Letter Pairs Research Articles

The Babylonian benefit: Neurological research shows that being bilingual enhances mental performance and may protect from Alzheimer's disease.

The Babylonian benefit: Neurological research shows that being bilingual enhances mental performance and may protect from Alzheimer's disease.

Does consolidation of visuospatial sequence knowledge depend on eye movements?

In the current study, we assessed whether visuospatial sequence knowledge is retained over 24 hours and whether this retention is dependent on the occurrence of eye movements. Participants performed two sessions of a serial reaction time (SRT) task in which they had to manually react to the identity of a target letter pair presented in one of four locations around a fixation cross. When the letter pair ‘XO’ was presented, a left response had to be given, when the letter pair ‘OX’ was presented, a right response was required. In the Eye Movements (EM) condition, eye movements were necessary to perform the task since the fixation cross and the target were separated by at least 9° visual angle. In the No Eye Movements (NEM) condition, on the other hand, eye movements were minimized by keeping the distance from the fixation cross to the target below 1° visual angle and by limiting the stimulus presentation to 100 ms. Since the target identity changed randomly in both conditions, no manual response sequence was present in the task. However, target location was structured according to a deterministic sequence in both the EM and NEM condition. Learning of the target location sequence was determined at the end of the first session and 24 hours after initial learning. Results indicated that the sequence learning effect in the SRT task diminished, yet remained significant, over the 24 hour interval in both conditions. Importantly, the difference in eye movements had no impact on the transfer of sequence knowledge. These results suggest that the retention of visuospatial sequence knowledge occurs alike, irrespective of whether this knowledge is supported by eye movements or not.

On the Möbius Function of Permutations with One Descent

The set of all permutations, ordered by pattern containment, is a poset. We give a formula for the Möbius function of intervals $[1,\pi]$ in this poset, for any permutation $\pi$ with at most one descent. We compute the Möbius function as a function of the number and positions of pairs of consecutive letters in $\pi$ that are consecutive in value. As a result of this we show that the Möbius function is unbounded on the poset of all permutations. We show that the Möbius function is zero on any interval $[1,\pi]$ where $\pi$ has a triple of consecutive letters whose values are consecutive and monotone. We also conjecture values of the Möbius function on some other intervals of permutations with at most one descent.

Epigenetics: a new way to look at kidney diseases

Only a few percent of the 3 billion pairs of chemical letters in the human genome is responsible for protein-coding sequences. Recent advances in the field of epigenomics have helped us to understand how most of the remaining sequences are responsible for gene regulation at baseline and in disease conditions. Here we discuss recent advances in the area of epigenetics--specifically in cytosine modifications--and its application in the field of nephrology.

Seeing changes: How familiarity alters our perception of change

The impact of object familiarity on change blindness was examined. Familiarity was operationalized by manipulating the orientation (upright vs. inverted) of letters: Upright letters formed familiar stimuli whereas inverted letters produced unfamiliar stimuli. Across four experiments, orientation was shown to affect the ability to detect change. In Experiment 1, the orientation effect was independent of the number of distractors (set size), suggesting that orientation and set size affect separate processes. In Experiment 1b, it was shown that the orientation effect did not depend on the alternation of a particular letter pair. In Experiment 2 an interaction between set size and stimulus quality suggests that set size has its effects early in processing, whereas additivity between stimulus quality and orientation suggests that orientation has an effect on later processing. Experiment 3 replicates and extends the findings from Experiments 1 and 2. A stage model of change blindness is proposed and extended by drawing on constructs from Rensink (2000b, 2002, 2005).

The analysis of perseverations in acquired dysgraphia reveals the internal structure of orthographic representations

At a minimum, our long-term memory representations of word spellings consist of ordered strings of single letter identities. While letter identity and position must certainly be represented, it is by no means obvious that this is the only information that is included in orthographic representations, nor that representations necessarily have a one-dimensional “flat” structure. Evidence favours the alternative hypothesis that orthographic representations, much like phonological ones, are internally rich, complex multidimensional structures, though many questions remain regarding the precise nature of the internal complexity of orthographic representations. In this investigation, we test competing accounts of the internal structure of orthographic representations by analysing the perseveration errors produced by an individual with acquired dysgraphia, L.S.S. The analysis of perseveration errors provides a novel and powerful method for investigating the question of the independence of different representational components. The results provide clear support for the hypothesis that letter quantity and syllabic role information are associated with, but separable from, letter identity information. Furthermore, the results indicate that digraphs—letter pairs associated with a single phoneme (e.g., the SH in FISH)—are units of orthographic representation. These results contribute substantially to the further development of the multidimensional hypothesis, providing both new and converging evidence regarding the nature of the internal complexity of orthographic representations.

Tests of a model of multi-word reading: Effects of parafoveal flanking letters on foveal word recognition

We used the “flanking letters lexical decision” paradigm of Dare and Shillcock (2013) in order to test a model of multi-word reading. In the model, multiple words (on fixation, and to the left and right of fixation) are processed in parallel by a bank of location-specific letter detectors. These letter detectors feed information forward to a “bag of bigrams” that represents location-invariant sublexical orthographic information for all words processed in parallel. Bigrams are only formed within words (i.e., between spaces) but activate all compatible word representations. The model accounts for a finding reported by Dare and Shillcock (2013): Word recognition is facilitated when flanking letter pairs are present in the target (e.g. RO ROCK CK) compared with different letter flankers (ST ROCK EN), but independently of the position of the flanking bigrams (e.g., CK ROCK RO). In the present study we replicate this key finding and show that, as predicted by the model, although bigram position does not matter, within-bigram letter position does. Word recognition is harder when the position of letters within bigram flankers is reversed (e.g., OR ROCK KC/KC ROCK OR), but these conditions still facilitate with respect to a different letter flanker condition.

Chinese Keyboard Layout Design Based on Polyphone Disambiguation and a Genetic Algorithm

This study suggests a new keyboard layout to efficiently type in Chinese characters. The layout was based on a statistical analysis of Chinese corpus and was derived from a genetic algorithm. In the semantic analysis, 6 million Chinese characters were transcribed into typing script. Macros of polyphone were disambiguated from either the context or the presence probabilities in the training data. Relative frequencies of single letter and letter pair were counted to investigate on tapping workload and sequence. In the genetic algorithm, five ergonomics criteria—tapping workload distribution, hand alternation, finger alternation, avoidance of big steps, and hit direction—were applied to evaluate keyboard layout alternatives. The result showed that the proposed layout is 43% better than the QWERTY layout in terms of the weighted sum of the five ergonomic criteria.

Letter order is not coded by open bigrams.

Open bigram (OB) models (e.g., SERIOL: Whitney, 2001, 2008; Binary OB, Grainger & van Heuven, 2003; Overlap OB, Grainger et al., 2006; Local combination detector model, Dehaene et al., 2005) posit that letter order in a word is coded by a set of ordered letter pairs. We report three experiments using bigram primes in the same-different match task, investigating the effects of order reversal and the number of letters intervening between the letters in the target. Reversed bigrams (e.g., fo-OF, ob-ABOLISH) produced robust priming, in direct contradiction to the assumption that letter order is coded by the presence of ordered letter pairs. Also in contradiction to the core assumption of current open bigram models, non-contiguous bigrams spanning three letters in the target (e.g., bs-ABOLISH) showed robust priming effects, equivalent in size to contiguous bigrams (e.g., bo-ABOLISH). These results question the role of open bigrams in coding letter order.

Non-crossing matchings

We model the secondary structure of an RNA molecule by means of a maximal non-crossing matching on a random word in a finite alphabet, where ties are only allowed between certain pairs of letters. We prove that the mean fraction of unmatched symbols does not vanish as the length of the word tends to infinity.

Resolving the orthographic ambiguity during visual word recognition in Arabic: an event-related potential investigation

The Arabic alphabetical orthographic system has various unique features that include the existence of emphatic phonemic letters. These represent several pairs of letters that share a phonological similarity and use the same parts of the articulation system. The phonological and articulatory similarities between these letters lead to spelling errors where the subject tends to produce a pseudohomophone (PHw) instead of the correct word. Here, we investigated whether or not the unique orthographic features of the written Arabic words modulate early orthographic processes. For this purpose, we analyzed event-related potentials (ERPs) collected from adult skilled readers during an orthographic decision task on real words and their corresponding PHw. The subjects' reaction times (RTs) were faster in words than in PHw. ERPs analysis revealed significant response differences between words and the PHw starting during the N170 and extending to the P2 component, with no difference during processing steps devoted to phonological and lexico-semantic processing. Amplitude and latency differences were found also during the P6 component which peaked earlier for words and where source localization indicated the involvement of the classical left language areas. Our findings replicate some of the previous findings on PHw processing and extend them to involve early orthographical processes.

Pliny’s Epistolary Re-Inscription: Writing the Tombs of Verginius Rufus and Pallas the Claudian Secretary A Rationibus

Present day appreciation for Pliny’s letters highlights the triadic inter-relationship of epistolary writing, self-representation and memory often seen in the permeability of epistolary boundaries between other literary genres that create lasting fame: oratory, history, lyric, even epigram. This paper examines two pairs of letters that confront memory in epigraphical form in ways that construct the letter writer as both reader and collaborator in ingesting inscribed information and reprocessing its significance in discursive writing. The letters amplify the elliptical communication of inscriptions by responding to commemorations that are provocative in opposite ways: in Letters 6.10 and 9.19 the funerary epigraph for Verginius Rufus because it has not been permanently incised; in Letters 7.29 and 8.6 the bronze sepulchral inscription honoring Claudius’ freedman secretary Pallas, because it has been posted on the Via Tiburtina, arouses Pliny’s indignation.

Maximum Size of Reverse-Free Sets of Permutations

Two words have a reverse if they have the same pair of distinct letters on the same pair of positions, but in reversed order. A set of words no two of which have a reverse is said to be reverse-free. Let F(n,k) be the maximum size of a reverse-free set of words from [n]^k where no letter repeats within a word. We show the following lower and upper bounds in the case n >= k: F(n,k) \in n^k k^{-k/2 + O(k/log k)}. As a consequence of the lower bound, a set of n-permutations each two having a reverse has size at most n^{n/2 + O(n/log n)}.

On Coding the Position of Letters in Words

Open-bigram and spatial-coding schemes provide different accounts of how letter position is encoded by the brain during visual word recognition. Open-bigram coding involves an explicit representation of order based on letter pairs, while spatial coding involves a comparison function operating over representations of individual letters. We identify a set of priming conditions (subset primes and reversed interior primes) for which the two types of coding schemes give opposing predictions, hence providing the opportunity for strong scientific inference. Experimental results are consistent with the open-bigram account, and inconsistent with the spatial-coding scheme.

Approximating the hard square entropy constant with probabilistic methods

For any two-dimensional nearest neighbor shift of finite type $X$ and any integer $n\geq1$, one can define the horizontal strip shift $H_{n}(X)$ to be the set of configurations on $\mathbb{Z}\times\{1,\ldots,n\}$ which do not contain any forbidden pairs of adjacent letters for $X$. It is always the case that the sequence $h^{\mathrm{top} }(H_{n}(X))/n$ of normalized topological entropies of the strip shifts converges to $h^{\mathrm{top} }(X)$, the topological entropy of $X$. In this paper, we combine ergodic theoretic techniques with methods from percolation theory and interacting particle systems to show that for the two-dimensional hard square shift $\mathcal{H}$, the sequence $h^{\mathrm{top} }(H_{n+1}(\mathcal{H}))-h^{\mathrm{top} }(H_{n}(\mathcal{H}))$ also converges to $h^{\mathrm{top} }(\mathcal{H})$, and that the rate of convergence is at least exponential. As a corollary, we show that $h^{\mathrm{top} }(\mathcal{H})$ is computable to any tolerance $\varepsilon$ in time polynomial in $1/\varepsilon$. We also show that this phenomenon is not true in general by defining a block gluing two-dimensional nearest neighbor shift of finite type $Y$ for which $h^{\mathrm{top} }(H_{n+1}(Y))-h^{\mathrm{top} }(H_{n}(Y))$ does not even approach a limit.

Towards Arabic Spell-Checker Based on N-Grams Scores

The main purpose of this paper is to develop a simple and flexible spell-checker for Arabic language. The proposed spell-checker is based on N-Grams scores. For this purpose, eleven matrices are built to present the combination between the Arabic letters word. Each matrix concerns in the connection between a 2-grams letters. Each cell in the generarated matrix is assigned an integer value 2, 1 or 0. The cell is assigned the value 2 in the corresponding matrix; if the word is ended by these two letter and assigned 1 if there is a connection and the word is not over yet, and is assigned 0 otherwise. On the other side searching process for any word that is by extracting each pair of letters in the word then it examines the value for each pair when the corresponding value is zero then the spell checker will consider the test word as wrong; otherwise it will check if it is assign with 1 that indicates that there is a connection it will be continue until reach to the value of 2 to determine that the word is correct. The overall accuracy for the proposed spell-checker is reached to 98.99%.

Priming of abstract letter representations may be universal: The case of Arabic

Recent research on the Roman alphabet has demonstrated that the magnitudes of masked repetition priming are equivalent for letter pairs that have similar visual features across cases (e.g., c-C) and for letter pairs with dissimilar features (e.g., g-G). Here, we examined whether priming of abstract letter representations occurs in an orthographic system, Arabic, in which the letters show an intricate number of contextual forms. Arabic does not have a lowercase/uppercase distinction, but the letters exhibit different forms that depend on their position (initial, medial, final, or isolated) and their connectivity. Importantly, some letters look quite different across positions (e.g., (symbol in text) and (symbol in text), which correspond to the letter 'ayn), whereas others look very similar (e.g. (symbol in text), and (symbol in text), which correspond to the letter fā'). We employed a masked priming same-different task, in which native speakers of Arabic decided whether a target letter was the same as or different from a reference letter presented in a different position (middle vs. isolated). The results showed masked repetition priming effects of the same magnitude for letter pairs with similar and with dissimilar visual features across letter positions. These data support the view that priming of abstract letter representations is a universal phenomenon.

Visuospatial Perceptual Sequence Learning and Eye Movements

We examined perceptual sequence learning by means of an adapted serial reaction time task in which eye movements were unnecessary for performing the sequence learning task. Participants had to respond to the identity of a target letter pair ("OX" or "XO") appearing in one of four locations. On the other locations, similar distractor letter pairs ("QY" or "YQ") were shown. While target identity changed randomly, target location was structured according to a deterministic sequence. To render eye movements superfluous, (1) stimulus letter pairs appeared around a fixation cross with a visual angle of 0.63°, which means that they appeared within the foveal visual area and (2) the letter pairs were presented for only 100 ms, a period too short to allow proper eye movements. Reliable sequence knowledge was acquired under these conditions, as responses were both slower and less accurate when the trained sequence was replaced by an untrained sequence. These results support the notion that perceptual sequence learning can be based on shifts of attention without overt oculomotor movements.

Detection and resolution of vanishing optotype letters in central and peripheral vision

Previous studies of peripheral vision have shown that detection acuity is superior to resolution acuity for gratings over a range of contrasts, which is attributed to different limiting mechanisms (contrast insufficiency and neural undersampling) for the two tasks. To extend the analysis to letters in a way that avoided luminance cues, we used “vanishing optotype” characters, conveying second-order information, and constructed from tripole strokes having the same mean luminance as the surround. We measured the minimum letter size for detection and identification tasks for two different pairs of vanishing optotype characters (O vs. + and orthogonally oriented Landolt-C’s) as a function of contrast in central and peripheral vision. Foveally there was no significant difference between detection acuity and resolution acuity for either pair of letters over a range of stimulus contrasts from 20% to 100%, indicating performance is contrast-limited for both tasks. The same result was obtained at 30° eccentricity in the peripheral field for the O vs. + letters, again indicating performance is contrast-limited for both tasks. However, resolution acuity for the Landolt-C letters was significantly worse than detection acuity in the periphery over the same range of contrasts, which suggests performance is limited by neural undersampling for these letters. All of our experimental results are explained by a model of neural sampling in which detection acuity is determined by the size of neural receptive fields relative to the dimensions of the tripole responsible for spatial contrast, whereas resolution acuity is determined by the spacing of receptive fields relative to the spacing between strokes responsible for letter form.

Influence of category identity on letter matching: Conceptual penetration of visual processing or response competition?

Participants performed same-different matching tasks, with physical-identity instructions, on letter pairs composed from the letters B, b, and p. The letters in a pair were presented simultaneously or sequentially, with the experiments differing in whether (1) the letters could appear in two or four positions, (2) two or five SOAs were used, (3) the font was Arial or one in which the two loops of the letter B were of the same size, and (4) p did or did not occur in same pairs. With sequential presentation, different RTs were longer when the letters had the same name (Bb; within-category pair) than when they did not (Bp; between-category pair), replicating a finding by Lupyan et al. (2010). However, unlike in their study, this category effect was also significant with simultaneous presentation, tending to be nonsignificantly smaller for RTs but larger for accuracy than that obtained with sequential presentation. A similar pattern was observed when we removed a bias to respond different whenever the letter p was detected in the experiments in which p did not appear in same pairs. The presence of a category effect with simultaneous presentation is predicted by a response competition account, but not by Lupyan et al.'s conceptual-penetration-of-visual-processing account.