John Christie - Academia.edu (original) (raw)

Papers by John Christie

... optically variable features on banknotes. Author(s): Ian M. Lancaster; Astrid Mitchell. Lates... more ... optically variable features on banknotes. Author(s): Ian M. Lancaster; Astrid Mitchell. Latest developments in on-and off-line inspection of bank notes during production. Author(s): Stephen C. Brown. New security features and ...

Optical Security and …, Jan 1, 2004

Commissioned by the Bank of Canada to help improve the detection of counterfeit currency, we desi... more Commissioned by the Bank of Canada to help improve the detection of counterfeit currency, we designed a series of tests of performance to explore the contributions of note quality, sensory modality, training, security features and demographic variables to the accuracy of counterfeit detection with three different note types. In each test, participants (general public, and cash handlers, divided amongst commercial cash handlers and bank tellers) were presented with notes, one at a time, for up to seven seconds, and were asked to judge whether each note was genuine or counterfeit. With whole note inspection, overall accuracy was about 80%. When the security features were tested individually, the Optical Security Device (OSD) was the best feature, the hidden number was the worst, and the portrait, maple leaves, fluorescence, and microprinting were intermediate. Accuracy was higher with notes that could be seen but not touched than vice versa. Cash handlers were 74% correct with touch alone and adding touch to vision significantly improved counterfeit detection. This paper will demonstrate how performance differences between the different note types can be explained in terms of the efficacy of the individual security features incorporated into the notes.

The New phytologist, Jan 28, 2015

Phototropins (phots) regulate a range of adaptive processes in plants that serve to optimize phot... more Phototropins (phots) regulate a range of adaptive processes in plants that serve to optimize photosynthetic efficiency and promote growth. Light sensing by Arabidopsis thaliana phots is predominantly mediated by the Light, Oxygen and Voltage sensing 2 (LOV2) flavin-binding motif located within the N-terminus of the photoreceptor. Here we characterize the photochemical and biochemical properties of phot from the marine picoalga Ostreococcus tauri phototropin (Otphot) and examine its ability to replace phot-mediated function in Arabidopsis. Photochemical properties of Otphot rely on both LOV1 and LOV2. Yet, biochemical analysis indicates that light-dependent receptor autophosphorylation is primarily dependent on LOV2. As found for Arabidopsis phots, Otphot associates with the plasma membrane and partially internalizes, albeit to a limited extent, in response to blue-light irradiation. Otphot is able to elicit a number of phot-regulated processes in Arabidopsis, including petiole posit...

Consciousness and Cognition, 2015

Lin and Murray published in the 2015 January Issue of Psychological Science a study that claims t... more Lin and Murray published in the 2015 January Issue of Psychological Science a study that claims to have made the surprising discovery of unconscious effects that are stronger than equivalent conscious effects. Specifically, the authors claim to have uncovered dissociable components of aware and unaware orienting and inhibition in exogenous cueing. They suggest an awareness-dependent location-based inhibition mechanism referred to as a negative attentional aftereffect. Here we argue for a simpler explanation, based on established literature, that all they have shown is response inhibition to a consciously perceived cue presented at a fixed location.

Current Biology, 2015

Plants are photoautotrophic sessile organisms that use environmental cues to optimize multiple fa... more Plants are photoautotrophic sessile organisms that use environmental cues to optimize multiple facets of growth and development. A classic example is phototropism - in shoots this is typically positive, leading to growth towards the light, while roots frequently show negative phototropism triggering growth away from the light. Shoot phototropism optimizes light capture of leaves in low light environments and hence increases photosynthetic productivity. Phototropins are plasma-membrane-associated UV-A/blue-light activated kinases that trigger phototropic growth. Light perception liberates their protein kinase domain from the inhibitory action of the amino-terminal photosensory portion of the photoreceptor. Following a series of still poorly understood events, phototropin activation leads to the formation of a gradient of the growth hormone auxin across the photo-stimulated stem. The greater auxin concentration on the shaded compared with the lit side of the stem enables growth reorientation towards the light. In this Minireview, we briefly summarize the signaling steps starting from photoreceptor activation until the establishment of a lateral auxin gradient, ultimately leading to phototropic growth in shoots.

Science, 2015

The present palette of opsin-based optogenetic tools lacks a light-gated potassium (K(+)) channel... more The present palette of opsin-based optogenetic tools lacks a light-gated potassium (K(+)) channel desirable for silencing of excitable cells. Here, we describe the construction of a blue-light-induced K(+) channel 1 (BLINK1) engineered by fusing the plant LOV2-Jα photosensory module to the small viral K(+) channel Kcv. BLINK1 exhibits biophysical features of Kcv, including K(+) selectivity and high single-channel conductance but reversibly photoactivates in blue light. Opening of BLINK1 channels hyperpolarizes the cell to the K(+) equilibrium potential. Ectopic expression of BLINK1 reversibly inhibits the escape response in light-exposed zebrafish larvae. BLINK1 therefore provides a single-component optogenetic tool that can establish prolonged, physiological hyperpolarization of cells at low light intensities.

Journal of the American Chemical Society, Jan 8, 2015

UVR8 is a novel UV-B photoreceptor that regulates a range of plant responses and is already used ... more UVR8 is a novel UV-B photoreceptor that regulates a range of plant responses and is already used as a versatile optogenetic tool. Instead of an exogenous chromophore, UVR8 uniquely employs tryptophan side chains to accomplish UV-B photoreception. UV-B absorption by homo-dimeric UVR8 induces monomerization and hence signaling, but the underlying photodynamic mechanisms are not known. Here, by using a combination of time resolved fluorescence and absorption spectroscopy from femto to microseconds we provide the first experimental evidence for the UVR8 molecular signaling mechanism. The results indicate that tryptophan residues at the dimer interface engage in photoinduced proton coupled electron transfer reactions that induce monomerization.

Optical Security and Counterfeit Deterrence Techniques V, 2004

The American journal of gastroenterology, 2012

Proceedings of the National Academy of Sciences of the United States of America, Jan 5, 2001

UV-A/blue light acts to regulate a number of physiological processes in higher plants. These incl... more UV-A/blue light acts to regulate a number of physiological processes in higher plants. These include light-driven chloroplast movement and phototropism. The NPH1 gene of Arabidopsis encodes an autophosphorylating protein kinase that functions as a photoreceptor for phototropism in response to low-intensity blue light. However, nph1 mutants have been reported to exhibit normal phototropic curvature under high-intensity blue light, indicating the presence of an additional phototropic receptor. A likely candidate is the nph1 homologue, npl1, which has recently been shown to mediate the avoidance response of chloroplasts to high-intensity blue light in Arabidopsis. Here we demonstrate that npl1, like nph1, noncovalently binds the chromophore flavin mononucleotide (FMN) within two specialized PAS domains, termed LOV domains. Furthermore, when expressed in insect cells, npl1, like nph1, undergoes light-dependent autophosphorylation, indicating that npl1 also functions as a light receptor ...

Experimental Brain Research, 2015

Prior oculomotor research has established that saccades tend to land near the center of multiple ... more Prior oculomotor research has established that saccades tend to land near the center of multiple saccade targets when they are near each other. This saccade averaging phenomenon (or global effect) has been ascribed to short-distance lateral excitation between neurons in the superior colliculus. Further, at greater inter-stimulus distances, eye movements tend toward the individual elements. This transition to control by local elements (individuation) with inter-stimulus distance has been attributed to long-range lateral inhibition between neurons in winner-take-all models of oculomotor behavior. We hypothesized that the traditional method of requiring a saccade to an array of multiple, simultaneous targets may entail response ambiguity that intensifies with distance. We resolved the ambiguity by focussing on reaction time of our human participants to a single saccade target after one or more simultaneous priming stimuli. At a 50-ms prime-target interval, saccadic reaction time was shortest for targets closer to the center of the prime stimuli independent of the distance between the primes. This effect was gone at 400 ms. These findings challenge the typical inferences about the neural control of oculomotor behavior that have been derived from the boundary between saccade averaging and individuation and provide a new method to explore eye movements with lessened impact from decision processes.

The use of time domain reflectometry (TDR) techniques for measuring the moisture content of compo... more The use of time domain reflectometry (TDR) techniques for measuring the moisture content of composite materials is a mature art but usually assumes homogeneity of the material in the transverse plane. As the basis of a forward solution to TDR imaging, we describe an integral equation approach to model the response of the TDR system to a lossless heterogeneous dielectric

Frontiers in Human Neuroscience, 2012

Previous studies using hierarchical figures (where a large global shape is composed of a series o... more Previous studies using hierarchical figures (where a large global shape is composed of a series of smaller local shapes) suggest that performance is better for local features presented in the right relative to left visual field, whereas the opposite pattern is observed for global features. However, these previous studies have focused on effects between hemifields. Recent data from patients with neurological damage suggest that local deficits can be allocentric (e.g., following left hemisphere injury, individuals are relatively slow to detect features on the right side of an object, regardless of visual field). Therefore, we decided to extend previous global versus local research by also observing local performance within hemifields. Specifically, on each trial we presented two hierarchical figures (one in each hemifield), but crucially the left and right side of each item were composed of different local features. In this task, the participant simply reports if a circle is present, regardless of location or whether this is a local or global feature. We observed that both neurologically healthy individuals, as well as an individual with brain injury, were relatively better detecting local information on the right side of objects, regardless of spatial location, while both showed better performance for global stimuli in the left visual field. This work is consistent with recent work in patients with neurological damage, and provides a new paradigm for exploring hemispheric specialization.

Plant Cell Monographs, 2010

Light is one of the most important environmental factors controlling plant development and its pe... more Light is one of the most important environmental factors controlling plant development and its perception is achieved through a suite of photoreceptor proteins. Like photoreceptors associated with our vision, plant photosensors can detect the presence, intensity, direction and color of light, and in turn, utilize this information to direct their growth accordingly. To date, four different types of photoreceptors have been identified in plants, namely the phytochromes, cryptochromes, phototropins and members of the Zeitlupe (ZTL) family. Phytochromes are photoreversible red/far-red photoreceptors whereas cryptochromes, phototropins and members of the ZTL family specifically absorb UV-A/blue wavelengths. Plants also respond to UV-B and green light, but the photosensors responsible for their detection remain elusive. A summary of light-regulated events that are known to occur at the plant plasma membrane will be discussed, as will the biochemical and photochemical properties of the photoreceptor proteins involved.

The Journal of Chemical Physics, 2015

Low-temperature scanning tunneling microscopy is used to observe self-assembled structures of fer... more Low-temperature scanning tunneling microscopy is used to observe self-assembled structures of ferrocenedicarboxylic acid (Fc(COOH)2) on the Au(111) surface. The surface is prepared by pulse-deposition of Fc(COOH)2 dissolved in methanol, and the solvent is evaporated before imaging. While the rows of hydrogen-bonded dimers that are common for carboxylic acid species are observed, the majority of adsorbed Fc(COOH)2 is instead found in six-molecule clusters with a well-defined and chiral geometry. The coverage and distribution of these clusters are consistent with a random sequential adsorption model, showing that solution-phase species are determinative of adsorbate distribution for this system under these reaction conditions.

Chemical communications (Cambridge, England), Jan 14, 2014

Self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH) contain two fundamental units, bot... more Self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH) contain two fundamental units, both stabilized by intermolecular hydrogen bonding: dimers and cyclic five-membered catemers. At surface coverages below a full monolayer, however, there is a significantly more varied structure that includes double-row clusters containing two to twelve FcCOOH molecules. Statistical analysis shows a distribution of cluster sizes that is sharply peaked compared to a binomial distribution. This rules out simple nucleation-and-growth mechanisms of cluster formation, and strongly suggests that clusters are formed in solution and collapse into rows when deposited on the Au(111) surface.

Plant Molecular Biology, 1998

To identify DNA sequences of the Arabidopsis thaliana chalcone synthase gene (CHS) concerned with... more To identify DNA sequences of the Arabidopsis thaliana chalcone synthase gene (CHS) concerned with induction by UV-B and UV-A/blue light, AtCHS promoter constructions were assayed by transient expression in protoplasts prepared from two different lines of cultured A. thaliana cells. The protoplasts responded similarly to A. thaliana leaf tissue in light-dependent CHS transcript accumulation. The reporter enzyme beta-glucuronidase (GUS) was used to monitor light-responsive promoter activity. A 1972 bp promoter conferred UV-B and UV-A/blue light induction of GUS activity. Deletion to 164 bp resulted in reduced promoter strength but retention of responsiveness to UV-B and UV-A/blue light. Further deletion abolished transcriptional activity. The 164 bp promoter contains sequences closely resembling LRUPcCHS, (light-responsive unit of the Petroselinum crispum CHS promoter). This A. thaliana CHS promoter region, designated LRUAtCHS, was sufficient to confer UV-B and UV-A/blue light responsiveness to a heterologous core promoter. Mutation of sequences in LRUAtCHS corresponding to the ACGT element and the MYB recognition element of LRUPcCHS resulted in inactivation of the 164 bp and 335 bp promoter deletions. However, the mutant 668 bp promoter retained residual UV-B and UV-A/blue light-induced expression, indicating the presence of additional functional sequences upstream of -335. Mutation of a single G-box-like sequence around -442 had no effect on light responsiveness, indicating that it does not function in light regulation of this promoter. Since no difference in responsiveness to UV-B and UV-A/blue light was observed with any promoter variant, we conclude that the two phototransduction pathways regulate transcription factors which interact with common promoter elements. The results from-our analysis of a A. thaliana light-responsive promoter will facilitate the study of light-dependent gene regulation by genetic means in Arabidopsis thaliana.

Psychonomic Bulletin & Review, 2008

Negative priming from distractors has attracted considerable interest because it appears to revea... more Negative priming from distractors has attracted considerable interest because it appears to reveal a fundamental mechanism of selective attention. Recently, the phenomenon has become muddled because it can be explained in far too many ways. This may partly be because the empirical foundation for the phenomenon has been handicapped by an overreliance on a simplistic comparison of a single experimental condition with control. A sounder approach requires that we collect data that can rule out alternatives to the hypothesis we might favor or test. Regardless of the paradigm used, we propose collecting data from a much fuller set of conditions than is typical. Despite the variety of underlying explanations, we show that the various theories that attribute negative priming to ignoring the distractor predict a common pattern of results across the full set of related conditions. Theories, such as inhibition of return, that do not attribute the cost in performance to ignoring the distractor do not predict this pattern.

Trends in Plant Science, 2002

Blue and ultraviolet-A light regulate a wide range of responses in plants, including phototropism... more Blue and ultraviolet-A light regulate a wide range of responses in plants, including phototropism, chloroplast migration and stomatal opening. However, the photoreceptors for these light responses have been identified only recently. The phototropins (phot1 and phot2) represent a new class of receptor kinases that appear to be exclusive to plants. Recent genetic analysis has shown that phot1 and phot2 exhibit partially overlapping functions in mediating phototropism, chloroplast migration, and stomatal opening in Arabidopsis. Although significant progress has been made in understanding the early photochemical and biochemical events that follow phototropin excitation, the details of how this excitation activates such different responses remain to be elucidated.