Letters, Words, Sentences, and Reading.

In this personal, and therefore highly selective, review article I summarize work performed in collaboration with numerous colleagues on how skilled adult readers perform identification tasks and speeded binary decision tasks involving single letters and visually presented words and sentences. The overarching aim is to highlight similarities in the processing performed at three key levels involved in written language comprehension (in languages that use an alphabetic script): letters, words, and sentences. The comparisons are made using behavioral data obtained with: i) speeded (response-limited) binary decision tasks; and ii) the effects of simultaneous surrounding context on letter and word identification using both data-limited (non-speeded) and response-limited procedures. I then propose a general framework that combines the three levels of processing, and that connects core processes at each level with the processing involved in tasks designed to reflect those core processes, and I end by suggesting possible avenues for future research with an aim to extend this general framework.

Investigating the crowding effect on letters and symbols in deaf adults.

Reading requires the transformation of a complex array of visual features into sounds and meaning. For deaf signers who experience changes in visual attention and have little or no access to the sounds of the language they read, understanding the visual constraints underlying reading is crucial. This study aims to explore a fundamental aspect of visual perception intertwined with reading: the crowding effect. This effect manifests as the struggle to distinguish a target letter when surrounded by flanker letters. Through a two-alternative forced choice task, we assessed the recognition of letters and symbols presented in isolation or flanked by two or four characters, positioned either to the left or right of fixation. Our findings reveal that while deaf individuals exhibit higher accuracy in processing letters compared to symbols, their performance falls short of that of their hearing counterparts. Interestingly, despite their proficiency with letters, deaf individuals didn't demonstrate quicker letter identification, particularly in the most challenging scenario where letters were flanked by four characters. These outcomes imply the development of a specialized letter processing system among deaf individuals, albeit one that may subtly diverge from that of their hearing counterparts.

Orthographic and feature-level contributions to letter identification.

Word recognition is facilitated by primes containing visually similar letters (dentjst-dentist), suggesting that letter identities are encoded with initial uncertainty. Orthographic knowledge also guides letter identification, as readers are more accurate at identifying letters in words compared with pseudowords. We investigated how high-level orthographic knowledge and low-level visual feature analysis operate in combination during letter identification. We conducted a Reicher-Wheeler task to compare readers' ability to discriminate between visually similar and dissimilar letters across different orthographic contexts (words, pseudowords, and consonant strings). Orthographic context and visual similarity had independent effects on letter identification, and there was no interaction between these factors. The magnitude of these effects indicated that high-level orthographic information plays a greater role than low-level visual feature information in letter identification. We propose that readers use orthographic knowledge to refine potential letter candidates while visual feature information is accumulated. This combination of high-level knowledge and low-level feature analysis may be essential in permitting the flexibility required to identify visual variations of the same letter (e.g., N-n) while maintaining enough precision to tell visually similar letters apart (e.g., n-h). These results provide new insights on the integration of visual and linguistic information and highlight the need for greater integration between models of reading and visual processing.

Perceptual Grouping Strategies in a Letter Identification Task: Strategic Connections, Selection, and Segmentation.

Although perceptual grouping has been widely studied, its mechanisms remain poorly understood. We propose a neural model of grouping that, through top-down control of its circuits, implements a grouping strategy involving both a connection strategy (which elements to connect) and a selection strategy (that defines spatiotemporal properties of a selection signal to segment target elements and facilitate identification). We apply the model to a letter discrimination task that investigated relationships among uniform connectedness and the grouping principles of proximity and shape similarity. Participants reported whether small circles formed a global letter E or H, and these circles could be connected by a line or be embedded in a matrix of squares. In the model, a good grouping strategy for this task consists of a connection strategy that connects circles but not squares for all conditions and a selection strategy that uses a selection signal of varying size, depending on whether squares were present. Consistent with empirical results, which were verified in two replication studies, model performance is worse with distractor squares, and line connectors improve performance only in the condition with squares. Rather than relying on abstract grouping principles, we show how the empirical results can be explained in terms of observers implementing a task-dependent grouping strategy that promotes overall performance.

Factors Influencing the Accurate Identification of Written Minimal Pairs with Graphemic Similarity: Evidence from Persian-Speaking Children and Adults.

In this study, we compared children's and adults' ability to accurately identify target words in written minimal pairs (WMPs) with graphemically similar letters while accounting for factors such as gender, similarity of the middle letter in WMPs, mono- versus dimorphemic WMPs, number of syllable, homography, and imageability. Fifty children and fifty adults were exposed to a distractor stimulus as a pre-mask, followed by the target, and then a post-mask stimulus. Subsequently, the corresponding WMPs including the target word and its graphemically minimal contrast were presented to the participants to obtain their reaction time (RT) in accurately identifying the target word. Results demonstrated that children tend to slow down their reaction as a compensatory strategy to circumvent their less mature knowledge of graphophonic units/morphemes to achieve accuracy during word recognition. In addition, among all controlled factors, children's RT was significantly influenced by similarity of the middle letter in the WMPs. Adults' RT, however, was influenced by factors such as gender, similarity of the middle letter in WMPs, and homography.

Positional cueing, string location variability, and letter-in-string identification.

In three experiments we measured accuracy in identifying a single letter among a string of five briefly presented consonants followed by a post-mask. The position of the to-be-identified letter was either indicated by an ordinal cue (e.g., position 2) or an underscore cue (e.g., #####). In Experiment 1 the ordinal cue was presented prior to onset of the letter string, and the underscore cue presented at string offset. In Experiments 2 and 3, both the ordinal and the underscore cues were pre-cues. In all experiments, letter strings could either appear centered on fixation or shifted randomly to the left or to the right. Participants were tested in separate blocks of trials for each of the four conditions generated by the combination of cue-type and string-location variability. In Experiment 1, letter identification accuracy was higher with ordinal cues and with fixed string locations, and ordinal cueing was more affected by string location variability. In Experiments 2 and 3, letter identification accuracy was higher with underscore pre-cues. We conclude that under conditions of brief stimulus durations (100 ms) and backward masking, letter-in-string identification accuracy is determined by read-out from location-specific letter detectors, independently of the type of cueing. Differences in the effectiveness of different types of cue are determined by differences in the ease of isolating a given gaze-centered location, and by differences in the ease with which attention can be directed to that location.

Evaluating the Effects of Instructional Prompts and Strategic Incremental Rehearsal on the Letter Identification Mastery of Two Typically Developing Kindergarteners.

Letter identification impacts the developmental progression of future reading skills. In this study, we evaluated the effects of instructional prompts on letter identification in a single-subject design for 2 kindergarten students who experienced difficulties with letter identification skills. In Phase 1, we evaluated the number of letters participants correctly identified without instructional prompts, and in Phase 2, we evaluated the effects of 2 different instructional prompts and rewards. Phase 3 evaluated the combined effects of strategic incremental rehearsal (SIR) and the most effective instructional prompt identified in Phase 2. Results showed that an effective, yet different instructional prompt was identified for each participant and that SIR plus an instructional prompt was effective for further increasing both participants' correct letter identification. The results of this study demonstrated a useful and effective method for identifying instructional prompts, strategies, or other interventions that improve students' academic responding.

Letter and word identification in the fovea and parafovea.

We investigated the extent to which accuracy in word identification in foveal and parafoveal vision is determined by variations in the visibility of the component letters of words. To do so we measured word identification accuracy in displays of three three-letter words, one on fixation and the others to the left and right of the central word. We also measured accuracy in identifying the component letters of these words when presented at the same location in a context of three three-letter nonword sequences. In the word identification block, accuracy was highest for central targets and significantly greater for words to the right compared with words to the left. In the letter identification block, we found an extended W-shaped function across all nine letters, with greatest accuracy for the three central letters and for the first and last letter in the complete sequence. Further analyses revealed significant correlations between average letter identification per nonword position and word identification at the corresponding position. We conclude that letters are processed in parallel across a sequence of three three-letter words, hence enabling parallel word identification when letter identification accuracy is high enough.

Enhancement of letter identification by concurrent auditory stimuli of varying duration.

Previously it has been shown that the concurrent presentation of a sound can improve processing of visual information at higher perceptual levels, for example, in letter identification tasks. Moreover, increasing the duration of the concurrent sounds can enhance performance in low-level tasks as contrast detection, which has been attributed to a sustained visual activation corresponding to the duration of the sound. Yet, the role of sound duration has so far not been investigated in higher-level visual processing. In a series of five Experiments, we again demonstrated that the mere presence of a concurrent sound can enhance the identification of a masked, centrally presented letter compared to unimodal presentation, even though this benefit was absent in one experiment for high-contrast letters yielding an especially high level of task-performance. In general, however, the sound-induced benefit was not modulated by a variation of target contrast or by the duration of the target-to-mask interstimulus interval. Taking individual performance differences into account, a further analysis suggested that the sound-induced facilitation effect may nevertheless be most pronounced at specific performance levels. Beyond this general sound-induced facilitation, letter identification performance was not further affected by the duration of the concurrent sounds, even though in a control experiment it could be established that letter identification performance improved with increasing letter duration, and perceived letter duration was prolonged with increasing auditory duration. The results and their interpretation with respect to the large observed interindividual performance differences are discussed in terms of potential underlying mechanisms of multisensory facilitation, as preparedness enhancement, signal enhancement, and object enhancement.

Knowledge about writing influences reading: Dynamic visual information about letter production facilitates letter identification.

How are reading and writing related? In this study, we address the relationship between letter identification and letter production, uncovering a link in which production information can be used to identify letters presented dynamically. By testing an individual with a deficit in letter identification, we identified a benefit which would be masked by ceiling effects in unimpaired readers. In Experiment 1 we found that letter stimuli defined by the direction of dot motion (tiny dots within letter move leftward, background dots move rightward) provided no advantage over static letters. In Experiment 2, we tested dynamic stimuli in which the letter shapes emerged over time: drawn as they would be written, drawn in reverse, or with the letter shape filled in randomly. Improved identification was observed only for letters drawn as they are typically written. These results demonstrate that information about letter production can be integrated into letter identification, and point to bi-directional connections between stored letter production information (used for writing) and abstract letter identity representations (used in both reading and writing). The links from stored production information to abstract letter identities allow the former to activate the latter. We also consider the implications of our results for remediation of acquired letter identification deficits, including letter-drawing treatments and the underlying cause of their efficacy.

Development of children's identity and position processing for letter, digit, and symbol strings: A cross-sectional study of the primary school years.

Letter recognition and digit recognition are critical skills for literate adults, yet few studies have considered the development of these skills in children. We conducted a nine-alternative forced-choice (9AFC) partial report task with strings of letters and digits, with typographical symbols (e.g., $, @) as a control, to investigate the development of identity and position processing in children. This task allows for the delineation of identity processing (as overall accuracy) and position coding (as the proportion of position errors). Our participants were students in Grade 1 to Grade 6, allowing us to track the development of these abilities across the primary school years. Our data suggest that although digit processing and letter processing end up with many similarities in adult readers, the developmental trajectories for identity and position processing for the two character types differ. Symbol processing showed little developmental change in terms of identity or position accuracy. We discuss the implications of our results for theories of identity and position coding: modified receptive field, multiple-route model, and lexical tuning. Despite moderate success for some theories, considerable theoretical work is required to explain the developmental trajectories of letter processing and digit processing, which might not be as closely tied in child readers as they are in adult readers.

Seeing the Meaning: Top-Down Effects on Letter Identification.

Most models of reading agree that visual word recognition is underpinned by a highly interactive network in which both bottom-up and top-down processes contribute. What remains unknown is whether evidence of top-down effects upon letter processing are restricted to word-form level information, or whether meaning-level information also plays a role. Here we sought to investigate top-down semantic influences upon letter detection using semantic manipulations of real word imageability and semantic priming, as well as a manipulation of nonword orthographic and phonological composition which varied degree of similarity to real words. A continuous adaptive staircase procedure was used, allowing us to assess the exposure duration needed for accurate letter perception in different stimulus types. Results revealed that in terms of both exposure duration and decision reaction times, words showed an advantage over pseudohomophones and pseudowords, which in turn showed advantages over consonant strings. High imageability words were processed more efficiently than low imageability words, both in terms of the exposure duration required for accurate letter identification and also decision reaction times. The presence of a related as opposed to unrelated semantic prime significantly shortened exposure duration, but also lengthened decision reaction times. This inhibitory semantic priming effect in reaction time was attributed to the interference at the decision stage by stronger activation of the prime letters in the case of related relative to unrelated trials. Taken together, the present results establish for the first time that the semantic dimensions of imageability and semantic priming exert significant effects on letter identification, indicating meaning-level influences on the very earliest stages of written word recognition.

What do we do with what we learn? Statistical learning of orthographic regularities impacts written word processing.

Individuals rapidly become sensitive to recurrent patterns present in the environment and this occurs in many situations. However, evidence of a role for statistical learning of orthographic regularities in reading is mixed, and its role has peripheral status in current theories of visual word recognition. Additionally, exactly which regularities readers learn to be sensitive to is still unclear. To address these two issues, three experiments were conducted with artificial scripts. In Experiments 1a and 1b, participants were exposed to a flow of artificial words (five characters) for a few minutes, with either two or four bigrams occurring very frequently. In Experiment 2, exposure took place over several days while participants had to learn the orthographic and phonological forms of new words entailing or not frequent bigrams. Sensitivity to these regularities was then tested in a wordlikeness task. Finally, participants performed a letter detection task, with letters being either of high frequency or not in the exposure phase. The results of the wordlikeness task showed that after only a few minutes, readers become sensitive to the positional frequency of letter clusters and to bigram frequency beyond single letter frequency. Moreover, this new knowledge influenced the performance in the letter detection task, with high-frequency letters being detected more rapidly than low-frequency ones. We discuss the implications of such results for models of orthographic encoding and reading.

Why are digits easier to identify than letters?

Beginning with Dejerine's report of pure alexia in 1892, numerous researchers have noted that individuals with acquired impairments of reading may show spared digit identification performance. This digit advantage has also been found in unimpaired adult readers across a number of tasks, and five main hypotheses have been proposed to explain how it arises. In this paper I consider these hypotheses in the context of recent theories of a unified alphanumeric character identification system, and evaluate them according to relevant empirical evidence. Despite some promising findings, none of the hypotheses currently provide a sufficient explanation of the digit advantage. Rather than developing new hypotheses to explain a categorical difference between digit and letter performance, I argue that future work should consider factors that affect identification performance specific to individual characters.

Drifting through Basic Subprocesses of Reading: A Hierarchical Diffusion Model Analysis of Age Effects on Visual Word Recognition.

Reading is one of the most popular leisure activities and it is routinely performed by most individuals even in old age. Successful reading enables older people to master and actively participate in everyday life and maintain functional independence. Yet, reading comprises a multitude of subprocesses and it is undoubtedly one of the most complex accomplishments of the human brain. Not surprisingly, findings of age-related effects on word recognition and reading have been partly contradictory and are often confined to only one of four central reading subprocesses, i.e., sublexical, orthographic, phonological and lexico-semantic processing. The aim of the present study was therefore to systematically investigate the impact of age on each of these subprocesses. A total of 1,807 participants (young, N = 384; old, N = 1,423) performed four decision tasks specifically designed to tap one of the subprocesses. To account for the behavioral heterogeneity in older adults, this subsample was split into high and low performing readers. Data were analyzed using a hierarchical diffusion modeling approach, which provides more information than standard response time/accuracy analyses. Taking into account incorrect and correct response times, their distributions and accuracy data, hierarchical diffusion modeling allowed us to differentiate between age-related changes in decision threshold, non-decision time and the speed of information uptake. We observed longer non-decision times for older adults and a more conservative decision threshold. More importantly, high-performing older readers outperformed younger adults at the speed of information uptake in orthographic and lexico-semantic processing, whereas a general age-disadvantage was observed at the sublexical and phonological levels. Low-performing older readers were slowest in information uptake in all four subprocesses. Discussing these results in terms of computational models of word recognition, we propose age-related disadvantages for older readers to be caused by inefficiencies in temporal sampling and activation and/or inhibition processes.

Assessing the modified receptive field (MRF) theory: Evidence from Sinhalese-English bilinguals.

The current study aimed to test the applicability of the modified receptive field (MRF) theory (Tydgat & Grainger, 2009) with English native speakers (Experiment 1) and Sinhalese native speakers (Experiment 2), who were skilled readers of both Sinhala and Roman scripts. A two-alternative forced choice (2AFC) procedure to measure identification accuracy for all positions in a string of five characters, which consisted of Roman script letters, Sinhala letters or symbols was conducted. For Roman script, the English and Sinhalese speakers displayed analogous results as in previous studies for Roman letters and symbols (i.e., an initial letter advantage and W-shaped function for Roman letters and a Λ-shaped function for symbols). In contrast for Sinhala script, the Sinhalese speakers displayed a strong linear function with accuracy for letter positions 1, 2 and 3 similarly advantaged. We propose that this characteristic pattern for Sinhala script has developed as a specialised adaptive mechanism to optimise the processing of letters when reading in this distinctive script.

ERPs Reveal the Time-Course of Aberrant Visual-Phonological Binding in Developmental Dyslexia.

New evidence is accumulating for a deficit in binding visual-orthographic information with the corresponding phonological code in developmental dyslexia. Here, we identify the mechanisms underpinning this deficit using event-related brain potentials (ERPs) in dyslexic and control adult readers performing a letter-matching task. In each trial, a printed letter was presented synchronously with an auditory letter name. Incongruent (mismatched), frequent trials were interleaved with congruent (matched) infrequent target pairs, which participants were asked to report by pressing a button. In critical trials, incongruent letter pairs were mismatched but confusable in terms of their visual or phonological features. Typical readers showed early detection of deviant trials, indicated by larger modulation in the range of the phonological mismatch negativity (PMN) compared with standard trials. This was followed by stronger modulation of the P3b wave for visually confusable deviants and an increased lateralized readiness potential (LRP) for phonological deviants, compared with standards. In contrast, dyslexic readers showed reduced sensitivity to deviancy in the PMN range. Responses to deviants in the P3b range indicated normal letter recognition processes, but the LRP calculation revealed a specific impairment for visual-orthographic information during response selection in dyslexia. In a follow-up experiment using an analogous non-lexical task in the same participants, we found no reading-group differences, indicating a degree of specificity to over-learnt visual-phonological binding. Our findings indicate early insensitivity to visual-phonological binding in developmental dyslexia, coupled with difficulty selecting the correct orthographic code.

Age-related inhibitory deficit, or lack of familiarity benefit? Evidence from letter identification among visual distractors.

Age-related deficits in processing complex visual scenes are often attributed to age-related declines in the cognitive abilities required for such tasks. For example, poorer or slower performance of a complex task in the presence of distractor items is often attributed to an age-related deficit in the ability to inhibit the processing of irrelevant information. To investigate the relative contributions of sensory and cognitive factors in such tasks, younger and older participants were asked to identify a letter presented simultaneously with distractors that were either other letters, pieces of letters, or visual noise controls with identical spatial frequency content or contrast profile. In Experiment 1, older adults performed much worse than younger adults when the masking field consisted of other letters. Surprisingly-and contrary to the predictions of inhibitory deficit or visual "pop-out" phenomena-this effect emerged because younger adults performed much better with letter-containing maskers than with any other type of masker, whereas older adults did not. Experiment 2 revealed that age-related changes in the time required to process the visual display do not appear to account for this effect. In Experiment 3, however, we replicated older adults' task performance in a younger adult sample by filtering the experimental stimuli to match the image contrast typically experienced by an older adult. The results of Experiment 3 suggest that age-related differences in task performance amidst distractors can emerge from age-related declines in contrast sensitivity, which set older adults up to fail at tasks in which younger adults may typically be able to benefit from the familiarity of the target and surrounding objects.

Context-dependent similarity effects in letter recognition.

In visual word recognition tasks, digit primes that are visually similar to letter string targets (e.g., 4/A, 8/B) are known to facilitate letter identification relative to visually dissimilar digits (e.g., 6/A, 7/B); in contrast, with letter primes, visual similarity effects have been elusive. In the present study we show that the visual similarity effect with letter primes can be made to come and go, depending on whether it is necessary to discriminate between visually similar letters. The results support a Bayesian view which regards letter recognition not as a passive activation process driven by the fixed stimulus properties, but as a dynamic evidence accumulation process for a decision that is guided by the task context.

Visual Performance With Small Concave and Convex Displays.

OBJECTIVE: In this study, we aim to investigate how users' visual performance with a small flexible display changes based on the direction (i.e., convex, concave) and the magnitude (i.e., low, high) of the display curvature. BACKGROUND: Despite the wide interest in flexible display materials and deformable displays, the potential effects of nonplanar display surfaces on human perception and performance have received little attention. This study is the first to demonstrate how curving affects visual performance with an actual flexible display (4.5-in. active-matrix organic light-emitting diode). METHOD: In a series of three experiments, we compared the performance with a planar display to the performance with concave and convex display surfaces with low and high curvature magnitudes. Two visual search tasks were employed that required the subject to detect target letters based on their contrast (Experiments 1 and 2) and identity (Experiment 3). Performance was measured as the sensitivity of target detection (d') and threshold time of the search, respectively. RESULTS: There were similar sensitivities for targets across the curvature variants, but the high-magnitude curvatures resulted in prolonged search times, especially for the convex form. In both of the tasks, performance was dependent on the display location, which was defined as the target's distance from the display center. CONCLUSION: High curvature magnitudes should be avoided, even in small displays, because large local changes in visual stimuli decrease processing speed outside the central display. APPLICATION: The findings have implications for the development of technologies, applications, and user interfaces for flexible displays and the design of visual display devices.