High-contrast Line Research Articles

Writing Into Water.

Writing is an ancient communication technique dating back at least 30 000 years. While even sophisticated contemporary writing techniques hinge on solid surfaces for engraving or the deposition of ink, writing within a liquid medium requires a fundamentally different approach. The study here demonstrates the writing of lines, letters, and complex patterns in water by assembling lines of colloidal particles. Unlike established techniques for underwater writing on solid substrates, these lines are fully reconfigurable and do not require any fixation onto the substrate. Exploiting gravity, an ion-exchange bead (pen) is rolled across a layer of sedimented colloidal particles (ink). The pen evokes a hydrodynamic flow collecting ink-particles into a durable, high-contrast line along its trajectory. Deliberate substrate-tilting sequences facilitate pen-steering and thus drawing and writing. The experiments are complemented with a minimal model that quantitatively predicts the observed parameter dependence for writing in fluids and highlights the generic character of writing by line-assembly. Overall, the approach opens a versatile route for writing, drawing, and patterning fluids-even at the micro-scale.

Neural activity shaping utilizing a partitioned target pattern

Electrical stimulation of neural tissue is used in both clinical and experimental devices to evoke a desired spatiotemporal pattern of neural activity. These devices induce a local field that drives neural activation, referred to as an activating function or generator signal. In visual prostheses, the spread of generator signal from each electrode within the neural tissue results in a spread of visual perception, referred to as a phosphene. Objective. In cases where neighbouring phosphenes overlap, it is desirable to use current steering or neural activity shaping strategies to manipulate the generator signal between the electrodes to provide greater control over the total pattern of neural activity. Applying opposite generator signal polarities in neighbouring regions of the retina forces the generator signal to pass through zero at an intermediate point, thus inducing low neural activity that may be perceived as a high-contrast line. This approach provides a form of high contrast visual perception, but it requires partitioning of the target pattern into those regions that use positive or negative generator signals. This discrete optimization is an NP-hard problem that is subject to being trapped in detrimental local minima. Approach. This investigation proposes a new partitioning method using image segmentation to determine the most beneficial positive and negative generator signal regions. Utilizing a database of 1000 natural images, the method is compared to alternative approaches based upon the mean squared error of the outcome. Main results. Under nominal conditions and with a set computation limit, partitioning provided improvement for 32% of these images. This percentage increased to 89% when utilizing image pre-processing to emphasize perceptual features of the images. The percentage of images that were dealt with most effectively with image segmentation increased as lower computation limits were imposed on the algorithms. Significance. These results provide a new method to increase the resolution of neural stimulating arrays and thus improve the experience of visual prosthesis users.

Use of acceleration and optical waypoint measurements to estimate piston trajectory in an impulse facility

This paper describes a prototype device to estimate the trajectory of the piston in a free-piston driver. The device, which screws to the front face of the piston, has an internal data acquisition system which triggers upon piston launch and records the acceleration history across the complete piston stroke. A key feature is the incorporation of an optical waypoint detector. This comprises a laser which is directed onto the compression tube wall, and a photodiode which measures the reflected intensity. A series of evenly spaced high-contrast lines are marked on the tube surface, which appear as a pattern of intensity changes in the photodiode signal and define a set of exact position–time coordinates along the trajectory. Optical pattern recognition has previously been shown to be effective to identify piston traversal past a fixed detector; in this application, the order is reversed so that the detector is on the piston, and the pattern is at the fixed location. Waypoint detection permits computation of a precise in situ calibration of the accelerometer and correction of the acceleration integration along the piston stroke. The key benefits of this concept are that it provides a complete, fully time-resolved, accurate estimate of piston position, is self-contained and portable, and can be readily utilised on any free-piston driver without significant modification to the facility.

The influence of stimulus format on drawing—a functional imaging study of decision making in portrait drawing

To copy a natural visual image as a line drawing, visual identification and extraction of features in the image must be guided by top-down decisions, and is usually influenced by prior knowledge. In parallel with other behavioral studies testing the relationship between eye and hand movements when drawing, we report here a functional brain imaging study in which we compared drawing of faces and abstract objects: the former can be strongly guided by prior knowledge, the latter less so. To manipulate the difficulty in extracting features to be drawn, each original image was presented in four formats including high contrast line drawings and silhouettes, and as high and low contrast photographic images. We confirmed the detailed eye–hand interaction measures reported in our other behavioral studies by using in-scanner eye-tracking and recording of pen movements with a touch screen. We also show that the brain activation pattern reflects the changes in presentation formats. In particular, by identifying the ventral and lateral occipital areas that were more highly activated during drawing of faces than abstract objects, we found a systematic increase in differential activation for the face-drawing condition, as the presentation format made the decisions more challenging. This study therefore supports theoretical models of how prior knowledge may influence perception in untrained participants, and lead to experience-driven perceptual modulation by trained artists.

Pattern and contrast dependent visual response in the box jellyfish Tripedalia cystophora

Cubomedusae possess a total of 24 eyes, some of which are structurally similar to vertebrate eyes. Accordingly, the medusae also display a range of light-guided behaviours including obstacle avoidance, diurnal activity patterns and navigation. Navigation is supported by spatial resolution and image formation in the so-called upper lens eye. Further, there are indications that obstacle avoidance requires image information from the lower lens eye. Here we use a behavioural assay to examine the obstacle avoidance behaviour of the Caribbean cubomedusa Tripedalia cystophora and test whether it requires spatial resolution. The possible influence of the contrast and orientation of the obstacles is also examined. We show that the medusae can only perform the behaviour when spatial information is present, and fail to avoid a uniformly dark wall, directly proving the use of spatial vision. We also show that the medusae respond stronger to high contrast lines than to low contrast lines in a graded fashion, and propose that the medusae use contrast as a semi-reliable measure of distance to the obstacle.

Reducing the effects of metal artefact using high keV monoenergetic reconstruction of dual energy CT (DECT) in hip replacements

The aim of this study was to determine whether high keV monoenergetic reconstruction of dual energy computed tomography (DECT) could be used to overcome the effects of beam hardening artefact that arise from preferential deflection of low energy photons. Two phantoms were used: a Charnley total hip replacement set in gelatine and a Catphan 500. DECT datasets were acquired at 100, 200 and 400 mA (Siemens Definition Flash, 100 and 140 kVp) and reconstructed using a standard combined algorithm (1:1) and then as monoenergetic reconstructions at 10 keV intervals from 40 to 190 keV. Semi-automated segmentation with threshold inpainting was used to obtain the attenuation values and standard deviation (SD) of the streak artefact. High contrast line pair resolution and background noise were assessed using the Catphan 500. Streak artefact is progressively reduced with increasing keV monoenergetic reconstructions. Reconstruction of a 400 mA acquisition at 150 keV results in reduction in the volume of streak artefact from 65 cm(3) to 17 cm(3) (74 %). There was a decrease in the contrast to noise ratio (CNR) at higher tube voltages, with the peak CNR seen at 70-80 keV. High contrast spatial resolution was maintained at high keV values. Monoenergetic reconstruction of dual energy CT at increasing theoretical kilovoltages reduces the streak artefact produced by beam hardening from orthopaedic prostheses, accompanied by a modest increase in heterogeneity of background image attenuation, and decrease in contrast to noise ratio, but no deterioration in high contrast line pair resolution.

Angiography with a multifunctional line scanning ophthalmoscope

A multifunctional line scanning ophthalmoscope (mLSO) was designed, constructed, and tested on human subjects. The mLSO could sequentially acquire wide-field, confocal, near-infrared reflectance, fluorescein angiography (FA), and indocyanine green angiography (ICGA) retinal images. The system also included a retinal tracker (RT) and a photodynamic therapy laser treatment port. The mLSO was tested in a pilot clinical study on human subjects with and without retinal disease. The instrument exhibited robust retinal tracking and high-contrast line scanning imaging. The FA and ICGA angiograms showed a similar appearance of hyper- and hypo-pigmented disease features and a nearly equivalent resolution of fine capillaries compared to a commercial flood-illumination fundus imager. An mLSO-based platform will enable researchers and clinicians to image human and animal eyes with a variety of modalities and deliver therapeutic beams from a single automated interface. This approach has the potential to improve patient comfort and reduce imaging session times, allowing clinicians to better diagnose, plan, and conduct patient procedures with improved outcomes.

Meridional anisotropy in visual processing: implications for the neural site of the oblique effect

The contention is examined that the oblique effect, i.e., the well-known performance deficit in detecting orientation difference in oblique lines as compared to vertical and horizontal ones, has its origin in a relative deficiency of neurons with obliquely-oriented receptive fields in the primary visual cortex. Psychophysical observations demonstrate a prominent oblique effect also in visual tasks involving widely-separated elements and other stimuli that would elicit little or no response in oriented neurons in the visual cortex. Conversely, some tasks, e.g. position discrimination, exhibit no oblique effect even with short, high-contrast lines. When the comparison with the reference can be accomplished during a single brief exposure rather than sequential ones, thresholds for orientation differences between adjacent contours in oblique meridians are also elevated compared to those in the vertical and horizontal, but to a lesser extent. In one particular texture discrimination task some but not all observers have a conspicuous oblique effect. The discrimination only of the direction of streaming random dots, not of their speed, is poorer for motions in oblique meridians. The findings imply that the neural locus for the oblique effect is more central than the primary visual cortex.

The perception of visual images encoded in musical form: a study in cross-modality information transfer.

This study demonstrates the ability of blind (previously sighted) and blindfolded (sighted) subjects in reconstructing and identifying a number of visual targets transformed into equivalent musical representations. Visual images are deconstructed through a process which selectively segregates different features of the image into separate packages. These are then encoded in sound and presented as a polyphonic musical melody which resembles a Baroque fugue with many voices, allowing subjects to analyse the component voices selectively in combination, or separately in sequence, in a manner which allows a subject to patch together and bind the different features of the object mentally into a mental percept of a single recognizable entity. The visual targets used in this study included a variety of geometrical figures, simple high-contrast line drawings of man-made objects, natural and urban scenes, etc., translated into sound and presented to the subject in polyphonic musical form.

Nanolithography using a laser focused neutral atom beam

Drawing on techniques developed for laser cooling and trapping of neutral atoms, we demonstrate a novel lithographic tool where near‐resonant laser light is used to directly control the position of neutral atoms during deposition. The power of this technique is demonstrated by focusing sodium atoms into narrow lines as they traverse a one‐dimensional standing wave. We have studied the dependence of the linewidth and contrast on the light field parameters, such as detuning, intensity, and interaction length. The dependencies follow the predictions from a simple model and, under optimal conditions, we obtain high contrast lines with a resolution of 45 nm over an area of 0.2×6 mm2. Numerical simulations indicate that further improvement below 10 nm is likely in the near future.

On naming a giraffe a zebra: Picture naming errors across different object categories.

Two experiments examined naming to deadline for pictures of objects from categories with structurally similar or dissimilar exemplars. In Experiment 1, a wider range of naming errors were made for objects from structurally similar categories, consistent with those items having a broader set of structural neighbors. Also, only visual + semantic errors were made to structurally similar objects, whereas modal errors for some structurally dissimilar objects were either purely visual or purely semantically related to targets. In Experiment 2, the names of visual + semantic primes occurred as perseverative responses to objects from both category types. The data fit a cascade model of picture naming, in which errors under deadline reflect the rate-limiting processes affecting naming. The naming of clearly drawn, high-contrast line drawings of objects is usually a relatively effortless task. However, such effortless performance masks a number of interlocking component processes, including those involved in accessing different types of stored knowledge. Techniques are needed to prize apart these processes to understand better the nature of the representations and transmission processes underlying picture naming. Consider what happens when, instead of being allowed sufficient time to recognize the object and retrieve its associated name, subjects are forced to respond rapidly, perhaps with the first name that comes to mind. Can the nature of the errors that occur add to one's understanding of the components of the picture naming system? Response deadline techniques have been used previously on various research topics, including studies of choice reaction time (Pachella, 1974), visual attention (Humphreys, 1981), visual word recognition (Antos, 1979), and shape perception (Humphreys & Quinlan, 1988). Such techniques can provide a useful tool for examining the earliest information that becomes available to response processes. In recent work (Vitkovitch & Humphreys, 1991), we have used a speeded naming technique to examine the interference effects of categorically related primes on the naming of picture targets. Errors to pictures reflected mainly the names of other items from the same category and, in particular, those of previously named related (prime) pictures; that is,

Camouflage by edge enhancement in animal coloration patterns and its implications for visual mechanisms

Animal camouflage patterns may exploit, and thus give an insight into, visual processing mechanisms. In one common type of camouflage the borders of the coloured patterns are enhanced by high contrast lines. This type of camouflage is seen on many frogs and we use it as the basis for speculating about vision in a small, frog-eating snake. It is argued that a simple categorization of intensity profiles, such as that invoked by a mechanism that detects phase-congruence, occurs at an early stage of snake vision. We show that edge-detectors using a phase-congruence strategy will be unable to distinguish between 'natural' step-edges and the enhanced border profiles commonly seen on cryptic animals, and that the camouflage will be effective over a wide range of spatial scales.

A method to test the accuracy of critical dimension measurement systems (CDMS)

As already shown in previous articles different combinations of SEM's with PC-based measurement systems are available to determine the linewidth in the submicron area. One common problem for all these measurement tools is a missing test for measuring the accuracy of these systems. This investigation presents a method describing how the measuring accuracy of these systems can be checked. For this purpose different calibration specimens for light microscopy were tested for usability in low-voltage SEM imaging. Chrome on glass micrometer specimens proved to be especially useful. In comparison with specimens manufactured by photographic methods they combine good imaging qualities with thin high contrast lines with sharp edges. The test for consistant linewidths was done using quantitative Image Analysis, allowing the measurement of a high volume of data quickly and accurately. The resulting value was used as the absolute value for the determination of the accuracy of the CDMS. As such a comparison value was not available before, the accuracy of measurements could only be given within certain confidence limits. This latest method can now prove how accurate the resulting values really are. Initial tests using an AMRAY 1830 SEM and Critical Dimension Measurement System showed a distortion of the measuring results of 0.3% or 0.5% compared with the true value. This means a difference of 0.6 or 0.8 pixels. This result is better than the theoretical accuracy of a CDMS. Using these values, the error of linewidth measurements in the 1 micron range is only about 0.005 μm.

Enhancement of Faint Images from UK Schmidt Telescope Plates

The UK Schmidt Telescope has taken several thousand photographs especially on fine grain Eastman Kodak IIIa-J and IIIa-F emulsions (see Cannon, 1984) which were hypersensitised before exposure in the telescope to improve their ability to record very faint signals.Relatively little work has been done on further post-processing techniques to enhance photographically the faint signal from sources very near to the sky background level. Work is currently being undertaken by Malin (AAO) and others including staff at ROE to enhance faint photographic signals without a corresponding increase in noise, either by making high contrast enlargements from small areas of the original plate, or by making contact copies of the whole plate onto high contrast line material.

Enhancement of visibility of structures in marly chalk: modification of the Bushinsky oil technique

The outwardly monotonous appearance of white chalk is deceptive, yet the several techniques that have been applied to enhance visibility of hidden structures have all had limited success. A technique published by Bushinsky in 1947 produces excellent results with chalks containing a trace of clay minerals. Bushin­sky's technique involves incomplete impregnation of chalk samples with light machine oil, but still better results were obtained by lightly brushing oil onto smoothed surfaces of chalk. The heightened contrast of the structures thereby achieved can be still further increased photographically by use of high contrast line copy film. The results obtained are compared with those using fluorescence by ultraviolet radiation or by merely wetting the chalk. Both contrast and resolution are better with oil than with water or ultraviolet.