Fixed vs. variable noise in 2AFC contrast discrimination: lessons from psychometric functions.

Recent discussion regarding whether the noise that limits 2AFC discrimination performance is fixed or variable has focused either on describing experimental methods that presumably dissociate the effects of response mean and variance or on reanalyzing a published data set with the aim of determining how to solve the question through goodness-of-fit statistics. This paper illustrates that the question cannot be solved by fitting models to data and assessing goodness-of-fit because data on detection and discrimination performance can be indistinguishably fitted by models that assume either type of noise when each is coupled with a convenient form for the transducer function. Thus, success or failure at fitting a transducer model merely illustrates the capability (or lack thereof) of some particular combination of transducer function and variance function to account for the data, but it cannot disclose the nature of the noise. We also comment on some of the issues that have been raised in recent exchange on the topic, namely, the existence of additional constraints for the models, the presence of asymmetric asymptotes, the likelihood of history-dependent noise, and the potential of certain experimental methods to dissociate the effects of response mean and variance.

The transducer model for contrast detection and discrimination: formal relations, implications, and an empirical test.

The transducer function mu for contrast perception describes the nonlinear mapping of stimulus contrast onto an internal response. Under a signal detection theory approach, the transducer model of contrast perception states that the internal response elicited by a stimulus of contrast c is a random variable with mean mu(c). Using this approach, we derive the formal relations between the transducer function, the threshold-versus-contrast (TvC) function, and the psychometric functions for contrast detection and discrimination in 2AFC tasks. We show that the mathematical form of the TvC function is determined only by mu, and that the psychometric functions for detection and discrimination have a common mathematical form with common parameters emanating from, and only from, the transducer function mu and the form of the distribution of the internal responses. We discuss the theoretical and practical implications of these relations, which have bearings on the tenability of certain mathematical forms for the psychometric function and on the suitability of empirical approaches to model validation. We also present the results of a comprehensive test of these relations using two alternative forms of the transducer model: a three-parameter version that renders logistic psychometric functions and a five-parameter version using Foley's variant of the Naka-Rushton equation as transducer function. Our results support the validity of the formal relations implied by the general transducer model, and the two versions that were contrasted account for our data equally well.

A nasalidade no dialeto quilombola do Norte de Minas: uma análise contrastiva baseada em corpus

This research investigated the nasality of vowels in the spontaneous speech of inhabitants of the quilombola communities of Brejo dos Crioulos and Poções (MG). As a theoretical framework, we based on the assumptions of Phonetics and Phonology, in renowned scholars on the investigation of nasality (CAGLIARI, 1977; CÂMARA JR., 1984, 2013; BISOL, 2013; ABAURRE; PAGOTTO, 1996; SILVA, 2015), with subsidies of the Corpus Linguistics. Its general goal was to investigate the occurrence of nasality, in the dialect of these quilombola communities, and their linguistic behavior, considering the linguistic factors that can interfere in the phenomenon. Specifically it was aimed to a) detect the occurrence of nasalized vowels with the help of the resources that the Corpus Linguistics provides (Praat and WorldSmith Tolls); b) discriminate the different types of occurring contexts of nasalized vowels; c) make quantitative and qualitative analyzes of the nasalized vowels in the study corpus; d) describe and analyze the behavior of nasalized vowels and; e) contrast the values of F1 and F2 of the oral and nasalized vowels. It was hypothesized that the nasality happens because it is conditioned by the nasal segment following the nasalized vowel - phonological process of “assimilation” - its position as the primary stress and grammatical category. It was believed that the quilombolas communities of Brejo dos Crioulos and Poções produce nasalized vowels in their speech and this linguistic phenomenon is favored by the adjacent presence of consonants or nasal vowels. Furthermore, it was hypothesized that the values of F1 and F2 of oral and nasalized vowels in these communities are distinct. The following research questions were elaborated: (i) is the presence of nasalized vowels in the speech of these quilombola communities conditioned to the presence of a nasal sound segment? (ii) does the nasal sound segment following the nasalized vowel favor the occurrence of the nasality phenomenon? is there a difference between the values of F1 and F2 of the oral and nasalized vowels in both quilombola communities considered? To compose our corpus, 24 interviews recordings were used (12 female speakers and 12 male speakers), a total of 24 participants. It was found that the following nasal sound segment tends to condition the nasalized vowel. In general, it assimilates the lowering of the soft palate of nasal consonant segment immediately following, but there are cases of nasal vowel segment - regressive assimilation; the stressed syllable tends to favor the nasality, but it occurs in pretonic and postonic position as well; F1 and F2 values of oral and nasalized vowels in the quilombola communities of Poções and Brejo dos Crioulos are distinct: the group of Brejo dos Crioulos tends to produce the F1 of oral and nasalized vowels more lowered than the group of Poções and the F2, in a more anterior position. The nasality tends to occur in verbs and nouns, although it is not specific to a grammatical category. This research found cases of spurious nasalization, confirming previous studies. In turn, it revealed cases of lexical items with favorable context for nasalization, but with its non-occurrence. This last case, considered as the lowering of the uniform soft palate in PB, presented pronounced vowels without the soft palate lowering. That is, it was detected variation in the phenomenon of nasalization in PB. With this work, it was promoted the discussion about nasality, in order to contribute to the linguistic studies about the functioning of Brazilian Portuguese in this geographical context.

Probing Tissue Microstructure Using Susceptibility Contrast Magnetic Resonance Imaging

Magnetic resonance imaging is a research and clinical tool that has been applied in a wide variety of sciences. One area of magnetic resonance imaging that has exhibited terrific promise and growth in the past decade is magnetic susceptibility imaging. Imaging tissue susceptibility provides insight into the microstructural organization and chemical properties of biological tissues, but this image contrast is not well understood. The purpose of this work is to develop effective approaches to image, assess, and model the mechanisms that generate both isotropic and anisotropic magnetic susceptibility contrast in biological tissues, including myocardium and central nervous system white matter.

This document contains the first report of MRI-measured susceptibility anisotropy in myocardium. Intact mouse heart specimens were scanned using MRI at 9.4 T to ascertain both the magnetic susceptibility and myofiber orientation of the tissue. The susceptibility anisotropy of myocardium was observed and measured by relating the apparent tissue susceptibility as a function of the myofiber angle with respect to the applied magnetic field. A multi-filament model of myocardial tissue revealed that the diamagnetically anisotropy α-helix peptide bonds in myofilament proteins are capable of producing bulk susceptibility anisotropy on a scale measurable by MRI, and are potentially the chief sources of the experimentally observed anisotropy.

The growing use of paramagnetic contrast agents in magnetic susceptibility imaging motivated a series of investigations regarding the effect of these exogenous agents on susceptibility imaging in the brain, heart, and kidney. In each of these organs, gadolinium increases susceptibility contrast and anisotropy, though the enhancements depend on the tissue type, compartmentalization of contrast agent, and complex multi-pool relaxation. In the brain, the introduction of paramagnetic contrast agents actually makes white matter tissue regions appear more diamagnetic relative to the reference susceptibility. Gadolinium-enhanced MRI yields tensor-valued susceptibility images with eigenvectors that more accurately reflect the underlying tissue orientation.

Despite the boost gadolinium provides, tensor-valued susceptibility image reconstruction is prone to image artifacts. A novel algorithm was developed to mitigate these artifacts by incorporating orientation-dependent tissue relaxation information into susceptibility tensor estimation. The technique was verified using a numerical phantom simulation, and improves susceptibility-based tractography in the brain, kidney, and heart. This work represents the first successful application of susceptibility-based tractography to a whole, intact heart.

The knowledge and tools developed throughout the course of this research were then applied to studying mouse models of Alzheimer’s disease in vivo, and studying hypertrophic human myocardium specimens ex vivo. Though a preliminary study using contrast-enhanced quantitative susceptibility mapping has revealed diamagnetic amyloid plaques associated with Alzheimer’s disease in the mouse brain ex vivo, non-contrast susceptibility imaging was unable to precisely identify these plaques in vivo. Susceptibility tensor imaging of human myocardium specimens at 9.4 T shows that susceptibility anisotropy is larger and mean susceptibility is more diamagnetic in hypertrophic tissue than in normal tissue. These findings support the hypothesis that myofilament proteins are a source of susceptibility contrast and anisotropy in myocardium. This collection of preclinical studies provides new tools and context for analyzing tissue structure, chemistry, and health in a variety of organs throughout the body.

Examining Cognitive Processing in Children with an Arithmetic Disability

Currently there is no consensus as to the specific cognitive impairments that characterize mathematical disabilities (MD) or specific subtypes such as an arithmetic disability (AD). The present study sought to address this concern by examining cognitive processes that might undergird AD in children. The present study utilized archival data to conduct two investigations. The first investigation examined the executive functioning and working memory of children with AD. An age-matched achievement-matched design was employed to explore whether children with AD exhibit developmental lags or deficits in these cognitive domains. While children with AD did not exhibit impairments in verbal working memory or colour word inhibition, they did demonstrate impairments in shifting attention, visual-spatial working memory, and quantity inhibition. As children with AD did not perform more poorly than their younger achievement-matched peers on any of these tasks, impairments in specific areas of executive functioning and working memory appeared to reflect a developmental lag rather than a cognitive deficit. The second study examined the phonological processing performance of children with AD compared to children with comorbid disabilities in arithmetic and word recognition (AD/WRD) and to typically achieving (TA) children. Results indicated that, while children with AD did demonstrate impairments on all isolated naming speed tasks, trail making digits, and memory for digits, they did not demonstrate impairments on measures of phonological awareness, nonword repetition, serial processing speed, or serial naming speed. In contrast, children with AD/WRD demonstrated impairments on measures of phonological awareness, phonological short-term memory, isolated naming speed, serial processing speed, and the alphabet a-z task. Overall, results suggested that phonological processing impairments are more prominent in children with a WRD than children with an AD. Together, these studies further our understanding of the nature of the cognitive processes that underlie AD by focusing upon rarely used methods (i.e., age-matched achievement-matched design) and under-examined cognitive domains (i.e., phonological processing).

A randomized controlled trial of an early-intervention, computer-based literacy program to boost phonological skills in 4- to 6-year-old children

Background: Many school-based interventions are being delivered in the absence of evidence of effectiveness (Snowling & Hulme, 2011, Br. J. Educ. Psychol., 81, 1).Aim: This study sought to address this oversight by evaluating the effectiveness of the commonly used the Lexia Reading Core5 intervention, with 4- to 6-year-old pupils in Northern Ireland.Sample: A total of 126 primary school pupils in year 1 and year 2 were screened on the Phonological Assessment Battery 2nd Edition (PhAB-2). Children were recruited from the equivalent year groups to Reception and Year 1 in England and Wales, and Pre-kindergarten and Kindergarten in North America.
Methods: A total of 98 below-average pupils were randomized (T0) to either an 8-week block (inline image = 647.51 min, SD = 158.21) of daily access to Lexia Reading Core5 (n = 49) or a waiting-list control group (n = 49). Assessment of phonological skills was completed at post-intervention (T1) and at 2-month follow-up (T2) for the intervention group only.
Results: Analysis of covariance which controlled for baseline scores found that the Lexia Reading Core5 intervention group made significantly greater gains in blending, F(1, 95) = 6.50, p = .012, partial η2 = .064 (small effect size) and non-word reading, F(1, 95) = 7.20, p = .009, partial η2 = .070 (small effect size). Analysis of the 2-month follow-up of the intervention group found that all group treatment gains were maintained. However, improvements were not uniform among the intervention group with 35% failing to make progress despite access to support. Post-hoc analysis revealed that higher T0 phonological working memory scores predicted improvements made in phonological skills.
Conclusions: An early-intervention, computer-based literacy program can be effective in boosting the phonological skills of 4- to 6-year-olds, particularly if these literacy difficulties are not linked to phonological working memory deficits.

Contrast Stretch Data

Resources created at the University of Southampton for the module Remote Sensing for Earth Observation

Upper Secondary Students’ Beliefs About Learning English as a Foreign Language : A contrast between the students’ beliefs and the Swedish curriculum

Learning English as a foreign language (EFL) entails different factors. Language learners use different strategies in order to make their language acquisition successful. Motivation and self-regulated learning are other factors that influence how successful the EFL learner is. This paper aims to analyze the beliefs of upper secondary students in a Swedish school about learning EFL, as well as how their beliefs relate to what is specified in the Swedish curriculum. An analysis of the differences between students’ beliefs and what is stated in the curriculum was done. A survey was conducted on a total of 54 students who were enrolled in the social sciences program. The results showed that students believed that motivation and self-regulated learning were important factors for a successful learning. For them, the language skill of reception is more important than production, which does not correspond with what it is stated in the national curriculum. First and second year students’ beliefs were similar in most of the cases, but not all of them.

Biliteracy effects on phonological awareness, oral language proficiency and reading skills in Taiwanese Mandarin-English bilingual children

The present study examined the effect of learning to read a heritage language on Taiwanese Mandarin-English bilingual children’s Chinese and English phonological awareness, Chinese and English oral language proficiency, and English reading skills. Participants were 40 Taiwanese Mandarin-English bilingual children and 20 English monolingual children in the U.S. Based on their performance on a Chinese character reading test, the bilingual participants were divided into two groups: the Chinese Beginning Reader and Chinese Nonreader groups. A single child categorized as a Chinese Advanced Reader also participated. Children received phonological awareness tasks, produced oral narrative samples from a wordless picture book, and took standardized English reading subtests. The bilingual participants received measures in both English and Chinese, whereas English monolingual children received only English measures. Additional demographic information was collected from a language background survey filled out by parents. Results of two MANOVAs indicated that the Chinese Beginning Reader group outperformed the Chinese Nonreader and English Monolingual groups on some phonological awareness measures and the English nonword reading test. In an oral narrative production task in English, the English Monolingual group produced a greater total number of words (TNW) and more different words (NDW) than the Chinese Nonreader group. Multiple regression analyses were conducted to determine whether bilingual children’s Chinese character reading ability would still account for a unique amount of variance in certain outcome variables, independent of nonverbal IQ and other potential demographic or performance variables and to clarify the direction of causality for bilingual children’s performance in the three domains. These results suggested that learning to read in a heritage language directly or indirectly enhances bilingual children’s ability in phonological awareness and certain English reading skills. It also appears that greater oral language proficiency in Chinese promotes early reading in the heritage language. Advanced heritage reading may produce even larger gains. Practical implications of learning a heritage language in the U.S. are discussed.

Using a voxel-based krogh cylinder array to simulate microvascular contrast enhancement

The goal of this study is to better simulate microscopic and voxel-based dynamic contrast enhancement in magnetic resonance imaging. Specifically, errors imposed by the traditional two-compartment model are reduced by introducing a novel Krogh cylinder network. The two-compartment model was developed for macroscopic pharmacokinetic analysis of dynamic contrast enhancement and generalizing it to voxel dimensions, due to the significant decrease in scale, imposes physiologically unrealistic assumptions. In the project, a system of microscopic exchange between plasma and extravascular-extracellular space is built while numerically simulating the local contrast agent flow between and inside image elements. To do this, tissue parameter maps were created, contrast agent was introduced to the tissue via a flow lattice, and various data sets were simulated. The effects of sources, tissue heterogeneity, and the contribution of individual tissue parameters to an image are modeled. Further, the study attempts to demonstrate the effects of a priori flow maps on image contrast, indicating that flow data is as important as permeability data when analyzing tumor contrast enhancement. In addition, the simulations indicate that it may be possible to obtain tumor-type diagnostic information by acquiring both flow and permeability data.

Added value of diffusion-weighted MRI in detection of cervical cancer recurrence compared with morphologic and dynamic contrast-enhanced MRI sequences

PURPOSE We aimed to evaluate the added value of diffusion-weighted imaging (DWI) to standard magnetic resonance imaging (MRI) for detecting post-treatment cervical cancer recurrence. The detection accuracy of T2-weighted (T2W) images was compared with that of T2W MRI combined with either dynamic contrast-enhanced (DCE) MRI or DWI. METHODS Thirty-eight women with clinically suspected uterine cervical cancer recurrence more than six months after treatment completion were examined with 1.5 Tesla MRI including T2W, DCE, and DWI sequences. Disease was confirmed histologically and correlated with MRI findings. The diagnostic performance of T2W imaging and its combination with either DCE or DWI were analyzed. Sensitivity, positive predictive value, and accuracy were calculated. RESULTS Thirty-six women had histologically proven recurrence. The accuracy for recurrence detection was 80% with T2W/DCE MRI and 92.1% with T2W/DWI. The addition of DCE sequences did not significantly improve the diagnostic ability of T2W imaging, and this sequence combination misclassified two patients as falsely positive and seven as falsely negative. The T2W/DWI combination revealed a positive predictive value of 100% and only three false negatives. CONCLUSION The addition of DWI to T2W sequences considerably improved the diagnostic ability of MRI. Our results support the inclusion of DWI in the initial MRI protocol for the detection of cervical cancer recurrence, leaving DCE sequences as an option for uncertain cases.

Maintenance or loss of dialect Andalusian features: Internal and external factors

In the last sixty years a steadily maintained process of convergence towards the Castilian national standard has been occurring in Southern Spain affecting urban middle-class speakers’ varieties, particularly phonology and lexis. As a consequence, unmarked features characterising innovative southern pronunciation have become less frequent and, at the same time, certain standard marked features have been adapted to the southern phonemic inventory. Then, urban middle-class varieties have progressively been stretching out the distance separating them from working-class and rural varieties, and bringing them closer to central Castilian varieties. Intermediate, yet incipient koineised varieties have been described including also transitional Murcia and Extremadura dialects (Hernández & Villena 2009, Villena, Vida & von Essen 2015). (1) Some of the standard phonologically marked features have spread out among southern speakers exclusively based on their mainstream social prestige and producing not only changes in obstruent phoneme inventory –i.e. acquisition of /s/ vs. /θ/ contrast, but also standstill and even reversion of old consonant push- or pull-chain shifts –e.g. /h/ or /d/ fortition, affricate /ʧ/, etc. as well as traditional lexis shift (Villena et al. 2016). Internal (grammar and word frequency) and external (stratification, network and style) factors constraining those features follow similar patterns in the Andalusian speech communities analysed so far (Granada, Malaga) but when we zoom in on central varieties, which are closer to the national standard and then more conservative, differences in frequency increase and conflict sites emerge. (2) Unmarked ‘natural’ phonological features characterising southern dialects, particularly deletion of syllable-final consonant, do not keep pace with this trend of convergence towards the standard. Thus a combination of southern innovative syllable-final and standard conservative onset-consonant features coexist. (3). The main idea is that this intermediate variety is formed through changes suggesting that Andalusian speakers look for the best way of accepting marked prestige features without altering coherence within their inventory. Either reorganisation of the innovative phonemic system in such a way that it may include Castilian and standard /s/ vs. /θ/ contrast or re-syllabification of aspirated /s/ before dental stop are excellent examples of how and why linguistic features are able to integrate intermediate varieties between the dialect-standard continuum.

A non-contrast self-navigated 3-dimensional MR technique for aortic root and vascular access route assessment in the context of transcatheter aortic valve replacement: proof of concept.

OBJECTIVES: Due to the high prevalence of renal failure in transcatheter aortic valve replacement (TAVR) candidates, a non-contrast MR technique is desirable for pre-procedural planning. We sought to evaluate the feasibility of a novel, non-contrast, free-breathing, self-navigated three-dimensional (SN3D) MR sequence for imaging the aorta from its root to the iliofemoral run-off in comparison to non-contrast two-dimensional-balanced steady-state free-precession (2D-bSSFP) imaging. METHODS: SN3D [field of view (FOV), 220-370 mm(3); slice thickness, 1.15 mm; repetition/echo time (TR/TE), 3.1/1.5 ms; and flip angle, 115°] and 2D-bSSFP acquisitions (FOV, 340 mm; slice thickness, 6 mm; TR/TE, 2.3/1.1 ms; flip angle, 77°) were performed in 10 healthy subjects (all male; mean age, 30.3 ± 4.3 yrs) using a 1.5-T MRI system. Aortic root measurements and qualitative image ratings (four-point Likert-scale) were compared. RESULTS: The mean effective aortic annulus diameter was similar for 2D-bSSFP and SN3D (26.7 ± 0.7 vs. 26.1 ± 0.9 mm, p = 0.23). The mean image quality of 2D-bSSFP (4; IQR 3-4) was rated slightly higher (p = 0.03) than SN3D (3; IQR 2-4). The mean total acquisition time for SN3D imaging was 12.8 ± 2.4 min. CONCLUSIONS: Our results suggest that a novel SN3D sequence allows rapid, free-breathing assessment of the aortic root and the aortoiliofemoral system without administration of contrast medium. KEY POINTS: • The prevalence of renal failure is high among TAVR candidates. • Non-contrast 3D MR angiography allows for TAVR procedure planning. • The self-navigated sequence provides a significantly reduced scanning time.