Letter-matching Task Research Articles

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.

Sensitivity of functional tympanic membrane thermometry (fTMT) as an index of hemispheric activation in cognition

The measure of hemispheric activation in cognitive and clinical studies remains out of reach of many scientists due to cost, analysis complexity, and practical consideration of the techniques available such as fMRI, EEG, or EMG. The present study was conducted to determine whether infrared functional tympanic membrane thermometry (fTMT) is a measure of lateralised activation sensitive enough to be used in typical cognitive and clinical experiments. A total of 24 participants had their tympanic membrane temperature measured while performing a letter-matching task. Activation in the two hemispheres was manipulated by changing the proportion of matches occurring in the left and right visual fields and by varying the task complexity. Changes in fTMT due to the greater proportion of matches presented in one visual field and due to the modulation in task complexity were detected. These findings suggest that fTMT is a measure of broad lateralised cerebral activation sensitive enough for use in typical psychological studies.

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.

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.

Development of letter-specific processing: The effect of reading ability

During development, perceptual processing is tuned to inputs in the environment such that certain frequently encountered classes of stimuli are processed more effectively than similar comparison stimuli. Letters represent a class of stimuli that are encountered frequently in the environment, at least in literate cultures. Thus, the present study examined the development of letter-specific processing in children 6–19years old by comparing the difference between performance on a letter-matching task and an unfamiliar non-letter-matching task in different subject groups. Results revealed an increase in letter-specific processing with development. Moreover, comparisons of letter-specific processing in groups of subjects matched either in age or reading ability indicate that the emergence of letter-specific processing is linked to increased reading skill, rather than increased age per se. Findings support theories of perceptual expertise, which suggest that skilled processing drives the specialization of perceptual mechanisms for certain classes of stimuli.

Efficiency of callosal transfer and hemispheric interaction.

The corpus callosum (CC) is essential to hemispheric interaction, but it is unclear how individual callosal properties affect interaction between the cerebral hemispheres. A number of studies have demonstrated some relationship between morphology or structure of the CC and measures of hemispheric interaction. However, to the authors' knowledge, none of these studies has been able to show a clear, direct relationship between a behavioral measure of transfer speed through the CC, interhemispheric transfer time (IHTT), and a behavioral measure of hemispheric interaction. Eighty participants were tested over 6 sessions on 2 tasks assessing IHTT and hemispheric interaction. The Poffenberger paradigm was used to measure IHTT, and a divided split-visual-field letter-matching task was used to assess hemispheric interaction. A significant correlation that could not be accounted for by other factors such as functional lateralization, handedness, age, sex, or attention was found between these 2 measures. These results are discussed in relation to CC morphology and structure and functional and structural hemispheric lateralization.

Hemispheric interactions are different in left-handed individuals.

In a previous study, N. Cherbuin and C. Brinkman (2006) showed that in right-handed participants, interhemispheric transfer time (measured with A. T. Poffenberger's, 1912, paradigm) was a significant predictor of the efficiency of hemispheric interactions (measured with a split visual field, letter-matching task). No effect was found for degree of handedness in this study. This was surprising because handedness has been shown to be associated with differences in the morphology and the structure of the corpus callosum, and cerebral anatomical lateralization, as well as functional lateralization both in behavioral and scanning studies. Because these findings were found in a large sample, but one limited to right-handed participants, the aim of the present study was to determine whether a similar relationship was present between interhemispheric transfer time and hemispheric interaction in left-handed participants (using identical measures) and to assess whether the analysis of a larger sample that comprised both left- and right-handed participants might reveal an effect of handedness. Results demonstrate significant handedness effects, suggesting that left-handed individuals tend to have more efficient hemispheric interactions.

Aging and Individual Variation in Interhemispheric Collaboration and Hemispheric Asymmetry

ABSTRACT Thirty younger (Mean Age = 19.9 years) and 20 older adults (Mean Age = 74.7 years) performed Physical and Name Identity letter-matching tasks (matches were either within or between hemispheres) to study age-related changes in 1) the efficiency with which the two hemispheres interact with each other and 2) hemispheric asymmetry. In order to determine whether age-related effects were associated with differences in cognitive resources, the same individuals completed a set of memory span tasks. Performance on the letter-matching tasks indicated that the costs of interhemispheric collaboration were greater for older than for younger participants. However, within the older group, the advantage of spreading processing across both hemispheres increased as memory span decreased, suggesting that older individuals who are challenged by cognitive complexity are more likely to show increased benefits from between-hemisphere processing than individuals who are not so challenged. There was also an overall left visual field/right hemisphere advantage for the younger but not for the older group, suggesting greater age-related declines in right- than left-hemisphere function.

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.

Age-related effects of novel visual stimuli in a letter-matching task: an event-related potential study

Younger and older participants ( n = 8 in each age group) performed a letter-matching task, where they had to respond to identical letters ( P = 0.15). Task-relevant ( target and non-target) letters were presented on two corners of an imagery square, while on the other two corners irrelevant letters were presented. In some trials ( P = 0.05), pictures of visual objects ( novels, unrelated to the matching task) were presented. Reaction times were slower and error rates higher for older adults. The amplitude of the N1 event-related potential component was smaller over anterior locations for the older adults. All target stimuli elicited a late positivity over anterior locations for both age groups, but the late positivity (P3b) was absent over posterior scalp for the older adults. For the younger adults, novel stimuli elicited a large negative component (N2 novel) that was maximal over the central location. No such activity was observed for older adults. Based on the results, processing of novel stimuli is considered to be compromised in the elderly.

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.

Retrieval of Incidental Stimulus-Response Associations as a Source of Negative Priming.

Priming effects of ignored distractor words were investigated in a task-switching situation that allowed an orthogonal variation of priming and response compatibility between prime and probe. Across 3 experiments, the authors obtained a disordinal interaction of priming and response relation. Responding was delayed in the ignored repetition condition if different responses were required for identical stimuli in the prime and probe (negative priming). Repeating the prime distractor in the probe facilitated responding if the same response was required in the prime and in the probe (positive priming). The same pattern of results was replicated in a letter-matching task without task switching (Experiment 4). Findings lend support to a new model that explains negative priming in terms of an automatic retrieval of incidental stimulus-response associations.

A split-brain model of Alzheimer's disease?: Behavioral evidence for comparable intra and interhemispheric decline

It has been proposed that features of Alzheimer-type dementia (AD) reflect a breakdown in cortical connectivity that can be likened to a disconnection syndrome. One hypothesized consequence of this pathology is that AD patients should be disproportionally impaired on measures of interhemispheric transfer. However, there is a paucity of studies bearing on this prediction. We report the results from two measures of interhemispheric interaction obtained from healthy younger and older adults, and older adults with probable AD. One measure examined speeded simple manual responses to a lateralized light flash (i.e., the Poffenberger task) and the other examined the interhemispheric coordination of computational resources using within and across hemifield variants of visual letter-matching tasks. AD patients show an overall impairment of performance on both intra and interhemispheric conditions in all tasks. However, there is no indication of disproportionate alteration of interhemispheric processes mediating either visuomotor transfer or visual letter-matching and the allocation of computational resources. The results, therefore, call into question the appropriateness of a “split-brain” model for AD, at least in the domain of visual processing. Although the results are not specifically diagnostic of a disconnection syndrome, they are consistent with the possibility of a breakdown of cortico-cortical connectivity both within and between the hemispheres in AD.

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.

Menstrual Cycle-Dependent Neural Plasticity in the Adult Human Brain Is Hormone, Task, and Region Specific

In rodents, cyclically fluctuating levels of gonadal steroid hormones modulate neural plasticity by altering synaptic transmission and synaptogenesis. Alterations of mood and cognition observed during the menstrual cycle suggest that steroid-related plasticity also occurs in humans. Cycle phase-dependent differences in cognitive performance have almost exclusively been found in tasks probing lateralized neuronal domains, i.e., cognitive domains such as language, which are predominantly executed by one hemisphere. To search for neural correlates of hormonally mediated neural plasticity in humans, we thus conducted a functional magnetic resonance imaging study measuring brain activity related to a semantic decision task in the language domain. This was contrasted with a letter-matching task in the perceptual domain, in which we expected no steroid hormone-mediated effect. We investigated 12 young healthy women in a counterbalanced repeated-measure design during low-steroid menstruation and high-steroid midluteal phase. Steroid serum levels correlated with the volume and lateralization of particular brain activations related to the semantic task but not with brain activity related to the perceptual task. More specifically, bilateral superior temporal recruitment correlated positively with progesterone and medial superior frontal recruitment with both progesterone and estradiol serum levels, whereas activations in inferior and middle frontal cortex were unaffected by steroid levels. In contrast to these specific interactions, testosterone levels correlated nonselectively with overall activation levels by neural and/or vascular factor(s). In conclusion, our data demonstrate steroid hormone responsivity in the adult human brain by revealing neural plasticity in the language domain, which appears hormone, task, and region specific.

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.

Reliability and magnitude of visual laterality effects: The influence of attention

Two studies investigated the test–retest reliability of laterality effects in visual tasks. In each of the studies, 160 right-handed participants were tested. In Experiment 1, a lexical decision task was used under four testing conditions: no control of attention, fixation control, bilateral presentation with endogenous cue, and bilateral presentation with exogenous cue. In Experiment 2, the same four conditions were used in a letter-matching task in which participants had to indicate whether two letters in a different case had the same name. Results showed a significant right visual field advantage in the first testing session. However, this advantage was eliminated in the second session, suggesting that attention was not fully controlled by any of the procedures. In addition, the reliability of laterality effects was greater when control of attention was applied. The discussion focuses on the importance of controlling attention when assessing laterality by means of a visual task. Alternative explanations of the present findings are also considered.

Reliability and magnitude of visual laterality effects: The influence of attention

Two studies investigated the test–retest reliability of laterality effects in visual tasks. In each of the studies, 160 right-handed participants were tested. In Experiment 1, a lexical decision task was used under four testing conditions: no control of attention, fixation control, bilateral presentation with endogenous cue, and bilateral presentation with exogenous cue. In Experiment 2, the same four conditions were used in a letter-matching task in which participants had to indicate whether two letters in a different case had the same name. Results showed a significant right visual field advantage in the first testing session. However, this advantage was eliminated in the second session, suggesting that attention was not fully controlled by any of the procedures. In addition, the reliability of laterality effects was greater when control of attention was applied. The discussion focuses on the importance of controlling attention when assessing laterality by means of a visual task. Alternative explanations of the present findings are also considered.

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.