bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Perception of Involuntary Prosaccades in an Antisaccade Task
Authors: Mokler A , Fischer B 
Published: December 2015

In an antisaccade task subjects are required to generate a voluntary saccade to the side opposite to a small visual stimulus. With fixation-point offset preceding stimulus onset (gap) subjects produce some involuntary saccades to the stimulus and correct them by a second saccade. We wanted to know whether the subjects recognised their errors and whether a recognised sequence (error followed by correction) is different from an unrecognised sequence. To test the access to the correction mechanism, subjects were asked in subsequent experiments to produce the error-correction sequence voluntarily (voluntary sequence). We used the gap = 200 ms condition. A valid cue was presented 100 ms before stimulus onset. This manipulation increased the error rate (Fischer and Weber, 1996 Experimental Brain Research109 507 – 512). Subjects indicated errors by key-press. The rate of recognised and unrecognised errors, saccadic size, reaction times (SRT), and correction times (CRT) were determined. Altogether 93 data sets (400 trials each) from 38 subjects were analysed. The mean error rate was 20%, of which 62% went unrecognised. In sessions with high error rates the fraction of unrecognised errors was high. The SRT of the errors ranged from 80 to 170 ms with a strong mode of express saccades at 100 ms. Both types of errors had the same mean SRT of 117 – 119 ms. The unrecognised errors were 0.4 deg smaller. They were corrected after a mean CRT of 95 ms. The recognised errors were corrected after 127 ms; in the voluntary sequence the correction occurred after 217 ms. The CRT distributions differ from each other with the unrecognised errors having an extra peak around 45 ms, suggesting different modes of correction, to which perception has different access. These results raise the question why the large and long-lasting changes of the retinal image escape the conscious perception so often.
When Stereopsis Does Not Improve with Increased Contrast
Authors: Wilcox L M , Hess R F 
Published: December 2015

It is well established that stereoacuity for conventional (1st-order) stimuli improves with increasing contrast, with slopes ranging from −0.5 to −1.0 on log - log axes (Halpern and Blake, 1988 Perception17 483 – 495; Legge and Gu, 1989 Vision Research29 989 – 1004). In the experiments reported here we used a variety of stimuli (Gabor patches, amplitude-modulated gratings, and 1-D noise patches) and tasks (stereoacuity and Dmax) to determine if 2nd-order stereopsis shows a similar square-root dependence, or if the contrast relationship is relatively flat as observed for monocular localisation tasks (Hess and Holliday, 1992 Vision Research32 1085 – 1097). Where possible, stereopsis was assessed with the use of the same stimuli for both 1st-order and 2nd-order stereopsis to ensure that the resulting data would be comparable. In all cases where stereopsis was based on 2nd-order processing there was little or no influence of contrast on performance; the average slope was approximately −0.15. In comparison, more typical slopes near −0.75 were obtained under 1st-order test conditions. The indifference of 2nd-order depth perception to changes in stimulus contrast not only supports the proposed distinctiveness of the two types of processing but places constraints on theoretical and computational models of 1st-order and 2nd-order stereopsis. Further, these data support the proposal that the same nonlinear position estimate is used for monocular localisation of nonabutting targets, and for 2nd-order stereopsis.
Phenomenal Shrinkage and Expansion of Visual Surfaces: Is Amodal Completion a Factor?
Authors: Purghé F , Olivero A 
Published: December 2015

When two figures intersect, two apparently paradoxical size effects take place (Kanizsa, 1979 Organization in Vision chapter 11): (1) the partly occluded figure looks shorter than an identical unoccluded figure, and (2) the modally visible parts of the occluded figure look larger than identical isolated parts. Kanizsa explains such effects as due to amodal completion. Three experiments were carried out by the method of adjustment to test this explanation: two were devoted to the shrinkage effect, and the third one was devoted to the expansion effect. The first experiment exploited the properties of the so-called Helmholtz - Ratoosh law (T-shaped vs Y-shaped junctions) to test whether a figural shrinkage is also present in a pattern in which amodal completion should not occur. The second experiment was aimed at checking whether stereoscopic displacement of the ‘occluded’ figure ‘behind’ or ‘in front of’ the ‘occluding’ one is capable of affecting the amount of shrinkage. In the third experiment the Helmholtz - Ratoosh law was again applied to the expansion. The results of all three experiments converge in showing that the amount of shrinkage of the whole ‘occluded’ figure as well as the ammount of expansion of the ‘modally visible’ parts are not affected by the presence or the absence of amodal completion. We conclude that both the shrinkage and the expansion effects are due to other factors, probably the same factors as those that affect classical optical-geometrical illusions, such as the Oppel - Kundt or the horizontal - vertical illusions.
A Neuromorphic Recurrent Model for Figure-Ground Segregation of Coherent Motion
Authors: Beaudot W H A 
Published: December 2015

A neuromorphic model of the retino-cortical motion processing stream is proposed which incorporates both feedforward and feedback mechanisms. The feedforward stream consists of motion integration from the retina to the MT area. Retinal spatiotemporal filtering provides X-like and Y-like visual inputs with band-pass characteristics to the V1 area (Beaudot, 1996 Perception25 Supplement, 30 – 31). V1 direction-selective cells respond to local motion resulting from nonlinear interactions between retinal inputs. MT direction-selective cells respond to global motion resulting from spatial convergence and temporal integration of V1 signals. This feedforward stream provides a fine representation of local motion in V1 and a coarse representation of global motion in MT. However, it is unable to deal with the aperture problem. Solving this problem requires the adjunction of local constraints related to both smoothness and discontinuity of coherent motion, as well as some minimisation techniques to obtain the optimal solution. We propose a plausible neural substrate for this computation by incorporating excitatory intracortical feedbacks in V1 and their modulation by reciprocal connections from MT. The underlying enhancement or depression of V1 responses according to the strength of MT responses reflects changes in the spatiotemporal properties of the V1 receptive fields. This mechanism induces a dynamic competition between local and global motion representations in V1. On convergence of these dynamics, responses of V1 direction-selective cells provide a fine representation of ‘true’ motion, thus solving the aperture problem and allowing a figure - ground segregation based on coherent motion. The model is compatible with recent anatomical, physiological, and psychophysical evidence [Bullier et al, 1996 Journal de Physiologie (Paris)90 217 – 220].
Perceived Speed of Moving Cyclopean Corrugations Increases with Increasing Disparity Amplitude
Authors: Johns A M , Rogers B J , Eagle R A 
Published: December 2015

In order to investigate how cyclopean motion is coded by the visual system, the points of subjective equality (PSEs) were measured for (i) speed, (ii) spatial frequency (SF), and (iii) temporal frequency (TF) as a function of peak-to-trough disparity amplitude for cyclopean corrugations. Two panels (3.0 deg × 7.0 deg) of dynamic random-dot stereograms were located 0.5 deg on either side of a central fixation spot. Each panel contained a horizontally oriented sinusoidal cyclopean corrugation whose SF, TF, and disparity amplitude were under experimental control. On each trial, the cyclopean corrugations were displaced vertically in opposite directions. Subjects judged which panel contained the higher SF, TF, or speed depending on condition. The reference stimulus was a sinusoidal corrugation with SF=0.4 cycles deg−1, TF=0.8 Hz, speed of 2.0 deg s−1, and peak-to-trough disparity amplitude of 8 min arc around fixation. We found that, as the peak-to-trough disparity amplitude of the test stimulus increased from 2 min arc to 32 min arc, the PSE for speed decreased from 2.21 deg s−1 to 1.67 deg s−1, compared to a reference speed of 2.00 deg s−1. However, across the same levels of disparity amplitude, the PSE for SF remained constant and the PSE for TF varied but with no consistent pattern. Thus, perceived speed increases with increased disparity amplitude. As all levels of disparity amplitude were above threshold, cyclopean speed cannot be detected by a purely ‘feature-tracking’ mechanism. These metamers and the poor TF matching performance suggest that cyclopean speed is coded by a sparse number of temporal mechanisms.
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.
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.
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.
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.