Studies of the Perception of Incomplete Outline Images of Different Sizes

The aim of the present work was to assess the range of angular sizes of fragmented images of objects at which perception of the images was scale-independent. Measurements were made of human subjects’ recognition thresholds for the shapes of the objects over a wide range of angular sizes (0.19–50°). The experiments used the Gollin test – a method for studying the recognition of fragmented outline images of objects with which the observer is familiar. The results obtained demonstrated that there is a wide range of angular sizes, from 1.0° to 50°, over which the perception thresholds of incomplete outline images do not change with changes in size, along with a narrow range of stimulus sizes, 0.19–1.0°, over which there is a significant size dependence. We suggest that the increase in thresholds and the failure to recognize images of small size occur as a result of an increased contribution of sampling noise at the level of the human retina.     

Optical-geometrical characteristics of fragmented figures and integral perception thresholds in repeated tests

The causes of reductions in the integral perception threshold for fragmented figures in repeat trials using the Gollin test were investigated. The first study involved four trials with 5-day intervals using one set of figures. The amplitude-frequency characteristics of the test stimuli were interpreted using correlation analysis, as were the thresholds in each trial. The second study involved two trials with a three-day interval. On repeat testing, half of the figures were known (from the first test) to the subjects. In addition, half of the figures (both familiar and unfamiliar) were fragmented such that their amplitude-frequency characteristics had values similar to those in the first test. The results showed that the decrease in thresholds were mainly due to optimization of the functioning of the mechanisms operating with the statistical rather than the subject characteristics of the images.     

The Threshold Signal:Noise Ratio in the Perception of Fragmented Figures

Perception thresholds were measured for fragmented outline figures (the Gollin test). A new approach to the question of the perception of incomplete images was developed. In this approach, figure fragmentation consisted of masking with multiplicative texture-like noise — this interference was termed “invisible” masking. The first series of studies established that the “similarity” between the amplitude-frequency spectra of test figures and “invisible” masks, expressed as a linear correlation coefficient, had significant effects on the recognition thresholds of these figures. The second series of experiments showed that progressing formation of the figures was accompanied by increases in the correlation between their spatial-frequency characteristics and the corresponding characteristics of the incomplete figure, while the correlation with the “invisible” mask decreased. It is suggested that the ratio of the correlation coefficients, characterizing the “similarity” of the fragmented figure with the intact figure and the “invisible” mask, corresponds to the signal:noise ratio. The psychophysical recognition threshold for figures for naive subjects not familiar with the test image alphabet was reached after the particular level of fragmentation at which this ratio was unity. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 90, No. 11, pp. 1348–1355, November, 2004.     

Perception of Fragmented Images of Three-Dimensional Objects as the Observation Angle Changes

Recognition thresholds for incomplete two-dimensional images of three-dimensional objects were measured as the observation angle was changed. A new experimental psychophysical method was developed and programmed for this purpose, this being a modification of the Gollin test, which measures perception thresholds of incomplete outline images. After training to a stimulus alphabet, observers’ responses were found to be invariant to changes in the observation angles of three-dimensional objects from 15° to 60°. It is suggested that possible algorithms for the formation of models of three-dimensional images in the human visual system do not operate on the basis of simple section, but involve invariance mechanisms.     

Parietal and frontal object areas underlie perception of object orientation in depth

Recent studies have shown that the human parietal and frontal cortices are involved in object image perception. We hypothesized that the parietal/frontal object areas play a role in differentiating the orientations (i.e., views) of an object. By using functional magnetic resonance imaging, we compared brain activations while human observers differentiated between two object images in depth-orientation (orientation task) and activations while they differentiated the images in object identity (identity task). The left intraparietal area, right angular gyrus, and right inferior frontal areas were activated more for the orientation task than for the identity task. The occipitotemporal object areas, however, were activated equally for the two tasks. No region showed greater activation for the identity task. These results suggested that the parietal/frontal object areas encode view-dependent visual features and underlie object orientation perception.     

3D shape perception from combined depth cues in human visual cortex

Our perception of the world's three-dimensional (3D) structure is critical for object recognition, navigation and planning actions. To accomplish this, the brain combines different types of visual information about depth structure, but at present, the neural architecture mediating this combination remains largely unknown. Here, we report neuroimaging correlates of human 3D shape perception from the combination of two depth cues. We measured fMRI responses while observers judged the 3D structure of two sequentially presented images of slanted planes defined by binocular disparity and perspective. We compared the behavioral and fMRI responses evoked by changes in one or both of the depth cues. fMRI responses in extrastriate areas (hMT+/V5 and lateral occipital complex), rather than responses in early retinotopic areas, reflected differences in perceived 3D shape, suggesting 'combined-cue' representations in higher visual areas. These findings provide insight into the neural circuits engaged when the human brain combines different information sources for unified 3D visual perception.     

Localization of human cortical areas activated on perception of ordered and chaotic images

The aims of this study were to identify the locations of areas in the human cortex responsible for describing fragmented test images of different degrees of ordering and to identify the areas taking decisions regarding stimuli of this type. The locations of higher visual functions were determined by functional magnetic resonance imaging (fMRI) using a scanner fitted with a superconducting magnet and a field strength of 1.5 T. The blood oxygen level-dependent (BOLD) method was based on measurements of the level of hemoglobin oxygenation in the blood supplied to the brain. This level was taken to be proportional to the extent of neuron activation in the corresponding part of the gray matter. Stimuli were matrixes consisting of Gabor elements of different orientations. The measure of matrix ordering was the ratio of the number of Gabor elements with identical orientations to the total number of elements in the image. Brain neurons were activated by simultaneous changes in the orientations of all the elements, leading to substitution of one matrix by another. Substitution of the orientation was perceived by observers as rotation of the elements in the matrix. Stimulation by matrixes with a high level of ordering was found to activate the occipital areas of the cortex, V1 and V2 (BA17-BA18), while presentation of matrixes with random element orientations also activated the parietal-temporal cortex, V3, V4, V5 (BA19), and the parietal area (BA7). Brain zones responsible for taking decisions regarding the level of order or chaos in the organization of the stimuli are located in different but close areas of the prefrontal and frontal cortex of the brain, including BA6, BA9, and BA10. The results are assessed in terms of concepts of the roles and interactions of different areas of the human brain during recognition of fragmented images of different degrees of complexity.     

Blurring of the senses: common cues for distance perception in diverse sensory systems

Distance perception is an essential task of sensory systems. Our visual systems effectively use binocular visual cues to determine an object's distance. Other visual, but monocular, cues are also available for distance perception. Visual contrast and image blur are two such cues [O'Shea et al., 1994. Vis. Res. 34, 1595-1604; O'Shea et al., 1997. Perception 26, 599-612; Mather, 1997. Perception 26, 1147-1158]. We show the effects of combining these cues using a simple psychophysical test. The novelty in our approach is that our exact choice of visual stimuli allows us to show a direct parallel between visual distance perception and distance perception using an entirely different sense, the electric sense of weakly electric fish. We discuss previous work on electrosensory psychophysics [von der Emde et al., 1998. Nature 395, 890-894] and show that cues used for electrosensory distance perception are analogous to visual contrast and blur. We also suggest that analogous cues are involved in auditory distance perception. The utilization of analogous cues implies that these diverse sensory systems perform similar computations for distance perception.     

Visual features of intermediate complexity and their use in classification

The human visual system analyzes shapes and objects in a series of stages in which stimulus features of increasing complexity are extracted and analyzed. The first stages use simple local features, and the image is subsequently represented in terms of larger and more complex features. These include features of intermediate complexity and partial object views. The nature and use of these higher-order representations remains an open question in the study of visual processing by the primate cortex. Here we show that intermediate complexity (IC) features are optimal for the basic visual task of classification. Moderately complex features are more informative for classification than very simple or very complex ones, and so they emerge naturally by the simple coding principle of information maximization with respect to a class of images. Our findings suggest a specific role for IC features in visual processing and a principle for their extraction.     

The neural signature of spatial frequency-based information integration in scene perception

Spatial frequency-based information plays an important role in visual perception. By combining behavioral and electroencephalogram (EEG) measurements, we investigated the mechanisms of the interaction and information integration between different spatial frequency bands. The observers performed a scene categorization task on hybrid images that were generated by combining the low spatial frequency (LSF) component of one image with the high spatial frequency (HSF) component of another image. The results showed that the recognition of the HSF component was interfered by the non-attended LSF component at semantic level. The strength of the semantic interference was modulated by the physical similarity between the LSF and HSF components. Analyses of the EEG data revealed an early anterior N1 component (122 ms from stimulus onset) that was related to the observed interaction of the semantic and physical information between the LSF and HSF components. These findings demonstrate that the semantic information from different spatial frequency bands can be integrated at early stage of the perceptual processing. This early integration is likely to occur at frontal areas in order to initiate top-down facilitation.     

Prioritization of brain MRI volumes using medical image perception model and tumor region segmentation

The objective of the present study is to explore prioritization methods in diagnostic imaging modalities to automatically determine the contents of medical images. In this paper, we propose an efficient prioritization of brain MRI. First, the visual perception of the radiologists is adapted to identify salient regions. Then this saliency information is used as an automatic label for accurate segmentation of brain lesion to determine the scientific value of that image. The qualitative and quantitative results prove that the rankings generated by the proposed method are closer to the rankings created by radiologists.     

Statistical efficiency of the object recognition with wire-frame stimuli

To investigate whether internal object representations in the brain are 2D or 3D, we measured discrimination thresholds and calculated statistical efficiencies in the object recognition task based on the ideal observer analysis. Stimulus images were created by orthographic projection of 3D wire-frame objects on a fronto-parallel plane. The discrimination task with the wire-frame stimuli was performed in the monocular (Experiment 1) and the binocular (Experiment 2) conditions. The results indicate that the subjects' statistical efficiencies relative to the 2D ideal observer exceeded 100%, suggesting that the internal object representations should be 3D. In addition, the results revealed that the object type with high-level symmetry led to better discrimination in both experiments. Furthermore, the interaction between 3D cue values and the object regularity was suggested to cause the viewpoint dependency.     

Cardinal rules: visual orientation perception reflects knowledge of environmental statistics

Humans are good at performing visual tasks, but experimental measurements have revealed substantial biases in the perception of basic visual attributes. An appealing hypothesis is that these biases arise through a process of statistical inference, in which information from noisy measurements is fused with a probabilistic model of the environment. However, such inference is optimal only if the observer's internal model matches the environment. We found this to be the case. We measured performance in an orientation-estimation task and found that orientation judgments were more accurate at cardinal (horizontal and vertical) orientations. Judgments made under conditions of uncertainty were strongly biased toward cardinal orientations. We estimated observers' internal models for orientation and found that they matched the local orientation distribution measured in photographs. In addition, we determined how a neural population could embed probabilistic information responsible for such biases.     

Human non-phase-locked gamma oscillations in experience-based perception of visual scenes

Perception results from ongoing interactions between stimulus-driven visual processes and cognitive context. These reciprocal relations are emphasized when a visual stimulus is degraded, forcing the perceiver to fill the missing information in, based on internal representations. The neural mechanisms by which internal representations facilitate visual perception are still unclear. Here we investigated the role of EEG oscillations in the gamma band, thought to reflect the elaboration of internal visual representations, in the experience-based perception of visual scenes. Twelve subjects were trained with degraded images of natural scenes. EEG was recorded while they performed a detection task on trained and untrained degraded stimuli. Non-phase-locked gamma band responses in a large frequency spectrum (55-85 Hz) were observed around 200 ms post-stimulus onset at posterior sites, and were larger when subjects reported an accurate perception based on previous experience. These results suggest that mid-latency gamma oscillations in the visual cortex underlie the experience-based perception of visual scenes.     

Electrotactile perception of scatterplots on the fingertips and abdomen

A comparison of auditory and visual perception of scatterplots showed similar correlation estimation performance in both modalities. The present study replicated this experiment using electrotactile (electrocutaneous) presentation of scatterplots on the fingertips and abdomen, as well as visual presentation. The correlation estimation task resulted in a slightly poorer performance on electrotactile scatterplots (abdomen r=+0.847; fingertip r=+0.723) compared with the previous Flowers auditory displays (r=+0.91). There were similar levels of performance in the visual (control) condition in both the studies (r for both approx.+0.91). The performance in the correlation estimation task was similar across the two electrotactile displays, with perhaps a slight, but not significant (p=0.077), advantage for the abdominal array. However, a preliminary digit identification task on both displays produced a better performance on the fingertip display (p<0.05), suggesting that the relative performance of the two displays may be task specific. The present results demonstrate electrotactile perception of complex graphs and provide useful information for improving future versions of tactile displays.     

Theory of mind and motion perception in schizophrenia

This study investigated the relationship between theory of mind (ToM) deficits and visual perception in patients with schizophrenia (N=52; 17 remitted and unmedicated) compared with healthy controls (N=30). ToM was assessed with the Eyes Test, which asked participants to choose which of 4 words best described the mental state of a person whose eyes were depicted in a photograph. Visual perception was evaluated with form and motion coherence threshold measurements. Results revealed that patients with schizophrenia (both remitted and nonremitted) showed deficits on the Eyes Test and the motion coherence task. ToM dysfunctions were associated with higher motion coherence thresholds and more severe negative symptoms. This suggests that ToM deficits are related to motion perception dysfunctions, which indicates a possible role of motion-sensitive areas in the pathophysiology of schizophrenia.     

Hemiface contributions to hemispheric dominance in visual speech perception

Lateralized displays are used widely to investigate hemispheric asymmetry in language perception. However, few studies have used lateralized displays to investigate hemispheric asymmetry in visual speech perception, and those that have yielded mixed results. This issue was investigated in the current study by presenting visual speech to either the left hemisphere (LH) or the right hemisphere (RH) using the face as recorded (normal), a mirror image of the normal face (reversed), and chimeric displays constructed by duplicating and reversing just one hemiface (left or right) to form symmetrical images (left-duplicated, right-duplicated). The projection of displays to each hemisphere was controlled precisely by an automated eye-tracking technique. Visual speech perception showed the same, clear LH advantage for normal and reversed displays, a greater LH advantage for right-duplicated displays, and no hemispheric difference for left-duplicated displays. Of particular note is that perception of LH displays was affected greatly by the presence of right-hemiface information, whereas perception of RH displays was unaffected by changes in hemiface content. Thus, when investigated under precise viewing conditions, the indications are not only that the dominant processes of visual speech perception are located in the LH but that these processes are uniquely sensitive to right-hemiface information.     

Quality evaluation of ultrasound imaging in the carotid artery based on normalization and speckle reduction filtering

Image quality is important when evaluating ultrasound images of the carotid for the assessment of the degree of atherosclerotic disease, or when transferring images through a telemedicine channel, and/or in other image processing tasks. The objective of this study was to investigate the usefulness of image quality evaluation based on image quality metrics and visual perception, in ultrasound imaging of the carotid artery after normalization and speckle reduction filtering. Image quality was evaluated based on statistical and texture features, image quality evaluation metrics, and visual perception evaluation made by two experts. These were computed on 80 longitudinal ultrasound images of the carotid bifurcation recorded from two different ultrasound scanners, the HDI ATL-3000 and the HDI ATL-5000 scanner, before (NF) and after (DS) speckle reduction filtering, after normalization (N), and after normalization and speckle reduction filtering (NDS). The results of this study showed that: (1) the normalized speckle reduction, NDS, images were rated visually better on both scanners; (2) the NDS images showed better statistical and texture analysis results on both scanners; (3) better image quality evaluation results were obtained between the original (NF) and normalized (N) images, i.e. NF–N, for both scanners, followed by the NF–DS images for the ATL HDI-5000 scanner and the NF–DS on the HDI ATL-3000 scanner; (4) the ATL HDI-5000 scanner images have considerable higher entropy than the ATL HDI-3000 scanner and thus more information content. However, based on the visual evaluation by the two experts, both scanners were rated similarly. The above findings are also in agreement with the visual perception evaluation, carried out by the two vascular experts. The results of this study showed that ultrasound image normalization and speckle reduction filtering are important preprocessing steps favoring image quality, and should be further investigated.     

Auditory influences on visual temporal rate perception

Visual stimuli are known to influence the perception of auditory stimuli in spatial tasks, giving rise to the ventriloquism effect. These influences can persist in the absence of visual input following a period of exposure to spatially disparate auditory and visual stimuli, a phenomenon termed the ventriloquism aftereffect. It has been speculated that the visual dominance over audition in spatial tasks is due to the superior spatial acuity of vision compared with audition. If that is the case, then the auditory system should dominate visual perception in a manner analogous to the ventriloquism effect and aftereffect if one uses a task in which the auditory system has superior acuity. To test this prediction, the interactions of visual and auditory stimuli were measured in a temporally based task in normal human subjects. The results show that the auditory system has a pronounced influence on visual temporal rate perception. This influence was independent of the spatial location, spectral bandwidth, and intensity of the auditory stimulus. The influence was, however, strongly dependent on the disparity in temporal rate between the two stimulus modalities. Further, aftereffects were observed following approximately 20 min of exposure to temporally disparate auditory and visual stimuli. These results show that the auditory system can strongly influence visual perception and are consistent with the idea that bimodal sensory conflicts are dominated by the sensory system with the greater acuity for the stimulus parameter being discriminated.     

运动领域中的视觉-运动知觉的神经生理研究进展

运动领域中的视觉-运动知觉的神经生理研究现状主要包括功能磁共振成像(fMRI)、事件相关电位(ERPs)和视觉诱发电位(VEPs)三个方面。fMRI通过比较运动员和非运动员在运动观察和运动预测时大脑激活的差异,从而在神经生理层面对运动员的视觉-运动知觉优势进行解释。ERPs证明了长期的体育训练能够加强神经系统网络结构和可塑性。VEPs的研究结果表明运动员在对运动画面进行视觉认知加工时的神经活动都是通过视觉通路来调节的,并且其神经细胞的调节也可能与其从事的特定运动项目有关。