bluuebunny/crossref_metadata_2025 huggingface dataset:
Gaze-Accuracy during Monocular and Binocular Viewing
Authors: Steinman R M , Forofonova T I , Epelboim J , Stepanov M R
Published: December 2015

Epelboim et al (1996 Vision Research35 3401 – 3422) reported that cyclopean gaze errors were smaller than either eye's during tapping and looking-only tasks. This raised two questions: (i) does cyclopean gaze accuracy require binocular input, and (ii) when only one eye sees, is its gaze more accurate than the patched eye's? Most oculomotorists probably expect an affirmative answer to both. Neither expectation was fulfilled.

The Maryland Revolving Field Monitor recorded, with exceptional accuracy, eye movements of two unrestrained subjects tapping or only looking, in a specified order, at four randomly positioned LEDs, with monocular or binocular viewing. Subjects either tapped with their finger tips naturally, or unnaturally via a rod (2 mm diameter, 1.5 cm long), glued to a sewing thimble. Instructions were to be fast, but make no order errors.

With binocular viewing, cyclopean gaze accuracy was best during looking-only. During natural tapping, gaze errors increased, becoming no smaller than success required. Both tasks were learned equally fast, but as expected, the younger subject (aged 27 years) performed ∼ 40% faster than the older subject (aged 69 years). Unnatural, monocular viewing produced odd results, eg cyclopean gaze error was smallest when only one eye could see in some conditions. Only the older subject served in the unnatural tapping task because the younger's errors were too close to his gaze control limit. The older subject, who was suitable, reduced his cyclopean gaze error by 56%, from 1.4 to 0.9 deg. These results support our claim that the gaze error allowed is adjusted to the visuomotor demands of different tasks.
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.
Human Efficiency in Numeral Recognition
Authors: Näsänen R , O'Leary C
Published: December 2015

Using a forced-choice method, we determined human contrast thresholds for recognising handwritten numerals. Digitised numerals were presented on a computer display with additive white static noise. The numerals were either unfiltered or were filtered to two-octave spatial-frequency bands of different centre frequencies varying from 1.2 to 17.7 cycles/object height. We had ten variations of each numeral representing the handwriting of different persons. Human performance was compared with the performance of an ideal ‘signals-known-exactly’ (template matching) observer, and the results were presented in terms of efficiency. The highest efficiency for the band-pass filtered numerals was about 11% at centre frequencies of 3 – 5 cycles/object. The efficiency declined towards lower and higher centre frequencies so that at 1.2 cycles/object and 18 cycles/object the efficiency was about 4%. The efficiencies for unfiltered numerals were about 10% – 14%, being thus slightly higher than or equal to the highest efficiency of the band-pass filtered numerals. If only a two-octave band of spatial frequencies contributed character recognition, as has been suggested previously, the unfiltered numerals would contain redundant low-frequency and high-frequency information. Band-pass filtered numerals of optimal centre frequency would contain less redundancy, and a larger proportion of contrast energy would be used. Therefore, efficiency for them should have been higher than for unfiltered numerals. Since this was not the case, it seems that human observers are able to use a relatively broad band of spatial frequencies in character recognition.
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.
Active Allocation of Attention and the Motion-Induction Effect
Authors: Iordanova M A , von Grünau M W
Published: December 2015

Motion induction refers to the illusory motion perceived within an extended stimulus (eg a bar) presented shortly after the abrupt onset of an adjacent localised cue. Motion is perceived in the direction away from the cue. The effect may reflect transient attentional activation triggered reflexively by the cue onset. In this study we examined the time course of the illusion at a cue to which attention was allocated deliberately, rather than in a stimulus-driven manner. While maintaining fixation, observers searched for a target cue defined by a unique conjunction of colour and orientation among irrelevant equiluminant distractors sharing the same features. Observers reported the direction of perceived motion within a horizontal bar which interrupted search at different delays, appearing in the middle between two randomly chosen cues. Because equivalent cues primed the bar from both sides, the direction of motion was balanced unless one of the cues was selected. In a related experiment we measured the effects of attention through cost/benefit analysis of detection times to a low contrast spot probing the vicinity of the cue instead of the bar. The incidence of motion induction was above chance at the target cue where reaction times were also reduced relative to nontarget locations. The two effects developed similarly over time, peaking at delays optimal for target selection. Also, active inhibition at irrelevant cues preceded facilitation at the target cue, suggesting that these two processes jointly determine the direction of perceived motion. The converging results from different paradigms support the attentional origin of the illusion.
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.
Goodness of Dot Patterns and Completion Variability: Effects of Equidistance and Collinearity of Dots
Authors: Markovic S
Published: December 2015

Visual patterns that are initially poorly specified can be perceptually completed into different Gestalten (eg dot patterns can impose the perception of different figures). In the present study the following hypothesis is evaluated. If the goodness of initial patterns is high enough (high Prägnanz), then the completion of initial patterns will result in a single Gestalt (high stability of percept). On the other hand, if the goodness is low (low Prägnanz), the completion will result in several Gestalten (perceptual multistability). In experiment 1 subjects estimated the goodness of four sets of initial 8-dot patterns. The distance between the dots was systematically varied. In experiment 2 the variability of completion of the same initial stimuli was examined. Subjects were asked to choose from a given set of figures the one that was most strongly suggested by the exposed initial dot pattern. The entropy, as a measure of the completion variability, was derived from the proportions of the choices of figures. The correlation between goodness estimates (Prägnanz level) and entropy (completion multistability) was significant: the higher the goodness, the lower the multistability of initial pattern completion. The arrangement of dots was an important stimulus constraint of the dependent variables. Increasing the number of equidistant extents between dots increased multistability and decreased goodness. Collinearity of dots induced a decrease of multistability and an increase of goodness.
Measurements of the Relative Tilt of Corresponding Vertical and Horizontal Meridians in the Two Eyes as a Function of Elevation and Eccentricity in the Visual Field
Authors: Ledgeway T , Rogers B J
Published: December 2015

Helmholtz first reported that when the horizontal meridians of the two eyes are aligned, the vertical meridians of the two eyes are tilted outwards (with respect to each other) by approximately 2°. We adapted Nakayama's technique (1977 Proceedings of the Society of Photo-Optical Instrument Engineers120 2 – 9) using the minimal apparent motion of alternating dichoptic images to measure the relative tilt of corresponding vertical and horizontal meridians located up to 20 deg away from the fovea. Observers were presented with the alternating dichoptic images of a pair of dots or a pair of extended lines which had a relative tilt (binocular orientation difference) of between −5° and +5°. The images were alternated at a rate of 0.2 Hz. Observers were asked to select the pair of images which produced the smallest amount of apparent orientation change. The vergence angle of the binocularly visible fixation point was varied between 28 cm and infinity. On the assumption that minimal apparent motion is a valid indicator of binocular correspondence, the corresponding vertical meridians of the two eyes remained offset by around 2 deg even when they were located 20 deg eccentrically. The corresponding horizontal meridians remained approximately aligned even when they were elevated by up to 20 deg. Corresponding horizontal meridians were altered when the vergence angle was changed but corresponding vertical meridians were unaffected for most individuals. With the eyes held in an elevated position, both vertical and horizontal meridians were altered by a similar amount when the vergence angle was altered, indicating a change in cyclovergence.
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.
Binocular Rivalry in Half-Occluded Regions of Coloured Stereograms Where the Background is a Drifting Grating
Authors: Suzuki M
Published: December 2015

Binocular rivalry in half-occluded (HO) regions was studied with coloured stereograms where the background was a drifting grating. The coloured stereograms consisted of a central square-shaped region, a background, and HO regions. The central square-shaped region was coloured green, and was presented in either crossed or uncrossed disparity. The background was a stationary or drifting vertical grating consisting of white and grey bars. The HO regions were coloured blue, and the luminance was fixed or was changed consistently with the drifting grating in the background. Subjects judged the disappearance of the HO regions, and the cumulative time of disappearance was measured during a 30 s period. When the luminance of the HO regions was fixed against the background of a drifting grating, the disappearance time was the same as for the static grating background. However, when the luminance of the HO regions was modulated consistently with the drifting background grating, the cumulative disappearance time was significantly less than when the background was a static grating. These results suggest that the HO regions escape binocular rivalry when they correlate with the background.
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.
Dynamic Visual Performance between the Ages of 4 and 80 Years: Results for 1850 Normal Subjects
Authors: Wist E R , Schrauf M , Ehrenstein W H
Published: December 2015

The effect of age on dynamic visual performance was investigated in a sample of 1850 healthy male and female subjects between the ages of 4 and 80 years with the use of a form-from-motion analogue to the Landolt ring (Wist et al, 1996 Pflügers Archiv431 O23). Within a random-dot display, Landolt rings of the same average luminance as their surrounds become visible only when the dots within the ring are moved briefly while those of the surround remain stationary. Thus detection of gap location is based upon motion contrast (form-from-motion) rather than luminance contrast. With the size and exposure duration of the centrally presented ring held constant, motion contrast is manipulated by varying the percentage of moving dots within the ring (100%, 50%, 30%, and 20%). Subjects reported gap location (top, bottom, left, or right) either verbally, by button press, or moving a joystick. An expected percent correct responses decreased from an average of 90% at 100% motion contrast to 65% at 20% motion contrast. A developmental trend was clear for the age variable with performance improving at all motion contrast levels from the age of 4 to 20 years followed by a plateau and a clear decline after the age of 50 years. Intersubject variability increased appreciably beyond this age, consistent with the hypothesis of a differential decline of dynamic vision with age. Applications of this test to date include the testing of glaucoma patients and truck drivers.
Contrast Polarity Affects Performance after Figure-Ground Coding
Authors: Linnell K J , Humphreys G W
Published: December 2015

Gilchrist et al (1997 Journal of Experimental Psychology: Human Perception and Performance23 464 – 480) proposed that some aspects of grouping are relatively insensitive to variations in contrast polarity between the elements to be grouped. We assessed the contrast-polarity sensitivity of grouping in a visual search experiment. Display elements were corner-brackets arranged at the vertices of regular polygons (see Donnelly et al, 1991 Journal of Experimental Psychology: Human Perception and Performance17 561 – 570), either aligned with polygon sides (strong-grouping condition), rotated through 20° (weak-grouping condition), or rotated through 180° (open condition). The background was grey; on same-contrast-polarity trials, elements were either all white or all black; on opposite-polarity trials, each element was white and black. The task was to detect a target element rotated 180° with respect to the others. With weak grouping present, opposite contrast polarity slowed reaction times dramatically: they were as slow as those to open displays. A second experiment in which display elements were pacmen showed that the contrast-polarity effect on performance is modulated by figure - ground relations: the dramatic effect of contrast polarity in the weak-grouping condition disappeared, presumably because search focused on the uniform grey illusory surface. These results suggest that grouping operates automatically to produce figure - ground coding of displays, but that contrast polarity differences within a figural surface affect the output of these codes to systems concerned with perceptual discriminations.
Figure-Ground Assignment of Stereo-Defined Contours Affects the Ease of Symmetry and Translation Detection
Authors: Sorensen R E , Driver J
Published: December 2015

When figure - ground assignment reverses for a given contour, convexities along it become concavi- ties, and vice versa. Baylis and Driver (1995 Journal of Experimental Psychology: Human Perception and Performance21 1323 – 1342) examined the possible implications of this effect for the perception of symmetry between contours. Using contrast reversal to determine figure - ground assignment, they argued that the ease of detecting symmetry between two contours depends on whether convexities along them match following figural assignment. However, their results might be attributed to the contrast polarity of individual edges instead. We used random-dot stereograms to vary figure - ground assignment for edges while holding contrast polarity constant. By placing the areas on either side of each contour at various depth planes, conditions were created in which the convex parts yielded for related contours either matched or mismatched following figural assignment. Particular depth arrangements which yielded matching convex parts for symmetrical contours yielded mismatching parts for translated contours, and vice versa. The results confirmed that the relative ease of symmetry-detection versus translation-detection depends on the convex parts yielded for each contour following figural assignment. These findings suggest that the perception of symmetry between contours arises only after they have been assigned to a figure on one of their sides, and is based on a higher-level interpretation of each contour in terms of convex parts, rather than lower-level properties of the image.
Colour Mechanisms Underlying Visual Search with Heterochromatic Distractors
Authors: Yamamoto H , Ejima Y
Published: December 2015

We studied the colour mechanisms involved in a visual search task. The test stimulus consisted of a coloured target randomly positioned among heterogeneous distractors of two colours. Colours of the target and distractors were specified in the equiluminous plane; a pair of distractors was set to lie on a circle around the target and characterised by the radius, central angle, and chromatic direction of a right bisector of the chord between the pair. The stimulus was presented briefly, and observers were asked to report whether a target was present. Target detectability quantified by d' depended on the central angle and the chromatic direction of the bisector. The central angle affected the detectability of the coloured target but not that of the white one. The coloured-target detectability decreased and reached chance level with increasing central angle from 0° to 180°. For a fixed obtuse central angle, maxima of the coloured-target detectability occurred at two bisector directions, one orthogonal to the target direction and the other along the target direction. This suggests that only two orthogonal colour mechanisms were at play and they changed with the colour of the target. These results and previous findings that the target was detected preattentively when it was linearly separable from the distractors in colour space (D'Zmura, 1991 Vision Research31 951 – 966; Bauer et al, 1996 Vision Research36 1439 – 1465) may be explained by the same processes, colour selective filters that linearly combine cone signals followed by peak detectors.
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.
Informational Estimates of Neuronal Responses
Authors: Ruksenas O , Urbonavicius A , Petrauskas V
Published: December 2015

We studied responses of visually driven neurons from the associative Clare - Bishop area of the cat cortex. Interspike intervals of neuronal responses were subdivided into four constituents: intervals between all spikes, intervals between spikes inside bursts, intervals between bursts, and intervals between events (in which case it has been assumed that a burst and an isolated spike are events of equal importance). Two informational parameters based on these distributions were calculated: the information capacity of the channel ( F) and the amount of information (entropy H). We found that (1) values for F and H are significantly higher when they are based on intervals between all spikes and intervals between events than when they are based on intervals inside bursts and intervals between bursts; (2) values of F and H are significantly higher for all cases where a neuronal response is present than those for spontaneous activity.
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 Detection of Orientation of Small Objects
Authors: Zanker J M , Davey M P
Published: December 2015

Visual information processing in primate cortex is based on a highly ordered representation of the surrounding world. In addition to the retinotopic mapping of the visual field, systematic variations of the orientation tuning of neurons are described electrophysiologically for the first stages of the visual stream. On the way to understanding the relation of position and orientation representation, in order to give an adequate account of cortical architecture, it will be an essential step to define the minimum spatial requirements for detection of orientation. We addressed the basic question of spatial limits for detecting orientation by comparing computer simulations of simple orientation filters with psychophysical experiments in which the orientation of small lines had to be detected at various positions in the visual field. At sufficiently high contrast levels, the minimum physical length of a line whose orientation can just be resolved is not constant when presented at various eccentricities, but covaries inversely with the cortical magnification factor. A line needs to span less than 0.2 mm on the cortical surface in order to be recognised as oriented, independently of the actual eccentricity at which the stimulus is presented. This seems to indicate that human performance for this task approaches the physical limits, requiring hardly more than approximately three input elements to be activated, in order to detect the orientation of a highly visible line segment. Combined with the estimates for receptive field sizes of orientation-selective filters derived from computer simulations, this experimental result may nourish speculations of how the rather local elementary process underlying orientation detection in the human visual system can be assembled to form much larger receptive fields of the orientation-sensitive neurons known to exist in the primate visual system.
Neurophysiological Contributions to Luminance and Chromatic Mechanisms in a Hyperacuity Task
Authors: Rüttiger L , Lee B B
Published: December 2015

We recently reported (paper presented at ARVO 1997) psychophysical evidence as to contributions of luminance and chromatic mechanism in a hyperacuity task, namely detection of small displacements. Achromatic or chromatic (430, 550, 690 nm) edges were presented on white or chromatic (550 nm) backgrounds, and displacement thresholds measured as a function of luminance contrast. Above 3% (achromatic detection threshold), all conditions yielded nearly identical contrast/threshold curves; we believe a luminance mechanism to be responsible. In chromatic conditions, below 3% contrast, large (>100 s arc) displacements were detectable; presumably chromatic mechanisms are responsible. We have now carried out equivalent physiological experiments. Data were consistent with cells of the magnocellular (MC) pathway underlying the luminance mechanism. Opponent S-cone or parvocellular (PC) cells became responsive to displacements in the chromatic conditions. S-cone cells were very responsive to the 430 nm edge, and responded at low contrasts matching the psychophysical thresholds. L, M-cone opponent cells were responsive to the 690 nm edge, but less so than was expected from the psychophysical data. Our data suggest MC-cells underlie a luminance hyperacuity mechanism. Additional factors (eg cell numerosity) may have to be considered for chromatic spatial mechanisms.
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.
Single Cortical Column in Area 17: The Distribution of Intrinsic Connections
Authors: Alexeenko S V , Toporova S N , Makarov F N
Published: December 2015

Intrinsic connections are one category of neuronal cortical connections, referring to axons that remain within the same cortical area and do not travel in the white matter. Our knowledge about these connections is based on extrapolations of results on the labelling of cells in different cortical layers, but there is no direct information about the complete connectivity of a single cortical column. To study how the population of cells sending axons to the same cortical column is distributed over the cortex we microiontophoretically injected horseradish peroxidase in single cortical columns of area 17 in cat. 3-D reconstruction of the region of labelled cells was performed by using serial frontal brain sections. It was shown that afferents from layer IV cells are short range (up to 0.5 mm) and from the supragranular (II, III) and the infragranular (V, VI) layer cells are long range (up to 5 mm). The regions with labelled cells in the supragranular and infragranular layers sending axons to the very same cortical column lie in register. For columns representing the central visual field, the distribution of labelling (in a tangential plane) is elongated in the mediolateral direction, and for peripheral columns there was a tendency towards elongation in the mediolateral and rostrocaudal directions. Moreover, the majority of labelled cells were located in regions representing peripheral parts of the visual field relative to the injection site. The described connections may represent the substrate for global linking tasks and underlie several psychophysical phenomena, such as meridional and peripheral effects.
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.
Stereo Depth Perception Uses First-Order Phase and Second-Order Position Disparities
Authors: Statham A K , Georgeson M A
Published: December 2015

We examined the nature and variety of cues underlying the use of binocular disparity in depth perception. Stimuli were Gabor patches (Gaussian-windowed sine-wave gratings, 2 cycles deg−1) and horizontal disparities were produced by varying the phase of the carrier grating or the position of the Gaussian envelope (SD=24 min arc), or both. Disparity varied from −180° to +180° of carrier phase (or the positional equivalent) at carrier orientations 0°, 30°, 60° or 90° from vertical. Direction and magnitude of perceived depth were reported in a 2IFC procedure where the comparison interval contained a zero disparity vertical patch. Use of different orientations allowed phase disparity to be distinguished from horizontal position disparity.

Two main conditions were tested. (1) In the ‘patch’ condition carrier and envelope disparity varied together, and perceived depth was found to vary monotonically with positional disparity. When carrier disparity was ambivalent (at ±180° phase disparity) or zero (with horizontal orientation) perceived depth followed envelope disparity, showing that 2nd-order (envelope) disparity alone can produce depth. (2) When carrier disparity was varied with the envelope held fixed, perceived depth and discrimination thresholds depended on phase disparity rather than horizontal position disparity, lending support to the phase-based theory of De Angelis, Ohzawa, and Freeman (1995 Perception24 3 – 31). At the larger crossed disparities (−90° to −180°) depth reversed sign, suggesting a role for occlusion cues as well as phase and envelope disparity in stereo depth coding.