Egocentric and allocentric localization during induced motion

This research examined motor measures of the apparent egocentric location and perceptual measures of the apparent allocentric location of a target that was being seen to undergo induced motion (IM). In Experiments 1 and 3, subjects fixated a stationary dot (IM target) while a rectangular surround stimulus (inducing stimulus) oscillated horizontally. The inducing stimulus motion caused the IM target to appear to move in the opposite direction. In Experiment 1, two dots (flashed targets) were flashed above and below the IM target when the surround had reached its leftmost or rightmost displacement from the subject’s midline. Subjects pointed open-loop at either the apparent egocentric location of the IM target or at the bottom of the two flashed targets. On separate trials, subjects made judgments of the Vernier alignment of the IM target with the flashed targets at the endpoints of the surround’s oscillation. The pointing responses were displaced in the direction of the previously seen IM for the IM target and to a lesser degree for the bottom flashed target. However, the allocentric Vernier judgments demonstrated no perceptual displacement of the IM target relative to the flashed targets. Thus, IM results in a dissociation of egocentric location measures from allocentric location measures. In Experiment 2, pointing and Vernier measures were obtained with stationary horizontally displaced surrounds and there was no dissociation of egocentric location measures from allocentric location measures. These results indicate that the Roelofs effect did not produce the pattern of results in Experiment 1. In Experiment 3, pointing and Vernier measures were obtained when the surround was at the midpoint of an oscillation. In this case, egocentric pointing responses were displaced in the direction of surround motion (opposite IM) for the IM target and to a greater degree for the bottom flashed target. However, there was no apparent displacement of the IM target relative to the flashed targets in the allocentric Vernier judgments. Therefore, in Experiment 3 egocentric location measures were again dissociated from allocentric location measures. The results of this experiment also demonstrate that IM does not generate an allocentric displacement illusion analogous to the “flash-lag” effect.

Visuomotor memory is independent of conscious awareness of target features

A recent study by our group showed that the scaling of reach trajectories to target size is independent of conscious visual awareness of that intrinsic target property (Binsted et al. in Proc Natl Acad Sci USA 104:12669–12672, 2007). The present investigation sought to extend previous work and determine whether unconscious target information represents a temporally durable or evanescent visuomotor characteristic. To accomplish that objective, we employed Di Lollo et al’s (J Exp Psychol Gen 129:481–507, 2000) object substitution masking paradigm and asked participants to complete verbal reports and reaching responses to different sized (1.5, 2.5, 3.5, 4.5, 5.5 cm) targets under masked and non-masked target conditions. To determine whether visuomotor networks retain unconscious target information, reaching trials were cued concurrent with target presentation or 1,000 or 2,000 ms after target presentation. For the perceptual trials, participants readily identified the size of non-masked trials but demonstrated only chance success identifying target size during masked trials. Interestingly, however, reaches directed to non-masked and masked targets exhibited comparable and robust scaling with target size; that is, lawful speed-accuracy relations related to movement planning and execution times were observed regardless of whether participants were aware (i.e., non-masked trials) or unaware (i.e., masked trials) of target size. What is more, the length of the visual delay period used here did not differentially influence the scaling of reach trajectories. These results indicate that a conscious visual percept is not necessary to support motor output and that unconscious visual information persists in visuomotor networks to support the kinematic parameterization of action.

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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Electroencephalographic correlates of target and outcome errors

Different neural systems underlie the evaluation of different types of errors. Recent electroencephalographic evidence suggests that outcome errors—errors indicating the failure to achieve a movement goal—are evaluated within medial-frontal cortex (Krigolson and Holroyd 2006, 2007a, b). Conversely, evidence from a variety of manual aiming studies has demonstrated that target errors—discrepancies between the actual and desired motor command brought about by an unexpected change in the movement environment—are mediated within posterior parietal cortex (e.g., Desmurget et al. 1999, 2001; Diedrichsen et al. 2005). Here, event-related brain potentials (ERP) were recorded to assess medial-frontal and parietal ERP components associated with the evaluation of outcome and target errors during performance of a manual aiming task. In line with previous results (Krigolson and Holroyd 2007a), we found that target perturbations elicited an ERP component with a parietal scalp distribution, the P300. However, the timing of kinematic changes associated with accommodation of the target perturbations relative to the timing of the P300 suggests that the P300 component was not related to the online control of movement. Instead, we believe that the P300 evoked by target perturbations reflects the updating of an internal model of the movement environment. Our results also revealed that an error-related negativity, an ERP component typically associated with the evaluation of speeded response errors and error feedback, was elicited when participants missed the movement target. Importantly, this result suggests that a reinforcement learning system within medial-frontal cortex may play a role in improving subsequent motor output. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Crossmodal interaction in saccadic reaction time: separating multisensory from warning effects in the time window of integration model

In a focused attention task saccadic reaction time (SRT) to a visual target stimulus (LED) was measured with an auditory (white noise burst) or tactile (vibration applied to palm) non-target presented in ipsi- or contralateral position to the target. Crossmodal facilitation of SRT was observed under all configurations and stimulus onset asynchrony (SOA) values ranging from  −500 (non-target prior to target) to 0 ms, but the effect was larger for ipsi- than for contralateral presentation within an SOA range from  −200 ms to 0. The time-window-of-integration (TWIN) model (Colonius and Diederich in J Cogn Neurosci 16:1000, 2004) is extended here to separate the effect of a spatially unspecific warning effect of the non-target from a spatially specific and genuine multisensory integration effect.

Reference systems for coding spatial information in normal subjects and a deafferented patient

To produce accurate goal-directed arm movements, subjects must determine the precise location of target object. Position of extracorporeal objects can be determined using: (a) an egocentric frame of reference, in which the target is localized in relation to the position of the body; and/or (b) an allocentric system, in which target position is determined in relation to stable visual landmarks surrounding the target (Bridgeman 1989; Paillard 1991). The present experiment was based on the premise that (a) the presence of a structured visual environment enables the use of an allocentric frame of reference, and (b) the sole presence of a visual target within a homogeneous background forces the registration of the target location by an egocentric system. Normal subjects and a deafferented patient (i.e., with an impaired egocentric system) pointed to visual targets presented in both visual environments to evaluate the efficiency of the two reference systems. For normals, the visual environment conditions did not affect pointing accuracy. However, kinematic parameters were affected by the presence or absence of a structured visual surrounding. For the deafferented patient, the presence of a structured visual environment permitted a decrease in spatial errors when compared with the unstructured surrounding condition (for movements with or without visual feedback of the trajectory). Overall, results support the existence of an egocentric and an allocentric reference system capable of organizing extracorporeal space during arm movements directed toward visual targets.     

Medium-latency reflex response of soleus elicited by peroneal nerve stimulation

We sought to determine whether mirror-symmetrical limb movements (so-called anti-pointing) elicit a pattern of endpoint bias commensurate with perceptual judgments. In particular, we examined whether asymmetries related to the perceptual over- and under-estimation of target extent in respective left and right visual space impacts the trajectories of anti-pointing. In Experiment 1, participants completed direct (i.e. pro-pointing) and mirror-symmetrical (i.e. anti-pointing) responses to targets in left and right visual space with their right hand. In line with the anti-saccade literature, anti-pointing yielded longer reaction times than pro-pointing: a result suggesting increased top-down processing for the sensorimotor transformations underlying a mirror-symmetrical response. Most interestingly, pro-pointing yielded comparable endpoint accuracy in left and right visual space; however, anti-pointing produced an under- and overshooting bias in respective left and right visual space. In Experiment 2, we replicated the findings from Experiment 1 and further demonstrate that the endpoint bias of anti-pointing is independent of the reaching limb (i.e. left vs. right hand) and between-task differences in saccadic drive. We thus propose that the visual field-specific endpoint bias observed here is related to the cognitive (i.e. top-down) nature of anti-pointing and the corollary use of visuo-perceptual networks to support the sensorimotor transformations underlying such actions.

Postural costs of performing cognitive tasks in non-coincident reference frames

Dual-task interactions in posture and cognitive tasks have been explained as a competition for spatial processing structures or as interference in the online sensorimotor adjustments required for sensory integration. Going beyond these general terms accounts, we propose that interference between spatial and temporal operations in posture–cognition arises at least partly from the need to share a common behavioral context, such as a spatial frame of reference. Using immersive visualization and motion-tracking techniques, we manipulated the spatial reference frames for a standing task and a conjunction visual search task into or out of coincidence. Aside from performance trade-offs due to task-load manipulations, performing visual search in a non-coincident reference frame led to cognitive task and postural task performance decrements (Experiment 1). Postural dual-task decrements were also observed when visual search was split between coincident and non-coincident frames and both frame conditions rendered identical in visual information relevant to posture control (Experiment 2). We concluded that the postural control costs observed for posture–cognition dual-tasking may in part reflect costs of keeping tasks’ reference frames in register.

Saccades and reaches,behaving differently

Previously, we have shown, both in humans and monkeys, that the latencies of exogenously generated saccades decrease with an increase in the number of response alternatives (Lawrence et al. in J Vis 8:26, 1–7, 2008). Because this pattern of latencies was in the direction opposite that predicted by Hick (Q J Exp Psychol 4:11–26, 1952), we termed the effect an “anti-Hick’s” effect. In contrast, previous research has shown that reach latencies increase with an increase in response alternatives (e.g., Wright et al. in Exp Brain Res 179:475–496, 2007). Given that there are known interactions between the saccade and reach systems, we examined whether the direction of the relationship between latencies and response alternatives differed when saccades and reaches are concomitantly executed. Interestingly, we found that the pattern of latencies nevertheless persisted in a visually guided saccade and reach task. These results place an important constraint on the anti-Hick’s effect, suggesting not only that the effect is localized within the saccade system, but also that it is localized in the saccade system at a level in which saccade and reach signals do not interact.

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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.

Evidence for an attentional component in saccadic inhibition of return

After presentation of a peripheral cue, facilitation at the cued location is followed by inhibition of return (IOR). It has been recently proposed that IOR may originate at different processing stages for manual and ocular responses, with manual IOR resulting from inhibited attentional orienting, and ocular IOR resulting form inhibited motor preparation. Contrary to this interpretation, we found an effect of target contrast on saccadic IOR. The effect of contrast decreased with increasing reaction times (RTs) for saccades, but not for manual key-press responses. This may have masked the effect of contrast on IOR with saccades in previous studies (Hunt and Kingstone in J Exp Psychol Hum Percept Perform 29:1068–1074, 2003) because only mean RTs were considered. We also found that background luminance strongly influenced the effects of gap and target contrast on IOR.

Accommodation and Size-Constancy of Virtual Objects

Accommodation has been suspected as a contributor to size illusions in virtual environments (VE) due to the lack of appropriate accommodative stimuli in a VE for the objects displayed. Previous experiments examining size-constancy in VE have shown that monocular cues to depth that accompany the object are a major contributor to correct size perception. When these accompanying cues are removed perceived size varied with the object’s distance from the subject, i.e., visual angle. If accommodation were the dominant mechanism contributing to a visual angle response [due to its action to keep physical objects clear] in this condition, an open-loop accommodation viewing condition might restore size-constancy to this condition. Pinhole apertures were used to open-loop accommodation and examine if size-constancy might be restored when few accompanying monocular cues to depth were present. Visual angle performance when viewing a low cue environment was found with and without the use of the pinhole apertures. Thus, these results signify that accommodation does not play a dominate role in the loss of size-constancy in sparse visual environments often used in VE. These results suggest that size-constancy is driven by the inclusion of the remaining monocular cues to depth in VE as it is in the physical world.

Crossmodal exogenous orienting improves the accuracy of temporal order judgments

Although many studies have demonstrated that crossmodal exogenous orienting can lead to a facilitation of reaction times, the issue of whether exogenous spatial orienting also affects the accuracy of perceptual judgments has proved to be much more controversial. Here, we examined whether or not exogenous spatial attentional orienting would affect sensitivity in a temporal discrimination task. Participants judged which of the two target letters, presented on either the same or opposite sides, had been presented first. A spatially non-predictive tone was presented 200 ms prior to the onset of the first visual stimulus. In two experiments, we observed improved performance (i.e., a decrease in the just noticeable difference) when the target letters were presented on opposite sides and the auditory cue was presented on the side of the first visual stimulus, even when central fixation was monitored ("Experiment 2"). A shift in the point of subjective simultaneity was also observed in both experiments, indicating ‘prior entry’ for cued as compared to uncued first target trials. No such JND or PSS effects were observed when the auditory tone was presented after the second visual stimulus ("Experiment 3"), thus confirming the attentional nature of the effects observed. These findings clearly show that the crossmodal exogenous orienting of spatial attention can affect the accuracy of temporal judgments.

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.

Motion sensitivity during fixation in straight-ahead and lateral eccentric gaze

Despite motion of the entire retinal image that results from fixational eye-movements, the visual scene is perceived as stationary. One hypothesis to account for this observation is that normal motion sensitivity is limited by the variability of fixational eye velocity. The present experiments tested this hypothesis by comparing motion sensitivity and the variability of fixational eye velocity in corresponding meridians. Speed thresholds to detect horizontal, vertical, and rotary motion in a set of eight random-dot patches were measured, while normal observers monocularly viewed the stimulus with gaze either straight-ahead or deviated to the left by 45°. Eye-movement recordings using the search-coil technique were used to estimate the variability of eye velocity in the horizontal, vertical, and torsional meridians during fixation. As reported previously by Murakami (2004), the averaged thresholds for horizontal and vertical motion correlated with the averaged variability of eye velocity in the horizontal and vertical meridians when observers looked straight-ahead. However, no relationship existed between the threshold for rotary motion and the variability of eye velocity in the torsional meridian. Furthermore, no relationship existed between the motion threshold and the variability of eye velocity in any meridian during fixation in lateral eccentric gaze. These results are only partly consistent with the hypothesis that fixation variability limits motion sensitivity.

Learning the visuomotor transformation of virtual and real sliding levers: simple approximations of complex transformations

Learning to operate a complex tool such as a sliding lever can be conceived as learning both a kinematic and a dynamic transformation. We investigated whether the presence of the dynamic transformation has an inhibitory or a facilitative effect on learning to control a sliding lever. Furthermore, we examined the characteristics of the internal model of the kinematic transformation of the lever in visual open-loop trials. In the experiment, one group of participants practiced with only the kinematic transformation of the lever (virtual lever), the other group practiced with both the kinematic and the dynamic transformation (physical lever). Visual feedback was continuously present during practice. Results showed only marginal differences between both groups in open-loop tests. This finding is likely to be related to the fact that in both groups a simplified approximation of the kinematic transformation was acquired, in particular a symmetry approximation. With such an approximation the target for the hand movement is derived from the visual target for the tip of the lever as the position which is symmetric around a sagittal axis.

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Location memory biases reveal the challenges of coordinating visual and kinesthetic reference frames

Five experiments explored the influence of visual and kinesthetic/proprioceptive reference frames on location memory. Experiments 1 and 2 compared visual and kinesthetic reference frames in a memory task using visually-specified locations and a visually-guided response. When the environment was visible, results replicated previous findings of biases away from the midline symmetry axis of the task space, with stability for targets aligned with this axis. When the environment was not visible, results showed some evidence of bias away from a kinesthetically-specified midline (trunk anterior–posterior [a–p] axis), but there was little evidence of stability when targets were aligned with body midline. This lack of stability may reflect the challenges of coordinating visual and kinesthetic information in the absence of an environmental reference frame. Thus, Experiments 3–5 examined kinesthetic guidance of hand movement to kinesthetically-defined targets. Performance in these experiments was generally accurate with no evidence of consistent biases away from the trunk a–p axis. We discuss these results in the context of the challenges of coordinating reference frames within versus between multiple sensori-motor systems.

Spontaneous reactions to health risk feedback: a network perspective

Research on the reception of health risk feedback has focused on the analysis of single, researcher-selected cognitive reactions. The full range of spontaneous reactions and their patterns have received little attention. The present paper explores content, interrelations, and adaptivity of spontaneous reactions to health risk feedback from a network perspective. Participants (n = 423) received blood pressure and cholesterol feedback and listed their thoughts afterwards. A network of reactions to health risk feedback was constructed from the responses. Emotions, risk feedback valence, future lifestyle, and expectedness emerged as strong and largely well-connected network nodes, while previously well-researched reactions like feedback acceptance formed small, less connected nodes. The majority of reaction patterns identified through the network appeared adaptive, even after negative feedback. The network provides a potentially useful tool for research and practice, highlighting previously neglected relevant reactions, and providing a group-level background against which individual reactions can be evaluated.

Children with cerebral palsy exhibit greater and more regular postural sway than typically developing children

Following recent advances in the analysis of centre-of-pressure (COP) recordings, we examined the structure of COP trajectories in ten children (nine in the analyses) with cerebral palsy (CP) and nine typically developing (TD) children while standing quietly with eyes open (EO) and eyes closed (EC) and with concurrent visual COP feedback (FB). In particular, we quantified COP trajectories in terms of both the amount and regularity of sway. We hypothesised that: (1) compared to TD children, CP children exhibit a greater amount of sway and more regular sway and (2) concurrent visual feedback (creating an external functional context for postural control, inducing a more external focus of attention) decreases both the amount of sway and sway regularity in TD and CP children alike, while closing the eyes has opposite effects. The data were largely in agreement with both hypotheses. Compared to TD children, the amount of sway tended to be larger in CP children, while sway was more regular. Furthermore, the presence of concurrent visual feedback resulted in less regular sway compared to the EO and EC conditions. This effect was less pronounced in the CP group where posturograms were most regular in the EO condition rather than in the EC condition, as in the control group. Nonetheless, we concluded that CP children might benefit from therapies involving postural tasks with an external functional context for postural control.

Calibrating grasp size and reach distance: interactions reveal integral organization of reaching-to-grasp movements

Feedback is a central feature of neural systems and of crucial importance to human behaviour as shown in goal directed actions such as reaching-to-grasp. One important source of feedback in reach-to-grasp behaviour arises from the haptic information obtained after grasping an object. We manipulated the felt distance and/or size of a visually constant object to explore the role of haptic information in the calibration of reaching and grasping. Crucially, our design explored post-adaptation effects rather than the previously documented role of haptic information in movement organisation. A post-adaptation reach-to-grasp task showed: (1) distorted haptic feedback caused recalibration; (2) reach distance and grasp size could be calibrated separately but, if calibrated simultaneously, then (3) recalibration was greater when distance and size changed in a consistent (e.g. reaching for a larger object at a greater distance) rather than an inconsistent (e.g. a smaller object at a greater distance) fashion. These interactions reveal the integral nature of reach-to-grasp organization, that is, that reaching and grasping are integrated components of a single action system.