bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cooperation of Priors for the Perception of Shaded Line Drawings
Authors: Mamassian P , Landy M S 
Published: December 2015

It is well known that observers have a bias that the light comes from above when they look at shaded objects. Recently, we have reported a similar bias for the interpretation of line drawings, which reflects an assumption concerning the location of the observer relative to the object (Mamassian, 1995 Perception24 Supplement, 35). We investigate here how the perception of shaded line drawings might demonstrate the interaction of these two priors. The stimuli were images of smoothly folded surface patches, painted with parallel stripes and illuminated from the side. The sign of curvature of the stripes and the direction of illumination were balanced across stimuli to enable a separate analysis of each prior. Two levels of contour curvature and two levels of ambient illumination were used. Each image was presented at a random orientation in the image plane, and subjects were asked whether the fold appeared concave or convex. The results were consistent with the use of the shading and contour interpretation biases by most observers. When the biases were weakened (by reducing contour curvature or by increasing ambient illumination), the stimuli became more ambiguous. Unexpectedly, the stimuli were also perceived as more ambiguous when the contour had vertical mirror symmetry. Recent work indicates that perceived depth from multiple cues is a weighted average, where the weights reflect the reliability of the individual cues (Landy et al, 1995 Vision Research35 389 – 412). Analogously, our results are reasonably consistent with the mixture of competing priors, modulated by the degree of evidence for each.
Parallel Processing of Luminance Steps in the Presence of Luminance Gradients
Authors: Grodon A , Fahle M 
Published: December 2015

Some features of complex visual displays are analysed effortlessly and in parallel by the human visual system, without requiring scrutiny. Examples for such features are changes of luminance, colour, orientation, and movement. We measured thresholds as well as reaction times for the detection of abrupt spatial changes in luminance in the presence of luminance gradients, in order to evaluate the ability of the system to ignore such gradients. Stimuli were presented on a 20 inch monitor under control of a Silicon Graphics workstation. Luminance was calibrated by means of a photometer (Minolta). We presented between 4 and 14 rectangles simultaneously on a homogeneous dark background. Rectangles were arranged on an incomplete, imaginary circle around the fixation point and luminance changed stepwise from one rectangle to the next. Five observers had to indicate whether all luminance steps between the rectangles were subjectively equal or whether one luminance step was larger. Detection thresholds were determined for the larger step as a function of the small steps (‘base step size’) by means of an adaptive staircase procedure. The smallest luminance steps were detected when the base step size was zero and when only few rectangles were presented. Thresholds increased slightly with the number of rectangles displayed simultaneously, and to a greater extent (by up to a factor of 2) with increasing base step size. The results of all observers improved significantly through practice, by about a factor of 2. We conclude that the visual system is unable to completely eliminate gradients of luminance and to isolate sharp transitions in luminance.
Asymmetries in Brightness and Darkness for Assimilation and Simultaneous Contrast?
Authors: Verstraten F A J , Intriligator J 
Published: December 2015

Recently, de Weert and Spillmann (1995 Vision Research35 1413 – 1419) reported a striking example of assimilation. Their stimulus was a pincushion formed by four arcs, each consisting of a number of black and white rings on a gray background (the area surrounded by the rings, see their figure 1). When the gray background is immediately surrounded by white rings, the background appears lighter and vice versa. When a subject is asked to match the luminance of a circle in a different spatial location for both the ‘lighter’ and the ‘darker’ pincushion, the matching luminance of the test is lower than the actual background luminance. This result is surprising but also counterintuitive. For example if a ‘light’ pincushion is matched with a ‘dark’ pincushion, it is expected that the luminance of a ‘light’ pincushion needs to be decreased in order to match the ‘dark’ pincushion. Conversely, the luminance of the ‘dark’ pincushion needs to be increased to match the ‘light’ pincushion. Therefore luminance values on both sides of the default background luminance are expected. We replicated their basic experiment and found the same results. In additional conditions, we had subjects adjust the background luminance of a ‘light’ pincushion compared to a ‘dark’ and vice versa. In that case the luminance values were symmetrical on either side of the default background luminance. It would seem that the method of testing is crucial here. Therefore we also tested simultaneous contrast stimuli (all rings were made black or white) using the circle-match-task as in their original experiment. We found that both values were nicely distributed on both sides of the background luminance value, indicating that de Weert and Spillmann's finding is not attributable to the test condition as such.
Bloch's Law for Contrast Increment Detection: The Effects of Pedestal Contrast and Light Level
Authors: Snowden R J 
Published: December 2015

The duration over which contrast detection improves (Bloch's regime) decreases with increasing light level and is often thought to reflect the temporal characteristics of the visual system. There is also some evidence to suggest that the temporal characteristics of the visual system might also change with increasing contrast level (M A Georgeson, 1987 Vision Research27 765 – 780). Here we compare temporal summation for stimuli presented on a blank field or on a high contrast background. On each trial a test grating was presented for X ms with the use of a spatial-alternate forced-choice procedure. The test grating (2 cycles deg−1) was presented superimposed on a similar pedestal grating which was also present for 500 ms prior to and after the test grating. Pedestal contrasts of 0% and 32% were tested at mean luminance levels of 150 cd m−2 and 1.5 cd m−2. The results show that both increasing light level and increasing contrast level resulted in smaller temporal summation times. In the current conditions both these effects approximately halve the summation time such that for a stimulus of low light level and of low pedestal contrast the summation time was ∼60 ms; low light, high contrast ∼30 ms; high light, low contrast ∼30 ms; and high light, high contrast ∼15 ms. The results imply that the temporal response of the visual system quickens with increasing contrast.
Modelling of Human Flicker Detection at Various Light Levels
Authors: Rovamo J , Raninen A 
Published: December 2015

Root-mean-square flicker sensitivity was measured within 0.2 – 2500 phot td and 0.5 – 30 Hz for a small spot with an equiluminous surround using computer graphics and a 2AFC method. In temporal noise, flicker sensitivity as a function of temporal frequency had a low-pass shape at all illuminances. Without temporal noise, the flicker sensitivity functions showed a band-pass shape at high illuminances, but changed to a low-pass shape at low illuminances. Our data are well described (goodness of fit 88%) by a model comprising: (i) low-pass temporal filtering by the modulation transfer function (MTF) of the photoreceptors ( R), (ii) high-pass temporal filtering by the MTF of the neural visual pathways ( P) resulting from lateral inhibition, (iii) addition of the temporal equivalent ( Nit) of internal neural noise, and (iv) detection by a temporal matched filter, provided that we take into account the fact that receptor responses become weaker and slower with decreasing illuminance despite adaptation. In our model detection efficiency was \eta( f)=0.148 f−0.568, Nit=46.3 μs and P( f) equal to f, where f is flicker frequency. In addition, R= R0[1+( f/ fc)2]−3, where R0=(1+24.1/ I)−0.5, fc=6.33 I0.172, and I is retinal illuminance. The model indicates that for the detection of a flickering spot in cone vision (i) the strength of lateral inhibition is independent of light level and (ii) quantal noise and dark light always remain insignificant sources of noise. (Mathematical expressions may not appear as intended)
Category Ratings of Visual Velocity Support Haubensak's Consistency Model
Authors: Ehrenstein W H , Sokolov A N 
Published: December 2015

Identical stimuli receive higher category ratings when presented in a positively skewed distribution (smaller stimuli occur more often than larger) and lower ratings in a negatively-skewed distribution (larger stimuli occur more often). This frequency effect has been explained by a tendency to assign the same categories to the same stimuli (‘consistency model’ by Haubensak, 1992 Journal of Experimental Psychology: Human Perception and Performance18 303) rather than by a tendency to assign the same number of stimuli to each category. The consistency model postulates the prime importance of stimuli that occur early in a sequence, with the underlying assumption that more frequent stimuli have higher probability of occurring earlier. Thus, presentation order rather than frequency of stimuli might be decisive. We asked whether a ‘frequency’ effect would still obtain when stimuli are in fact presented with equal frequency, but in a sequence derived from positively or negatively skewed source samples. Ratings of visual velocity were obtained for a dot that started to move at 0.5 deg below fixation in leftward or rightward direction for 2, 2.5, or 3 deg. Five velocities (3.0, 4.5, 6.0, 7.5, 9.0 deg s−1) were presented 10 times each (in a balanced combination of stimulus duration and displacement) and were rated by 32 subjects using three categories (slow, medium, fast). Our results clearly support Haubensak's model: identical velocities were rated higher/lower in presentation sequences that mimicked the order effects of positive/negative skewing, respectively. Moreover, computer simulation of the Haubensak model reveals good agreement between predicted and observed results.
Evidence for Good Recovery of Lengths of Real Objects Seen with Natural Stereo Viewing
Authors: Frisby J P , Buckley D , Duke P A 
Published: December 2015

How good is human size constancy for real objects seen with natural stereo viewing, which minimises the opportunity for monocular size cues to play a role? This question has attracted renewed interest in recent years, arising mainly from the work of Todd and his colleagues. They have argued, initially from experiments in which stereograms were used, but more recently from studies based on real scenes, that poor performance on length judgment tasks suggests that human vision is weak at computing metric representations. At ECVP '95, we described several experiments demonstrating quite good performance on the task of matching the lengths of two stationary real objects, gnarled wooden sticks, under binocular viewing with head held fixed (1995 Perception24 Supplement, 129). We now report extensions to that work aimed at checking whether this good performance is maintained over three viewing distances (79, 158, and 355 cm), and when test and matching sticks are of different thicknesses. Matching performance was measured with a variety of indices: reliability, accuracy, Weber fraction, and absolute error. Relatively poor performance was observed when the sticks were viewed monocularly at the near and far distances but binocular viewing produced good performance at all distances. These results suggest that stereo can support good representations of metric scene structure when length judgments of natural objects are required under (quasi-)natural viewing. The implications of these results for theories of structure-from-stereo are discussed, and reasons are suggested why our results might differ from those of Todd and his colleagues.
The Dominance of Static Depth Cues over Motion Parallax in the Perception of Surface Orientation
Authors: Cornilleau-Pérès V , Marin E , Droulez J 
Published: December 2015

Under polar projection (the natural projection for visual scenes) motion parallax is a powerful cue specifying relative depth. For small-field stimuli, it is ambiguous in the sense that a concave surface can be perceived as convex and deforming. By contrast, concavity/convexity of wide-field surfaces is unambiguously perceived. This led us to hypothesise a critical role of the 3-D rigidity constraint for large visual scenes in motion (Dijkstra et al, 1995 Vision Research35 453 – 462). To examine this hypothesis, we exposed subjects to planes inclined in space, and asked them to report the tilt (direction of inclination). Depth was specified either by motion parallax (MP, the surface oscillated around a frontoparallel axis) or by static perspective cues (SP, orthogonal square grids drawn on the plane). At ECVP95, we had reported a predominance of SP over MP when the tilts specified by these two cues ( tMP and tSP respectively) differed (1995 Perception24 Supplement, 137). Since these results were obtained for fast movements (oscillation frequency for MP: 3.6 Hz), we extended our investigation to a slower frequency (0.5 Hz) which is more likely to be involved during natural head-movements. We found that: (i) errors in tilt reports were larger for MP than for SP, and decreased with increasing field-size; (ii) in the case of conflict ( tMP= tSP±90°), the reported tilt was either tMP or tSP, rather than an average of these two values; (iii) in this case, tilt was most often reported according to SP, rather than to MP cues; this effect occurred even when the accuracies for the two individual cues were similar. Therefore, in a conflict situation between MP and SP, surface orientation is reported according to a winner-take-all rule, which is largely in favour of static grid-cues. Hence, even for wide-field movements, the image contrast distribution can lead the visual system to prefer an unrigid, rather than rigid, solution to the 3-D shape-from-motion problem.
Conflict between Stereo and Perspective in Resolving the Slant of Cyclopean Trapezoids
Authors: Gillam B , Cook M , Blackburn S 
Published: December 2015

Cue theory has had a resurgence in recent years as part of modular approaches to vision. Cues often seem to combine according to a weighted linear sum, although interactions may also occur. Conflict studies show that linear perspective and stereo combine to influence slant perception, with perspective weighted surprisingly heavily. We investigated the effect of conflicting linear perspective in reducing stereo slant when perspective is present as a purely cyclopean outline shape, compared with conditions when the shape is also monocularly present. In experiment 1, random line stereograms were generated with cyclopean trapezoids standing out from a background. Their outline convergence either conflicted with or supported a stereo gradient across the surface of the trapezoid. Two stereo slants and two standing disparities were used. In experiment 2, an aperture condition was included with the cyclopean trapezoids behind the surround. There was strong influence of trapezoid direction on perceived slant. This influence was only marginally increased by outlining the trapezoid. These findings demonstrate the effectiveness of cyclopean shape as perspective information. As expected, when the trapezoid was an area seen through an aperture, its direction did not significantly affect stereo slant. We conclude that stereo and perspective cannot be considered as separate modules. In binocular vision, perspective is conveyed stereoscopically.
Perception of Photographic-Quality Caricatures of Emotional Facial Expressions
Authors: Calder A J , Young A W , Rowland D , Gibbenson D R , Hayes B M , Perrett D I 
Published: December 2015

G Rhodes, S E Brennan, S Carey (1987 Cognitive Psychology19 473 – 497) and P J Benson and D I Perrett (1991 European Journal of Cognitive Psychology3 105 – 135) have shown that computer-enhanced (caricatured) representations of familiar faces are named faster and rated as better likenesses than veridical (undistorted) representations. Here we have applied Benson and Perrett's graphic technique to examine subjects' perception of enhanced representations of photographic-quality facial expressions of basic emotions. To enhance a facial expression the target face is compared to a norm or prototype face, and, by exaggerating the differences between the two, a caricatured image is produced; reducing the differences results in an anticaricatured image. In experiment 1 we examined the effect of degree of caricature and types of norm on subjects' ratings for ‘intensity of expression’. Three facial expressions (fear, anger, and sadness) were caricatured at seven levels (−50%, −30%, −15%, 0%, +15%, +30%, and +50%) relative to three different norms; (1) an average norm prepared by blending pictures of six different emotional expressions; (2) a neutral expression norm; and (3) a different expression norm (eg anger caricatured relative to a happy expression). Irrespective of norm, the caricatured expressions were rated as significantly more intense than the veridical images. Furthermore, for the average and neutral norm sets, the anticaricatures were rated as significantly less intense. We also examined subjects' reaction times to recognise caricatured (−50%, 0%, and +50%) representations of six emotional facial expressions. The results showed that the caricatured images were identified fastest, followed by the veridical, and then anticaricatured images. Hence the perception of facial expression and identity is facilitated by caricaturing; this has important implications for the mental representation of facial expressions.
Memory Representation of Object Colours
Authors: Yendrikhovskij S N , Blommaert F J J , de Ridder H 
Published: December 2015

Memory colours, ie colours recalled in association with familiar objects, impose a powerful constraint on colour appraisal of images of natural scenes. The purpose of this study is to specify the memory representation of one particular object colour. To this end, the colour of a banana was manipulated by varying hue-angle and saturation in the CIELUV colour space. Subjects' task was to rate the similarity in colour of the resulting banana samples displayed on the screen to the typical ripe banana stored in their mind. In order to examine the dependence of memory colour on texture information and context, three ways of presentation were used: original (banana among other fruit), isolated (the same banana against a homogenous gray background), and contour (silhouette of the banana with its average colour against the gray background). The relationships between the similarity judgments and chromaticity coordinates of the manipulated banana-represented points in the CIELUV colour space is described by a bivariate normal distribution with four parameters: two means and two variances of the Gaussians on the hue and saturation dimensions. For all three types of presentation, the variance of hue is significantly smaller than the variance of saturation; this suggests that memory description of hue is more precise than that of saturation. The data show systematic differences in the hue of memory colour between the original, isolated, and contour presentations of the banana. A model describing the hue shift in terms of illuminant and surface information content in the images is discussed.
Changes in Perceived Object Shape with Changes in Lighting Model and Surface Properties
Authors: Maloney L T , Mamassian P , Landy M S 
Published: December 2015

We examined the influence of lighting and bidirectional surface reflectance distribution function (BRDF) on the perceived shape of real objects viewed monocularly and binocularly. We asked observers to adjust a ‘circle-stick’ gradient probe optically superimposed on a smooth, asymmetric, pear-shaped wooden object placed directly in front of the observer at a distance of 60 cm. By using real objects, we avoid problems with unrealistic rendering algorithms and CRT presentation of stimuli. The lighting models used were simple (a single near-punctate source and a flat black background), the viewing conditions (in the binocular case) realistic, and the BDRFs selected not implausible. We did not assume that the viewer's perception of shape is veridical under any of the conditions considered, nor did we assume that surface shape estimated from gradient probe settings is an unbiased estimate of perceived shape. We sought to establish whether changes in lighting model and BRDF affect observer performance and, by implication, perceived shape. Observers viewed the object under all eight of the possible combinations of the binary factors: (a) monocular and binocular viewing of the object, (b) near-punctate illumination from above-left or above-right, and (c) matte wooden BRDF (the natural surface of the object) and gloss white BRDF (the same object painted). For each condition there was a total of ten gradient settings at each of over one hundred surface locations. The same locations were used for each of the eight conditions. We report results of analyses and discuss their implications.
Biography vs Biology in Visual Aesthetic Preference
Authors: Rentschler I , Jüttner M , Unzicker A 
Published: December 2015

Theories concerning the human aesthetic sense are rarely based on moderate views. While Immanuel Kant argued that the aesthetic judgment is strictly independent of the knowledge of things ( Critique of Judgment, §15, page 1795), modern biological research suggests that the aesthetic sense emerged as a by-product of natural selection for the recognition of signals. We tested such theories by measuring the effect of cognitive training on aesthetic preference. Using a psychometric method of paired comparisons we obtained preference data by presenting to twenty-two naive observers 16 compound Gabor signals that were equally spaced on a full ‘circle of form’ in a 2-D feature space. Subjects were then trained to classify the same patterns into four deliberately defined pattern classes. The effect of this learning procedure was then assessed in another preference experiment. We show that our preference data can be explained in terms of two factors: pattern complexity and pattern symmetry. Cognitive learning (ie biography) significantly affected the complexity factor, while the symmetry factor remained invariant. We argue that these findings are inconsistent with the extreme positions of both Kant and the biologists. Rather, they imply that aesthetic preference is being determined by the interplay of ‘pre-wired’ biological functions of signal recognition and of individual experience.