Letter Counting Research Articles

Visual Performance of Subjects Wearing Presbyopic Contact Lenses

The purpose of this study is to assess the visual performance of subjects wearing gas-permeable (GP) multifocal contact lenses, soft bifocal contact lenses, GP monovision lenses and spectacles. The study included 32 subjects between the ages of 42 and 65 years wearing GP monovision, the Acuvue Bifocal (Vistakon), the Essentials GP Multifocal (Blanchard), and progressive addition lenses (PAL; spectacles group). There were eight subjects in each of these groups who were already wearing these modalities. Binocular low (18%) and high (95%) contrast acuities were recorded using the Bailey-Lovie chart; binocular contrast sensitivity from 1.5 to 18 cycles per degree (cpd) measured with the Vistech VCTS 6500 system, and monocular glare sensitivity at three luminance settings (400, 100, and 12 foot lamberts) was measured using the brightness acuity tester (BAT). Binocular near visual task performance (a modified version of letter counting method used in previous presbyopic studies) was also assessed. For the contact lens-wearing groups, subjects wearing GP multifocals provided the best binocular high and low contrast acuity followed by soft bifocal wearers. There was relative parity between the binocular high and low contrast acuity with PAL and GP multifocal wearers. Monovision acuity, measured binocularly, was determined to be lower than the other three groups with this difference being most significant with high contrast acuity. Among contact lens-wearing groups, it was observed that GP multifocal lens wearers experienced the lowest amount of monocular disability glare followed by soft bifocal wearers and monovision wearers. Subjects wearing soft bifocal lenses and monovision demonstrated slightly reduced binocular contrast sensitivity at all spatial frequencies. In the contact lens groups, GP multifocal lens wearers had the highest binocular contrast sensitivity at all spatial frequencies, on parity with PAL wearers, except at the highest spatial frequency (18 cpd) at which PAL wearers had better vision. Error scores for the binocular near visual task performance between the four groups revealed subjects with GP multifocal lenses and PAL wearers to have the least errors, followed by monovision users and then soft bifocal wearers with the most errors. Subjects wearing GP multifocals, soft bifocals, monovision, and PAL spectacles have good binocular contrast sensitivity, satisfactory binocular low and high contrast acuity, and increased sensitivity to glare. Presbyopic subjects requiring the use of contact lenses under dim light levels could benefit from GP multifocal lenses. Contrast and glare sensitivity evaluations provide significant information regarding the visual performance of the presbyopic contact lenses and should be included in regular presbyopic contact lens fitting.

Filters on computer displays – effects on legibility, performance and comfort

The hypothesis is that using a contrast-enhancing filter (CEF) on a computer display will improve display legibility, reading speed and visual comfort. Twenty subjects performed reading tasks, letter counting tasks, and legibility measurements on eight display conditions: a cathode ray tube (CRT) and liquid crystal display (LCD) matched for size and luminance – each at high luminance, with two different CEFs and a lower luminance to match one of the CEFs. The CEFs decreased both luminance and contrast when applied to the displays with the brightness set high, although the contrast was better with the filters compared to a matched luminance display without a filter. The legibility measurements support the positive effect of the CEFs due to improved contrast but the larger negative effect due to reduction in luminance results in a net loss of legibility. Performance on the reading and letter counting tasks was not improved with the CEFs.

A peripheral reading deficit under conditions of diffuse visual attention

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

A peripheral reading deficit under conditions of diffuse visual attention

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

Recognition of jagged (pixelated) letters in the periphery

Previous studies found that for a group of mixed low vision observers, letter counting with smooth (anti-aliased) letters was better than with jagged (pixelated) letters on a CRT display (Bailey et al., Am J Optom Physiol Opt 1987;64:678-685). However,using a tachistoscopic presentation, Geiger and Lettvin (Perception 1998;27(Suppl.):15) found that for normally sighted observers, recognition of jagged letters was more accurate than that of smooth letters in the periphery. In the present study,we further investigated this effect using a high-resolution CRT display. Our results indicate that for normally sighted observers, recognition of jagged letters is not different from that of smooth letters in the periphery. This suggests that letter smoothing on a CRT display might not benefit reading of low vision patients with central field loss.

The role of attention in the shift from orientation-dependent to orientation-invariant identification of disoriented objects

In two experiments, the naming of rotated line drawings of natural objects was examined after a training phase in which the objects were either attended or ignored. In the training phase of Experiment 1, subjects were presented with objects in a number of orientations over five repeated blocks of trials. In the center of each object, seven letters (Xs and Ts, colored red or blue) were presented in rapid succession. Half the subjects named aloud the rotated object and ignored the changing letter display (object-attend). The other half ignored the object and counted the number of red Ts, and then used this number to perform a simple multiplication (object-ignore). In the test phase, all subjects named the rotated objects. The results showed that in the first block of trials in the training phase, mean naming time in the object-attend condition increased the further an object was rotated from the upright. This effect of orientation for attended objects was much reduced in the later presentations of the test phase. In contrast, there was no such benefit of prior presentation observed for the naming of objects that had previously been ignored. Instead, a substantial orientation effect was shown for the naming of previously ignored objects, which was similar to the orientation effect observed for attended objects named in the first block. Similar results were found in Experiment 2, in which object-attend subjects in training covertly named the objects and then performed a letter count and multiplication task. In both experiments, performance on the letter count and multiplication task varied with the angle of the ignored object. The results suggest that full attentional resources must be allocated in order for orientation-invariant representations to be formed and used in the identification of rotated objects.

Brain Potentials during Memory Retrieval Provide Neurophysiological Support for the Distinction between Conscious Recollection and Priming

Event-related brain potentials were recorded from subjects as they attempted to identify words displayed tachistoscopically. Words that had also been presented a few minutes earlier in a different context were identified more often than were words that had not been presented before. This priming effect was observed for words initially seen in an imagery task requiring size estimations as well as for words initially seen in an orthographic task requiring letter counting. Unlike priming, recall and recognition were much better for words repeated from the imagery task than from the orthographic task. Brain potentials elicited during word identification also differed as a function of task. Based on these differences, a potential from 500 to 800 msec was interpreted as an index of recollection processes. Earlier potentials may have indexed processing related to priming. These effects thus provide measures of the hypothetical processes underlying memory performance and demonstrate that recollection and priming are associated with distinct neural events.

Sight Word Reading in Prereaders: Use of Logographic vs. Alphabetic Access Routes

In a previous study, Ehri and Wilce (1985) found that prereaders who had not mastered letters were better at forming logographic access routes than letter-sound access routes into memory to read words by sight. Of interest here was whether prereaders who knew all their letters would reveal the same pattern. Preschoolers and kindergartners who could read few if any words out of context but who knew letters were taught to read either six simplified phonetic spellings whose letters corresponded to sounds (e.g., JRF for “giraffe”), or six logographic spellings whose letters were non-phonetic but were more visually distinctive (e.g., JRF for “candy”). Word reading practice included either naming or counting letters in phonetic spellings or counting letters in visual spellings. Letter naming was expected to draw prereaders' attention to phonetic cues. Letter counting was the control. Results revealed that phonetic spellings were learned better than visual spellings regardless of whether letters were named or counted. We conclude that prereaders become capable of forming letter-sound access routes when they learn letters well enough to take advantage of the phonetic cues they provide.

Readability of computer display print enlarged for low vision.

A letter counting task was presented on a Macintosh computer screen using two different versions of 24 point Times Roman print. One version, called "grainy," had 12 matrix units per font height and the other, called "smooth," had 24. A mixed group of low vision subjects and a normally sighted group had speed and accuracy measured as they performed the test task from two different viewing distances. For both population groups, the remote test distances were arranged individually so that the letters subtended an angular size scarcely larger than threshold. The close distances were fairly representative of practical working distances. It was shown that, for both groups of subjects, smooth letters allowed faster performance for the closer working distances only. Smoothing the letters helped accuracy of performance at the far distances, and at the close distances, smoothing improved the accuracy for the low vision group but not for the normals. The implications are discussed.

Knowledge of the alphabet: A comparison between letter counts and subjective reports

Subjects’ estimates of the frequency of occurrence of the letters of the alphabet were compared with previously reported letter-frequency counts. The results indicated an overall good relationship between actual and judged rank, but there were consistent letter-specific under- and overestimations. These inaccuracies were not accounted for by letter versatility, first-position frequency, or order in the alphabet. There was evidence that subject-derived estimates of letter frequency were somewhat better predictors of reaction time performance on letter-processing tasks.

The frequency and versatility of initial and terminal letters in English words

A review of previous word and letter counts in addition to the applications of these counts were reported. A comprehensive count of initial and terminal letters and bigrams was compiled based on the Kucera and Francis (Computational analysis of present-day American English. Providence: Brown Univ. Press, 1967 ) corpus of English words. The count included frequency of occurrence and versatility, or number of different words in which letters or bigrams occurred. It was shown how such counts can be used to describe “Englishness” and make predictions as to the information load of letters in words and pseudo words.

Visual interference in the parafoveal recognition of initial and final letters of words

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A Study of the Structural Elements of the French Language

Arthur's Summary— A scientific investigation of the relation between pronunciation and spelling in modern French as evidenced by detailed comparison of the elements of letter and sound frequency counts, supplementing recent studies leading to word, verb and idiom counts.)