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PubMed2004

Procedural and declarative knowledge of word recognition and letter decoding in reading an artificial script.

In a previous study [Cogn. Brain Res. 16 (2003) 325], we found that letter knowledge did not evolve from implicit training on whole-word recognition in an artificial Morse-like script, although the participants were adults, experienced in alphabetical reading. Here we show minimal conditions in which letter knowledge may evolve in some individuals from training on whole-word recognition. Participants received multi-session training in reading nonsense words, written in an artificial script, in which each phoneme was represented by two discrete symbols. Three training conditions were compared: alphabetical whole words with letter decoding instruction (Explicit), alphabetical whole words (Implicit), and non-alphabetical whole words (Arbitrary). Subjects were assigned to training either on the explicit and arbitrary or on the implicit and arbitrary conditions. Our results show that: (a) Letter-decoding knowledge evolved implicitly from training on alphabetical whole-word recognition, in some individuals. However, (b) a clear double dissociation was found between effectively applied implicit letter knowledge and declarative letter knowledge. (c) There was no advantage of the implicitly derived over the explicitly instructed letter knowledge. (d) Long-term retention was more effective in the explicit compared to the arbitrary condition. (e) Word-specific recognition contributed significantly to performance in all three training conditions, i.e. even under conditions that presumably afford advantage for word segmentation. Altogether, our results suggest that both declarative and procedural knowledge contributed to letter decoding as well as to word-specific recognition performance. Moreover, a greater dependency on declarative knowledge may not be an inherent characteristic of word-specific recognition, but rather that both letter decoding and word-recognition routines can become proceduralized given sufficient practice.

Adolescent↗
PubMed2006

Learning of letter names follows similar principles across languages: Evidence from Hebrew.

Letter names play an important role in early literacy. Previous studies of letter name learning have examined the Latin alphabet. The current study tested learners of Hebrew, comparing their patterns of performance and types of errors with those of English learners. We analyzed letter-naming data from 645 Israeli children who had not begun formal reading instruction: a younger group (mean age 5 years 2 months) and an older group (mean age 6 years 2 months). Children's errors often involved letters with similar shapes or letters adjacent to one another in the alphabet. Most Hebrew letter names are not very similar to one another phonologically, and there were fewer phonologically based confusions than in English. We found both general frequency effects and frequency effects that reflected the letters in individual children's names. On average, girls knew more letter names than did boys. The results suggest that letter name learning follows similar principles across languages.

Child↗
PubMed2005

Selective response to letter categorization within the left fusiform gyrus.

Neuroimaging studies that look at reading processes using words, pseudowords, nonwords and letters frequently report specific left fusiform gyrus (BA37) activations. In the present study, we examined fMRI signal variations within the left and right BA37 for paired Latin letters, Korean letters and geometrical figures in discrimination and categorization tasks. Data of Pernet et al. (Pernet, C., Franceries, X., Basan, S., Cassol, E., Démonet, J.F., Celsis, P., 2004. Anatomy and time course of discrimination and categorization processes in vision: an fMRI study. NeuroImage 22, 1563-1577) were re-analyzed using a ROI methodology that highlights the selective response of the left BA37 to Latin letter categorization. First, differences according to stimulus type were observed for the categorization task only. Second, we found weaker activation for Latin letter categorization than for both geometrical figure and Korean letter categorization. Third, only Latin letter categorization elicited as left-sided activation, although the direct comparison between regions did not demonstrate a significant difference. These data suggest that the left fusiform gyrus sustains access to letter representations in memory; and results are discussed with reference to the relationship between letter categorization and word recognition and to selective vs. specific (i.e. task-independent) neural response.

Adult↗
PubMed2004

What do lateralized displays tell us about visual word perception? A cautionary indication from the word-letter effect.

A common assumption underlying laterality research is that visual field asymmetries in lateralized word perception indicate the hemispheric specialisation of processes generally available for the perception of words, including words viewed in a more typical setting (i.e. in the central visual field). We tested the validity of this assumption using a phenomenon (the word-letter effect) frequently reported for displays viewed in the central visual field, where letters in words are perceived more accurately than the same letters in isolation. Words and isolated letters were presented in the left visual field (LVF), right visual field (RVF) and central visual field (CVF), the Reicher-Wheeler task was used to suppress influences of guesswork, and an eye-tracker ensured central fixation. In line with previous findings, lateralized displays revealed a RVF-LVF advantage for words (but not isolated letters) and CVF displays revealed an advantage for words over isolated letters (the word-letter effect). However, RVF and LVF displays both produced an advantage for isolated letters over words (a letter-word effect), indicating that processing subserving the advantage for words when participants viewed stimuli in the central visual field was unavailable for lateralized displays. Implications of these findings for studies of lateralized word perception are discussed.

Attention↗
PubMed2006

Feature detection and letter identification.

Seeking to understand how people recognize objects, we have examined how they identify letters. We expected this 26-way classification of familiar forms to challenge the popular notion of independent feature detection ("probability summation"), but find instead that this theory parsimoniously accounts for our results. We measured the contrast required for identification of a letter briefly presented in visual noise. We tested a wide range of alphabets and scripts (English, Arabic, Armenian, Chinese, Devanagari, Hebrew, and several artificial ones), three- and five-letter words, and various type styles, sizes, contrasts, durations, and eccentricities, with observers ranging widely in age (3 to 68) and experience (none to fluent). Foreign alphabets are learned quickly. In just three thousand trials, new observers attain the same proficiency in letter identification as fluent readers. Surprisingly, despite this training, the observers-like clinical letter-by-letter readers-have the same meager memory span for random strings of these characters as observers seeing them for the first time. We compare performance across tasks and stimuli that vary in difficulty by pitting the human against the ideal observer, and expressing the results as efficiency. We find that efficiency for letter identification is independent of duration, overall contrast, and eccentricity, and only weakly dependent on size, suggesting that letters are identified by a similar computation across this wide range of viewing conditions. Efficiency is also independent of age and years of reading. However, efficiency does vary across alphabets and type styles, with more complex forms yielding lower efficiencies, as one might expect from Gestalt theories of perception. In fact, we find that efficiency is inversely proportional to perimetric complexity (perimeter squared over "ink" area) and nearly independent of everything else. This, and the surprisingly fixed ratio of detection and identification thresholds, indicate that identifying a letter is mediated by detection of about 7 visual features.

Adolescent↗
PubMed2002

Evidence for magnocellular involvement in the identification of flanked letters.

Little is known about the role of the magno system in reading. One important hypothesis is that this system is involved in the allocation of attention. We reasoned that the presentation of a single letter automatically draws attention to this letter, whereas in the case of a flanked letter, an additional process of attention allocation is required for identification to occur. In three letter-naming experiments with 24 subjects each, normally reading adults were presented with flanked (e.g. xax) and with single (e.g. a) letters at three possible (para)foveal locations. The letters appeared in magno-disadvantageous colour contrast or in parvo-disadvantageous weak luminance contrast with the background. A control experiment verified that colour contrast had generated less magnocellular activity than had luminance contrast. Colour-contrast presentation led to a significantly lower naming performance for flanked letters than did luminance-contrast presentation, despite the fact that the two contrasts did not elicit differences in naming performance when the letters were presented in isolation. This latter finding rules out the possibility that colour contrast had generated not only less magno- but also less parvocellular activity than had luminance contrast. Thus, it can be concluded that the magno system is involved in the identification of flanked letters. This conclusion supports the hypothesis that the magno system is important to the allocation of attention. Further, it may provide an explanation for the frequent finding that people with developmental dyslexia have impairments in their magnocellular system.

Adolescent↗
PubMed2002

The role of spatial frequency channels in letter identification.

How we see is today explained by physical optics and retinal transduction, followed by feature detection, in the cortex, by a bank of parallel independent spatial-frequency-selective channels. It is assumed that the observer uses whichever channels are best for the task at hand. Our current results demand a revision of this framework: Observers are not free to choose which channels they use. We used critical-band masking to characterize the channels mediating identification of broadband signals: letters in a wide range of fonts (Sloan, Bookman, Künstler, Yung), alphabets (Roman and Chinese), and sizes (0.1-55 degrees ). We also tested sinewave and squarewave gratings. Masking always revealed a single channel, 1.6+/-0.7 octaves wide, with a center frequency that depends on letter size and alphabet. We define an alphabet's stroke frequency as the average number of lines crossed by a slice through a letter, divided by the letter width. For sharp-edged (i.e. broadband) signals, we find that stroke frequency completely determines channel frequency, independent of alphabet, font, and size. Moreover, even though observers have multiple channels, they always use the same channel for the same signals, even after hundreds of trials, regardless of whether the noise is low-pass, high-pass, or all-pass. This shows that observers identify letters through a single channel that is selected bottom-up, by the signal, not top-down by the observer. We thought shape would be processed similarly at all sizes. Bandlimited signals conform more to this expectation than do broadband signals. Here, we characterize processing by channel frequency. For sinewave gratings, as expected, channel frequency equals sinewave frequency f(channel)=f. For bandpass-filtered letters, channel frequency is proportional to center frequency f(channel) proportional, variantf(center) (log-log slope 1) when size is varied and the band (c/letter) is fixed, but channel frequency is less than proportional to center frequency f(channel) proportional, variantf(center)(2/3) (log-log slope 2/3) when the band is varied and size is fixed. Finally, our main result, for sharp-edged (i.e. broadband) letters and squarewaves, channel frequency depends solely on stroke frequency, f(channel)/10c/deg=(2/3), with a log-log slope of 2/3. Thus, large letters (and coarse squarewaves) are identified by their edges; small letters (and fine squarewaves) are identified by their gross strokes.

Contrast Sensitivity↗
PubMed2003

Visual presentation of single letters activates a premotor area involved in writing.

In the present fMRI study, we addressed the question as to whether motor-perceptual interactions might be involved in reading. Recognizing the letters encountered when reading is generally assumed to be a purely visual process, yet because we know how to write, we also possess a sensorimotor representation of the letters. Does simply viewing a letter suffice to activate the corresponding motor representation? To answer this question, we asked right-handed subjects first to look at and then to copy single letters or pseudoletters. We established that the visual presentation of letters activated a part of the left premotor cortex (BA6) that was also activated when the letters were being written by the subjects. This premotor zone resembles Exner's area, which is thought to contain the motor programs necessary for producing letters. Visually presented pseudoletters, which had never been written before by the subjects, did not activate this region. These results indicate that the writing motor processes are implicitly evoked when passively observing letters. The cerebral representation of letters is therefore presumably not strictly visual, but based on a multicomponent neural network built up while learning concomitantly to read and write. One of the components might be a sensorimotor one associated with handwriting. This finding shows the existence of close functional relations between the reading and writing processes, and suggests that our reading abilities might be somehow dependent on the way we write.

Adult↗
PubMed1978

Letter identification as a function of type of perceptual limitation and type of attribute.

It is argued that the distribution of errors in letter identification depends on two factors: (a) whether the set of letters is defined by features that exist or do not exist or by dimensions that exist at some positive value, and (b) whether errors are produced by process limitation in which the letter patterns are distorted or by state limitation in which there is inadequate energy. A specific hypothesis tested was that error distributions reflect the attribute structure under both types of limitation if dimensions define the letter set, but only under a process limitation if features define the letter set. Under a state limitation, feature set errors are primarily produced by a loss of features, so that a letter with more features is called a letter with fewer features more often than conversely. An experiment completely validated the hypothesis under test. In addition, the relative discriminabilities of two dimensions defining a dimension set of letters was reversed from state to process limitation. Thus the attribute structure derived from error distributions is not invariant across types of perceptual limitation, nor are distances between letter pairs always symmetric.

Discrimination, Psychological↗
PubMed2002

Diagnostic utility of letter fluency, category fluency, and fluency difference scores in Alzheimer's disease.

Word generation tasks, specifically letter fluency and category fluency, are a standard part of most test protocols used by clinical neuropsychologists to measure aspects of language and executive retrieval functions. Given the reliance on these measures as clinical tools, it is important to understand the diagnostic implications of patients' performances. In Alzheimer's disease (AD), category fluency has generally been found to be disproportionately impaired, whereas letter fluency is usually more mildly impaired. It has been proposed that this performance pattern occurs because access to temporal-lobe semantic stores is necessary for category fluency but not letter fluency. In this study, the diagnostic utility of category fluency, letter fluency, and difference scores (letter fluency minus category fluency) in AD were examined. Forty AD patients and 221 normal control subjects took category fluency and letter fluency tests. Traditional t-test comparisons revealed that the groups differed significantly on the two test tasks and in terms of mean difference scores. However, using sensitivity and specificity to calculate predictive values, only category fluency and letter fluency (but not difference scores) were useful in predicting AD in individuals. Furthermore, category fluency was superior to letter fluency in this regard. Likelihood ratio tables are provided for use in calculating the odds of AD for specific category fluency and letter fluency scores generated by individual patients.

Adult↗
PubMedDate not supplied

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.

Adult↗
PubMed1986

National survey of writers of dean's letters for residency applications.

The purpose of the study reported here was to provide descriptive information about dean's letters, which are comprehensive summary letters sent near the end of students' undergraduate medical training by medical school deans to be part of the students' residency applications. Deans of student affairs at 124 U.S. medical schools were surveyed regarding composition of these letters at their institution. They were asked to describe themselves and the letters they write. Responses were received from 87 percent of these schools and provided data on types of information included in the letters, the decision to edit evaluations, student participation in the letter-writing process, use of final summary statements, cost and length of letters, and attitudes toward the development of national letter-writing guidelines. Major findings of the survey show that 97 percent of the writers allocated more space for clinical evaluations than basic science evaluations. Less than 50 percent of the writers included the student's class rank. Almost all included narrative evaluations of the student's performance during the clinical years. Negative information on students was addressed inconsistently by the writers. Eighty-five percent of the writers categorized their students in final summary statements, but many of these failed to provide descriptions of the categories used or explanatory data. The present authors make recommendations for writing more credible and useful letters.

Educational Measurement↗
PubMed2000

Relative legibility and confusions of letter acuity targets in the peripheral and central retina.

BACKGROUND: Patients with macular disease may image optotypes at a peripheral retinal locus during visual acuity testing. In this study, we asked if the relative legibility and confusions between letters are similar in the fovea and at 10 degrees in the peripheral retina. METHODS: Twenty five upper-case alphabet letters (all except "I"), constructed to the same specifications as the Sloan letters, were presented one at a time on a computer monitor at the fovea and at 10 degrees in the temporal, superior and superior-temporal retina. RESULTS: The range of relative legibility at peripheral loci was generally larger than in the fovea, for all letters and for the subset of 10 Sloan letters. Although many confusion pairs were similar in the fovea and periphery, additional confusion pairs, preferentially involving curved letters, occurred uniquely in the periphery. CONCLUSION: The increased range of relative legibility for letter targets in the peripheral retina underscores the importance of using letter-by-letter scoring to obtain precise measures of visual acuity in patients without central vision.

Adult↗
PubMed2000

Recognition thresholds for letters with simulated dioptric blur.

We examined the effects of simulated dioptric blur on the degradation of visual acuity using digitally filtered letters. Four types of digital filters were applied to 5 letters (C, D, E, O, and S), constructed to the specifications of Sloan optotypes. These filters were: (1) "normal," designed to simulate the positive and negative lobes of the modulation transfer function (MTF) produced by dioptric blur; (2) "truncated," which passed only those spatial frequencies up to the first zero of the MTF; (3) "phase-rectified," which inverted all of the negative lobes of the MTF to positive; and (4) "truncated-plus-negative," which eliminated all positive lobes above the first zero of the MTF. The letter size required to achieve 60%-correct identification was determined for letters that were filtered to simulate +1, +2, and +4 D of blur. Letters subjected to normal, truncated, and truncated-plus-negative filtering had approximately the same acuity threshold, whereas the threshold size for phase-rectified letters was significantly better. Our interpretation of these results is that dioptric blur hinders letter recognition because useful spatial frequency information is limited to that below the first zero of the MTF, and not because of interference from the phase-reversed spatial frequency information above the first zero. Our letter identification thresholds are consistent with recent evidence that the critical information for letter acuity corresponds to approximately 1.5 cycles/letter.

Adult↗
PubMed2005

Measuring the quality of referral letters about patients with upper gastrointestinal symptoms.

BACKGROUND: General practitioners state the reason for referring patients in referral letters. The paucity of information in these letters has been the source of criticism from specialist colleagues. OBJECTIVE: To invite general practitioners to set standards for referral letters to gastroenterologists and to apply these standards to actual referral letters to one specialist gastroenterology unit. METHODS: A scoring schedule was designed based on the responses to a questionnaire survey of a large sample of all general practitioners in one locality. Altogether 350 consecutive letters to a district general hospital about patients referred for an upper gastrointestinal specialist opinion were subsequently scored using the schedule. RESULTS: 102 practitioners responded to the survey. Their responses imply that colleagues assess and record findings on 18 potential features of upper bowel disease. In practice most referral letters address fewer than six features of upper bowel disease. The mean number of positive features of upper gastrointestinal disease reported in each letter was one. CONCLUSIONS: This study reported a failure to meet "peer defined" standards for the content of referral letters set by colleagues in one locality. Referral letters serve many purposes, however, encouraging full documentation of specific clinical findings may serve to increase the pre-referral assessments performed in practice.

Adult↗
PubMed1984

Letter legibility and the construction of a new visual acuity chart.

The ability to identify letters of different size remains, in relation to the allowed effort, the most informative measure of visual capacity. Numerous letter charts have been produced with varying design, size, and size progression of the letters. Attempts to 'standardize' letter testing have been fruitless. In Sweden, the most commonly used letter charts show deficiencies in letter selection, size, and progression. In the present study, letter legibility was studied. 10 letters of average legibility were selected and a new chart constructed using these letters in sizes corresponding to acuities from 0.1 to 2.0. A geometric size progression was found optimal (factor 1.26).

Humans↗
PubMed1994

The take-home message: patients prefer consultation audiotapes to summary letters.

PURPOSE: Despite reports of poor patient understanding and recall after cancer consultations, few doctors provide communication aids. We conducted a randomized trial comparing an audiotape of the consultation versus individualized summary letters to patients after their first consultation with a medical oncologist. METHODS: One hundred eighty-two cancer patients were randomized to receive either (1) the audiotape followed 7 to 10 days later by the letter or (2) the letter followed by the audiotape. Outcome measures included patient recall, anxiety and depression, satisfaction with and use of the communication aids, and patient preferences for six communication options. Demographic and disease variables and information and involvement preferences were documented. RESULTS: Eighty percent of patients wanted all information and 72% wanted to participate in treatment decisions. Patients listened to the tape on average 2.3 times and read the letter 2.8 times over 4 weeks, and 90% showed the tape or letter to a friend, relative, or doctor. Satisfaction with the tape and letter were uniformly high and they did not differentially affect recall, anxiety, or depression. When asked to rank six communication options, 46% of patients gave the highest rank to the tape and 21% to the letter. CONCLUSION: Patients use audiotapes of their cancer consultation and individualized letters to review the information given and communicate information to relatives and friends. They prefer audiotapes to letters. Clinicians should consider installing audiotape-recording facilities that could be used to tape new-patient consultations.

Adult↗
PubMed2005

Referral letters: are we prioritizing consistently?

OBJECTIVES: To determine the levels of intra- and inter-grade variability of the vetting of general practice (GP) letters as well as the intra-rater reliability of letter prioritization. DESIGN: Prospective assessment of letter vetting and questionnaire survey. SETTING: Three otolaryngology secondary referral centres in Bristol and Bath, UK. PARTICIPANTS: Twelve consultants, nine registrars, four staff and associate specialists (SAS) and 16 senior house officers (SHOs) in otolaryngology. METHODS: Fifty GP letters (not including 'fast-track' referrals) addressed to one of the ENT departments were chosen sequentially. These were anonymized, photocopied and included in the questionnaire to all participating staff. Participants were asked to vet the letters as 'urgent', 'soon' or 'routine' according to supplied waiting time criteria. The same letters were sent out again six weeks later. RESULTS: There was no significant difference between grades for the mean number of letters vetted into each category. Intra-grade variability was high; the number of letters vetted urgent varied from one out of 50 to 15 out of 50 for the consultants. The intra-rater reliability was high. CONCLUSION: The grade of trainee seems to make little difference with regard to ability to prioritize referrals, but within grades there is little agreement on what constitutes an urgent referral. We suggest further research, looking at the final outcome of patients, needs to be done to try to establish evidence-based guidelines to assist with letter vetting.

Correspondence as Topic↗