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.     

The contribution of the thumb to reaching movements

Transport of the hand towards an object and the formation of grasp are logically separable components of reaching. It has been suggested that, although the two components must be temporally co-ordinated, their spatial parameters are under the control of independent visuo-motor channels. A case study of reaching by a proficient user of a manually-operated artificial hand is presented. A pattern of natural hand usage was observed in which the index finger rather than the thumb was responsible for reduction of grasp aperture as the hand approached an object. The same pattern of usage was also observed in the artificial hand even though the mechanics of that hand make it no easier to move the finger than the thumb. This suggests that the relative stability of the thumb in the natural hand is determined, not simply by anatomy, but by a role in guiding the transport component of reaching. At least part of the spatial aspect of grasp formation is closely related to the transport component of reaching and this is evidence against theories postulating two independent visuo-motor channels controlling the spatial parameters of grasp and transport.     

Central response selection is present during memory scanning, but hand-specific response preparation is absent

Two experiments were performed to replicate the results of Ilan and Miller that response selection but no response-hand specific preparation is present during memory scanning. Letter-case determined which hand would respond, while memory set membership status determined whether the response was to be executed (go) or withheld (nogo). In Exp. 1, the LRP was observed as an index of response-hand specific preparation. In Exp. 2, the consistency effect derived from the response priming paradigm was observed as an index of more central response selection. The results replicate those of Ilan and Miller and suggest that central response selection is present during short-term memory scanning, but hand-specific response preparation is absent. Apparently, preliminary information is transmitted to the response selection stage during memory scanning, a finding that is inconsistent with serial stage models, but memory scanning interferes with hand-specific response preparation. Received: 30 March 1998 / Accepted: 30 November 1998     

Language-induced motor perturbations during the execution of a reaching movement

In a recent study Boulenger et al. (2006) found that processing action verbs assisted reaching movement when the word was processed prior to movement onset and interfered with the movement when the word was processed at movement onset. The present study aimed to further corroborate the existence of such cross-talk between language processes and overt motor behaviour by demonstrating that the reaching movement can be disturbed by action words even when the words are presented delayed with respect to movement onset (50 ms and 200 ms). The results are compared to studies that show language-motor interaction in conditions where the word is presented prior to movement onset and are discussed within the context of embodied theories of language comprehension.     

The temporal organization of hand, eye, and head movements during reaching and pointing

Two experiments are reported that address the issue of coordination of the eyes, head, and hand during reaching and pointing. Movement initiation of the eyes, head, and hand were monitored in order to make inferences about the type of movement control used. In the first experiment, when subjects pointed with the finger to predictable or unpredictable locations marked by the appearance of a light, no differences between head and eye movement initiation were found. In the second experiment, when subjects pointed very fast with the finger, the head started to move before the eyes did. Conversely, when subjects pointed accurately, and thus more slowly, with the finger, the eyes started to move first, followed by the head and finger. When subjects were instructed to point to the same visual target only with their eyes and head, both fast and accurately, however, eye movement always started before head movement, regardless of speed-accuracy instructions. These results indicate that the behavior of the eye and head system can be altered by introducing arm movements. This, along with the variable movement initiation patterns, contradicts the idea that the eye, head, and hand system is controlled by a single motor program. The time of movement termination was also monitored, and across both experiments, the eyes always reached the target first, followed by the finger, and then the head. This finding suggests that movement termination patterns may be a fundamental control variable.     

Conceptual activation of distractors during selection is not sufficient to produce negative priming

Negative priming (NP) occurs when responses are slower because the targets were distractors on the preceding trial. Word-naming NP occurs only with words that have been presented repeatedly as targets; novel words do not show NP. The activation-inhibition explanation is that representations of repeated-word distractors are activated already and must be inhibited; the inhibition carries over to the next trial. If this explanation is correct, novel-word NP should occur if the word is semantically primed (thus activating its representation) before it occurs as a distractor. In two experiments, there was NP for words from a repeated set, and the magnitude of NP increased when the same word could occur as a target on consecutive trials. There was positive, rather than negative, priming for novel-word targets that had been semantically primed as distractors. Either the activation from semantic priming was not sufficiently strong to require inhibition, or the activation-inhibition hypothesis does not refer to activation of conceptual representations.     

Accurate reaching after active but not passive movements of the hand: evidence for forward modeling

Converging behavioral findings support recent models of motor control suggesting that estimates of the future positions of a limb as well as the expected sensory consequences of a planned movement may be derived, in part, from efference copies of motor commands. These estimates are referred to as forward models. However, relatively little behavioral evidence has been obtained for proposed forward models that provide on-line estimates of current position. We report data from a patient (JD) who reached accurately to visualized targets with and without vision of her hand despite substantial proprioceptive loss. Additionally, we administered a double-start reaching test to examine the possibility that efference copy information could be used to estimate current limb position. JD reached accurately, without vision, to a final target after actively reaching to a landmark, but exhibited severely impaired reaching after passive movements to the landmark. This finding suggests that forward modeling of efference copy signals may provide relatively accurate estimates of current limb position for the purpose of motor planning. The possibility that such estimates may also contribute to the awareness of body position and to self-recognition is discussed.     

The effects of instructions to subjects on the programming of visually directed reaching movements

Numerous studies of human motor control have examined the effects of constraints on the programming and execution of visually directed limb movements. Only a few studies, however, have explored how the subject's objective in making the movement affects the coordinated sequence of eye and limb movements that unfolds as the subject points to or grasps an object in space. In the present study, the characteristics of the targets and the environment remained constant while the demands for speed and accuracy were varied across blocks of trials by changing the instructions to the subject. In other words, the constraints operating in the situation were kept constant, but the objective of the movement was systematically varied by changing the relative demands for speed and accuracy. All subjects were required to point to visual targets presented on a screen in front of them. Eye position was monitored by infrared reflection. The position of each subject's hand in three-dimensional space was reconstructed by a computer-assisted analysis of the images provided by two rotary-shutter video cameras. The speed and accuracy demands of the task were varied in blocks of trials by requiring the subjects to point to the target "as quickly as you can" (speed condition); "as accurately as you can" (accuracy condition); or both "quickly and accurately" (speed/accuracy condition). The time to initiate an eye movement to the target was found to be reduced by increasing either the speed or accuracy demands of the task although the time to initiate the hand movement was reduced only in the speed condition. While the duration of the acceleration phase of the reach remained constant in real time, the duration of the deceleration phase was increased with increased demands for accuracy. As expected, both variable and absolute errors were largest in the speed condition. The findings indicated that the programming of the limb movement and its coordination with the associated eye movements were affected by varying the objective of the task.     

Priming,not inhibition,of related concepts during future imagining

Remembering the past and imagining the future both involve the retrieval of details stored in episodic memory and rely on the same core network of brain regions. Given these parallels, one might expect similar component processes to be involved in remembering and imagining. While a strong case can be made for the role of inhibition in memory retrieval, few studies have examined whether inhibition is also necessary for future imagining and results to-date have been mixed. In the current study, we test whether related concepts are inhibited during future imagining using a modified priming approach. Participants first generated a list of familiar places and for each place, the people they most strongly associate with it. A week later, participants imagined future events involving recombinations of people and places, immediately followed by a speeded response task in which participants made familiarity decisions about people’s names. Across two experiments, our results suggest that related concepts are not inhibited during future imagining, but rather are automatically primed. These results fit with recent work showing that autobiographically significant concepts (e.g., friends’ names) are more episodic than semantic in nature, automatically activating related details in memory and potentially fuelling the flexible simulation of future events.     

If it is easy to remember,then it is not secure: Metacognitive beliefs affect password selection

In this research, we applied current theories of metacognition to study computer security and tested the idea that users' password selection is affected by the metacognitive belief that if a password is memorable, then it is not secure. In two experiments, different types of eight‐character passwords and longer, more secure sentences were presented. Participants rated perceived memorability and perceived security of the passwords and indicated whether they would use them in a critical and in a noncritical service. The results confirmed the belief. Sentences that are in fact highly secure and perceived as highly memorable were also perceived as weak passwords. The belief strongly affected password selection for critical services, but it had no effect on noncritical services. In sum, long sentences are a particularly interesting type of password because they meet both security and memorability criteria, but their use is limited by a false belief.     

Task related modulation of the motor system during language processing

Recent neurophysiological and brain imaging studies have shown that the motor system is involved in language processing. However, it is an open question whether this involvement is a necessary requisite to understand language or rather a side effect of distinct cognitive processes underlying it. In order to clarify this issue we carried out three behavioral experiments, using a go-no go paradigm. Italian verbs expressing hand actions, foot actions or an abstract content served as stimuli. Participants used their right hands to respond. In Experiment 1, in which a semantics decision task with an early delivery of the go signal (during processing language material) was used, slower responses were found for hand action-related verbs than for foot action-related verbs. In Experiment 2, using the same task with either an early or a delayed delivery of the go signal (when language material had been already processed), no difference was found between responses to the two verb categories in the delayed delivery condition. In Experiment 3, in which a lexical decision task with an early delivery of the go signal was used, again no difference between the two verb categories was found. The present findings demonstrate that during language processing the modulation of the motor system crucially occurs while performing a semantics decision task, thus supporting the notion that this involvement is a necessary step to understand language rather than a side effect of upstream cognitive processes.     

Cue response dissociates inhibitory processes: task identity information is related to backward inhibition but not to competitor rule suppression

Psychological Research - In task switching, a conflict between competing task-sets is resolved by inhibiting the interfering task-set. Recent models have proposed a framework of the task-set as...     

Modulation of motor variability related to experimental muscle pain during elbow-flexion contractions

Experimental muscle pain typically reorganizes the motor control. The pain effects may decrease when the three-dimensional force components are voluntarily adjusted, but it is not known if this could have negative consequences on other structures of the motor system. The present study assessed the effects of acute pain on the force variability during sustained elbow flexion when controlling task-related (one-dimensional) and all (three-dimensional) contraction force components via visual feedback. Experimental muscle pain was induced by bolus injection of hypertonic saline into m. biceps brachii, and isotonic saline was used as control. Twelve subjects performed sustained elbow flexion at different levels of the maximal voluntary contraction (5–30% MVC) before, during, and after the injections. Three-dimensional force components were measured simultaneously with surface electromyography (EMG) from elbow flexors and auxiliary muscles. Results showed that force variability was increased during pain compared to baseline for contractions using one-dimensional feedback (P < .05), but no significant differences were found for three-dimensional feedback. During painful contractions (1) EMG activity from m. trapezius was increased during contractions using both one-dimensional and three-dimensional feedback (P < .05), and (2) the complexity of EMG from m. triceps brachii and m. deltoid was higher for the three-dimensional feedback (P < .05). In conclusion, the three-dimensional feedback reduced the pain-related functional distortion at the cost of a more complex control of synergistic muscles.     

Temporal selection is suppressed, delayed, and diffused during the attentional blink

How does temporal selection work, and along what dimensions does it vary from one instance to the next? We explored these questions using a phenomenon in which temporal selection goes awry. In the attentional blink, subjects fail to report the second of a pair of targets (T1 and T2) when they are presented at stimulus onset asynchronies (SOAs) of roughly 200 to 500 ms. We directly tested the properties of temporal selection during the blink by analyzing distractor intrusions at a fast rate of item presentation. Our analysis shows that attentional selection is (a) suppressed, (b) delayed, and (c) diffused in time during the attentional blink. These effects are dissociated by their time course: The measure of each effect returns to the baseline value at a different SOA. Our results constrain theories of the attentional blink and indicate that temporal selection varies along at least three dissociable dimensions: efficacy, latency, and precision.     

Visual orienting in response to attentional cues: Spatial correspondence is critical,conscious awareness is not

Three experiments examined visual orienting in response to spatial precues. In Experiments 1 and 2, attentional effects of central letters were stimulus driven: Orienting was dependent on the spatial layout of the cue display. When there were no correspondences between spatial features of the cue display and target location, attentional effects were absent, despite a conscious intention to orient in response to the symbolic information carried by the cue letters. In Experiment 3 clear orienting effects were observed when target location corresponded with spatial features of the cue display, but the magnitude of these effects was unaffected by whether participants were aware or unaware of the cue–target relationship. These findings are consistent with the view that (1) spatial correspondences between cues and targets are a critical factor driving visual orienting in cueing paradigms, and (2) attentional effects of spatial precues are largely independent of participants’ conscious awareness of the cue–target relationship.     

Activity engagement is related to level, but not change in cognitive ability across adulthood

It is unclear whether the longitudinal relation between activity participation and cognitive ability is due to preserved differentiation (active individuals have higher initial levels of cognitive ability), or differential preservation (active individuals show less negative change across time). This distinction has never been evaluated after dividing time-varying activity into its two sources of variation: between-person and within-person variability. Further, few studies have investigated how the association between activity participation and cognitive ability may differ from early to older adulthood. Using the PATH Through Life Project, we evaluated whether between- and within-person variation in activity participation was associated with cognitive ability and change within cohorts aged 20-24 years, 40-44 years, and 60-64 years at baseline (n = 7,152) assessed on three occasions over an 8-year interval. Multilevel models indicated that between-person differences in activity significantly predicted baseline cognitive ability for all age cohorts and for each assessed cognitive domain (perceptual speed, short-term memory, working memory, episodic memory, and vocabulary), even after accounting for sex, education, occupational status, and physical and mental health. In each case, greater average participation was associated with higher baseline cognitive ability. However, the size of the relationship involving average activity participation and baseline cognitive ability did not differ across adulthood. Between-person activity and within-person variation in activity level were both not significantly associated with change in cognitive test performance. Results suggest that activity participation is indeed related to cognitive ability across adulthood, but only in relation to the starting value of cognitive ability, and not change over time.     

Semantic interference in language production is due to graded similarity,not response relevance

There is an ongoing debate on the question whether semantic interference effects in language production reflect competitive processes at the level of lexical selection or whether they reflect a post-lexical bottleneck, occupied in particular by response-relevant distractor words. To disentangle item-inherent categorical relatedness and task-related response relevance effects, we combined the picture–word interference task with the conditional naming paradigm in an orthogonal design, varying categorical relatedness and task-related response relevance independent of each other. Participants were instructed to name only objects that are typically seen in or on the water (e.g. canoe) and refrain from naming objects that are typically located outside the water (e.g. bike), and vice versa. Semantic relatedness and the response relevance of superimposed distractor words were manipulated orthogonally. The pattern of results revealed no evidence for response relevance as a major source of semantic interference effects in the PWI paradigm. In contrast, our data demonstrate that semantic similarity beyond categorical relations is critical for interference effects to be observed. Together, these findings provide support for the assumption that lexical selection is competitive and that semantic interference effects in the PWI paradigm reflect this competition.     

Agreeableness is related to social‐cognitive,but not social‐perceptual,theory of mind

We hypothesise on a number of grounds that the personality dimension of Agreeableness may be associated with inter‐individual differences in theory of mind (ToM) functioning. However, it is important to distinguish social‐perceptual from social‐cognitive ToM. Previous findings on ToM in psychopathic individuals, sex differences in ToM and the associations between ToM and social relationships, all suggest that social‐cognitive ToM is more likely than social‐perceptual ToM to relate to Agreeableness. In separate empirical studies, we find that Agreeableness is substantially correlated with social‐cognitive ToM performance, but uncorrelated with social‐perceptual ToM performance. We suggest that the propensity or motivation to attend to the mental states of others may be central to the personality dimension of Agreeableness. Copyright © 2008 John Wiley & Sons, Ltd.     

Action rules: why the visual control of reaching and grasping is not always influenced by perceptual illusions

It is generally accepted that vision first evolved for the distal control of movement and that perception or 'representational' vision emerged much later. Vision-for-action operates in real time and uses egocentric frames of reference and the real metrics of the world. Vision-for-perception can operate over longer time scales and is much more scene-based in its computations. These differences in the timing and metrics of the two systems have been examined in experiments that have looked at the way in which each system deals with visual illusions. Although controversial, the consensus is that actions such as grasping and reaching are often unaffected by high-level pictorial illusions, which by definition affect percetion. However, recent experiments have shown that, for actions to escape the effects of such illusions, they must be highly practiced actions, preferably with the right hand, and must be directed in real time at visible targets. This latter finding suggests that some of the critical components of the encapsulated (bottom-up) systems that mediate the visual control of skilled reaching and grasping movements are lateralised to the left hemisphere.