bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studying Colour Appearance by the Uniform Scaling of Colour Circles
Authors: Ovenston C A 
Published: December 2015

Scaling experiments presented at ECVP 1996 (Ovenston and Whittle, 1996 Perception25 Supplement, 16) demonstrated the importance of the background chromaticity in setting subjective equal-interval colour scales along the L(-M)-cone and S-cone axes of Macleod - Boynton isoluminant chromaticity space. In the current experiments we also investigate colour scaling but around circles centred on different background chromaticity points. This is done in a logarithmic version of the MacLeod - Boynton diagram, which is much closer to an equal-subjective-interval diagram than the linear version. However, colour circles set with even geometrical spacing in the log diagram do not appear to have even subjective spacing. Preliminary results show that setting hue to even subjective spacing is a convenient and powerful method for studying the role of constant-cone-excitations and opponent-colour axes in determining hue.
Noisy Template Matching: A Model for Detection and Discrimination
Authors: McIlhagga W , Pääkkönen A 
Published: December 2015

The detection and discrimination of simple patterns occupies a central place in visual psychophysics. A wide variety of phenomena have been observed in this paradigm, such as: Weber's law; masking (simultaneous, forward, and backward); masking by noise; spatial frequency tuning; orientation tuning; and area summation. We suggest that many of these phenomena can be explained by a simple model which we call ‘noisy template matching’. In this model, the encoded stimulus is matched to a memorised template. Both stimulus and template are corrupted by additive noise. The template matching operation yields a decision variable, to which more noise is added. This model is very simple, but it has many interesting consequences. It provides qualitative explanations for many of the phenomena mentioned above, and with additional (but we think reasonable) assumptions about lens blur, contrast nonlinearity (Whittle, 1986 Vision Research26 1677 – 1691), uncertainty (Pelli, 1985 Journal of the Optical Society of America2 1508 – 1532), and suboptimal templates, the model also provides good quantitative accounts of these phenomena.
Eye Movements during Geometrical Problem Solving
Authors: Epelboim J , Suppes P 
Published: December 2015

Diagrams are used extensively in posing and solving geometry problems. It is likely that strategies that good problem-solvers have developed for looking at diagrams reflect their reasoning about each problem. This suggested that the eye-movement patterns of geometry experts, observed while they solve problems posed with diagrams, are likely to contain new information about their reasoning. Eye-movement data, collected while subjects solved geometry problems posed as diagrams, were examined. Three subjects participated. Two of the subjects (‘experts’) were skilled at solving geometry problems. The third subject (‘non-expert’) had last solved such problems over 50 years prior to the experiment, and did not know how to proceed on most of the problems. The eye-movement pattern reflected cognitive operations used to solve each problem. Fixation durations depended, to some extent, on cognitive or perceptual processing of features at each gaze location. For example, fixations were longer when gaze was on the angle in question, than when gaze was on other angles or line-segments. Likewise, saccades were made to features that were being considered, as indicated by verbal protocols. Expert subjects combined simple features into more complex, imaginary structures, as was required to solve the problem. They scanned the areas of the diagram that fell within the imagined contours of these structures. The non-expert did not construct such structures. He only scanned visible features of the diagram. Variability in durations of fixations and landing positions of saccades was not due solely to the probabilistic nature of the oculomotor processes. Such processes, however, clearly play an important role in determining the eye-movement pattern in this task, as they do in other visually-guided tasks.
Complexity of Chinese Ideograms is Related to the Number of Sampling Elements
Authors: Danilova M V , Bondarko V M , Shelepin Y E 
Published: December 2015

Two sets of psychophysical experiments were carried out to find a qualitative measure of the complexity of visual images. The stimuli were 15 Chinese ideograms of the same size. In experiment 1, observers were asked to rate the complexity of images. In experiment 2, for each stimulus the threshold size was determined, defined as the smallest size for which the perceived quality of the image was the same as for large (2 deg) stimuli, ie all details were clearly seen and the stimuli had the same contrast. The measured threshold sizes were in the range 7.9 – 27.6 min arc. Analysing the data further, we found that for some ideograms the sizes of the minimal details (strokes, dots) corresponded to the resolution limit (1 min arc). Some ideograms contained parts with parallel stripes forming quasi-gratings. The distances between stripes at threshold were 1.8 min arc which corresponds to the tuning frequency of the highest spatial frequency channel (Wilson et al, 1983 Vision Research23 873 – 882). The average order of ideograms sorted by degree of complexity was similar to the order according to threshold size. Thus we found a direct correspondence between the complexity of an object and a description in terms of the minimal number of elements needed to preserve the quality of a reduced image. Our results are in agreement with concepts of complexity expressed as a number of details in objects as suggested by Landolt and Snellen, or as a number of spatial-frequency channels as suggested by Ginsburg (1971 IEEE Proceedings 283 – 290).
What Statistics Determine Segmentation of Orientation-Defined Textures?
Authors: Rosenholtz R 
Published: December 2015

Beck suggested that texture segmentation is based upon differences in the first-order statistics of stimulus features such as orientation, size, and contrast. However, this theory does not indicate how these differences might be quantified, or what properties of the statistics might be used. Some alternative models postulate that texture segmentation is determined by the responses of spatial-frequency channels, where the channels contain both a linear filtering mechanism and various nonlinearities. Such models do a good job of predicting human performance, but do not give us much insight into what textures will segment, since the comparison carried out by the model is often obscured by the details of the filtering, nonlinearity, and image-based decision processes. It is suggested here that, for orientation-defined textures (eg in which each ‘texel’ has a single orientation), segmentation is well-described by something like the ‘significance’ of the differences between (1) the mean orientations, and (2) the angular variances of the two textures. The ‘significance’ of the difference in means takes into account the variability in the texture, so that two homogeneous textures with means differing by 30° may easily segment, while two heterogeneous textures with the same difference in mean may not. Furthermore, it is shown that these statistics may be computed in a biologically plausible way, which greatly resembles the typical filter-based approaches to texture segmentation. Thus the connection between statistical theories of texture segmentation and spatial-frequency channel models becomes more transparent.
Peripheral Advantage in Texture Segmentation: The Role of Spatial and Temporal Factors
Authors: Morikawa K 
Published: December 2015

Previous studies (eg Kehrer, 1989 Spatial Vision4 45 – 62; Gurnsey et al, 1996 Journal of Experimental Psychology: Human Perception and Performance22 738 – 757) have shown that performance peaks several degrees from fixation in texture segmentation tasks, and performance falls as the target texture moves closer to the fovea or further into the periphery. There are two theories for this phenomenon: (1) neural processing speed in the fovea is slower than in the periphery (Kehrer 1989), and (2) the spatial frequency band of the texture is too low (ie too coarse) for the foveal receptive fields (Gurnsey et al 1996). However, the use of backward masking in previous studies made it impossible to decide between the two factors. The purpose of the present study was to isolate them. In experiment 1 a new stimulus configuration with backward masking was used, and previous reports were replicated. In experiment 2, the same texture was presented for 110 ms without a mask, but with added random-dot noise. Without limitations on processing time, the mid-peripheral advantage disappeared, which indicated that the previous findings were due to slower neural processing in the fovea. In experiment 3, a new type of texture was devised consisting of pairs of vertical lines with a horizontal offset. The offset was reversed for the target. Performance for unmasked 110 ms presentation was worst near the fovea and improved monotonically up to 12 deg. This peripheral advantage was spatial, not temporal, because it arose from larger receptive field sizes in periphery. When these results are taken together, the present study demonstrates that there are two independent causes for the mid-peripheral advantage in texture segregation.
Mistaken Identity: Temporal-Order Biases in the Perception of Speed
Authors: Harris J M , Rushton S K 
Published: December 2015

Biases in the perceived speed of a moving stimulus have been observed for various spatial configurations of a motion stimulus (eg Norman et al, 1996 Perception25 815 – 830). In general, psychophysical studies are designed to remove any possible source of bias due to the temporal order of presentation. Here, we examined biases in speed perception between the first and second temporal interval in a 2IFC procedure. The stimulus was a circular patch (∼ 2 deg) containing 50 translating dots. A standard speed was always presented in the first interval (∼ 6 deg s−1), with one of 7 test speeds in the second interval. A range of ISIs (0 – 2.3 s) and stimulus durations (100 – 900 ms) was tested. We also dissociated spatial location (left/right of fixation point) and direction of dot travel (left/right and vertical/horizontal) of the two stimuli, whilst maintaining the temporal separation. In all cases we found an increase in perceived speed from 1st to 2nd interval and further, the effect was independent of direction, ISI, duration, and the spatial position of the 1st and 2nd stimuli. We can suggest no simple account of the results based upon neural fatigue in motion detectors, temporal sampling windows, or representational momentum. Tentative models are currently being explored with three interval stimuli.
Investigating the Time-Course of Task-Dependent Perceptual Grouping
Authors: Freeman E D 
Published: December 2015

At what stage do factors such as task experience and expectation interact with the perception of whole objects? Recent work (Freeman, 1995 Perception24 Supplement, 134; 1996 Perception25 Supplement, 51) suggests that perceptual grouping of ambiguous 1-Whole/2-Wholes stimuli is dependent upon learning and task predictability, as inferred from changes in performance in a Whole - Whole/Whole - Part shape matching paradigm. Thus, subjects seemed able to offset the effect of a stimulus parameter known to influence perceived grouping, in order to see the grouping they had been trained to see or were expecting to see. In the present research the timing of these interactive processes was investigated, with the use of backward masking to take a snapshot of visual processes at different stages in their development. Stimulus and task-context factors were found to interact even at the shortest masking interval (50 ms), suggesting that top - down knowledge constrains perceptual grouping processes from an early stage onwards. A simple model of the development of 1-Whole and 2-Whole percepts implies two further conclusions. First, task and stimulus factors both seem to work by modifying the rate of development of the alternative percepts. Second, and counter-intuitively, it appears that, given the appropriate task-context and stimuli, it is possible to group the stimulus in several different ways at once. These results shed light on issues concerning the nature of perceptual grouping, and the process by which our experience of objects is brought to bear on our selection of functional perceptual groups.
Awareness and Confidence Ratings in Motion Discrimination
Authors: Sahraie A , Weiskrantz L , Barbur J L 
Published: December 2015

We have extended our earlier investigations that demonstrated above chance direction discrimination of a moving single-dot target, presented within the blindfield of a hemianope (Weiskrantz et al, 1995 Proceedings of the National Academy of Sciences of the USA92 6122 – 6126). Previous investigations pointed towards two distinct modes of processing, namely correctly discriminating the stimulus direction of motion when ‘aware’ or ‘unaware’ of its presentation. There have been arguments and counter arguments for the relationship between confidence and discrimination scores in normal observers [Kolb and Braun, 1995 Nature (London)377 336 – 338; Morgan et al, 1997 Nature (London)385 401 – 402]. We have investigated the relationship between correct direction-discrimination scores and both the awareness of a visual event and the confidence with which the discrimination is made as a function of the stimulus speed in a blindsight subject using binary and graded scales. Results show that the introduction of a six-point scale for the expressed level of awareness yielded similar results to those when the subject was given a binary choice to indicate the presence or absence of conscious awareness. Although the subject's confidence ratings in making a discrimination varied monotonically as a function of stimulus speed, the data obtained suggest that confidence and awareness, although related, are not functionally identical. The correct discrimination scores remained significantly above chance for a range of speeds even when the subject reported nonconfident. The correct discrimination scores were poorer but nevertheless well above chance for conditions where the subject was asked to report both confidence and awareness and improved if required to report only one of these parameters.
The Human Contrast Sensitivity Function Reflects Nonlinear Dynamics
Authors: Trifonov M I 
Published: December 2015

Many processes of visual perception may be modelled by nonlinear systems. I here present a novel nonlinear analysis of contrast sensitivity data. My point of departure was the similarity in shape of (i) curves giving threshold contrast as a function of spatial modulation frequency, and (ii) the envelope of bifurcational diagrams obtained from the logistic equation. It should be noted that the well-known changes of curvature for spatial frequencies above 20 cycles deg−1 are now being discussed in the literature as a problem of the last or finest channel [Kulikowski, 1991, in Limits of Vision Eds J J Kulikowski, V Walsh, I J Murray, volume 5 of Vision and Visual Dysfunction Ed. J Cronly-Dillon (London: Macmillan) pp 286–329]. Numerical simulations of threshold contrast as a function of spatial frequency were carried out on the basis of the logistic equation appropriately adapted to the problem. Several linear transformations of the equation were used for determining the parameters that would provide the best fit to the experimental data. The model introduces the concept of perceptual cycle that can be used for characterising the dynamics of selectivity in the spatial frequency domain in its dependence on grating contrast.
The Effect of Implied Mass on Representational Momentum: Negative Evidence from a Two-Body Collision Paradigm
Authors: Shyi G C-W , Hsieh F-M 
Published: December 2015

The phenomenon of representational momentum (RM) refers to distortions of visual memory for the final position of an object whenever the object is preceded by a series of displays that imply smooth transformations of the object in the picture plane. Past research has demonstrated that the magnitude of memory distortion observed in RM is closedly related to kinematic factors such as implied velocity and acceleration depicted in the inducing displays, suggesting that, as a mental analogue to physical momentum, RM may arise from an internalisation of regularities governing the physical world. It is not clear, however, whether or not RM is equally affected by regularities in the kinetic or dynamic domain (eg mass). We examined this issue in three experiments, using a two-body collision paradigm. The impression of the implied mass was created by simulating the collision of a moving ball of less mass with a stationary ball of greater mass. Although subjects were able to experience and report momentary sensation of objects with different mass, such impressions were not carried over to affect the magnitude of memory distortions in the subsequent RM task where those objects were used as inducing displays. These results imply that the sensation of mass cannot be reliably sustained over a long period by visual information, and as a consequence RM revealed by distortions of visual memory is not affected by implied mass.
Completion under Isoluminance
Authors: Puts M J H , de Weert C M M 
Published: December 2015

It is known that monocular depth cues become much less effective under isoluminance. One of these depth cues, occlusion, gives rise to surface completion. A study is reported in which the loss of completion under isoluminance was tested. A pair of horizontally aligned bars of different lengths is detected automatically in a display filled with pairs of bars of the same length. The pair is detected serially, when vertical bars are placed over the gaps between the pairs. Because the vertical bars are occluders, and the pairs of horizontal bars are aligned, completion behind the vertical bars takes place and the two parts together behave perceptually as a single bar. We used this knowledge to measure completion under isoluminance. When occlusion is lost under isoluminance, we expect that an occluding surface, isoluminant with the background, will not lead to object completion and as a consequence, the pair with unequal lengths of the parts will pop out. Using this procedure we have demonstrated that completion is lost under isoluminance.
Perceptual Integration of Motion and Form in a Visual Search Task
Authors: von Mühlenen A , Müller H J , Groner R 
Published: December 2015

Three visual search experiments were designed to investigate the processes involved in the efficient detection of motion - form conjunction targets. In experiment 1 the number of movement directions in the display were varied, and we tried to establish whether or not the target direction was predictable. Search was less efficient when items moved in multiple directions compared to just one direction; whether items moved in two, three, or four directions made relatively little difference. Pre-cuing of the target direction facilitated the search to a small, but non-negligible, extent; the facilitation was not due to better predictability of the display region that contained the target at the start of a trial. Experiment 2 was designed to estimate the relative contributions of stationary and moving nontargets to the search rate. Search rates were primarily determined by the number of moving nontargets; stationary nontargets sharing the target form also exerted a significant effect, but this was only about half as strong as that of moving nontargets; stationary nontargets not sharing the target form had little influence. In experiment 3 we examined the effects of movement speed and item size on search performance. Increasing the speed of the moving items (> 1.5 deg s−1) facilitated target detection when the task required segregation of the moving from the stationary items; when no segregation was necessary, increasing the movement speed impaired performance. When the display items were ‘large’, motion speed had little effect on target detection; but when the items were ‘small’, search efficiency declined with item movement faster than 1.5 deg s−1. A ‘parallel continuous processing’ account of motion form conjunction search is proposed.
Spatial Causality in Bilateral Symmetry Detection
Authors: Hulleman J , Oomes A H J 
Published: December 2015

We studied the influence of spatial scale on the detection of vertical and horizontal bilateral symmetry. The causality principle in scale - space theory states that increasing the spatial scale in a representation can only result in a decrease of structure. Consequently, a pattern can be random on the fine scale and symmetric on the coarse scale, never the reverse. Stimuli were bilaterally symmetric or random patterns, black-and-white on a grey background, with a circular aperture. The minimal scale was systematically varied and stimuli ranged from conventional noise patterns, through Dalmatian texture, to cow-like patterns. Observers had to judge whether a briefly presented pattern was ‘symmetric’ or ‘random’. Symmetric patterns resulted in a high accuracy (95%) with no influence of scale, and reaction times with a small linear decrease for increasing scale. Random patterns yielded an accuracy increasing from 70% at the smallest scale to 95% at the middle scales. Reaction times showed a similar pattern: largest at the smallest scales and decreasing to values equal to the symmetric condition at the middle scales. Results were similar for vertical and horizontal bilateral symmetry, though the effect for small scales in the random condition was more pronounced in the horizontal case. We conclude that bilateral symmetry is processed at multiple scales with coarse structures available slightly earlier than fine ones. The dramatic decrease of performance for fine-scale patterns is due to the causality effect; random patterns are judged as symmetric when the smallest scale information is not (yet) available.
Peripheral and Central Factors Limiting Spatial Contrast Sensitivity in Infant Macaque Monkeys
Authors: Kiorpes L , Movshon J A 
Published: December 2015

To evaluate the contribution of peripheral and central factors to the development of visual sensitivity, we measured contrast thresholds for sinusoidal gratings (0.5 – 4.2 cycles deg−1), presented alone and in the presence of added dynamic visual noise, in infant monkeys. We wished to use the changes in contrast threshold during development, in the presence and absence of masking noise, to establish what mechanisms might be responsible for this developmental process. We tested Macaca nemestrina monkeys, aged 1 – 18 months, on a spatial contrast detection task, and analysed the masking functions to calculate two parameters: equivalent intrinsic noise ( Neq, the noise contrast at which squared contrast threshold was doubled), and signal-to-noise ratio ( Rsn, the asymptotic ratio of threshold to noise contrast at high noise contrasts). We hypothesise, following Pelli, that Neq measures a peripheral limit while Rsn measures a central one. Our data suggest that intrinsic noise is high in infants and falls with contrast threshold during development, thus supporting the hypothesis that peripheral factors set an important limit on the development of contrast sensitivity. However, the relationship between Neq and contrast threshold varied somewhat with spatial frequency. At low spatial frequencies, contrast threshold was well specified by knowledge of Neq, whereas at higher spatial frequencies, changes in Rsn had a relatively greater weight. We conclude that peripheral factors set an important limit on the development of sensitivity at all spatial frequencies; central factors are needed to account for some aspects of development at higher frequencies.