Biomedical subjects

M L Howe

Publications and source records attributed to M L Howe.

35 records · Page 2Linked to original sources

PubMed1990

Children's cognitive triage: optimal retrieval or effortful processing?

Cognitive triage is a surprising nonmonotonic relationship that exists between the order in which children read words out of long-term memory and the memory strengths of those same words. Two forgetting experiments with 7- and 12-year-old children are reported in which fuzzy-trace theory's explanation of this effect was pitted against an effortful processing explanation. The two explanations make different predictions about the relative rates of forgetting for words that are recalled at the primacy and recency positions of output queues. The data consistently favored fuzzy-trace theory's predictions. We discuss the implications of our results for two assumptions that are commonly made in theories of memory development--namely, that recall accuracy is a monotonic-increasing function of memory strength and that recall order is a monotonic-decreasing function of memory strength.

Attention↗

PubMed1990

The development of forgetting and reminiscence.

Many theoretical positions on memory development anticipate that forgetting rates should vary substantially with age. The nature of these age variations is also relevant to many applied questions about child development that have major social policy implications, such as the veracity of children's eyewitness testimony and the long-term effectiveness of classroom instruction. Surprisingly, developmental studies of long-term retention have repeatedly produced the puzzling finding that forgetting rates are age invariant. It now seems, however, that these null age trends may have been artifacts of variables such as measurement insensitivity, floor effects, and stages-of-learning confounds. Assuming, as some later studies suggest, that forgetting rates vary with age when these factors are controlled, there are three overriding questions that must be dealt with in the developmental analysis of forgetting: the relative importance of storage failure versus retrieval failure, the relative importance of true forgetting processes versus test-induced processes, and the relative importance of storage-based reminiscence versus retrieval-based reminiscence. We describe a framework (disintegration/redintegation theory) that provides a conceptual environment within which research on these questions can progress. This framework, which evolved from fuzzy-trace theory, reinterprets processes such as storage failure, retrieval failure, restorage, and retrieval relearning in terms of levels of featural integration in traces (i.e., the extent to which contextual information is integrated with core semantic gist to produce a coherent representation). The theory is implemented in a mathematical model (the trace-integrity model) whose parameters deliver measurements of relevant memory processes on a common ratio scale. In a series of experiments, the model was used to study the theory's predictions about the contributions of these memory processes to long-term retention in subjects between the ages of 7 and 70. All the experiments were standard long-term retention designs (an initial acquisition session, followed by a 1-2-week forgetting interval, followed by a series of retention tests).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1986

Middle ear cilia activity as a determinant of tympanostomy tube placement.

Three hundred and twenty-six patients with diagnoses of serous otitis media--or mucoid otitis media--were reviewed for the presence or absence of middle ear cilia activity. This study strongly suggests that if active cilia can be observed, ventilating tubes are not needed. This easily observed activity in the anterior-inferior quadrant offers the otolaryngologist an accurate tool for determination of the future health of the middle ear.

Child↗

PubMed1985

Storage-retrieval processes of normal and learning-disabled children: a stages-of-learning analysis of picture-word effects.

Previous research comparing acquisition performance of learning-disabled and normally achieving children has led to the suggestion that the locus of memory differences lies in either the storage or retrieval components of recall. In this paper we report a free-recall experiment in which a new stages-of-learning model was used to examine the effects of a picture-word manipulation on storage and retrieval differences between nondisabled and disabled grade 2 and 6 children. Although the results of this experiment were consistent with the idea that disabled students are poorer at memory tasks than nondisabled students, the stages-of-learning analysis provided information regarding the precise locus of the deficiencies. Specifically, although disabled and nondisabled children benefited from the presentation of information in pictorial format, normally achieving children were consistently better than their learning-disabled counterparts at storing and learning to retrieve both pictures and words. From a developmental standpoint, the most important finding was that while differences between learning-disabled and normally achieving students at storage remained age invariant, differences in learning to retrieve increased with age. As it turned out, however, differences between disabled and nondisabled children were absent when it came to retaining traces once they had been stored in memory and in retrieval performance between the time a trace was stored and retrieval learning was complete. These results are consistent with previous research in which it has been shown that the ability to learn how to reliably retrieve information that has been stored in memory develops more slowly for disabled than nondisabled children.

Age Factors↗

PubMed1979

Mechanisms of leukemogenesis. I. Generation of autoreactive lymphocytes in response to a murine leukemia virus.

Examined in this paper is the capacity of 334C murine leukemia virus (MuLV) to stimulate the generation of virus-specific cytotoxic effector cells in mice of the C57BL/6 strain that are relatively resistant to Friend, Moloney, and Rauscher (FMR) MuLV-induced leukemia, and in BALB/c mice that are relatively susceptible to leukemia induced by FMR MuLV. Generation of cytotoxicity requires in vivo administration of the virus followed by in vitro culture of lymphoid cells from virus-injected animals. Lymphoid cells from MuLV-resistant C57BL/6 donors develop high levels of specific cytotoxicity after secondary in vitro stimulation with syngeneic MuLV-induced tumor cells. Cells derived from these same donors, cultured in the absence of MuLV-induced tumor cells, fail to exhibit cytotoxicity. Secondary in vitro stimulation of lymphocytes from MuLV-susceptible BALB/c animals results not only in generation of cytotoxic reactivity against syngeneic MuLV-induced tumor cells but also induces apparently autoreactive effector cells capable of lysing other H-2d tumor cells as well as normal peritoneal cells bearing H-2d antigens. Moreover, generation of cytotoxicity by BALB/c lymphocytes occurs whether or not MuLV-induced tumor cells are included in the secondary culture system.

Animals↗

PubMed1976

Primary in vitro sensitization of murine lymphocytes against isogeneic and allogeneic cells transformed by simian virus 40.

Primary in vitro sensitization of murine lymphocytes to isogeneic and allogeneic cells transformed by simian virus 40 (SV40) is described. The results of specificity studies utilizing cytotoxic effector lymphocytes obtained by in vitro immunization indicate that SV40 transformation results in the expression of tumor-specific antigens which are recognized by cytotoxic effector cells. Moreover, the studies demonstrate that expression of tumor-specific antigens on transformed cells is associated with a reduction in the functional expression of normal histocompatibility antigens.

Animals↗

PubMed1975

Lymphoid cell subpopulations. II. Characterization of cell populations responsible for syngery in the mixed lymphocyte interaction.

Mixtures of isogeneic lymph node cells (LNC) and thymocytes (TC) exhibit far greater responsiveness in the murine MLI, as measured by proliferation and development of cytotoxic effector cells, than either cell type cultured alone. Pretreatment of either lnc or TC with mitomycin-C or ultraviolet irradiation completely abolished their synergistic interaction. Administration of cortisone acetate to cell donors 20 hr before sacrifice reduced the capacity of LNC and enhanced the capacity of TC to synergize. The LNC and TC populations participating in synergy, were found to be thymus dependent. LNC were shown to be responsible for the bulk of proliferative and effector activity observed in synergizing cultures, whereas TC appeared to amplify the activation of LNC. These findings provide the basis for a three cell model of MLI responsiveness.

Animals↗

PubMed1975

Lymphoid cell subpopulations. I. Synergy between lymph node cells and thymocytes in response to alloantigens and mitogens.

Mixtures of isogenic thymocytes (TC) and lymph node cells (LNC) were shown to exhibit synergistic responsiveness to M and H-2 alloantigens in the mixed lymphocyte interaction (MLI). With respect to the kinetics and magnitude of proliferation and effector cell generation, the response occurring in synergizing cultures closely resembled that of optimal numbers of LNC or spleen cells (SC). In addition, the antigen specificity of effector cells generated by synergizing cultures was similar to that of effectors derived from cultures containing optimal numbers of responding SC. LNC-TC mixtures also exhibited synergy in response to the phytomitogens concanavalin A and pokeweed mitogen but not to phytohemagglutinin. Weakly positive synergy was observed in response to bacterial lipopolysaccharide. It is proposed that the phenomenon of synergy is not restricted to cultures containing mixtures of LNC and TC but also occurs in cultures containing optimal numbers of LNC or SC as a result of interactions between subpopulations of lymphocytes contained within these tissues.

Animals↗

PubMed1973

Enumeration of activated thymus-derived lymphocytes by the virus plaque assay.

Lymphocytes activated by antigens or mitogens acquire the capacity to replicate viruses, and the number of activated lymphocytes can be estimated by the virus plaque assay. Concanavalin A and pokeweed mitogen produced 33-fold and 17-fold increases in virus plaqueforming cells (V-PFC), respectively, above background, while lipopolysaccharide produced only a 2- to 3-fold increase. T (thymus-derived lymphocyte)-depleted lymphocyte populations, derived from anti-theta-treated or nude (arthymic) mouse spleens, failed to produce V-PFC after culture with concanavalin A or pokeweed mitogen. The present studies thus demonstrate that the virus plaque assay measures activated T-lymphocytes.A dissociation between the V-PFC response and cell proliferation was previously observed in antigen-stimulated cells cultured in the presence of mitotic inhibitors. In the present studies, while stimulation of CBA (H2(k)) lymphocytes by DBA/2 (H2(d)) cells produced high levels of thymidine incorporation, lymphocyte target-cell cytotoxicity, and V-PFC, stimulation of BALB/c (H2(d)) lymphocytes against DBA/2 (H2(d)) cells resulted in even higher levels of thymidine incorporation with a virtual absence of cytotoxic lymphocytes or V-PFC. These results indicate that proliferation is not a sufficient condition for permitting lymphocytes either to exert cytotoxicity on target cells or to replicate viruses, and suggest that there may be a correlation between the development of V-PFC and cytotoxic lymphocytes. They are consistent with the view that there are at least two functional subpopulations of T-lymphocytes.

Animals↗

PubMed1973

Synergism between subpopulations of thymus-derived cells mediating the proliferative and effector phases of the mixed lymphocyte reaction.

The mixed lymphocyte reaction is characterized by proliferation and generation of specifically cytotoxic effector lymphocytes. These two phases of the mixed lymphocyte reaction have been shown to be mediated by distinct subpopulations of thymus-derived cells. The current investigation demonstrates that combinations of cells from thymus and lymph nodes of CBA mice exhibit synergism with respect to proliferation and effector cell production in response to Balb/c alloantigens. That is, the magnitude of the proliferative and effector phases of the mixed lymphocyte reaction exhibited by combinations of thymus cells and lymph node cells was greater than that given by equal numbers of the two cell types cultured separately. This cooperative interaction between lymphoid cell subpopulations in the mixed lymphocyte reaction parallels that which is responsible for the graftversus-host reaction. It is proposed, therefore, that the mixed lymphocyte reaction provides an in vitro model for the study of in vivo thymus cell interactions occurring in the graft-versus-host reaction.

Animals↗

PubMed1973