bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoreceptor Nonlinearities Can Account for the MacAdam Ellipses
Authors: Alleysson D , Hérault J 
Published: December 2015

Colour perception is known to be nonlinear, as highlighted by D L MacAdam (1942 Journal of the Optical Society of America32 247). He showed that the just noticeable difference (JND) between two colours is not constant and depends nonuniformly on the values of these two colours: under constant illumination, the constant-JND loci, drawn in the xy colour space around various centres, appear as ellipses of different orientations and eccentricities. Though this phenomenon encompasses the whole perception chain, from receptors to higher levels, we show that it can be accounted for mainly by the nonlinearity of receptor transduction. We start from the colorimetric space XYZ defined by the CIE (1931) and its linear transformation into the cone-excitation space LMS, using data from V C Smith and J Pokorny (1996 Color Research and Applications21 5). Then we consider a perceptual colour space obtained by the nonlinear correspondence between the L, M, and S cone inputs and the l, m, and s cone outputs, through a compression law of Michaelis - Menten type, eg: l = L/( L + L0). In this space, the JNDs are circles, drawn on the surface corresponding to the nonlinear transformation of the constant-luminance plane in LMS, around the corresponding centres. By looking at the projections of those circles onto the constant-luminance plane in LMS, and their representations in the colorimetric space xy, we naturally obtain the ellipses of MacAdam. The formulas, fitted to the data, provide the parameters of the LMS-to- lms transformations.
Sensitivity of LGN Neurons in Infant Macaque Monkeys
Authors: Movshon J A , Kiorpes L , Hawken M J , Skoczenski A M , Cavanaugh J R , Graham N V 
Published: December 2015

To understand the neuronal factors limiting visual sensitivity in infant primates, we studied the responses of neurons recorded in parts of the LGN representing the central visual fields in paralysed, opiate-anesthetised 1-week-old and 4-weeks-old macaque monkeys; comparison data were taken from animals older than 6 months. We tested each neuron with achromatic sinusoidal gratings varying in spatial and temporal frequency and contrast, and we also studied the effects of added spatiotemporal white noise. In agreement with earlier reports, we found that neurons in the infant monkeys had relatively poor spatial resolution; sensitivity to high temporal frequencies was also lower than in adults. When tested with gratings of near-optimal spatiotemporal frequency, however, most LGN neurons in the infant monkeys gave brisk and reliable visual responses that were qualitatively similar to those seen in older animals. Spontaneous and evoked response rates and contrast gain were modestly lower in the infants, but response variability was also lower, and therefore statistical measures of sensitivity and susceptibility to masking noise showed little difference between infant and adult neurons. Especially, in the 1-week-old animals, a substantial fraction of neurons lacked spontaneous activity. This resulted in ‘hard’ contrast thresholds not seen in adult animals. As a consequence, masking noise often paradoxically enhanced visual responses in these animals by subthreshold summation, a result not seen in the adults. The maturation of visual responses in macaque LGN consists largely of changes in spatial and temporal scale, accompanied by modest changes in responsiveness and little or no change in sensitivity.
Comparative Analysis of Brightness and Lightness Functions
Authors: Biondini A R , de Mattiello M L F , Spinadell V 
Published: December 2015

A study is reported of twelve chromatic functions and one achromatic function of brightness, and fourteen chromatic functions and one achromatic function of lightness with the aim of establishing the change in the exponent of the functions, a phenomenon considered as being related to: (a) the brightness or lightness response of a subject; (b) the influence of hue and saturation; (c) the level of the background surrounding the stimulus; (d) the Helmholtz - Kohlrausch effect. Different authors agree that these differences are produced by specific contributions of the tristimulus value Y and of chromaticity, the complexity of the problem arising from the fact that chromaticity would be expected to play a different role in each hue. They also agree that the Helmholtz - Kohlrausch effect is independent of the appearance of colour. We show that the variation due to hue and saturation does not prevent the lightness and brightness functions from showing a specific response that permits differentiation between them and other functions, for instance the saturation functions. Finally, we correlate chromatic and achromatic functions by means of the quadratic fluctuation function which allows us to define a self-correlation function. This mathematical analysis extends to all the samples without taking into account their variation in wavelength and purity. It shows the existence of a solid and stable coding system for luminance, a system that achieves stability through its instability, reflected in the variation of the exponent of the functions.
Measuring Object-Centred Attention Based on a Cueing Paradigm
Authors: Lafosse C , Westerhuis M F , Vandenbussche E 
Published: December 2015

Visual attention can be allocated to a location in visual space and/or to a representation of an object in the visual field, independently of their spatial location. In Posner's cueing paradigm, it is assumed that attention is moved to and then engaged at a cued location. If the target appears at an uncued location, attention first has to be disengaged from the cued location before moving to and engaging the target location. On the basis of this paradigm, we designed an experiment to measure the disengaging of attention from objects, independently of location. For this purpose we used the bistable Necker cube that can be perceived as two different object configurations, depending on the position of the front side of the cube (lower left or upper right). The subject was instructed to react when he perceived the Necker cube as a previously presented model configuration, ie a stable cube. Each condition started with a bistable cube (with equal luminance of the ribs) that gradually evolved into the model configuration, by manipulating the luminance of the ribs of the cube. Prior to this the subject was cued by a cube similar to the model in the valid condition and cued by a dissimilar cube in the invalid condition. The results showed a significant difference (F1,10=7.35; p<0.05) between the valid and invalid cue condition, indicating a significant cost for the invalid cue condition. This effect is in accord with the well-known set effect found previously with bistable figures. The difference between the valid and the invalid cue conditions will be interpreted as disengaging attention from an object. Thus, object-based components of attention can be examined by paradigms similar to Posner's paradigm for location-based attention.
Identifying Facial Images in the Visual Periphery
Authors: Mäkelä P , Näsänen R , Rovamo J 
Published: December 2015

Identification sensitivity for four different faces was measured at the fovea and in the periphery to find out whether foveal and peripheral visual performance in this complex spatial task can be made equivalent simply by changing image magnification. Identification sensitivity was measured as a function of image magnification. The lowest contrast for identification was determined by a 4AFC method. Observers indicated via the keyboard which of the four faces was presented on the CRT screen. The images were shown monocularly at the fovea and at 2.5, 5, and 10 deg eccentricities in the nasal visual field of the right eye (eccentricity measured from the right- hand edge of the image). If scaling is successful, the foveal and peripheral sensitivity vs size functions collapse together when shifted along the size dimension only (Watson, 1987 Journal of the Optical Society of America A4 1579). Although the foveal and peripheral sensitivity functions could be superimposed, they did not fully superimpose without also shifting them in vertical direction, as foveal sensitivity at largest sizes was slightly superior to that of any eccentric location. Thus, size scaling alone was not adequate for this task, in agreement with the contrast sensitivity results of Valeton and Watson (1990 Perception19 Supplement, 393). In this identification task, performance deteriorated towards the periphery at approximately the same rate as visual acuity, when the size corresponding to half-maximal sensitivity at each eccentricity was used as a measure.
Plasmas: A New Class of Motion-Induced Brightness Illusion
Authors: Tse P 
Published: December 2015

When a white figure is set in smooth continuous motion against a dark background, a ‘shadowy’ region forms around and behind it, somewhat similar to the wake that a boat leaves in water. Conversely, when a dark figure moves against a white background, this ‘wake’ appears lighter than the background. When several such figures move, these ‘wakes’ can link up in surprising ways. For example, if four white circles of radius r are positioned on a dark background at the vertices of an imaginary square whose width is, say, 4 r, and this imaginary square rotates about its centre, bands darker than the background form between the four circles, linking them through the centre. This ‘black cross’ is nonrigid, and is accompanied by dark ‘wakes’ on the outside of the circles. I call these illusory brightness regions ‘plasmas’. The relation of this effect to other motion-induced brightness illusions is considered. In particular, this effect has different properties than either induced gratings (McCourt, 1982 Vision Research22 119 – 134) or phantom gratings (Tynan and Sekuler, 1975 Science188 951 – 952). Plasmas are not due to retinal afterimages or persistence, since they form in regions never traversed by the moving figure. Nor are they an artifact of the computer screen, since the illusion occurs equally well in displays constructed from paper. Plasmas have the opposite phase relative to the inducing figure, disappear when a figure stops moving, are strongest at high background/inducer contrast, and are most visible when the luminance of the inducers is in the photopic range. Experiments measuring the strength of plasmas as a function of angular velocity and visual angle are described. A model is proposed according to which plasmas are due to a phase lag in luminance-edge induced lateral inhibition.
ASIDT: Adaptive Signal Detection Testing
Authors: Treutwein B 
Published: December 2015

Two-alternative forced choice (2AFC) methods which are routinely used in psychophysics provide criterion-free sensitivity measures but at a high price: 2AFC procedures generally need 2 – 3 times the number of trials than a simple yes/no design to achieve the same level of threshold variability. Similarly, signal detection methods provide measures for criterion and sensitivity, but they require predetermined signal levels for the presented stimuli and also need a large number of trials. ASIDT (adaptive signal detection testing) combines rating responses with an adaptive stimulus placement strategy according to the accelerated stochastic approximation method (see Treutwein, 1995 Vision Research35 2503 – 2522). More specifically, during the course of the experiment the rating responses are collapsed into two groups (yes/no). The border between these two groups is set at the current median of the rating categories actually used by the subject. With the collapsed yes/no responses the stimuli are placed according to accelerated stochastic approximation. This placement strategy is based on very simple rules and distributes the stimulus values asymptotically according to a normal distribution around the median. After the experiment, the rating responses can be used to compute a nonparametric and criterion-free sensitivity measure, the area under the empirical ROC, which is equivalent to the percentage correct in a 2AFC experiment. The usage of ASIDT is demonstrated by psychophysical data.
An Illusory Contour Induces Texture Segmentation
Authors: Peromaa T-L , Laurinen P I 
Published: December 2015

It is known that neurons in V1 can signal a contour between two out-of-phase gratings [Grosof et al, 1993 Nature (London)365 550 – 552]. We demonstrate that this type of illusory contour can segregate areas of surfaces without any luminance, contrast, or textural difference between the areas. We have studied the conditions under which the illusory contour induces texture segmentation. The target was a circular contrast-inverted area (diameter 0.22 – 8.3 deg) in the centre of an isotropic narrow-band noise texture (centre spatial frequency 0.4 – 7 cycles deg−1). Generally, segmentation was effortless in low-spatial-frequency textures but gradually disappeared with increasing spatial frequency although the contour remained visible. In a staircase experiment, the highest spatial frequency allowing segmentation was measured for each target size. The task was to tell whether the stimulus contained an object or just a contour. A negative power function relates the target diameter and the highest spatial frequency allowing segmentation. The visibility of the contour was independent of the target size. The illusory contour ‘captures’ the texture inside. However, the process is spatially limited. In a separate experiment, the subject used a cursor to point out how far from the contour the capture spreads. A negative relationship between the spatial spread and the spatial frequency of the texture was found. These findings are consistent with the idea that low-level mechanisms signalling illusory contours are involved in perceptual scene segmentation.
The Conditions under which Opposing Motion is Seen in Transparency or as Flicker
Authors: Del Viva M M , Morrone M C 
Published: December 2015

We present several examples of moving stimuli comprising several harmonic components that can be perceived either as moving independently, or together as a coherent moving pattern. A simple example is two sinusoidal gratings of equal contrast and spatial frequencies moving in opposite directions that are perceived as a single grating modulated sinusoidally over time (counterphase). However, two square waves drifting in opposite directions, while being a superposition of counterphasing pairs, are perceived as two distinct patterns drifting in transparency one over the other. Intermediate situations such as pairs of counterphase gratings can be perceived alternatively as counterphases or as drifting in two directions. We show that the relative phase of the components plays a fundamental role in whether they group or become transparent. The tendency of a component to become part of a pattern is maximal when the phase relationship is 0 deg, and gradually decreases to a minimum at 90 deg. This agrees quantitatively with previous measurements on different stimuli (paper presented at Del Viva and Morrone, ARVO96), suggesting a common computational mechanism. The data were well modelled by a nonlinear model of motion analysis based on feature tracking, showing sensitivity to the exact degree of nonlinearity.
Separation of Figure from Ground as an Adaptive Image Processing
Authors: Mironov S V , Dudkin K N , Doudkine A K 
Published: December 2015

We define the separation of figure from ground as a visual-attribute-dependent and task-dependent representation of sensory information in higher-level visual processes. A computer model for adaptive segmentation of 2-D visual objects (Dudkin et al, 1995 Proceedings of SPIE 122) was developed in these studies. The description and separation of figure from ground are implemented by spatial frequency filters and feature detectors performing as self-organising mechanisms. The simulation of control processes caused by attention (top - down), and lateral, frequency-selective, and cross-orientation inhibition (bottom - up) determines the adaptive image processing. The first stage is the estimation of input image produced by the analysis of the spatial brightness distribution by algorithms calculating the vector of primary descriptive attributes. These results provide the synthesis of control processes based on several algorithms, each of which transforms descriptive attributes into separate control parameters. The creation of two primary descriptions: ‘sustained’ (contours) and ‘transient’ (fragments with homogeneous intensity), and the selection of feature-detection operators are governed by the complete set of control parameters. The primary descriptions allow formation of the intermediate image description in which similar elements are grouped by identical brightness, colour, spatial position, curvature, and texture according to Gestalt concepts. To divide the image into basic areas and to extract fragments which belong to a putative figure, all these descriptions are combined into the final integrated image representation. The model has been tested on various images.
Top-Down versus Bottom-up Control of Saccades in Texture Perception
Authors: Groner R , von Mühlenen A , Groner M 
Published: December 2015

An experiment was conducted to examine the influence of luminance, contrast, and spatial frequency content on saccadic eye movements. 112 pictures of natural textures from Brodatz were low-pass filtered (0.04 – 0.76 cycles deg−1) and high-pass filtered (1.91 – 19.56 cycles deg−1) and varied in luminance (low and high) and contrast (low and high), resulting in eight images per texture. Circular clippings of the central parts of the images (approximately 15% of the whole image) were used as stimuli. In the condition of bottom - up processing, the eight stimuli derived from one texture were presented for 1500 ms in a circular arrangement around the fixation cross. They were followed by a briefly presented target stimulus in the centre, which in half the trials was identical to one of the eight test stimuli. Participants had to decide whether the target stimulus was identical to any of the preceding stimuli. During a trial, their eye movements were recorded by means of a Dual-Purkinje-Image eye tracker. In the top - down condition, the target stimulus was presented in each trial prior to the display of the test stimulus. It was assumed that the priming with a target produced a top - down processing of the test stimuli. The latency and landing site of the first saccade were computed and compared between the top - down and bottom - up conditions. It is hypothesised that stimulus characteristics (luminance, contrast, and spatial frequency) play a more prominent role in bottom - up processing, while top - down processing is adjusted to the particular characteristics of the prime.
The Dynamics of Perceptual Learning in Different Visual Search Tasks: Psychophysics and Psychophysiology
Authors: Leonards U , Rettenbach R , Sireteanu R 
Published: December 2015

Serial visual search can become parallel with practice (Sireteanu and Rettenbach, 1995 Vision Research35 2037 – 2043). Our purpose was to examine whether psychophysiological indices reflect the changes in reaction time during training. We used targets and distractors that differed either in orientation (‘tilt’), or in local brightness: closed circles with or without an additional line element (‘added line’), or circles with gaps of different width (‘gap’). The subjects’ task was to indicate the presence or absence of a target on a computer screen by immediately pressing a button and pointing to the location of the target if the trial was positive, or raise the hand if negative. No feedback was given. Response time and error rate were recorded. In addition, electrocardiograms, galvanic skin response, respiration rate and amplitude, horizontal eye movements, and electromyograms were monitored. Two naive and two experienced subjects participated in at least 16 experimental sessions. Before training, slopes differed for the three tasks, ranging from parallel search for the feature ‘tilt’ to a very steep serial search for the feature ‘gap’. These differences were reflected in the psychophysiological parameters. Reaction time and error rate decreased continuously with learning, leading to parallel search after prolonged practice for all three tasks (see Nase et al, 1995 Perception24 Supplement, 84). Preliminary results indicate that the psychophysiological measures do not follow the perceptual changes during learning. We conclude that, despite the perceptual parallelisation with practice, the attentional load remains high for initially serial tasks.
Are Angles Transformed into Blobs in Early Vision?
Authors: Kehrer L , Meinecke C 
Published: December 2015

When textures used in visual segmentation experiments are composed of angle elements, these angles seem to be transformed into ‘blobs’ at early stages of visual processing (‘blob hypothesis’; see Meinecke and Kehrer, 1994 Perception & Psychophysics56 326 – 334). These blobs can be imagined as ellipses in which the angles are embedded. Thus, ellipses/blobs are more or less elongated depending on the width of the underlying angle. We tested the blob hypothesis in a psychophysical experiment using two experimental conditions with angle textures. In condition A, subjects had to detect a target texture, in which the resulting blobs had a well-defined orientation, within a background texture, in which the blobs had a less-well-defined orientation. Condition B was identical, except that the target elements became the background elements and vice versa. If angles are really transformed into blobs in early vision, then condition A should yield a better performance than condition B, because it is much easier to detect ellipses among circles than circles among ellipses (Treisman and Gormican, 1988 Psychological Review95 15 – 48). Our results replicated this asymmetry and thus support the blob hypothesis. In a simulation study, in which Gabor filters were used as the input layer in a spatial filter model, we tried to gain a better understanding of the underlying mechanisms. The simulation indicated that the experimentally observed asymmetry might be due to particular features of the target textures, leading to higher Gabor target responses in condition A than in condition B, whereas background responses were very similar in both conditions.