Interactions among end-effectors and movement parameters influence reaction time in discrete, rapid aimed movements.

Two reliable findings in discrete, rapid aimed movements are that reaction time increases with decrease in target diameter (for the short-length movements), and reaction time is not affected by movement length [Journal of Experimental Psychology, Human Perception and Performance 104 (2) (1975) 147]. Participants normally use a short stylus (SS) to tap targets located on either side of a central (aligned with body midline) start-point with no restrictions imposed on the initial posture of the limb or segmental recruitment except as determined by movement conditions. Thus, the effects of movement parameters on reaction time in previous work are potentially confounded with the effect of initial posture of the limb at the start-point, along with order and amount of the contribution of segments recruited in response execution. Two experiments were performed to resolve the confounding between initial posture and recruitment of limb segments. In the first experiment a conventional stylus (pen-like) was employed and the starting position of the limb was aligned either with the body midline or with the participant's right shoulder. The effect of starting position on reaction time was not significant. In the second experiment the starting position was in line with the right shoulder. Two groups participated. One group used a conventional stylus. For the second group a modified (lengthened) stylus was used that permitted initial limb posture and number of limb segments recruited to be held constant across an extended range of movement lengths. When similar sets of limb segments were used, reaction time increased with decreasing movement length and diminishing target diameter. These findings suggest that uncontrolled initial limb posture, uncontrolled order of joint(s) recruitment, and the subsequent inclusion of reaction time values from incompatible sources may, in the final analysis, have confounded previous work investigating movement amplitude and target diameter effects on reaction time.     

Fitts' reciprocal tapping task, a measure of motor capacity?

Employing Fitts' reciprocal tapping task, the capacity of the motor system in bits processed/second was assessed across different ages. In Exp. I a comparison was made among Grades 1, 5, 9, and university females. Motor capacity and average movement time/tap were significantly lower for Grade 1 girls than the other three grades. In addition, within-subject variability and percentage error rate decreased with increasing grade level. These findings were discussed in comparison to other studies looking at motor capacity changes across ages. Exp. II was designed to study the changes in motor capacity throughout 25 days of practice by two 5-yr.-old children. Two different methods were used to calculate motor capacity. One method (Kay, 1962) which assessed motor capacity separately for each tapping condition led to the conclusion that capacity increased with practice. A second method (Fitts & Peterson, 1964) treating all tapping conditions together in a regression equation and measuring capacity as the reciprocal of the slope (1/b) showed capacity to decrease with practice for one subject and oscillate with practice for the other subject. The general conclusion drawn from the two experiments was that motor capacity, as assessed by Fitts' tapping task, is not an extremely useful measure. Consideration of movement time is usually just as informative.     

Programmed control of aimed movements revisited the role of target visibility and symmetry

Reaction time prior to starting a 2-mm amplitude aimed movement was studied as a function to target size and experimental procedure. Consistent with a report by Klapp, choice reaction time increased as target size decreased when the visual signal that initiated the reaction time interval also indicated which of two targets was to be hit. This result implies response programming during the reaction time interval, with more programming time for slower movements to smaller targets. By contrast, in a simple reaction time procedure, there was no effect of target size on reaction time, suggesting that the response can be programmed in advance when the appropriate target is precued. This provided a control for speed-accuracy trade-off, supporting the programming interpretation of the choice reaction time result. In another condition in which both targets could be viewed while waiting for the auditory signal that initiated the reaction time interval and indicated which target to hit, choice reaction time was independent of target size provided that both possible targets on each trial were of the same size. The overall results suggest that response programs include both spatial and temporal information, and that parallel programming of different spatial goals is possible provided that the responses are of the same duration.     

Targeted Paced and Unpaced Movements in the Transverse and Sagittal Planes

Five experiments are reported related to control of arm movement in the sagittal and transverse planes when making paced and unpaced movements. A single group of 12 participants and the same equipment were used in the main experiments to allow comparisons across conditions. As well as the 2 different directions of movement, there were movements that were time-constrained (as in the W. D. A. Beggs &; C. I. Howarth, 1971, 1972a,b paradigm) and movements that were constrained by the ending tolerance (as in Fitts' paradigm). Results showed that, for movement times as high as 900 ms, the Schmidt and Beggs and Howarth models appeared to describe the time for movements that had time constraint. Fitts' law (P. M. Fitts, 1954 Fitts, P. M. (1954). The information capacity of the human motor system in controlling the amplitude of movement. Journal of Experimental Psychology, 47, 381–391.[Crossref], [PubMed] , [Google Scholar]; P. M. Fitts &; J. R. Peterson, 1964) applied to movements that were constrained by final accuracy. These results were independent of whether the target was in the aiming or stopping movement direction. A new interpretation of data for movements with time constraint is presented, based on the possible number of accuracy submovements available when near the target. This model suggests that the standard deviation of hits at the target is not dependent on the time spent in reaching the target region, but largely on the time remaining in order to produce final accuracy at the target.     

Partial advance information,number of alternatives,and motor processes: an electromyographic study

We present evidence that advance information reducing the number of stimulus-response alternatives in a choice reaction time (RT) task can shorten the very latest motoric stages of RT. Effects of such advance information on late stages of RT have been demonstrated recently by Osman, Moore, and Ulrich (Acta Psychol. 90 (1995) 111), Leuthold, Sommer, and Ulrich (J. Exp. Psychol: Gen. 125 (1996) 307), Müller-Gethmann, Rinkenauer, Stahl, and Ulrich (Psychophysiology 37 (2000) 507). These studies found that advance information shortens the portion of the RT interval following onset of a movement-related brain potential (lateralized readiness potential). Osman et al. and Müller-Gethmann et al. also examined the portion of the RT interval following the start of electromyographic (EMG) activity and found no effect of advance information. Based on Osman et al.'s null result, Leuthold et al. speculated that advance information may shorten only the RT stages preceding EMG activity. This conclusion, however, is questionable because of limitations in the EMG measures employed by both Osman et al. and Müller-Gethmann et al. We have reanalyzed the results of a previously reported experiment (Acta Psychol. 101 (1999) 243) to show that advance information can in fact affect the rate of recruitment of motor units in the prime mover of the responding limb.     

The effect of movement amplitude and target diameter on reaction time: comments on Siegel (1977)

Siegel's (1977) interpretation that his reaction time results were solely a function of response factors (movement amplitude and target diameter) was discussed and criticized. It was argued that Siegel's interpretation was inappropriate because stimulus factors (eccentric and visual angle) and response factors were confounded. It was also argued that the surprising U-shaped relation between reaction time and movement amplitude was probably the result of the confounding between stimulus and response factors.     

Violations of Fitts’ Law in a Ballistic Task

ABSTRACT

The authors explored changes in the postural preparation and movement times during jumps into targets of different sizes placed at different distances from the participant. Both movement and preparation times scaled with movement distance. Neither movement nor preparation time showed an effect of target size, although preparation time showed a tendency to increase for smaller targets. These observations show that the classical Fitts’ law can be violated in tasks that involve a ballistic component. The data corroborate a hypothesis that Fitts’ law originates at the level of movement planning.     

Anticipatory postural adjustments during a Fitts’ task: Comparing young versus older adults and the effects of different foci of attention

Anticipatory postural adjustments (APAs) are an integral part of standing balance. Previous research with balance control has shown that adopting an external focus of attention, compared to an internal focus of attention, yields better performance during motor skills. Despite the importance of APAs, especially among older adults, and the potential benefits of adopting an external focus of attention, studies investigating methods for improving APAs are limited. The aim of this study was to compare behavioral, kinematic and APAs measures while adopting different foci of attention among young and older adults when performing a lower extremity Fitts’ task. Ten young adults (mean age 24 years ± 4.37) and ten older adults (mean age 75 years ± 5.85) performed a lower-extremity reaching task (Fitts’ task) while adopting an external focus (focus on target) and an internal focus (focus on limb) in a within-subject design. A motion capture system was used to record participants’ movement data. Custom software derived movement time (MT), peak velocity (PV), time to peak velocity (ttPV) and variability at target (SD_T). Electromyography (EMG) was used to determine APAs onset and magnitude. The findings showed that an external focus of attention led to significantly shorter MT, higher PV, shorter ttPV and more accuracy when reaching the target (SD_T) for both age groups. Also, EMG results showed that, with an external focus, APAs onset occurred earlier and APAs magnitude was more efficient. As predicted by Fitts’ Law, participants spent more time executing movements to targets with higher indices of difficulty. Older adults compared to young adults were more adversely affected by the increase of difficulty of the Fitts’ task, specifically, on measures of APAs. In conclusion, adopting an external focus of attention led to better overall movement performance when performing a lower extremity Fitts’ task. The task used in the present study can distinguish between APAs for older and young adults. We recommend that future studies expand on our findings in order to establish a performance-based objective measure of APAs to assess clinical interventions for postural control impairment.     

Goal-directed aiming under restricted viewing conditions with confirmatory sensory feedback

A substantial body of research has examined the speed-accuracy tradeoff captured by Fitts’ law, demonstrating increases in movement time that occur as aiming tasks are made more difficult by decreasing target width and/or increasing the distance between targets. Yet, serial aiming movements guided by internal spatial representations, rather than by visual views of targets have not been examined in this manner, and the value of confirmatory feedback via different sensory modalities within this paradigm is unknown. Here we examined goal-directed serial aiming movements (tapping back and forth between two targets), wherein targets were visually unavailable during the task. However, confirmatory feedback (auditory, haptic, visual, and bimodal combinations of each) was delivered upon each target acquisition, in a counterbalanced, within-subjects design. Each participant performed the aiming task with their pointer finger, represented within an immersive virtual environment as a 1 cm white sphere, while wearing a head-mounted display. Despite visual target occlusion, movement times increased in accordance with Fitts’ law. Though Fitts’ law captured performance for each of the sensory feedback conditions, the slopes differed. The effect of increasing difficulty on movement times was least influential in the haptic condition, suggesting more efficient processing of confirmatory haptic feedback during aiming movements guided by internal spatial representations.     

Three-dimensional movement trajectories in Fitts' task: Implications for control

According to Fitts (1954), movement time (MT) is a function of the combined effects of movement amplitude and target width (index of difficulty). Aiming movements with the same index of difficulty and MT may have different planning and control processes depending on the specific combination of movement amplitude and target size. Trajectories were evaluated for a broad range of amplitudes and target sizes. A three-dimensional motion recording system (WATSMART) monitored the position of a stylus during aiming movements. MT results replicated Fitts' Law. Analysis of the resultant velocity profiles indicated the following significant effects: As amplitude of movement increased, so did the time to peak resultant velocity; peak resultant velocity increased slightly with target size, and to a greater extent with increases in the amplitude of movement; the time after peak resultant velocity was a function of both amplitude and target size. Resultant velocity profiles were normalized in the time domain to look for scalar relation in the trajectory shape. This revealed that: the resultant velocity profiles were not symmetrical; the proportion of time spent prior to and after peak speed was sensitive to target size only, i.e. as target size decreased, the profiles became more skewed to the right, indicating a longer decelerative phase; for a given target size, a family of curves might be defined and scaled on movement amplitude. These results suggest that a generalized program (base trajectory representation) exists for a given target width and is parameterized or scaled according to the amplitude of movement.     

The Effect of Movement Amplitude and Target Diameter on Reaction Time

Siegel’s (1977) interpretation that his reaction time results were solely a function of response factors (movement amplitude and target diameter) was discussed and criticized. It was argued that Siegel’s interpretation was inappropriate because stimulus factors (eccentric and visual angle) and response factors were confounded. It was also argued that the surprising U-shaped relation between reaction time and movement amplitude was probably the result of the confounding between stimulus and response factors.     

Technical considerations regarding the short (dit)-long (dah) key press paradigm

The finding of longer reaction time prior to longer-lasting responses (e.g., Klapp, 1977a; Klapp, Wyatt. & Lingo, 1974) was not replicated by Kerr (1979) in a statistically powerful attempt. The present experiment confirms that this effect is not reliable when duration knowledge of results is similar to that used by Kerr, although a reliable long-short effect was obtained with other knowledge of results arrangements. This unexpected sensitivity to knowledge of results suggest that previous results from this paradigm must be interpreted with caution.     

Intention superiority effect: A context-switching account

Intention superiority effect [J. Exp. Psychol. Learn. Mem. Cogn. 19 (1993) 1211; J. Exp. Psychol. Learn. Mem. Cogn. 24 (1998) 350] is the finding that the times to retrieve memory items related to uncompleted or partially completed intentions are faster than for those with no associated intentions. However, this relationship reverses when the intended tasks are completed [J. Exp. Psychol. Learn. Mem. Cogn. 24 (1998) 350; Mem. Cogn. 27 (1999) 320]. That is, the times to retrieve memory items related to completed intentions are slower than for those with no associated intentions. In this paper, we present a computational account of the intention superiority effect using the ACT-R cognitive architecture [Atomic components of thought. Mahwah, NJ: Lawrence Erlbaum Associates, 1998]. Our modeling approach is based on the idea that uncompleted or partially completed intentions are available as context in the current goal, and they prime related memory items while inhibiting unrelated memory items. However, once the intended tasks are completed, they are removed from the current goal, which produces an inhibitory effect on memory items associated with them. We describe an ACT-R model that is able to reproduce all of the effects reported in Marsh et al. [J. Exp. Psychol. Learn. Mem. Cogn. 24 (1998) 350].     

Bimanual and Unimanual Convergent Goal-Directed Movement Times

Three experiments are reported, investigating the effects of using 1 or 2 hands when making convergent low index of difficulty (ID) and visually controlled movements (2 hands meeting together). The experiments involved movements in four different cases—a probe held in the right hand and moved to a target held in the stationary left hand, vice versa of this arrangement, both hands moving with the probe in the right hand and target in the left hand, and vice-versa of this arrangement. Experiments were the standard Fitts’ paradigm, moving a pin into a hole and a low-ID task. In Fitts’ task, 2-hand movements were faster than 1 hand only at higher IDs; this was also the case in the pin-to-hole transfer task and the movement times were lower when the pin was held in the preferred hand. Movements made with low ID showed a small effect of 1- or 2-handed movements, with the effective amplitude of the movement being reduced by about 20% when 2 hands were used.     

Fitts’ Theorem in Oculomotor Control: Dissociable Movement Times for Amplitude and Width Manipulations

The authors examined whether movement times (MT) for discrete saccades are constant given equivalent index of difficulty (ID) values (i.e., unitary nature of Fitts’ theorem). To that end, we contrasted ID/MT relations for saccades equated for ID but differing with respect to their target amplitudes and widths. Results showed that MT increased with increasing ID within amplitude and width conditions; however, the ID/MT slope was markedly steeper in the former condition. Thus, the amplitude condition imposed greater information processing demands than the width condition—a result indicating that the constituent elements of Fitts’ theorem are dissociable (i.e., nonunitary). Further, examination of saccade kinematics demonstrated that the optimal MT for a given target amplitude was largely independent of target width.     

Development of movement schema in young children

To examine the development of movement schema in young school-age children, i.e., whether principles which govern fine eye-hand coordination skill learning as suggested by Schmidt's schema theory apply to the learning of gross motor skills Exp. 1 involved 48 right-handed first-grade children. On a modification of the Fitts Reciprocal Tapping task children moved a stylus (held in the hand or attached to a special shoe worn on the foot) between two metal targets separated by different distances. Children were randomly assigned to one of eight groups: two control or no-practice groups and six experimental or transfer groups. A one-way analysis of variance followed by appropriate Scheffé post hoc tests indicated that movements of the lower limbs were not organized into a movement schema, but a pattern of schema of movement for the upper limbs developed. That no movement schema developed for lower limb movements suggests development of movement schema is intricately linked to both the existing as well as the potential for developing precise movement in those limbs. Exp. 2 involved 40 first-grade children who were randomly assigned to perform a gross-motor agility task under one of three conditions: direct practice on the criterion task, constant practice on a modification of the criterion task, or variable practice on several different modifications of the criterion task. A groups X trials analysis of variance with appropriate post hoc tests indicated that there were no significant differences among direct, constant, or variable practice groups. Data suggest that the amount of practice may be as important as the type of practice in developing movement schema involved in gross motor skills in young children.     

Modification in movement accuracy in the triphasic pattern during a rapid forearm-flexion task

The present study was designed to investigate modifications in the triphasic EMG pattern during a forearm-flexion task at maximum speed which required three levels of movement accuracy. 36 subjects participated in 4 training sessions, performing a total of 200 repetitions of each movement. The fastest movement time was associated with the least accurate movement task. Likewise, the slowest movement time was found for the movement requiring the greatest accuracy. Differences in the duration and amplitude of agonist 1 activity, the start of agonist 2 activity, and the start and amplitude of antagonist activity were observed for the three movements. The results indicate that agonist 1 provides a propulsive force to initiate limb movement. The antagonist EMG activity was thought responsible for braking and correcting limb movement. Modifications in agonist 2 activity suggest this burst is related to movement velocity.     

Combined visual illusion effects on the perceived index of difficulty and movement outcomes in discrete and continuous fitts’ tapping

The speed-accuracy trade-off is a fundamental movement problem that has been extensively investigated. It has been established that the speed at which one can move to tap targets depends on how large the targets are and how far they are apart. These spatial properties of the targets can be quantified by the index of difficulty (ID). Two visual illusions are known to affect the perception of target size and movement amplitude: the Ebbinghaus illusion and Muller-Lyer illusion. We created visual images that combined these two visual illusions to manipulate the perceived ID, and then examined people’s visual perception of the targets in illusory context as well as their performance in tapping those targets in both discrete and continuous manners. The findings revealed that the combined visual illusions affected the perceived ID similarly in both discrete and continuous judgment conditions. However, the movement outcomes were affected by the combined visual illusions according to the tapping mode. In discrete tapping, the combined visual illusions affected both movement accuracy and movement amplitude such that the effective ID resembled the perceived ID. In continuous tapping, none of the movement outcomes were affected by the combined visual illusions. Participants tapped the targets with higher speed and accuracy in all visual conditions. Based on these findings, we concluded that distinct visual-motor control mechanisms were responsible for execution of discrete and continuous Fitts’ tapping. Although discrete tapping relies on allocentric information (object-centered) to plan for action, continuous tapping relies on egocentric information (self-centered) to control for action. The planning-control model for rapid aiming movements is supported.     

Direction of association between targets in a RSVP task influences priming at very short but not long SOAs

When two targets are presented using rapid serial visual presentation (RSVP) and the interval between the targets is 200–500 ms, detection or identification of the second target is impaired. This impairment in second target report is known as the attentional blink (AB). This study sought to examine the impact of the direction of target association on priming during an AB task using very short and long SOAs. Two experiments were conducted using dual-stream RSVP tasks and targets that either shared an associative relationship or were unrelated to one another. The direction of association between the targets was also varied so that associatively related targets were presented in the forward (strongest association from target 1 to target 2) or backward directions of association (strongest association from target 2 to target 1). In Experiment 1 very short SOAs between targets (27–213 ms) were used. Priming was evident at the same SOAs for both targets presented in the backward direction of association. However, for targets presented in the forward direction of association, priming occurred for target 1 and target 2 at different SOAs. Experiment 2 used longer SOAs between targets (107 to 535 ms) and it was determined that while direction of association between the targets did not affect priming, there was a larger priming effect for target 2 than for target 1. The results of the two experiments indicate that direction of association between targets influences priming in RSVP tasks that use very short but not long SOAs. The results are discussed in relation to the two-stage response competition model of Potter et al. (J Exp Psychol Hum Percept Perform 28:1149–1162, 2002).     

Feedback versus motor programming in the control of aimed movements.

In the Fitts paradigm the subject moves a stylus to the left or right of an initial rest position to reach targets that vary in size and in distance from the initial position. The classic finding for relatively long movements is that movement time, measured from leaving the initial position until contact with the target, depends on both distance and target size according to a relationship known as "Fitts' law." By contrast, reaction time, measured from the signal to move until the stylus leaves the initial position, is independent of these parameters. While replicating these results for long movements, the present data show a different pattern for very short movements, for which Fitts' law no longer holds and for which reaction time increases as the size of the target is decreased. These findings were interpreted as implying that long movements are under feedback control, whereas short movements are predominately programmed and ballistic. This conclusion was supported by the additional finding that elimination of visual feedback was more disruptive to the long than to the short movements.