Which Factors Modulate Letter Position Coding in Pre-literate Children?

One of the central landmarks of learning to read is the emergence of orthographic processing (i.e., the encoding of letter identity and letter order): it constitutes the necessary link between the low-level stages of visual processing and the higher-level processing of words. Regarding the processing of letter position, many experiments have shown worse performance in various tasks for the transposed-letter pair judge-JUDGE than for the orthographic control jupte-JUDGE. Importantly, 4-y.o. pre-literate children also show letter transposition effects in a same-different task: TZ-ZT is more error-prone than TZ-PH. Here, we examined whether this effect with pre-literate children is related to the cognitive and linguistic skills required to learn to read. Specifically, we examined the relation of the transposed-letter in a same-different task with the scores of these children in phonological, alphabetic and metalinguistic awareness, linguistic skills, and basic cognitive processes. To that end, we used a standardized battery to assess the abilities related with early reading acquisition. Results showed that the size of the transposed-letter effect in pre-literate children was strongly associated with the sub-test on basic cognitive processes (i.e., memory and perception) but not with the other sub-tests. Importantly, identifying children who may need a pre-literacy intervention is crucial to minimize eventual reading difficulties. We discuss how this marker can be used as a tool to anticipate reading difficulties in beginning readers.

Life as a Machine

Bacteria are a source of many of the tools used in biotechnology. A technique called the polymerase chain reaction, or PCR, made it possible for the first time to amplify tiny starting amounts of DNA and has revolutionised medical diagnosis, testing of IVF embryos for mutations, and forensic science. PCR involves the repeated generation of DNA from a starting sequence in a cycle, one stage of which occurs at boiling point. Because of this PCR uses a DNA polymerase enzyme purified from an ‘extremophile’ bacterium that lives in hot springs. More recently scientists have constructed artificial bacterial or yeast genomes from scratch. The next step will be to create reconfigured bacteria and yeast with enhanced characteristics for use in agriculture, energy production, or generation of new materials. Some scientists are now seeking to expand the genetic code itself. The DNA code that human beings share with all other species on the planet has four ‘letters’, A, C, G, and T, which pair as A:T and C:G to join the two strands of the DNA double helix. And each particular triplet of DNA letters, for instance CGA, or TGC, codes for a specific amino acid, the 20 different amino acids joining together in a specific sequence to make up a particular protein. Scientists have now developed a new DNA letter pair, X:Y. By introducing this into an artificial bacterial genome, it is becoming possible to create many more amino acids than the current 20 naturally occurring ones, and thereby allowing many new types of proteins.

Towards a Linguistic Stylometric Model for the Authorship Detection in Cybercrime Investigations

This study proposes an integrated framework that considers letter-pair frequencies/combinations along with the lexical features of documents as a means to identifying the authorship of short texts posted anonymously on social media. Taking a quantitative morpho-lexical approach, this study tests the hypothesis that letter information, or mapping, can identify unique stylistic features. As such, stable word combinations and morphological patterns can be used successfully for authorship detection in relation to very short texts. This method offers significant potential in the fight against online hate speech, which is often posted anonymously and where authorship is difficult to identify. The data analyzed is from a corpus of 12,240 tweets derived from 87 Twitter accounts. A self-organizing map (SOM) model was used to classify input patterns in the tweets that shared common features. Tweets grouped in a particular class displayed features that suggested they were written by a particular author. The results indicate that the accuracy of classification according to the proposed system was around 76%. Up to 22% of this accuracy was lost, however, when only distinctive words were used and 26% was lost when the classification procedure was based solely on letter combinations and morphological patterns. The integration of letter-pairs and morphological patterns had the advantage of improving accuracy when determining the author of a given tweet. This indicates that the integration of different linguistic variables into an integrated system leads to better performance in classifying very short texts. It is also clear that the use of a self-organizing map (SOM) led to better clustering performance because of its capacity to integrate two different linguistic levels for each author profile.

Busting a myth with the Bayes Factor

Psycholinguistic researchers identify linguistic variables and assess if they affect cognitive processes. One such variable is letter bigram frequency, or the frequency with which a given letter pair co-occurs in an orthography. While early studies reported that bigram frequency affects visual lexical decision, subsequent, well-controlled studies not shown this effect. Still, researchers continue to use it as a control variable in psycholinguistic experiments. We propose two reasons for the persistence of this variable: (1) Reporting no significant effect of bigram frequency cannot provide evidence for no effect. (2) Despite empirical work, theoretical implications of bigram frequency are largely neglected. We perform Bayes Factor analyses to address the first issue. In analyses of existing large-scale databases, we find no effect of bigram frequency in lexical decision in the British Lexicon Project, and some evidence for an inhibitory effect in the English Lexicon Project. We find strong evidence for an effect in reading aloud. This suggests that, for lexical decision, the effect is unstable, and may depend on item characteristics and task demands rather than reflecting cognitive processes underlying visual word recognition. We call for more consideration of theoretical implications of the presence or absence of a bigram frequency effect.

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.

Combining Letter-Matching and Tone Discrimination: Evidence of Automatic Perceptual and Spatial Congruity Effects

Dual task and priming paradigms were combined to investigate the distinction between automatic and attentional processes. Subjects in two experiments performed a primed letter-matching and a tone discrimination task separately and concurrently. The interval between prime onset and letter pair (SOA) was varied from 50 to 500 msec. Cost-benefit analyses in Experiment 1 indicated that primes that matched target letter pairs began to facilitate performance at an SOA of 150 msec. Primes inhibited performance when they mismatched identical letter pairs at SOA 100. In the dual-task situation, the benefits of priming letter targets were reflected in probe latencies with no evidence of concurrent costs in tone latencies. Experiment 2 revealed that two tasks could be primed simultaneously as effectively as when each was primed alone. Findings are discussed in reference to Posner and Snyder's (1975a, 1975b) two-process theory of priming and the applicability of a secondary task technique.

Intertrial Effects of Same-Different Judgements

Specific intertrial effects (repetition effects) and general intertrial effects (refractoriness or persisting attention to the preceding trial) were studied with the same-different judgment task, which dissociates the effects of response repetition and stimulus repetition. Response repetition alone did not facilitate performance. Stimulus repetition did aid performance, but mainly when accompanied by response repetition. Subjects tended to avoid the normal comparison process by using the (invalid!) “bypass rule” (Fletcher and Rabbitt, 1978): repeat the response if the stimulus or some aspect thereof (letter contents, size, position) is repeated from the preceding trial, otherwise change the response. As to general effects, partial refractoriness was evident at response execution, but not at earlier processing stages. Mean RT increased, but errors decreased, as the response-stimulus interval (RSI) between trials decreased. Presenting a new letter pair immediately after the preceding response produced a delay, but subjects used the waiting time, while the response system recovered or was redirected to the present trial, to improve the accuracy of their decision.