bluuebunny/crossref_metadata_2025 huggingface dataset:
Photochemical charges separation and photoelectric properties of flexible solar cells with two types of heterostructures
Authors: Liu Xiangyang , Wang Shun , Zheng Haiwu , Cheng Xiuying , Gu Yuzong
Published: December 2015

Photochemical charges generation, separation, and transport at nanocrystal interfaces are central to energy conversion for solar cells. Here, Zn2SnO4 nanowires/Cu4Bi4S9 (ZTO/CBS), ZTO nanowires/CBS-reduced graphene oxide (ZTO/CBS-RGO), and bulk heterojunction (BHJ) solar cells were measured. The signals of steady state and electric field-induced surface photovoltage indicate that RGO with high electron mobility can evidently improve the photovoltaic response. Besides, ZTO/CBS and ZTO/CBS-RGO cells exhibit the excellent performance and the highest efficiencies of 1.2% and 2.8%, respectively. The internal relations of photoelectric properties to some factors, such as film thickness, direct paths, RGO conductive network, energy level matching, etc., were discussed in detail. Qualitative and quantitative analyses further verified the comprehensive effect of RGO and other factors. Importantly, the fine bendable characteristic of BHJ solar cells with excellent efficiency and facile, scalable production gives the as-made flexible solar cells device potential for practical application in future.
Note: An automated image analysis method for high-throughput classification of surface-bound bacterial cell motions
Authors: Shen Simon , Syal Karan , Tao Nongjian , Wang Shaopeng
Published: December 2015

We present a Single-Cell Motion Characterization System (SiCMoCS) to automatically extract bacterial cell morphological features from microscope images and use those features to automatically classify cell motion for rod shaped motile bacterial cells. In some imaging based studies, bacteria cells need to be attached to the surface for time-lapse observation of cellular processes such as cell membrane-protein interactions and membrane elasticity. These studies often generate large volumes of images. Extracting accurate bacterial cell morphology features from these images is critical for quantitative assessment. Using SiCMoCS, we demonstrated simultaneous and automated motion tracking and classification of hundreds of individual cells in an image sequence of several hundred frames. This is a significant improvement from traditional manual and semi-automated approaches to segmenting bacterial cells based on empirical thresholds, and a first attempt to automatically classify bacterial motion types for motile rod shaped bacterial cells, which enables rapid and quantitative analysis of various types of bacterial motion.
Dynamic model based on voltage transfer curve for pattern formation in dielectric barrier glow discharge
Authors: Li Ben , He Feng , Duan Xiaoxi , Ouyang Jiting
Published: December 2015

Simulation work is very important for understanding the formation of self-organized discharge patterns. Previous works have witnessed different models derived from other systems for simulation of discharge pattern, but most of these models are complicated and time-consuming. In this paper, we introduce a convenient phenomenological dynamic model based on the basic dynamic process of glow discharge and the voltage transfer curve (VTC) to study the dielectric barrier glow discharge (DBGD) pattern. VTC is an important characteristic of DBGD, which plots the change of wall voltage after a discharge as a function of the initial total gap voltage. In the modeling, the combined effect of the discharge conditions is included in VTC, and the activation-inhibition effect is expressed by a spatial interaction term. Besides, the model reduces the dimensionality of the system by just considering the integration effect of current flow. All these greatly facilitate the construction of this model. Numerical simulations turn out to be in good accordance with our previous fluid modeling and experimental result.
Interfacial charge-induced polarization switching in Al2O3/Pb(Zr,Ti)O3 bi-layer
Authors: Kim Yu Jin , Park Min Hyuk , Jeon Woojin , Kim Han Joon , Moon Taehwan , Lee Young Hwan , Kim Keum Do , Hyun Seung Dam , Hwang Cheol Seong
Published: December 2015

Detailed polarization switching behavior of an Al2O3/Pb(Zr,Ti)O3 (AO/PZT) structure is examined by comparing the phenomenological thermodynamic model to the experimental polarization–voltage (P-V) results. Amorphous AO films with various thicknesses (2–10 nm) were deposited on the polycrystalline 150-nm-thick PZT film. The thermodynamic calculation showed that the transition from the ferroelectric-like state to the paraelectric-like state with increasing AO thickness occurs at ∼3 nm thickness. This paraelectric-like state should have exhibited a negative capacitance effect without permanent polarization switching if no other adverse effects are involved. However, experiments showed typical ferroelectric-like hysteresis loops where the coercive voltage increased with the increasing AO thickness, which could be explained by the carrier injection through the thin AO layer and trapping of the carriers at the AO/PZT interface. The fitting of the experimental P-V loops using the thermodynamic model considering the depolarization energy effect showed that trapped charge density was ∼±0.1 Cm−2 and critical electric field at the Pt electrode/AO interface, at which the carrier transport occurs, was ∼±10 MV/cm irrespective of the AO thickness. Energy band model at each electrostatic state along the P-V loop was provided to elucidate correlation between macroscopic polarization and internal charge state of the stacked films.
Characterization of leakage current mechanisms in long wavelength infrared HgCdTe photodiodes from a study of current–voltage characteristics under low illumination
Authors: Gopal Vishnu , Hu Weida
Published: December 2015

This paper presents an improved method to characterize the current–voltage (I-V) characteristics of a HgCdTe photodiode under low illumination. Such characteristics exhibit relatively small but finite zero-bias minority carrier current. The open circuit voltage of the diode is generally small and remains un-noticed due to inappropriate measurement conditions. These characteristics are often mistaken as the dark characteristics of the diode. It is shown here that these kinds of lowly illuminated characteristics may be characterized by using a recently proposed model to analyze the illuminated I-V characteristics that make use of experimentally observed photo-current due to illumination and the resulting open circuit voltage in modelling the current characteristics of the photodiode. An example of long-wavelength HgCdTe diode's I-V characteristics under low illumination that was previously analyzed as dark characteristics is discussed here to illustrate the improved method and to further emphasize the importance of taking into account the influence of illumination on the current characteristics while investigating the leakage currents in infrared photodiodes. Our results show that, by taking into account the effect of illumination, the agreement between the theory and experiment has significantly improved.
Wideband resonator arrays for electromagnetic energy harvesting and wireless power transfer
Authors: Alavikia Babak , Almoneef Thamer S. , Ramahi Omar M.
Published: December 2015

This work demonstrates the viability of wideband Ground-backed Complementary Split-Ring Resonator (WG-CSRR) arrays with significant power conversion efficiency and bandwidth enhancement in comparison to the technology used in current electromagnetic energy harvesting systems. Through numerical full-wave analysis, we demonstrated the correlation between the topology of the WG-CSRR patch and the electric current distribution over the patch at different frequencies. A comparative study of power harvesting efficiency and frequency bandwidth through numerical analysis was presented where an array of WG-CSRRs is compared to an array of G-CSRRs and an array of microstrip patch antennas. A significant improvement in bandwidth is achieved in comparison to the G-CSRR array reported in earlier work.
Note: Fast compact laser shutter using a direct current motor and three-dimensional printing
Authors: Zhang Grace H. , Braverman Boris , Kawasaki Akio , Vuletić Vladan
Published: December 2015

We present a mechanical laser shutter design that utilizes a direct current electric motor to rotate a blade which blocks and unblocks a light beam. The blade and the main body of the shutter are modeled with computer aided design (CAD) and are produced by 3D printing. Rubber flaps are used to limit the blade’s range of motion, reducing vibrations and preventing undesirable blade oscillations. At its nominal operating voltage, the shutter achieves a switching speed of (1.22 ± 0.02) m/s with 1 ms activation delay and 10 μs jitter in its timing performance. The shutter design is simple, easy to replicate, and highly reliable, showing no failure or degradation in performance over more than 108 cycles.
Development of elasticity sensors for instrumented socks and wearable devices
Authors: Zhang Song , Rajamani Rajesh , Alexander Lee , Sezen Serdar A.
Published: December 2015

Accumulation of fluid in the lower legs occurs due to acute decompensated heart failure, venous deficiency, lymphedema, and a number of other medical conditions. An instrumented sock using an elasticity sensor is developed for the purpose of monitoring lower leg fluid status. The design and sensing principles of the sock are introduced. Two generations of prototype elasticity sensors have been constructed to verify the sensing principles. Their performances are analyzed and compared. Both in vivo and in vitro tests using the fabricated sensor prototypes show promising results.
Direct measurement of second-order coupling in a waveguide lattice
Authors: Keil Robert , Pressl Benedikt , Heilmann René , Gräfe Markus , Weihs Gregor , Szameit Alexander
Published: December 2015

We measure the next-nearest-neighbour coupling in an array of coupled optical waveguides directly via an integrated eigenmode interferometer. In contrast to light propagation experiments, the technique is insensitive to nearest-neighbour dynamics. Our results show that second-order coupling in a linear configuration can be suppressed well below the level expected from the exponential decay of the guided modes.
Perfect Von Kries Contrast Colours
Authors: Whittle P
Published: December 2015

Under certain viewing conditions, the colour of a light in a surround is determined by the vector from the surround to the colour in a 3-D colour space. This behaviour has been explored with a computer graphics tool that allows sets of such vectors to be drawn from two surrounds in any plane in any colour space, and allows the resulting lights-in-surrounds to be compared haploscopically. In a log cone-excitation space contrast colours with the same surround-to-colour vectors match well, over a surprisingly wide range of chromaticities and luminance contrasts. This implies that the contrast colours are determined by the three cone contrasts; the absolute chromaticities and luminances do not matter. Some limits and implications of this behaviour are discussed.
Perceptual Classification Images from Vernier Acuity Masked by Noise
Authors: Ahumada A J
Published: December 2015

Letting external noise rather than internal noise limit discrimination performance allows information to be extracted about the observer's stimulus classification rule. A perceptual classification image is the correlation over trials between the noise amplitude at a spatial location and the observer's responses. If, for example, the observer followed the rule of the ideal observer, the response correlation image would be an estimate of the ideal observer filter, the difference between the two unmasked images being discriminated.

Perceptual classification images were estimated for a Vernier discrimination task. The display screen had 48 pixels deg−1 horizontally and vertically. The no-offset image had a dark horizontal line of 4 pixels, a 1 pixel space, and 4 more dark pixels. Classification images were based on 1600 discrimination trials with the line contrast adjusted to keep the error rate near 25%. In the offset image, the second line was one pixel higher. Unlike the ideal observer filter (a horizontal dipole), the observer perceptual classification images are strongly oriented. Fourier transforms of the classification images had a peak amplitude near 1 cycle deg−1 and an orientation near 25 deg. The spatial spread is much more than image blur predicts, and probably indicates the spatial position uncertainty in the task.
Pointing in Three-Dimensional Space
Authors: Schoumans N , Sittig A C , van der Gon J J D
Published: December 2015

We studied the localisation of objects in three-dimensional space. We had subjects direct a small pointer towards a small goal object, from 20 positions on a virtual sphere around the goal. Images of the pointer and the goal were generated by presenting computer images to the subject's left and right eye alternately. The distance between the goal and pointer was approximately 10 deg arc, the length of the pointer was approximately 2 deg arc. Subjects could manipulate the pointer by pressing specific keys on the keyboard. We tested 7 subjects. The adjustments were repeated 5 – 7 times, which resulted in a cluster of indicated directions for each of the 20 pointer positions and each subject. These clusters appeared to lie in a plane perpendicular to the frontoparallel plane. In other words, the variance in the in-depth component of the adjustments was considerably larger than the frontoparallel component. Subjects showed consistent and individual deviations in the in-depth adjustments. All subjects showed very similar constant deviations in the frontoparallel components of the adjustments. These constant deviations proved comparable to the deviations demonstrated earlier in a three-dot alignment task in the frontoparallel plane. We conclude that the three-dimensional pointing task can be seen as a combination of two independent tasks: an in-depth adjustment and a frontoparallel task.
Depth Illusion by Delayed 3-D Perception (‘Delayed Stereopsis Illusion’): A Novel Way to Determine Computation Times in Human Vision by Depth Reversal in Partially Occluded Moving Objects
Authors: Wolf R , Schuchardt M , Rosenzweig R
Published: December 2015

Viewed through depth-reversing spectacles, nontransparent objects appear to cut ‘gaps’ into a patterned background. In moving objects this gap is seen to extend beyond the occluded area (‘delayed stereopsis illusion’, DSI): Its trailing border appears to lag behind by a precisely measurable distance, indicating a processing time of approximately 0.13 s to accomplish stereopsis [cf Morgan and Castet, 1995 Nature (London)378 380 – 383]. Other than in thigmaesthesia, there is no correction by antedating.

Why is this delay not perceived in normal stereopsis? If an object is moving before some background, the background usually maintains its position; it may be occluded, or not. Depth information thus might be extrapolated to the continuously uncovered regions of the patterned background. Depth reversal demands that the occluded region of the background must jump behind the moving, occluding object. As this object is perceived to retain its distance, the background, as it is getting uncovered, must jump back into the foreground, where it can be perceived only after renewed calculation of binocular depth. The dependence of DSI on eye movements, disparity, velocity, motion direction, surface texture, illuminance, spatial frequency, and fractal dimension of the objects involved is currently being investigated in model systems which allow us to determine processing times of human stereopsis under well-defined conditions.
The Conscious Vision of the Blind
Authors: Zeki S
Published: December 2015

The most fundamental function of the visual brain is to acquire knowledge about the constant, essential properties of the visual world, in conditions in which the information reaching the brain is never constant from moment to moment. This requires the brain to undertake complex operations on the incoming visual signals, discounting all that is not essential for it to acquire knowledge about the world, selecting that which is important, and subjecting the latter to operations that make the brain independent of the continually changing and non-essential information reaching it. One strategy that the brain uses in undertaking this task is that of functional specialisation, through which different essential features, such as motion and colour, are extracted in specialised and geographically distinct visual areas lying outside the primary visual cortex area V1. Our recent psychophysical experiments show that, just as the processing systems for different attributes of vision are separate, so are the final perceptual systems, since different attributes of the visual scene such as colour, form, and motion are perceived at different times, with colour being ahead of motion by about 80 ms, thus leading to a perceptual asynchrony in terms of real time. The end-result of the operations in these individual areas is the acquisition of knowledge. But knowledge can only be acquired in the conscious state. A conscious awareness is therefore the corollary of activity in the specialised areas. Recent experiments using imaging and time resolution methods as well as patients blinded by lesions either in V1 or in more extensive parts of the visual cortex show that the activity in one or a small number of visual areas, without involvement of V1, can give rise to both conscious experience and a crude knowledge about the visual world. This leads us to the conclusion that consciousness itself may be modular.
Psychophysical Studies of Visual Dysfunction in Glaucoma: Lessons Learned and Questions Raised
Authors: Trick G L
Published: December 2015

The study of visual dysfunction in ophthalmic disease is important for both elucidating the pathophysiological basis of visual loss and improving patient care. The application of psychophysical procedures in contemporary glaucoma research illustrates this point. Although achromatic automated perimetry (ie differential luminance thresholds) remains the ‘gold standard’ for the clinical diagnosis of glaucomatous optic neuropathy, psychophysical studies of other visual functions (motion discrimination, blue - yellow perimetry, temporal resolution, and contrast sensitivity) have led to the development of a more comprehensive framework for investigating the mechanisms underlying glaucoma-induced visual impairment. For example, psychophysical studies of the mechanisms mediating visual dysfunction in glaucoma suggest that neurodegenerative changes reduce redundancy in the neural circuitry in a manner that may be selective for, but possibly not specific to, particular neural pathways. In addition, psychophysical studies have significantly advanced our understanding of the nature and scope of visual deterioration in this disease. As a direct result of these studies new clinical tools have been designed which (1) increase sensitivity for detecting early signs of visual impairment, (2) more accurately predict which glaucoma suspects will develop the disease, and (3) provide a more precise metric for both monitoring disease progression and evaluating treatment efficacy (eg in clinical trials). In this presentation I describe the status of our knowledge of visual impairment in glaucoma and highlight the contributions of visual psychophysics to the evolution of this understanding.
Human Brain Regions Involved in Visual Discriminations
Authors: Orban G A
Published: December 2015

We have used simple visual discriminations as a tool to investigate the human visual system with PET and fMRI. In discrimination tasks, stimuli in which an attribute is defined by a cue are presented in a position in the visual field and the subjects compare the stimuli with each other or with a standard. We have manipulated each of these four aspects. Manipulation of stimulus position engages visuo-spatial attention mechanisms in parietal and frontal cortex (Vandenberghe et al, 1996 Brain119 1263 – 1276; 1997 Journal of Neuroscience in press). Manipulation of the cue has revealed the kinetic occipital (KO) region involved in the processing of kinetic contours (Orban et al, 1995 Proceedings of the National Academy of Sciences of the USA92 993 – 997; Dupont et al, 1997 Cerebral Cortex in press). Using luminance-defined patterns presented centrally and contrasting successive orientation discrimination with identification we have demonstrated the involvement of right fusiform cortex in temporal comparison of orientation (Orban et al, 1997 European Journal of Neurosciences9 246 – 259). The same region is involved in spatial comparison of orientation as well as in temporal comparison of speed and direction of random-dot motion. This set of experiments shows that processing in the human visual system depends not only on the attribute used but also on the nature of the task to be performed. The direction and speed discrimination experiments also reveal the involvement of the lingual motion area in these tasks, but surprisingly very little involvement of human MT/V5.
The Development of Multisensory Integration in the Brain
Authors: Wallace M T
Published: December 2015

Multisensory integration in the superior colliculus (SC) of the cat requires a protracted postnatal developmental time course. Kittens 3 – 135 days postnatal (dpn) were examined and the first neuron capable of responding to two different sensory inputs (auditory and somatosensory) was not seen until 12 dpn. Visually responsive multisensory neurons were not encountered until 20 dpn. These early multisensory neurons responded weakly to sensory stimuli, had long response latencies, large receptive fields, and poorly developed response selectivities. Most striking, however, was their inability to integrate cross-modality cues in order to produce the significant response enhancement or depression characteristic of these neurons in adults.

The incidence of multisensory neurons increased gradually over the next 10 – 12 weeks. During this period, sensory responses became more robust, latencies shortened, receptive fields decreased in size, and unimodal selectivities matured. The first neurons capable of cross-modality integration were seen at 28 dpn. For the following two months, the incidence of such integrative neurons rose gradually until adult-like values were achieved. Surprisingly, however, as soon as a multisensory neuron exhibited this capacity, most of its integrative features were indistinguishable from those in adults. Given what is known about the requirements for multisensory integration in adult animals, this observation suggests that the appearance of multisensory integration reflects the onset of functional corticotectal inputs.
Single Units and Sensation: 25 Years on
Authors: Lee B
Published: December 2015

In 1972 Horace Barlow (“Single units and sensation: a neuron doctrine for perceptual psychology?” Perception1 371 – 394) proposed a set of dogmas to guide vision scientists in interpreting neurophysiological data. The 20th anniversary of ECVP is an appropriate occasion to ask if single-unit recordings have really helped us understand the visual system. The answer may be affirmative, but interpreting single-unit data has proved to be much more of a challenge than was anticipated in that early and optimistic era of single-unit recording. I review data from retinal and cortical experiments to illustrate this thesis, and ask if Barlow's dogmas are still relevant to current visual neuroscience.
Organisation and Interrelationships of Functional Maps in Cat and Monkey Striate Cortex
Authors: Shoham D , Hübener M , Bonhoeffer T , Grinvald A
Published: December 2015

Optical imaging of intrinsic signals allows mapping of the cortical functional architecture in vivo at high spatial resolution. The ability to image activity patterns evoked by many different stimuli in the same piece of cortex can provide information on the spatial relationships between different functional maps. Our findings on the organisation of multiple functional maps in cat and monkey striate cortex are reviewed. The main focus is on the recent finding in cat of two subsystems differing in their response to spatiotemporal aspects of the stimulus.

We used grating stimuli of different spatial frequencies in an attempt to verify the existence of spatial frequency columns in cat area 17. Rather than observing a map of continuously changing spatial frequency across the cortical surface we found two distinct sets of domains, one preferring low and one preferring high spatial frequencies. By using different drift velocities we also found that the low-spatial-frequency domains preferred higher speeds than the high-spatial-frequency domains. Comparison of these spatiotemporal frequency domains with the cytochrome oxidase staining pattern revealed that the cytochrome oxidase blobs in cat striate cortex coincide with domains devoted to the processing of the low-spatial-frequency and high-temporal-frequency contents of the visual scene. Together with recent anatomical results these data suggest that spatiotemporal frequency domains are the manifestation of parallel streams in cat visual cortex with distinct patterns of thalamic inputs and extrastriate projections.

In the same experiments we also imaged the orientation preference and ocular dominance maps. We investigated the relationships between these three columnar systems, and compared them to an earlier study of orientation, ocular dominance, and blobs in macaque striate cortex. We found systematic relationships between the three systems. While some of these relationships were much weaker than those found in monkey, the organisational principles are similar.
Effects of Gaze Direction in Vision and Audition
Authors: Ehrenstein W H , Lewald J , Schlykowa L
Published: December 2015

We asked to what extent the respective gaze direction influences (i) the spatial congruence of perceived direction of auditory and visual cues, and (ii) the discrimination of the direction of target motion.

With fixed head position, subjects directed their gaze in various positions and localised auditory targets (band-pass noise, 2 kHz) presented at one of nine positions (straight ahead, or four symmetric positions to the left or right separated by 2.75 deg, respectively). Forced-choice judgements, whether the sound was perceived to the left or right of a visual reference light, show that the azimuth of the sound was perceived as slightly shifted to the left of a visual reference when the gaze was directed to the left, and vice versa. The maximum of this relative auditory - visual shift was 4.7 deg over a range of 45 deg (left or right) of gaze directions.

In (ii), a spot of light started at the centre of a monitor and moved at 2 or 12 deg s−1 leftward or rightward. Subjects reported the direction by pressing a key; their gaze was directed at 0, 8, or 16 deg to the left or right. Mean choice-reaction times increased with increasing gaze eccentricity, but differently depending on stimulus direction and speed: with left fixation they were shorter for leftward than rightward motion; with right fixation they were shorter for rightward motion. This effect was stronger for the slow than for the fast stimulus speed. Thus, facilitation occurs when stimuli move with moderate velocity toward the direction of gaze.

While the auditory-visual shift in (i) may reflect an incomplete transformation of spatial (craniocentric and oculocentric) coordinates as suggested by recordings in the primate midbrain, the results in (ii) conform with reports of specialised units in the posterior parietal cortex (areas LIP, 7a, MST) that, in registering oculomotor position, modulate visual sensitivity.
The LEO-Reading Test: A Set of Nine Reading Charts with M-Units
Authors: Kooijman A C , Beerthuizen J J G
Published: December 2015

Visual acuity, near-distance visual acuity, and reading ability all depend on the minimal angle of resolution. Visual acuity is defined as the inverse of the minimal angle of resolution, measured at a distance of 4 – 6 m, and expressed in units of (min arc)−1. Near visual acuity and reading ability are measured at reading distance. The preferred reading distance is not the same for every subject. A practical way to combine character size and reading distance is to use the ‘M-unit’ for text size and ‘Dioptre’ for the reading distance. For example, a character size of 1 M at a viewing distance of 1 m corresponds to a visual acuity of 1. A character size of 0.20 M at a viewing distance of 25 cm (=4 D) corresponds to a visual acuity of 1/(0.2 × 4)=1.25.

In the rehabilitation institute we had a need for reading charts with different text blocks for repeated testing (OD, OS, OU, and at various illumination levels). Furthermore we wanted text blocks with a comparable layout and reading difficulty. Such reading charts exist in other languages and we preferred to adopt a similar design, together with the M-unit and Dioptre notation. We composed the text and tested the equivalence of text blocks by measuring the reading speed of young (aged 18 – 27 years) and old (aged 60 – 69 years) subjects. We present the resulting set of nine reading charts with a plea for general use of the M-unit and Dioptre notation for near-distance visual acuity and reading ability assessment in visually impaired people.
Does Inverting Text Improve Reading Performance in Homonymous Hemianopes?
Authors: Baker M R , Henderson J , Hill A
Published: December 2015

Anecdotal information from rehabilitation practice of reading performance and low-vision practice suggests that where right homonymous parafoveal field loss impairs reading at the visual-sensory level, an improvement in reading speed can be achieved by inverting the text. This is because whilst left-field loss is considered to impair return eye movements to the beginning of a line, right-field loss is considered to reduce the spatial size of the perceptual window and increase its temporal extent by prolonging fixations times, reducing the amplitudes of saccades to the right, and introducing frequent regressive saccades. Inverting the text was thought to reverse these effects as the leading edge of the perceptual window is ‘returned’ to the sighted field so that in-line saccades can be visually guided.

Here we report that this does not appear to be the case. In our study we measured the eye movements of patients with right homonymous hemianopia and others with peripheral loss due to retinitis pigmentosa as well as normal controls using an infrared video eye-tracker. All groups display a similar proportional prolongation of fixations times, reduction of saccadic amplitude, and proportion of regressive saccades when asked to read inverted text, which suggests a cognitive component of impairment independent of visual field loss in right homonymous hemianopes.
Studying Colour Appearance by the Uniform Scaling of Colour Circles
Authors: Ovenston C A
Published: December 2015

Scaling experiments presented at ECVP 1996 (Ovenston and Whittle, 1996 Perception25 Supplement, 16) demonstrated the importance of the background chromaticity in setting subjective equal-interval colour scales along the L(-M)-cone and S-cone axes of Macleod - Boynton isoluminant chromaticity space.

In the current experiments we also investigate colour scaling but around circles centred on different background chromaticity points. This is done in a logarithmic version of the MacLeod - Boynton diagram, which is much closer to an equal-subjective-interval diagram than the linear version. However, colour circles set with even geometrical spacing in the log diagram do not appear to have even subjective spacing. Preliminary results show that setting hue to even subjective spacing is a convenient and powerful method for studying the role of constant-cone-excitations and opponent-colour axes in determining hue.
Noisy Template Matching: A Model for Detection and Discrimination
Authors: McIlhagga W , Pääkkönen A
Published: December 2015

The detection and discrimination of simple patterns occupies a central place in visual psychophysics. A wide variety of phenomena have been observed in this paradigm, such as: Weber's law; masking (simultaneous, forward, and backward); masking by noise; spatial frequency tuning; orientation tuning; and area summation. We suggest that many of these phenomena can be explained by a simple model which we call ‘noisy template matching’.

In this model, the encoded stimulus is matched to a memorised template. Both stimulus and template are corrupted by additive noise. The template matching operation yields a decision variable, to which more noise is added. This model is very simple, but it has many interesting consequences. It provides qualitative explanations for many of the phenomena mentioned above, and with additional (but we think reasonable) assumptions about lens blur, contrast nonlinearity (Whittle, 1986 Vision Research26 1677 – 1691), uncertainty (Pelli, 1985 Journal of the Optical Society of America2 1508 – 1532), and suboptimal templates, the model also provides good quantitative accounts of these phenomena.
Eye Movements during Geometrical Problem Solving
Authors: Epelboim J , Suppes P
Published: December 2015

Diagrams are used extensively in posing and solving geometry problems. It is likely that strategies that good problem-solvers have developed for looking at diagrams reflect their reasoning about each problem. This suggested that the eye-movement patterns of geometry experts, observed while they solve problems posed with diagrams, are likely to contain new information about their reasoning.

Eye-movement data, collected while subjects solved geometry problems posed as diagrams, were examined. Three subjects participated. Two of the subjects (‘experts’) were skilled at solving geometry problems. The third subject (‘non-expert’) had last solved such problems over 50 years prior to the experiment, and did not know how to proceed on most of the problems.

The eye-movement pattern reflected cognitive operations used to solve each problem. Fixation durations depended, to some extent, on cognitive or perceptual processing of features at each gaze location. For example, fixations were longer when gaze was on the angle in question, than when gaze was on other angles or line-segments. Likewise, saccades were made to features that were being considered, as indicated by verbal protocols. Expert subjects combined simple features into more complex, imaginary structures, as was required to solve the problem. They scanned the areas of the diagram that fell within the imagined contours of these structures. The non-expert did not construct such structures. He only scanned visible features of the diagram.

Variability in durations of fixations and landing positions of saccades was not due solely to the probabilistic nature of the oculomotor processes. Such processes, however, clearly play an important role in determining the eye-movement pattern in this task, as they do in other visually-guided tasks.
Nonlinearities of Near-Threshold Contrast Transduction
Authors: Kontsevich L L , Tyler C W
Published: December 2015

The existence of analytic threshold nonlinearities was probed with a variety of local and extended stimuli. Incremental thresholds were measured by the 2AFC procedure for same-sign and opposite-sign stationary pedestals. In contrast to the dipper effect for same-sign pedestals, subthreshold bumper effects were observed of threshold elevation (up to a factor of 4 in some conditions). The results for local difference of Gaussians (DoG) and 10 cycles deg−1 Gabors were consistent with accurate hard-threshold behaviour. The results for negative DoG (whose increment corresponds to the darkening of the central spot) and 2 cycles deg−1 Gabor profiles revealed a quadratic nonlinearity for one observer and linear transduction for the other. These results repudiate the uncertainty explanation for the steep psychometric function near threshold, and suggest that there are two different hard-wired nonlinearities: one for luminance increments and another for luminance decrements. According to our analysis, in low-spatial-frequency gratings, a contrast change is detected within those bars that become darker; in high-frequency gratings, transient changes are detected in the bars that become brighter.
Complexity of Chinese Ideograms is Related to the Number of Sampling Elements
Authors: Danilova M V , Bondarko V M , Shelepin Y E
Published: December 2015

Two sets of psychophysical experiments were carried out to find a qualitative measure of the complexity of visual images. The stimuli were 15 Chinese ideograms of the same size. In experiment 1, observers were asked to rate the complexity of images. In experiment 2, for each stimulus the threshold size was determined, defined as the smallest size for which the perceived quality of the image was the same as for large (2 deg) stimuli, ie all details were clearly seen and the stimuli had the same contrast. The measured threshold sizes were in the range 7.9 – 27.6 min arc. Analysing the data further, we found that for some ideograms the sizes of the minimal details (strokes, dots) corresponded to the resolution limit (1 min arc). Some ideograms contained parts with parallel stripes forming quasi-gratings. The distances between stripes at threshold were 1.8 min arc which corresponds to the tuning frequency of the highest spatial frequency channel (Wilson et al, 1983 Vision Research23 873 – 882).

The average order of ideograms sorted by degree of complexity was similar to the order according to threshold size. Thus we found a direct correspondence between the complexity of an object and a description in terms of the minimal number of elements needed to preserve the quality of a reduced image. Our results are in agreement with concepts of complexity expressed as a number of details in objects as suggested by Landolt and Snellen, or as a number of spatial-frequency channels as suggested by Ginsburg (1971 IEEE Proceedings 283 – 290).
What Statistics Determine Segmentation of Orientation-Defined Textures?
Authors: Rosenholtz R
Published: December 2015

Beck suggested that texture segmentation is based upon differences in the first-order statistics of stimulus features such as orientation, size, and contrast. However, this theory does not indicate how these differences might be quantified, or what properties of the statistics might be used. Some alternative models postulate that texture segmentation is determined by the responses of spatial-frequency channels, where the channels contain both a linear filtering mechanism and various nonlinearities. Such models do a good job of predicting human performance, but do not give us much insight into what textures will segment, since the comparison carried out by the model is often obscured by the details of the filtering, nonlinearity, and image-based decision processes.

It is suggested here that, for orientation-defined textures (eg in which each ‘texel’ has a single orientation), segmentation is well-described by something like the ‘significance’ of the differences between (1) the mean orientations, and (2) the angular variances of the two textures. The ‘significance’ of the difference in means takes into account the variability in the texture, so that two homogeneous textures with means differing by 30° may easily segment, while two heterogeneous textures with the same difference in mean may not. Furthermore, it is shown that these statistics may be computed in a biologically plausible way, which greatly resembles the typical filter-based approaches to texture segmentation. Thus the connection between statistical theories of texture segmentation and spatial-frequency channel models becomes more transparent.
A Model of Shape Recognition and Categorisation
Authors: Edelman S , Duvdevani-Bar S
Published: December 2015

To recognise a previously seen object, the visual system must overcome the variability in the object's appearance caused by factors such as illumination and pose. It is possible to counter the influence of these factors, by learning to interpolate between stored views of the target object, taken under representative combinations of viewing conditions. Routine visual tasks, however, typically require not so much recognition as categorisation, that is making sense of objects not seen before. Despite persistent practical difficulties, theorists in computer vision and visual perception traditionally favour the structural route to categorisation, according to which forming a description of a novel shape in terms of its parts and their spatial relationships is a prerequisite to the ability to categorise it. In comparison, we demonstrate that knowledge of instances of each of several representative categories can provide the necessary computational substrate for the categorisation of their new instances, as well as for representation and processing of radically novel shapes, not belonging to any of the familiar categories. The representational scheme underlying this approach, according to which objects are encoded by their similarities to entire reference shapes (S Edelman, 1997 Behavioral and Brain Sciences in press), is computationally viable, and is readily mapped onto the mechanisms of biological vision revealed by recent psychophysical and physiological studies.
Peripheral Advantage in Texture Segmentation: The Role of Spatial and Temporal Factors
Authors: Morikawa K
Published: December 2015

Previous studies (eg Kehrer, 1989 Spatial Vision4 45 – 62; Gurnsey et al, 1996 Journal of Experimental Psychology: Human Perception and Performance22 738 – 757) have shown that performance peaks several degrees from fixation in texture segmentation tasks, and performance falls as the target texture moves closer to the fovea or further into the periphery. There are two theories for this phenomenon: (1) neural processing speed in the fovea is slower than in the periphery (Kehrer 1989), and (2) the spatial frequency band of the texture is too low (ie too coarse) for the foveal receptive fields (Gurnsey et al 1996). However, the use of backward masking in previous studies made it impossible to decide between the two factors. The purpose of the present study was to isolate them.

In experiment 1 a new stimulus configuration with backward masking was used, and previous reports were replicated. In experiment 2, the same texture was presented for 110 ms without a mask, but with added random-dot noise. Without limitations on processing time, the mid-peripheral advantage disappeared, which indicated that the previous findings were due to slower neural processing in the fovea. In experiment 3, a new type of texture was devised consisting of pairs of vertical lines with a horizontal offset. The offset was reversed for the target. Performance for unmasked 110 ms presentation was worst near the fovea and improved monotonically up to 12 deg. This peripheral advantage was spatial, not temporal, because it arose from larger receptive field sizes in periphery. When these results are taken together, the present study demonstrates that there are two independent causes for the mid-peripheral advantage in texture segregation.
Suprathreshold Motion Sensitivity and Ocular Dominance
Authors: Arnold-Schultz-Gahmen B E , Ehrenstein W H , Schlykowa L
Published: December 2015

Sensitivity to visual motion was investigated by measuring the time required to deflect a joystick in the direction of movement. The stimulus was a small light spot that moved at 2 deg s−1 for 1 s to the left or right; observation was binocular. Two conditions were tested: (A) a single moving stimulus suddenly appeared 5 deg left or right of fixation; (B) two stimuli were constantly visible at 5 deg left and 5 deg right of fixation before one of them began to move. Walls' (1951 A.M.A. Archives of Ophthalmology45 387 – 412) pointing test and a subset of Coren's (1993 Bulletin of the Psychonomic Society31 1 – 3) laterality questionnaire were used to identify two groups of eight subjects (matched for age, handedness, and gender) with pronounced dominance of their left or right eyes, respectively. The data suggest a higher suprathreshold motion sensitivity (better visuomotor performance) for right-eyed persons who were, on average, faster by 11 ms (A) and by 32 ms (B) than left-eyed persons. Although a similar effect of ocular dominance on suprathreshold motion sensitivity had been shown before [Schlykowa and Ehrenstein, 1993, in Gene - Brain - Behaviour Eds N Elsner, M Heisenberg (Stuttgart: Thieme) page 439], this was for monocular comparison of the dominant versus nondominant eye. Here, however, eye-dominance effects still occur with binocular vision, especially in condition B where motion has to be detected from two mirror-symmetric stimulus locations.
Mistaken Identity: Temporal-Order Biases in the Perception of Speed
Authors: Harris J M , Rushton S K
Published: December 2015

Biases in the perceived speed of a moving stimulus have been observed for various spatial configurations of a motion stimulus (eg Norman et al, 1996 Perception25 815 – 830). In general, psychophysical studies are designed to remove any possible source of bias due to the temporal order of presentation. Here, we examined biases in speed perception between the first and second temporal interval in a 2IFC procedure. The stimulus was a circular patch (∼ 2 deg) containing 50 translating dots. A standard speed was always presented in the first interval (∼ 6 deg s−1), with one of 7 test speeds in the second interval. A range of ISIs (0 – 2.3 s) and stimulus durations (100 – 900 ms) was tested. We also dissociated spatial location (left/right of fixation point) and direction of dot travel (left/right and vertical/horizontal) of the two stimuli, whilst maintaining the temporal separation.

In all cases we found an increase in perceived speed from 1st to 2nd interval and further, the effect was independent of direction, ISI, duration, and the spatial position of the 1st and 2nd stimuli. We can suggest no simple account of the results based upon neural fatigue in motion detectors, temporal sampling windows, or representational momentum. Tentative models are currently being explored with three interval stimuli.
Investigating the Time-Course of Task-Dependent Perceptual Grouping
Authors: Freeman E D
Published: December 2015

At what stage do factors such as task experience and expectation interact with the perception of whole objects? Recent work (Freeman, 1995 Perception24 Supplement, 134; 1996 Perception25 Supplement, 51) suggests that perceptual grouping of ambiguous 1-Whole/2-Wholes stimuli is dependent upon learning and task predictability, as inferred from changes in performance in a Whole - Whole/Whole - Part shape matching paradigm. Thus, subjects seemed able to offset the effect of a stimulus parameter known to influence perceived grouping, in order to see the grouping they had been trained to see or were expecting to see. In the present research the timing of these interactive processes was investigated, with the use of backward masking to take a snapshot of visual processes at different stages in their development.

Stimulus and task-context factors were found to interact even at the shortest masking interval (50 ms), suggesting that top - down knowledge constrains perceptual grouping processes from an early stage onwards. A simple model of the development of 1-Whole and 2-Whole percepts implies two further conclusions. First, task and stimulus factors both seem to work by modifying the rate of development of the alternative percepts. Second, and counter-intuitively, it appears that, given the appropriate task-context and stimuli, it is possible to group the stimulus in several different ways at once. These results shed light on issues concerning the nature of perceptual grouping, and the process by which our experience of objects is brought to bear on our selection of functional perceptual groups.