bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Discrimination near the Background Field: Transfer of the ‘Crispening Effect’ to Colour
Authors: Ovenston C , Whittle P
Published: December 2015

Experiments are described which look for a ‘crispening effect’ in the hue domain. This effect—an enhanced discrimination around the adaptation level—has been shown for achromatic stimuli by both brightness scaling and contrast discrimination techniques (Whittle, 1992 Vision Research32 1493 – 1507). In the present experiments these techniques are applied to chromatic variations along L(-M)L-cone and S-cone axes (MacLeod — Boynton isoluminant chromaticity space). Results so far support a crispening effect for the L(-M)-cone axis but not the S-cone axis. This enhanced discriminatory power in the vicinity of the background luminance and hue accords with the importance of relative, rather than absolute, values for coding by the visual system.
The Binocular Summation of Chromatic Contrast
Authors: Simmons D R , Kingdom F A A
Published: December 2015

The level of binocularity possessed by mechanisms sensitive to chromatic contrast is still unclear. Recent studies of stereopsis and chromatic contrast have suggested that stereopsis is maintained at isoluminance, although the contrast sensitivity and disparity ranges of chromatic stereopsis mechanisms are reduced compared to luminance stereopsis mechanisms. Rose, Blake, and Halpern (1988 Investigative Ophthalmology and Visual Science29 283 – 290) hypothesised a link between binocular summation (ie the superiority of binocular detection over monocular detection) and stereopsis. Is this link maintained with heterochromatic isoluminant stimuli? To address this question, the binocular and monocular contrast thresholds for the detection of 0.5 cycle deg−1 Gabor patches were measured. The stimuli possessed different relative amounts of colour and luminance contrast ranging from isoluminance (red/green) to isochrominance (yellow/black) through intermediate values. It was found that, with these stimuli, binocular detection was well modelled by assuming independent mechanisms sensitive to chromatic contrast and luminance contrast. Furthermore, with isoluminant stimuli, levels of binocular summation were above those expected from probability summation between the eyes, thus providing evidence for binocular neural summation within chromatic detection mechanisms. Given that stereoscopic depth identification is impossible at contrast detection threshold with isoluminant heterochromatic stimuli, these results suggest that the link between stereopsis and levels of binocular neural summation may not be a particularly strong one. These results also provide clear evidence for the binocularity of chromatic detection mechanisms.
Effects of Adaptation on Perceived Location for First-Order and Second-Order Visual Stimuli
Authors: Whitaker D , McGraw P V , Levi D M
Published: December 2015

Observers adapted to a stimulus consisting of two vertically separated antisymmetric Gaussian blobs. This was immediately followed by a 3-Gaussian-blob alignment task, whose outer two elements were spatially coincident with those of the adapting stimulus. The adapting antisymmetric stimulus resulted in a perceived misalignment of the central element of the test stimulus, and the magnitude of this perceived offset was established by the method of constant stimuli. The apparent offset increased as a power function of the adapting stimulus contrast at all test contrast levels. Perceived offset was greater for low-contrast test stimuli, although dependence upon the contrast of the adapting stimulus was less pronounced. When expressed as a function of adapting/test contrast ratio, data for all conditions collapsed together to form a single, saturating function which was well described by the formula k/[ k'+(1/ratio)], where k and k' are constants. Thus, at high adapting/test ratios, the function saturated at an offset of k/ k'. Adaptation effects were measured for luminance-defined first-order stimuli, and also stimuli defined by variations in texture contrast, which can be termed second-order. The effects of adaptation on perceived offset for second-order stimuli were at least as large as those for first-order, but little or no crossover adaptation occurred, ie adapting to a second-order antisymmetric stimulus produced no effect on a first-order test stimulus and vice versa. This suggests that the mechanisms involved in the localisation of first-order and second-order stimuli are independent.
Segregation of Chromatic Element-Arrangement Textures
Authors: Oddo S , Beck J , Mingolla E
Published: December 2015

We compared the perceived segregation of patterns composed of the same two element types arranged in vertical stripes in the top and bottom regions and in a checkerboard in the middle region. The elements in all patterns differed in hue. Some patterns were equated for luminance and others for brightness. We investigated the effects of hue, spatial scale, and background luminance on the segregation of the element-arrangement patterns. Hue similarity, as rated by subjects in a separate procedure, was a relatively weak factor for predicting perceived segregation. The effects of brightness differences and luminance differences interacted with background luminance and spatial scale. Perceived segregation was stronger with a black background than with a white background (Pessoa, Beck, and Mingolla, ARVO '94; Vision Research, in press) and stronger for higher spatial frequencies. The results are discussed in terms of the relative importance of ‘low-order’ factors such as cone contrasts and ‘high-order’ factors such as similarity in mediating texture segregation.
Inhibition of Return without Visual Awareness
Authors: Watanabe K , Shimojo S
Published: December 2015

When a cue and a target are successively presented at the same location, reaction times to discriminate the location of the target are longer than when they are at different locations (inhibition of return: IOR). We found that visual awareness of the cue was not necessary for IOR to occur. Both eyes dichoptically viewed 9 × 9 scattered arrays of vertical or horizontal line segments. To avoid effects of eye dominance and binocular rivalry, cue displays were presented briefly (33, 50, or 200 ms). Three types of cue displays were randomised: (i) no cue: horizontal segments for the left (right) eye and vertical segments for the right (left) eye; subjects perceived scattered binocularly-combined crosses, (ii) binocular (fusible) cue: displays for both eyes had cue elements (a horizontal or vertical segment popping out among orthogonal background segments) and identical interocularly; subjects easily perceived the cue; (iii) dichoptic cue: displays for both eyes had cues at the same location, but all the segments were interocularly orthogonal. Here, because of the brief presentation that horizontal and vertical segments were just combined binocularly, and subjects could see only scattered crosses. Thus, they could not be aware of the cue, which exists at the monocular level. After the cue display disappeared, the target displays [same as the cue display in (ii), but with an independent location of the pop-out target] were presented (ISI=400, 800, or 1200 ms). Reaction time to discriminate location of the target was measured for three subjects who fixated on a fixation point. In our results, IOR took place in conditions (ii) and (iii). This suggests that localisation of the cue occurs without visual awareness, which then leads to IOR.
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.
Reaction Time and Time Course of Neuronal Responses in MT and MST at Different Stimulus Contrasts
Authors: Thiele A , Hoffmann K-P
Published: December 2015

Direction-selective neurons from the middle temporal area (MT) and the middle superior temporal area (MST) were recorded while a monkey performed a direction discrimination task. Stimuli consisted of evenly spaced bars moving in one of the four cardinal directions. Monkey's reaction time, single-cell latency, and direction selectivity were calculated when stimuli of 53%, 24%, and 4% contrast were presented, and the monkey indicated a correct decision. Mean reaction time was 359±77 ms at 53% contrast, 391±107 ms at 24% contrast, and 582±374 ms at 4% contrast. Most neurons exhibiting direction selective responses at 53% contrast was also active at 24% contrast (MT, 99%; MST, 88%). The number of neurons still exhibiting stimulus-related activity at 4% contrast dramatically decreased (MT to 28%; MST to 41%). Shortest latencies were found at high contrast level (53% contrast; MT, 29 ms; population mean, 76±40 ms; MST, 35 ms; population mean, 77±27 ms). Single cell and population latency increased at lower contrast (4% contrast: MT minimum, 86 ms; population mean, 180±76 ms; MST minimum, 97 ms; population mean, 205±56 ms). This indicates that the mean increase in latency at the single-cell level only partially reflects the increase in reaction time (mean reaction time increased by 223 ms, while mean single-cell latency increased by ∼100 ms in MT and MST). We therefore calculated the normalised population response at different contrast levels. The maximal population activity was always found at the highest contrast level and this was set to 1. In MT it took 75 – 80 ms from stimulus onset until half maximal activity (0.5) was reached at 53% contrast. To reach 0.5 took 85 – 90 ms at 24% contrast and 205 – 210 ms at 4% contrast. For MST the respective values were 85 ms (53% contrast), 90 ms (24% contrast) and 255 ms (4%) contrast. Thus the time to reach half the maximal population activity much better reflects the reaction time than the mean of the latencies calculated from single cells.
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)
Increment and Decrement Detection across the Mach-Band Stimulus
Authors: Henning G B , Hill N J , Millar R W , Green G G R
Published: December 2015

The ability of observers to detect bright and dark horizontally oriented lines was measured using standard 2AFC procedures. The lines to be detected were either increments or decrements in luminance superimposed on a luminance pattern that produced horizontally oriented Mach bands. Measurements were made in the uniform regions of high and low luminance that flank the Mach-band-producing luminance ramp as well as in the vicinity of the bright and dark Mach bands. Detection performance was significantly affected by both dark and bright Mach bands. The reliability of the results makes it reasonable to attempt to infer, following E M Lowry and J J DePalmer (1961 Journal of the Optical Society of America51 740 – 746), spatial weighting functions for (one-dimensional) pattern vision.
Neural Dynamics for Preattentive Perceptual Grouping: Linking Gestalt Laws and Cortical Synchronisation
Authors: Fellenz W A
Published: December 2015

As revealed by the Gestalt school in the first half of the century, visual perception is governed by certain simple rules which group parts into wholes in accordance to ‘laws’ like grouping by proximity, similarity, closure, symmetry, and good continuation. Although these principles can be investigated by experiment, their underlying neural computation is largely unknown. It has been speculated that synchronisations of visual cortical neurons may serve as the carrier for the observed perceptual grouping phenomenon. We present a neural network for preattentive perceptual grouping derived from neurophysiological and psychophysical findings, incorporating a relaxation phase labeling and diffusion process. The network groups visual features into perceptual entities by (de)synchronising parametric phase labels of simple neural oscillators using a constraint satisfaction mechanism. The local constraints between features, which model the Gestaltist grouping principles of proximity and good continuation, act horizontally in and vertically between feature dimensions to allow for the emergent segregation of globally salient contours in phase space, suppressing false responses generated from the edge detection stage. By applying the grouping mechanism to various contour types ranging from dotted lines to intensity edges we show that the phase-based object representation is able to account for various perceptual phenomena like the closing of small contour gaps and the perception of illusory contours. Based solely on edge responses and local interactions thereupon, the neural dynamics allows the emergent formation of globally distinguishable objects in phase space, which can be extracted by an attentional mechanism tracking the spatially modulated phase information.
Dynamics of Visual Supervised Learning: A Statistical-Physics Approach
Authors: Unzicker A , Jüttner M , Rentschler I
Published: December 2015

We analysed human supervised learning and classification performance for compound Gabor gray-level patterns. We found that internal visual representations for supervised learning and classification may not be constructed in a smooth process of gradual development (Jüttner and Rentschler, 1996 Vision Research in press). Rather, it seemed that certain learning states (‘stereotypes’) recur that may be considered as ‘perceptual hypotheses’. Such effects have a transient character and cannot, therefore, be studied on the basis of cumulative learning data, which allow smoothing at the expense of temporal resolution. Thus, we analyse classification behaviour in terms of the evolution of a thermodynamic system, that is a system characterised by Gibbs statistics. Here it is assumed that a classification error occurs when a noise-influenced decision process passes an ‘energy gap’ related to the distance of signals in feature space. This approach has been extended to a wide range of distance-based models, originated by different fields, such as classical psychometrics, signal detection theory, technical pattern recognition, and connectionism. We made use of the finding that all these models can be related to a uniform mathematical structure (Unzicker et al, 1995 Perception24 Supplement, 95). The subjects' performance can then be described as a cooling process that reveals adaptive feature extraction during learning.
Cortical Circuitry Revealed by Reverse Correlation in the Orientation Domain
Authors: Ringach D L , Carandini M , Sapiro G , Shapley R
Published: December 2015

We applied a novel ‘white-noise’-like stimulation technique to study the neural circuitry underlying the orientation tuning of simple cortical cells in cats and monkeys. We generate an image sequence (the stimulus) by selecting, at each refresh time, a random image from a finite set s of orthonormal images. For simple cells, we have shown that the above stimulus allows one to compute the projection of the receptive field onto the subspace spanned by the vectors in s (Ringach et al, 1996 ARVO Proceedings in press). The calculation is based on the cross-correlation between the input image sequence and the cell's spike train output. In the present study, we selected s to be the subspace spanned by sine-wave gratings having a fixed spatial frequency but different orientations and spatial phases. A finite orthonormal basis for this subspace is a subset of the complete two-dimensional discrete Hartley basis functions. The choice of this ‘orientation-subspace’ allowed us to measure how the orientation tuning of the cells evolved in time at a particular spatial frequency. In addition to a sharp peak of activity at the optimal orientation of the cell, we observed secondary peaks of the orientation tuning curve at off-optimal orientations. Off-peak inhibition was also observed frequently. These results are difficult to reconcile with feedforward models of the neural network producing orientation tuning, but are consistent with recurrent cortical network models (Carandini and Ringach, 1996, paper presented at the Computation and Neural Systems Conference).
Evoked Magnetic Field Elicited by Motion and Motion Aftereffect
Authors: Osaka N , Ashida H , Osaka M , Koyama S , Kakigi R
Published: December 2015

Motion aftereffect (MAE) is a negative aftereffect caused by prolonged viewing of visual motion: after gazing at a moving grating for a while, a stationary image will appear to move in the opposite direction (Ashida and Osaka, 1995 Vision Research35 1825). Evoked magnetic field (magnetoencephalogram: MEG) was measured on a human subject observing visual motion and MAE. Magnetic evoked field (80 averagings) was measured from 37 points over occipital and parietal areas (Magnes SQUID biomagnetometer, BTi) during watching a horizontally moving sinusoidal grating with low spatial frequency (2 cycles deg−1 with 5 Hz: motion condition) and immediately after stopping the moving grating (MAE condition). Dipole estimates based on equal magnetic field contour suggest that the main loci subserving visual motion and MAE appear to be the surrounding region over occipital and parietal areas in the human brain. Further analysis is now underway. In general, this appears to be in good agreement with another study using fMRI-based MAE measures [Tootell et al, 1995 Nature (London)375 139] in which a clear increase in activity in these areas was observed when subjects viewed MAE.
Temporal and Spatial Frequency Tuning of the Flicker Motion Aftereffect
Authors: Bex P J , Verstraten F A J , Mareschal I
Published: December 2015

The motion aftereffect (MAE) was used to study the temporal-frequency and spatial-frequency selectivity of the visual system at suprathreshold contrasts. Observers adapted to drifting sine-wave gratings of a range of spatial and temporal frequencies. The magnitude of the MAE induced by the adaptation was measured with counterphasing test gratings of a variety of spatial and temporal frequencies. Independently of the spatial or temporal frequency of the adapting grating, the largest MAE was found with slowly counterphasing test gratings (∼0.125 – 0.25 Hz). For slowly counterphasing test gratings (<∼2 Hz), the largest MAEs were found when the test grating was of similar spatial frequency to that of the adapting grating, even at very low spatial frequencies (0.125 cycle deg−1). However, such narrow spatial frequency tuning was lost when the temporal frequency of the test grating was increased. The data suggest that MAEs are dominated by a single, low-pass temporal-frequency mechanism and by a series of band-pass spatial-frequency mechanisms at low temporal frequencies. At higher test temporal frequencies, the loss of spatial-frequency tuning implicates separate mechanisms with broader spatial frequency tuning.
Short-Term Memory for Speed
Authors: Thompson P , Stone R , Walton E
Published: December 2015

We have measured the retention of information about stimulus speed in visual short-term memory by measuring speed discrimination in a two-interval forced-choice task. We have also measured such discrimination in conditions where a ‘memory masker’ is presented during the interstimulus interval (ISI) in a fashion analogous to the experiment of Magnussen et al (1991 Vision Research31 1213 – 1219). Magnussen et al found that spatial frequency discrimination was disrupted when the mask had a spatial frequency that differed from the test spatial frequency by an octave or more. We have investigated the speed discrimination of 8 Hz, 1 cycle deg−1 drifting sine-wave gratings with the following drifting masks presented in the ISI: (i) 8 Hz 1 cycle deg−1, same direction as the test; (ii) 8 Hz, 8 cycles deg−1, opposite direction to the test; (iii) 8 Hz, 8 cycles deg−1, same direction as the test; (iv) 24 Hz, 3 cycles deg−1, same direction as the test. These masks were chosen to investigate whether the temporal frequency, the spatial frequency, the speed, or the direction of motion of the mask affected retention. We found that in none of these conditions was the discrimination of the test gratings impaired significantly. This pattern of results is therefore different from that found with spatial frequency discrimination and suggests that, whatever mechanism is responsible for the retention of information about speed, it is different from that responsible for the retention of information about spatial frequency.
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.
Rapid Categorisation of Natural Images with Extrafoveal Presentations
Authors: Thorpe S , Fabre-Thorpe M , Richard G
Published: December 2015

Last year, we showed that most of the visual processing for categorising centrally presented images could be done in 150 ms. The human subjects were given a go — no go categorisation task in which they had to release a button when they could identify an animal. All the pictures were natural scenes taken from a vast CD-ROM data bank allowing access to several thousands of stimuli so that each image was only seen once. Targets (animals) included fish, birds, mammals, reptiles, insects in their natural environment; distractors included landscapes, trees, flowers, fruits. They were presented for a very short duration (20 ms) in order to avoid eye movement. In the present study we wanted to evaluate how the performance was affected with extrafoveal stimulations. We used the same task, but the visual stimuli could be presented at random, either centrally where subjects had to maintain fixation or laterally (left or right hemifield). Behavioural data and concomitant evoked potentials were recorded. The subject's performance was extremely good with a mean score of 90% correct and a mean reaction time of 500 ms. Comparison of performance between central and lateral stimulations showed that most subjects could process lateral and central stimuli with the same speed (reaction time distributions were not statistically different), and that, although extrafoveal presentations induced a drop in the percentage of correct responses (mean decrease 5%), it was not significant in all subjects. Moreover, when compared with last year's study the increase of the number of spatial locations where the visual stimulus could appear did not induce a significant behavioural cost, in terms of speed or accuracy of the response. We also looked at a possible hemispheric specialisation with no clear results. The results obtained here show that even with shared spatial attention and extrafoveal vision, the human visual system is remarkably efficient in an identification task.
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.
Is Coarse-to-Fine Tuning in Object Recognition One of Size or Scale?
Authors: Fiser J , Subramaniam S , Biederman I
Published: December 2015

Subjects attempted to detect a target object specified by name (eg “chair”) in rapid serial visual presentation sequences, with each sequence consisting of 40 gray level, 72 ms images of common objects. On the 50% of the trials in which a target was present it was never in the first or last eight positions. In homogeneous sequences, the images were all of the same size (all large or all small differing by a factor of five) or scale (spatial frequency, SF, either all low-passed [2 cycles deg−1] or all high passed [10 cycles deg−1], in a 1.5 octave band). There was no difference in detection accuracy between the different sizes or the different scales. In the switched sequences, the target could differ in size or scale from all the other images in the sequence. A strong asymmetry now emerged in that small-size or high-passed targets were much more difficult to detect than when in homogeneous sequences, whereas the large-size or low-passed images were much easier! Is this coarse-to-fine tuning based on size or scale? When size was pitted against scale, in that targets could either be of small size and low SF or large size and high SF, the large-size objects were much easier to detect, with only a slight modulating effect of scale. Size — scale tuning thus operates on space (={size}) rather than SF, and requires some time for its implementation, though less than that required for the first eight images. Once implemented, the tuning can be completely efficient, as evidenced by the equivalent levels of performance in the homogeneous conditions.
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.
Holding an Object: Kinesthesia Does Not Influence the Visually Perceived Size
Authors: Brenner E , Smeets J B J , van Damme W J
Published: December 2015

Because of the inverse relationship between an object's distance and its retinal image size, visual judgments of size require information on distance. Holding an object can obviously influence where one considers it to be. Does kinesthetic information on the posture of one's arm influence visual judgments of the object's size?

Subjects were given a 5 cm cube at which they were asked to look before the experiment started, and to hold under the table in their left hand during the experiment. In their right hand, they held a rod behind a mirror. A simulated cube was presented binocularly—at the tip of the rod—via the mirror. Each presentation started with the subject placing the rod somewhere on a surface behind the mirror. The simulated cube appeared at that position (or 2.5 cm closer or further away) for 4 s, after which the subject had to indicate whether the cube he/she had seen was larger, the same, or smaller than the reference. The size of the simulated cube was varied between trials.

Whether the simulated cube was closer, at the same position, or further than the rod influenced the point of subjective equality (the size of the simulation at which subjects judged it to match the reference). However, the average distance between the subject and the simulation was also different. When the latter differences were taken into account (by selecting data with the same average distance between the subject and the simulation) the abovementioned influence of the distance between the rod and the simulated cube disappeared.