The effect of intrinsic image memorability on recollection and familiarity.

Many photographs of real-life scenes are very consistently remembered or forgotten by most people, making these images intrinsically memorable or forgettable. Although machine vision algorithms can predict a given image's memorability very well, nothing is known about the subjective quality of these memories: are memorable images recognized based on strong feelings of familiarity or on recollection of episodic details? We tested people's recognition memory for memorable and forgettable scenes selected from image memorability databases, which contain memorability scores for each image, based on large-scale recognition memory experiments. Specifically, we tested the effect of intrinsic memorability on recollection and familiarity using cognitive computational models based on receiver operating characteristics (ROCs; Experiment 1 and 2) and on remember/know (R/K) judgments (Experiment 2). The ROC data of Experiment 2 indicated that image memorability boosted memory strength, but did not find a specific effect on recollection or familiarity. By contrast, ROC data from Experiment 2, which was designed to facilitate encoding and, in turn, recollection, found evidence for a specific effect of image memorability on recollection. Moreover, R/K judgments showed that, on average, memorability boosts recollection rather than familiarity. However, we also found a large degree of variability in these judgments across individual images: some images actually achieved high recognition rates by exclusively boosting familiarity rather than recollection. Together, these results show that current machine vision algorithms that can predict an image's intrinsic memorability in terms of hit rates fall short of describing the subjective quality of human memories.

Membrane transport: a mathematical investigation.

It is known that the primary constituents of the membranes of cells are lipids. These lipids are arranged in two layers and the membrane is frequently called a bilipid layer. Recent low intensity scanning electron micrographs of the bilipid layer has revealed that the bilipid layer has revealed that the bilipid membrane layer also contains proteins. The proteins in the bilipid membrane layer pass from one side of the layer to the other and thus constitute a "hole" in the membrane layer. The structure of the proteins is such that an essentially void space exists surrounded by the molecular structures of the protein. The exact functioning of the proteins has not yet been determined. The thesis of this paper is that the proteins act as mediators for the transport of specific catabolites. The supporting arguments for the thesis are in the form of mathematical models for the catabolite - protein interactions, and the results of simulations based upon the mathematical models. Physical verifications of the results presented in this paper await physiological experimental data. However the results of this work indicate that modest changes in the membrane proteins result in a significant change in the amount of catabolite transported across the cell membrane. The mediation of the catabolite transport by the proteins has the pathological implications that long term post-disease states of the cells may be linked closely to the altered states of the membrane proteins: which may occur during the period of the disease state.

Oxygen boundary crossing probabilities.

The probability that an oxygen particle will reach a time dependent boundary is required in oxygen transport studies involving solution methods based on probability considerations. A Volterra integral equation is presented, the solution of which gives directly the boundary crossing probability density function. The boundary crossing probability is the probability that the oxygen particle will reach a boundary within a specified time interval. When the motion of the oxygen particle may be described as strongly Markovian, then the Volterra integral equation can be rewritten as a generalized Abel equation, the solution of which has been widely studied.

Approximate-analytical solution of the diffusion, convection and reaction problem in homogeneous media.

In convex homogeneous domains, the diffusion, convection and reaction (DCR) problem may be solved by applying Green's function solution technique. When this technique is applied, the solution to the DCR problem consists of the sum of a set of integrals whose integrands involve the Green's function. The Green's function is singular at the upper limit of the time integral and is nonuniformly convergent at the boundaries of the domain. Due to this behaviour, numerical evaluation of the integrals is prohibitively expensive and in some cases, the integrals are incorrectly evaluated. The method presented in this work circumvents all the difficulties inherent with the numerical quadrature of the intergrals and in preliminary case studies (in rectangular coordinates) has reduced the required computation time by up to five orders of magnitude while increasing the accuracy of the results by as much as eight orders of magnitude. The method involves transforming the function in the integrand, which multiplies the Green's function, into a series of Legendre polynomials. The integral of the product of the Green's function and Legendre polynomials can be evaluated analytically. This produces both a rapid and accurate evaluation of the integral and subsequently the solution to the DCR problem.

Three dimensional reconstruction of branched tree structures from serial sections.

A process is described for the automatic registration and reconstruction of anatomical tree structures such as capillary networks in the microstructure of tissue. The technique uses images of, or images representing, a set of closely spaced parallel slices called "serial sections". The source of the serial sections may be MRI, multi-planar X-ray, multi-planar infra-red scans, or simple histological sections. A tree structure is defined as a structure consisting of a network of nested ducts, vessels or solid cores which branch and join with another such that one structure may appear as more than one distinct area in a single section, or in a series of sections. The reconstruction of such an object poses many problems which do not occur when restructuring objects which are so shaped that they can give rise to only one area in each section.

Identification of viable regions in "in vitro" spheroidal tumors: a mathematical investigation.

In the treatment of solid tumors by hyperthermia, a major question is how to obtain an a priori knowledge of which tumors can be effectively treated with this modality. The key question is; given a solid tumor, what parameters in the various regions of the tumor, need to be measured so that a tumor-tissue model can provide a meaningful real time simulation of the hyperthermic treatment. This paper addresses the former question as a mathematical investigation, and the latter as a consequence of the former.

Mathematical analysis of transport and consumption of molecules in heterogeneous brain tissue (methodology).

A computer model of metabolite transport and consumption in heterogeneous brain tissue, using a combination of probabilistic and deterministic techniques is being developed. The metabolites are put into two separate classes: (I) those that have reached a membrane for the first time during a small time step, delta t, and (II) those that have not yet reached a cell membrane for the first time during that time step. The time dependent spatial distribution of class (I) molecules is determined using random walk theory, which takes into account the actual paths of the molecules. The variation of the spatial distribution of class (II) molecules with time is determined using the time dependent diffusion equation with a boundary condition of zero concentration on the enclosing membrane boundaries.

On the classification of equine force traces.

Evidence indicating that comparison of a particular animal trace with a population average is an insufficient test of the health of a limb is presented. The methodology involves representing each of three recorded force components (vertical, lateral, and transverse) as a Fourier-Legendre series; the coefficients in the series represent the trace. A history for the horse is built by accumulating the coefficients (along with pertinent experimental data such as date, sex, weight, height, and in the case of race horses the date of last race) over a long duration. Then, on each subsequent recording, the trace is first compared with the animal's history to identify the occurrence of injury or pathology. If the limb is found to be normal, the trace is added to the history. Otherwise, it is recommended that the animal be further examined by a veterinarian. Preliminary results indicate that an animal trace needs to be compared with a history of traces for the same animal to identify alterations in the locomotive behavior of the limb.

Ongoing EEG Phase as a Trial-by-Trial Predictor of Perceptual and Attentional Variability.

Even in well-controlled laboratory environments, apparently identical repetitions of an experimental trial can give rise to highly variable perceptual outcomes and behavioral responses. This variability is generally discarded as a reflection of intrinsic noise in neuronal systems. However, part of this variability may be accounted for by trial-by-trial fluctuations of the phase of ongoing oscillations at the moment of stimulus presentation. For example, the phase of an electro-encephalogram (EEG) oscillation reflecting the rapid waxing and waning of sustained attention can predict the perception of a subsequent visual stimulus at threshold. Similar ongoing periodicities account for a portion of the trial-by-trial variability of visual reaction times. We review the available experimental evidence linking ongoing EEG phase to perceptual and attentional variability, and the corresponding methodology. We propose future tests of this relation, and discuss the theoretical implications for understanding the neuronal dynamics of sensory perception.

A theoretical formalism for aggregation of peroxidized lipids and plasma membrane stability during photolysis.

The objective of this investigation was to examine, from a theoretical perspective, the mechanism underlying the lysis of plasma membranes by photoinduced, chemically mediated damage such as is found in photolysis. Toward this end, a model is presented which relates the membrane lifetime to the thermodynamic parameters of the membrane components based upon the kinetic theory of aggregate formation. The formalism includes a standard birth/death process for the formation of damaged membrane components (i.e., peroxidized lipids) as well as a terminating condensation process for the formation of aggregates of peroxidized plasma membrane lipids. Our theory predicts that 1) the membrane lifetime is inversely correlated with predicted rate of membrane damage; 2) an upper limit on the duration of membrane damage exists, above which the mean and variance of the membrane lifetime is independent of further membrane damage; and 3) both the mean and variance of the time of membrane lifetime distribution are correlated with the number of sites that may be damaged to form a single membrane defect. The model provides a framework to optimize the lysis of cell membranes by photodynamic therapy.

Intracellular calcium dynamics during photolysis.

The objective of this investigation was to gain a deeper understanding of the intracellular events that precede photolysis of cells. A model system, consisting of malignant melanoma cells pretreated with the calcium sensitive fluorescent dye, Fluo-3, was used to examine the intracellular calcium dynamics in single-cell photolysis experiments. Exposure of the cells to 632 nm laser light in the presence of photosensitizer, tin chlorin e6, resulted in a rise in intracellular calcium. The increase in intracellular calcium was blocked using a variety of calcium channel blocking agents, including verapamil, nifedipine, and nickel. Treatment with the channel blockers was also effective in either decreasing or eliminating cell death despite the presence of lethal doses of photosensitizer and irradiation. These results show that intracellular calcium rises prior to plasma membrane lysis, and that this early rise in intracellular calcium is necessary for membrane rupture.

A model of infected burn wounds using Escherichia coli O18:K1:H7 for the study of gram-negative bacteremia and sepsis.

A difficulty that has emerged in the development and preclinical evaluation of adjuvant therapies for gram-negative sepsis is the lack of easily studied animal models that closely mimic human infection. An objective of this study was to adapt a previously described model of infection in burned mice to rats with a defined bacterial strain of Escherichia coli. Challenge with two colonies of live E. coli O18:K1:H7 bacteria into an 8% full-thickness burn of the dorsal skin surface of rats produced predictable bacteremia at 24 to 48 h and 80 to 100% mortality at 3 to 4 days. E. coli O18:K1:H7 was approximately 10-million-fold more virulent than several other gram-negative bacterial strains. The model should be a useful tool in studying the pathogenicity of burn wound infections and in evaluating the efficacy of novel adjuvant therapies for gram-negative sepsis.