Precision hypothesis and the end-state comfort effect

Recently, motor control research has emphasized the planning of macroscopic aspects of control. In object manipulation studies, when participants complete a movement in a comfortable posture, an end-state comfort effect is attained. One explanation for this effect is the precision hypothesis, which states that precision increases when participants are in a comfortable position. This research directly tests the precision hypothesis in two experiments. In Experiment 1, participants picked up a dowel and touched a large or small target on a wall. For the second experiment, the same procedure was followed using a pinpoint target. The probability analyses of the first experiment indicated that the end-state comfort effect was magnified in the small target condition and that the point-of-change effect (Short and Cauraugh, 1997) appeared only when end-state comfort was magnified. Error analyses in Experiment 2 showed that participants were more accurate when in a more comfortable position. The present findings indicate that the precision hypothesis plays a significant role in the end-state comfort effect.     

A test of motor (not executive) planning in developmental coordination disorder and autism.

Grip selection tasks have been used to test “planning” in both autism and developmental coordination disorder (DCD). We differentiate between motor and executive planning and present a modified motor planning task. Participants grasped a cylinder in 1 of 2 orientations before turning it clockwise or anticlockwise. The rotation resulted in a comfortable final posture at the cost of a harder initial reaching action on 50% of trials. We hypothesized that grip selection would be dominated by motoric developmental status. Adults were always biased towards a comfortable end-state with their dominant hand, but occasionally ended uncomfortably with their nondominant hand. Most 9- to 14-year-olds with and without autism also showed this “end-state comfort” bias but only 50% of 5- to 8-year-olds. In contrast, children with DCD were biased towards selecting the simplest initial movement. Our results are best understood in terms of motor planning, with selection of an easier initial grip resulting from poor reach-to-grasp control rather than an executive planning deficit. The absence of differences between autism and controls may reflect the low demand this particular task places on executive planning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time course of movement planning: Selection of handgrips for object manipulation.

A goal of research on the cognitive control of movement is to determine how movements are chosen when many movements are possible. The authors addressed this issue by studying how Ss reached for a bar to be moved as quickly as possible from a home location to a target location. Ss generally grabbed the bar in a way that afforded a comfortable posture at the target location (the end-state comfort effect) and with the thumb toward the end of the bar that would be aligned with the target (the thumb-toward bias). The data suggest that Ss chose handgrips by retrieving instances of previous reaches, not by carrying out computations that treated candidate reaches as new behavioral events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evolutionary roots of motor planning: The end-state comfort effect in lemurs.

Humans (Homo sapiens) anticipate the consequences of their forthcoming actions. For example, they grasp objects with uncomfortable grasps to afford comfortable end positions—the end-state comfort (ESC) effect. When did such sophisticated motor planning abilities emerge in evolution? We addressed this question by asking whether humans' most distant living primate relatives—lemurs—also exhibit the ESC effect. We presented 6 species of lemurs (Lemur catta, Eulemur mongoz, Eulemur coronatus, Eulemur collaris, Hapalemur griseus, and Varecia rubra) with a food extraction task and measured the grasp used—either a canonical thumb-up posture or a noncanonical thumb-down posture. The lemurs adopted the thumb-down posture when that hand position afforded a thumb-up posture following object transport, thereby exhibiting the ESC effect. We conclude that the planning abilities underlying the ESC effect evolved at least 65 million years ago, or 25 million years earlier than previously supposed based on an earlier demonstration of the ESC effect in cotton-top tamarins (Saguinus oedipus; Weiss, Wark, & Rosenbaum, 2007). Because neither cotton-tops nor lemurs are tool users, the data suggest that the cognitive abilities implicated by the ESC effect are not sufficient, although they may be necessary, for tool use. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of masked stimuli on motor activation: Behavioral and electrophysiological evidence.

Three experiments investigated the influence of unperceived events on response activation. Masked primes were presented before a target. On compatible trials, primes and targets were identical; on incompatible trials, opposite responses were assigned to them. Forced-choice performance indicated that prime identification was prevented by the masking procedure, but overt performance and motor activation as mirrored by the lateralized readiness potential (LRP) were systematically influenced by the prime. The direction of these effects was unexpected: Performance costs for compatible and performance benefits for incompatible trials were obtained relative to a neutral trial condition. The LRP revealed a sequential pattern of motor activation. A partial activation of the response corresponding to the prime was followed by a reverse activation pattern. It is argued that these effects primarily reflect an inhibition of the response initially triggered by the prime. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

La planification d'un mouvement corporel: Un processus de consommation de ressources.

According to a theoretical framework about the resource-limited and data-limited processes (Norman & Bobrow, 1975), this experiment attempts to assess the attention demand related to the planning of a body movement. In the main task, subjects point to a visual target which is exposed cither at 10° or 30° in the right visual hemi-field. In the subsidiary task, subjects discriminate between two sounds which are slightly different in frequency. One of the two sounds is delivered randomly in the middle part of the motor planning interval. The duration of the motor planning interval varies randomly in accordance to the following values: 200, 300, 400, 500, 600, 700, 800, 900, and 1000 msec. Four right-handed volunteers participated in the experiment. Taking the duration of the motor planning interval into account, it clearly appears that the reaction time (main task) at the onset of the target decreases linearly as a function of the increase of the percentage of correct responses (subsidiary task). The motor planning operation which occurs just before the initiation of a body movement seems to correspond to a resource-limited process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relationship between curvature and velocity in two-dimensional smooth pursuit eye movements

Curvature and tangential velocity of voluntary hand movements are constrained by an empirical relation known as the Two-Thirds Power Law. It has been argued that the law reflects the working of central control mechanisms, but it is not known whether these mechanisms are specific to the hand or shared also by other types of movement. Three experiments tested whether the power law applies to the smooth pursuit movements of the eye, which are controlled by distinct neural motor structures and a peculiar set of muscles. The first experiment showed that smooth pursuit of elliptic targets with various curvature-velocity relationships was most accurate when targets were compatible with the Two-Thirds Power Law. Tracking errors in all other cases reflected the fact that, irrespective of target kinematics, eye movements tended to comply with the law. Using only compatible targets, the second experiment demonstrated that kinematics per se cannot account for the pattern of pursuit errors. The third experiment showed that two-dimensional performance cannot be fully predicted on the basis of the performance observed when the horizontal and vertical components of the targets used in the first condition were tracked separately. We conclude that the Two-Thirds Power Law, in its various manifestations, reflects neural mechanisms common to otherwise distinct control modules.     

单轴压缩试验中减弱端部效应新型方法研究

为了减弱端部效应对单轴抗压强度测量的影响,提出一种新型的单轴压缩试验方法.该方法采用与试件材质相同的岩石作为垫块进行单轴压缩试验,设置了(25+50+25)mm和(20+60+20)mm 2种试件高度组合进行试验,并与高度为50 mm、60 mm的单一试件的试验结果进行对比.结果表明:该新型试验方法可以降低单轴压缩试验...     

Blinded by headlights.

Abstract Target identification is impaired when targets are presented during the planning or execution of a compatible response (e.g., right-pointing arrow during a right keypress) relative to an incompatible response (J. Müsseler and B. Hommel, 1997 a, b). Examinations of this blindness to response-compatible stimuli have typically used arrowheads as targets. The importance of the target symbol was examined by manipulating subjects' (aged 18-30 yrs) interpretation of that symbol. Targets were presented at varying times during the planning or execution of a response in order to examine the time-course of the effect. Results showed that the interpretation, and not the physical identity, of the target was important for the blindness effect. Although the blindness effect was largest during the planning and execution of a response, it was not always confined to that temporal interval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Word recognition and temporal order judgments: Semantics turns back the clock.

Investigated the consequences that codes activated during reading have on activities unrelated to reading by investigating the effects of semantics on temporal order judgments. Participants judged which of 2 word targets appeared first. Undergraduate students served as Ss. Targets appeared either synchronously, or were separated by varying stimulus onset asynchronies. For 1 group of participants, 1 target on each trial was related to a prime word shown at the beginning of the trial. This priming relation affected temporal order judgments such that participants sometimes reported related targets as having appeared first, even when they appeared second. It is suggested that this effect is best explained as showing that codes activated during word recognition affect the attentional selection aspects of the temporal order judgment task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Don't look down: Emotional arousal elevates height perception.

In a series of experiments, it was found that emotional arousal can influence height perception. In Experiment 1, participants viewed either arousing or nonarousing images before estimating the height of a 2-story balcony and the size of a target on the ground below the balcony. People who viewed arousing images overestimated height and target size more than did those who viewed nonarousing images. However, in Experiment 2, estimates of horizontal distances were not influenced by emotional arousal. In Experiment 3, both valence and arousal cues were manipulated, and it was found that arousal, but not valence, moderated height perception. In Experiment 4, participants either up-regulated or down-regulated their emotional experience while viewing emotionally arousing images, and a control group simply viewed the arousing images. Those participants who up-regulated their emotional experience overestimated height more than did the control or down-regulated participants. In sum, emotional arousal influences estimates of height, and this influence can be moderated by emotion regulation strategies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial patterns in the control of human arm movement

Generalized Procrustes analysis was used to investigate the spatial paths of pointing movements. In Experiment 1, 3 participants produced similar spatial paths of the hand when repeating a pointing movement many times, despite variability in the position and orientation of the movements. The average spatial path indicates a fundamental spatial pattern of the motor system, or motor primitive. This pattern varied across the workspace. Anterioposterior movements were straight, but repeated movements had variable spatial patterns. Lateral movements were curved away from the body but had regular spatial patterns. Experiment 2 extended these results to movements of different amplitudes in 7 participants. The motor primitive seems to be abandoned at the end of the movement in favor of final adjustments to bring the hand to the target position. In Experiment 3, the same participants produced similar motor primitives both with and without vision.     

Cognitive channels computing action distance and direction

Visually guided, goal-directed reaching requires encoding action distance and direction from attributes of visual landmarks. We identified a cognitive mechanism that seemingly performs visual motor extension before action initiation and replicated and extended previous results that identified a mechanism for visual motor mental rotation. We find that humans systematically delay action onset while newly planning increasingly distant arm movements beyond a visual landmark, consistent with an internal representation for visual motor extension. Onset times also changed systematically during concurrent mental rotation and visual motor extension computations required to process new directions and distances. Visual motor extension associated with reaching slowed when participants needed to plan action direction within the same time frame, whereas mental rotation efficiency was unaffected by concurrent needs to prepare action distance. In contrast to parallel direction and distance computations needed for direct aiming to a visual target, the planning of new directions and distances likely occurs at distinct times. When considered with previous findings, the current results suggest the existence of an intermediate component of motor preparation that engages a covert mechanism of cognitive motor planning.     

When is it best to hear a verb? The effects of the timing and focus of verb models on children''s learning of verbs

Recent neurophysiological studies of the saccadic ocular motor system have lent support to the hypothesis that this system uses a motor error signal in retinotopic coordinates to direct saccades to both visual and auditory targets. With visual targets, the coordinates of the sensory and motor error signals will be identical unless the eyes move between the time of target presentation and the time of saccade onset. However, targets from other modalities must undergo different sensory-motor transformations to access the same motor error map. Because auditory targets are initially localized in head-centered coordinates, analyzing the metrics of saccades from different starting positions allows a determination of whether the coordinates of the motor signals are those of the sensory system. We studied six human subjects who made saccades to visual or auditory targets from a central fixation point or from one at 10 degrees to the right or left of the midline of the head. Although the latencies of saccades to visual targets increased as stimulus eccentricity increased, the latencies of saccades to auditory targets decreased as stimulus eccentricity increased. The longest auditory latencies were for the smallest values of motor error (the difference between target position and fixation eye position) or desired saccade size, regardless of the position of the auditory target relative to the head or the amplitude of the executed saccade. Similarly, differences in initial eye position did not affect the accuracy of saccades of the same desired size. When saccadic error was plotted as a function of motor error, the curves obtained at the different fixation positions overlapped completely. Thus, saccadic programs in the central nervous system compensated for eye position regardless of the modality of the saccade target, supporting the hypothesis that the saccadic ocular motor system uses motor error signals to direct saccades to auditory targets.     

Hand path priming in manual obstacle avoidance: Evidence for abstract spatiotemporal forms in human motor control.

Previous research suggests that motor equivalence is achieved through reliance on effector-independent spatiotemporal forms. Here the authors report a series of experiments investigating the role of such forms in the production of movement sequences. Participants were asked to complete series of arm movements in time with a metronome and, on some trials, with an obstacle between 1 or more of the target pairs. In moves following an obstacle, participants only gradually reduced the peak heights of their manual jumping movements. This hand path priming effect, scaled with obstacle height, was preserved when participants cleared the obstacle with 1 hand and continued with the other, and it was modulated by future task demands. The results are consistent with the hypothesis that the control of movement sequences relies on abstract spatiotemporal forms. The data also support the view that motor programming is largely achieved by changing just those features that distinguish the next movement to be made from the movement that was just made. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Skill in expert dogs.

The motor control of novice participants is often cognitively demanding and susceptible to interference by other tasks. As people develop expertise, their motor control becomes less susceptible to interference from other tasks. Researchers propose a transition in human motor skill from active control to automaticity. This progression may also be the case with nonhuman animals. Differences in performance characteristics between expert, advanced, intermediate, and novice dogs competing in the sport of agility were investigated. There were statistically significant differences between dogs of varying competitive levels in speed, motor control, and signal detections suggestive of increasing motor control automaticity in highly skilled, or expert, dogs. The largest sequential motor control difference was between novice and intermediate dogs, d = .96, whereas the largest sequential signal detection difference was between advanced and expert dogs, d = .90. These findings have two significant implications for expertise researchers: first, the observed similarities between dogs and humans may enable dogs to be used as expert models; and second, expertise science and methods may be profitably employed in the future to create more proficient canine workers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential priming in hierarchically organized figures: Effects of target level and target resolution.

Three experiments are reported in which participants identified target letters that appeared at either the global or local level of hierarchically organized stimuli. It has been previously reported that response time is facilitated when targets on successive trials appear at the same level (L. M. Ward, 1982; L. C. Robertson, 1996). Experiments 1 and 2 showed that this sequential priming effect can be mediated by target-level information alone, independent of the resolution, or actual physical size, of targets. Target level and resolution were unconfounded by manipulating total stimulus size, such that global elements of the smaller stimuli subtended the same amount of visual angle as local elements of the larger stimuli. Experiment 3, however, showed that when level information is less useful than resolution in parsing targets from distractors, resolution does become critical in intertrial priming. These data are discussed as they relate to the role of attention in local vs. global (part vs. whole) processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Encouraging the perceptual underdog: Positive affective priming of nonpreferred local–global processes.

Two experiments examined affective priming of global and local perception. Participants attempted to detect a target that might be present as either a global or a local shape. Verbal primes were used in 1 experiment, and pictorial primes were used in the other. In both experiments, positive primes led to improved performance on the nonpreferred dimension. For participants exhibiting global precedence, detection of local targets was significantly improved, whereas for participants exhibiting local precedence, detection of global targets was significantly improved. The results provide support for an interpretation of the effects of positive affective priming in terms of increased perceptual flexibility. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reevaluating encoding-capacity limitations as a cause of the attentional blink.

A number of researchers have emphasized the role of distractors intervening between successive targets as the primary determinant of the attentional blink (AB) phenomenon. They argued that the AB is abolished when 3 or more targets are displayed as temporally contiguous items in rapidly presented serial sequences. In 3 experiments, the authors embedded 1-, 2-, or 3-digit targets among letter distractors in rapidly presented visual sequences. Across the experiments, both the number of targets and the lag between them were manipulated, producing different proportion of trials in which 3 temporally contiguous targets were presented in the test session. Evidence of an AB affecting the targets that followed the first target in these sequences was found in each experiment when the probability of a given target report was conditionalized on a correct response to the preceding targets, thus reinforcing the notion that some form of capacity limitation in the encoding of targets plays a central role in the elicitation and modulation of the AB effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Four heads are better than one: Combining face composites yields improvements in face likeness.

Four participants constructed face composites, of familiar and unfamiliar targets, using Pro-Fit, with reference images present or from memory. The "mean" of all 4 composites, created by morphing (4-morph) was rated as a better likeness than individual composites on average and was as good as the best individual likeness. When participants attempted to identify targets from line-ups, 4-morphs again performed as well as the best individual composite. In a second experiment, participants familiar with target women attempted to identify composites, and the trend showed better recognition from multiple composites, whether combined or shown together. In a line-up task with unfamiliar participants, 4-morphs produced most correct choices and fewest false positives from target-absent or target-present arrays. These results have practical implications for the way evidence from different witnesses is used in police investigations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)