Brendan D. Cameron

Enhanced orienting effects: Evidence for an interaction principle

Predictive arrow cues, as used in the classic “Posner paradigm”, that were long thought to engage and isolate voluntary attention, may in fact trigger a strong interaction between voluntary and involuntary attention (Ristic & Kingstone, 2006). This interaction produces an orienting effect that exceeds both the effects of involuntary and voluntary attention alone, and the additive combination of involuntary and voluntary orienting. The present study shows that nonpredictive peripheral cues—understood to engage and isolate involuntary attention—if made predictive, result in enhanced orienting effects similar to predictive arrows. The important contribution of these data is that they suggest an “interaction principle”: If attention cues can elicit reliable involuntary orienting, then when they are made spatially predictive, the resulting attention effect will be greater than the sum of involuntary and voluntary orienting alone.

Cognitive constraint on the 'automatic pilot' for the hand: Movement intention influences the hand's susceptibility to involuntary online corrections

Research suggests that the reaching hand automatically deviates toward a target that changes location (jumps) during the reach. In the current study, we investigated whether movement intention can influence the target jumps impact on the hand. We compared the degree of trajectory deviation to a jumped target under three instruction conditions: (1) GO, in which participants were told to go to the target if it jumped, (2) STOP, in which participants were told to immediately stop their movement if the target jumped, and (3) IGNORE, in which participants were told to ignore the target if it jumped and to continue to its initial location. We observed a reduced response to the jump in the IGNORE condition relative to the other conditions, suggesting that the response to the jump is contingent on the jump being a task-relevant event.

Comparing movement preparation of unimanual, bimanual symmetric, and bimanual asymmetric movements.

Abstract The goal of this study was to determine the process or processes most likely to be involved in reaction-time costs for spatially cued bimanual reaching. We used reaction time to measure the cost of bimanual symmetric movements compared to unimanual movements (a bimanual symmetric cost) and the cost for bimanual asymmetric movements compared to symmetric movements (a bimanual asymmetric cost). The results showed that reaction times were comparable for all types of movements in simple reaction time; that is, there was neither a bimanual symmetric cost nor an asymmetric cost. Therefore, unimanual, bimanual symmetric, and bimanual asymmetric movements have comparable complexity during response initiation. In choice conditions, there was no bimanual symmetric cost but there was a bimanual asymmetric cost, indicating that the preparation of asymmetric movements is more complex than symmetric movements. This asymmetric cost is likely the result of interference during response programming.

Reach adaptation to explicit vs. implicit target error

The adaptation of reaching movements has typically been investigated by either distorting visual feedback of the reaching limb or by distorting the forces acting upon the reaching limb. Here, we investigate reach adaptation when error is created by systematically perturbing the target of the reach rather than the limb itself (Magescas and Prablanc in J Cogn Neurosci 18: 75–83, 2006). Specifically, we investigate how adaptation is affected by (1) the timing of the perturbation with respect to the movement of the eye and the hand and (2) participant awareness of the perturbation. In Experiment 1, participants looked and pointed to a target that disappeared either at the onset of their eye movement or shortly after their eye movement and then reappeared, displaced to the right, at the completion of the reach. In Experiment 2, we made the target displacement more explicit by leaving the target at its initial location until the end of the reach, at which point it was displaced to the right. In Experiment 3, we extinguished the target at the onset of the eye movement but also informed participants about the presence and magnitude of the perturbation. In the no-feedback post-test phase, participants for whom the target disappeared during the reach demonstrated much stronger aftereffects of the perturbation, misreaching to the right, whereas participants for whom the target stayed on until reach completion demonstrated rapid extinction of rightward misreaching. Furthermore, participants who were informed about the target perturbation exhibited faster de-adaptation than those who were not. Our results suggest that adaptation to a target displacement is contingent on the explicitness of the target perturbation, whether this is achieved by manipulating stimulus timing or instruction.

The hand's automatic pilot can update visual information while the eye is in motion

When participants reach for a target, their hand can adjust to a change in target position that occurs while their eyes are in motion (the hand’s automatic pilot) even though they are not aware of the target’s displacement (saccadic suppression of perceptual experience). However, previous studies of this effect have displayed the target without interruption, such that the new target position remains visible during the fixation that follows the saccade. Here we test whether a change in target position that begins and ends during the saccade can be used to update aiming movements. We also ask whether such information can be acquired from two targets at a time. The results showed that participants responded to single and double target jumps even when these targets were extinguished prior to saccade termination. The results imply that the hand’s automatic pilot is updated with new visual information even when the eye is in motion.

The role of differential delays in integrating transient visual and proprioceptive information

Many actions involve limb movements toward a target. Visual and proprioceptive estimates are available online, and by optimally combining (Ernst and Banks, 2002) both modalities during the movement, the system can increase the precision of the hand estimate. The notion that both sensory modalities are integrated is also motivated by the intuition that we do not consciously perceive any discrepancy between the felt and seen hands positions. This coherence as a result of integration does not necessarily imply realignment between the two modalities (Smeets et al., 2006). For example, the two estimates (visual and proprioceptive) might be different without either of them (e.g., proprioception) ever being adjusted after recovering the other (e.g., vision). The implication that the felt and seen positions might be different has a temporal analog. Because the actual feedback from the hand at a given instantaneous position reaches brain areas at different times for proprioception and vision (shorter for proprioception), the corresponding instantaneous unisensory position estimates will be different, with the proprioceptive one being ahead of the visual one. Based on the assumption that the system integrates optimally and online the available evidence from both senses, we introduce a temporal mechanism that explains the reported overestimation of hand positions when vision is occluded for active and passive movements (Gritsenko et al., 2007) without the need to resort to initial feedforward estimates (Wolpert et al., 1995). We set up hypotheses to test the validity of the model, and we contrast simulation-based predictions with empirical data.

Do preparation or control processes result in the modulation to Fitts' law for movements to targets with placeholders?

It is remarkable that the movement time of a goal-directed movement, the result of complex coordination in the nervous system, can be predicted by a simple mathematical equation. That equation is Fitts’ law, and it is one of only a few laws that capture human motor performance. It has recently been shown that reaches to targets with placeholders modulate Fitts’ law (e.g. Adam et al. in Psychol Sci 17(9):794–798, 2006). The purpose of this study was to further test whether the modulation to Fitts’ law is a result of processes related to movement preparation or movement execution. Preparation and control processes were isolated with trajectory analysis; specifically, the durations of the primary submovement and the secondary submovement were selected to reflect the preparation and control processes, respectively. The time available for movement preparation was also manipulated by precuing the target in some blocks. We found that the modulation to Fitts’ law in total movement time with target placeholders occurred during the secondary submovement, suggesting that control processes were the locus of the modulation. However, extending the duration of preparation with a precue eliminated the modulation in total movement time, which suggests that preparation processes were the locus of the modulation. Based on these results, it is premature to isolate unequivocally the modulation to either preparation or control processes. The modulation to Fitts’ law during the secondary submovement presents the possibility that facilitated online control may contribute to the modulation.

The adaptability of self-action perception and movement control when the limb is passively versus actively moved

Research suggests that perceptual experience of our movements adapts together with movement control when we are the agents of our actions. Is this agency critical for perceptual and motor adaptation? We had participants view cursor feedback during elbow extension-flexion movements when they (1) actively moved their arm, or (2) had their arm passively moved. We probed adaptation of movement perception by having participants report the reversal point of their unseen movement. We probed adaptation of movement control by having them aim to a target. Perception and control of active movement were influenced by both types of exposure, although adaptation was stronger following active exposure. Furthermore, both types of exposure led to a change in the perception of passive movements. Our findings support the notion that perception and control adapt together, and they suggest that some adaptation is due to recalibrated proprioception that arises independently of active engagement with the environment.

Implicit motor learning from target error during explicit reach control

Many studies have shown adapted reaching in the face of altered visual feedback. These studies typically involve iterative corrections to the error induced by the perturbation until relatively normal performance is achieved. Here, we investigate whether adaptation (indexed by aftereffects) can occur when direct corrections to a target are inhibited by giving participants an explicit reach task. During the exposure phase of our study, participants were instructed to undershoot a target that imperceptibly moved between movement onset and movement end. The size of the target displacement was gradually increased, while the instructed undershoot distance was equivalently increased, such that participants were, unknowingly, aiming to the same location throughout exposure. When participants were subsequently instructed to aim at the target during the post-test, they overshot the target, suggesting that adaptation had occurred in the presence of an explicit task and in the absence of direct corrections to the target perturbation.

Bimanual reaches with symbolic cues exhibit errors in target selection

We examined the movement trajectories of symmetric and asymmetric bimanual reaches to targets specified by direct spatial cues and by indirect symbolic cues. Symbolically cued asymmetric reaches have been shown to exhibit longer reaction times compared with symmetric reaches, whereas no such reaction time cost is observed when targets are spatially cued—a pattern thought to implicate increased demands on response selection (Diedrichsen et al. in Psychol Sci 12(6):493–498, 2001). As symbolically cued reaches impose greater demands on cognitive visuomotor translation than spatially cued reaches (Diedrichsen et al. in Cereb Cortex 16(12):1729–1738, 2006), we asked whether bimanual movements exhibit more spatial coupling with symbolic cues than with spatial cues. Participants made bimanual symmetric and asymmetric reaches to short- and long-distance targets cued either symbolically or spatially. We replicated the reaction time cost for symbolically cued asymmetric movements. A subset of these asymmetric reaches also showed large trajectory modulations. It appeared that this subset had been incorrectly prepared and the movements required of the left and right arms had been switched. No such errors in target selection were observed when targets were spatially cued. In contrast to the reaction time cost and errors in selection for symbolically cued movements, we observed little evidence of increased spatial coupling with symbolic cues when movements were initiated towards the correct targets. We conclude that cognitive visuomotor translation demands during response selection increases bimanual coupling at the level of response selection (reaction time cost, errors in target selection) but not at the level of movement execution (spatial coupling).