Letter Spacing Research Articles

The impact of letter spacing on reading: A test of the bigram coding hypothesis

Identifying letters and their relative positions is the basis of reading in literate adults. The Local Combinations Detector model hypothesizes that this ability results from the general organization of the visual system, whereby object encoding proceeds through a hierarchy of neural detectors that, in the case of reading, would be tuned to letters, bigrams, or other letter combinations. Given the increase of receptive fields by a factor of 2 to 3 from one neural level to the next, detectors should integrate information only for letters separated by at most 2 other characters. We test this prediction by measuring the impact of letter spacing on reading, purifying this effect from confounding variables. We establish that performance deteriorates non-linearly whenever letters are separated by at least 2 blank spaces, with the concomitant emergence of a word length effect. We then show that this cannot be reduced to an effect of physical size nor of visual eccentricity. Finally, we demonstrate that the threshold of about 2 spaces is constant across variations in font size. Those results support the hypothesis that the fast recognition of combinations of nearby letters plays a central role in the coding of words, such that interfering with this representation prevents the parallel analysis of letter strings.

Handwriting in healthy people aged 65 years and over

Handwriting is an important activity that is commonly affected by neurological and orthopaedic conditions. Handwriting research has predominantly involved children. Little is known about handwriting behaviour in healthy older adults. This study aims to describe the handwriting practices of 30 unimpaired adults aged 65 years and over. In this cross-sectional observational study, data were collected from 30 older adults using a self-report questionnaire, digital pen recordings over three days and a handwriting log. Data were analysed using descriptive statistics. The mean age of participants was 75.1 years (standard deviation=6.9). Variations in handwriting were evident in letter size, slant and spacing. Participants wrote very little--a median of 18 words per occasion (interquartile range=10.5-26.9 words). Most handwriting involved self-generated text (85%), not copied or transcribed text. Participants stood while writing for 17% of handwriting occasions. The most common reasons for handwriting were note taking (23%) and puzzles (22%). Legibility may not depend exclusively on the handwriting script that a beginning writer is taught, but may be a result of other factors as the person ages. A comprehensive adult handwriting assessment and retraining programme should be relevant to older adults, including common handwriting activities, involving self-generated text and few words.

SHRiMP2: Sensitive yet Practical Short Read Mapping

We report on a major update (version 2) of the original SHort Read Mapping Program (SHRiMP). SHRiMP2 primarily targets mapping sensitivity, and is able to achieve high accuracy at a very reasonable speed. SHRiMP2 supports both letter space and color space (AB/SOLiD) reads, enables for direct alignment of paired reads and uses parallel computation to fully utilize multi-core architectures. SHRiMP2 executables and source code are freely available at: http://compbio.cs.toronto.edu/shrimp/.

Two different mechanisms for omission and substitution errors in neglect dyslexia

Neglect dyslexia is a reading disorder often associated with right-sided brain lesions. In reading single words, errors are mostly substitutions or omissions of letters that occupy the left-sided positions. Typically, these errors have been thought to depend on a single mechanism. Conversely, we propose that they are due to different mechanisms. In particular, a visuo-spatial mechanism is responsible for omissions and a perceptual integration process for substitution errors. We measured the performance of six patients with both neglect and neglect dyslexia, analyzing their reading errors as a function of letter spacing. According to our conjecture, letter spacing should increase omissions by moving part of the string further in the unattended space, while it should reduce substitutions by restoring the integration processes. Furthermore, we predict that letter spacing should be more effective with pseudowords compared to words, in that in this latter case lexical effects are supposed to influence attentional and perceptual processes. Accordingly, we found that for pseudowords only the two types of errors are differently affected by this manipulation and only omissions correlate with the severity of the disorder in visuo-spatial tasks.

Effects of increased letter spacing on word identification and eye guidance during reading

The effect of increasing the space between the letters in words on eye movements during reading was investigated under various word-spacing conditions. Participants read sentences that included a high- or low-frequency target word, letters were displayed normally or with an additional space between adjacent letters, and one, two, or three spaces were present between each word. The spacing manipulations were found to modulate the effect of word frequency on the number and duration of fixations on target words, indicating, more specifically, that letter spacing affected actual word identification under various word-spacing conditions. In addition, whereas initial fixations landed at the preferred viewing position (i.e., to the left of a word's center) for sentences presented normally, landing positions were nearer the beginnings of words when letter spacing was increased, and even nearer the beginnings of words when word boundary information was lacking. Findings are discussed in terms of the influence of textual spacing on eye movement control.

VARiD: A variation detection framework for color-space and letter-space platforms

Motivation: High-throughput sequencing (HTS) technologies are transforming the study of genomic variation. The various HTS technologies have different sequencing biases and error rates, and while most HTS technologies sequence the residues of the genome directly, generating base calls for each position, the Applied Biosystem's SOLiD platform generates dibase-coded (color space) sequences. While combining data from the various platforms should increase the accuracy of variation detection, to date there are only a few tools that can identify variants from color space data, and none that can analyze color space and regular (letter space) data together.Results: We present VARiD—a probabilistic method for variation detection from both letter- and color-space reads simultaneously. VARiD is based on a hidden Markov model and uses the forward-backward algorithm to accurately identify heterozygous, homozygous and tri-allelic SNPs, as well as micro-indels. Our analysis shows that VARiD performs better than the AB SOLiD toolset at detecting variants from color-space data alone, and improves the calls dramatically when letter- and color-space reads are combined.Availability: The toolset is freely available at http://compbio.cs.utoronto.ca/varidContact: varid@cs.toronto.edu

Effect of letter spacing on legibility, eye movements, and reading speed

Effect of letter spacing on legibility, eye movements, and reading speed

Reduced contrast does not reduce visual crowding

Background: Previous studies have reported reduced crowding for low contrast stimuli (Kothe & Regan, 1990: Optom Vis Sci; Simmers et al., 1999: Ophthal Physiol Opt). Both defined crowding as a change in acuity for single vs. flanked letters, and used foveal viewing. This study sought to confirm these findings using a more traditional crowding task (i.e. comparison of single and flanked letter identification at different retinal eccentricities). Methods: 10 observers (18–34 yo; VA 20/14) identified 0.34 deg letters and letters flanked by an ‘x’ on either side (xax) at fixation and ±1, 3, 5, and 7 letter spaces (±0.34, ±1.02, ±1.70, and ±2.38 deg) from fixation on the horizontal meridian. All 25 letters (other than x) were presented at each location; letter and position were randomly selected from trial-to-trial. In separate blocks, the stimuli were ∼100, 30, and 10% contrast. Crowding was defined as the difference between single letter and flanked letter performance. Results: There was little difference in crowding for the three contrasts. Averaged across position, there was 14±0.3, 15±0.1, and 19±0.2% crowding for the 100, 30, and 10% contrasts, respectively [F(2, 18) = 2.3, p = 0.127]. There was little change from 100% contrast for single or flanked letters presented with 30% contrast, but with 10% contrast, performance was significantly reduced for both stimulus types. Accuracy was similar across positions for single letters presented with 10% contrast and flanked letters presented with 100% contrast. Conclusions: Unlike previous reports, these data show no change in crowding with reduced contrast stimuli. It is possible that 10% is not sufficiently reduced for crowding to disappear, but Kothe and Regan showed reduced crowding for 11% contrast stimuli. The data suggest that the effect of flanking letters may be to reduce the effective contrast of the target letters.

Reading quickly in the periphery

Chung, S.T.L., (2002) The effect of letter spacing on reading speed in central and peripheral vision. Invest Ophthalmol Vis Sci. 43(4):1270-6. Latham, K. & Whitaker, D. (1996). A comparison of word recognition and reading performance in foveal and peripheral vision. Vision Res. 36(17):2665-74. reading in the fovea is very easy with ordered words rxxdxxg sxxxlxtxd cxxxdxxg is pxxxxble wxth oxdxrxd wxxds not words the unordered hard fovea reading too is with in

What type of practice improves reading rates for nonstandard letter spacing: visual or text?

What type of practice improves reading rates for nonstandard letter spacing: visual or text?

Effect of letter separation on computerised visual acuity measurements: comparison with the gold standard Early Treatment Diabetic Retinopathy Study (ETDRS) chart

Contour interaction plays an important role in letter recognition and has long been known to influence clinical visual acuity measurements. LogMAR charts originally employed between-letter and line spacing of one letter width/height; however, in more recent designs, half letter width spacing has become accepted without validation. COMPlog is a computerised visual acuity measurement device being developed and validated for routine and research clinical use and is available commercially. This study was performed to investigate the effect of letter separation on computerised visual acuity measurements. An iterative series of experiments was performed in which test and retest fully interpolated five letters-per-line logMAR visual acuity measurements were taken in three groups of a total 100 adult subjects. Each group had visual acuity measured using ETDRS charts 1 and 2 and on COMPlog using various combinations of letter and line spacing. The first group consisted of 31 subjects tested using 3.75 and 2.50 stroke width spacing, the second 45 subjects using 2.50 and 1.25 stroke width spacing and the last group, 24 subjects tested using 1.90 stroke width spacing. The methods of Bland and Altman were used to analyse the data. No significant bias was noted between the gold standard ETDRS measurements and those taken using COMPlog with 3.75 stroke width spacing. Significant bias of half a logMAR line was found with crowding of 1.90 and 1.25 stroke widths. A small systematic bias with a reduction of 1 ETDRS letter was found with spacing of 2.50 stroke widths which has not been demonstrated in previous validation studies. Crowding of 2.50 stroke widths is the smallest spacing which can be used in the design of COMPlog.

‘Clearer and Better’: Preferences of Children with Reading Difficulties for the Typography and Illustration in Literacy Materials

Preference inluences how an individual chooses graphic material and is therefore an important consideration in the design of literacy materials for children with reading dificulties, such as those associated with dyslexia. However, little is known about what this group of children like and dislike about the typography and the illustrations in their reading materials. Children with reading dificulties are likely to be less motivated to practise their literacy skills, and as luency in literacy can only be gained through practice, it is important to understand how reading materials can be created that these children will be more motivated to read. Through case-studies of six children with reading dificulties, their typographic (parts one and two) and illustrative (part three) preferences were tested. Parts one and two were concerned with the effects of typesetting and looked at the inluence of letter, word, and line spacing, and also type size. The typographic preferences of these six children were analysed and were then compared to their reading performance. Part three focused on the illustrative preferences of these children and looked at the use of colour and the level of detail included in this kind of visual information. By creating reading materials that correspond to the preferences of children with reading dificulties it is more likely that they will be motivated to read those books. These casestudies are part of ongoing research into the development of alternative materials for teaching literacy skills to children with dyslexia.

Improving a Child's Writing Skills for Increased Attention to Academic Activities

Children who have difficulty attending to graphomotor tasks may subsequently need remediation of their low-level handwriting skills to help them increase the legibility and speed of their written academic output. This article discusses how to evaluate a child's handwriting skills, including orthographic coding abilities and the ability to keep a student's attention focused on learning legible letter formation, alignment, and spacing. We put forward guidelines for intervention for an occupational therapist and occupational therapy assistant to aid in the child's automatization of these low-level writing skills. Once a child masters basic graphomotor skills, higher-level writing skills may be targeted so that overall academic performance will increase.

Effects of ocular transverse chromatic aberration on near foveal letter recognition

Transverse chromatic aberration (TCA) smears retinal images of peripheral stimuli. In reading, text information is extracted from both foveal and near fovea, where TCA magnitude is relatively small and variable. The present study investigated whether TCA significantly affects near foveal letter identification. Subjects were briefly presented a string of five letters centered one degree of visual angle to the left or right of fixation. They indicated whether the middle letter was the same as a comparison letter subsequently presented. Letter strings were rendered with a reddish fringe on the left edge of each letter and a bluish fringe on the right edge, consistent with expected left periphery TCA, or with the opposite fringe consistent with expected right periphery TCA. Effect of the color fringing on letter recognition was measured by comparing the response accuracy for fringed and non-fringed stimuli. Effects of lateral interference were examined by manipulating inter-letter spacing and similarity of neighboring letters. Results demonstrated significantly improved response accuracy with the color fringe opposite to the expected TCA, but decreased accuracy when consistent with it. Narrower letter spacing exacerbated the effect of the color fringe, whereas letter similarity did not. Our results suggest that TCA significantly reduces the ability to recognize letters in the near fovea by impeding recognition of individual letters and by enhancing lateral interference between letters.

The relationship between visual crowding and letter confusability: Towards an understanding of dyslexia in posterior cortical atrophy

Visual crowding is a form of masking in which target identification is hindered by excessive feature integration from other stimuli in the vicinity. It has previously been suggested that excessive visual crowding constitutes one specific form of early-visual-processing deficit, which may be observed in individuals with posterior cortical atrophy (PCA). This study investigated whether excessive visual crowding plays a significant role in the acquired dyslexia of two PCA patients, whose reading was characterized by visual paralexias. The patients were administered a series of letter, flanked letter, and word recognition tasks, and the effects of letter spacing and letter confusability upon response accuracy and latency were measured. In both patients, the results showed (a) evidence of excessive visual crowding, (b) a significant interaction between letter spacing and confusability on flanked letter identification tasks, and (c) effects of letter confusability affecting flanked but not unflanked letter identification. However, only mild improvements in reading accuracy were achieved in the experimental manipulations of interletter spacing within words because these manipulations had a dual effect: Increasing spacing improved individual letter identification but damaged whole-word form and/or parallel letter processing. We consider the implications of these results for the characterization of dyslexia in PCA, the design of reading rehabilitation strategies, and the relationship between visual crowding and letter confusability. In particular, we argue that the reading deficits observed in our patients cannot be accounted for solely in terms of a very low signal-to-noise ratio for letter identification, and that an additional crowding deficit is implicated in which excessive integration of fundamental letter features leads to the formation of incorrect letter percepts.

Critical Thinking in Anesthesia

Critical Thinking in Anesthesia

Reading normal and degraded words: Contribution of the dorsal and ventral visual pathways

Fast, parallel word recognition, in expert readers, relies on sectors of the left ventral occipito-temporal pathway collectively known as the visual word form area. This expertise is thought to arise from perceptual learning mechanisms that extract informative features from the input strings. The perceptual expertise hypothesis leads to two predictions: (1) parallel word recognition, based on the ventral visual system, should be limited to words displayed in a familiar format (foveal horizontal words with normally spaced letters); (2) words displayed in formats outside this field of expertise should be read serially, under supervision of dorsal parietal attention systems. We presented adult readers with words that were progressively degraded in three different ways (word rotation, letter spacing, and displacement to the visual periphery). Behaviorally, we identified degradation thresholds above which reading difficulty increased non-linearly, with the concomitant emergence of a word length effect on reading latencies reflecting serial reading strategies. fMRI activations were correlated with reading difficulty in bilateral occipito-temporal and parietal regions, reflecting the strategies required to identify degraded words. A core region of the intraparietal cortex was engaged in all modes of degradation. Furthermore, in the ventral pathway, word degradation led to an amplification of activation in the posterior visual word form area, at a level thought to encode single letters. We also found an effect of word length restricted to highly degraded words in bilateral occipitoparietal regions. Those results clarify when and how the ventral parallel visual word form system needs to be supplemented by the deployment of dorsal serial reading strategies.

Crowding and eccentricity determine reading rate

Bouma's law of crowding predicts an uncrowded central window through which we can read and a crowded periphery through which we cannot. The old discovery that readers make several fixations per second, rather than a continuous sweep across the text, suggests that reading is limited by the number of letters that can be acquired in one fixation, without moving one's eyes. That "visual span" has been measured in various ways, but remains unexplained. Here we show (1) that the visual span is simply the number of characters that are not crowded and (2) that, at each vertical eccentricity, reading rate is proportional to the uncrowded span. We measure rapid serial visual presentation (RSVP) reading rate for text, in both original and scrambled word order, as a function of size and spacing at central and peripheral locations. As text size increases, reading rate rises abruptly from zero to maximum rate. This classic reading rate curve consists of a cliff and a plateau, characterized by two parameters, critical print size and maximum reading rate. Joining two ideas from the literature explains the whole curve. These ideas are Bouma's law of crowding and Legge's conjecture that reading rate is proportional to visual span. We show that Legge's visual span is the uncrowded span predicted by Bouma's law. This result joins Bouma and Legge to explain reading rate's dependence on letter size and spacing. Well-corrected fluent observers reading ordinary text with adequate light are limited by letter spacing (crowding), not size (acuity). More generally, it seems that this account holds true, independent of size, contrast, and luminance, provided only that text contrast is at least four times the threshold contrast for an isolated letter. For any given spacing, there is a central uncrowded span through which we read. This uncrowded span model explains the shape of the reading rate curve. We test the model in several ways. We use a "silent substitution" technique to measure the uncrowded span during reading. These substitutions spoil letter identification but are undetectable when the letters are crowded. Critical spacing is the smallest distance between letters that avoids crowding. We find that the critical spacing for letter identification predicts both the critical spacing and the span for reading. Thus, crowding predicts the parameters that characterize both the cliff and the plateau of the reading rate curve. Previous studies have found worrisome differences across observers and laboratories in the measured peripheral reading rates for ordinary text, which may reflect differences in print exposure, but we find that reading rate is much more consistent when word order is scrambled. In all conditions tested--all sizes and spacings, central and peripheral, ordered and scrambled--reading is limited by crowding. For each observer, at each vertical eccentricity, reading rate is proportional to the uncrowded span.

A study of the effect of letter spacing on the reading speed of young readers with low vision

The aims of this study were two-fold: firstly, to establish a method of applying consistent letter spacing to documents using MS Word, and secondly, to investigate the effect of increased letter spacing on the reading speeds of readers with low vision. Tests on 14 readers with low vision showed that increased letter spacing benefited their reading speed and also reduced the critical print size of the majority of subjects tested. These findings could have a significant impact on the format of modified large print material used by low-vision readers in mainstream schools and lead to more inclusive practise in the classroom. Additionally, a simple to follow table has been produced to quantify the effect of increased letter spacing in MS Word. Although MS Word is almost universally used in mainstream schools to modify teaching resources, for low-vision readers, the method of applying letter spacing and its effect are not clear.

Effect of letter spacing on visual span and reading speed.

S. T. L. Chung (2002) has shown that rapid serial visual presentation (RSVP) reading speed varies with letter spacing, peaking near the standard letter spacing for text and decreasing for both smaller and larger spacings. In this study, we tested the hypothesis that the dependence of reading speed on letter spacing is mediated by the size of the visual span-the number of letters recognized with high accuracy without moving the eyes. If so, the size of the visual span and reading speed should show a similar dependence on letter spacing. We tested this prediction for RSVP reading and asked whether it generalizes to the reading of blocks of text requiring eye movements. We measured visual-span profiles and reading speeds as a function of letter spacing. Visual-span profiles, measured with trigrams (strings of three random letters), are plots of letter-recognition accuracy as a function of letter position left or right of fixation. Size of the visual span was quantified by a measure of the area under the visual-span profile. Reading performance was measured using two presentation methods: RSVP and flashcard (a short block of text on four lines). We found that the size of the visual span and the reading speeds measured by the two presentation methods showed a qualitatively similar dependence on letter spacing and that they were highly correlated. These results are consistent with the view that the size of the visual span is a primary visual factor that limits reading speed.