Straight ahead acts as a reference for visuomotor adaptation

One can adapt movement planning to compensate for a mismatch between vision and action. Previous research with prismatic lenses has shown this adaptation to be accompanied with a shift in the evaluation of one’s body midline, suggesting an important role of this reference for successful adaptation. This interpretation leads to the prediction that rotation adaptation could be more difficult to learn for some directions than others. Specifically, we hypothesized that targets seen to the right of the body midline but for which a rotation imposes a movement to its left would generate a conflict leading to a bias in movement planning. As expected, we observed different movement planning biases across movement directions. The same pattern of biases was observed in a second experiment in which the starting position was translated 15 cm to the right of the participants’ midline. This indicates that the “straight ahead” direction, not one’s midline, serves as an important reference for movement planning during rotation adaptation.

Dopamine and inhibitory action control: evidence from spontaneous eye blink rates

The inhibitory control of actions has been claimed to rely on dopaminergic pathways. Given that this hypothesis is mainly based on patient and drug studies, some authors have questioned its validity and suggested that beneficial effects of dopaminergic stimulants on response inhibition may be limited to cases of suboptimal inhibitory functioning. We present evidence that, in carefully selected healthy adults, spontaneous eyeblink rate, a marker of central dopaminergic functioning, reliably predicts the efficiency in inhibiting unwanted action tendencies in a stop-signal task. These findings support the assumption of a modulatory role for dopamine in inhibitory action control.

Misperceiving the speed-accuracy tradeoff: imagined movements and perceptual decisions

Research has suggested that prospective motor decisions are consistent with actual motor action. In a study that we recently published (Young et al. in Exp Brain Res 185:681–688, 2008), however, participants demonstrated a preference for closer targets that was inconsistent with the predictions of Fitts’s law. With a pair of experiments, the present paper investigates the underlying basis of this non-optimal behaviour. Participants showed a similar deviation from Fitts’s law when imagining movements—believing that movement duration increased with distance within the same index of difficulty. Participants did not behave similarly, however, in a perceptual version of the decision task. These results suggest that imagined movements and motor decisions are linked, as well as demonstrating one situation in which both show a similar deviation from the patterns of actual movement duration.

Effects of seeing and hearing speech on speech production: a response time study

Research demonstrates that listening to and viewing speech excites tongue and lip motor areas involved in speech production. This perceptual-motor relationship was investigated behaviourally by presenting video clips of a speaker producing vowel-consonant-vowel syllables in three conditions: visual-only, audio-only, and audiovisual. Participants identified target letters that were flashed over the mouth during the video, either manually or verbally as quickly as possible. Verbal responses were fastest when the target matched the speech stimuli in all modality conditions, yet optimal facilitation was observed when participants were presented with visual-only stimuli. Critically, no such facilitation occurred when participants were asked to identify the target manually. Our findings support previous research suggesting a close relationship between speech perception and production by demonstrating that viewing speech can ‘prime’ our motor system for subsequent speech production.

How voluntary actions modulate time perception

Distortions of time perception are generally explained either by variations in the rate of pacing signals of an “internal clock”, or by lag-adaptation mechanisms that recalibrate the perceived time of one event relative to another. This study compares these accounts directly for one temporal illusion: the subjective compression of the interval between voluntary actions and their effects, known as ‘intentional binding’. Participants discriminated whether two cutaneous stimuli presented after voluntary or passive movements were simultaneous or successive. In other trials, they judged the temporal interval between their movement and an ensuing tone. Temporal discrimination was impaired following voluntary movements compared to passive movements early in the action-tone interval. In a control experiment, active movements without subsequent tones produced no impairment in temporal discrimination. These results suggest that voluntary actions transiently slow down an internal clock during the action-effect interval. This in turn leads to intentional binding, and links the effects of voluntary actions to the self.

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Randomizing visual feedback in manual aiming: reminiscence of the previous trial condition and prior knowledge of feedback availability

A trial-by-trial analysis was used to systematically examine the influence of switching visual conditions on visual feedback utilization for a manual aiming movement. In experiment one, vision was randomly manipulated from trial to trial with no more than four consecutive trials in the same visual condition. In experiment two, participants were provided with certainty of visual feedback availability prior to every trial. Results of both studies revealed that movement endpoint variability was most associated with visual feedback availability on the previous trial. Furthermore, correlation analyses comparing movement trajectory at 25, 50 and 75% with movement end (i.e. 100%) revealed that the efficiency of online corrections also depends on the availability of visual feedback on the previous trial. These results suggest that the accuracy of an aiming movement is highly dependent on processing of offline visual information from the preceding trial. This study was supported by a grant from the Natural Sciences and Engineering Research Council of Canada (NSERC) awarded to Luc Tremblay.

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The common magnitude code underlying numerical and size processing for action but not for perception

The interaction between numbers and action-related process has received increasing attention in the literature of numerical cognition. In the current study, two dual-task experiments were conducted to explore the interaction among numerical, prehension, and perceptual color/size judgments. The results revealed the commonality and distinctness of the magnitude representations that are involved in these tasks. Specifically, a photograph of a graspable object with a superimposed Arabic digit was presented in each trial. Participants were required to first judge the parity of the digit with a manual response while simultaneously planning a subsequent vocal response pertaining to the depicted object. When parity and action judgments were performed close in time, the compatibility effect between the numerical magnitude of the digit and the appropriate action (pinch vs. clutch) for the object was demonstrated in both manual and vocal responses. In contrast, such compatibility effect was absent when parity judgment was coupled with color-related or perceptual size judgment. The findings of the current study support the existence of a common magnitude code underlying numerical and non-numerical dimensions for action-related purposes, as proposed by the ATOM model (Walsh in Trends Cogn Sci 7:483–488, 2003). Furthermore, based on the selective presence of the compatibility effect, we argue that the interaction among different quantity dimensions conforms to the “dorsal-action and ventral-perception” organizational principle of the human brain.

Adaptations of lateral hand movements to early and late visual occlusion in catching

Recent studies suggested that the control of hand movements in catching involves continuous vision-based adjustments. More insight into these adjustments may be gained by examining the effects of occluding different parts of the ball trajectory. Here, we examined the effects of such occlusion on lateral hand movements when catching balls approaching from different directions, with the occlusion conditions presented in blocks or in randomized order. The analyses showed that late occlusion only had an effect during the blocked presentation, and early occlusion only during the randomized presentation. During the randomized presentation movement biases were more leftward if the preceding trial was an early occlusion trial. The effect of early occlusion during the randomized presentation suggests that the observed leftward movement bias relates to the rightward visual acceleration inherent to the ball trajectories used, while its absence during the blocked presentation seems to reflect trial-by-trial adaptations in the visuomotor gain, reminiscent of dynamic gain control in the smooth pursuit system. The movement biases during the late occlusion block were interpreted in terms of an incomplete motion extrapolation—a reduction of the velocity gain—caused by the fact that participants never saw the to-be-extrapolated part of the ball trajectory. These results underscore that continuous movement adjustments for catching do not only depend on visual information, but also on visuomotor adaptations based on non-visual information.

The impact of real and illusory target perturbations on manual aiming

This experiment was designed to determine if real and illusory shifts in target position at movement initiation affect the same online corrective processes. Adult participants completed rapid goal-directed movements toward the vertex of a target “T” located at the midline, 25 cm distal to a small home position. At movement initiation, the target either stayed the same, shifted its real position, its illusory position or both. The real perturbation involved a 2.5 mm shift either toward or away from the body. For the illusory perturbation, the horizontal portion of the “T” changed to inward or outward Müller–Lyer wings. Both the real and the illusory perturbation affected movement outcome. The two manipulations began to have their impact at peak velocity. Because both perturbations affected mid to late trajectory control and because their effects were not independent, we concluded that real and illusory target shifts impact late visual motor control associated with a comparison between the position of the limb and the perceived position of the target.

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Integration of auditory and visual information in the recognition of realistic objects

Recognizing a natural object requires one to pool information from various sensory modalities, and to ignore information from competing objects. That the same semantic knowledge can be accessed through different modalities makes it possible to explore the retrieval of supramodal object concepts. Here, object-recognition processes were investigated by manipulating the relationships between sensory modalities, specifically, semantic content, and spatial alignment between auditory and visual information. Experiments were run under realistic virtual environment. Participants were asked to react as fast as possible to a target object presented in the visual and/or the auditory modality and to inhibit a distractor object (go/no-go task). Spatial alignment had no effect on object-recognition time. The only spatial effect observed was a stimulus–response compatibility between the auditory stimulus and the hand position. Reaction times were significantly shorter for semantically congruent bimodal stimuli than would be predicted by independent processing of information about the auditory and visual targets. Interestingly, this bimodal facilitation effect was twice as large as found in previous studies that also used information-rich stimuli. An interference effect was observed (i.e. longer reaction times to semantically incongruent stimuli than to the corresponding unimodal stimulus) only when the distractor was auditory. When the distractor was visual, the semantic incongruence did not interfere with object recognition. Our results show that immersive displays with large visual stimuli may provide large multimodal integration effects, and reveal a possible asymmetry in the attentional filtering of irrelevant auditory and visual information.

When vision ‘extinguishes’ touch in neurologically-normal people: extending the Colavita visual dominance effect

Research has shown that people fail to report the presence of the auditory component of suprathreshold audiovisual targets significantly more often than they fail to detect the visual component in speeded response tasks. Here, we investigated whether this phenomenon, known as the “Colavita effect”, also affects people’s perception of visuotactile stimuli as well. In Experiments 1 and 2, participants made speeded detection/discrimination responses to unimodal visual, unimodal tactile, and bimodal (visual and tactile) stimuli. A significant Colavita visual dominance effect was observed (i.e., participants failed to respond to touch far more often than they failed to respond to vision on the bimodal trials). This dominance of vision over touch was significantly larger when the stimuli were presented from the same position than when they were presented from different positions (Experiment 3), and still occurred even when the subjective intensities of the visual and tactile stimuli had been matched (Experiment 4), thus ruling out a simple intensity-based account of the results. These results suggest that the Colavita visual dominance effect (over touch) may result from a competition between the neural representations of the two stimuli for access to consciousness and/or the recruitment of attentional resources.

Attention modulates the specificity of automatic imitation to human actors

The perception of actions performed by others activates one’s own motor system. Recent studies disagree as to whether this effect is specific to actions performed by other humans, an issue complicated by differences in perceptual salience between human and non-human stimuli. We addressed this issue by examining the automatic imitation of actions stimulated by viewing a virtual, computer-generated, hand. This stimulus was held constant across conditions, but participants’ attention to the virtualness of the hand was manipulated by informing some participants during instructions that they would see a “computer-generated model of a hand,” while making no mention of this to others. In spite of this attentional manipulation, participants in both conditions were generally aware of the virtualness of the hand. Nevertheless, automatic imitation of the virtual hand was significantly reduced––but not eliminated––when participants were told they would see a virtual hand. These results demonstrate that attention modulates the “human bias” of automatic imitation to non-human actors.

Unmasking Word Processing with ERPs: Two Novel Linear Techniques for the Estimation of Temporally Overlapped Waveforms

Masked priming experiments are frequently used to study automatic aspects of word processing. Direct measures of such processing obtained with functional neuroimaging techniques (ERPs, fMRI, etc.) need to isolate the neural activation related to relevant events when they are rapidly followed by others (a situation found in other popular paradigms such as the attentional blink and repetition blindness). Here we examine the assumption of “simple insertion”, which underlies the use of subtraction to isolate components of temporally overlapping waveforms. We propose two novel linear methods and illustrate how they extract temporal and spatial ERP components that the subtraction method fails to detect. We show this through the analysis of ERP data from a masked semantic priming procedure. The new techniques reveal activation generated by unconscious (masked) prime words as early as 100 ms and 200 ms post stimulus-onset; a pattern which simple subtraction fails to detect.

Preparation and inhibition of interceptive actions

Two experiments aimed to provide an estimate of the last moment at which visual information needs to be obtained in order for it to be used to initiate execution of an interceptive movement or to withhold execution of such a movement. In experiment 1, we sought to estimate the minimum time required to suppress the movement when the participants were first asked to intercept a moving target. In experiment 2, we sought to determine the minimum time required to initiate an interceptive movement when the participants were initially asked to keep stationary. Participants were trained to hit moving targets using movements of a pre-specified duration. This permitted an estimate of movement onset (MO) time. In both experiments the requirement to switch from one prepared course of action to the other was indicated by changing the colour of the moving target at times prior to the estimated MO. The results of the experiments showed that the decision to execute or suppress the interception must be made no less than about 200 ms before MO.

Role of the lateral prefrontal cortex in visual object-based selective attention

We demonstrate that attention to object representations is vitally dependent on the prefrontal cortex. Object-based selective attention was compared in neurologic patients with unilateral damage to either the dorsolateral prefrontal cortex (DLPFC) or the parietal cortex and in healthy controls. Our task required a top–down attentional modulation of object representations in which spatial location played no role. All groups could invoke top–down object-based selection, but the DLPFC patients showed a selective deficit when target stimuli were in the hemifield contralateral to the lesioned hemisphere. Our findings indicate that in the healthy brain, anterior cortical mechanisms are crucial for attending to object-centered representations, whereas posterior cortical mechanisms are necessary for attending to objects at locations in the visual scene.

A Judd illusion in far-aiming: evidence of a contribution to action by vision for perception

The present study addresses the role of vision for perception in determining the location of a target in far-aiming. Participants (N = 12) slid a disk toward a distant target embedded in illusory Judd figures. Additionally, in a perception task, participants indicated when a moving pointer reached the midpoint of the Judd figures. The number of hits, the number of misses to the left and to the right of the target, the sliding error (in mm) and perceptual judgment error (in mm) served as dependent variables. Results showed an illusory bias in sliding, the magnitude of which was comparable to the bias in the perception of target location. The determination of target location in far-aiming is thus based on relative metrics. We argue that vision for perception sets the boundary constraints for action and that within these constraints vision for action autonomously controls movement execution, but alternative accounts are discussed as well.

Response preparation changes during practice of an asynchronous bimanual movement

For synchronous bimanual movements, we have shown that a different amplitude can be prepared for each limb in advance and this preparation improves with practice (Maslovat et al. 2008). In the present study, we tested whether an asynchronous bimanual movement can also be prepared in advance and be improved with practice. Participants practiced (160 trials) a discrete bimanual movement in which the right arm led the left by 100 ms in response to an auditory “go” signal (either 80 dB control stimulus or 124 dB startle stimulus). The startle stimulus was used to gauge whether inter-limb timing could be pre-programed. During startle trials, the asynchronous bimanual movement was triggered at early latency suggesting the entire movement could be prepared in advance. However, the triggered movement had a shorter between-arm delay and a temporally compressed within-arm EMG pattern, results that we attribute to increased neural activation caused by the startling stimulus. However, as both startle and control trials improved over time, it does appear response preparation of interval timing can improve with practice.

On rhythmic and discrete movements: reflections,definitions and implications for motor control

At present, rhythmic and discrete movements are investigated by largely distinct research communities using different experimental paradigms and theoretical constructs. As these two classes of movements are tightly interlinked in everyday behavior, a common theoretical foundation spanning across these two types of movements would be valuable. Furthermore, it has been argued that these two movement types may constitute primitives for more complex behavior. The goal of this paper is to develop a rigorous taxonomic foundation that not only permits better communication between different research communities, but also helps in defining movement types in experimental design and thereby clarifies fundamental questions about primitives in motor control. We propose formal definitions for discrete and rhythmic movements, analyze some of their variants, and discuss the application of a smoothness measure to both types that enables quantification of discreteness and rhythmicity. Central to the definition of discrete movement is their separation by postures. Based on this intuitive definition, certain variants of rhythmic movement are indistinguishable from a sequence of discrete movements, reflecting an ongoing debate in the motor neuroscience literature. Conversely, there exist rhythmic movements that cannot be composed of a sequence of discrete movements. As such, this taxonomy may provide a language for studying more complex behaviors in a principled fashion.

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The time course of alerting effect over orienting in the attention network test

In the present experiment we used a version of the attention network test (ANT) similar to that of Callejas et al. (Exp Brain Res 167:27–37, 2005) to assess the Posner’s attention networks (alerting, orienting and conflict), and their interactions. We observed shorter reaction times with alerting tone than with no alerting tone trials (the alerting effect); with cued than with uncued trials (the orienting effect); and with congruent than with incongruent trials (the conflict effect). These results replicate previous findings with the ANT. We also manipulated cue–target interval at five stimulus onset asynchrony (SOA) values (100, 300, 500, 800, and 1,200 ms) to trace the alerting network influence over the orienting network. The SOA manipulation showed that cuing effects peaked at 300 ms SOA irrespective of whether an alerting tone was present or not, and the alerting tone improved the cuing effect equally for 100–500 SOAs, but it did not at the longest 800–1,200 ms SOAs. These results suggest that alerting improves rather than accelerates orienting effects, a result that agrees with data from neuropsychological rehabilitation of parietal patients with spatial bias.

Discriminating smooth from grooved surfaces: effects of random variations in skin penetration

The ability to discriminate a smooth surface from a grooved one depends on several variables, including the width of the grooves and the force with which the skin is contacted. It has been hypothesized that this smooth–grooved discrimination with statically presented stimuli is based on intensity cues, namely, the overall difference in perceived intensity between the smooth and grooved surfaces. To test this hypothesis, the perceived intensities of test stimuli were varied on a trial-by-trial basis by varying the depth of penetration the contactor was allowed to travel into the skin. As compared to a control condition in which stimuli were presented with the same average penetration and contrary to the hypothesis, random variations in penetration produced no decline in smooth–grooved performance. The total amount of conformance was an accurate predictor of sensitivity across various penetrations and across two test sites (distal finger pad and finger base). It appears that subjects are making absolute rather than comparative judgments in the smooth–grooved task. A recently developed continuum mechanical model of the responses of first-order mechanoreceptive afferents to static stimuli provided both a good fit to the data and indicated what aspect of the peripheral neural image was relevant for discriminating smooth surfaces from grooved surfaces.