Moving to Directly Cued Locations Abolishes Spatial Interference During Bimanual Actions

Interference is frequently observed during bimanual movements if the two hands perform nonsymmetric actions. We examined the source of bimanual interference in two experiments in which we compared conditions involving symmetric movements with conditions in which the movements were of different amplitudes or different directions. The target movements were cued either symbolically by letters or directly by the onset of the target locations. With symbolic cues, reaction times were longer when the movements of the two hands were not symmetric. With direct cues, reaction times were the same for symmetric and nonsymmetric movements. These results indicate that directly cued actions can be programmed in parallel for the two hands. Our results challenge the hypothesis that the cost to initiate nonsymmetric movements is due to spatial interference in a motor-programming stage. Rather, the cost appears to be caused by stimulus identification, response-selection processes connected to the processing of symbolic cues, or both.     

Re-examining structural constraints on the initiation of bimanual movements: the role of starting locations, movement amplitudes, and target locations

Structural constraints affect the coordination of bimanual movements in ways that have been taken to suggest that the specification of different movement amplitudes is subject to strong intermanual interference effects. Most experiments taken to support this notion, however, confounded variations of movement amplitudes with symmetry in starting locations and variations in target location. The present experiment was designed to further investigate the relative influence of the parameters starting location, movement amplitude, and target location on bimanual movement coordination. Participants performed simultaneous reaching movements with the left and right hand from same and different starting locations to same and different target locations. On each trial, two movements could match on none, one, or all of the parameters. We assessed the influence of each parameter by comparing conditions in which only a single parameter matched between the two hands with conditions in which all parameters differed. The reaction-time data revealed some challenging results for previous studies: (1) same starting locations significantly delayed movement initiation; (2) specifying movement amplitudes had virtually no effect on movement initiation, whereas (3) selecting same target locations significantly benefited the bimanual responses. These findings cannot be taken to support the notion that amplitude specification affects the initiation of bimanual movements. Rather, they support the notion that the initial starting locations of the two hands and the selection of target locations decide about the ease with which we perform bimanual reaching movements.     

Bimanual interference associated with the selection of target locations

Four experiments were conducted to identify the locus of interference observed during the preparation of bimanual reaching movements. Target locations were specified by color, and the right-hand and left-hand targets could be either the same or a different color. Movements of different amplitudes (Experiment 1) or different directions (Experiment 2) to targets of the same color were initiated more quickly than symmetric movements to targets of different colors. These results indicate that costs observed during bimanual movements arise during target selection rather than during motor programming. Experiments 3 and 4 further examined the interference associated with target selection. Reaction time costs were found with unimanual movements when the target was presented among distractors associated with responses for the other hand. Interference observed during bimanual reaching appears to reflect difficulty in segregating the response rules assigned to each hand.     

The influence of movement cues on intermanual interactions

In two experiments, we studied intermanual interactions in bimanual reversal movements and bimanual aiming movements. Targets were presented on a monitor or directly on the table on which the movements were produced. Amplitudes for each hand were cued symbolically or spatially either in advance of an imperative signal or simultaneous with it. In contrast to findings of Diedrichsen et al. (Psychological Science, 12, 493–498, 2001), reaction times for different-amplitude movements were longer than for same-amplitude movements both for symbolic and spatial cues presented on the monitor and directly on the table. However, with symbolic cues the effect of the relation between target amplitudes was considerably stronger than with spatial cues, no matter where the cues were presented. Intermanual correlations of amplitudes, movement times, and reaction times were smaller with different than with same target amplitudes, and this modulation was more pronounced when targets and cues were presented on the monitor than when they were presented on the table. The findings are taken to suggest that the basic reaction-time disadvantage of different-amplitude movements results from interference between concurrent processes of amplitude specification. Additional factors like interference between concurrent processes of mapping cues on movement characteristics may add strongly to it.     

Intermanual interactions related to movement amplitudes and endpoint locations

In almost all studies of bimanual movements with same and different amplitudes, the difference between amplitudes has been confounded with a difference between endpoint locations. The present authors varied those parameters orthogonally. In addition, they presented target locations on the surface on which the movements were produced (direct cues) and on a monitor (indirect cues). Participants' (N = 12) reaction times were longer when both amplitudes and endpoint locations differed than when they were the same. Intermanual amplitude correlations were reduced whenever 1 of the movement parameters differed for the 2 hands; only when cues were presented on the monitor was the amplitude correlation further reduced when both movement parameters were different. The results indicate that structural constraints on bimanual movements take effect on both amplitudes and endpoint locations. The relative importance of those 2 parameters is largely independent of the type of cue.     

Reflexive and voluntary orienting of visual attention: time course of activation and resistance to interruption

To study the mechanisms underlying covert orienting of attention in visual space, subjects were given advance cues indicating the probable locations of targets that they had to discriminate and localize. Direct peripheral cues (brightening of one of four boxes in peripheral vision) and symbolic central cues (an arrow at the fixation point indicating a probable peripheral box) were compared. Peripheral and central cues are believed to activate different reflexive and voluntary modes of orienting (Jonides, 1981; Posner, 1980). Experiment 1 showed that the time courses of facilitation and inhibition from peripheral and central cues were characteristic and different. Experiment 2 showed that voluntary orienting in response to symbolic central cues is interrupted by reflexive orienting to random peripheral flashes. Experiment 3 showed that irrelevant peripheral flashes also compete with relevant peripheral cues. The amount of interference varied systematically with the interval between the onset of the relevant cue and of the distracting flash (cue-flash onset asynchrony) and with the cuing condition. Taken together, these effects support a model for spatial attention with distinct but interacting reflexive and voluntary orienting mechanisms.     

Bimanual interference with compatible and incompatible tool transformations

The present study investigates bimanual interference in a tool-use task, in which two target locations had to be touched concurrently with two tools, one for each hand. Target locations were either in the same, or in different directions for the two hands. Furthermore, the tools implemented either a compatible or an incompatible relationship between the direction of target locations and the direction of associated bodily movements. Results indicated bimanual interference when the tools had to be moved to targets in different directions. Furthermore, this interference was much more pronounced when the tools required body movements that were spatially incompatible to the cued target locations as compared to when they were compatible. These results show that incompatible relationships between target directions and bodily movement directions can aggravate bimanual interference in tool use.     

Target selection during bimanual reaching to direct cues is unaffected by the perceptual similarity of the targets

Investigations of bimanual movements have shed considerable insight on the constraints underlying our ability to perform coordinated actions. One prominent limitation is evident when people are required to produce reaching movements in which the two trajectories are of different amplitudes and/or directions. This effect, however, is only obtained when the movements are cued symbolically (e.g., letters indicate target locations); these planning costs are absent when the target locations are directly cued (J. Diedrichsen, E. Hazeltine, S. Kennerley, & R. B. Ivry, 2001). The present experiments test whether the absence of planning costs under the latter condition is due to the perceptual similarity of the direct cues. The results demonstrate that measures of response planning and execution do not depend on the perceptual similarity of the direct cues. Limitations in our ability to perform distinct actions with the two hands appear to reflect interactions related to response selection involving the translation of symbolic cues into their associated movements rather than arise from interactions associated with perception, motor programming, and motor execution.     

Spatial Error Detection and Assimilation Effects in Rapid Single and Bimanual Aiming Movements

In 2 experiments, spatial error detection capability and movement accuracy were investigated in both single and bimanual rapid aiming movements. In both experiments, right-handed college-age participants (N = 40 [Experiment 1]; N = 24 [Experiment 2]) used light, aluminum levers to make quick single and dual reversal movements in the sagittal plane in a time to reversal of 210 ms to either the same or different target locations involving identical (Experiment 1) or mirror-image (Experiment 2) movements. In Experiment 1, the shorter-distance limb overshot the target by 15-23&percent; when paired with a limb traveling at least 20 degrees farther, but no spatial assimilations were shown when movements differed by 20 degrees or less. In Experiment 2, the shorter-distance limb overshot 22-29&percent; when paired with a limb traveling 20 degrees farther, but spatial assimilations were not mitigated when both limbs moved to the same target position. Participants underestimated movement amplitude in all dual conditions but particularly when spatial assimilations were noted. Correlations between actual and estimated errors decreased from single to dual trials in both experiments. The findings suggest that spatial assimilations are caused by bimanual differences in movement amplitude, regardless of movement direction, and that individuals have greater difficulty identifying errors in simultaneous actions, especially when spatial assimilations are present, than identifying errors in single-limb actions.     

Aging and shifts of visual spatial attention.

Three experiments examined adult age differences in the efficiency of endogenous (voluntary) and exogenous (involuntary) attention shifts. Younger and older subjects performed a spatial cuing task in which abruptly onset peripheral cues (Experiment 1) or central, symbolic cues (Experiments 2 and 3) were presented before a target stimulus at intervals ranging from 50 to 250 ms. With peripheral cues, the magnitude of cuing effects was at least as great for older as for younger adults and followed a similar time course. Similar results were obtained with symbolic cues, although cuing effects for older adults varied with cue difficulty. The results suggest that cue encoding may decline with advancing age but that the efficiency of the shift process is preserved.     

Cognitive constraints on motor imagery

Executed bimanual movements are prepared slower when moving to symbolically different than when moving to symbolically same targets and when targets are mapped to target locations in a left/right fashion than when they are mapped in an inner/outer fashion [Weigelt et al. (Psychol Res 71:238–447, 2007)]. We investigated whether these cognitive bimanual coordination constraints are observable in motor imagery. Participants performed fast bimanual reaching movements from start to target buttons. Symbolic target similarity and mapping were manipulated. Participants performed four action conditions: one execution and three imagination conditions. In the latter they indicated starting, ending, or starting and ending of the movement. We measured movement preparation (RT), movement execution (MT) and the combined duration of movement preparation and execution (RTMT). In all action conditions RTs and MTs were longer in movements towards different targets than in movements towards same targets. Further, RTMTs were longer when targets were mapped to target locations in a left/right fashion than when they were mapped in an inner/outer fashion, again in all action conditions. RTMTs in imagination and execution were similar, apart from the imagination condition in which participants indicated the start and the end of the movement. Here MTs, but not RTs, were longer than in the execution condition. In conclusion, cognitive coordination constraints are present in the motor imagery of fast (<1600 ms) bimanual movements. Further, alternations between inhibition and execution may prolong the duration of motor imagery.     

Luminance-increment detection: capacity-limited or not?

Three experiments investigated whether spatial cuing influences luminance-increment detection accuracy. Ss saw multiple-target displays and responded yes or no to 4 locations, including cued position. To test whether cuing effects are due to the load on visual short-term memory from the number of locations, Experiments 1 and 2 presented displays with 4 or 8 relevant locations. Experiment 1 used peripheral cues; Experiment 2 used central cues. Significant cuing effects were less marked with 4- than 8-location displays. Cuing effects were largest with multiple targets, but a small reliable effect remained even with single targets. Experiment 3 replicated the single-target effect with predominantly multiple- and single-target displays. A capacity-limited selection account is developed for these findings and their implications are discussed for separate central and peripheral cuing mechanisms and the locus of spatial cuing effects.     

Audiovisual links in exogenous covert spatial orienting

Subjects judged the elevation (up vs. down, regardless of laterality) of peripheral auditory or visual targets, following uninformative cues on either side with an intermediate elevation. Judgments were better for targets in either modality when preceded by an uninformative auditory cue on the side of the target. Experiment 2 ruled out nonattentional accounts for these spatial cuing effects. Experiment 3 found that visual cues affected elevation judgments for visual but not auditory targets. Experiment 4 confirmed that the effect on visual targets was attentional. In Experiment 5, visual cues produced spatial cuing when targets were always auditory, but saccades toward the cue may have been responsible. No such visual-to-auditory cuing effects were found in Experiment 6 when saccades were prevented, though they were present when eye movements were not monitored. These results suggest a one-way cross-modal dependence in exogenous covert orienting whereby audition influences vision, but not vice versa. Possible reasons for this asymmetry are discussed in terms of the representation of space within the brain.     

Metacognition and part-set cuing: Can interference be predicted at retrieval?

Although prior research has examined predictions of memory performance under conditions of interference at encoding, predictions of memory performance have not been examined for interference introduced via cues at retrieval. This was investigated in the present study by exposing participants to a random subset of to-be-recalled items just prior to retrieval (part-set cuing) and then eliciting an overall prediction of memory performance. Across three experiments, participants in part-set cuing conditions recalled proportionally fewer items than did participants who were not exposed to any cues. However, participants were unable to predict the detrimental effect of part-set cues on memory performance in either a semantic (Experiment 1) or an episodic (Experiment 2) memory task. Predictions were better calibrated after practice with part-set cuing, and there was evidence that prior experience with part-set cuing transferred to predictions made for a different part-set cuing task (Experiment 3). This suggests that only under some conditions are participants sensitive to the diminished accessibility of memories wrought by part-set cues and illustrates situations in which participants are or are not aware of variables at retrieval that influence memory performance.     

Attentional localization prior to simple and directed manual responses

The relationship between attention and the programming of motor responses was investigated, using a paradigm in which the onsets of targets for movements were preceded by peripheral attentional cues. Simple (button release) and reaching manual responses were compared under conditions in which the subjects either made saccades toward the target location or refrained from making eye movements. The timing of the movement onset was used as the dependent measure for both simple and reaching manual responses. Eye movement latencies were also measured. A follow-up experiment measured the effect of the same peripheral cuing procedure on purely visual processes, using signal detection measures of visual sensitivity and response bias. The results of the first experiment showed that reaction time (RT) increased with the distance between the cued and the target locations. Stronger distance effects were observed when goal-directed responses were required, which suggests enhanced attentional localization of target positions under these conditions. The requirement to generate an eye movement response was found to delay simple manual RTs. However, mean reaching RTs were unaffected by the eye movement condition. Distance gradients on eye movement latencies were relatively shallow, as compared with those on goal-directed manual responses. The second experiment showed that the peripheral cue had only a very small effect on visual detection sensitivity in the absence of directed motor responses. It is concluded that cue-target distance effects with peripheral cues are modulated by the motor-programming requirements of the task. The effect of the peripheral cue on eye movement latencies was qualitatively different from that observed on manual RTs, indicating the existence of separate neural representations underlying both response types. At the same time, the interactions between response modalities are consistent with a supramodal representation of attentional space, within which different motor programs may interact.     

Interaction between endogenous and exogenous orienting in crossmodal attention

Using a cue-target paradigm, we investigated the interaction between endogenous and exogenous orienting in cross-modal attention. A peripheral (exogenous) cue was presented after a central (endogenous) cue with a variable time interval. The endogenous and exogenous cues were presented in one sensory modality (auditory in Experiment 1 and visual in Experiment 2) whereas the target was presented in another modality. Both experiments showed a significant endogenous cuing effect (longer reaction times in the invalid condition than in the valid condition). However, exogenous cuing produced a facilitatory effect in both experiments in response to the target when endogenous cuing was valid, but it elicited a facilitatory effect in Experiment 1 and an inhibitory effect in Experiment 2 when endogenous cuing was invalid. These findings indicate that endogenous and exogenous cuing can co-operate in orienting attention to the crossmodal target. Moreover, the interaction between endogenous and exogenous orienting of attention is modulated by the modality between the cue and the target.     

Attentional localization prior to simpleand directed manual responses

The relationship between attention and the programming of motor responses was investigated, using a paradigm in which the onsets of targets for movements were preceded by peripheral attentional cues. Simple (button release) and reaching manual responses were compared under conditions in which the subjects either made saccades toward the target location or refrained from making eye movements. The timing of the movement onset was used as the dependent measure for both simple and reaching manual responses. Eye movement latencies were also measured. A follow-up experiment measured the effect of the same peripheral cuing procedure on purely visual processes, using signal detection mea-sures of visual sensitivity and response bias. The results of the first experiment showed that reaction time (RT) increased with the distance between the cued and the target locations. Stronger distance ef-fects were observed when goal-directed responses were required, which suggests enhanced attentional localization of target positions under these conditions. The requirement to generate an eye movement response was found to delay simple manual RTs. However, mean reaching RTs were unaffected by the eye movement condition. Distance gradients on eye movement latencies were relatively shallow, as compared with those on goal-directed manual responses. The second experiment showed that the peripheral cue had only a very small effect on visual detection sensitivity in the absence of directed motor responses. It is concluded that cue-target distance effects with peripheral cues are modulated by the motor-programming requirements of the task. The effect of the peripheral cue on eye movement latencies was qualitatively different from that observed on manual RTs, indicating the existence of separate neural representations underlying both response types. At the same time, the interactions be-tween response modalities are consistent with a supramodal representation of attentional space, within which different motor programs may interact.     

Similarity in Spatial Origin of Information Facilitates Cue Competition and Interference

Two lick suppression studies were conducted with water-deprived rats to investigate the influence of spatial similarity in cue interaction. Experiment 1 assessed the influence of similarity of the spatial origin of competing cues in a blocking procedure. Greater blocking was observed in the condition in which the auditory blocking cue and the auditory blocked cue originated at the same spatial location. Recent investigations have demonstrated that manipulations that impact competition between cues trained together have similar effects on interference between cues trained apart. Therefore, Experiment 2 investigated the influence of similarity of the spatial origin in proactive interference of Pavlovian conditioning by separately pairing two auditory cues with a common outcome, originating at the same spatial location or different spatial locations. Greater proactive interference was observed in the condition in which the interfering cue and target cue originated at the same spatial location. The results are considered in light of the possibility that a similar mechanism may underlie interference between cues trained apart and cue competition between cues trained together.     

Interference Effects in Learning Similar Sequences of Discrete Movements

Three experiments were conducted to examine proactive and retroactive interference effects in learning 2 similar sequences of discrete movements. In each experiment, the participants in the experimental group practiced 2 movement sequences on consecutive days (1 on each day, order counterbalanced across participants) followed by retention tests on the third day. In all, 2 out of 8 target locations differed between the 2 sequences. Experiment 1 established the nature of the interference effects in the present setup. Clear evidence was found for button-specific proactive and retroactive interference effects. Experiments 2 and 3 further probed the mechanisms underlying those effects, by varying the numbers of repetitions (50 or 250) of the 1st and 2nd sequence (Experiment 2) and the hand, dominant or nondominant, with which the sequences were practiced (Experiment 3). Experiment 2 showed that after a mere 50 repetitions, the representation of the movement structure was strong enough to evoke the effects observed in Experiment 1. Experiment 3 revealed that learning with the dominant hand did not result in more pronounced interference effects compared with learning with the nondominant hand. In combination, these results suggest that changes in the representation of the movement structure are primarily responsible for the observed interference effects.     

The impact of perceptual, cognitive and motor factors on bimanual coordination

Bimanual coordination is governed by constraints that permit congruent movements to be performed more easily than incongruent movements. Theories concerning the origin of these constraints range from low level motor-muscle explanations to high level perceptual–cognitive ones. To elucidate the processes underlying coordinative constraints, we asked subjects to use a pair of left–right joysticks to acquire corresponding pairs of congruent and incongruent targets presented on a video monitor under task conditions designed to systematically modulate the impact of several perceptual–cognitive processes commonly required for bimanual task performance. These processes included decoding symbolic cues, detecting goal targets, conceptualizing movements in terms of goal target configuration, planning movement trajectories, producing saccades and perceiving visual feedback. Results demonstrate that constraints arise from target detection and trajectory planning processes that can occur prior to movement initiation as well as from inherent muscle properties that emerge during movement execution, and that the manifestation of these constraints can be significantly altered by the ability to visually monitor movement progress.