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At least 343 records · Page 19Linked to original sources
PubMed1999

Dynamics of letter string perception in the human occipitotemporal cortex.

The inferior occipitotemporal brain areas, especially in the left hemisphere, have been shown to be involved in the processing of written words and letter strings. This processing probably occurs within 200 ms after presentation of the letter string. It has also been suggested that this activation may differ between fluent and dyslexic readers. Using whole-head magnetoencephalography, we studied the spatiotemporal dynamics of brain processes evoked by visually presented letter strings in 12 healthy adult subjects. Our achromatic stimuli consisted of rectangular patches in which single letters, two-letter syllables, four-letter words, or symbol strings of equal length were embedded and to which variable noise was added. This manipulation dissociated three different response patterns. The first of these patterns took place approximately 100 ms after stimulus onset, originated in areas surrounding the V1 cortex and was distributed along the ventral visual stream, extending laterally as far as V4v. This response was systematically modulated by noise but was insensitive to the stimulus content, suggesting involvement in early visual analysis. The second pattern took place approximately 150 ms after stimulus onset and was concentrated in the inferior occipitotemporal region with left-hemisphere dominance. This activation showed a preference for letter strings, and its strength and timing correlated with the speed at which the subjects were able to read words aloud. The third pattern also occurred in the time window approximately 150 ms after stimulus onset, but originated mainly in the right occipital area. Like the second pattern, it was modulated by string length, but showed no preference for letters compared with symbols. The present data strongly support the special role of the left inferior occipitotemporal cortex in visual word processing within 200 ms after stimulus onset.

Adult↗
PubMed1993

Age differences in letter and color matching: selective attention or internal noise?

We tested healthy young and older adults on a letter-matching task that varied letter identity and letter color (Experiment 1) and on a color matching task that varied letter color and letter identity (Experiment 2). The goal of this investigation was to empirically disentangle the theoretical concepts of internal noise and selective attention. The results from Experiment 1 indicated that both young and older adults exhibited "fast-same" effects for reaction time and "false-different" effects for errors, and older adults exhibited a relatively larger "false-different" effect. However, letter color did not affect performance. The data from Experiment 2 indicated that older adults, compared with young adults, evidenced greater interference from "different-similar" letter pairs than "different-dissimilar" letter pairs even though the task was color matching. These data suggest that older adults evidenced greater levels of internal noise, and that this factor may modulate age differences in selective attention.

Adolescent↗
PubMed1998

Poison pen letters, due process, and medical schools' policies toward anonymous correspondence that disparages medical school faculty.

PURPOSE: To learn more about the frequency of and response to poison pen letters (anonymous correspondence that disparages faculty members) in academic medicine. METHOD: The authors surveyed all 143 deans of medical schools that are members of the AAMC about their practices and policies regarding the handling of poison pen letters. RESULTS: Of the deans surveyed, 119 (83%) responded. Sixty-seven deans (56%) reported having received poison pen letters during their tenure. Of those, 16 (24%) reported that they had discarded the letters based solely on the anonymity of the authors. The remaining 51 deans (76%) reported that they had either sequestered, investigated, or placed the letters into the faculty members' files, or that they had based their decisions to discard the letters on factors other than the authors' anonymity. Only one dean reported having a written policy for handling such correspondence. CONCLUSION: This survey of AAMC schools indicates that poison pen letters are not uncommon. The authors recommend a policy by which anonymous letters that disparage current or prospective faculty members would be categorically discarded.

Anonyms and Pseudonyms↗
PubMed1989

Contrast sensitivity for letter and grating targets under various stimulus conditions.

Measurement of visual acuity for letters of different contrasts has been suggested as a clinical way to evaluate contrast sensitivity in patients with vision abnormalities. If variable-contrast letter acuity provides information similar to the contrast sensitivity function (CSF), then comparable effects should be seen in stimulus manipulations which simulate decreased vision. Using both our own and published data, we compared the effects of diffusive blur, dioptric blur, and eccentric viewing on contrast sensitivity for letter and grating targets. A diffuser placed close to the eye reduces contrast sensitivity fairly evenly across all spatial frequencies, with similar results for letters and gratings. However, dioptric blur reduces sensitivity substantially more to letters than to comparably fine gratings. Eccentric viewing also produces a larger sensitivity loss for letters than for gratings. Because some stimulus manipulations produce dissimilar changes in contrast sensitivity for letters and gratings, it is questionable whether the results of one measure can be used to draw inferences about the other. It is proposed that local or relative phase discrimination has an important role in explaining the different responses to letter and grating targets.

Adult↗
PubMed1997

Computer-generated recall letters for underimmunized children: how cost-effective?

OBJECTIVE: To evaluate the effectiveness and cost effectiveness of computer-generated recall letters to parents of children overdue for immunizations. METHODS: This randomized controlled trial included children of two facilities in a regional health maintenance organization. Parents of 20-month-olds who had not yet received a measles-mumps-rubella (MMR) immunization were identified via a computerized immunization tracking system. One half were mailed personalized letters that included the recommended immunization schedule and a request to call for an appointment; the other half served as a control group. Receipt of the MMR between 20 and 24 months of age was evaluated with the computerized tracking system. A telephone survey was conducted with parents whose children had not received the MMR by 24 months. Decision analysis was used to project the theoretical outcomes and costs of a recall letter policy for other populations. RESULTS: Among 20-month-old children 10% had not received the MMR; 289 families were included in the analysis. Of families who were mailed letters, 54% (82 of 153) received the MMR by 24 months of age, compared with 35% (47 of 136) of those in the control group (P = 0.001). The telephone survey was completed with 110 parents of children who still did not appear on the health plan computer as having received the MMR by 24 months. Fifteen percent said the child had received an immunization at an outside provider, and of the rest 62% said they had not been aware that an immunization was due. In the cost effectiveness analysis it was projected that recall letters would increase the immunization rate for the regional population of approximately 30000 children from 86% to 90% at a total cost of $5031 annually. The cost per additional child appropriately immunized was $4.04. In sensitivity analyses this cost effectiveness ratio varied depending on the baseline population coverage rate as well as the estimated effectiveness of recall letters. CONCLUSIONS: Computer-generated letters to recall children overdue for immunizations resulted in a higher proportion of children appropriately immunized in this setting. However, the strategy was not as cost-effective as intuition might suggest. Further studies in health maintenance organization (HMO) settings should compare the cost effectiveness of letters with other low cost strategies including automated telephone reminders.

California↗
PubMed1993

Glasgow Acuity Cards: a new test for the measurement of letter acuity in children.

Problems with design and format of the traditional Snellen chart have led to the development of alternative charts for the measurement of visual acuity in adults. However, advances in chart design for the measurement of visual acuity in pre-school children have not paralleled those used in adult test charts. Visual acuity can be measured in infants and very young children using behavioural and electrophysiological techniques but clinical measurement of letter acuity tends to commence when the child is old enough to interact and co-operate with the examiner. Charts which are commercially available in the UK for measuring letter acuity in pre-school children (3-5 years old) either use single optotypes or are derivatives of the Snellen format. There is a need for a test of letter acuity for use with this young age group which is accurate, reliable and based upon sound and established design principles. Glasgow Acuity Cards have been designed to include features that should allow change in letter acuity to be detected in pre-school children, especially those undergoing vision therapy training. The test is performed at 3 m and incorporates several design features which have been used previously in adult charts but are new to childrens' test charts. These include: linear progression of letter sizes using a log scale; letters of approximately equal legibility; equal number of letters per line; control of contour interaction; screening cards to determine initial level of acuity. The test is quick and easy to perform and should provide a means of detecting change in letter acuity, with increased confidence.

Amblyopia↗
PubMed1988

Early-visual factors in letter confusions.

For the purpose of quantifying models of letter recognition, similarities are often specified in terms of stimulus properties. In this paper, an approach is advocated based on similarities between internal letter representations or internal letter images, i.e. it is argued that optical and retinal factors play a more prominent role in letter confusions than is usually assumed. To illustrate this, letter images were calculated on the basis of earlier experimentally determined point spread functions (Blommaert et al., Spatial Vision 2, 99-115, 1987). Next, data on confusion matrices from Bouma (Vision Res. 11, 459-474, 1971) were taken to evaluate different measures which might be useful for quantifying similarities between internal letter representations. In the analysis of experimental data, Luce's (In: Handbook of Mathematical Psychology, 1963) choice model was used. It was found that if similarities were expressed in terms of differences between image contours, a fair first order approximation of Bouma's experimental results could be formulated (overall correlation coefficient of 0.95). Other measures like correlations between spatial frequency spectra of letter images were found to be less successful. The method used provides a means to relate quantitatively stimulus features and optical and early-visual factors to letter confusions.

Form Perception↗
PubMed2004

Using visual noise to characterize amblyopic letter identification.

Amblyopia is a much-studied but poorly understood developmental visual disorder that reduces acuity, profoundly reducing contrast sensitivity for small targets. Here we use visual noise to probe the letter identification process and characterize its impairment by amblyopia. We apply five levels of analysis - threshold, threshold in noise, equivalent noise, optical MTF, and noise modeling - to obtain a two-factor model of the amblyopic deficit: substantially reduced efficiency for small letters and negligibly increased cortical noise. Cortical noise, expressed as an equivalent input noise, varies among amblyopes but is roughly 1.4x normal, as though only 1/1.4 the normal number of cortical spikes are devoted to the amblyopic eye. This raises threshold contrast for large letters by a factor of radical1.4 = 1.2x, a negligible effect. All 16 amblyopic observers showed near-normal efficiency for large letters (> 4x acuity) and greatly reduced efficiency for small letters: 1/4 normal at 2x acuity and approaching 1/16 normal at acuity. Finding that the acuity loss represents a loss of efficiency rules out all models of amblyopia except those that predict the same sensitivity loss on blank and noisy backgrounds. One such model is the last-channel hypothesis, which supposes that the highest-spatial-frequency channels are missing, leaving the remaining highest-frequency channel struggling to identify the smallest letters. However, this hypothesis is rejected by critical band masking of letter identification, which shows that the channels used by the amblyopic eye have normal tuning for even the smallest letters. Finally, based on these results, we introduce a new "Dual Acuity" chart that promises to be a quick diagnostic test for amblyopia.

Adult↗
PubMedDate not supplied

Understanding the relations between RAN letter subtest components and word reading in first-grade students.

First-grade students (N = 221) were individually tested on a battery of cognitive and achievement measures of verbal fluency, visual attention, phonological awareness, orthographic recognition, rapid automatized naming (RAN) of letters and objects, and reading. All tests were subjected to postacquisition scoring, and all RAN measures were segregated into measures of articulation time, pause time, and consistency of the pause time. Structural equation modeling demonstrated that word reading was directly and significantly predicted by RAN letter naming and general RAN cognitive processing time of objects. Moreover, RAN letter reading constructs were significantly and directly predicted by the latent variables of phonological awareness, orthographic recognition, and general RAN object articulation and cognitive processing times. RAN letter naming constructs were also significantly and indirectly predicted by visual attention. The reading model was found to be consistent with a total mediation of the relation of phonological awareness and reading through RAN letter naming and supported the validity of the RAN letter naming subtest as a basic letter reading test. These findings supported the double-deficit hypothesis for letter reading. We suggest that phonological memory is a basic factor underlying general RAN cognitive processing time of objects and domain-specific information associated with phonemes and their graphic representations.

Attention↗
PubMed1978

The effects of feedback and consequences on transitional cursive letter formation.

Twelve first-grade students were employed to analyze the effects of (1) Verbal and Visual Feedback, (2) Verbal and Visual Feedback plus immediate rewriting of trained letters with one or more incorrect letter strokes, and (3) Potential Reinforcement on cursive letter strokes. Students practised both a set of trained and a set of untrained letters during each session. Feedback and reinforcement was administered only for trained letter strokes. The percentage of correct trained letter strokes increased during all conditions. Performance on the untrained but practiced and trained letter strokes followed the same general trend in response pattern. No consistent pattern of generalization was demonstrated with untrained and unpracticed letter strokes.

Journal Article↗
PubMed2004

The relative benefit of word context is a constant proportion of letter identification time.

Letter identification is reduced when the target letter is surrounded by other, flanking letters. This visual crowding is known to be impacted by physical changes to the target and flanks, such as spatial frequency content, polarity, and interletter spacing. There is also evidence that visual crowding is reduced when the flanking letters and the target letter form a word. The research reported here investigated whether these two phenomena are independent of each other or whether the degree of visual crowding impacts the benefit of word context. Stimulus duration thresholds for letters presented alone and for the middle letters of 3-letter words and nonwords were determined for stimuli presented at the fovea and at the periphery. In Experiment 1, the benefit of word context was found to be the same at the fovea, where visual crowding is minimal, and at the periphery, where visual crowding is substantial. In Experiment 2, visual crowding was manipulated by changing the interletter spacing. Here, too, the benefit of word context was fairly constant for the two retinal locations (fovea or periphery), as well as with changes in interletter spacing. These data call into question both the idea that the benefit of word context is greater when stimulus quality is reduced (as is the case with visual crowding) and the idea that words are processed more effectively when they are presented at the fovea.

Fixation, Ocular↗
PubMed2003

The PIG in sPrInG: evidence on letter grouping from the reading of buried words.

We introduce a novel procedure for investigating factors that determine selective attention to letters in words. Participants were presented with words (in Experiments 1 and 3) and nonwords (in Experiment 2) that contained a buried word whose letters differed in color relative to the other letters present (e.g., pig, in spring). The strings were presented in single case or mixed case, keeping the letters of the buried words in one case (SpRiNg). The time in which the whole stimulus was named was shorter for same-case than for mixed-case strings (for spring: spring < SpRiNg). In contrast, the time in which buried words were named was shorter in mixed- than in same-case strings (for pig: spring > SpRiNg). Across items, the effects of case mixing were negatively correlated across the two tasks. The positive effect of case mixing for buried words also occurred irrespective of whether the whole string was a word or a nonword, and there were contributions from similarity of both letter size and case. The results suggest that case mixing can facilitate selective attention to letters, which is otherwise disrupted by size- and case-based grouping across letter strings. The study provides evidence for letter grouping using size and case information.

Attention↗
PubMed1991

On the role of refixations in letter strings: the influence of oculomotor factors.

Recent studies of reading and word recognition have shown that eye-movement behavior depends strongly on the position in the word that the eye first fixates; the probability of refixating in a word is lowest with the eye near the middle of the word, and it increases as the eye fixates to either side. It has generally been assumed that the cause for this optimal landing position phenomenon lies in the very strong drop-off of visual acuity even within the fovea; refixation should be more likely when the eye starts from a noncentral position, because here less information can be extracted during one fixation. It may, however, be the case that the phenomenon is caused not by acuity drop-off, but by differences in within-word oculomotor scanning tactics as a function of the position that the eye initially fixates. To test this, in the present experiment we kept visual information constant while we varied the initial fixation position. We used homogeneous strings of letters of different length. One letter in each string was different from the rest (e.g., kkkkkok), and this was the letter that the subject initially fixated. This target letter had to be identified before saccading to a comparison string. The position of the target letter in the string was varied from trial to trial. If, owing to acuity limitations, refixations reflect insufficient information extraction, then, because the target letter is always directly fixated, the pattern of refixations in this condition should be independent of the first fixation position. However, the obtained refixation probability showed a strong dependence on the position of first fixation. The number of refixations was independent of the absolute length of the letter strings, but it seemed to be influenced by the proportion of the string over which the eye had to pass. The larger this proportion, the higher the probability of refixation. The results suggest that to a certain extent refixations in letter strings (or words) reflect properties of the oculomotor system rather than visual information extraction.

Adult↗
PubMed1995

Letter-position coding in random constant arrays.

The processing of letter-position information in randomly arranged consonant strings was investigated using a masked prime variant of the alphabetic decision (letter/nonletter classification) task. In Experiment 1, primes were uppercase consonant trigrams (e.g., FMH) and targets were two uppercase Xs accompanied by the target letter or a nonletter (e.g., XMX X%X). Response times were systematically faster when target letters were present in the prime string than when target letters were not present in the primer string. These constituent letter-priming effects were significantly stronger when the target letter appeared in the same position in the prime and target stimuli. This contrast between position-specific and position-independent priming was accentuated when subjects responded only when all the characters in the target string were letters (multiple alphabetic decision) in Experiment 2 and 3. In Experiment 4, when prime exposure duration was varied, it was found that position-specific priming develops earlier than position-independent priming. Finally, Experiment 5 ruled out a perceptual-matching interpretation of these result. An interpretation is offered in terms of position-specific and position-independent letter-detector units in an interactive-activation framework.

Humans↗
PubMed1996

Searching for solutions: health concerns expressed in letters to an east African newspaper column.

This study examined health care questions from an unusual data set: 1252 unsolicited letters written over a three-year period to an advice column in an East African newspaper. Analysis of the letters was a non-intrusive method of ascertaining prevalent health questions and opinions. People wrote seeking information, advice, solutions, and reassurance about health problems. Emotions expressed in the letters ranged from hope to fear and frustration. The written format allowed questions which are generally too embarrassing or stigmatized to present in other public or interpersonal settings. More than half the total letters raised questions about sexual behaviour, sexually transmitted diseases, and HIV/AIDS. The letters present not only personal health concerns, but also expectations of health-care quality and reflections on the medical options presently available in Uganda. As a whole, the letters express dissatisfaction not only with the outcomes of health encounters, but with the process. Of the letter writers with specific physical complaints, more than one-third had already sought medical care and were dissatisfied with the results. The letters were seeking solutions, especially for alleviation of symptoms and discomfort. Almost equally prevalent was a plea for accurate and relevant health information; people not only want to feel better, but they also want to understand their own health.

Adolescent↗
PubMed2001

[Significance of letters published in the Dutch Journal of Medicine, 1997/98].

OBJECTIVE: To determine whether in the correspondence section of the Nederlands Tijdschrift voor Geneeskunde (Dutch Journal of Medicine, NTvG) serious criticism is formulated or important mistakes in the original articles are pointed out. DESIGN: Descriptive, retrospective bibliometric study. METHOD: Correspondence in the period July 5, 1997-June 27, 1998 published in the NTvG (n = 196 letters) was scored for 10 items and categorized in categories: 'agree', 'do not agree' (criticizing methods or results or interpretation, or unmotivated criticism) and 'political reaction'. The questions were studied to what category of published articles the letters referred and how many letters referred to the same articles. 22 letters from the period October-December 1998 were judged separately as the peer review reports of the original articles were still available. RESULTS: In 115 (58.7%) letters the writers expressed agreement with the original article. Almost 40% (77) of the 196 letters contained scientific discussion on the subject in question. Most reactions concerned 'Original articles' (25%) and 'Clinical lessons' (19.4%). In 8/196 (4.1%) a mistake was revealed; 6 of these reactions led to the publication of a 'Correction' (to 3 articles). There was no criticism which would have led to rejection of the article involved had it been known before publication. The letters about articles of which the peer reviews were still available contained no criticism of points the peer reviewers had missed. CONCLUSION: Of the correspondence letters of the NTvG 4.1% contained scientific criticism which could have led to changes in the article if it had been known before publication.

Bibliometrics↗
PubMed2001

Are individual or consecutive letters the unit affected by repetition blindness?

When 2 similar words (e.g., react reach) are briefly sequentially displayed, the 2nd word may be omitted from the report, a phenomenon known as repetition blindness (RB). Previous researchers have suggested that consecutive letters are the unit affected by RB. Six experiments provided new data on orthographic RB. Two letters at the beginning or end of words resulted in RB, as did alternating interior letters (tactile earthly) and 3 letters with different relative positions (arid bird). However, no RB was found with a single final letter (show view). Observed RB may reflect pattern completion because RB for pairs like throat theory was reduced when the nonrepeated letters (eory) were consistent with only a single word. The experiments point to a model of orthographic RB in which both individual letters and letter sequences of length 2 or more play a role.

Adult↗
PubMed1975

Interaction between two letters in visual perception.

Letters were exposed by tachistoscope for 17 ms to adult subjects. In Experiment I, single letters were exposed. The proportion of errors differed strongly for particular letters. In Experiment II pairs of letters were exposed. The first letter of a pair was recognized more easily than when exposed alone in Experiment I. In Experiment III pairs of letters were exposed but the subject's task was to recognize only one letter of the pair. Both, first and second letters of the pair were then recognized better than in Experiment I. The results were interpreted in terms of facilitatory and inhibitory effects occurring on different levels of the visual system.

Adult↗