Objects In Natural Images Research Articles

Sustained extrastriate cortical activation without visual awareness revealed by fMRI studies of hemianopic patients

Patients with lesions in the primary visual cortex (V1) may show processing of visual stimuli presented in their field of cortical blindness even when they report being unaware of the stimuli. To elucidate the neuroanatomical basis of their residual visual functions, we used functional magnetic resonance imaging in two hemianopic patients, FS and GY. In the first experiment, a rotating spiral stimulus was used to assess the responsiveness of dorsal stream areas. Although no response was detectable within denervated or destroyed early visual cortex, motion-sensitive areas (hMT+/V5) ipsilateral to the lesion showed a strong sustained hemodynamic response. In GY, this activation was at least as strong as that of his contralesional hMT+/V5 to the stimulus in the normal hemifield. In the second experiment, coloured images of natural objects were used to assess the responsiveness of ventral stream areas. Again, no activity was detectable in ipsilesional early visual areas, but extrastriate areas in the lateral occipital cortex (hMT+/V5 and LO) and within the posterior fusiform gyrus (V4/V8) showed a robust sustained hemodynamic response. In both experiments, we observed that ipsilesional areas responded to stimuli presented in either hemifield, whereas the normal hemisphere responded preferentially to stimuli in the sighted hemifield. As only one subject occasionally noticed the onset of stimuluation in the impaired field, the unexpectedly strong sustained activity in ipsilesional dorsal and ventral cortical areas appears to be insufficient to generate conscious vision.

Afterimages: A Tool for Defining the Neural Correlate of Visual Consciousness

Our visual system not only mediates information about the visual environment but is capable of generating pictures of nonexistent worlds: afterimages, illusions, phosphenes, etc. We are “aware” of these pictures just as we are aware of the images of natural, physical objects. This raises the question: is the neural correlate of consciousness (NCC) of such images the same as that of images of physical objects? Images of natural objects have some properties in common with afterimages (e.g., stability of verticality) but there are also obvious differences (e.g., images maintain size constancy, whereas afterimages follow Emmert's Law: when seen while screens at different distances are observed, an afterimage looks larger, the greater the distance of the screen). The differences can be explained by differences in the retinal extent of images and afterimages, which favors the view that both have the same NCC. It seems reasonable to assume that before neural activity can produce awareness, all the computations necessary for a veridical representation of, e.g., an object, must be completed within the neural substrate and that information characteristic of a particular object must be available within the NCC. Given these assumptions, it can be shown that no retinotopic (in a strict sense) cortical areas can serve as the NCC, although some type of topographic representation is necessary. It seems also to be unlikely that neurons classified as cardinal cells alone can serve as NCC.

Effect of image scrambling on inferior temporal cortical responses.

Imaging studies compared activations elicited by images of objects and scrambled versions of these same images in order to localize human brain regions involved in object recognition. Given these studies and the known role of macaque temporal cortex in object recognition, I determined the effect of image scrambling on the responses of macaque inferior temporal neurons. Images of natural objects were scrambled to different degrees. The response of most neurons decreased with increasing degrees of scrambling. In 26% of the neurons, response was reduced by 50% when the image was scrambled using only four parts, but most neurons tolerated higher degrees of scrambling, suggesting that these neurons code object parts instead of entire objects. These results are related to human functional imaging studies.

A sequence of object-processing stages revealed by fMRI in the human occipital lobe

Functional magnetic resonance imaging was used in combined functional selectivity and retinotopic mapping tests to reveal object-related visual areas in the human occipital lobe. Subjects were tested with right, left, up, or down hemivisual field stimuli which were composed of images of natural objects (faces, animals, man-made objects) or highly scrambled (1,024 elements) versions of the same images. In a similar fashion, the horizontal and vertical meridians were mapped to define the borders of these areas. Concurrently, the same cortical sites were tested for their sensitivity to image-scrambling by varying the number of scrambled picture fragments (from 16-1,024) while controlling for the Fourier power spectrum of the pictures and their order of presentation. Our results reveal a stagewise decrease in retinotopy and an increase in sensitivity to image-scrambling. Three main distinct foci were found in the human visual object recognition pathway (Ungerleider and Haxby [1994]: Curr Opin Neurobiol 4:157-165): 1) Retinotopic primary areas V1-3 did not exhibit significant reduction in activation to scrambled images. 2) Areas V4v (Sereno et al., [1995]: Science 268:889-893) and V3A (De Yoe et al., [1996]: Proc Natl Acad Sci USA 93:2382-2386; Tootell et al., [1997]: J Neurosci 71:7060-7078) manifested both retinotopy and decreased activation to highly scrambled images. 3) The essentially nonretinotopic lateral occipital complex (LO) (Malach et al., [1995]: Proc Natl Acad Sci USA 92:8135-8139; Tootell et al., [1996]: Trends Neurosci 19:481-489) exhibited the highest sensitivity to image scrambling, and appears to be homologous to macaque the infero-temporal (IT) cortex (Tanaka [1996]: Curr Opin Neurobiol 523-529). Breaking the images into 64, 256, or 1,024 randomly scrambled blocks reduced activation in LO voxels. However, many LO voxels remained significantly activated by mildly scrambled images (16 blocks). These results suggest the existence of object-fragment representation in LO.

A sequence of object‐processing stages revealed by fMRI in the human occipital lobe

Functional magnetic resonance imaging was used in combined functional selectivity and retinotopic mapping tests to reveal object-related visual areas in the human occpital lobe. Subjects were tested with right, left, up, or down hemivisual field stimuli which were composed of images of natural objects (faces, animals, man-made objects) or highly scrambled (1,024 elements) versions of the same images. In a similar fashion, the horizontal and vertical meridians were mapped to define the borders of these areas. Concurrently, the same cortical sites were tested for their sensitivity to image-scrambling by varying the number of scrambled picture fragments (from 16–1,024) while controlling for the Fourier power spectrum of the pictures and their order of presentation. Our results reveal a stagewise decrease in retinotopy and an increase in sensitivity to image-scrambling. Three main distinct foci were found in the human visual object recognition pathway (Ungerleider and Haxby [1994]: Curr Opin Neurobiol 4:157–165): 1) Retinotopic primary areas V1–3 did not exhibit significant reduction in activation to scrambled images. 2) Areas V4v (Sereno et al., [1995]: Science 268:889–893) and V3A (DeYoe et al., [1996]: Proc Natl Acad Sci USA 93:2382–2386; Tootell et al., [1997]: J Neurosci 71:7060–7078) manifested both retinotopy and decreased activation to highly scrambled images. 3) The essentially nonretinotopic lateral occipital complex (LO) (Malach et al., [1995]: Proc Natl Acad Sci USA 92:8135–8139; Tootell et al., [1996]: Trends Neurosci 19:481–489) exhibited the highest sensitivity to image scrambling, and appears to be homologous to macaque the infero-temporal (IT) cortex (Tanaka [1996]: Curr Opin Neurobiol 523–529). Breaking the images into 64, 256, or 1,024 randomly scrambled blocks reduced activation in LO voxels. However, many LO voxels remained significantly activated by mildly scrambled images (16 blocks). These results suggest the existence of object-fragment representation in LO. Hum. Brain Mapping 6:316–328, 1998. © 1998 Wiley-Liss, Inc.

The use of digital images in pathology.

Digital images are routinely used by the publishing industry, but most diagnostic pathologists are unfamiliar with the technology and its possibilities. This review aims to explain the basic principles of digital image acquisition, storage, manipulation and use, and the possibilities provided not only in research, but also in teaching and in routine diagnostic pathology. Images of natural objects are usually expressed digitally as 'bitmaps'--rectilinear arrays of small dots. The size of each dot can vary, but so can its information content in terms, for example, of colour, greyscale or opacity. Various file formats and compression algorithms are available. Video cameras connected to microscopes are familiar to most pathologists; video images can be converted directly to a digital form by a suitably equipped computer. Digital cameras and scanners are alternative acquisition tools of relevance to pathologists. Once acquired, a digital image can easily be subjected to the digital equivalent of any conventional darkroom manipulation and modern software allows much more flexibility, to such an extent that a new tool for scientific fraud has been created. For research, image enhancement and analysis is an increasingly powerful and affordable tool. Morphometric measurements are, after many predictions, at last beginning to be part of the toolkit of the diagnostic pathologist. In teaching, the potential to create dramatic yet informative presentations is demonstrated daily by the publishing industry; such methods are readily applicable to the classroom. The combination of digital images and the Internet raises many possibilities; for example, instead of seeking one expert diagnostic opinion, one could simultaneously seek the opinion of many, all around the globe. It is inevitable that in the coming years the use of digital images will spread from the laboratory to the medical curriculum and to the whole of diagnostic pathology.

A neural network approach to computation of optical flow: [formula omitted]. Signal and Image Processing Institute, Department of EE-Systems, University of Southern California, CA 90089-0272 USA

In this paper the authors present a method for computing optical flow using a neural network. Usually, the measurement primitives used for computing optical flow from successive image frames are the image intensity values and their spatial and temporal derivatives, and tokens such as edges, corners and linear features. The intensity value may be corrupted by noise, especially for natural images and in addition, their partial derivatives are rotation variant. It is difficult to detect the rotating objects in natural images, based on such measurement primitives. Meanwhile, the token based approaches give the information about the object motion and shape only at edges, corners and linear features. Hence, an interpolation procedure has to be included when dense data are required. Conventional methods based on such primitives suffer from edge sparsity, noise distortion or sensitivity to rotation. Recently, several researchers have been using neural networks for computing optical flow based on either intensity values (1, 2) or tokens (3). The authors first fit a 2-D polynomial to find a smooth continuous image intensity function in a window and estimate the subpixel intensity values and their principle curvatures. Under local rigidity assumption and smoothness constraints, a neural network is then employed tomore » implement the computing procedure based on the estimated intensity values and their principle curvatures. A deterministic decision rule is used for the updating scheme, Owing to the dense measured primitives, a dense optical flow with subpixel accuracy is obtained with only a few iterations. Since all neurons are updated in parallel, this algorithm can be implemented in real time. Experimental results using synthetic and natural image sequences will be presented to demonstrate the efficacy of their method.« less

Finding the illuminant direction

Shading is important for estimation of three-dimensional shape from the two-dimensional image, for instance, for distinguishing between the smooth occluding contour generated by the edge of a sphere and the sharp occluding contour generated by the edge of a disk. In order to use shading information to solve such problems, one must know the illuminant direction L. This is because variations in image intensity (shading) are caused by changes in surface orientation relative to the illuminant. Each illuminant direction L has a unique effect on the distribution of changes in image intensity dI, potentially permitting the estimation of L. However, because dI is a function of bothL and the surface curvature, L can be estimated from the image only by making an assumption about the imaged surface curvature. One assumption that is sufficient to disentangle L and surface curvature is that changes in surface orientation are isotropically distributed. This condition is true of images of convex objects bounded by a smooth occluding contour and is true on average over all scenes. Estimates made by using this assumption agree with estimates of illuminant direction given by human subjects for images of natural objects, even when both are objectively wrong. Further, there is a significant correlation between the variance of these estimates and the variance of the human subjects’ estimates.

Practical description of the process called the Daguerreotype, which consists in the spontaneous reproduction of the images of natural objects, in the Camera Obscura, not with their colours, but with great delicacy in the gradation of the tints

Adhesion after abdominal and pelvic surgery results in severe clinical outcomes and a negative impact on the quality of life of a patient. Implanting barrier materials is a common strategy for preventing postoperative adhesion, and non-adhesive carboxymethylcellulose (CMC) is a widely used material for such purpose. Herein, we present CMC/gelatin (CMC/G) hybrid hydrogels as novel barrier materials that aim to reduce the foreign body response (FBR) by combining the biocompatibility and biodegradability of gelatin and the non-adhesiveness of CMC and by realizing mechanical matching with the host tissue. The hydrogels were prepared by the simple reagent-free γ-ray irradiation-induced cross-linking of CMC and gelatin. The hydrogel composition was controlled by varying the initial mixing ratio. The gelatin fraction provided enzyme-mediated degradability at a content ≥ 40%, and the degradation rate was controlled by the radiation dose. The compressive moduli of the hydrogels were tuned to be identical to that of target abdominal organs (several tens of kPa) via 10–30 kGy radiation. The hydrogels sufficiently prevented adhesion of 3T3-Swiss fibroblast cells owing to the non-adhesive capability of CMC which surpassed the high cell adhesiveness of gelatin in the hydrogels. On the other hand, the added gelatin significantly improved the viability of the few cells that adhered to the hydrogels. We found that hydrogels composed of 60% CMC and 40% gelatin exhibited significantly higher cell viabilities while maintaining the non-adhesiveness which is desirable as barrier materials. The in vitro assessments demonstrated the potential of the hydrogel as a novel barrier material with excellent biocompatibility, wound healing promoting effect, and FBR reducing effect by realizing mechanical matching with the host abdominal organs, especially when it was composed of 60% CMC and 40% gelatin and cross-linked at 10–30 kGy to impart compressive modulus of 20–100 kPa.