No description available.

After exposure to a short, constant delay between voluntary movement and sensory stimuli, temporal recalibration (TR) arises to realign asynchronous stimuli. The objective of this study was to determine if awareness of the temporal lag between a motor response (i.e., a keypress) and a sensory event (i.e., a visual flash) is necessary for TR to occur. We further investigated whether manipulating the motor and judgment tasks required modifies the influence of awareness on TR due to the cognitive processes engaged. Participants (n = 22) were randomly divided between two groups (Group 1: Aware and Group 2: Unaware). The Aware group was told of the temporal lag between their keypress and visual flash at the beginning of the experiment, whereas the Unaware group was not. All participants completed 8 blocks of trials, in which the motor tasks (e.g., a single or repetitive tap), judgment tasks (e.g., judging the order of the keypress in relation to the visual flash or judging whether the two stimuli were simultaneous or not), and temporal lag between keypress and visual flash (e.g., a 0 ms or 100 ms lag) varied. TR was determined by comparing judgments between corresponding blocks of trials in which the temporal lag was 0 ms to 100 ms. Results revealed that both the Aware and Unaware groups of participants demonstrated TR across both motor and judgment tasks, and that the magnitude of TR did not vary across Aware and Unaware participants or tasks. Thus, results of the present study revealed that awareness of a temporal lag does not influence the magnitude of motor-sensory TR achieved.

When subjects are presented with distorted visual feedback of their hand during a goal-directed movement (i.e. subjects view a cursor representing their hand that is rotated from their hand’s actual position while reaching in a virtual reality environment), they typically adapt their movements so that the cursor is brought to the target, thus reducing reaching errors. In addition to motor adaptation, it has recently been shown that reaching with distorted visual feedback of the hand results in sensory changes, such that proprioceptive estimates of hand position are shifted in the direction of the visual feedback (Cressman and Henriques 2009). The current study looked to establish how quickly these sensory changes arise while training to reach with distorted visual feedback of the hand. Additionally, by comparing sensory to motor changes across time, we looked to determine the relationship between their underlying processes. Subjects trained to reach to a single visual target while seeing a cursor that was aligned with their actual hand position (50 trials: aligned reach training), or rotated 30° clockwise (CW) relative to their actual hand position (150 trials: rotated reach training). Reach errors and proprioceptive estimates of felt hand position were assessed following the aligned reach training trials and at 7 different times during the rotated reach training trials by having subjects reach to the target without visual feedback, and provide estimates of the position of their hand relative to a visual reference marker respectively. Results revealed a slow change in proprioceptive estimates over the course of reach training with the rotated cursor relative to estimates after the aligned reach training, and in fact, significant sensory changes were not observed until after 70 trials. In contrast, reach adaptation showed a much steeper increase and significant adaptation after a limited number of reach training trials with a rotated cursor. These different time courses suggest that proprioceptive recalibration and reach adaptation arise due to separate neural processes.

Proprioception is recalibrated following reaches with misaligned visual feedback of the hand, such that one’s sense of felt hand position is shifted in the direction of the visual feedback provided (Cressman & Henriques 2009). In the current experiment, we examined the ability of proprioceptive recalibration to be retained over an extended period of time (i.e. 4 days), and the benefits of additional training on retention in the form of recall and savings (i.e. faster re-learning on subsequent testing days). Twenty-four participants trained to reach to a target while seeing a cursor that was rotated 30° clockwise relative to their hand on an initial day of testing. Half of the participants then completed additional reach training trials on 4 subsequent testing days (Training group), whereas the second half of participants did not complete additional training (Non-Training group). Participants provided estimates of their felt hand position on all 5 testing days to establish retention of proprioceptive recalibration. Results revealed that proprioceptive recalibration was recalled 24 hours after initial training and that there was no benefit of additional training. Retention in the form of savings was observed on all days for the Training group and on Day 5 in the Non-Training group. These results reveal that proprioceptive recalibration does not benefit from additional training but is retained in the form of recall and savings. Taken together, results from the two groups of participants showed that the sensory system’s ability to change over time appeared to saturate early on, within two days of training. Moreover, the different time scales (i.e. 1 day for recall versus 4 days for savings), suggested that distinct processes may underlie recall and savings of proprioceptive recalibration.

No description available.

O objetivo desta pesquisa foi recalibrar um modelo de simulação de rodovias de pista simples a fim de seja possível usá-lo no estudo de estradas do Estado de São Paulo. O modelo escolhido para recalibração é o TRARR (TRAffic on Rural Roads) versão 4.0, desenvolvido na Austrália pelo ARRB Transport Research Ltd. A recalibração do modelo consistiu em alterar parâmetros referentes ao desempenho (relação potência/massa) e características (massa, comprimento) dos veículos pesados e um parâmetro relativo ao comportamento dos veículos quando viajando em pelotões, de tal modo que os resultados da simulação ficassem compatíveis com os observados em campo. As medidas de desempenho escolhidas para a recalibração foram: a porcentagem de veículos trafegando em pelotões, a velocidade média dos veículos e a taxa de ultrapassagens. Os dados para a recalibração do modelo foram coletados num trecho de 2,8 km de extensão, na rodovia SP 255, entre as cidades paulistas de Araraquara e Ribeirão Preto. No processo de recalibração, as medidas de desempenho observadas no campo foram comparadas com as produzidas pelas versões recalibrada e original do simulador. Ao final da recalibração, pôde-se concluir que as duas versões do modelo são capazes de simular adequadamente o trecho estudado, sendo que o modelo recalibrado produz resultados ligeiramente melhores que os da versão original. O modelo recalibrado foi validado simulando-se um trecho de 10 km de extensão da SP 255 e comparando-se os valores medidos no trecho para as medidas de desempenho escolhidas com os valores produzidos pela versão recalibrada do simulador. Os resultados dessa comparação indicam que o modelo pode ser considerado capaz de simular adequadamente a operação de rodovias de pista simples no Estado de São Paulo. Os resultados do estudo também sugerem que a precisão pode ser melhorada com um ajuste fino de alguns dos parâmetros não modificados durante a recalibração. / The objective of this research is to recalibrate a two-lane highway simulation model to allow its employment within the context of the São Paulo state highways, Brazil. The model chosen for this recalibration is TRARR (TRAffic on Rural Roads) version 4.0, originally developed a in Australia by ARRB Transport Research Ltd. The procedure used for the model recalibration consisted in modifying input parameters related to heavy vehicle dimensions and performance characteristics (power/mass ratio, weight and length) as well as to the behavior of vehicles in platoons, in such a way that the model outputs are compatible with real traffic behavior. Three measures of performance were chosen for recalibration of the model: percent of jouney time spent following, average speed and overtaking rate. Data for model recalibration were collected at a 2.8 km rural section of SP 225, a highway which connects the cities of Ribeirão Preto and Araraquara in the state of São Paulo (Brazil). The recalibration procedure was based on comparisons of the measures of performance observed on the real highway with those produced by the simulator\'s recalibrated and original versions. At the end of the recalibration process, both the recalibrated and the original models were considered capable of reproducing the traffic behavior on a two-lane highway similar to the ones in the state of São Paulo. Furthermore, it was concluded that the recalibrated model is capable of producing results slightly better than the original one. The recalibrated model was submitted to a validation procedure in which a 10 km section of SP 255 was simulated and the measures of perfomance obtained with the model were compared to field observations. The results of the validation procedure indicate that recalibrated version of TRARR is capable of simulating traffic operations on rural two-lane highways in the state of São Paulo. The results of the research also suggest that the model results may be improved with fine-tuning of some of the parameters that were not modified during the recalibration procedure.

Yes / Background: Our motor actions normally generate sensory events, but how do we know which events were self generated and which have external causes? Here we use temporal adaptation to investigate the processing stage and generality of our sensorimotor timing estimates. Methodology/Principal Findings: Adaptation to artificially-induced delays between action and event can produce a startling percept¿upon removal of the delay it feels as if the sensory event precedes its causative action. This temporal recalibration of action and event occurs in a quantitatively similar manner across the sensory modalities. Critically, it is robust to the replacement of one sense during the adaptation phase with another sense during the test judgment. Conclusions/Significance: Our findings suggest a high-level, supramodal recalibration mechanism. The effects are well described by a simple model which attempts to preserve the expected synchrony between action and event, but only when causality indicates it is reasonable to do so. We further demonstrate that this model successfully characterises related adaptation data from outside the sensorimotor domain.

No description available.

Evidence suggests that human time perception is likely to reflect an ensemble of recent temporal experience. For example, prolonged exposure to consistent temporal patterns can adaptively realign the perception of event order, both within and between sensory modalities (e.g. Fujisaki et al., 2004 Nat. Neurosci., 7, 773-778). In addition, the observation that 'a watched pot never boils' serves to illustrate the fact that dynamic shifts in our attentional state can also produce marked distortions in our temporal estimates. In the current study we provide evidence for a hitherto unknown link between adaptation, temporal perception and our attentional state. We show that our ability to use recent sensory history as a perceptual baseline for ongoing temporal judgments is subject to striking top-down modulation via shifts in the observer's selective attention. Specifically, attending to the temporal structure of asynchronous auditory and visual adapting stimuli generates a substantial increase in the temporal recalibration induced by these stimuli. We propose a conceptual framework accounting for our findings whereby attention modulates the perceived salience of temporal patterns. This heightened salience allows the formation of audiovisual perceptual 'objects', defined solely by their temporal structure. Repeated exposure to these objects induces high-level pattern adaptation effects, akin to those found in visual and auditory domains (e.g. Leopold & Bondar (2005) Fitting the Mind to the World: Adaptation and Aftereffects in High-Level Vision. Oxford University Press, Oxford, 189-211; Schweinberger et al. (2008) Curr. Biol., 18, 684-688). / Wellcome Trust, College of Optometrists

During multisensory integration, information from distinct sensory systems that refers to the same physical event is combined. For example, the sound and image that an individual generates as s/he interacts with the world, will provide the nervous system with multiple cues which can be integrated to estimate the individual’s position in the environment. However, the information that is perceived through different sensory pathways/systems can be qualitatively different. The information can be redundant and describe the same property of an event in a common reference frame (i.e., the image and sound referring to the individual’s location), or it can be complementary. Combining complementary information can be advantageous in that it extends the range and richness of the information available to the nervous system, but can also be superfluous and unnecessary to the task at hand – i.e. olfactory cues about the individuals perfume can increase the richness of the representation but not necessarily aid in localisation. Over the last century or so, a large body of research has focused on different aspects of multisensory interactions at both the behavioural and neural levels. It is currently unclear whether the mechanisms underlying multisensory interactions for both type of cue are similar or not. Moreover, the evidence for differences in behavioural outcome, dependent on the nature of the cue, is growing. Such cue property effects possibly reflect a processing heuristic for more efficient parsing of the vast amount of sensory information available to the nervous system at any one time. The present thesis assesses the effects of cue properties (i.e., redundant or complementary) on multisensory processing and reports a series of experiments demonstrating that the nature of the cue, defined by the task of the observer, influences whether the cues compete for representation as a result of interacting, or whether instead multisensory information produces an optimal increase in reliability of the event estimate. Moreover, a bridging series of experiments demonstrate the key role of redundancy in inferring that two signals have a common physical cause and should be integrated, despite conflict in the cues. The experiments provide insights into the different strategies adopted by the nervous system and some tentative evidence for possible, distinct underlying mechanisms.