Structure learning in a sensorimotor association task.

Learning is often understood as an organism's gradual acquisition of the association between a given sensory stimulus and the correct motor response. Mathematically, this corresponds to regressing a mapping between the set of observations and the set of actions. Recently, however, it has been shown both in cognitive and motor neuroscience that humans are not only able to learn particular stimulus-response mappings, but are also able to extract abstract structural invariants that facilitate generalization to novel tasks. Here we show how such structure learning can enhance facilitation in a sensorimotor association task performed by human subjects. Using regression and reinforcement learning models we show that the observed facilitation cannot be explained by these basic models of learning stimulus-response associations. We show, however, that the observed data can be explained by a hierarchical Bayesian model that performs structure learning. In line with previous results from cognitive tasks, this suggests that hierarchical Bayesian inference might provide a common framework to explain both the learning of specific stimulus-response associations and the learning of abstract structures that are shared by different task environments.

Motor learning.

Although learning a motor skill, such as a tennis stroke, feels like a unitary experience, researchers who study motor control and learning break the processes involved into a number of interacting components. These components can be organized into four main groups. First, skilled performance requires the effective and efficient gathering of sensory information, such as deciding where and when to direct one's gaze around the court, and thus an important component of skill acquisition involves learning how best to extract task-relevant information. Second, the performer must learn key features of the task such as the geometry and mechanics of the tennis racket and ball, the properties of the court surface, and how the wind affects the ball's flight. Third, the player needs to set up different classes of control that include predictive and reactive control mechanisms that generate appropriate motor commands to achieve the task goals, as well as compliance control that specifies, for example, the stiffness with which the arm holds the racket. Finally, the successful performer can learn higher-level skills such as anticipating and countering the opponent's strategy and making effective decisions about shot selection. In this Primer we shall consider these components of motor learning using as an example how we learn to play tennis.

Attenuation of self-generated tactile sensations is predictive, not postdictive.

When one finger touches the other, the resulting tactile sensation is perceived as weaker than the same stimulus externally imposed. This attenuation of sensation could result from a predictive process that subtracts the expected sensory consequences of the action, or from a postdictive process that alters the perception of sensations that are judged after the event to be self-generated. In this study we observe attenuation even when the fingers unexpectedly fail to make contact, supporting a predictive process. This predictive attenuation of self-generated sensation may have evolved to enhance the perception of sensations with an external cause.

Context-dependent partitioning of motor learning in bimanual movements.

Human subjects easily adapt to single dynamic or visuomotor perturbations. In contrast, when two opposing dynamic or visuomotor perturbations are presented sequentially, interference is often observed. We examined the effect of bimanual movement context on interference between opposing perturbations using pairs of contexts, in which the relative direction of movement between the two arms was different across the pair. When each perturbation direction was associated with a different bimanual context, such as movement of the arms in the same direction versus movement in the opposite direction, interference was dramatically reduced. This occurred over a short period of training and was seen for both dynamic and visuomotor perturbations, suggesting a partitioning of motor learning for the different bimanual contexts. Further support for this was found in a series of transfer experiments. Having learned a single dynamic or visuomotor perturbation in one bimanual context, subjects showed incomplete transfer of this learning when the context changed, even though the perturbation remained the same. In addition, we examined a bimanual context in which one arm was moved passively and show that the reduction in interference requires active movement. The sensory consequences of movement are thus insufficient to allow opposing perturbations to be co-represented. Our results suggest different bimanual movement contexts engage at least partially separate representations of dynamics and kinematics in the motor system.

Historical knowledge of sharks: ancient science, earliest American encounters, and American science, fisheries, and utilization

In western civilization, the knowledge of the elasmobranch or selachian fishes (sharks and rays) begins with Aristotle (384–322 B.C.). Two of his extant works, the “Historia Animalium” and the “Generation of Animals,” both written about 330 B.C., demonstrate knowledge of elasmobranch fishes acquired by observation. Roman writers of works on natural history, such as Aelian and Pliny, who followed Aristotle, were compilers of available information. Their contribution was that they prevented the Greek knowledge from being lost, but they added few original observations. The fall of Rome, around 476 A.D., brought a period of economic regression and political chaos. These in turn brought intellectual thought to a standstill for nearly one thousand years, the period known as the Dark Ages. It would not be until the middle of the sixteenth century, well into the Renaissance, that knowledge of elasmobranchs would advance again. The works of Belon, Salviani, Rondelet, and Steno mark the beginnings of ichthyology, including the study of sharks and rays. The knowledge of sharks and rays increased slowly during and after the Renaissance, and the introduction of the Linnaean System of Nomenclature in 1735 marks the beginning of modern ichthyology. However, the first major work on sharks would not appear until the early nineteenth century. Knowledge acquired about sea animals usually follows their economic importance and exploitation, and this was also true with sharks. The first to learn about sharks in North America were the native fishermen who learned how, when, and where to catch them for food or for their oils. The early naturalists in America studied the land animals and plants; they had little interest in sharks. When faunistic works on fishes started to appear, naturalists just enumerated the species of sharks that they could discern. Throughout the U.S. colonial period, sharks were seldom utilized for food, although their liver oil or skins were often utilized. Throughout the nineteenth century, the Spiny Dogfish, Squalus acanthias, was the only shark species utilized in a large scale on both coasts. It was fished for its liver oil, which was used as a lubricant, and for lighting and tanning, and for its skin which was used as an abrasive. During the early part of the twentieth century, the Ocean Leather Company was started to process sea animals (primarily sharks) into leather, oil, fertilizer, fins, etc. The Ocean Leather Company enjoyed a monopoly on the shark leather industry for several decades. In 1937, the liver of the Soupfin Shark, Galeorhinus galeus, was found to be a rich source of vitamin A, and because the outbreak of World War II in 1938 interrupted the shipping of vitamin A from European sources, an intensive shark fishery soon developed along the U.S. West Coast. By 1939 the American shark leather fishery had transformed into the shark liver oil fishery of the early 1940’s, encompassing both coasts. By the late 1940’s, these fisheries were depleted because of overfishing and fishing in the nursery areas. Synthetic vitamin A appeared on the market in 1950, causing the fishery to be discontinued. During World War II, shark attacks on the survivors of sunken ships and downed aviators engendered the search for a shark repellent. This led to research aimed at understanding shark behavior and the sensory biology of sharks. From the late 1950’s to the 1980’s, funding from the Office of Naval Research was responsible for most of what was learned about the sensory biology of sharks.

Statistics of natural movements are reflected in motor errors.

Humans use their arms to engage in a wide variety of motor tasks during everyday life. However, little is known about the statistics of these natural arm movements. Studies of the sensory system have shown that the statistics of sensory inputs are key to determining sensory processing. We hypothesized that the statistics of natural everyday movements may, in a similar way, influence motor performance as measured in laboratory-based tasks. We developed a portable motion-tracking system that could be worn by subjects as they went about their daily routine outside of a laboratory setting. We found that the well-documented symmetry bias is reflected in the relative incidence of movements made during everyday tasks. Specifically, symmetric and antisymmetric movements are predominant at low frequencies, whereas only symmetric movements are predominant at high frequencies. Moreover, the statistics of natural movements, that is, their relative incidence, correlated with subjects' performance on a laboratory-based phase-tracking task. These results provide a link between natural movement statistics and motor performance and confirm that the symmetry bias documented in laboratory studies is a natural feature of human movement.

Inferring visuomotor priors for sensorimotor learning.

Sensorimotor learning has been shown to depend on both prior expectations and sensory evidence in a way that is consistent with Bayesian integration. Thus, prior beliefs play a key role during the learning process, especially when only ambiguous sensory information is available. Here we develop a novel technique to estimate the covariance structure of the prior over visuomotor transformations--the mapping between actual and visual location of the hand--during a learning task. Subjects performed reaching movements under multiple visuomotor transformations in which they received visual feedback of their hand position only at the end of the movement. After experiencing a particular transformation for one reach, subjects have insufficient information to determine the exact transformation, and so their second reach reflects a combination of their prior over visuomotor transformations and the sensory evidence from the first reach. We developed a Bayesian observer model in order to infer the covariance structure of the subjects' prior, which was found to give high probability to parameter settings consistent with visuomotor rotations. Therefore, although the set of visuomotor transformations experienced had little structure, the subjects had a strong tendency to interpret ambiguous sensory evidence as arising from rotation-like transformations. We then exposed the same subjects to a highly-structured set of visuomotor transformations, designed to be very different from the set of visuomotor rotations. During this exposure the prior was found to have changed significantly to have a covariance structure that no longer favored rotation-like transformations. In summary, we have developed a technique which can estimate the full covariance structure of a prior in a sensorimotor task and have shown that the prior over visuomotor transformations favor a rotation-like structure. Moreover, through experience of a novel task structure, participants can appropriately alter the covariance structure of their prior.

Nutritional properties of the invasive lionfish: A delicious and nutritious approach for controlling the invasion

Lionfish, Pterois volitans and P. miles, are native to the Indo-Pacific and have recently invaded the Western Atlantic Ocean. Strategies for control of this invasion have included limited removal programs and promotion of lionfish consumption at both local and commercial scales. We demonstrate that lionfish meat contains higher levels of healthy n-3 fatty acids than some frequently consumed native marine fish species. Mean lionfish fillet yield was 30.5% of the total body wet weight, a value that is similar to that of some grouper and porgy species. A sensory evaluation indicated that lionfish meet the acceptability threshold of most consumers.

Nonautonomous elementary net systems and their application to programmable logic control

In this paper, a novel approach to Petri net modeling of programmable logic controller (PLC) programs is presented. The modeling approach is a simple extension of elementary net systems, and a graphical design tool that supports the use of this modeling approach is provided. A key characteristic of the model is that the binary sensory inputs and binary actuation outputs of the PLC are explicitly represented. This leads to the following two improvements: outputs are unambiguous, and interaction patterns are more clearly represented in the graphical form. The use of this modeling approach produces programs that are simple, lightweight, and portable. The approach is demonstrated by applying it to the development of a control module for a MonTech Positioning Station. © 2008 IEEE.

Histochemical studies on the olfactory epithelium of some hillstream teleosts

Living specimens of Barilius bendelisis, Crossocheilus latius latius, Torputitora, Glyptothorax pectinopterus and Pseudecheneis sulcatus were collected from the streams and rivers of Garhwal Himalaya. Histochemical localization of carbohydrates (1:2 glycol groups, glycogen, B-metachromasia and acid mucopolysaccharides), proteins and protein bound NH sub(2) group, bound lipids and the enzymes (acid and alkaline phosphatases) in the olfactory epithelium were studied. The receptor, supporting basal and mucous cells show varying degrees of distinction and distribution of these substances. The enzymes are present on the surface of the epithelium, sensory hairs and the boundaries of mucous cells only.

An objective method to monitor and quantify texture of salted herring during ripening in barrels at 4°C

Changes in the texture (elastic nature) of the flesh of barrel salted herring during the ripening process at 4°C have been monitored. The method employs the analysis of stress-relaxation curves after compression to half of the sample thickness on an lnstron Model 1112. The parameter 'T/P' for each sample represents the reciprocal of the gradient of a line connecting P and T0.368p. This parameter characteristic of each sample's texture was calculated as the ratio of 'T/P' where, T is the relaxation time and is defined as the time required for a stress at constant strain to decrease to 1/e of its original value, where 'e' is the base of natural logarithms (2.7183). Since 1/e=0.368, the relaxation time is the time required for the force to decay to 36.8% of its original value. P is the peak height of the curve (i.e. the force value at the maximum height). This method was adopted from the bakery industry for testing the degree of gluten development in bread dough. The 'T/P' values obtained over the course of ripening for differently treated salted-herring in barrels ranged between 1 and 12. The trends in 'T/P' value, during ripening period for the different samples, appeared to be parallel changes in texture perceived by sensory observation (subjective measurement), although the heterogeneous nature of the samples gave standard deviations, about the replicate sample mean, around 5%. The method appears promising as an objective measure for monitoring this aspect of the textural quality of barrel salted-herring through ripening if reproducibility of test results can be improved by more careful standardization of sample preparation and test protocol.

Effect of gibbing on protein hydrolysis during the ripening of salted herring at 4°C in polypropylene barrels

Effect of gibbing process on the protein hydrolysis in terms of free alpha amino nitrogen (FAN) content during the ripening of barrel salted herring at low temperature (4°C) was investigated. For this purpose North Sea herring (Clupea harengus) from north-east British coast was salted in polypropylene barrels and allowed to ripen at 4°C. This process of barrel salting was carried out for whole fish in one batch and gibbed fish in another batch. The investigation was performed by using new salt and used salt in separate barrels for each batch of experimental fish. Results of the present study show that protein hydrolysis was significantly higher in the ripened salt-herring produced from whole fish which was found to have more characteristic sensory properties than those produced from gibbed fish. Similar result (proteolysis) was obtained when the investigation was repeated for the spent herring although the spent herring fails to produce a ripened product with the desired characteristic sensory attributes, compared to those of pre-spawning herring.

Preparation of prawn pickle and its storage characteristics

Prawn pickle was produced using smaller variety of prawn. Vinegar and salt was used to preserve the prawn muscle against spoilage. Different spices were used to get desired attractive flavour. Benzoic acid to the extent of 200 ppm was used as preservative. Several trials were carried out using different amounts of spices and different methods of preparation. After each trial the sample was subjected to sensory evaluation by judges consisting of five members who had previous experience of acting as panel members. Several trials were carried out to arrive at a final recipe as judged best by the taste panel. Utilizing this final recipe, a product was prepared and subjected to biochemical, bacteriological and organoleptic evaluation and found to be quite acceptable after seven months of storage in glass jar at ambient temperature. The product was subjected to large scale consumer acceptance trial involving 140 consumers, 42% of them ranked it excellent, 41% rated very good, 12% rated good while 5% of the consumers rated it as average.

Maintaining internal representations: The role of the human superior parietal lobe

In sensorimotor integration, sensory input and motor output signals are combined to provide an internal estimate of the state of both the world and one's own body. Although a single perceptual and motor snapshot can provide information about the current state, computational models show that the state can be optimally estimated by a recursive process in which an internal estimate is maintained and updated by the current sensory and motor signals. These models predict that an internal state estimate is maintained or stored in the brain. Here we report a patient with a lesion of the superior parietal lobe who shows both sensory and motor deficits consistent with an inability to maintain such an internal representation between updates. Our findings suggest that the superior parietal lobe is critical for sensorimotor integration, by maintaining an internal representation of the body's state.

Central cancellation of self-produced tickle sensation

A self-produced tactile stimulus is perceived as less ticklish than the same stimulus generated externally. We used fMRI to examine neural responses when subjects experienced a tactile stimulus that was either self-produced or externally produced. More activity was found in somatosensory cortex when the stimulus was externally produced. In the cerebellum, less activity was associated with a movement that generated a tactile stimulus than with a movement that did not. This difference suggests that the cerebellum is involved in predicting the specific sensory consequences of movements, providing the signal that is used to cancel the sensory response to self-generated stimulation.