ERP component linked with sublexical processes in speech perception. We demonstrate that these results can be modeled in an interactive speech perception model and are not well fit by any established feed-forward mechanisms of lexical bias. These results support interactive speech perception theories over feed-forward theories in which sublexical speech perception processes are only driven by bottom-up information.
Reading is a rapid, distributed process that engages multiple components of the ventral visual stream. To understand the neural constituents and their interactions that allow us to identify written ...words, we performed direct intra-cranial recordings in a large cohort of humans. This allowed us to isolate the spatiotemporal dynamics of visual word recognition across the entire left ventral occipitotemporal cortex. We found that mid-fusiform cortex is the first brain region sensitive to lexicality, preceding the traditional visual word form area. The magnitude and duration of its activation are driven by the statistics of natural language. Information regarding lexicality and word frequency propagates posteriorly from this region to visual word form regions and to earlier visual cortex, which, while active earlier, show sensitivity to words later. Further, direct electrical stimulation of this region results in reading arrest, further illustrating its crucial role in reading. This unique sensitivity of mid-fusiform cortex to sub-lexical and lexical characteristics points to its central role as the orthographic lexicon-the long-term memory representations of visual word forms.
Knowledge about how characters are written has been argued to play a particularly important role in how children learn to read Chinese. In the current study, we investigate the role that knowledge ...about writing characters plays in visual word processing in skilled adult readers. While there is clear neuropsychological evidence against the strong version of the hypothesis that reading depends on writing in Chinese even once literacy is acquired, it is still possible that writing could have a modulatory influence on how visually presented Chinese characters are processed in literate readers. The present study addressed this hypothesis using a visual same/different judgment task on pairs of characters that vary in how similar the 2 characters are visually and how similar they are in terms of motor plan, using 24 expert readers and writers of Chinese and 24 naïve participants with no prior experience with written Chinese as subjects. The results of linear mixed-effects modeling indicate that the speed of same/different judgments is influenced by visual similarity, but not by how similar they are written, even in the group of skilled readers. These results suggest that knowledge of how Chinese characters are written does not influence visual character processing in skilled readers.
Single case cognitive neuropsychological investigations involve the precise characterization of cognitive impairment at the level of an individual participant. This deep data precision affords a more ...fine-grained understanding of the cognitive and neural underpinnings of complex tasks, and continues to provide unique insights that inform theory in cognitive neuroscience. Here, we present a single case study of an individual, F.R., who suffered a stroke that led to chronic reading and writing problems that include an impairment to the orthographic working memory system proposed to be involved in both written language production and comprehension. Individuals who have been previously reported with a similar cognitive impairment commonly have left parietal lesions. However, F.R.’s orthographic working memory deficit resulted from damage to the right cerebellum, specifically to a region that is both structurally and functionally connected to the left parietal lobe and has been identified as part of the spelling network in previous meta-analyses of writing fMRI studies. From this lesion-symptom association, we argue that orthographic working memory is subserved by a cortical-cerebellar circuit, with damage at any point in the circuit resulting in an impairment to this function. Such a conclusion is warranted by observations from this single case approach, and we argue that these observations would likely have been missed if F.R. had been included in a larger, shallower group study. In addition to elucidating our understanding of the neural basis of spelling, this case study demonstrates the value that single case neuropsychology can continue to bring to cognitive neuroscience.
Damage to certain left hemisphere regions leads to reading impairments, at least acutely, though some individuals eventually recover reading. Previous neuroimaging studies have shown a relationship ...between reading recovery and increases in contralesional and perilesional activation during word reading tasks, relative to controls. Questions remain about how to interpret these changes in activation. Do these changes reflect functional take-over, a reorganization of functions in the damaged brain? Or do they reveal compensatory masquerade or the use of alternative neural pathways to reading that are available in both patients and controls? We address these questions by studying a single individual, CH, who has made a partial recovery of reading familiar words following stroke. We use an fMRI analysis technique, representational similarity analysis (RSA), which allows us to decode cognitive function from distributed patterns of neural activity. Relative to controls, we find that CH shows a shift from visual to orthographic processing in contralesional regions, with a marginally significant result in perilesional regions as well. This pattern supports a contralesional reorganization of orthographic processing following stroke. More generally, these analyses demonstrate how powerful RSA can be for mapping the neural plasticity of language function.
In immediate serial recall, participants are asked to recall novel sequences of items in the correct order. Theories of the representations and processes required for this task differ in how order ...information is maintained; some have argued that order is represented through item-to-item associations, while others have argued that each item is coded for its position in a sequence, with position being defined either by distance from the start of the sequence, or by distance from both the start and the end of the sequence. Previous researchers have used error analyses to adjudicate between these different proposals. However, these previous attempts have not allowed researchers to examine the full set of alternative proposals. In the current study, we analyzed errors produced in 2 immediate serial recall experiments that differ in the modality of input (visual vs. aural presentation of words) and the modality of output (typed vs. spoken responses), using new analysis methods that allow for a greater number of alternative hypotheses to be considered. We find evidence that sequence positions are represented relative to both the start and the end of the sequence, and show a contribution of the end-based representation beyond the final item in the sequence. We also find limited evidence for item-to-item associations, suggesting that both a start-end positional scheme and item-to-item associations play a role in representing item order in immediate serial recall.
The ability to read requires processing the letter identities in the word and their order, but it is by no means obvious that our long-term memory representations of words spellings consist of only ...these dimensions of information. The current investigation focuses on whether we process information about another dimension—letter doubling (i.e., that there is a double letter in WEED)—independently of the identity of the letter being doubled. Two experiments that use the illusory word paradigm are reported to test this question. In both experiments, participants are more likely to misperceive a target word with only singleton letters (e.g., WED) as a word with a double (e.g., WEED) when the target is presented with a distractor that contains a different double letter (e.g., WOOD) than when the distractor does not contain a double letter (e.g., WORD). This pattern of results is not predicted by existing computational models of word reading but is consistent with the hypothesis that written language separately represents letter identity and letter doubling information, as previously shown in written language production. These results support a view that the orthographic representations that underlie our ability to read are internally complex and suggest that reading and writing rely on a common level of orthographic representation.
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