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.     

Développement de la connaissance des lettres capitales. Étude transversale chez les enfants français de trois à six ans

The present study examined the knowledge of uppercase letters in 160 children aged from three to six. Three tasks were administrated: letter saying, letter naming, letter recognition. Children's responses were analyzed according to several variables: school level, gender, task, letter type, letter frequency, etc. Letter knowledge improved from three to six years, but with huge differences among children, namely the superiority of girls over boys. Letter by letter analyses showed that scores were highly consistent between tasks and school levels. They also revealed that letter knowledge was affected by letter type, letter frequency, alphabetic rank and the presence of letters in the child's first name. The findings are discussed for their contribution to the understanding of letter learning.     

Application of geometric models to letter recognition: distance and density

This article reviews studies in which a single letter is visually presented under adverse conditions and the subject's task is to identify the letter. The typical results for such studies are (a) certain pairs of letters are more often confused than other pairs of letters; (b) certain letters are more easily recognized than others; and (c) confusion errors for a letter pair are often asymmetric, the number of errors differing depending on which letter of the pair is presented as the stimulus. A geometric model incorporating the properties of distance and spatial density (after Krumhansl) is presented to account for these results. The present application of the distance-density model assumes that each letter is constructed in a typical 5 X 7 dot matrix. Each letter is represented in 35-dimensional space based on its constituent dots. A central idea behind the model, embodied in the property of spatial density, is that an explanation of typical results must take into account the relationship of the entire stimulus set to both the presented letter and the responded letter. Specifically, according to the model, (a) pairs of letters that are close in geometric space are more often confused than pairs of letters that are distant; (b) letters that are in less spatially dense regions are more easily recognized than letters that are in more spatially dense regions; and (c) asymmetric confusion errors result when one member of a letter pair is in a denser region than the other member of the letter pair. The distance-density model is applied to published and unpublished results of the authors as well as published results from two other laboratories. Alternative explanations of the three typical letter recognition results are also considered. The most successful alternative explanations are (a) confusions are an increasing function of the number of dots that two letters share; (b) letters constructed from fewer dots are easier to recognize; and (c) asymmetries arise when one member of a letter pair is more easily recognized, since that letter then has fewer confusion errors to give to the other letter of the pair. The model is discussed in terms of the distinction between template matching and feature analysis. An alternative classification of letter recognition models is proposed based on the global versus local qualities of features and the spatial information associated with each feature. The model is extended to explain reaction time study results. It is suggested that the distance-density model can be used to create optimal letter fonts by minimizing interletter confusions and maximizing letter recognizability.     

Naming and locating simultaneously and sequentially presented letters

Two letters varying in level of confusability were presented either simultaneously for 75 msec or sequentially for 75 msec each in adjacent retinal locations. The retinal locus of presentation varied from trial to trial, and subjects both identified and located the presented letters. Identification accuracy was higher on nonconfusable than on confusable letter pairs in the simultaneous condition, but not in the sequential condition. This result is interpreted as support for the notion that inhibition between similar or identical features shared by confusable letters occurs only when letters are presented simultaneously. A relative position effect, with performance on the peripheral letter higher than on the central letter, was found for simultaneously and second sequentially presented letters, but not for first sequentially presented letters. This result is interpreted in terms of the assumption that feature perturbations, with foveal perturbations more likely than peripheral perturbations, affect simultaneously and secondpresented letters, but not first-presented letters. The pattern of results for relative location accuracy showed many of the same effects as identification performance. A model assuming location errors reflect feature transpositions is outlined and is able to account for the absolute and relative location results and the correlation between relative location and identification accuracy.     

Memory of a speaker's voice: Reaction time to same- or different-voiced letters

Subjects were presented with a sequence of two letters, each letter spoken in either a male or female voice. On each trial, the subject was required to indicate, as quickly as possible, whether the two letters had the same name. Reaction times (RTs) were faster for letters spoken in the same voice for both “same” and “different” responses, even when letters were separated by 8 s. These results are incompatible with the notion of physical and name codes in auditory memory since a “different” response should always be based on a comparison of letter names and should not be influenced by voice quality. It was also found that RTs were not influenced by the phonemic distinctive feature similarity of the letters.     

Frequency discrimination: assessing global-level and element-level units in memory

Subjects' knowledge of how often various events occur was used to assess the retention of memory units for word-like strings of letters. A series of strings was presented at one of three exposure durations. Within the series, the frequencies of occurrence of different strings and of the letters composing the strings were varied orthogonally. At relatively long exposure durations, subjects could discriminate the frequency of occurrence for both strings and their constituent letters. The formation of global-level (string) memory units was indicated by judgments of string frequency being unaffected by either the frequencies of their component letters or experimental conditions (brief exposures) that prohibited accurate judgment of letter frequency. Although judgments of letter frequency were sometimes biased by the frequency of the strings containing the letters, the success with which the judgments discriminated different levels of letter frequency did not depend on the activation of string-level memory units. Furthermore, subjects' frequency judgments for letters were not predictable from their recall of the strings containing the letters. These results, which could not be explained by Tversky and Kahneman's (1973) "availability heuristic," provided evidence for the formation of element-level (letter) memory units. A converging experiment established that element-level frequency information could be abstracted from words as well as nonwords, and further, that this information was stored in long-term memory.     

Identification confusions among letters of the alphabet

Black, uppercase letters, subtending 6.0' of arc in height, were presented tachistoscopically to 6 subjects. An exposure duration was chosen to keep the subject's identification performance at about 50% correct. On each trial a single letter was presented, and the subject was required to identify the letter by verbal response. The resulting 26 X 26 confusion matrix was based on 3,900 trials (150 trials per letter). Several models of visual processing were used to generate predicted confusions among letter pairs. Models based on template overlap, geometric features, and two-dimensional spatial frequency content (Fourier transforms) were tested. The highest correlation (.70) between actual and predicted confusions was attained by the model based on the Fourier transformed letters filtered by the human contrast sensitivity function. These results demonstrate that the spatial frequency content of visual patterns can provide a valuable metric for predicting their psychological similarity. The results further suggest that spatial frequency models of visual processing are competitive with feature analysis models.     

Letter Interactions in Brief Visual Displays

Three experiments were conducted to examine the influence of non-target letters on target detection performance. It was hypothesised that letters which are similar would exert a stronger masking influence on each other than letters which have a low level of feature similarity. The results indicate, however, that every letter has the same inhibitory potential regardless of its similarity rating to other letters. The highly significant letter interactions which did occur in the study were interpreted as evidence for an additive, rather than a subtractive, influence by the non-targets. It is proposed that when a target has an ambiguous identity, due to an impoverished representation, it may be disambiguated by the addition of feature information from the immediate letter context. The effect of filling in the target representation with a feature value from a non-target letter will be to weight the final representation towards the target which has the value most similar to the one substituted. In a sense, then, non-targets which are similar to a target can actually enhance target detection scores.     

Case-sensitive letter and bigram frequency counts from large-scale English corpora

We tabulated upper- and lowercase letter frequency using several large-scale English corpora (∼183 million words in total). The results indicate that the relative frequencies for upper- and lowercase letters are not equivalent. We report a letter-naming experiment in which uppercase frequency predicted response time to uppercase letters better than did lowercase frequency. Tables of case-sensitive letter and bigram frequency are provided, including common nonalphabetic characters. Because subjects are sensitive to frequency relationships among letters, we recommend that experimenters use case-sensitive counts when constructing stimuli from letters.     

On letter frequency effects

In four experiments we examined whether the frequency of occurrence of letters affects performance in the alphabetic decision task (speeded letter vs. pseudo-letter classification). Experiments 1A and 1B tested isolated letters and pseudo-letters presented at fixation, and Experiments 2A and 2B tested the same stimuli inserted at the 1st, 3rd, or 5th position in a string of Xs. Significant negative correlations between letter frequency and response times to letter targets were found in all experiments. The correlations were found to be stronger for token frequency counts compared with both type frequency and frequency rank, stronger for frequency counts based on a book corpus compared with film subtitles, and stronger for measures counting occurrences as the first letter of words compared with inner letters and final letters. Correlations for letters presented in strings of Xs were found to depend on letter case and position-in-string. The results are in favor of models of word recognition that implement case-specific and position-specific letter representations.     

When do letter features migrate? A boundary condition for feature-integration theory

Feature-integration theory postulates that a lapse of attention will allow letter features to change position and to recombine as illusory conjunctions (Treisman & Paterson, 1984). To study such errors, we used a set of uppercase letters known to yield illusory conjunctions in each of three tasks. The first, a bar-probe task, showed whole-character mislocations but not errors based on feature migration and recombination. The second, a two-alternative forced-choice detection task, allowed subjects to focus on the presence or absence of subletter features and showed illusory conjunctions based on feature migration and recombination. The third was also a two-alternative forced-choice detection task, but we manipulated the subjects' knowledge of the shape of the stimuli: In the case-certain condition, the stimuli were always in uppercase, but in the case-uncertain condition, the stimuli could appear in either upper- or lowercase. Subjects in the case-certain condition produced illusory conjunctions based on feature recombination, whereas subjects in the case-uncertain condition did not. The results suggest that when subjects can view the stimuli as feature groups, letter features regroup as illusory conjunctions; when subjects encode the stimuli as letters, whole items may be mislocated, but subletter features are not. Thus, illusory conjunctions reflect the subject's processing strategy, rather than the architecture of the visual system.     

A LISP program to determine similarity relations in letter displays

Similarity relations between letters are important in displays used in tacbistoscopic recognition experiments. A LISP program is described that calculates similarity relations on the basis of an empirical letter-similarity matrix or on the basis of feature sharing in a feature-set definition supplied by the user. With either derivation method, there are three options for the type of average to be calculated for target display: (1) the average for the whole target, (2) the average for each letter in the target paired to all other letters in the target, and (3) the average of each letter in the target paired with its immediate neighbors.     

Directional letter-by-letter analysis and the word-superiority effect

Manipulations were introduced in three experiments to produce letter-by-letter analysis of orthographic (CVC) and nonorthographic (CCV or VCC) trigrams. Letters in the trigrams were presented in a different form (normal orientation and order, normal orientation but reversed order, reversed orientation but normal order, or reversed orientation and order) to each of four groups in the first experiment, and in each of the two normal orientation forms to different groups in the second experiment. Subjects both detected the presence or absence of a target letter and classified each trigram as a word or nonword. Additional changes were introduced in the third experiment to ensure that letters were being analyzed in the desired order. Performance was consistently better on orthographic trigrams, but only if the letters were oriented normally. This word-superiority effect (WSE) was related to feature testing that may be carried out letter by letter, with more efficient testing on words. Failiar orientation of letter features seems to be necessary; otherwise, testing becomes so difficult that there is no WSE. However, testing apparently is not finished on a given letter before it is begun on the next.     

Letter information and orthographic context in word perception

Theories of word perception in reading can be categorized in terms of the assumption made about whether or not a word context modifies the feature analysis of its component letters. Independence theories assume that the visual information passed on by feature analysis is independent of word context. Nonindependence theories assume that a word context directly influences visual analysis. Some nonindependence theories have assumed that word context enhances feature analysis of letters, others have assumed that word context overrides feature analysis of letters, and some have assumed that word context directs which letters are analyzed. The present experiment provided a critical test between the two classes of theories by independently varying orthographic context and visual letter information in a letter recognition task. The results contradict the qualitative predictions of the class of nonindependence theories and are accurately described by a quantification of independence theory.     

Case-sensitive letter and bigram frequency counts from large-scale English corpora.

We tabulated upper- and lowercase letter frequency using several large-scale English corpora (approximately 183 million words in total). The results indicate that the relative frequencies for upper- and lowercase letters are not equivalent. We report a letter-naming experiment in which uppercase frequency predicted response time to uppercase letters better than did lowercase frequency. Tables of case-sensitive letter and bigram frequency are provided, including common nonalphabetic characters. Because subjects are sensitive to frequency relationships among letters, we recommend that experimenters use case-sensitive counts when constructing stimuli from letters.     

Temporal separation of two part-letter arrays and size changes in a nonmasking work-superiority effect

In two experiments subjects were asked to report the identity of a position-cued critical letter in an array of four letters. Four types of arrays were used: (i) unpronounceable nonwords; (ii) pronounceable nonwords ('pseudowords'); (iii) words in which the critical letter was minimally constrained by the context letters; and (iv) words in which the critical letter was maximally constrained by the context letters. All four-letter stimuli were presented in two parts. A leading array in which the information from two quadrants of a vertical by horizontal division of each letter was presented, and, after intervals of 0, 20, 40, 80, 100, 120, 160, 320, and 480 ms and infinity (ie, no trailing array), a trailing array of the complementary letter parts. In experiment 1 a single group of eight subjects responded to the one hundred and sixty combinations of the four types of letter strings, the four serial positions, and the ten stimulus onset asynchrony values. In experiment 2 the stimulus onset asynchrony values were varied among subjects, with twelve subjects responding at each value. The results from these two studies were generally similar. Performance in the word conditions was consistently superior to performance in the nonword conditions, and the magnitude of this difference (ie, the word-superiority effect) increased with increasing stimulus onset asynchrony up to 120 ms, and then gradually declined. The fact that the magnitude of the word-superiority effect initially increased with the separation of leading and trailing arrays was interpreted as support for Johnston's suggestion that letters in words are represented during visual encoding both in the form of individual letter percepts and in a decay-resistant word percept, as opposed to letters in nonwords, which are represented only as decay-susceptible letter percepts. The experimental findings are discussed in relation to the 'interactive activation' model of word perception.     

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.     

Second-order mappings in grapheme–color synesthesia

Typically, the search for order in grapheme–color synesthesia has been conducted by looking at the frequency of certain letter–color associations. Here, we report stronger associations when second-order similarity mappings are examined—specifically, mappings between the synesthetic colors of letters and letter shape, frequency, and position in the alphabet. The analyses demonstrate that these relations are independent of one other. More strikingly, our analyses show that each of the letter–color mappings is restricted to one dimension of color, with letter shape and ordinality linked to hue, and letter frequency linked to luminance. These results imply that synesthetic associations are acquired as the alphabet is learned, with associations involving letter shape, ordinality, and frequency being made independently and idiosyncratically. Because these mappings of similarity structure between domains (letters and colors) are similar to those found in numerous other cognitive and perceptual domains, they imply that synesthetic associations operate on principles common to many aspects of human cognition.     

Letter names and phonological awareness help children to learn letter-sound relations

Two experimental training studies with Portuguese-speaking preschoolers in Brazil were conducted to investigate whether children benefit from letter name knowledge and phonological awareness in learning letter-sound relations. In Experiment 1, two groups of children were compared. The experimental group was taught the names of letters whose sounds occur either at the beginning (e.g., the letter /be/) or in the middle (e.g., the letter /‘eli/) of the letter name. The control group was taught the shapes of the letters but not their names. Then both groups were taught the sounds of the letters. Results showed an advantage for the experimental group, but only for beginning-sound letters. Experiment 2 investigated whether training in phonological awareness could boost the learning of letter sounds, particularly middle-sound letters. In addition to learning the names of beginning- and middle-sound letters, children in the experimental group were taught to categorize words according to rhyme and alliteration, whereas controls were taught to categorize the same words semantically. All children were then taught the sounds of the letters. Results showed that children who were given phonological awareness training found it easier to learn letter sounds than controls. This was true for both types of letters, but especially for middle-sound letters.