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Jason B. Boyle, Deanna M. Kennedy, Chaoyi Wang, and Charles Shea

An experiment by Boyle, Kennedy, and Shea (2012) demonstrated that practice tracking a template created from a sine wave results in enhanced performance and transfer on a reciprocal aiming task with an index of difficulty (ID) of 6. An experiment was conducted to determine whether tracking a template constructed from recorded participants' performance with ID = 6 would provide the same benefit. Participants were assigned to one of four groups (Fitts–master, Fitts–yoked, sine–master, and sine–yoked). After acquisition, visual templates were constructed for the Fitts–yoked and sine–yoked conditions. The templates were generated from the unique displacement data of the Fitts– and sine–master participants. These made up the training template for the Fitts– and sine–yoked participants. After acquisition, all participants were asked to perform test trials under their respective acquisition conditions (Test 1) and test trials under ID = 6 reciprocal aiming conditions (Test 2). Results indicated faster movement times in the sine-wave training groups on Test 2 than in both Fitts groups. These results indicate that the presentation of a tracking template can result in lower dwell times in the Fitts–yoked pairing on Test 2. However, the findings indicate the need to use templates that guide the movement in a way that promotes an equal acceleration–deceleration profile paired with smooth target reversal.

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Alessia Longo and Ruud Meulenbroek

hands are moving together with the same index of difficulty (ID) or with different IDs. Kelso, Southard, and Goodman ( 1979 ) encouraged the notion that during two-handed tasks, the intrinsic dynamics of movement-related processes at the behavioral and neural level constrain the motion system to act as

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Paola Cesari and Karl M. Newell

The experiment reported examined: (a) the role of the geometrical body scaled informational invariant for the transition of human grip configurations; (b) whether the same invariant can be scaled considering also the force applied during the grasp phase; and (c) how the temporal duration of the grasp and displacement phases of prehension are scaled to the object properties of size and mass. Adult subjects performed a series of trials in reaching, grasping, and displacing spheres that varied in size and mass. The grip transitions were described by the body scaled relation:
where Ls and Ms are, respectively, the diameter and the mass of the spheres grasped and Lh and Mh are the length and the mass of the hand. The impulse during the grasp phase was linearly related with the mass of the spheres within each density. The temporal durations of the grasp and displacement components were scaled coherently to the object properties. These findings provide support to the hypothesis that the grasp and displacement components of prehension are organized coherently within a single action.
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Marlowe Pecora, Luc Tremblay, and Matthew Heath

Plamondon & Alimi, 1997 ), movement times (MTs) adhere to Fitts’ ( 1954 ) equation asserting that a task’s index of difficulty (ID Fitts : represented in bits of information) is reflected by ID Fitts  = log 2 (2 A / W ), where A represents movement amplitude and W the width associated with a goal

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Mark L. Latash and Irina L. Mikaelian

We explored the relations between task difficulty and speech time in picture description tasks. Six native speakers of Mandarin Chinese (CH group) and six native speakers or Indo-European languages (IE group) produced quick and accurate verbal descriptions of pictures in a self-paced manner. The pictures always involved two objects, a plate and one of the three objects (a stick, a fork, or a knife) located and oriented differently with respect to the plate in different trials. An index of difficulty was assigned to each picture. CH group showed lower reaction time and much lower speech time. Speech time scaled linearly with the log-transformed index of difficulty in all subjects. The results suggest generality of Fitts’ law for movement and speech tasks, and possibly for other cognitive tasks as well. The differences between the CH and IE groups may be due to specific task features, differences in the grammatical rules of CH and IE languages, and possible use of tone for information transmission.

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Timothy N. Welsh and Michele Zbinden

The “proximity-to-hand” effect refers to the finding that distractors between the home position and the target cause more interference in a selective reaching movement than distractors farther from the home position. Based largely on the proximity-to-hand effect, Tipper, Lortie, and Baylis (1992) proposed that attention is distributed in an action-centered framework such that the interference caused by a specific stimulus depends on the action. The current experiments sought to determine if there is an attentional preference for stimuli closer to home or for stimuli that activate more efficiently executed actions regardless of the location. Results supported the latter hypothesis in that the greatest interference was observed when the distractor activated an action with a lower index of difficulty than the target, even though that distractor was farther from home than the target. These findings indicate that the action context mediates the influence that nontarget stimuli have on the processing of target responses.

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Steven R. Passmore, Jeanmarie Burke, and Jim Lyons

A discrete aiming head movement task was developed to replicate Fitts’ movement paradigm. Movement time (MT) differences between young (age range 24-29 years, n = 8) and old adults (age range 75-85 years, n = 8) were examined. Cervical spine (CS) range of motion (ROM) was recorded. A head mounted motion capture device was used to evaluate task performance. Three amplitudes and three target widths generated nine indexes of difficulty (IDs). Global ROM was decreased in old adults. The ID and MT relationship was maintained with age; however, old adults were slower, more variable, and more affected by ID. Variations in target size were used as the accuracy variable for both groups. As target size increased, the old population overshot their endpoint. These data support the hypothesis that, besides musculoskeletal slowing with age, there may be age-related deterioration of central processing, planning, or perception mechanisms.

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Cheryl M. Glazebrook, Digby Elliott, and James Lyons

We examined the planning and control of goal-directed aiming movements in young adults with autism. Participants performed rapid manual aiming movements to one of two targets. We manipulated the difficulty of the planning and control process by varying both target size and amplitude of the movements. Consistent with previous research, participants with autism took longer to prepare and execute movements, particularly when the index of difficulty was high. Although there were no group differences for accuracy, participants with autism exhibited more temporal and spatial variability over the initial phase of the movement even though mean peak accelerations and velocities were lower than for control participants. Our results suggest that although persons with autism have difficulty specifying muscular force, they compensate for this initial variability during limb deceleration. Perhaps persons with autism have learned to keep initial impulses low to minimize the spatial variability that needs to be corrected for during the online control phase of the movement.

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François Bonnetblanc

Fitts’s law states that movement time (MT) is related to precision (index of difficulty, ID). The introduction of a new effector in a Fitts’s task induces an increase of the MT/ID slopes (Langolf et al., 1976). It is unclear, however, whether kinetics or pure coordinative constraints based on the introduction of new degrees of freedom (at the joint or muscular level) are responsible for this effect. To determine the influence of body kinetics on the MT/ID slope when pointing beyond reach, we compared pointing movements executed within (control) or beyond reach, and in this latter case with (loaded) and without (distant) an additional mass applied to the trunk. Eight subjects were required to point as fast and as accurately as possible to a target (width: 0.5, 1.0, or 2.5 cm; amplitude: 30 cm). The MT/ID slope increased when pointing beyond reach (control versus distant or loaded). This slope did not increase with an additional load applied to the trunk (distant versus loaded). Therefore, we conclude that the MT/ID slope is more likely a function of the number of degrees of freedom introduced in the task rather than a function of the kinetics constraints.

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Howard N. Zelaznik

, the greater coefficient of variation in movement timing found in the Fitts task compared to the Schmidt task, is related to the temporal consistency cost of the execution of submovements as index of difficulty is increased. The results of the McKeeman and Zelaznik ( 2018 ) work highlights the