Phasic firing and coincidence detection by subthreshold negative feedback: divisive or subtractive or, better, both

Phasic neurons typically fire only for a fast-rising input, say at the onset of a step current, but not for steady or slow inputs, a property associated with type III excitability. Phasic neurons can show extraordinary temporal precision for phase locking and coincidence detection. Exemplars are found in the auditory brain stem where precise timing is used in sound localization. Phasicness at the cellular level arises from a dynamic, voltage-gated, negative feedback that can be recruited subthreshold, preventing the neuron from reaching spike threshold if the voltage does not rise fast enough. We consider two mechanisms for phasicness: a low threshold potassium current (subtractive mechanism) and a sodium current with subthreshold inactivation (divisive mechanism). We develop and analyze three reduced models with either divisive or subtractive mechanisms or both to gain insight into the dynamical mechanisms for the potentially high temporal precision of type III-excitable neurons. We compare their firing properties and performance for a range of stimuli. The models have characteristic non-monotonic input-output relations, firing rate vs. input intensity, for either stochastic current injection or Poisson-timed excitatory synaptic conductance trains. We assess performance according to precision of phase-locking and coincidence detection by the models' responses to repetitive packets of unitary excitatory synaptic inputs with more or less temporal coherence. We find that each mechanism contributes features but best performance is attained if both are present. The subtractive mechanism confers extraordinary precision for phase locking and coincidence detection but only within a restricted parameter range when the divisive mechanism of sodium inactivation is inoperative. The divisive mechanism guarantees robustness of phasic properties, without compromising excitability, although with somewhat less precision. Finally, we demonstrate that brief transient inhibition if properly timed can enhance the reliability of firing.Postprint (published version

English Spelling Knowledge and Word Reading Skills of Arabic and Japanese ESL Learners

Previous research has demonstrated that L1 orthographic features and literacy experiences may influence some lower-level processing skills in L2 literacy development. The goal of this study is to expand understanding of this influence on the development of ESL word reading and spelling skills among a group of 49 intermediate-level Arabic learners of English as a Second Language (ESL) and a corresponding comparison group of 50 Japanese ESL learners. Data were collected on a spelling test, a reading comprehension test, and a series of word reading tasks which include reading words with a missing vowel, reading words with a missing consonant, reading a regular wordlist, and reading pseudo-words. The results indicated that at the same level of reading comprehension, the Japanese ESL group performed significantly better than the Arabic group on spelling and all the word reading measures except the accuracy and speed in reading words with a missing vowel. The study also found that the Arabic ESL learners were more adversely affected in both accuracy and speed of reading words with a missing consonant compared with reading words with a missing vowel. Furthermore, accuracy in reading words with a missing consonant was found to be the best predictor of reading comprehension for the Arabic group but for the Japanese group, spelling and accuracy in reading words with a missing consonant were both significant predictors of ESL reading comprehension. The findings were discussed in relation to previous research. Pedagogical implications were also addressed

"You Don't Look Like a Professor": An Autoethnographic Study of how Racial Identity, Legitimacy and Language Intersect at a Canadian Higher Education Writing Centre

With the rapid spread of English as a lingua franca, the number of non-native English teachers far exceeds that of native English-speaking teachers worldwide. In recent years, there has been considerable debate on what characteristics represent the ideal English speaker qua language teacher, mostly revolving around the notion of the native speaker. English, with a colonial history and as an imperial legacy, has created the native speaker-non-native speaker dichotomy, a hegemonic construct that assumes a monocultural and monolingual lens as a frame of reference. It has thus become challenging for non-native English-speaking teachers to teach English and questions of identity and legitimacy of non-native English-speaking teachers and their students have become central to these debates. This dissertation contributes to this broader discussion through an autobiographic ethnography of the challenges confronting a non-native English-speaking instructor at a Canadian higher education Writing Center. My experience, examined through the prism of a case study, highlighted the intersections of power, race, and ideology as they relate to issues of identity and legitimacy of non-native English-speaking teachers. To illuminate my research problem, I employed two conceptual frameworks -- Critical Race Theory and Bourdieus concepts of cultural capital and legitimate language. My methodology employs various approaches, including reflective journal entries on my teaching experience at the Writing Center, autobiographic interviews with my six native and non-native English-speaking students, and field notes of my six respondents about their perceptions of me as their non-native English instructor. My findings reveal that questions of identity and legitimacy of non-native English-teachers are complex and dependent on the power, race, and ideology of both the students and the instructors. My students demonstrated initial resistance in accepting my identity as a non-native English-speaking teacher and also questioned my legitimacy and knowledge; however, their perceptions about me also evolved over time, eventually shifting to appreciation and acceptance. My findings also uncovered the limited exposure students have to non-native English-speaking instructors and to diverse teachers, thus raising fundamental questions about the role of universities in challenging racism and implementing ethical internationalization to tackle global hierarchy and hegemony

Lower-Level Processing Skills in English-as-a-Second-Language Reading Comprehension: Possible Influence of First Language Orthography

Cross-linguistic studies on second language (L2) reading reveal that component skills of reading such as word recognition, phonemic decoding, spelling, and oral text reading are prone to the influence of first language (L1) orthography but few empirical studies have examined the possible influence of L1 orthography on these skills. This study investigates how adult ESL learners of two different L1 backgrounds (Spanish and Chinese) compare in their performances on word recognition efficiency, phonemic decoding efficiency, spelling, and oral text reading fluency and how these skills are related to their overall ability in reading comprehension. The differences in the learners’ performances on the component skills and the variations in the role of these skills in ESL reading comprehension indicated possible influence of the orthographic features of learners’ first language

Effects of discourse structure graphic organizers of EFL reading comprehension

This study investigated the effects of a 16-week reading instruction program with discourse structure graphic organizers (DSGOs) on the development of English reading comprehension among college-level English as a Foreign Language (EFL) students. A total of 340 first and third semester students of non-English majors at a Chinese university participated in this study. A DSGO completion test and a TOEFL (Test of English as a Foreign Language) reading comprehension test were administered before, immediately after, and 7 weeks following the instructional treatment. The results showed that the DSGO instruction significantly improved discourse comprehension as measured by the DSGO completion task, and the effect was retained 7 weeks after the instructional treatment. Significant improvement was also observed in the general reading ability as measured by TOEFL reading comprehension in the immediate posttest, but the effect did not persist in the delayed posttest. These findings apply to both the first and third semester students. Pedagogical implications of the DSGO instruction are discussed

Radical Recognition in Off-Line Handwritten Chinese Characters Using Non-Negative Matrix Factorization

In the past decade, handwritten Chinese character recognition has received renewed interest with the emergence of touch screen devices. Other popular applications include on-line Chinese character dictionary look-up and visual translation in mobile phone applications. Due to the complex structure of Chinese characters, this classification task is not exactly an easy one, as it involves knowledge from mathematics, computer science, and linguistics. Given a large image database of handwritten character data, the goal of my senior project is to use Non-Negative Matrix Factorization (NMF), a recent method for finding a suitable representation (parts-based representation) of image data, to detect specific sub-components in Chinese characters. NMF has only been applied to typed (printed) Chinese characters in different fonts. This project focuses specifically on how well NMF works on handwritten characters. In addition, research in Chinese character classification has mainly been done using holistic approaches - treating each character as an inseparable unit. By using NMF, this project takes a different approach by focusing on a more specific problem in Chinese character classification: radical (sub-component) detection. Finally, a possible application of radical detection will be proposed. This interactive application can potentially help Chinese language learners better recognize characters by radicals