Biomedical subjects

Richard L Marsh

Publications and source records attributed to Richard L Marsh.

At least 19 recordsLinked to original sources

PubMed2005

Blood flow in guinea fowl Numida meleagris as an indicator of energy expenditure by individual muscles during walking and running.

Running and walking are mechanically complex activities. Leg muscles must exert forces to support weight and provide stability, do work to accelerate the limbs and body centre of mass, and absorb work to act as brakes. Current understanding of energy use during legged locomotion has been limited by the lack of measurements of energy use by individual muscles. Our study is based on the correlation between blood flow and aerobic energy expenditure in active skeletal muscle during locomotion. This correlation is strongly supported by the available evidence concerning control of blood flow to active muscle, and the relationship between blood flow and the rate of muscle oxygen consumption. We used injectable microspheres to measure the blood flow to the hind-limb muscles, and other body tissues, in guinea fowl (Numida meleagris) at rest, and across a range of walking and running speeds. Combined with data concerning the various mechanical functions of the leg muscles, this approach has enabled the first direct estimates of the energetic costs of some of these functions. Cardiac output increased from 350 ml min(-1) at rest, to 1700 ml min(-1) at a running speed ( approximately 2.6 m s(-1)) eliciting a of 90% of . The increase in cardiac output was achieved via approximately equal factorial increases in heart rate and stroke volume. Approximately 90% of the increased cardiac output was directed to the active muscles of the hind limbs, without redistribution of blood flow from the viscera. Values of mass-specific blood flow to the ventricles, approximately 15 ml min(-1) g(-1), and one of the hind-limb muscles, approximately 9 ml min(-1) g(-1), were the highest yet recorded for blood flow to active muscle. The patterns of increasing blood flow with increasing speed varied greatly among different muscles. The increases in flow correlated with the likely fibre type distribution of the muscles. Muscles expected to have many high-oxidative fibres preferentially increased flow at low exercise intensities. We estimated substantial energetic costs associated with swinging the limbs, co-contraction to stabilize the knee and work production by the hind-limb muscles. Our data provide a basis for evaluating hypotheses relating the mechanics and energetics of legged locomotion.

Animals↗

PubMed2005

On the relationship between effort toward an ongoing task and cue detection in event-based prospective memory.

In recent theories of event-based prospective memory, researchers have debated what degree of resources are necessary to identify a cue as related to a previously established intention. In order to simulate natural variations in attention, the authors manipulated effort toward an ongoing cognitive task in which intention-related cues were embedded in 3 experiments. High effort toward the ongoing task resulted in decreased prospective memory only when the cognitive processing required to identify the cue was similar to the cognitive processing required to complete the ongoing activity. When the required processing was different for the 2 tasks, cue detection was not affected by manipulated effort, despite there being an overall cost to decision latencies in the ongoing tasks from possessing the intention. Resource allocation policies and factors that affect them are proposed to account for ongoing vs. prospective memory task performance.

Attention↗

PubMed2005

Performance of guinea fowl Numida meleagris during jumping requires storage and release of elastic energy.

The ability of birds to perform effective jumps may play an important role in predator avoidance and flight initiation. Jumping can provide the vertical acceleration necessary for a rapid takeoff, which may be particularly important for ground-dwelling birds such as phasianids. We hypothesized that by making use of elastic energy storage and release, the leg muscles could provide the large power outputs needed for achieving high velocities after takeoff. We investigated the performance of the leg muscles of the guinea fowl Numida meleagris during jumping using kinematic and force-plate analyses. Comparison of the methods indicated that in this species the wings did not supply energy to power takeoff and thus all the work and power came from the leg muscles. Guinea fowl produced a peak vertical force of 5.3 times body weight. Despite having lower muscle-mass-specific power output in comparison to more specialized jumpers, guinea fowl demonstrated surprisingly good performance by producing muscle-mass-specific work outputs of 45 J kg(-1), a value approximately two thirds of the maximal expected value for skeletal muscle. The muscle-mass-specific peak power output during jumping was nearly 800 W kg(-1), which is more than twice the peak isotonic power estimated for guinea fowl leg muscles. To account for high power outputs, we concluded that energy has to be stored early in the jumps and released later during peak power production, presumably using mechanisms similar to those found in more specialized jumpers.

Animals↗

PubMed2005

Detecting event-based prospective memory cues occurring within and outside the focus of attention.

Event-based prospective memory cues are environmental stimuli that are associated with a previously established intention to perform an activity. Such cues traditionally have been placed in materials that receive focal attention during an ongoing activity. This article reports a direct comparison of event-based cues that occurred either within the focus of attention or at the periphery of such attention. When the cue occurred outside focal attention, manipulating that cue changed event-based prospective memory. The identical manipulation had no effect on event-based responding if the cue occurred within focal attention. These results suggest that cue characteristics can compensate for attention being directed away from an aspect of an ongoing task that contains event-based prospective memory.

Attention↗

PubMed2004

Partitioning the energetics of walking and running: swinging the limbs is expensive.

Explaining the energetics of walking and running has been difficult because the distribution of energy use among individual muscles has not been known. We estimated energy use by measuring blood flow to the hindlimb muscles in guinea fowl. Blood flow to skeletal muscles is controlled locally and varies directly with metabolic rate. We estimate that the swing-phase muscles consume 26% of the energy used by the limbs and the stance-phase muscles consume the remaining 74%, independent of speed. Thus, contrary to some previous suggestions, swinging the limbs requires an appreciable fraction of the energy used during terrestrial legged locomotion. Models integrating the energetics and mechanics of running will benefit from more detailed information on the distribution of energy use by the muscles.

Animals↗

PubMed2004

The influence of partial-match cues on event-based prospective memory.

In event-based prospective memory tasks people form an intention to respond when an environmental cue signals that conditions are appropriate to fulfil an intended activity. In the ongoing activity the authors embedded partial-match cues that only partially, but not completely, satisfied the conditions required to make a prospective response. The consequence of encountering these partial-match cues was to increase responses to appropriate prospective memory cues encountered later. This outcome occurred both with semantic and orthographic cues, but only the former led to longer processing latencies of the partial-match cues. This asymmetry suggests that partial-match cues may not need to be processed consciously in order to benefit event-based prospective memory. A parametric manipulation of the number of partial-match cues resulted in numerically but not statistically better prospective memory. Consequently, partial-match cues may function as overt reminders of the intention to respond or they may serve to engage participants in self-initiated remindings of the intention.

Adult↗

PubMed2004

Focused attention on one contextual attribute does not reduce source memory for a different attribute.

In three experiments, participants were asked to learn a particular contextual dimension of a study episode for a later memory test. The hypothesis being evaluated was that focused attention towards learning a particular source-specifying attribute would decrease memory for a different attribute dimension. Although source memory for the attribute dimensions in the focus of attention were generally improved, memory was not diminished for contextual attributes ostensibly outside the focus of primary attention. The absence of any decrease in memory appears to be a somewhat general phenomenon because it was found with external-external, internal-external, and internal-internal combinations of attribute dimensions. The results may be most consistent with a model of cognitive processing in which people have separate pools of attentional resources rather than a single pool of general resources.

Adult↗

PubMed2003

Season and testosterone affect contractile properties of fast calling muscles in the gray tree frog Hyla chrysoscelis.

In anurans, circulating levels of androgens influence certain secondary sexual characteristics that are expressed only during the breeding season. We studied the contractile properties of external oblique muscles (used to power sound production) in a species of North American gray tree frog, Hyla chrysoscelis, during the breeding season and also in testosterone-treated captive males and females after the breeding season. Compared with the muscles of breeding-season males, the trunk muscles of postbreeding-season males have 50% less mass, 60% longer twitches, and 40% slower shortening velocities. Testosterone levels similar to those found in breeding-season male hylid frogs restore the contractile speed and mass of male trunk muscles and also convert the small slow trunk muscles of females into larger fast-contracting muscles. We conclude that androgens likely play a key role in altering the contractile properties of these muscles in males during the annual cycle, allowing them to operate in the breeding season at the frequencies required to produce the characteristic rapidly pulsed calls of this species. Females as well as nonbreeding-season males do not produce advertising calls, and therefore the slower muscles found in these animals may allow more economic operation of these muscles. The effects of testosterone on female trunk muscles indicate the potential of this hormone in contributing to the sexual dimorphism in size and contractile properties of these muscles, but this dimorphism is likely due to the interaction of more than one hormone.

Animals↗

PubMed2003

Investigating the encoding and retrieval of intentions with event-related potentials.

Strong evidence exists in the literature that remembering to complete intentions involves executive processing subserved by the frontal lobes. Event-related potentials were measured during the encoding of actions with the intention to perform versus more neutral material about which there was no such intentionality. Event-related potentials were also measured in a two-alternative discrimination task requiring identification of the to-be-performed actions and to-be-memorized actions. The results suggest that formation and retrieval of intentions differs from encoding and retrieval of similar material committed to memory. Additionally, the results suggest that right frontal areas may play an important role in the formation of prospective actions and that intentions are kept active in memory by processing mediated by the left frontal pole.

Adolescent↗

PubMed2003

Halo and devil effects demonstrate valenced-based influences on source-monitoring decisions.

Source attributions based on positive versus negative valence were examined in four experiments. The two sources were individuals who were depicted positively or negatively, and the content of their statements was similarly valenced. When valenced information about the sources was provided after learning the statements, test biases to attribute positive statements to the positive source and negative statements to the negative source were strongly present. Providing the same information prior to learning improved memory, but did not entirely eliminate test biases based on valence. Signal detection analysis suggests that these "halo effect" biases are criterion-based and not memory-based. Therefore, the results are more consistent with descriptions of source-monitoring processes that can benefit from familiarity-based partial information as opposed to descriptions in which source monitoring is primarily recollection-based.

Adolescent↗

PubMed2003

Interference to ongoing activities covaries with the characteristics of an event-based intention.

Previous studies of event-based prospective memory have demonstrated that the character of an ongoing task can affect cue detection. By contrast, this study demonstrated that there is a reciprocal relationship insofar as cue-verification and response-retrieval processes interfered with making a response in the ongoing task. The amount of interference was determined by the type of intention, which was manipulated to affect the complexity of verification and retrospective response retrieval. These relationships were true even when the interference caused by cue detection was separated from a more general effect to ongoing-task performance caused by shifts in attentional allocation policies. The results have theoretical implications for models that attempt to specify the cognitive microstructure of event-based prospective memory.

Attention↗

PubMed2003

Probing the limits to muscle-powered accelerations: lessons from jumping bullfrogs.

The function of many muscles during natural movements is to accelerate a mass. We used a simple model containing the essential elements of this functional system to investigate which musculoskeletal features are important for increasing the mechanical work done in a muscle-powered acceleration. The muscle model consisted of a muscle-like actuator with frog hindlimb muscle properties, operating across a lever to accelerate a load. We tested this model in configurations with and without a series elastic element and with and without a variable mechanical advantage. When total muscle shortening was held constant at 30%, the model produced the most work when the muscle operated with a series elastic element and an effective mechanical advantage that increased throughout the contraction (31 J kg(-1) muscle vs 26.6 J kg(-1) muscle for the non-compliant, constant mechanical advantage configuration). We also compared the model output with the dynamics of jumping bullfrogs, measured by high-speed video analysis, and the length changes of the plantaris muscle, measured by sonomicrometry. This comparison revealed that the length, force and power trajectory of the body of jumping frogs could be accurately replicated by a model of a fully active muscle operating against an inertial load, but only if the model muscle included a series elastic element. Sonomicrometer measurements of the plantaris muscle revealed an unusual, biphasic pattern of shortening, with high muscle velocities early and late in the contraction, separated by a period of slow contraction. The model muscle produced this pattern of shortening only when an elastic element was included. These results demonstrate that an elastic element can increase the work output in a muscle-powered acceleration. Elastic elements uncouple muscle fiber shortening velocity from body movement to allow the muscle fibers to operate at slower shortening velocities and higher force outputs. A variable muscle mechanical advantage improves the effectiveness of elastic energy storage and recovery by providing an inertial catch mechanism. These results can explain the high power outputs observed in jumping frogs. More generally, our model suggests how the function of non-muscular elements of the musculoskeletal system enhances performance in muscle-powered accelerations.

Animals↗

PubMed2003

Measuring the activation level of critical lures in the Deese-Roediger-McDermott paradigm.

In four experiments, the activation level in memory of critical lures was assessed after encoding Deese-Roediger-McDermott (DRM) lists. The results demonstrated that studying longer, 14-item lists resulted in superadditive priming of the lures because they were more available in memory than truly studied items. Studying shorter DRM lists resulted in activation levels of the lures that was similar to studied items. Collectively, the results suggest that a first stage in creating false memories with the DRM paradigm is making the critical lures highly available in memory during list encoding. Moreover, the results suggest that false memories are likely to have occurred at the time a list is studied by a mechanism such as an implicit associative response, but a monitoring phase at retrieval is acknowledged that could be used to avoid them. Other theoretical accounts are also considered.

Association Learning↗

PubMed2003

Test modality affects source monitoring and event-related potentials.

Two experiments investigated the effect of test modality (visual or auditory) on source memory and event-related potentials (ERPs). Test modality influenced source monitoring such that source memory was better when the source and test modalities were congruent. Test modality had less of an influence when alternative information (i.e., cognitive operations) could be used to inform source judgments in Experiment 2. Test modality also affected ERP activity. Variation in parietal ERPs suggested that this activity reflects activation of sensory information, which can be attenuated when the sensory information is misleading. Changes in frontal ERPs support the hypothesis that frontal systems are used to evaluate source-specifying information present in the memory trace.

Adolescent↗

PubMed2002

Effects of exercise on the biomechanical, biochemical and structural properties of tendons.

Tendon has been shown to undergo remodeling in response to strength or endurance training, however, compared to muscle, studies of the effects of exercise on tendon are limited and the information is inconsistent. Exercise may influence the structure, chemical composition and/or mechanical properties of tendon. Studies that have examined mechanical changes of tendon in response to endurance training suggest that ultimate failure strength and stiffness increase with training. Available reports indicate that increases in tensile strength and stiffness are probably not associated with increases in collagen concentration or with tendon hypertrophy. The paucity of data renders it impossible to evaluate the response of other structural, chemical and mechanical parameters to training. Furthermore, few investigators have included discrete measures of structural, biomechanical and biochemical variables within a single study. The lack of integrative studies makes it difficult to definitively associate changes in the mechanical properties of tendon with chemical composition and structure.

Adaptation, Physiological↗

PubMed2002

The dynamics of intention retrieval and coordination of action in event-based prospective memory.

Event-based prospective memory requires responding to cues in the environment that are associated with a previously established intention. Some researchers believe that intentions reside in memory with an above baseline level of activation, a phenomenon called the intention superiority effect. The authors of this study predicted that intention superiority would be masked by additional cognitive processes associated with successful event-based prospective memory. These additional processes include noticing the cue, retrieving the intention, and coordinating intention execution with the ongoing activity. In 3 experiments, intention superiority was demonstrated by faster latencies to the ongoing activity on failed prospective trials and the existence of the additional processes was demonstrated by slower latencies on successful trials. This study demonstrates the importance of investigating the microstructure of the cognitive components involved with processing and responding to an event-based prospective memory cue.

Attention↗

PubMed2002

Muscle designed for maximum short-term power output: quail flight muscle.

Take-off in birds at high speeds and steep angles of elevation requires a high burst power output. The mean power output of the pectoralis muscle of blue-breasted quail (Coturnix chinensis) during take-off is approximately 400 W kg(-1) muscle, as determined using two independent methods. This burst power output is much higher than has been measured in any other cyclically contracting muscle. The power output of muscle is determined by the interactions between the physiological properties of the muscle, the stimulation regime imposed by the central nervous system and the details of the strain cycle, which are determined by the reciprocal interaction between the muscle properties and the environmental load. The physiological adaptations that enable a high power output to be achieved are those that allow the muscle to develop high stresses whilst shortening rapidly. These characteristics include a high myofibrillar density, rapid twitch contraction kinetics and a high maximum intrinsic velocity of shortening. In addition, several features of the strain cycle increase the power output of the quail pectoralis muscle. First, the muscle operates at a mean length shorter than the plateau of the length/force relationship. Second, the muscle length trajectory is asymmetrical, with 70 % of the cycle spent shortening. The asymmetrical cycle is expected to increase the power output substantially. Third, subtle deviations in the velocity profile improve power output compared with a simple asymmetrical cycle with constant lengthening and shortening rates. The high burst power outputs found in the flight muscles of quail and similar birds are limited to very brief efforts before fatigue occurs. This strong but short flight performance is well-suited to the rapid-response anti-predation strategy of these birds that involves a short flight coupled with a subsequent sustained escape by running. These considerations serve as a reminder that the maximum power-producing capacities of muscles need to be considered in the context of the in vivo situation within which the muscles operate.

Animals↗

PubMed2002

On predicting the future states of awareness for recognition of unrecallable items.

Two experiments were conducted that examined people's predictive accuracy for their future states of awareness. In both experiments, participants learned word pairs and were tested with a cued recall test. When recall failed, predictive judgments were obtained. In Experiment 1, feeling of knowing judgments predicted not only future recognition but also the state of awareness as remembered or known that was associated with that recognition. In Experiment 2, predictive remember-know judgments were found to be accurately diagnostic of future states of awareness as well. One conclusion to be drawn from these data is that recollective details are among the partial knowledge that is retrieved in the absence of successful cued recall. General implications for theories of feeling of knowing are discussed.

Adult↗