bluuebunny/crossref_metadata_2025 huggingface dataset:
Can Learning One Grasp Facilitate Novel Grasps?
Authors: Ernst M O , van Veen H A H C , Bülthoff H H
Published: December 2015

We investigated whether knowledge acquired during repetitive grasping can be used to grasp a similar object differing in position or size. We conducted two experiments using a mirror to project a computer-generated image to the location of an object to be grasped. Subjects saw the image until initiation of the grasp but were unable to see either their hand or the real object. The training phase consisted of repetitive grasps to a single cube in a fixed position displaying a corresponding image. In the test phase we used the same cube in different positions but displayed only a small position-marker (experiment 1). In experiment 2 subjects grasped for differently sized cubes in the trained position. To indicate size changes we displayed appropriately sized cubes at a different location. In the subsequent control phase of each experiment subjects saw fully rendered cubes in appropriate positions and sizes instead of the position-marker or size cue.

Performance in the test and control phase was similar for all measured grasp parameters, including maximum preshape aperture, maximum speed, and grasp duration. In experiment 2, in which the size of the cubes changed, variability in grasp duration (±110 ms vs ±40 ms) and maximum preshape aperture (±10 mm vs ±4 mm) was greater in the test phase than in the control phase, indicating increased uncertainty in grasping.

Had subjects learned a single motor routine they would not have been able to grasp so well for objects differing in position or size. Together with our previous results (Ernst et al, 1997, paper presented at ARVO) these findings indicate that subjects can make use of stored representations of an object's position and size to produce an appropriate grasp under open-loop conditions.
Dark Adaptation in Patients with Thyroid Optic Neuropathy
Authors: Lukauskiene R , Jankauskiene J , Mickiene B
Published: December 2015

In patients with thyroid optic neuropathy, vision may deteriorate because of compression of the optic nerve by swollen extraocular muscles. We examined dark adaptation in nineteen patients, aged 25 – 59 years, with thyroid optic neuropathy with an ARP adaptometer. The duration of the disease was less than 1 month in five patients, 1 – 3 months in eight patients, and more than 3 months in six patients. The age-matched control group consisted of twelve healthy people with normal visual acuity.

We found that visual acuity was reduced in fourteen of the patients. In patients with duration of the illness of 1 – 3 months and over 3 months, dark adaptation was impaired. In patients with less than 1 month duration of the disease, all measurements were within normal limits.

The results show that characteristics of dark-adaptation change progressively during thyroid optic neuropathy, thus providing objective and additional information for diagnosis and prognosis. These data are useful in choosing the tactics of treatment.
Visual Memory for Multiple Gabor Targets
Authors: Baker S S , Wright M J
Published: December 2015

Visual memory for spatial frequency in stationary Gabor targets was measured as a function of interstimulus interval (ISI 2 or 8 s), number of targets (2, 3, or 4), and pre-cueing versus post-cueing of the critical target. The width of the Gabor and the initial and final spatial frequency were varied to eliminate confounding variables such as number of cycles, apparent contrast, and initial or final spatial frequency. A signal-detection analysis was employed, in which the subject was required to determine whether the spatial frequency of a selected Gabor target was the same or different over the ISI. The data were analysed by plotting d' as a function of spatial- frequency difference.

The results show only small and inconsistent decreases in d' as a function of the ISI. There was little change in d' in any condition except certain 3 and 4 target post-cueing conditions, where its magnitude was halved. It was expected that pre-cueing should be superior to post-cueing because, although the Gabor displays are the same, effectively only one pre-cued target needs to be retained over the ISI. However, the expected effect did not always occur. In some spatial-frequency conditions, discrimination performance was maintained even for the most difficult condition (4 targets, 8 s ISI, post-cueing). It is concluded that there is a durable representation of stimulus spatial frequency in visual memory. Under optimum conditions, 2 – 4 targets can be remembered for 8 s with minimal change in d'.
Detection Thresholds for Light Pulses Superimposed on Backgrounds with Temporally Modulated Luminance
Authors: Snippe H P , Poot L , van Hateren J H
Published: December 2015

We investigated the effects of sinusoidal modulation of the luminance of a large (17 deg) spatially homogeneous field on detection thresholds for a brief (7.5 ms) light pulse 46 min arc or 17 deg in size. The average luminance of the background field was at a high photopic level (2800 Td) throughout the experiment. Temporal frequency f (0.4 – 200 Hz) and contrast C (0.05 – 0.8) of the background modulation were varied, together with the timing t of the test pulse in the modulation cycle.

As a function of f, thresholds reach maximum around 15 – 20 Hz, and steeply decline at higher frequencies. At frequencies above flicker fusion, thresholds do not depend on t, and are equal to the detection threshold on a constant background with the time-averaged luminance, in accordance with Talbot's law. At frequencies below 15 Hz, threshold elevations above threshold at constant background depend on f as a power law, with a power exponent (0.8 – 1.0) that is close to 1. Also threshold elevation as a function of modulation contrast conforms to a power law, with a similar power exponent (0.8 – 1.0). The effects of t are complex, and depend on both the frequency and the contrast of the background modulation.

Our results yield constraints for models of luminance adaptation and contrast masking. In particular, the results at high frequencies indicate that the first stage of such models should consist of a linear low-pass filtering of the input luminance. The results at low frequency suggest a temporal derivative operation of the resulting signal. We discuss to what extent existing models can explain the dynamics of the measurements.
Detection Efficiency for Gratings with Various Frequency Gradients
Authors: Syväjärvi A , Näsänen R , Rovamo J
Published: December 2015

We investigated the effects of spatial frequency gradients on human grating-detection efficiency. Both polar-circular and vertical cosine gratings of different central spatial frequencies (1 – 4 cycles deg−1) and frequency gradients were used. The local spatial frequency either increased or decreased with the radial distance from image centre. Contrast energy thresholds were determined by a 2AFC method. The gratings were embedded in strong spatial noise, which allowed us to investigate detection performance in terms of efficiency. The experimental results were described as a function of a scale-invariant measure of image complexity ( Z) calculated as Z= Af2, where A is the grating area and f is the highest local spatial frequency of the gradient grating.

The results showed that efficiency behaves similarly for vastly different gratings in visual noise. Efficiency for all spatial frequency gradients obeyed a single function of complexity independently of the central spatial frequency or the steepness of the frequency gradient. At small values of complexity, efficiency was constant, but decreased at higher values of complexity. Thus, the proportion of contrast information used decreased with increasing image complexity. The results can be understood by assuming that the highest local spatial frequencies of the image determine the spatial extent over which the human visual system integrates contrast information of grating images. With increasing highest spatial frequency the extent of the integration area becomes smaller.
Influence of Progressive Lenses in the Retinal Image Quality
Authors: Gispets J , Arjona M , Pujol J
Published: December 2015

Progressive lenses (PL) are widely used to correct presbyopia, a visual dysfunction that affects most of the population aged over 40 years. The methods used to evaluate the optical quality of these lenses are mainly based on ray-tracing and optical bench testing. Psychophysical studies based on measurements of the contrast sensitivity function of human subjects also exist. However, all these methods exhibit important limitations because, in general, they do not take into account the optics of the eye. One of the objective techniques that permits evaluation of the retinal image in-vivo is the double pass method (Santamaria et al, 1987 Journal of the Optical Society of America A4 1109 – 1114). It has been possible to study the retinal image quality for different correcting optical systems, such as contact lenses, with this technique (Torrents et al, 1996 Perception25 Supplement, 112 – 113).

We studied the retinal image quality of the optical system formed by the eye and a progressive lens. The retinal image quality, characterised by the modulation transfer function (MTF), was measured for different observers as a variety of lines of sight that covered a lens diameter of 50 mm. We show the MTF variation as a function of the lens region and the capacity of this technique to characterise these optical systems.
Some New Effects: Phenomenal Glare, Luminous ‘Mist’ and Dark ‘Smoke’
Authors: Zavagno D
Published: December 2015

The impression of glare is caused by a very intense light source. However, here I show that this impression can also be generated with normal light intensities. The strength of the effect depends on the number of elements used to produce it. The elements are 2 cm × 5 cm rectangles. A single horizontal achromatic rectangle is first used on a homogeneous white or black background. From left to right, the brightness of the rectangle varies smoothly from black to white. The left part of the rectangle appears to progressively bend toward the background when the background is black, while the rectangle appears straight and to fade into an apparent white mist near its right side when the background is white. When the background is black, two horizontal rectangles, mirror-shaded from black to white, so that their black ends face each other with a 2 cm gap between them, appear either to bend toward the background or to be straight and to fade into a sort of dark ‘smoke’. When the background is white with the left rectangle varying in brightness from black to white and the right one from white to black, the rectangles look straight with a sort of white glare appearing to come out from the gap. The black ‘smoke’ and the white glare look more compelling when there are four rectangles forming a cross with a central square gap. It can be argued that this and the neon spreading effect are unrelated. Instead, psychophysical experiments suggest that the glare and smoke effects depend on a relation between the grey scale gradient and the background brightness.
Calibration of a Spatiotemporal Discrimination Model from Forward, Simultaneous, and Backward Masking
Authors: Ahumada A J , Beard B L
Published: December 2015

We have been developing a simplified spatiotemporal discrimination model similar to our simplified spatial model in that masking is assumed to be a function of the local visible contrast energy. The overall spatiotemporal sensitivity of the model is calibrated to predict the detectability of targets on a uniform background. To calibrate the spatiotemporal integration functions that define local visible contrast energy, spatiotemporal masking data are required.

Observer thresholds were measured (2IFC) for the detection of a 12 ms target stimulus in the presence of a 700 ms mask. Targets were 1, 3, or 9 cycles deg−1 sine-wave gratings. Masks were either one of these gratings or two of them combined. The target was presented in 17 temporal positions with respect to the mask, including positions before, during, and after the mask. Peak masking was found near mask onset and offset for 1 and 3 cycles deg−1 targets, while masking effects were more nearly uniform during the mask for the 9 cycles deg−1 target.

As in the purely spatial case, the simplified model cannot predict all the details of masking as a function of masking component spatial frequencies, but overall the prediction errors are small.
What Spatial Frames of Reference are Used to Guide Off-Axis Aiming?
Authors: Sowden P T , Davies I R L , Boyles S K , Simpson T J , Skinner L A
Published: December 2015

What spatial frames of reference are used to guide body centred actions such as pointing and aiming? Do observers learn to use body-scaled frames of reference with specific points of origin (eg hip vs shoulder)? Do they extrapolate general information about body scaling? Do they learn about the position of the body (and its individual parts) in absolute space? We investigated these questions using two kinds of aiming: off-axis aiming vs along-axis aiming. Subjects aimed a ‘gun’ (a laser pointer mounted at the end of a stick with a button at the other end) at various targets under three conditions. They practised aiming in one position for 60 ‘shots’ and then changed to a new position and completed another 60 shots. Transfer across position of ‘gun’ in absolute space, across position of body in absolute space, and across position of gun relative to body were assessed. Results suggested that off-axis aiming was controlled by a closed-loop error correction system requiring sight of results for learning to occur. Further, changes in the position of the body in absolute space (from kneeling to standing or vice versa) led to the worst aiming performance. Changes in gun position relative to the body or in absolute space had less effect on aiming accuracy, which suggests that it is not dependent on specific learned sensory - motor linkages. On the basis of these results we propose a preliminary model for off-axis training.
Detection of Chromatic and Achromatic Patterns at Threshold: RT Evidence of Sustained and Transient Mechanisms
Authors: Parry N R A , Murray I J
Published: December 2015

In primates, relatively slow sustained-like physiological mechanisms mediate chromatic processing and rapid transient-like mechanisms mediate low-spatial-frequency achromatic processing. Our objective was to investigate the role of transient and sustained mechanisms in the detection of chromatic and achromatic gratings with the use of a reaction time (RT) paradigm. Following Tolhurst (1975 Vision Research15 1143 – 1149), we constructed RT histograms using near-threshold grating stimuli. Tolhurst showed that, for low-spatial-frequency achromatic patterns, the RT histograms cluster around the onset and the offset of the pattern, indicating transient detection. His onset and offset distributions were consistent with probability theory. With high spatial frequencies, RTs are evenly distributed over the duration of the stimulus presentation, showing the operation of a sustained mechanism.

When we used low-spatial-frequency (0.22 cycle deg−1) isoluminant red - green gratings, the RT histograms were unimodal, revealing detection mechanisms with predominantly sustained characteristics, as expected. RT histograms obtained with low-spatial-frequency achromatic stimuli in our study were bimodal. However, when we compared small and large fields, the shape of the RT histogram varied in a manner which could not be accounted for by a simple probabilistic model. This can be rationalised if onsets and offsets are not equally detectable.
Suprathreshold Contrast Increment Detection is not Affected by Grating Edge-Type
Authors: Melmoth D R , Kukkonen H T
Published: December 2015

We have shown that the spatial frequency components introduced by sharply truncating the edge of a sinusoidal grating do not affect detection thresholds (Kukkonen et al, 1996 Perception25 Supplement, 117). This could be due to the fact that contrast energy at these spatial frequencies is much lower than at the nominal frequency. Any effect upon detection attributable to the broadening of the Fourier spectrum might therefore exert itself most strongly at suprathreshold rather than threshold contrast levels. To establish whether these extra components interfere with performance at higher contrasts, we measured contrast increment thresholds of circular-aperture sinusoidal gratings with a pedestal contrast of 0.5. Gratings were either sharply truncated or Gaussian-edged having a half-contrast diameter equal to that of its corresponding sharp-edged stimulus. Gratings of 0.125 and 0.5 cycle deg−1 were used, each tested with 1 – 8 cycles. There was no significant difference between contrast increment thresholds for the sharp-edged and Gaussian-edged gratings, which were spectrally narrower. The frequency components introduced into the Fourier spectrum by the abrupt edge of the truncated gratings appear to have no effect upon subject performance even in suprathreshold contrast increment detection.
Perception of a Point-Light Walker Produced by Eight Lights Attached to the Back of the Walker
Authors: Sumi S
Published: December 2015

The Johansson demonstration, achieved with point-lights placed on the main joints of a walker, gives a vivid impression of an invisible human being. An experiment was devised to test the degree to which gender and age of an individual could be correctly identified by observing a point-light-walker (PLW).

Eight point-lights were attached to the backs of each of eight actors, four men and four women, aged 18 to 62 years, at the shoulders, hips, knees, and heels. In a dimly lit room, the actors stood on a treadmill and walked for 1 min on an endless belt moving at speeds from 1.0 to 3.0 km h−1. The movements made by the point-lights were recorded with a video camera and projected on a screen (96 cm high and 120 cm wide). The PLW demonstrations were viewed by 144 undergraduates, divided into five groups, at observation distances of 4.8 to 13.3 m. They were asked to identify and write the gender and age of the perceived gait. On average, there was a 74% correct identification of the genders, especially of the PLWs of the older actors, which were 80% or more correctly identified. Recognition of age, however, was less robust and the PLWs were mostly judged as 20 to 40 years old. Of particular interest was that the PLW demonstrations by two actors of about the same age were quite differently judged; one as old and the other as young. Comparison of these two PLWs revealed that the point-lights corresponding to the shoulders and heels moved very differently. The extents of both the horizontal distance of the right shoulder and the vertical distance of the left heel were measured at intervals of 100 ms. When the obtained values were plotted on the abscissa (shoulder) and ordinate (heel), the relation between the movements could be represented as a pattern corresponding to the italic letters 8, O, and D; pattern 8 was typical of the PLWs judged as ‘young’, pattern O as ‘old’, and pattern D as in between. These findings lead to the suggestion that the correlative changes between the movements of point-lights could become a useful aid in the studies of gender and age recognition in the PLWs.
Flicker Fusion Frequency in Ophthalmic Express-Diagnosis
Authors: Golubtsov K V , Orlov O Y
Published: December 2015

The critical flicker fusion frequency (CFF) for full-field illumination is an easily accessible measure for evaluating the functional state of the visual system. A decrease of the CFF is a symptom of some disorder and reason for medical care. Owing to the great number of components of the visual system (which includes the retina, neural pathways, and visual centres), however, diagnosis based on this single measure may be rather uncertain. This is possibly the reason why the diagnostic value of the CFF seems to be underestimated and why corresponding devices are not represented among everyday health evaluation procedures.

We suggest a simple and convenient (even though not precise) device for CFF testing, useful for express-diagnosis of (i) general visual fatigue due to visual strain and (ii) abnormalities related to ophthalmopathology, implying the need of medical care. The simplicity and convenience of the device make it appropriate for monitoring, for example, school pupils in classrooms. A toy-like modification of the device enables testing of pre-school children.

The diagnostic value of simple devices can be increased if the functional differences (relevant to the CFF: colour, movement, etc) of distinct parts of the human visual system are taken into account. Their deviations from the norm can be especially useful for selective diagnosis in some cases. This may be considered when developing further devices for simple express-diagnosis of ophthalmic diseases.
Two New Dynamic Effects: Light Explosion and Night Crash
Authors: Zavagno D , Caputo G
Published: December 2015

Starting from an achromatic display used by Zavagno to study a glare and a ‘smoke’ effect, we show two new dynamic effects that we call (a) ‘light explosion’ and (b) ‘night crash’.

On a uniform white or black background four black or white rectangles (inducers, 1 deg × 5.7 deg) were arranged to form an orthogonal cross with a square gap in its centre. (a) When the luminance of black inducers on a white background is transformed into a smooth gray scale gradient with the lighter ends facing the square gap, a luminous mist with a glare effect is seen. When such a transformation is performed dynamically by changing the gradient from outside to inside (with the outside ends remaining black and the inside changing toward white), a sudden explosion of light is seen. (b) When the luminance of white inducers on a black background is transformed into a smooth gray scale gradient with their darker ends facing the square gap, a sort of dark ‘smoke’ is seen. If such a transformation is performed dynamically by changing the gradient from inside to outside (with the outside ends remaining white and the inside changing toward black), a sudden and instantaneous black diffusion (a sort of night crash) is seen.

Both the light explosion and the night crash effects have an exponential course followed by an immediate drop. Psychophysical data show that both effects depend on an interaction between the lightness of the background, the lightness of the square gap, and the transformation rate of the gray scale gradient.
Spatial Parameters Affecting the Hermann Grid and the Scintillating-Grid Illusions
Authors: Schrauf M , Wist E R
Published: December 2015

The Hermann grid and the scintillating grid are examples of brightness-contrast illusions. The scintillating grid consists of a Hermann grid with bright disks about 1.4 times the diameter of the grid elements superimposed upon the intersections. The resulting scintillation effect can be described as striking illusory spots, darker than the background, perceived as flashing within the bright disks with each flick of the eye. Although the scintillation effect is different from the classical Hermann grid illusion, one prerequisite for its occurrence is the presence of a grid eliciting the Hermann grid illusion (Schrauf et al, Vision Research in press). At the 12th ECVP we showed that the Hermann grid illusion can be reduced by bright diagonals within the squares of the grid which have the effect of suppressing the 45°/135° components of the Fourier spectrum (Lingelbach et al, 1989 Perception18 536 – 537). In a pilot study we successively reduced the length of the diagonals, and found that this suppression works well even if the diagonals are reduced to small tips near the grid intersections. According to Baumgartner's receptive-field account (Baumgartner, 1960 Pflügers Archiv272 21 – 22), such elements should cause additional inhibition, thus decreasing the neuronal discharge rate and corresponding illusory percept. This is not the case: if any illusion is perceived, it is considerably weaker. The strength of the scintillation effect is similarly reduced by this manipulation. Thus the present results cannot easily be accounted for by Baumgartner's model.
Is Rotation of Visual Mental Images a Motor Act?
Authors: Wexler M
Published: December 2015

The relationship between the mechanisms of vision and of visual mental imagery, such as mental rotation, has been well established. The relations between mental rotation and motor action, on the other hand, have hardly been studied, despite the fact that, ecologically, most non-mental rotation is the result of motor actions such as manual manipulation of medium-sized objects. I propose the following motor/imagery hypothesis: transformations of visual mental images are functionally closely related to the planning stages of the motor system. There is a certain amount of indirect support for this hypothesis in the literature. In the present work the motor/imagery hypothesis was tested directly, by means of a dual task paradigm. Subjects performed two tasks simultaneously: the Shepard - Cooper visual imagery task, which involves mental rotation; and a motor rotation (which could not be seen), turning a joystick handle in the plane of the visual image at a previously learned angular speed and direction. The motor/imagery hypothesis predicts a correlation between corresponding features of the two rotations.

The results strongly confirm the motor/imagery hypothesis. The concurrent motor task shifts the classic V-shaped mental rotation RT curve: mental rotation is faster and less error-prone when it is in the same direction as the motor rotation than when it is in the opposite direction. Moreover, there is a strong correlation between the speeds of the two rotations: all else being equal, subjects' mental rotations were slower when their manual rotations were slower, and vice versa.
Poor Recovery of Surface Orientation from VDU Images Predicts Poor Performance in Laparoscopic Surgery
Authors: Gallagher A , Cowie R , Crothers I
Published: December 2015

There are large, and vitally important individual differences in aptitude for laparoscopic (‘keyhole’) surgery. Intuitively it seems likely that an important component is ability to recover the shape of 3-D structures (patients’ internal organs) from displays on a video monitor. The issue was studied empirically with PICSOR, a test based on research reported by Cowie and Byth (1995 Perception24 118 – 119). Subjects adjust a probe, which consists of a rotating arrowhead, until it appears perpendicular to a specified surface in a simple object (a sphere or a cube). Both probe and surface are depicted on a VDU screen. Measures of apparent slope are derived and related to the theoretical slope. Eight trainee surgeons were studied. They completed a battery of simulated laparoscopic tasks and the PICSOR tests. Two measures of performance on PICSOR were derived from simple regressions relating apparent and theoretical slope, R, and the slope of the fitted line. These were used in multiple regressions to predict performance in the simulated laparoscopic tasks. Performance on the PICSOR cubes task predicted performance in simulated surgery ( F2,7=29.5, p=0.0017). Both measures ( R and slope) contributed significantly. Relationships are probably not linear. One subject performed very badly on both PICSOR and simulated operations. If his data are excluded, both low R and high slope would appear to be related to poor laparoscopic performance. The nature of the area makes large-scale studies difficult, but the data suggest that they ought to be conducted.
Judging the Orientation of Human Faces: Effects Induced by Varying the Illumination
Authors: Siebeck U , Troje N F
Published: December 2015

How do people estimate the orientation of other people's faces? We observed that two images of a face seen from the same orientation, but illuminated from different angles, appeared to have different orientations. The first experiment was designed to document and quantify this phenomenon with respect to the average orientation of the face. The images were rendered on a black background that made it impossible to discriminate the shadowed facial parts from the background. We determined the physical orientation shift necessary to compensate for the illumination-induced effect. Results showed that the measured illumination-induced apparent orientaion shift (IAOS) correlates positively with the average orientation of the face and reaches values of up to 9°. This correlation implies that the mechanism is not based on local surface attitude judgements. We propose a model in which the symmetry plane of the face is detected, and then a comparison is made between the visible parts on both sides of this plane. The effect of the shadow occluding parts of the faces would then be responsible for the apparent orientation shift. To test this hypothesis we repeated the first experiment using a background colour that allowed subjects to perceive the true outline of the faces. We found that the IAOS was reduced to values of less than 2° and no longer depended on the average orientation of the faces. The results imply that orientation may be judged by comparing the size of the visible parts of the left and right halves of the face.
Retinal Mechanisms Underlying Pedestal Effects in Brightness Discrimination: A Model
Authors: Donner K , Hemilä S
Published: December 2015

The dependence of the minimal discriminable intensity difference (MDD) of two flashed stimuli on the pedestal (the intensity of the dimmer one) is known to follow a nonmonotonic ‘dipper’ function. When the pedestal is zero, the MDD is by definition identical to the threshold for light detection. Very dim pedestals have little effect on the MDD, but there is a range of fairly dim pedestals, of intensities around the detection threshold, where the MDD decreases with increasing intensity. Beyond that range, the MDD is a monotonically increasing function of intensity. Functions of this type have been observed with spatially very different stimuli.

We propose that dipper functions arise owing to the fact that different aspects of the primary light response of photoreceptors are relevant to near-threshold and suprathreshold visual signals. Decisions near the detection threshold are based on signals determined by the peak amplitude of photoreceptor responses, which for dim stimuli grows linearly with intensity. By contrast, visual signals for clearly suprathreshold stimuli reflect the rate of rise of early parts of the photoreceptor response, tracing only a short segment of the photoreceptor response just after the point where it has reached threshold amplitude. The latter type of signal shows a similar intensity dependence as do psychophysical brightness judgments, starting with a supralinear segment and passing via linearity into a compressive power function at high stimulus intensities (Donner, 1989 Visual Neuroscience3 39 – 51; Djupsund et al, 1996 Vision Research36 3253 – 3264). Discrimination sensitivity is in principle proportional to the derivative of this function. The transition from the ‘peak-amplitude-based’ linear signalling range around detection threshold to the ‘early-rise-based’ signalling range described by the nonlinear brightness function implies a sharp contraction of the response time window. Intensity discrimination improves, because the intensity dependence of the signal scaled by its variability becomes steeper than linear. As pedestal intensity is raised further, however, the MDD begins to increase again, basically in inverse proportion to the decreasing derivative of the brightness function.
Deafness and Attentional Visual Search: A Developmental Study
Authors: Marendaz C , Robert C , Bonthoux F
Published: December 2015

Neurophysiological (epigenetic specialisation of cortical areas) as well as behavioural (sign language, visual control of spatial surroundings) constraints suggest that deaf people should develop heightened abilities of processing parafoveal/peripheral visual information. Electrophysiological (visual event-related potentials) and psychophysical research using visual detection tasks on congenitally deaf adults corroborates this viewpoint (Neville, 1994 The Cognitive Neurosciences 219 – 231). The aim of this study was to examine whether this ability remains when the visual detection task requires a spatiotemporal organisation of attention.

Forty congenitally bilaterally deaf (from a specialised institution) and sixty-four hearing subjects, subdivided into five age groups (from 7 years of age to young adults) performed four visual search tasks. The results showed that the younger deaf children performed dramatically worse than the aged-matched hearing children. This difference in performance between deaf and hearing children, however, disappeared at an age level of 11 years. Deaf adults did not perform significantly better than hearing adults. The data obtained in children have been replicated in a longitudinal study (re-test two years after). We are currently trying to determine which attentional mechanisms are more deficient in young deaf children (spatiotemporal organisation of search, engagement/disengagement of attention, etc) and what underlies the apparent amelioration of their deficit during development.
The Stereokinetic Phenomenon from Two or Three Points
Authors: Komatsu H
Published: December 2015

The stereokinetic phenomenon occurs when certain 2-D patterns are rotated in the frontoparallel plane. Zanforlin explained this phenomenon by the hypothesis of the minimisation of velocity differences. Our visual system minimises relative velocity differences between the various points of the pattern, which determines the apparent height of the stereokinetic cone.

Zanforlin and Vallortigara applied the hypothesis to a rotating straight line or the two end-points of a straight line. They showed that the apparent length of the line does not depend on the absolute physical velocities of the end-points but rather on the relative velocities, and the absolute physical velocities merely affect the apparent position of the line with respect to the plane of the disk.

In the present experiments with two points, the apparent length indeed depended on the relative velocities, but the absolute velocities did not affect the apparent position. The apparent position of the line with respect to the plane of the disk depended on whether or not the centre of rotation was between the two end-points.

Adding one more point gave a triangle that appeared slanted into 3-D space. The shape composed of three points was held constant, even when rotated and slanted. The height of the apparent triangle also depended on the relative velocities.
Experimental Evaluation of the Reliability of the Method of Constant Stimuli
Authors: Dubrovskii V E , Lovi O V
Published: December 2015

Although the method of constant stimuli is commonly used in psychophysical investigations, special statistical procedures for testing its reliability are rarely employed. Measurement errors are usually ignored, and their potential effect on the overall efficiency of the measurement procedure is not taken into consideration. In reality, the decision-making strategy of the subject may change during the course of the experiment, and responses may be correlated.

We suggest a completely nonparametric method for testing hypotheses about a subject's decision-making strategy. It is based on the analysis of contingency tables and includes the method of primary-data grouping. This technique was applied to address two questions: (1) whether the results of a set of experiments, conducted independently of each other, may be considered as statistically equivalent; (2) whether the subject's response depends statistically on his preceding decisions.

Specially designed experiments on discrimination of the length of lines were performed with a large number of untrained subjects. Exploratory analysis of primary data typical for experiments of this kind has revealed some features that are usually not detected by ordinary statistical data processing, but may affect the final results. It appeared that untrained subjects often used a decision-making strategy biased towards the preceding response. This does not seem to be dependent on the personal characteristics of the subject. Some psychophysical procedures in fact encourage subjects to use this strategy.
Vertical Visual-Field Differences in Schematic Persistence for Colour Information
Authors: Heider B , Groner R
Published: December 2015

The functional specialisation in the upper and lower visual fields is related to the distinction between far and near vision, and may parallel differences between the ventral and dorsal processing streams. Here, we studied possible differences in colour processing. According to postulates of Previc (1990 Behavioral and Brain Sciences13 519 – 575), we expected longer persistence and an advantage in colour classification for stimuli presented in the upper visual field. Performance was tested in a modified partial-report task to estimate duration of schematic persistence for colour and verbal information. The targets were letter strings—either red, yellow, blue, or green—presented in three combinations: (a) nonsense strings, (b) congruent colour-words, and (c) incongruent colour-words. Eight targets were simultaneously presented in a circular array for 60 ms. After a variable interstimulus interval (ISI, 0 – 900 ms), a coloured marker was briefly displayed pointing to one of the original target positions, and the participants had to report whether the colours of target and marker were identical or not. The responses were analysed separately for upper and lower visual-field presentations. The verbal content of the targets did not affect performance. There were no differences in performance between the two visual fields. However, analyses of both accuracy and reaction latencies showed significant interactions between visual field and ISI, ie performance decreased at a slower rate in the upper visual field. These results suggest longer schematic persistence for colour stimuli presented in the upper visual field.
Chromatic Cues for Face Detection in Natural Scenes
Authors: Oliva A , Akamatsu S , Schyns P G
Published: December 2015

One of the challenging problems of human and machine vision is the detection of objects against complex backgrounds. Our research addresses the question of how faces can be very quickly detected in naturalistic scenes on the basis of luminance and chromatic cues. Although luminance information varies with pose and illumination differences, chromatic information is by and large invariant under these transformations. Hence, chromatic information might be a very powerful cue for segmentation and detection.

We compared faces of different pigmentation against background scenes of different colours. Specifically, colour histograms were computed in a perceptually uniform colour space (L*u*v*). We computed the Euclidian distances between the averages of the colour histograms of faces and scenes in L*u*v*. This metric was used to calibrate the contrast between face and scene colour in the experimental design. In a face detection task, subjects saw faces against scene backgrounds at a different distance in colour space. Each combination face - scene was presented for 120 ms (to prevent saccadic explorations), and the subject's task was to indicate whether or not a face was present. Controls involved face - scene pairs on an isoluminant background. Results revealed that luminance information did not affect detection on the basis of chromatic cues. Importantly, the metric of detectability in L*u*v* space between scene and faces predicted reaction times to detection.
Fusion of Visual and Proprioceptive Information about Hand Position Prior to Movement
Authors: Desmurget M , Rossetti Y , Prablanc C
Published: December 2015

The problem whether movement accuracy is better in the full open-loop condition (FOL, hand never visible) than in the static closed-loop condition (SCL, hand only visible prior to movement onset) remains widely debated. To investigate this controversial question, we studied conditions for which visual information available to the subject prior to movement onset was strictly controlled. The results of our investigation showed that the accuracy improvement observed when human subjects were allowed to see their hand, in the peripheral visual field, prior to movement: (1) concerned only the variable errors; (2) did not depend on the simultaneous vision of the hand and target (hand and target viewed simultaneously vs sequentially); (3) remained significant when pointing to proprioceptive targets; and (4) was not suppressed when the visual information was temporally (visual presentation for less than 300 ms) or spatially (vision of only the index fingertip) restricted. In addition, dissociating vision and proprioception with wedge prisms showed that a weighed hand position was used to program hand trajectory.

When considered together, these results suggest that: (i) knowledge of the initial upper limb configuration or position is necessary to plan accurately goal-directed movements; (ii) static proprioceptive receptors are partially ineffective in providing an accurate estimate of the limb posture, and/or hand location relative to the body, and (iii) visual and proprioceptive information is not used in an exclusive way, but combined to furnish an accurate representation of the state of the effector prior to movement.
Perception of Slope in Photographs
Authors: Huber J W , Davies I R L
Published: December 2015

Perceptions of characteristics of space such as slope, distance, and depth are frequently inaccurate, both in the real world and in pictures. We carried out experiments to study factors that influence the accuracy of perceived slope in photographs. Slopes varied in angle from 5° to 45° inclinations against the horizontal, and in the information available to the observer (outline shape and texture characteristics). We found that perceived slope is correlated with real slope ( r=0.99), but that observers consistently overestimate slope. The latter depends not only on the available information, but also on the focal length of the lens with which slopes were photographed. Overestimation is less pronounced for the wide-angle lens compared to the standard lens. A comparison of free viewing and viewing from the correct station-point showed that the latter leads to less overestimation of slope. Since the viewing distance was too far under free viewing, the results are compatible with geometrical optics. In a further experiment the effects of magnification and minification were studied by deliberately viewing the photographs from fixed points closer or further away than the station-point; this led to an increase and decrease in overestimation, respectively. Finally, results are frequently dependent on task characteristics: magnitude judgements of photographs without an anchoring point can only be accurate to a level of scale. Thus using an action-based matching task may lead to more accurate slope perception. We therefore carried out a comparison experiment using a matching task to check for the generality and action-dependence of our results. Practical implications for the use of photographs as surrogates for natural viewing are discussed.
Motion Integration over Time and Space
Authors: Takahashi N , Groner R
Published: December 2015

The effect of temporal and spatial overlap on globally coherent motion was studied. Two lines oriented 60° and 300°, respectively, moved horizontally, creating the perception of either an integrated coherent motion on the horizontal axis, or two distinct component motions orthogonal to each line. The overlap of presentation time was varied: 100% (simultaneous), 50% (partial overlap), and 0% (successive). With respect to the spatial condition, the two lines were presented (1) superimposed in a single aperture, (2) in two adjacent apertures, or (3) in two distant apertures.

We found that, when the lines were presented simultaneously, the percentage of perceived coherent motion was consistently high, regardless of spatial condition. However, when temporal overlap was lower, the percentage of perceived coherent motion decreased according to the number of apertures and their distance. In the 0% condition there were fewer than 50% coherent motions reported, even in the single-aperture condition. An effect of the intersection of the two lines was observed in the 50% condition, but not in the 100% condition. These and other findings suggest that timing is the most critical factor, and spatial effects, as expressed by the distance between the lines and by the intersections, play a less important role.
Velocity Threshold for Relative and Uniform Motion
Authors: Shioiri S , Ito S , Yaguchi H
Published: December 2015

We measured velocity thresholds for relative and uniform motion as functions of spatial frequency and contrast. Stimuli were two horizontal bands on top of each other, both filled with vertical sinusoidal gratings. The gratings drifted either to the right or to the left, in opposite directions in the relative-motion condition but in the same direction in the uniform-motion condition. Observers had to report the direction of motion, and the velocity was varied until a velocity threshold was obtained. The results showed that the shapes of the threshold function plotted against spatial frequency are quite different for uniform and relative motion. The threshold for relative motion had a minimum at around 5 cycles deg−1, whereas the threshold for uniform motion had no such minimum, at least at higher contrasts (10% or higher). The difference was unclear for lower-contrast stimuli, however. The threshold profile as a function of contrast was also different between relative and uniform motion. Although the threshold decreased with increasing contrast in both cases, this dependence saturated at around 10% contrast for uniform motion, while it continued up to the highest contrast (85%) for relative motion. This difference held for all the spatial frequencies examined (from 0.75 to 12.1 cycles deg−1). The results suggest that the detection mechanisms for relative motion and uniform motion are different.
Visual Motion Induces Effector Movement
Authors: Nattkemper D
Published: December 2015

A left-hand response to a left-hand stimulus is faster than a right-hand response to the same stimulus, even when spatial location is irrelevant to the task at hand. The existence of this spatial stimulus-response correspondence effect suggests that spatial properties of actions to be performed can be pre-specified by spatial properties of perceived events, so that actions are induced by perceptual content. If this view is correct, one should be able to show that not only spatial positions of actions can be pre-specified by properties of perceived events, but other features of actions as well. Specifically, I attempt to show that the direction of a to-be-executed movement can be specified by the direction of a moving stimulus.

To study this question a variant of the Simon paradigm was developed: subjects were required to monitor a spot-like stimulus moving from left to right or from right to left on a display. At some point in time the spot would change its colour (from white to blue or red) and the subject had to respond differentially to the respective colour. Two aspects of this situation were varied. First, the type of the action-relevant signal was varied: it could either be a dynamic moving signal or a static non-moving one. Second, the type of response was varied: subjects were required to respond to the colour either with a dynamic response (moving a stylus to the left or right) or with a more static response (pressing a button on the left or on the right).