Viewpoint invariance in the recognition of 3-D depth-rotated figures

The aim of our experiments was to investigate the central mechanisms of visual perception involved in the identification of 3-D objects. We have made psychophysical measurements of the recognition thresholds of incomplete 2-D images of 3-D objects, varying their perspective during a participant's learning and testing, using the Gollin test. The results we obtained showed a dependence of recognition thresholds of a 3-D object upon (i) the number of times it had been previously presented and (ii) the viewing angle of the 3-D object. The threshold was about 20% of contour length at first presentation. Recognition was improved at the second presentation, irrespective of whether a different angle of viewing was used, after which recognition was constant. It appears that a template forms immediately after the first presentation of a 2-D projection of an object. This template has invariance properties since its use for object identification does not depend on the object's orientation when subsequently presented, at least up to an angle of 60 degrees

Incomplete figure perception - the problem of invisible masking

Our previous findings (2002 Perception 31 Supplement, 116) suggested that the Gollin test of incomplete figure perception (Foreman and Hemmings, 1987 Perception 16 543 - 548) and the Mooney test of incomplete silhouette faces may be considered as signal masking problems, in this sense similar to the Poppelreuter test of contour figure extraction from noisy overlapping figures. We considered the incompleteness of a Gollin figure to be the result of its masking by multiplicative noise similar to the texture of transparent windows and opaque elements. The brightness and colour of the opaque elements are identical to the background and size of transparent windows corresponding with the size of fragments of the incomplete figure. In other words, incomplete figures are figures occluded by an 'invisible' mask. The purpose of this work has been to determine the statistical properties of the 'invisible' mask and to show their connection with thresholds of incompleteness of figures at recognition. We have made additional investigations, which show that the incompleteness thresholds depend on the level of similarity of the spatial-frequency bands of the figure and the 'invisible' mask. The thresholds are reduced when the 'invisible' mask changes to a visible one. We presented in psychophysical experiments incomplete figures with two sizes, covering the foveal or macular areas. We measured the thresholds of recognition of incomplete figures in normal participants and in neurological patients with 'filtration agnosia' and showed recognition-threshold differences for the different tests. This difference depends on the similarity between the spatial-frequency spectra of the visible (Poppelreuter) and 'invisible' (Gollin, Mooney) masks with those of the incomplete figure, and also with the localisation of visual system damage

The optical-geometrical characteristics and thresholds of perception of fragmented outline figures

Measurements were made of the threshold of recognition of cumulatively forming line figures. The threshold value of the outline, expressed in pixels, depended on the length of the outline of the whole unfragmented figure. Relative threshold values were constant, and for the measures of figure fragments used in the present study, averaged 12.5%. A spatial frequency analysis of the test images was performed. Variation of the amplitude-frequency parameters of the spectra of the images of various figures with threshold fragmentation was minimal as compared with the variation of these parameters in figures with subthreshold or suprathreshold levels of fragmentation

The Gollin incomplete figure test as a masking problem

The Gollin test of incomplete figure perception is usually employed to measure the thresholds of recognition in children and adults, and to study a process which provides a basis for the perception of incomplete figures as Gestalts (Foreman and Hemmings, 1987 Perception 16 543 ^ 548). Here we suggest that this test, along with such tests as the Poppelreuter test of figure extraction, and the Mooney faces test, may be considered as a visual masking problem. Digital image processing allows us to measure the spatial properties and spatial-frequency spectrum of the absent part of the image as a mask. We compare incomplete masking with other traditional types of masking. Using a noise paradigm, we have measured the signal-to-noise ratio for incomplete figure perception in normal participants and in neurological patients. This is the most powerful aspect of this new approach. Clinically, the new paradigm may provide a quantitative measure of agnosia. We have developed the hypothesis that some forms of visual agnosia arise primarily from an especially high level of noise within higher visual processing, including memory systems. We classify this type of agnosia as ‘filtration agnosia’. The concept of incomplete figure perception as noise filtration is therefore important for clinical purposes

Incomplete figure perception and invisible masking

The Gollin test (measuring recognition thresholds for fragmented line drawings of everyday objects and animals) has traditionally been regarded as a test of incomplete figure perception or ‘closure’, though there is a debate about how such closure is achieved. Here, figural incompleteness is considered to be the result of masking, such that absence of contour elements of a fragmented figure is the result of the influence of an ‘invisible’ mask. It is as though the figure is partly obscured by a mask having parameters identical to those of the background. This mask is ‘invisible’ only consciously, but for the early stages of visual processing it is real and has properties of multiplicative noise. Incomplete Gollin figures were modeled as the figure covered by the mask with randomly distributed transparent and opaque patches. We adjusted the statistical characteristics of the contour image and empty noise patches and processed those using spatial and spatial-frequency measures. Across 73 figures, despite inter-subject variability, mean recognition threshold was always approximately 15% of total contour in naive observers. Recognition worsened with increasing spectral similarity between the figure and the ‘invisible’ mask. Near threshold, the spectrum of the fragmented image was equally similar to that of the ‘invisible’ mask and complete image. The correlation between spectral parameters of figures at threshold and complete figures was greatest for figures that were most easily recognised. Across test sessions, thresholds reduced when either figure or mask parameters were familiar. We argue that recognition thresholds for Gollin stimuli in part reflect the extraction of signal from noise

Invariance of visual perception

Perception and thinking is based largely on the ability of the brain to find in the world invariant features. The purpose of the study – to determine the ranges invariant perception, for various transformations of images of objects (angular size – magnitude, turn corners-projections), under which quantitative characteristics of their perceptions remained unchanged. The recognition psychophysical threshold measuring of incomplete line drawing images (Gollin-test) with different sizes and rotations was provided. The experimental data of invariance perception to the image size transformation and rotating of images are presented. We demonstrate that there is a wide range of angular sizes (from 1.0 up to 50 degrees of visual angle) across which the threshold of recognition of incomplete images does not depend on object size. However, there was found to be a narrow range of small sizes of stimulus (0.19–1, 0 degrees of visual angle) at which there was found to be a dependence of performance on object size. The thresholds of recognition of 3-D objects when viewed as incomplete 2-D images were measured at psychophysical experiments varying perspective of 3-D objects during testing. The memory template of the test objects description has "invariance" properties from 15 up to an angle of 60 degrees. The algorithm for template formation of 3-D objects in the human visual system need to be modeled, taking account of the invariance mechanism. The model of invariant perception, combining well-known model log-polar model and wavelet transform as the primary stage of filtration, and then match filtering and decision-making

The Gollin test and the optical properties of incomplete figures at threshold

The Gollin test is a developmental test for measuring visual perceptual skills (Gollin, 1960 Perceptual and Motor Skills 11 289 - 298). The aim of our work was to measure the thresholds of recognition of incomplete figures when presented for the first time to observers, and relate this to their contour lengths and 2-D Fourier spectra. We generated 73 contour images of familiar objects. They were presented as incomplete figures, beginning from 0% of contour to 100% via the random addition of small fragments. The observers' task was to recognise figures as quickly as possible. Their score was the percentage of contour displayed at the moment of recognition. We found that the value of the threshold, in terms of percentage of contour length displayed, was similar for all images, averaging 12%, irrespective of the total length of contour of the full figure. For both complete and incomplete figures at threshold we carried out 2-D Fourier transform analysis, measuring the centroids of their spectra. The energy spectrum of each figure was transformed into an averaged amplitude spatial-frequency profile, representing the total energy within each of three orientation profiles, and the centroid was then calculated. We found that the value of the centroid at threshold was similar across the figures employed, averaging 6.3 cycles deg-1. We showed that the centroid of the amplitude spatial-frequency spectrum of an image coincides with the maximum on the curve of human contrast sensitivity

The estimation of quantitative ranges of invariance in visual perception

To determine the quantitative ranges of invariance in the visual perception of objects viewed at different distances and different viewing angles, we have provided a set of psychophysical measurements of recognition thresholds of incomplete line drawings (Gollin-test) with different sizes and rotations. New experimental data are presented, relating invariance to image size transformation and image rotation. We demonstrated that there is a wide range of angular sizes (from 1.0 up to 50 deg) across which the threshold of recognition of incomplete images does not depend on object size. However, there was found to be a narrow range of small stimulus sizes (0.19 - 1.0 deg) within which there was found to be a dependence of performance on object size. In additional experiments with naive participants, we extended our earlier investigations (Chikhman et al, 2008 Perception 37 Supplement, 119) by making more exact threshold measurements for the recognition of 3-D objects when viewed as incomplete 2-D images, varying the perspective of 3-D objects during testing. The possible algorithms for template formation for 3-D objects in the human visual system are discussed and modeled, taking into account the invariance mechanism

The recognition of incomplete contour and half-tone figures

The recognition of incomplete figures of everyday objects in fovea and beyond was the aim of our project. For fifteen subjects with high visual acuity, aged 18 to 24 years, we measured the necessary minimum of randomly presented parts of the contour. Fixation point was in the centre of the figure corresponding to the centre of the screen. The figure sizes were varied from 5 min of arc up to 20 deg by using different viewing distances. The contour minimum for recognition corresponds to figure size equal to foveola size. Beyond 20 min of arc, up to the resolution limit of 5 min of arc, recognition decreased linearly. For 0.5 to 5 deg sizes the threshold was relatively invariant to the size. The psychophysics and event-related potentials were investigated within the frequency range from 1 to 45 Hz. The relative perceptual availability of global and local features in sparse patterns was investigated during different stages of learning. Interpolation algorithms were proposed and tested in additional experiments. We measured the threshold of incomplete natural half-tone scene recognition. In these experiments, incompleteness was produced with wavelet transforms. The internal noise limitation of recognition was measured. A match filter model of the perception of incomplete figures is proposed

Harbour Grace Standard

The Harbor Grace Standard was published from December 1859 to 1936[?], providing coverage of the Conception Bay area as well as other news. The frequency was weekly save for a brief semiweekly interlude between 1888-94 and there is a publication gap between 1868 and February 1871. Many issues are missing in the later years.Alternative title from common misspelling, as the city's modern name features a "u.