Visual sensitivity, blur and the sources of variability in the amplitude spectra of natural scenes

AbstractA number of researchers have suggested that in order to understand the response properties of cells in the visual pathway, we must consider the statistical structure of the natural environment. In this paper, we focus on one aspect of that structure, namely, the correlational structure which is described by the amplitude or power spectra of natural scenes. We propose that the principle insight one gains from considering the image spectra is in understanding the relative sensitivity of cells tuned to different spatial frequencies. This study employs a model in which the peak sensitivity is constant as a function of frequency with linear bandwith increasing (i.e., approximately constant in octaves). In such a model, the “response magnitude” (i.e., vector length) of cells increases as a function of their optimal (or central) spatial frequency out to about 20 cyc/deg. The result is a code in which the response to natural scenes, whose amplitude spectra typically fall as 1/f, is roughly constant out to 20 cyc/deg. An important consideration in evaluating this model of sensitivity is the fact that natural scenes show considerable variability in their amplitude spectra, with individual scenes showing falloffs which are often steeper or shallower than 1/f. Using a new measure of image structure (the “rectified contrast spectrum” or “RCS”) on a set of calibrated natural images, it is shown that a large part of the variability in the spectra is due to differences in the sparseness of local structure at different scales. That is, an image which is “in focus” will have structure (e.g., edges) which has roughly the same magnitude across scale. That is, the loss of high frequency energy in some images is due to the reduction of the number of regions that contain structure rather than the amplitude of that structure. An “in focus” image will have structure (e.g., edges) across scale that have roughly equal magnitude but may vary in the area covered by structure. The slope of the RCS was found to provide a reasonable prediction of physical blur across a variety of scenes in spite of the variability in their amplitude spectra. It was also found to produce a good prediction of perceived blur as judged by human subjects

A spatial covariance (123)I-5IA-85380 SPECT study of α4β2 nicotinic receptors in Alzheimer's disease

Alzheimer's disease (AD) is characterized by widespread degeneration of cholinergic neurons, particularly in the basal forebrain. However, the pattern of these deficits and relationship with known brain networks is unknown. In this study, we sought to clarify this and used 123I-5-iodo-3-[2(S)-2-azetidinylmethoxy] pyridine (1235IA-85380) single photon emission computed tomography to investigate spatial covariance of α4β2 nicotinic acetylcholine receptors in AD and healthy controls. Thirteen AD and 16 controls underwent 1235IA-85380 and regional cerebral blood flow (99mTc-exametazime) single photon emission computed tomography scanning. We applied voxel principal component (PC) analysis, generating series of principal component images representing common intercorrelated voxels across subjects. Linear regression generated specific α4β2 and regional cerebral blood flow covariance patterns that differentiated AD from controls. The α4β2 pattern showed relative decreased uptake in numerous brain regions implicating several networks including default mode, salience, and Papez hubs. Thus, as well as basal forebrain and brainstem cholinergic system dysfunction, cholinergic deficits mediated through nicotinic acetylcholine receptors could be evident within key networks in AD. These findings may be important for the pathophysiology of AD and its associated cognitive and behavioral phenotypes

Analysis of grain-boundary structure in Al–Cu interconnects

The role of crystallographic texture in electromigration resistance of interconnect lines is well documented. The presence of a strong (111) fiber texture results in a more reliable interconnect structure. It is also generally accepted that grain-boundary diffusion is the primary mechanism by which electromigration failures occur. It has been difficult to this point, however, to obtain statistically reliable information of grain-boundary structure in these materials as transmission electron microscopy investigations are limited by tedious specimen preparation and small, nonrepresentative, imaging regions. The present work focuses upon characterization of texture and grain-boundary structure of interconnect lines using orientation imaging microscopy, and particularly, upon the linewidth dependence of these measures. Conventionally processed Al–1%Cu lines were investigated to determine the affects of a postpatterning anneal on boundary structure as a function of linewidth. It was observed that texture tended to strengthen slightly with decreasing linewidth subsequent to the anneal procedure. Grain morphology changed substantially as the narrow lines became near bamboo in character and the crystallographic character of the boundary plane changed as a function of linewidth. These results are contrasted with those obtained from Al–1%Cu lines, which were fabricated using the damascene process. The damascene lines show a marked weakening in texture as the linewidth decreases, accompanied by a more random misorientation distribution. A description of the competing energetics, which result in the observed microstructures, is included. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71133/2/JAPIAU-82-5-2383-1.pd

Dynamic Electrode-to-Image (DETI) mapping reveals the human brain’s spatiotemporal code of visual information

A number of neuroimaging techniques have been employed to understand how visual information is transformed along the visual pathway. Although each technique has spatial and temporal limitations, they can each provide important insights into the visual code. While the BOLD signal of fMRI can be quite informative, the visual code is not static and this can be obscured by fMRI’s poor temporal resolution. In this study, we leveraged the high temporal resolution of EEG to develop an encoding technique based on the distribution of responses generated by a population of real-world scenes. This approach maps neural signals to each pixel within a given image and reveals location-specific transformations of the visual code, providing a spatiotemporal signature for the image at each electrode. Our analyses of the mapping results revealed that scenes undergo a series of nonuniform transformations that prioritize different spatial frequencies at different regions of scenes over time. This mapping technique offers a potential avenue for future studies to explore how dynamic feedforward and recurrent processes inform and refine high-level representations of our visual world

Platelet Factor 4 Regulation of Monocyte KLF4 in Experimental Cerebral Malaria

Cerebral malaria continues to be a difficult to treat complication of Plasmodium falciparum infection in children. We have shown that platelets can have major deleterious immune functions in experimental cerebral malaria (ECM). One of the platelet derived mediators we have identified as particularly important is platelet factor 4/CXCL4. Our prior work demonstrated that PF4−/− mice are protected from ECM, have reduced plasma cytokines, and have reduced T-cell trafficking to the brain. We now show that PF4 drives monocyte cytokine production in a Kruppel like factor 4 (KLF4) dependent manner. Monocyte depleted Plasmodium berghei infected mice have improved survival, and KLF4 is greatly increased in control, but not monocyte depleted mice. PF4−/− mice have less cerebral monocyte trafficking and no change in KLF4 expression. These data indicate that PF4 induction of monocyte KLF4 expression may be an important step in the pathogenesis of ECM

Upper Limb Capabilities, Self-Care and Fine Motor Activities with and Without Equipment in Persons with Cervical Spinal Cord Injury at Discharge from Rehabilitation and 1 Year Post-Injury

Introduction: There is little information on the impact of assistive technology or devices (AT) on function. The purpose of this project was to explore the impact of AT on self-care (SC) and fine motor (FM) function in persons with cervical SCI, and to examine the functional capabilities of those who benefit from AT. Methods: Persons with acute cervical SCI, all levels and AIS grades, with an upper extremity motor score (UEMS) \u3e 0 were enrolled. At discharge from rehabilitation and 1 year post-injury we collected the Capabilities of Upper Extremity questionnaire (CUE-Q), and the combined SC and FM questions of the SCI Functional Index (SCI-FI) and SCI-FI/AT short forms. The arm with the highest CUE-Q side score was designated the better side. The impact of AT on SC and FM function was evaluated by looking at the difference in SCI-FI and SCI-FI/AT scores, and changes over time. Results: There were 67 participants with data at rehab discharge and 1-year post-injury, 50 male and 17 female, average age 43.3 ± 15.6 years. Median scores by neurologic groupings are shown in the table. All groups demonstrated improvements in CUE-Q and SCI-FI scores from discharge to 1 year post-injury (table and radar charts). By neurologic group, AT was useful for the greatest percentage of persons classified as C4-C5 AB for FM and C6-T1 AB for SC), least useful for C6-T1 CD (charts at right). AT was helpful for the greatest number of items for SC in the C4-C5 CD group at discharge (bolded numbers in table). There tended to be less use of AT for tasks at 1 year compared to rehab discharge. For example, the percentage of persons using AT for brushing teeth at discharge was 48%, while at 1 year it was only 25%. Conclusion: Many persons with tetraplegia are able to perform self-care and fine motor tasks easier using AT, but the benefit depends on the level and severity of injury. There is a decreased reliance on AT over time, which may in part be due to continued recovery after rehabilitation discharge.https://jdc.jefferson.edu/rmposters/1013/thumbnail.jp