Vector Symbolic Architectures (VSAs) such as Holographic Reduced Representations (HRRs) are computational associative memories used by cognitive psychologists to model behavioural and neurological aspects of human memory. We present a novel analysis of the mathematics of VSAs and a novel technique for representing data in HRRs. Encoding and decoding in VSAs can be characterised by Latin squares. Successful encoding requires the structure of the data to be orthogonal to the structure of the Latin squares. However, HRRs can successfully encode vectors of locally structured data if vectors are shuffled. Shuffling results are illustrated using images but are applicable to any nonrandom data. The ability to use locally structured vectors provides a technique for detailed modelling of stimuli in HRR models.
The southern stingray, Dasyatis americana, displays aplacental viviparity, embryos being retained in the maternal uterus throughout gestation and initially nourished by the yolk sac contents. During gestation the uterus develops vascularized appendages, trophonemata, that secrete viscous nutrient histotroph that is subsequently ingested by the embryo as it grows to term. There is a 3750% increase in wet mass from the egg to the term fetus. Trophonemata are 1.5 cm long, narrower at the base, and spatulate at the tip. Surface epithelial cells form a pattern of surface cables, each with a small blood vessel at its core. In females containing fertilized eggs, the epithelium is simple and cuboidal. In contrast, in uteri containing late-term fetuses, the epithelium is squamous. Epithelial cells, with periodic acid – Schiff positive cytoplasmic vesicles, form invaginated crypts. Epithelial cells produce proteinaceous, mucous, and lipid secretions, thus we have coined the term uterolactation to describe this phenomenon.
We describe the DSHM (Dynamically Structured Holographic Memory) model of human memory, which uses high dimensional vectors to represent items in memory. The complexity and intelligence of human behavior can be attributed, in part, to our ability to utilize vast knowledge acquired over a lifetime of experience with our environment. Thus models of memory, particularly models that can scale up to lifetime learning, are critical to modeling human intelligence. DHSM is based on the BEAGLE model of language acquisition (Jones and Mewhort, 2007) and extends this type of model to general memory phenomena. We demonstrate that DHSM can model a wide variety of human memory effects. Specifically, we model the fan effect, the problem size effect (from math cognition), dynamic game playing (detecting sequential dependencies from memories of past moves), and time delay learning (using an instance based approach). This work suggests that DSHM is suitable as a basis for learning both over the short-term and over the lifetime of the agent, and as a basis for both procedural and declarative memory. We argue that cognition needs to be understood at both the symbolic and sub-symbolic levels, and demonstrate that DSHM intrinsically operates at both of these levels of description. In order to situate DSHM in a familiar context, we discuss the relationship between DHSM and ACT-R. Dynamically Structured Holographic Memory 3 Dynamically Structured Holographic Memory Cognitive science, as a discipline, provides explanations for why cognitive phenomena occur and how they occur. The explanation for how a phenomenon occurs often involves a description of what processes underlie it. This need for process level accounts makes modeling, which is explicit in mechanical details, a particularly useful tool in generating explanations for cognitive phenomena. To achieve a full, theoretical understanding of a cognitive process, explanations need to be provided at both symbolic (i.e., representational) and sub-symbolic levels of description. The classic symbolic approaches to modeling do not account for how the symbol manipulations described in the model could arise from neural tissue, nor do they account for how the symbols themselves come into existence. Classic connectionist approaches are more concerned with neural plausibility, but are notoriously opaque, doing little to aid our understanding of the cognitive processes modeled. By contrast, the vector-symbolic approach to modeling explicitly provides an account at both levels of description. Vector Symbolic Architectures (VSAs), a term coined by Gayler (2003), are a set of techniques for instantiating and manipulating symbolic structures in distributed representations. Research into VSAs has been motivated by limitations in the ability of traditional connectionist models (i.e., non-recurrent models with one or two layers of connections) to represent knowledge with complicated structure (Plate, 1995). Like human memory, vector symbolic architectures can store complicated and recursive relations be...
Elasmobranch fishes utilize a variety of means to provide nourishment for their developing young. All employ internal fertilization and sperm storage within the female genital tract. Some elasmobranchs, including all the skates and some sharks, are oviparous. In these species, fertilized eggs are enclosed in a tough egg case that is secreted by the nidamental or shell gland. The female lays the egg cases and development is entirely dependent on the yolk stores sequestered in the yolk sac. Upon oviposition, the embryo weighs less than the fertilized egg. The majority of elasmobranchs are viviparous, however, and utilize a variety of strategies to provide nourishment and satisfy respiratory demands of the developing young. Some sharks simply retain their young in the dilated posterior segment of the oviduct. In its simplest form, the maternal uterus does not provide any additional nutrients to the embryos. Other elasmobranchs develop secretory uterine villi that produce nutrient histotroph to supplement oocyte yolk stores. Uterine secretions find their zenith in the stingrays. Following yolk depletion, the uterine lining hypertrophies into secretory appendages termed trophonemata. The process by which the uterine secretions, also known as uterine milk or histotroph, are elaborated resembles the production of breast milk in higher vertebrates, and the milk is rich in protein and lipid. Concurrent with growth of the embryos, the vascular bed of the trophonemata enlarges to form sinusoids that project out to the surface to form a functional respiratory membrane. In lamnoid sharks, following yolk use, the embryos develop precocious dentition and feed on intrauterine eggs and siblings. There is generally one fetus per uterus and it grows to enormous proportions of up to 4 feet in length. In placental sharks the yolk sac is not withdrawn to become incorporated into the abdominal wall. Instead, it lengthens to form an umbilical cord and the yolk sac becomes modified into a functional epitheliochorial placenta. o 1993 Wiley-Liss, Inc.Elasmobranchs have evolved many diverse adaptations for fetal nutrition. In terms of maternal-fetal nutrition, embryos are either totally yolk reliant and lay eggs (oviparous) or are only initially reliant on yolk and give birth to living young (viviparous). By default, viviparous species are internal uterine incubators and differ only in the manner of delivery and type of maternally derived nutrients that they supply to their embryos. Internal incubators have been categorized as 1) species with or without secretory uterine villi, 2) species, primarily the stingrays, that develop uterine trophonemata, 3) species that practice egg eating (oophagy) and/or intrauterine cannibalism, and 4) species that develop a yolk sac placenta (Hamlett, '89a; Hamlett et al., '92).All elasmobranchs are initially reliant on yolk reserves sequestered in the egg. This is true if the mother is oviparous or viviparous. Their earliest nutritional needs are provided by yolk that is internalized by blastoderm ce...
Background During the height of the coronavirus disease 2019 (COVID-19) pandemic, elective surgeries, including oncologic surgeries, were delayed. Little prospective data existed to guide practice, and professional surgical societies issued recommendations grounded mainly in common sense and expert consensus, such as medical therapy for early-stage breast and prostate cancer patients. To understand the patient experience of delay in cancer surgery during the pandemic, we interviewed breast and prostate cancer patients whose surgeries were delayed due to the pandemic. Patients and Methods Patients with early-stage breast or prostate cancer who suffered surgical postponement at Brigham and Women’s Hospital (BWH) were invited to participate. Semi-structured telephone interviews were conducted with 21 breast and prostate cancer patients. Interviews were transcribed, and qualitative analysis using ground-theory approach was performed. Results Most patients reported significant distress due to cancer and COVID. Key themes that emerged included the lack of surprise and acceptance of the surgical delays but endorsed persistent cancer- and delay-related worries. Satisfaction with patient–physician communication and the availability of a delay strategy were key factors in patients’ acceptance of the situation; perceived lack of communication prompted a few patients to seek care elsewhere. Discussion The clinical effect of delay in cancer surgery will take years to fully understand, but there are immediate steps that can be taken to improve the patient experience of delays in care, including elicitation of individual patient perspectives and ongoing communication. More work is needed to understand the wider experiences of patients, especially minority, socioeconomically disadvantaged, and uninsured patients, who encounter delays in oncologic care. Graphical Abstract Supplementary Information The online version contains supplementary material available at 10.1245/s10434-021-10319-0.
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