Letter Matching Research Articles

Bilateral saccades increase intrahemispheric processing but not interhemispheric interaction: Implications for saccade-induced retrieval enhancement

Retrieval of memories is enhanced when bilateral saccades are made immediately before attempting retrieval. One hypothesis is that saccades enhance retrieval by increasing interaction of the brain hemispheres. To test this, subjects viewed arrays of lateralized letters and indicated whether target letters matched either of two probe letters. Matching targets and probes were presented to either the same hemisphere (within-hemisphere trials) or separate hemispheres (across-hemisphere trials). Match detection requires interhemispheric interaction on across-hemisphere trials but primarily intrahemispheric processing on within-hemisphere trials. Subjects performed letter matching following saccades and a fixation control condition. Saccades increased match-detection accuracy on within-hemisphere trials only, suggesting that, counter to the hypothesis, saccades enhance intrahemispheric processing but not interhemispheric interaction. Across-hemisphere accuracy was higher, however, for subjects who were not strongly right-handed, versus those who were, and the absence of strong right-handedness may reflect greater interhemispheric interaction. We discuss implications for accounts of saccade-induced retrieval enhancement.

Cognitive Performance In Relation To APOE Genotype, Physical Activity, And Cardiovascular Fitness

Physical activity has been correlated with improved cognitive function for older adult APOE-e4 carriers, but it is unclear whether the association is related to physical activity level as indicated by kilocalories expended or to cardiovascular fitness as indicated by VO2 max. PURPOSE: To determine if there is a positive relationship between physical activity level or cardiovascular fitness and cognitive function for carriers of the APOE-e4 allele. We predicted that there would be a greater magnitude of effect for e4 carriers compared to non-carriers. METHODS: Study participants, ages 50-70, were screened for depression using Beck Depression Inventory (BDI) and for dementia using the Cambridge Cognitive Exam (CAMCOG). APOE genotype was determined through DNA analysis of whole blood or saliva. Body mass index (BMI) was determined from measured height and weight. Salthouse Activity Inventory was used to assess intellectual activity. Weekly kilocalorie expenditure was calculated from Yale Physical Activity Survey. Estimated VO2 max was determined using the Rockport Walk Test. 78 participants completed the Sternberg working memory task and 80 completed the Wisconsin Card-Sorting Test (WCST) to determine cognitive function. RESULTS: Hierarchical regression revealed a significant inverse relationship for APOE-e4 carriers between 6 letter match reaction time on the Sternberg task and self-reported weekly kilocalorie expenditure (ΔR2 =.068, p =.022), as well as an inverse relationship between % perseverative error on the WCST and estimated VO2 max (ΔR2 =.075, p =.015), after accounting for age, education, intellectual activity, and BMI. The pattern of findings revealed no such relationship in non-carriers. CONCLUSION: The results support a benefit of cardiovascular fitness and physical activity on cognitive performance for carriers of the APOE-e4 allele. The associations appeared to be task dependent, with different findings for cardiovascular fitness or physical activity possibly relating to unique neural processes involved in each cognitive test. Because the APOE-e4 allele is associated with increased risk for development of late-onset Alzheimer's disease, these findings may have implications for a possible protective advantage for individuals genetically at risk for dementia.

A masked priming ERP study of letter processing using single letters and false fonts

Previous event-related potential (ERP) research on letter processing has suggested that a P150 reflects low-level, featural processing, whereas a P260 reflects high-level, abstract letter processing. In order to investigate the specificity of these effects, ERPs were recorded in a masked priming paradigm using matching and nonmatching pairs of letters (e.g., g-g, g-j) and false fonts (e.g.,[SYMBOL: SEE TEXT], [SYMBOL: SEE TEXT]). If the P150 priming effect indexes featural processing, there should be no effect of condition on the P150, since the letters and false fonts shared visual features. If the P260 priming effect indexes the processing of abstract letter representations, it should be evident only in the letter condition. As was expected, the P150 priming effect was similar for letters and false fonts; however, the P260 priming effect was also similar between conditions. Thus, the P260 priming effect may not be sensitive to abstract letter processing per se, or such processing may be extremely abstract.

Priming of Abstract Letter Identities in the Letter Match Task

Previous studies of letter recognition have not found priming for abstract letter identities. We used a task that required participants to decide whether a target is the same or different from a reference letter presented in opposite case, which avoids the shortcomings of tasks used in previous studies. We found robust priming effects in this task, which were the same size for letter pairs that have similar visual features across case (e.g., c/C, x/X) and dissimilar features (e.g., a/A, b/B). Also, the pattern of priming was the same whether the prime was in the same or different case as the reference. We take these findings as evidence that abstract letter identities support priming in this task. We suggest that the same-different match task is a useful tool for studying representations used to support masked priming in letter recognition and with other stimuli with limited set size.

Altered effective connectivity within the language network in primary progressive aphasia.

Primary progressive aphasia (PPA) is a neurodegenerative dementia syndrome principally characterized by the gradual dissolution of language functions, especially in the early stages of disorder. In a previous functional neuroimaging study, PPA patients were found to activate core language areas similarly to control subjects when performing semantic and phonological processing tasks (Sonty et al., 2003). In the present study, functional magnetic resonance imaging (fMRI) and dynamic causal modeling (DCM) were used to study multiregional effective connectivity in early-stage PPA (n = 8) and control (n = 8) subjects performing semantic word matching and visual letter matching tasks. fMRI analysis showed semantic task-specific activations in the left inferior frontal (Broca's area) and posterior superior temporal (Wernicke's area) regions, in addition to other language regions, in both groups. Using a model language network consisting of six left hemisphere regions, the DCM analysis demonstrated reduced language-specific effective connectivity between Wernicke's and Broca's areas in the PPA patient group. Furthermore, this decrement in connectivity was predictive of semantic task accuracy. These results demonstrate for the first time that dysfunctional network interactions (effective connectivity), rather than hypoactivity within individual brain regions, may contribute to the emergence of language deficits seen in PPA.

Waiting for regulatory sequences to appear

One possible explanation for the substantial organismal differences between humans and chimpanzees is that there have been changes in gene regulation. Given what is known about transcription factor binding sites, this motivates the following probability question: given a 1000 nucleotide region in our genome, how long does it take for a specified six to nine letter word to appear in that region in some individual? Stone and Wray [Mol. Biol. Evol. 18 (2001) 1764–1770] computed 5,950 years as the answer for six letter words. Here, we will show that for words of length 6, the average waiting time is 100,000 years, while for words of length 8, the waiting time has mean 375,000 years when there is a 7 out of 8 letter match in the population consensus sequence (an event of probability roughly 5/16) and has mean 650 million years when there is not. Fortunately, in biological reality, the match to the target word does not have to be perfect for binding to occur. If we model this by saying that a 7 out of 8 letter match is good enough, the mean reduces to about 60,000 years.

NAME LETTER MATCHING AND IMPLICIT EGOTISM: FRIENDS AS SELF-EXTENSIONS

Favorable evaluations of letters appearing in peoples' names were examined and found to vary according to a focus on the self versus others. Students described their personal preferences after thinking about either positive or negative qualities of themselves or a friend. Matches of consonant letters in preferences with consonants in first and last names was higher when the self-concept was challenged by an induced focus on negative personal traits, as well as when people thought about something of “theirs.” Thus, evidence of implicit egotism was seen when students thought (for good or for ill) of one of their self-chosen items, their best friend, or when they required a self-esteem boost, but not when they were focused on their own positive personal qualities. Results are discussed in terms of how name letter matching reflects a desire to keep a complimentary outlook about ourselves.

FMRI correlates of cortical specialization and generalization for letter processing

The present study used functional magnetic resonance imaging to examine cortical specialization for letter processing. We assessed whether brain regions that were involved in letter processing exhibited domain-specific and/or mandatory responses, following Fodor's definition of properties of modular systems (Fodor, J.A., 1983. The Modularity of Mind. The MIT Press, Cambridge, MA.). Domain-specificity was operationalized as selective, or exclusive, activation for letters relative to object and visual noise processing and a baseline fixation task. Mandatory processing was operationalized as selective activation for letters during both a silent naming and a perceptual matching task. In addition to these operational definitions, other operational definitions of selectivity for letter processing discussed by [Pernet, C., Celsis, P., Demonet, J., 2005. Selective response to letter categorization within the left fusiform gyrus. NeuroImage 28, 738–744] were applied to the data. Although the left fusiform gyrus showed a specialized response to letters using the definition of selectivity put forth by [Pernet, C., Celsis, P., Demonet, J., 2005. Selective response to letter categorization within the left fusiform gyrus. NeuroImage 28, 738–744], this region did not exhibit specialization for letters according to our more conservative definition of selectivity. Instead, this region showed equivalent activation by letters and objects in both the naming and matching tasks. Hence, the left fusiform gyrus does not exhibit domain-specific or mandatory processing but may reflect a shared input system for both stimulus types. The left insula and some portions of the left inferior parietal lobule, however, did show a domain-specific response for letter naming but not for letter matching. These regions likely subserve some linguistically oriented cognitive process that is unique to letters, such as grapheme-to-phoneme translation or retrieval of phonological codes for letter names. Hence, cortical specialization for letters emerged in the naming task in some peri-sylvian language related cortices, but not in occipito-temporal cortex. Given that the domain-specific response for letters in left peri-sylvian regions was only present in the naming task, these regions do not process letters in a mandatory fashion, but are instead modulated by the linguistic nature of the task.

Achievement, underachievement and cortical activation: a comparative EEG study of adolescents of average and above‐average intelligence

In this study the neural efficiency phenomenon (more efficient brain function in brighter as compared to less intelligent individuals) was investigated regarding differences in intelligence (average vs. above‐average intelligence) and scholastic achievement (achievers vs. underachievers). The cortical activation (assessed by event‐related desynchronisation in the EEG) of 31 male adolescents was measured while performing a verbal and figural version of Posner's letter matching task and two creativity tasks. During the figural Posner task, average intelligent underachievers showed higher frontal activation than similarly intelligent achievers and brighter underachievers, whereas average intelligent achievers showed higher posterior activation. During one creativity task underachievers were frontally less activated than achievers. The results provide first evidence that different achievement levels are also reflected in different levels of cortical activation.

Hemispheric activation and interaction: Past activity affects future performance

Previous studies have shown that when hemispheric activation is modulated by a lateralised task performed concurrently with a second task, performance in the second task is affected by the side of the more active hemisphere. This effect is thought to be produced by competition for limited resources required to complete the two tasks and/or by a greater allocation of attention to the hemifield contralateral to the more active hemisphere. Little is known on how task performance is affected by the pattern of activation in the two cerebral hemispheres before a target task is conducted. The present study investigated how manipulation of hemispheric activity influenced performance of a non-lateralised task (letter matching). Greater left hemisphere activity interfered most with performance of the letter- matching task and was more pronounced in the early learning stage. Male participants were most affected by this effect. The results are discussed in relation to hemispheric interaction, functional lateralisation, and allocation of attention.

The late Nd reflects a memory trace containing amodal spatial information

The early Nd reflects the analysis of simple features of selectively attended auditory stimuli, but the precise nature of the more complex processing reflected by the late Nd is unclear. The late but not the early Nd is sensitive to interference from a concurrently presented visual spatial attention switching task. This experiment investigated whether the late Nd is also sensitive to deeper visual attention switching. Twenty-one subjects performed a dichotic listening task concurrently with either visual spatial or visual letter matching attention switching tasks. Late Nd amplitude was reduced by the spatial but not the letter matching task, indicating insensitivity to deeper attention switching. P300 amplitude was reduced by both tasks. Reductions in N100 and P200 were uncorrelated. We propose that, in part, the late Nd reflects an amodal memory trace containing spatial information, possibly involving a "where" rather than a "what" auditory pathway.

EFFECTS OF LEARNING EXPERIENCE ON BIHEMISPHERIC PROCESSING

The purpose of this study was to examine the effect of learning experience on benefits of bihemispheric processing. First, right-handed students were given the paired-associated learning task that required them to memorize the pairs of a familiar-font letter with an unfamiliar-font letter. After this task, both the letters were presented in the unilateral (UVF) and bilateral visual-fields (BVF) (Test 1). They were asked to decide if both the letters were the match. Second, the learning task was given to them, followed by the same letter–matching task (Test 2). The results showed that a UVF-advantage in Test 1 shifted toward a BVF-advantage in Test 2. These findings suggested that, as the amount of learning increased, the benefits of bihemispheric processing would be enhanced.

Visual letter matching: Hemispheric functioning or scanning biases?

Finding two mixed-case letters that share the same name is easier to do when the letters are presented in opposite visual fields than when they are both in the same field. By contrast, finding a match between two same-case letters is easier when they are in the same field. These visual field effects have been attributed to the ability of the corpus callosum to coordinate the work of the cerebral hemispheres [Banich, M. T. (1998). The missing link: The role of interhemispheric interaction in attentional processing. Brain and Cognition, 36, 128–157; Weissman, D. H., & Banich, M. T. (2000). The cerebral hemispheres cooperate to perform complex but not simple tasks. Neuropsychology, 14, 41–59]. The present study considers the alternative hypothesis that attentional scanning biases may be at work. Experiment 1 examined the effects of explicit instructions to scan items in a specific order; Experiment 2 examined influences of implicit location biasing; Experiment 3 considered the possibility that same-case letter matching is different because a perceptual grouping mechanism can be used in that task. In each experiment, we first interpreted the results within the hemispheric framework before considering the alternative accounts. We concluded that two scanning biases may be in effect: (1) an automatic bias favoring items in locations relatively distant from the current focus of attention and (2) a learned bias to scan letters in a left-to-right direction.

Right hemisphere reading mechanisms in a global alexic patient

We investigated the implicit, or covert, reading ability of a global alexic patient (EA) to help determine the contribution of the right hemisphere to reading. Previous studies of alexic patients with left hemisphere damage have suggested that the ability to derive meaning from printed words that cannot be read out loud may reflect right hemisphere reading mechanisms. Other investigators have argued that residual left hemisphere abilities are sufficient to account for implicit reading and moreover do not require the postulation of a right hemisphere system that has no role in normal reading processes. However, few studies have assessed covert reading in patients with lesions as extensive as the one in EA, which affected left medial, inferior temporal–occipital cortex, hippocampus, splenium, and dorsal white matter. EA was presented with lexical decision, semantic categorization, phonemic categorization, and letter matching tasks. Although EA was unable to access phonology and could not overtly name words or letters, she was nevertheless capable of making lexical and semantic decisions at above chance levels, with an advantage for concrete versus abstract words. Her oral and written spelling were relatively intact, suggesting that orthographic knowledge is retained, although inaccessible through the visual modality. Based on her ability to access lexical and semantic information without contacting phonological representations, we propose that EA’s implicit reading emerges from, and is supported, by the right hemisphere. Finally, we conclude that her spelling and writing abilities are supported by left hemisphere mechanisms.

Neural gate keeping: the role of interhemispheric interactions in resource allocation and selective filtering.

The corpus callosum has been proposed to contribute to attention by modulating resource allocation between the hemispheres and filtering interhemispheric signal transmission (M. T. Banich, 1998). The resource allocation hypothesis predicts that interhemispheric interactions become more advantageous with increasing resource demands. The selective filtering hypothesis predicts that interhemispheric interactions become less advantageous as filtering requirements increase. The authors tested both predictions by comparing within- and across-hemisphere letter matching under dual-task (Experiment 1) and selective attention conditions (Experiment 2). Task-specific resource demands (i.e., letter processing load) alter the bihemispheric advantage, but the general demand imposed by an unrelated secondary task does not. Filtering requirements influenced the advantage from interhemispheric interactions, providing new evidence for the role of the corpus callosum in selective attention.

Impact of Stimulus Integrity on Age Differences in Letter Matching

Young and older adults were tested in both a letter-identification and a letter-matching task in which the integrity of the letter stimuli was manipulated through contrast reduction and low-pass spatial frequency filtering. The use of the contrast and filtering manipulations was an attempt to increase encoding difficulty in an effort to examine whether stimulus integrity impacts more than just the initial encoding of the letter pairs in a letter-matching task, namely the comparison process as indexed by fast-same and false-different effects. Of interest in terms of aging is whether a decline in information-processing performance often reported in the aging literature is related to the known encoding deficits of older adults. In the letter-identification task, both contrast reduction and filtering slowed letter-identification speed for both groups, with the effect being larger for the older adults. In the letter-matching task, decreased processing efficiency produced by the contrast-reduction and low-pass-filtering manipulations led to an overall increase in reaction time and errors, but it did not interact with the magnitude of the fast-same effect or false-different effects for either subject group. These findings suggest that the stimulus integrity manipulations only impact the encoding of the letter pairs in the matching task and not the comparison process. The results of the present study support a dual-process model of the matching task consisting of separate encoding and comparison processes. The finding of a larger fast-same effect for older adults suggests that the age effect is occurring at the comparison stage, but it is not impacted by the stimulus integrity manipulations. The findings are described within a generalized slowing framework.

Functional MR Imaging to Evaluate Sensory Processing in Dyslexia

Dyslexia is a common neurobehavioral disorder affecting a large percentage of the population, with reported prevalence rates of 5%–10% of school-age children and 5% of the global population (1–5). Dyslexia manifests as reading difficulty, typically measured as single-word reading, in people who otherwise have sufficient education, intelligence, and motivation to read normally (6). Researchers agree that dyslexia has a neurobiologic and genetic basis, and such knowledge has been gleaned from numerous research techniques, including postmortem anatomic studies (7), genetic linkage studies (8,9), electroand magnetoencephalography (10–14), and neuroimaging, including positron emission tomography (15–20) and functional magnetic resonance (MR) imaging (1,21–23). These myriad studies point to a biologic basis for dyslexia, but the exact mechanisms at the core of this disorder remain unknown, as researchers actively pursue a theory to describe its constellation of deficits. There are several theories concerning the core deficits of language processing seen in dyslexics. Researchers have shown that many dyslexics have difficulty processing basic sensory information from at least one modality, such as auditory or visual stimuli. In addition, recent reports suggest that the temporal processing impairments seen in dyslexics are not limited to single sensory modalities (24,25). Our proposed research aims to study both unimodal (auditory or visual stimuli separately) and cross-modal (auditory and visual together) sensory processing in dyslexia by means of psychophysiological studies and functional MR imaging brain-mapping studies in dyslexics. The broad, long-term objective of this project is to determine the role played by sensory processing abnormalities in the language deficits observed in dyslexia. Our specific aims include testing hypotheses that dyslexics and control subjects will exhibit different neural activation patterns while performing two different paradigms: a unimodal (auditory or visual) letter discrimination task and a crossmodal letter matching task. We hope through our research on sensory processing to gain a better understanding of the neurobiology of dyslexia, thereby optimizing treatment strategies.

A peripheral reading deficit under conditions of diffuse visual attention

We report a single case study of a patient, FL, who has a peripheral dyslexia with symptoms resembling attentional dyslexia. FL demonstrated impaired identification of letters within strings, and better identification of words than their constituent letters. We found that FL was impaired at both letter counting and same-case letter matching with letter strings, and his matching and naming performance were strongly affected by letter spacing. The effects of these visual variables on performance suggest an early locus to FL's deficit. We propose that letter identification was disrupted by abnormal lateral masking and poor location coding within words. These peripheral processing deficits were reduced when the task required focused attention on the central letter location. Nevertheless, even with impaired letter coding, word representations could be accessed to some degree, via supra-letter units. We discuss the implications of the data for understanding normal reading.

A peripheral reading deficit under conditions of diffuse visual attention

We report a single case study of a patient, FL, who has a peripheral dyslexia with symptoms resembling attentional dyslexia. FL demonstrated impaired identification of letters within strings, and better identification of words than their constituent letters. We found that FL was impaired at both letter counting and same-case letter matching with letter strings, and his matching and naming performance were strongly affected by letter spacing. The effects of these visual variables on performance suggest an early locus to FL's deficit. We propose that letter identification was disrupted by abnormal lateral masking and poor location coding within words. These peripheral processing deficits were reduced when the task required focused attention on the central letter location. Nevertheless, even with impaired letter coding, word representations could be accessed to some degree, via supra-letter units. We discuss the implications of the data for understanding normal reading.

Language Mapping in Less Than 15 Minutes: Real-Time Functional MRI during Routine Clinical Investigation

Neurosurgical interventions often require the presurgical determination of language dominance or mapping of language areas. Results obtained by fMRI are closely correlated with invasive procedures such as electrical stimulation mapping or the intracarotid amobarbital test. However, language fMRI is not used routinely, because postprocessing is time-consuming. We utilized a real-time analysis software installed directly on the MR console computer and SPM99 as reference postprocessing software. We assessed the reliability of the immediate determination of language dominance based on individual activation maps by comparing the results of the visual analysis of images derived from conventional postprocessing with those produced by the real-time tool. All images were rated independently by six senior neurologists blinded to other data. We validated the robustness of the real-time method statistically by comparing global and regional lateralization indices derived from real-time and postprocessing analysis. Functional MRI was performed with a standard 1.5-T whole-body scanner. Brain activity was contrasted between an alternating semantic judgment and letter matching task. Twelve right-handed, healthy control subjects and 12 consecutive patients with drug-resistant, localization-related epilepsy were investigated. The semantic condition induced almost invariably left hemispheric activations in Broca's area, the premotor cortex, the dorsolateral prefrontal cortex, and the temporoparietal region. Although real-time analysis reduced noise less effectively than SPM99, visual ratings and lateralization indices produced highly concordant results with both methods. In conclusion, real-time fMRI, as used here, allowed reliable language lateralization and mapping in less than 15 min during routine clinical MRI investigation with no need for postprocessing.