bluuebunny/crossref_metadata_2025 huggingface dataset:
Successive versus Simultaneous Processes in the Recognition of Visual Patterns
Authors: Soliuñas A , Guriniene O
Published: December 2015

In earlier experiments with known nonverbal figures that subjects had to memorise, we found that, at the beginning of practice, recognition probability fell with increasing number of elements in a figure. Thus, the recognition process obeyed the principle of successiveness (Guriniene, 1993 Perception22 Supplement, 50 – 51). In order to localise the successiveness at the lower levels of visual information processing, we investigated how the recognition probability for unknown patterns depended on their complexity. Test patterns were nonverbal geometrical figures consisting of four, five, six, seven, or eight vertical and horizontal line-segments. The sequence of each trial was as follows: a sound signal for attention fixation; the test pattern (10 ms); an individually determined interstimulus interval (20 – 125 ms); the masking pattern (200 ms); a pause (0 s, 0.5 s, 1.5 s, 2.5 s, or 4.5 s); three sample patterns. Subjects were asked to identify which one of the three sample patterns presented was the test figure.

No dependence of the recognition probability of unknown figures on their complexity was found. We suppose that, in our experimental situation, the feature extraction from the stimulus is a simultaneous process, but the matching of extracted features with information from long-term memory is carried out successively.
Atmospheric Boundaries in Lightness Perception
Authors: Adelson E H , Somers D C
Published: December 2015

In judging the lightness of a surface, an observer must estimate and discount the optical viewing conditions: these include illumination level, haze, and interposed filters. The physical effects can be captured in terms of additive and multiplicative factors, which we call ‘atmosphere’. Local atmosphere can be estimated by gathering gray-level statistics over a local window. If the window is too small, the statistics will be impoverished. If the window is too large, it may encompass multiple atmospheres, making the statistics unreliable. We find evidence that the visual system imposes limits on the size and shape of the window, in accord with configural cues that signal atmospheric boundaries. Junctions with proper gray-level arrangements offer powerful cues to atmospheric boundaries; T-, X-, and psi-junctions are especially important. By combining statistics and configural cues, we have generated new lightness illusions that are much stronger than those seen in typical simultaneous-contrast displays. By changing the junctions we can also generate illusions that are quite weak, also in accord with the model.
From Contour to Texture: Static Texture Flow is a Strong Cue to Surface Shape
Authors: Knill D C
Published: December 2015

Contours projected from geodesic boundaries of developable surfaces (as are formed by folding and twisting flat surfaces) are particularly salient cues to 3-D surface shape. Textures which are strongly anisotropic (highly oriented) provide a similar source of information. The natural definition of homogeneity for such textures leads to the constraint that the oriented ‘flow’ of texture on a surface follows geodesics of the surface (on average). In the current work, it is shown that the shapes of contours projected from geodesics of developable surfaces, and analogously of oriented texture flow, reliably determine the shapes of the surfaces. On the basis of this analysis, it is suggested that human perception of surface shape from texture has two modes of operation: an isotropic mode, in which the visual system infers surface shape from local texture compression information, and a texture flow mode, in which the curvature of local texture flow determines local surface curvature, based on a geodesic constraint. In order to test the theory, planar texture patterns have been isometrically mapped with varying degrees of global orientation (ranging from isotropic to purely oriented) onto developable surfaces. The theory predicts that subjects' ability to make judgements about surface shape will be good for the isotropic textures and for highly oriented textures, but not for anisotropic textures that are only weakly oriented. As predicted, images of the surfaces with isotropic texture patterns induce strong percepts of shape, as do those of highly oriented textures. Images of anisotropic, weakly oriented patterns, however, elicit only weak percepts of shape.
Visual Search Processes in Healthy Aging
Authors: Tales A , Troscianko T , Butler S R
Published: December 2015

It is well established that there are two limiting types of visual search, a pre-attentive parallel and an attention-related serial process. Such different types of processing may depend upon different regions of the visual cortex and such a measurable dissociation of function could provide a useful marker for particular types of cortical pathology, such as that associated with Parkinson's disease, aging, and Alzheimer's disease. For example, recent studies in this laboratory have shown that people with Parkinson's disease have abnormal parallel but normal serial search functions. Plude and Doussard-Roosevelt (1989 Psychology and Aging4 98 – 105) found no difference in parallel processing between older and young adults, but found that older adults performed worse on a conjunction task. The aim of the present experiment was to extend this research and look at the effect of aging on other types of visual search task and to compare these findings to patients with Parkinson's disease and Alzheimer's disease to determine if different patterns of visual function occur.

Twenty-five young adults (mean age 32.6 years) and twenty-five older adults (mean age 63.4 years) performed both a conjunction task and a task involving the detection of a target only slightly larger than the distractors (the ‘size’ task). Our hypothesis was that for both types of visual search there would be an increase in search slope in the older adult group compared to the younger adults.

Results of a 2-factor (1 between and 1 within) ANOVA performed on the slope values indicate statistically significant main effects of both age ( F=7.661, p<0.008) and search task ( F=25.426, p<0.0001), where in both the conjunction and size task the slope value was significantly greater for the older than for the younger adults. The slope for the size task was significantly greater than that for the conjunction task for both age groups. The results therefore support our hypothesis and further work is in progress to determine the effects of Alzheimer's disease on different types of visual search processing.
Different Spatial Scales for Different Face Categorisations
Authors: Oliva A , Schyns P G
Published: December 2015

When people categorise complex stimuli such as faces, they might flexibly use the perceptual information available from the visual input. Three experiments were run to test this hypothesis with two different categorisations (gender and expression) of identical face stimuli. Stimuli were hybrids (Schyns and Oliva, 1994 Psychological Science5 195 – 200): they combined either a man or a woman with a particular expression at a coarse spatial scale with a face of the opposite gender with a different expression at the fine spatial scale. In experiment 1 we tested whether a gender vs an expression categorisation task tapped preferentially into a different spatial scale of the hybrids. Results showed that expression was biased to the fine scale, but that gender was not biased. In experiment 2 the same task was replicated, following a learning of the identity of the faces. It was then found that gender also became biased to the fine scale. In experiment 3 the expression task was changed to an identification of each expression to establish whether this could revert the scale biases observed in experiments 1 and 2. Results suggest that different categorisations of identical faces use different perceptual cues. This suggests that the nature of a task changes the representation of a stimulus.
Fading of Textured Targets on Textured Background
Authors: Teichmann R , Spillmann L
Published: December 2015

In 1804 Troxler reported that with strict fixation, a small, low-contrast target presented to the peripheral visual field will tend to fade and ultimately become invisible. Further studies have shown that, in addition to stationary targets, moving and flickering targets will also fade. We studied the role of a texture difference between the target and its background on fading. We found that textured targets fade as quickly as, or even faster than, uniform targets. Typically, the target becomes less salient and after a while disappears in the background.

Specifically, we asked whether orientation contrast would influence the time of perceptual disappearance. A grating disk of 2 deg diameter and 0.8 cycle deg−1 spatial frequency was presented binocularly on an equally striped background, 15 deg from the fixation point. The orientation of the target relative to that of the background was varied in steps of 15°, yielding eleven stimuli which were presented in a random order. Each orientation was shown a total of nine times. Luminance, spatial frequency, and contrast were the same for both the target and the background. Time to fading was measured for each target orientation.

The results show that orientation contrast strongly affects fading. Time to fading was longest when the grating target and the background were oriented at right angles and decreased symmetrically with decreasing orientation contrast. This result supports the hypothesis that fading is an active neuronal process of long-range lateral interactions.
Does the Gamma Distribution Refer to an Underlying Mechanism in Binocular Rivalry?
Authors: Vallen P H C , Snoeren P R , de Weert Ch M M
Published: December 2015

Thirty years ago, Levelt (1967 British Journal of Psychology58 143 – 145) fitted the distribution of dominance times in binocular rivalry with the gamma distribution (the distribution function of waiting times for N random events with process speed lambda). Ever since, the gamma distribution has been used to describe the rivalry phase durations, without an explanatory underlying mechanism being given. Although Levelt suggested lambda to be proportional to the stimulus strength (eg contrast, luminance, blur, amount of contour) and N to be ‘successive neural spikes’, this suggestion has never been tested. The purpose of this study was to test whether or not N and lambda represent characteristics of the observer and the stimulus, respectively.

To collect the data as accurately as possible, we performed a large number of measurements involving different designs and stimuli. In contrast to previous experiments, collected data were not pooled but were compared within each subject. We tested the hypothesis by collecting time intervals from subjects responding to numerous conditions in which disk - ring stimuli were varied in contrast, blur, or amount of contour in one eye.
Late Maturation (Age >5 Years) of Long-Range Spatial Interactions in Humans
Authors: Kozma P , Kovács I , Benedek G
Published: December 2015

We have studied the development of long-range spatial interactions in children (age 5 – 14 years) with normal vision. In our field study involving 410 normal children we used a battery of contour-integration cards that were developed earlier to test amblyopic patients (Kovács, Polat, and Norcia, paper presented at ARVO 1996). Each card consisted of a closed chain of collinearly aligned Gabor patches (contour) and a background of randomly oriented and positioned Gabor patches (noise). Subjects were asked to identify the location of the contour, and also to trace the contour within each card. The value of P was varied across cards (1.1 > P > 0.65), where P is the ratio of noise spacing to contour spacing. It is assumed that long-range, orientation-specific facilitatory interactions connect collinear contour segments together for P < 1. The strength of long-range interactions is defined by the minimal value of P yielding contour segregation. Children in the 13 – 14 years age group were able to see most of the contours ( Pmin < 0.7), while 5 – 6-year-old children missed the contours in about half of the cards ( Pmin < 0.9). This result indicates a very late maturation of long-range spatial interactions. It is possible that the late formation of horizontal connections in superficial layers of the human primary visual cortex (Burkhalter et al, 1993 Journal of Neuroscience13 1916 – 1931) is the neural basis of our developmental finding.
Improvement of Visual Short-Term Memory Characteristics in Monkeys: Effect of an Antioxidant
Authors: Chueva I V , Dudkin K N
Published: December 2015

Visual short-term memory was tested in a delayed-discrimination task on rhesus monkeys before and after a systemic injection of the antioxidant oxymetacil (4 – 7 mg kg−1). Monkeys had to discriminate stimuli with different visual attributes (colour, orientation, spatial frequency, size, contrast, spatial relationships between visual objects) by a delayed (0 – 32 s) instrumental reflex. Oxymetacil had no influence upon visual discrimination without delay, but after injection of this drug the delayed discrimination (associated with mechanisms of short-term memory) of different stimuli was significantly improved. Oxymetacil increased the duration of short-term storage of spatial information by a factor of 2 – 4 and decreased motor reaction time. Application of oxymetacil in the same doses produced similar results for delayed discrimination of black-and-white gratings, or geometrical figures of different orientations and size. The duration of short-term information storage was doubled or trebled and the motor reaction time was decreased. If monkeys were required to discriminate colour figures, the duration of short-term information storage was also doubled, being longer than for any of the other tasks. The results are discussed in terms of effects on cortical interregional synchronisation mechanisms responsible for control processes such as attention.
Rating Visual Velocities: Presentation Order versus Frequency of Occurrence
Authors: Sokolov A N , Ehrenstein W H , Pavlova M A
Published: December 2015

Given equal frequencies of occurrence of stimuli, identical velocities receive higher or lower ratings depending on whether slow or fast velocities happen to occur on the early trials of a run (Ehrenstein and Sokolov, 1996 Perception25 Supplement, 34 – 35). When stimuli vary in their frequency of occurrence, this presentation-order effect might enhance or substitute the well-known frequency effect (Parducci's range - frequency theory) on category ratings. The aim of the present study was to contrast these two effects for ratings of visual velocities. Two groups of observers had to rate five stimulus velocities (3, 4.5, 6, 7.5, and 9 deg s−1) of a single luminous dot using three categories (slow, medium, fast). Respective frequencies of occurrence for these velocities were either 4 - 4 - 8 - 14 - 20 (group 1, negative skewing for frequency) or 20 - 14 - 8 - 4 - 4 (group 2, positive skewing). The quasi-random presentation order of each set, on the contrary, corresponded to either positively skewed (group 1) or negatively skewed (group 2) frequency distributions. No significant differences in the ratings of two groups (other than a slight preference for the presentation-order effect beyond 6 deg s−1) were found, as if the presentation order and frequency effects had cancelled each other. This suggests that the presentation order of velocities is at least as powerful as their frequency of occurrence. Lack of agreement between our results and predictions of computer-simulated Haubensak's consistency model as well as of Parducci's range - frequency theory requires a model which accounts for an interaction of the two effects.
Relevant Perceptual Factors in Stereoscopic Displays: Image Disparity, Convergence Distance, and Focus Length
Authors: IJsselsteijn W A , de Ridder H , Hamberg R
Published: December 2015

Traditionally, visually relevant factors in stereoscopic displays have been investigated within a performance-oriented framework, focusing on the veridicality of depth perception. However, for some applications, most notably in the areas of broadcasting and entertainment, an appreciation-oriented approach seems to be more relevant. Within this framework, we investigated the influence of image disparity, convergence distance, and focus length on the subjective assessment of depth, naturalness of depth, and quality of depth (or preference).

Twelve observers with normal or corrected-to-normal vision and good stereopsis viewed a fully randomised presentation of stereoscopic still images that varied systematically in image disparity (six levels of camera base difference: 0, 4, 8, 12, 16, and 24 cm), convergence distance (two levels: 1.30 m and 2.60 m) and focus length (two levels: 10 mm and 20 mm). Each observer was asked to rate, in separate counterbalanced sessions, his/her impression of depth, naturalness of depth, and quality of depth.

The results indicate that observers prefer a stereoscopic presentation of images over a monoscopic presentation. A clear optimum was found at 4 cm image disparity for subjective judgments of naturalness and of quality. Depth judgements increased up to an image disparity of 12 cm, a result that is in line with earlier psychophysical literature. There was an effect of focus length only at extreme image disparities. An effect of convergence distance was also found that can be adequately explained by rescaling to match the effective visual disparities. Although there was a strong linear correlation between naturalness and quality (r = 0.96), a small but systematic deviation could be observed. This deviation was best modelled by a linear quality model that incorporates both naturalness and depth.
Summation of Contrast in Perceived Form from Texture
Authors: Laurinen P I , Olzak L A
Published: December 2015

The relative contrast of two superimposed triangles formed by truncated sinusoidal gratings determines which appears more salient. We have previously reported that the saliency of one triangle is selectively enhanced by superimposing a third grating of similar frequency but different orientation. We now ask how the contrasts of the three gratings combine to determine saliency.

Stimuli were two superimposed isosceles triangles, formed by overlaying sharply truncated patches of a sinusoidal grating, one at 1.5 cycles deg−1 tilted +45°, the other at 6 cycles deg−1, tilted −45° from vertical. The sharpest-angle apexes pointed in opposite directions (left or right). Contrasts of the gratings were initially adjusted to yield equal performance when observers chose whether the more salient target pointed left or right following a brief (400 ms) monocular exposure. In each test condition a third grating of vertical orientation (spatial frequency 1.5, 3, or 6 cycles deg−1) was added to the entire stimulus at one of six contrast levels ranging from near threshold to 10 × threshold. The point of equal saliency was re-determined from psychometric functions by varying the contrast of one triangle in a 2AFC staircase procedure.

The saliency of each triangle was enhanced when the third grating was matched in frequency, but no effect occurred when the third grating differed by an octave (eg was 3 cycles deg−1). Beyond some threshold value of the third grating contrast, the contrast needed to reinstate equal salience was found to be inversely proportional to the contrast of the third grating. Our results are in agreement with the characteristics of higher-level mechanisms that mediate spatial-grain and/or pattern contrast discrimination, and suggest that form-from-texture mechanisms sum component contrasts linearly over a wide range of orientations within a narrow frequency band.
Interaction of Direction and Speed Selectivity in Cat Primary Visual Cortex
Authors: Satinskas R , Ruksenas O , Pleskaciauskas A , Stabinyte D , Vaitkevicius H
Published: December 2015

We have studied the selectivity for speed and direction of directionally selective (DS) cells in the primary visual cortex of the cat. Most of the 37 DS neurons tested were velocity tuned. From a set of velocities in the range from 2 to 80 deg s−1, each velocity was optimal for a certain proportion of these cells. The distribution was as follows: 2 deg s−1 was optimal for 16% of all tested neurons, 5 deg s−1 for 14%, 10 deg s−1 for 27%, 20 deg s−1 for 30%, 40 deg s−1 for 8%, and 80 deg s−1 for 5%. The preferred direction determined with a single light spot was compared with that obtained with a pair of spots moving at a mutual angle of 60° over the receptive field. For 40% of the neurons tested the preferred direction to the single moving spot coincided with that obtained with the two-spot stimulus. The responses to the latter could be successfully computed as a combination of responses to single spots moving in the given directions. This result indicates a high capacity for motion processing in the primary visual cortex of the cat.
Eye Movements in Judgements of Facial Expressions
Authors: Osada Y , Nagasaka Y , Yamazaki R
Published: December 2015

We recorded eye movements by the method of corneal reflection while ten subjects viewed schematic faces drawn by lines. Each subject viewed different emotional faces: happy, angry, sad, disgusted, interested, frightened, and surprised. We measured the subject's judgements in terms of percentage ‘correct’ and reaction time. Schematic faces were composed of the face outline contours and of the brow, eyes, nose, and mouth which could all be modified to produce particular expressions. By masking parts of the face, we examined which features would have the greatest effects on judgements of emotion.

Subjects always gave a saccade to the eyes and fixated even when the eyes were not important for the judgement. They also gave a saccade to the centre of the face and fixated it even when only the mouth was presented. The presentation of only the brow decreased the correct rate on the expression of ‘surprise’ but played an important role in the ‘sad’ judgement. The ‘angry’ judgement depended significantly on the brow and mouth. The eyes contributed greatly to the ‘disgusted’ judgement. These results suggest that the judgement of facial expressions of emotion can be strongly affected by each part of the schematic face. The concentration of saccades on the centre of the face suggests that the ‘configuration balance’ of the face is also likely to be important.
The Detection of Interocular Phase Differences
Authors: Morgan M J
Published: December 2015

When dynamic visual noise such as the ‘snow’ on a detuned television receiver is viewed with a temporal delay between the two eyes, the noise appears to rotate in depth around a vertical axis [Ross, 1974 Nature (London)248 363 – 364; Morgan and Tyler, 1995 Proceedings of the Royal Society of London, Series B262 371 – 376]. Random noise evidently contains a wide spread of spatiotemporal Fourier components, including those for horizontal motion, which may cause a Pulfrich effect when there is an interocular delay. To investigate the temporal-frequency components necessary for the effect, a display was designed containing only a single temporal frequency. Spatially broad-band grey-level noise was flickered, such that each pixel of the noise was sinusoidally modulated over time. An interocular delay was introduced as a phase lag of the flicker in one eye. This produced a rotating depth effect. The threshold for detecting the phase shift was about 5° of phase angle, irrespective of temporal frequency, except for frequencies greater than ∼20 Hz, when the depth effect was no longer seen. Tests of several models of the phase-lag detection are described, including the possibility that there are dichoptic motion detectors also tuned to stereodisparity.
Effects of Position and Contour Blurring of Cast Shadow on Depth Perception
Authors: Ujike H , Shimokawa K , Saida S
Published: December 2015

Shadows are known as a qualitative depth cue. Moreover, dynamic changes of shadow position were recently reported to lead to the perception of a looming object, suggesting that shadows can be a quantitative depth cue as well. If this is the case, the position and/or contour blurring of shadows would contain quantitative depth information; however, the visual system needs to assume a direction and/or size of a light source to use this information. To examine this idea, we measured perceived depth between a target object and a background for different positions and different contour blurrings of the shadow of the object on the background. The displays were 2-D drawings (18 deg × 18 deg) produced by computer software on a CRT screen and seen through a 3 cm × 3 cm aperture in a sheet of black cardboard. The position of the shadow to the lower right of the object was varied in terms of angular distance between the two. The contour of the shadow was blurred by Gaussian filters of different diameters. We found that perceived depth increased with angular distance, but was independent of contour blurring. This result indicates that the visual system makes an assumption on the direction of the light source, but not the size of it, to derive the amount of depth from the object's shadow.
Neuronal Connections in Cat Striate Cortex as Revealed by HRP Staining
Authors: Toporova S N , Alexeenko S V , Makarov F N
Published: December 2015

Injecting horseradish peroxidase (HRP) into area 17 of tree shrews, Rockland and Lund (1982 Science215 1532 – 1533) found connection-specific columnar staining superimposed on a Gaussian decrease of staining intensity with distance from the injection site. Such data are important when constructing models of neuronal nets. We have investigated in more detail the staining of different types of neurons after HRP injection into one orientation column of cat striate cortex. The intensity of staining was classified as dark, intermediate, or light. Cells with different staining intensities were found in all cortical layers and at different distances from the injection site of HRP. According to the shape of their somata and the organisation of their dendritic trees, the labelled cells were identified as pyramidal, small pyramidal, non pyramidal, or modified pyramidal (inverted and fusiform). The ratio of dark : light : intermediate cells within all identified morphological types was 2 : 1 : 1, except for the inverted pyramidal cells (1 : 1 : 1). Thus the intensity of staining depends not only on the physical uptake and transportation of HRP but also on the organisation of axonal terminals and neuron location in the functional structure of the cortex.
On the Nature of the Gated Colour Opponency in the On-Units of the Frog Retina: Electrophysiological Study and Model
Authors: Maximova E M , Maximov V V , Orlov O Y
Published: December 2015

Ganglion cells of the ON-type in the frog retina produce colour-dependent responses differing in temporal patterns (short bursts to excitation of red-sensitive cones as opposed to prolonged discharges if blue-sensitive ‘green rods’ are excited). Their gated colour opponency (Kicliter et al, 1981 Brain Research210 103 – 113; Maximov et al, 1985 Vision Research25 1037 – 1049) becomes apparent from the OFF-responses in conditions when the test stimuli are superimposed on a background of another colour. So, when blue glass is introduced in the light beam (decreasing the excitation mainly of red-sensitive cones), an OFF-response is observed, much like the response to the onset of blue light. It has been suggested that opponency in ON-cells is asymmetric, ie that the red signal reaches the blue channel with reversed sign, but not vice versa.

A single-unit-recording study revealed the dependence of ON-cell responses both on the colour of stimuli presented in the centre of the receptive field and on the steady illumination of its surround. Surround illumination was found to favour OFF-responses in ON-units. In some cases even the cessation of blue light elicited an OFF-response with a discharge pattern resembling that of the onset of red light. In these cases an ON-response to yellow glass could also be obtained. These observations prove some degree of symmetry in the opponency of the red and blue channels. It is suggested that feedback from horizontal cells onto photoreceptor terminals is involved in the gated colour opponency. A circuit model that reproduces the observed phenomena is presented.
Search Asymmetries in the Detection of Shape Orientation: The Role of Implicit Axes of Elongation and Symmetry
Authors: Boutsen L , Marendaz C
Published: December 2015

Two-dimensional (2-D) shape identification is sometimes described in terms of access to structural descriptions based on the extraction of principal axes of elongation and symmetry. In four experiments we examined the effects of implicit axes of elongation and symmetry on visual search for shape orientation, on the basis of previous observations of search asymmetries in the detection of the orientation of line segments. We found search asymmetries in the detection of vertical versus oblique line segments and in 2-D shapes, studied earlier by Quinlan and Humphreys (1993 Perception22 1343 – 1364): search times for a vertical target among oblique distractors (rotated 18° from the vertical) are higher than those for an oblique target among vertical distractors.

We found that the search asymmetry in the detection of shape orientation is larger when the shape contains an unambiguous axis of elongation or symmetry. Search asymmetries disappear when the principal axis of the shape is oriented horizontally, or when the shape contains no unambiguous axis of elongation or symmetry. Overall search times tend to decrease when the axis of elongation is aligned with an axis of symmetry. These results suggest that the detection of implicit axes plays a role in the perception of object shape and orientation.
Far Distance Perception
Authors: Watt S J , Davies I R L , Sowden P T , Davies L
Published: December 2015

Determining how people perceive distance is a central issue in the study of visual perception. Whilst near-distance perception has been extensively researched, far-distance perception has received little attention. We review the literature and illustrate key points with new data, focusing on analysis of available information/cues, degree of accuracy, measurement procedures, perceptual/cognitive influences, and geometry of perceived space. Analysis of available cues suggests that under natural viewing there is sufficient information for veridical distance perception. However, distance judgements are inaccurate and vary with mode of measurement (eg absolute vs relative judgements). Inaccuracy includes compression of distance. This has been modelled with the use of different geometries—most commonly power functions. Exponents often average 1.0 but this conceals considerable individual variation (in our data individual exponents ranged from 0.5 to over 1.0). Further, even for averaged exponents values vary between 0.8 and 1.25, as a function of viewing conditions, experimental method, and of the relative contribution of cognitive and perceptual factors. Evidence suggests that distance is encoded at an ordinal level, but for many practical tasks the final judgement must be metric (eg range finding) and this transformation is error-prone (in our data numerical estimates could be a factor of 10 out). Further, many natural judgements require perception of the full layout of the scene (including exocentric distances) rather than the more commonly investigated perception of egocentric distance. Evidence suggests that training based on practice with feedback produces some improvement in accuracy, but this is highly context-specific.
Conflicts with Extraretinal and Monocular Cues Cause the Small Range of the Induced Effect
Authors: Banks M S , Backus B T
Published: December 2015

A vertical magnifier before one eye causes the induced effect: an apparent rotation of frontal surfaces toward that eye. The rotation required to restore apparent frontoparallelism grows linearly up to ∼4% magnification, but plateaus at 8%. We examined the cause of the plateau.

Horizontal disparities (quantified by horizontal size ratios, HSRs) are ambiguous indicators of surface slant. Various retinal and nonretinal signals can allow veridical slant estimation from HSR, sensed eye position, vertical disparities (vertical size ratios, VSRs), and monocular cues. Vertical or horizontal magnification of one eye's image alters the natural relationships among HSR, VSR, eye position, and monocular cues. We argue that the induced-effect plateau is caused by conflicts between these means of estimating slant. A plateau is not observed in the geometric effect because some of the conflicts do not occur with horizontal magnification. Two experiments were designed to test this hypothesis. When strong monocular cues were present, plateaux occurred at ∼8% magnification in the induced, but not the geometric effect. When monocular slant cues were made useless, induced-effect plateaux were abolished. Even with strong monocular cues present, plateaux in the induced effect were eliminated when eye position was consistent with the vertical magnification in the retinal images. The smaller range of the induced effect can only be understood from consideration of all the signals involved in slant estimation.
A Formal Mapping Model for Striate Cortex
Authors: von Berg J
Published: December 2015

Cortical magnification has been measured with different techniques in many primates, including humans. The most popular models assume a value reciprocal to eccentricity, and are therefore rotation symmetric. To simulate the location of a projected stimulus, a real mapping function is needed. We use the complex logarithm log( z+ a)—introduced for this purpose by Schwartz (1977 Biological Cybernetics25 181 – 194), which is close to recent brain imaging results in humans and macaque monkeys. The model contradicts the idea of symmetric magnification and the linear model implicitly used by most anatomists. Our model gives a quantitative correspondence from visual field to striate cortex and vice versa, which we use to relate topology and geometry of cortical structures such as ocular dominance stripes, orientation fields, and cytochrome oxidase blobs in V1 to the visual field. This model may serve to relate empirical knowledge about spatial properties of these brain structures to psychophysical stimulus arrangements. Together with the description of cell densities, the point-to-point (and thus simplified) model may be used as a basis for formalising convergence and divergence properties of connections in neural maps.
Discrimination between Plaids: Do Oriented Filters Combine Dichoptically?
Authors: Olzak L A , Wong R L
Published: December 2015

Two oblique gratings combine perceptually to form a chequerboard appearance under monoptic presentation but not under dichoptic presentation (Georgeson and Meese, 1996 Perception25 Supplement, 121), suggesting an early combination process. Combining processes that operate over orthogonal orientations are also observed in complex pattern discrimination tasks (Olzak and Thomas, 1991 Vision Research31 1885 – 1898). We ask here whether the interactions observed in discrimination tasks occur before or beyond the site of binocular interaction.

Observers discriminated between two patterns that differed slightly in their spatial-frequency content. On each trial, one of the two patterns was presented. Observers judged which stimulus had been presented on a 1 – 6 confidence scale. In control conditions, the stimuli were single sinusoidal gratings near 3 cycles deg−1, and were always presented monoptically. In test conditions, a second component was added to the first in each stimulus. The second component was either presented to the same eye as the first component (monoptic presentation), or to the other eye (dichoptic presentation). The second component was either a mask of exactly 3 cycles deg−1, or varied to give a second cue to discrimination. Second cues either varied with the first (both components lower frequency or both higher) or varied in opposite sign (high with low). Rivalry was eliminated by using low contrast (10 × threshold) and small (1.2 deg) patterns. Our results suggest that the combination processes we observe occur beyond the site of binocular combination and differ from those mediating the percept.
Centre-Surround Tuning of Orientation Detectors in Human Vision
Authors: Ringach D L , Shapley R
Published: December 2015

We present a new psychophysical method to study the tuning of orientation detectors in the human visual system. The stimulus consists of a sequence of sinusoidal gratings of random orientations and spatial phases (but of fixed spatial frequency) shown at a high presentation rate (30 Hz) in 60 s long trials. The gratings are seen through a circular aperture. The subject's task is to report, as fast as possible, by pressing a key, when the presence of a horizontal grating is seen embedded in the stimulus sequence. The data are analysed by calculating the distribution of orientations present in the stimulus sequence at different times [before] the key was pressed. Similar experiments can be done by asking the subject to detect vertical and oblique orientations. In these experiments we used 100% contrast, a 3 deg diameter circular aperture, and spatial frequencies ranging from 1 to 4 cycles deg−1.

The resulting orientation-tuning profiles have a ‘centre—surround’ (or Mexican hat) shape in the orientation domain. These findings are consistent with the idea of fast ‘lateral inhibition’ between orientation detectors. The centre—surround profiles may explain systematic errors in visual angle judgments, such as the perceptual expansion of acute angles and the contraction of obtuse angles, the tilt aftereffect, and the effects observed in the Zöllner, Hering, Ponzo, and Poggendorff illusions.
A Subliminal Effect in a Colour-Discrimination Task and its Modulation by Spatial Attention
Authors: Sakaguchi Y , Pashler H E
Published: December 2015

Three experiments were performed to examine the effects of masked colour stimuli on the response to masking stimuli. In experiment 1, two coloured squares were presented successively at the same position so that the first one could not be perceived owing to backward masking. The task was to respond to the colour of the second square as quickly as possible. The results showed that the subject's response was affected by the unperceived first square: both error rate and reaction time increased when the two squares had different colours. It was also found that reaction times for wrong responses were shorter than those for correct responses; this suggests that wrong responses occurred when the neural activation representing the first square succeeded in triggering a motor response before being suppressed. In experiment 2 we examined whether spatial attention modulated this effect or not. Eight squares (one coloured and seven white) were displayed and the spatial relation between the coloured square in the first frame (prime) and that in the second frame (target) was varied. The performance of subjects when the target location was pre-cued and when no cue was given was compared. The results indicate that in the no-cue condition the subliminal effect was observed uniformly irrespective of the spatial relation. In contrast, in the pre-cue condition the effect was diminished when prime and target occupied different positions, that is when the prime appeared outside the attended region. The result of experiment 3, with another stimulus configuration, showed a similar attentional modulation. The underlying mechanism is discussed.
The Task-Dependent use of Binocular Disparity and Motion Parallax under Natural Viewing Conditions
Authors: Bradshaw M F , De Bruyn B , Eagle R A , Parton A D
Published: December 2015

The use of binocular disparity and motion parallax information was compared in three different psychophysical tasks for which natural viewing and physical stimuli were used. Natural viewing may be an important factor in interpreting experiments which have addressed the ability to use disparity and parallax both separately and in combination (see Frisby et al, 1996 Perception25 129 – 154). The stimuli consisted of configurations of three bright LEDs carefully aligned in the horizontal meridian and presented in darkness. The distance of the middle LED (flashing at 5 Hz) could be adjusted along the midline in accordance with the tasks which included: (i) a depth nulling task, (ii) a depth matching task, and (iii) a shape task—match base/height of triangle. Each task was performed at two viewing distances (1.5 and 3.0 m) and under four different viewing conditions: (i) monocular-static, (ii) monocular-moving, (iii) binocular-static, and (iv) binocular-moving. Note that the different tasks differ in their dependence on viewing distance, and the available cues for viewing distance differ between viewing conditions. Four observers made ten settings in each condition at each distance. Observers, as expected, performed badly (bias and accuracy) in all tasks in the monocular-static condition. Nulling was accurate in the other viewing conditions (no estimate of viewing distance required). Performance was best in the matching task (ratio of viewing distances) but although binocular-static was significantly better than monocular-moving performance in this and in the shape task (absolute distance required), there was no additional improvement in the binocular-moving condition. Results show that observers can recover structure accurately from parallax or disparity information in real-world stimuli.
Effects of Aging on Photoreceptors and Implications for Visual Performance
Authors: Leibovic K N , Bandarchi J
Published: December 2015

Visual performance depends in the initial stages on the properties of retinal photoreceptors. In this context we consider the effects of rod outer segment (OS) renewal and OS response gradient on performance. The OS renews itself by forming new membrane near the cilium, at the base of the OS. This membrane then advances towards the tip where it is shed and phagocytosed in the pigment epithelium. Thus the OS is older at the tip than the base, and it has been proposed that it is due to this aging that the observed light responses are smaller and slower at the tip than at the base.

We have tested this hypothesis by exposing Xenopus laevis in a controlled manner to altered temperature and lighting conditions which are known either to slow down or to accelerate OS renewal. We have recorded the light responses of the OS base and tip and found that they are, indeed, correlated with the age differences. In addition to OS membrane age we have also investigated the effects of animal age on the response gradient along the OS. Here we found that during development the response differences decrease and then stabilise at maturity. Concurrently with the decrease of the gradient the response kinetics are slowed down. There is thus a changing trade-off between response gradient and kinetics up to maturity in this animal.

These results have important implications for visual performance. Visual reaction times depend on photoreceptor kinetics; and since photons can be absorbed anywhere along the OS, the response gradient, especially at low light levels, directly affects the reliability of detecting stimulus intensity. We conclude that visual performance in Xenopus laevis is related to the rates of OS renewal and the resulting response gradient in an age-dependent manner.
Relevant Image Features for Vernier Acuity
Authors: Beard B L , Ahumada A J
Published: December 2015

The extraction of relevant image features is a key part of discrimination learning (E Gibson, 1969 Principles of Perceptual Learning and Development) and the identification of those features is necessary for the understanding of observer performance. Two mechanisms are thought to limit Vernier acuity judgments: orientation-selective and local-sign mechanisms (Waugh and Levi, 1993 Vision Research33 539 – 552; Beard et al, 1997 Vision Research37 325 – 346). The linear component of relevant image features can be determined for a Vernier task by adding external noise to the image and then averaging the noises separately for the four types of stimulus/response trials.

The Vernier stimulus consisted of two short, dark, horizontal lines presented within low-contrast white noise. Two spatial separations were tested: nearly abutting and a wide horizontal separation. The task was to determine if the target lines were aligned or offset in the vertical direction. The noises were averaged separately for the groups of trials, corresponding to each of the four possible stimulus/response combinations (eg, stimulus=offset, response=aligned). The sum of the two ‘not aligned’ images was then subtracted from the sum of the ‘aligned’ images to obtain an overall image. We then computed a weighted average of adjacent pixels, smoothing the image and fostering visualisation of the relevant feature pattern. Our image analysis supports the view that as the vernier line separation narrows, oriented features play a larger role in the Vernier discrimination.
Up-Down Asymmetries in Speed Perception
Authors: Thompson P , Stone L S
Published: December 2015

We compared speed matches for pairs of stimuli that moved in opposite directions (upward and downward). Stimuli were elliptical patches (2 deg horizontally by 1 deg vertically) of horizontal sinusoidal gratings of spatial frequency 2 cycles deg−1. Two sequential 380 ms foveal presentations were compared. One of each pair of gratings (the standard) moved at 4 Hz (2 deg s−1), the other (the test) moved at a rate determined by a simple up - down staircase. The point of subjectively equal speed was calculated from the average of the last eight reversals. The task was to fixate a central point and to determine which one of the pair appeared to move faster. Eight of ten observers perceived the upward drifting grating as moving faster than a grating moving downward but otherwise identical. On average (N = 10), when the standard moved downward, it was matched by a test moving upward at 94.7± 1.7(SE)% of the standard speed, and when the standard moved upward it was matched by a test moving downward at 105.1± 2.3(SE)% of the standard speed.

On extending this paradigm over a range of spatial (1.5 to 13.5 cycles deg−1) and temporal (1.5 to 13.5 Hz) frequencies, preliminary results (N = 4) suggest that, under the conditions of our experiment, upward motion is seen as faster than downward motion for speeds greater than ∼1 deg s−1, but the effect appears to reverse at speeds below ∼1 deg s−1 with downward motion perceived as faster. Given that an up - down asymmetry has been observed by other investigators for the optokinetic response, both perceptual and oculomotor contributions to this phenomenon deserve exploration.