bluuebunny/crossref_metadata_2025_split huggingface dataset:
Asymmetric Masking: Luminance Gratings Mask Second-Order Gratings, but Not Vice Versa
Authors: Schofield A J , Georgeson M A 
Published: December 2015

Human vision can detect spatiotemporal information conveyed by first-order modulations of luminance and by second-order, non-Fourier modulations of image contrast. Models for second-order motion have suggested two filtering stages separated by a rectifying nonlinearity. We explore here the encoding of stationary first-order and second-order gratings, and their interaction. Stimuli consisted of 2-D broad-band static visual noise sinusoidally modulated in luminance (first-order, LM) or contrast (second-order, CM). Modulation thresholds were measured in a two-interval forced-choice staircase procedure. With increasing noise contrast, first-order sensitivity decreased (owing to masking) but sensitivity to contrast modulation increased. Weak background gratings present in both intervals produced order-specific facilitation: LM background facilitated LM detection (the ‘dipper function’) and CM facilitated CM detection. LM did not facilitate CM, nor vice versa, and this is strong evidence that LM and CM are detected via different mechanisms. Nevertheless, suprathreshold LM gratings masked CM detection, but not vice versa. High-amplitude CM masks had little or no effect on CM or LM detection. A broadly tuned divisive gain-control mechanism applied to the first-order filtering stage has been proposed by Foley (1994 Journal of the Optical Society of America A11 1710 – 1719) to account for masking of luminance gratings, and this might also explain the masking of second-order by first-order stimuli. First-order maskers would drive down the effective contrast of the carrier, thus reducing second-order sensitivity. But for second-order maskers the mean contrast, and hence contrast gain, remained constant, independent of modulation depth. Thus second-order gratings would produce no masking effects, as observed.
Colour Constancy in Birds: An Alternative Mechanism?
Authors: Maximov V V , Derim-Oglu E N 
Published: December 2015

When recognising a surface colour, the visual system discounts the illumination, apparently by using some reference surfaces (like a spectrophotometer). To recover the illuminant colour it uses signals from different, sometimes remote, parts of the scene viewed either in sequence or in parallel. As a result, humans and animals fail to recognise the colour of a patch that is locally illuminated with a narrow light beam different in colour from the ambient illumination, but show good colour constancy when the beam envelops the surrounding scene. The results obtained in birds distinguish them from humans and all animals hitherto investigated. The behaviour of hole-dwelling birds was studied in the wild by the method of alternative choice of entrance into experimental nesting-boxes having three entrances marked with coloured stimuli made from papers painted in different shades of blue, grey, or orange (see Maximov and Derim-Oglu, 1996 Perception25 Supplement, 98, and the corresponding WWW site: http://www.digipark.com/science/meta ). The spectral content of the direct sunlight illumination was changed by filters, either locally at the stimuli or over the whole front panel of the experimental box. In such artificial lighting conditions the birds proved to be incapable of using a neighbouring white surface as a sign of the illumination to discount its effect on the colour of objects. These unexpected results can be explained by the ability of animals with colour vision of rather high dimensionality to take recourse to local mechanisms of colour constancy that extract the colour information which is invariant to changes of the illumination, using certain a priori constraints on environmental light spectra. Natural daylight spectra have been shown to satisfy these constraints.
Layout Perception during Simulated Locomotion
Authors: Flückiger M , Baumberger B 
Published: December 2015

Our purpose was to show how the modification of visual information available to moving observers can change the way they perceive their path and the structure of the environments they pass through. Stimulus trials simulated locomotion across a tree-filled plane while the gaze was directed at a particular tree. In the first experiment we varied the angle between the line of gaze and the simulated direction of movement (GMA) between 0° and 20°. In the second experiment we used either inward displacement (ID) of some objects (moving towards the fovea) or other flow patterns. After each trial, participants drew their path or the position of the particular tree on a schematic map of the environment. In the first experiment, with respect to the fixation point, as GMA increased so did the shift in the drawn paths, and we measured a significant correlation between the two. In the second, ID changed the accuracy of depth representation for the most distant objects in the visual field. In conclusion, the strong relation between GMA and the reproduced paths, even though they are discrepant from the true paths, suggests that the maintenance of course in the real world may not be based on a maplike mental representation of one's trajectory. In addition, opposite motions in the same region of the visual field (as encountered with ID patterns), may significantly modify the information used for integrating spatial relationships in the environment. The attractive power of these regions in gaze control may also renew our theoretical interest in selective attention.
Can the Visual System Measure Expansion Rates without using Optic Flow?
Authors: Schrater P R , Knill D C , Simoncelli E P 
Published: December 2015

As an observer moves towards a surface, the visual image of the surface expands over time. Traditional approaches to measuring this expansion rely on computing the divergence of the local flow field. A complementary approach which would work well in contexts with poor flow information would be to measure shifts in the Fourier amplitude spectra of textures over time (analogous to size changes). To test whether the visual system uses the information provided by such a measure, we have created a set of novel stimuli which contain, on average, no local flow. We filtered successive frames of spatiotemporally white noise with band-pass spatial filters whose peak frequency varied in inverse proportion to time. The resulting stimulus is temporally uncorrelated, but contains changes in the spatial Fourier amplitude spectrum consistent with a constant expansion rate. We tested whether subjects could consistently match the expansion rate of such stimuli, which have no local flow information, to the expansion in random-dot kinematograms designed to have no change in their Fourier amplitude spectrum over time. A temporal 2AFC task was employed to find points of subjectively equal expansion between the two types of stimuli. Several rates of expansion were tested and the start and end frequencies in the textured non-flow stimuli were randomised between trials. We found that the matched expansion rates of the non-flow texture stimuli were monotonic and nearly linear with the true expansion rates of the dot (flow) stimuli. Settings were also consistent across different start and end frequencies. The results suggest that the visual system can use the change in the amplitude spectra of textures over time to make judgments about expansion.
Fundamental Comparison of Image Quality Metrics
Authors: Barten P G J 
Published: December 2015

In most image quality metrics (eg MTFA, ICS, SQF, DDD, SQRI) use is made of the modulation transfer function (MTF) of the imaging system and the contrast sensitivity function (CSF) of the human visual system. All metrics usually show a positive correlation with perceived image quality. This does not, however, say much about the correctness of the underlying equations. Defocusing experiments where an image is defocused by one just-noticeable difference can give information about the contribution of different spatial-frequency ranges to image quality. By performing defocusing experiments with images where contrast is also varied, information can be obtained about the dependence of image quality on contrast. In our investigation defocusing measurements from Baldwin (1940), Carlson and Cohen (1980) and Watt and Morgan (1983) were used. Comparison of the results with the fundamental dependence of some image quality metrics on spatial frequency and contrast indicates that only the SQRI (square-root integral) showed the right behaviour with respect to these parameters.
Continuous Use of Perceived Velocity While Hitting Running Spiders
Authors: Brenner E , Smeets J B J , de Lussanet M H E 
Published: December 2015

From previous studies examining how we hit moving targets we concluded that the speed and the direction of the hand are determined independently, the former being based on the perceived velocity of the target and the latter on its perceived position. It is known that the direction in which the hand moves is continuously adjusted on the basis of the perceived target position, with a delay of about 110 ms. In the present study we examined whether the speed of the hand is also under such continuous control, or whether it is determined in advance. Subjects were instructed to hit targets (spiders) as quickly as possible with a rod. They were presented with moving targets that appeared at unpredictable moments on a screen in front of them. Some time within 400 ms of their appearing on the screen, the velocity of the target abruptly changed. We found that this influenced the speed with which the rod hit the target as long as the change occurred at least 200 ms before the hit. Considering that the movement time of the hand was more than 200 ms, the perceived velocity must have influenced the speed of the hand during its motion. We conclude that the speed of the hand is continuously adjusted to maintain its relationship with the speed of the target.
Temporal Phase Affects Spatial Binding in Depth Perception
Authors: Kojima H , Blake R 
Published: December 2015

The temporal linking of spatial information is essential for coherent space perception. We investigated the effect of the temporal phase of flickering ‘inducers’ in depth perception. Stereo half-images were generated on the left and right halves of a large-screen video monitor and viewed through a mirror stereoscope. The half-images portrayed a solid-black vertically oriented bar seen against a white background. Two brackets immediately flanking this bar could be placed in crossed or uncrossed disparity relative to the bar. A pair of thin white ‘bridging lines’ could appear on the black bar, always at zero disparity. Brackets and bridging lines could be flickered either in-phase or out-of-phase. Observers judged whether the brackets appeared in front of or behind the black bar, with disparity varied over trials according to a method of constant stimuli. We found that when bridging lines were absent, the depth location of the brackets was predictably dependent on disparity sign, with a small bias for “behind” judgements owing to occlusion. When bridging lines and brackets flashed in temporal phase, depth judgements were markedly biased toward “in front”; when the bridging lines and brackets flashed out of phase, this bias was much reduced. This biasing effect also depended on the spatial offset of lines and brackets. We conclude that depth perception is strongly influenced by the temporal phase of the spatial information.
The Role of Subcortical Visual Structures in Target Foveation Control
Authors: Novikov G I 
Published: December 2015

The role of subcortical levels—the lateral geniculate body (LGB) and superior colliculus (SC) of cat—in the control of foveation eye movements is described by a model based on our own electrophysiological data. These data include the characteristics of eye movements elicited by local electrical microstimulation of neuronal structures in the LGB and the SC. The model represents a multilevel system forming the program of foveation eye movements by performing the following actions in temporal sequence: determination of the position of the visual target in retinotopic coordinates, determination of its craniotopic coordinates and determination of the direction and calculation of the velocity of the moving visual target. I discuss algorithms and neuronal mechanisms (including electrophysiological data on single neurons and neuronal populations) of subcortical levels of the cat visual system taking part in foveation eye-movement control for stationary and moving visual objects, as well as the role of directional and orientation properties of receptive fields of subcortical neurons in this control.
Visual Discrimination Learning in Monkeys with Bilateral Parietal Cortex Lesions
Authors: Dudkin K N , Chueva I V , Makarov F N , Orlov I V 
Published: December 2015

The characteristics of visual discrimination learning were tested on rhesus monkeys during elaboration of an instrumental reflex after bilateral extirpation of the parietal cortex area 7. The animals were trained to discriminate stimuli with different visual attributes (shape, colour, orientation, size, spatial relationships). Their decisions and motor reaction times were recorded. Bilateral extirpation of area 7 did not influence learning characteristics for shape and colour discrimination. The duration of the learning process and the motor reaction time were shortest with these visual attributes. When monkeys were required to discriminate geometrical figures of different orientations and size, these learning characteristics slightly increased. However, learning to discriminate spatial relationships was dramatically impaired. As a result, the duration of the learning process and motor reaction time significantly increased and the level of correct decisions after training significantly decreased. Visual stimuli associated with identical learning characteristics formed distinct groups in a cluster analysis. These results support the suggestion that area 7 is a structural and functional component of mechanisms involved in evaluation of spatial relationships. The impairment of the learning to discriminate spatial relationships can be explained by a change of learning strategy upon disturbance of this mechanism, associated with visual-vestibular interactions and synchronisation processes which bind distributed neurons across different cortical areas into synchronised assemblies.
Disparity Information in the Peripheral Visual Field for Pattern Perception
Authors: Kaneko H , Bourgoin C 
Published: December 2015

Although it is known that stereo-acuity declines with increasing eccentricity of the targets, it is not clear how we use disparity information in the peripheral visual field for pattern perception. To examine this question, we investigated pattern perception by restricting the area that presented stereo or luminance information in the periphery. We measured the reaction time for recognising a letter defined by binocular disparity or by luminance in a random-dot display. We restricted the area containing the specific information (disparity or luminance) using an eye-contingent window technique. Disparity or luminance information was thus present only inside a window centred on the fixation point. Observers viewed the display with free eye movement. The magnitudes of the disparity and luminance contrast were chosen so as to give the same reaction times when the area containing the pattern information was not restricted. Eye movements were measured by a limbus-tracking system and the signal was fed into a computer for real-time control of the window position. The reaction time increased as the window size decreased. The increase in reaction time, however, was steeper for the stimuli defined by disparity than for the stimuli defined by luminance. We conclude that disparity information in the periphery is used for recognising a pattern and is more effective than luminance information for a given window size.
Volume Perception with Binocular Viewing
Authors: Idesawa M , Iwamoto T , Hara Y , Sakaguchi Y 
Published: December 2015

We reported earlier that the binocularly unpaired region plays an essential role in the perception of the volume of a solid object (Idesawa, 1991 Japanese Journal of Applied Physics30-4B L751 - L754). We have investigated this volume perception using both illusory and physical objects. The illusory objects used in the tests were of two types, either with or without binocularly unpaired contours. The physical objects used as stimuli in the present experiments were half-moon-shaped textured cylindrical objects, one with and one without a binocularly unpaired region. A rectangular probe was placed beyond the object, and subjects were asked to adjust its position in depth until they felt that the probe just touched the object. We found that the chosen depth settings were systematically ‘behind’ the objects with unpaired parts, while they were almost ‘correct’ for the objects without unpaired parts. In the former case, subjects thus had the impression that the volume extended further back. We also found that the rim of an object is important for volume perception, especially for objects without textures. A typical example is an imaginary cone occluding two disks, one a little larger than the bottom surface and placed near the bottom, the other a small one located just beyond the top. A complete illusory cone with volume (just like a ‘Santa cap’) could be seen!
Visual Associative Memory Simulates the McCollough Effect
Authors: Maximov P V , Maximov V V 
Published: December 2015

The McCollough effect (ME) refers to the phenomenon that, after a few minutes' exposure to gratings differing in both orientation and colour, subjects perceive similarly oriented achromatic gratings as if they were tinted with complementary hues. The traditional explanation of the ME as an adaptation of detectors selective for colour and orientation suffers from a number of inconsistencies: (i) the ME lasts much longer than ordinary adaptation, the decay of the effect being completely arrested during a night's sleep, or by occluding the eye for a long time; (ii) the strength of the ME is practically independent of the intensity of the adapting light; and (iii) a set of related pattern-contingent aftereffects discovered later would require, for explanation on similar lines, new detectors specific to other patterns. These properties can be explained, however, in the framework of associative memory and novelty filters. A computational model has been developed which consists of (i) an input layer of two (left and right eyes) square matrices with two analog receptors (red and green) in each pixel; (ii) an isomorphic associative neural layer, each neuron being synaptically connected with all receptors of both eyes; and (iii) an output layer (novelty filter). Modification of synaptic efficacies conforms to the Hebb learning rule. After a few presentations of coloured gratings the model displays the ME, which is slowly destroyed by subsequent presentations of random pictures. With a sufficiently large receptor matrix the effect lasts a thousand times longer than the period of learning. Continuous darkness does not change the strength of the effect. Like the real ME, the model does not display interocular transfer, but with other adapting patterns it shows the disparity-contingent colour aftereffect (thus confirming the connections with both eyes). The model can account for different pattern-contingent colour aftereffects without assuming any predetermined specific detectors. Such detectors are constructed in the course of adaptation to specific stimuli (gratings).
The Assignment of Absolute and Relative Depth in Constructing a 3-D Mental Model from Viewed Orthographic Displays
Authors: Huang S T , Shyi G C-W 
Published: December 2015

Constructing the 3-D mental structure from viewed 2-D orthographic displays may require establishing both the relative depth relation (RD) between adjacent areas in the orthographic displays and the exact magnitude of absolute depth (AD) for a given area. We examined the processes of depth assignment involved in 3-D model construction by asking subjects to mentally imagine the 3-D object portrayed by a pair of orthographic projections, and then choose among four alternative isometrics the one that matched the imagined 3-D model. One alternative corresponded to the previously shown orthographic views (ie, target). The other alternatives were distractors that differed from the target in terms of RD, AD, or both. Results from four experiments show that (a) when subjects mistook a distractor for target, they were more likely to misidentify the distractor sharing the same RD with target but with different AD, than to misidentify the distractor sharing the same AD but with different RD; (b) subjects could shorten their solution time by 40% without greatly compromising their performances when times available for imagining 3-D models were reduced in proportion to those consumed in a self-pacing condition. The implications of these results are discussed in terms of a model in which an observer may try to decide the relative depth prior to figuring out the exact absolute depth, although it is necessary to consider both aspects of depth assignment in the construction of 3-D mental models.
The Tilt Illusion and the Orientation Bandwidth of Primary Level Filters
Authors: Hulsi A , Laurinen P I 
Published: December 2015

Models for pattern discrimination can be applied successfully to simple orientation discrimination tasks. However, the mechanisms underlying long-range spatial effects, such as the tilt illusion, are not well understood. The magnitude of the tilt illusion and its sensitivity to the polarity of the inducers were measured by means of tests with varying orientation bandwidths. The orientation tuning bandwidth of the primary-level filters, whose peak frequency is 1.7 cycles deg−1, was estimated in a 2AFC orientation-discrimination task. The luminance distribution of the stimulus was jointly normal. First, the orientation bandwidth of a single elongated test stimulus was increased by reducing its length-to-width ratio from 7.5:1 to 1.5:1. The orientation discrimination performance rapidly decreased after the ratio became less than 3.5:1, which is in good agreement with the estimates of the shape of the filters (Wilson, 1986 Vision Research26 453 – 469). These optimally shaped stimuli were used as inducers in the tilt illusion experiment. Six 20° tilted inducers were added around the test stimulus at the radial distance of 1.25 deg. When the length-to-width ratio of the test stimulus was varied as in the first experiment, the magnitude of the tilt illusion increased after the ratio was less than 3.5:1. However, the precision of the orientation discrimination when compared to the first experiment did not change. Changing the polarity of the inducers did not affect the illusion. The results suggest that the tilt effects of the inducers are not mediated by the primary-level filters. Rather, strengthening of the tilt illusion as the orientation bandwidth of the test stimulus increases suggests that long-range interactions between second-order orientation mechanisms might underlie the described phenomena.