Working Memory and Second‐Language Accent Acquisition

We explored the proposal that overt repetition of verbal information improves the acquisition of a native accent in a second language. Mandarin-speaking Chinese learners of English were recorded while repeating and reading out English sentences before and after one of three treatments: (1) Repeating native English sentences subvocally, "covert repetition,"(2) Repeating sentences out loud, "overt repetition," and(3) Unfilled time of comparable duration. The sentences were rated by English speakers for their nativeness, fluency, and intelligibility. Overt repetition improved accent rating for read-out sentences. Covert repetition did not. Neither condition improved accent rating for repeated sentences, suggesting that immediate repetition depends on temporary rather than long-term representations. Our results provide some support for the use of overt repetition in accent learning. From a theoretical perspective, an interpretation is proposed in terms of a separation between phonological and articulatory coding within the phonological loop component of working memory

Is the Levels of Processing effect language-limited?

The concept of Levels of Processing (LOP), proposing that deep coding enhances retention,has played a central role in the study of episodic memory. Evidence has however been based almost entirely on retention of individual words. Across five experiments, we compare LOP effects between visual and verbal stimuli, using judgments of pleasantness as a method of inducing deep encoding and a range of shallow encoding judgments selected so as to be applicable to both verbal and visual stimuli. LOP effects were consistent but modest across the visual stimuli (mean effect size 0.5). In contrast, LOP effects for verbal stimuli varied widely, from modest for people’s names and unfamiliar animals (mean effect size 0.6) to large for familiar animals and household items (mean effect size 1.4), typical of the dramatic LOP effects that characterize the existing verbal literature. We interpret our data through the Gibsonian concept of ‘‘affordance”, proposing that visual and verbal stimuli vary in the number and richness of features they afford, and that access to such features will in turn depend on encoding strategy. Our hypothesis links readily with Nairne’s feature model of long-term memory

Precision measurements with SMI and 4PiMicroscopy

Newly developed farfield light microscopy techniques such as Spatially Modulated Illumination and 4Pi microscopy allow structural measurements on biological objects with a precision very much better than the conventional imaging resolution. This thesis focuses on the improvement of this measurement accuracy, encompassing both changes to the experimental SMI setup and new data analysis procedures. An aberration resistant fit algorithm for SMI microscopy is presented along with similar model based procedures for the analysis of 4Pi and confocal data. These are combined in a framework which allows for robust automatic analysis. A method for deconvolving 4Pi data which shows a refractive index mismatch induced phase shift is also introduced. The devices and the associated algorithms were applied to various biological problems most notably the size of replication foci and the structure of the inner kinetochore. Virtual microscopy simulations were performed to support the interpretation of this data and to obtain insight into the results of the SMI gene structure measurements performed by other group members

Demographic quantification of carbon and nitrogen dynamics associated with root turnover in white clover

ACKNOWLEDGEMENTS This work formed part of Gavin Scott’s PhD at the University of Aberdeen, funded by the Scottish Executive Rural Affairs Department (now the Scottish Government's Rural and Environment Science and Analytical Services Division). We thank Prof Ian Bingham and two anonymous reviewers for their helpful comments.Peer reviewedPostprin

Intention, Attention and Long-term Memory for Visual Scenes : It all depends on the scenes

Humans have an ability to remember up to 10,000 previously viewed scenes with apparently robust memory for visual detail, a phenomenon that has been interpreted as suggesting a visual memory system of massive capacity. Attempts at explanation have largely focused on the nature of the stimuli and been influenced by theoretical accounts of object recognition. Our own study aims to supplement this by considering two observer-based aspects of visual long-term memory, one strategic, whether the observers are aware or not that their memory will subsequently be tested and the other executive, based on the amount of attentional capacity available during encoding. We describe six studies involving visual scenes ranging in difficulty from complex manmade scenes (d’ = 2.54), to door scenes with prominent features removed (d’ = 0.79). To ensure processing of the stimuli, all participants have to make a judgement of pleasantness (Experiments 1 and 2) or of the presence or absence of a dot (Experiment 3). Intention to learn influence performance only in the most impoverished condition comprising doors with prominent features removed. Experiments 4 to 6 investigated the attentional demands of visual long-term memory using a concurrent task procedure. While the demanding task of counting back in threes clearly impaired performance across the range of materials, a lighter load, counting back in ones influences only the most difficult door scenes. Detailed analysis of error patterns indicated that clear differences in performance level between manmade and natural scenes and between unmodified and modified door scenes was reflected in false alarm scores not detections, while concurrent task load affected both. We suggest an interpretation in terms of a two-level process of encoding at the visual feature rather than the whole scene level, with natural images containing many features encoded richly, rapidly and without explicit intent. Only when scenes are selected from a single category and with distinctive detail minimised does memory depend on intention to remember and on the availability of substantial executive capacity

Algorithmic corrections for localization microscopy with sCMOS cameras - characterisation of a computationally efficient localization approach

Modern sCMOS cameras are attractive for single molecule localization microscopy (SMLM) due to their high speed but suffer from pixel non-uniformities that can affect localization precision and accuracy. We present a simplified sCMOS non-uniform noise model that incorporates pixel specific read-noise, offset and sensitivity variation. Using this model we develop a new weighted least squared (WLS) fitting method designed to remove the effect of sCMOS pixel non-uniformities. Simulations with the sCMOS noise model, performed to test under which conditions sCMOS specific localization corrections are required, suggested that pixel specific offsets should always be removed. In many applications with thick biological samples photon fluxes are sufficiently high that corrections of read-noise and sensitivity correction may be neglected. When correction is required, e.g. during fast imaging in thin samples, our WLS fit procedure recovered the performance of an equivalent sensor with uniform pixel properties and the fit estimates also attained the Cramer-Rao lower bound. Experiments with sub-resolution beads and a DNA origami test sample confirmed the results of the simulations. The WLS localization procedure is fast to converge, compatible with 2D, 3D and multi-emitter localization and thus provides a computationally efficient sCMOS localization approach compatible with most SMLM modalities

A novel physiological role for ARF1 in the formation of bidirectional tubules from the Golgi.

Capitalizing on CRISPR/Cas9 gene-editing techniques and super-resolution nanoscopy, we explore the role of the small GTPase ARF1 in mediating transport steps at the Golgi. Besides its well-established role in generating COPI vesicles, we find that ARF1 is also involved in the formation of long (∼3 µm), thin (∼110 nm diameter) tubular carriers. The anterograde and retrograde tubular carriers are both largely free of the classical Golgi coat proteins coatomer (COPI) and clathrin. Instead, they contain ARF1 along their entire length at a density estimated to be in the range of close packing. Experiments using a mutant form of ARF1 affecting GTP hydrolysis suggest that ARF1[GTP] is functionally required for the tubules to form. Dynamic confocal and stimulated emission depletion imaging shows that ARF1-rich tubular compartments fall into two distinct classes containing 1) anterograde cargoes and clathrin clusters or 2) retrograde cargoes and coatomer clusters

Nanoscale Distribution of Ryanodine Receptors and Caveolin-3 in Mouse Ventricular Myocytes: Dilation of T-Tubules near Junctions

AbstractWe conducted super-resolution light microscopy (LM) imaging of the distribution of ryanodine receptors (RyRs) and caveolin-3 (CAV3) in mouse ventricular myocytes. Quantitative analysis of data at the surface sarcolemma showed that 4.8% of RyR labeling colocalized with CAV3 whereas 3.5% of CAV3 was in areas with RyR labeling. These values increased to 9.2 and 9.0%, respectively, in the interior of myocytes where CAV3 was widely expressed in the t-system but reduced in regions associated with junctional couplings. Electron microscopic (EM) tomography independently showed only few couplings with caveolae and little evidence for caveolar shapes on the t-system. Unexpectedly, both super-resolution LM and three-dimensional EM data (including serial block-face scanning EM) revealed significant increases in local t-system diameters in many regions associated with junctions. We suggest that this regional specialization helps reduce ionic accumulation and depletion in t-system lumen during excitation-contraction coupling to ensure effective local Ca2+ release. Our data demonstrate that super-resolution LM and volume EM techniques complementarily enhance information on subcellular structure at the nanoscale