Measurement of Photon Statistics with Live Photoreceptor Cells

We analyzed the electrophysiological response of an isolated rod photoreceptor of Xenopus laevis under stimulation by coherent and pseudo-thermal light sources. Using the suction electrode technique for single cell recordings and a fiber optics setup for light delivery allowed measurements of the major statistical characteristics of the rod response. The results indicate differences in average responses of rod cells to coherent and pseudo-thermal light of the same intensity and also differences in signal-to-noise ratios and second order intensity correlation functions. These findings should be relevant for interdisciplinary studies seeking applications of quantum optics in biology.Comment: 6 pages, 7 figure

Origin and Functional Impact of Dark Noise in Retinal Cones

AbstractSpontaneous fluctuations in the electrical signals of the retina's photoreceptors impose a fundamental limit on visual sensitivity. While noise in the rods has been studied extensively, relatively little is known about the noise of cones. We show that the origin of the dark noise in salamander cones varies with cone type. Most of the noise in long wavelength–sensitive (L) cones arose from spontaneous activation of the photopigment, which is a million-fold less stable than the rod photopigment rhodopsin. Most of the noise in short wavelength–sensitive (S) cones arose in a later stage of the transduction cascade, as the photopigment was relatively stable. Spontaneous pigment activation effectively light adapted L cones in darkness, causing them to have a smaller and briefer dim flash response than S cones

Recoverin Regulates Light-dependent Phosphodiesterase Activity in Retinal Rods

The Ca2+-binding protein recoverin may regulate visual transduction in retinal rods and cones, but its functional role and mechanism of action remain controversial. We compared the photoresponses of rods from control mice and from mice in which the recoverin gene was knocked out. Our analysis indicates that Ca2+-recoverin prolongs the dark-adapted flash response and increases the rod's sensitivity to dim steady light. Knockout rods had faster Ca2+ dynamics, indicating that recoverin is a significant Ca2+ buffer in the outer segment, but incorporation of exogenous buffer did not restore wild-type behavior. We infer that Ca2+-recoverin potentiates light-triggered phosphodiesterase activity, probably by effectively prolonging the catalytic activity of photoexcited rhodopsin

Possum stole the pumpkin: finding voice in Cajun music in Australia

This research project explores how I have found a musical voice in Cajun music and have created styles of fiddle –playing and composition which reflect an Australian experience. The exegesis details the historical and cultural backgrounds of Cajun music and discusses questions of authenticity, the nature of tradition and problems associated with performance of the style in Australia. The work discusses my own search for a personal identity in the Australian music scene and presents original music for fiddle and percussion. I have included transcriptions and analysis of the tunes which describe technical aspects of the music and a commentary which illuminates the underlying sense of meaning in the music. I have used several methodologies including autoethnography, professional practice-based research, and ethnomusicology. These approaches have enabled me 1) to situate my own personal journey as an artist in broader social and historical contexts; 2) to reflect on thirty years of professional music –making ; 3) to present knowledge of Cajun music as played in Louisiana; and 4) to offer insights into my sources of inspiration, both musical and extra-musical. A field trip to Southwest Louisiana in July 2005 where I received lessons and shared tunes with many leading Cajun musicians has also informed and inspired the project. In effect, this research project explores how music and culture from other times and places can be re-interpreted in a contemporary Australian setting

Dynamics of Cyclic GMP Synthesis in Retinal Rods

AbstractIn retinal rods, Ca2+ exerts negative feedback control on cGMP synthesis by guanylate cyclase (GC). This feedback loop was disrupted in mouse rods lacking guanylate cyclase activating proteins GCAP1 and GCAP2 (GCAPs−/−). Comparison of the behavior of wild-type and GCAPs−/− rods allowed us to investigate the role of the feedback loop in normal rod function. We have found that regulation of GC is apparently the only Ca2+ feedback loop operating during the single photon response. Analysis of the rods' light responses and cellular dark noise suggests that GC normally responds to light-driven changes in [Ca2+] rapidly and highly cooperatively. Rapid feedback to GC speeds the rod's temporal responsiveness and improves its signal-to-noise ratio by minimizing fluctuations in cGMP

Patient Perspectives of an Intensive Comprehensive Aphasia Program for Stroke Survivors

Introduction: Persons with aphasia (PWA) who participate in intensive comprehensive poststroke language rehabilitation programs make a variety of significant investments. While intensive aphasia programs and intensive comprehensive aphasia programs (ICAPs) are becoming increasingly prevalent across health care settings, patient perspectives of ICAPs have not been explored. The purpose of this qualitative study was to examine patient perspectives about the experience of participating in an ICAP at the University of Montana. The primary research question of this study was: “what is it like to be a PWA in an ICAP?” Methods: Researchers used an interpretive phenomenological approach to conduct nine structured interviews from PWAs who described their lived experiences in the ICAP. All interviews were audiovisually recorded and transcribed from the video recordings. Analysis involved an iterative and collaborative coding process. Transcripts were coded and themes were developed from the PWAs’ shared perspectives. Results: Three primary themes emerged from patient perspectives including: (1) experience with each of the ICAP components is generally positive, (2) we notice the impact of the ICAP on our communication, and (3) relationships with people in the ICAP are important. Discussion: Results support emerging evidence that ICAPs can be a positive experience for PWA due to the perceptible impact on communication improvement and frequent and varied opportunities to interact with others. ICAPs may be a worthwhile investment for PWA, thereby contributing to the cost-benefit utility and implementation feasibility of the service delivery model

A pattern-recognition theory of search in expert problem solving

Understanding how look-ahead search and pattern recognition interact is one of the important research questions in the study of expert problem-solving. This paper examines the implications of the template theory (Gobet & Simon, 1996a), a recent theory of expert memory, on the theory of problem solving in chess. Templates are "chunks" (Chase & Simon, 1973) that have evolved into more complex data structures and that possess slots allowing values to be encoded rapidly. Templates may facilitate search in three ways: (a) by allowing information to be stored into LTM rapidly; (b) by allowing a search in the template space in addition to a search in the move space; and (c) by compensating loss in the "mind's eye" due to interference and decay. A computer model implementing the main ideas of the theory is presented, and simulations of its search behaviour are discussed. The template theory accounts for the slight skill difference in average depth of search found in chess players, as well as for other empirical data

Analysis of D Pellet Injection Experiments in the W7-AS Stellarator

A centrifugal injector was used to inject deuterium pellets (with 3--5 x 10{sup 19} atoms) at approx. equal 600 m/s into current-less, nearly shear-less plasmas in the Wendelstein 7-AS (W7-AS) stellarator. The D pellet was injected horizontally at a location where the non-circular and non-axisymmetric plasma cross section is nearly triangular. Visible-light TV pictures usually showed the pellet as a single ablating mass in the plasma, although the pellet occasionally broke in two or splintered into a cloud of small particles. The density evolution following pellet injection and the effect of pellet injection on energy confinement and fluctuations are discussed