Bimanual reaching across the hemispace: Which hand is yoked to which?

When both hands perform concurrent goal-directed reaches, they become yoked to one another. To investigate the direction of this coupling (i.e., which hand is yoked to which), the temporal dynamics of bimanual reaches were compared with equivalent-amplitude unimanual reaches. These reaches were to target pairs located on either the left or right sides of space; meaning that in the bimanual condition, one hand's contralateral (more difficult) reach accompanied by the other hand's ipsilateral (easier) reach. By comparing which hand's difficult reach was improved more by the presence of the other hand's easier ipsilateral reach, we were able to demonstrate asymmetries in the coupling. When the cost of bimanual reaching was controlled for the contralateral reaching left hand's performance was improved, suggesting that the left hand is yoked to the right during motor output. In contrast, the right hand showed the greatest improvements for contralateral reaching in terms of reaction time, pointing toward a dominant role for the left hand in the processes prior to movement onset. The results may point toward a mechanism for integrating the unitary system of attention with bimanual coordination.     

The effect of attending to motor overflow on its voluntary inhibition in young and older adults

Motor overflow refers to involuntary movement or muscle activity coinciding with voluntary movement. We examined whether 16 young adults (18-30 years) and 16 older adults (50-80 years) could voluntarily inhibit overflow. Participants performed a finger pressing task, exerting 50% of their maximal force. Overflow was concurrently recorded in the non-task hand. In the first condition, participants were not made aware of their motor overflow. Then participants, though informed of it, were asked to ignore their overflow. Finally, participants were requested to inhibit overflow with, and then without visual feedback, or vice versa. Overflow was exacerbated when older adults were unaware of it, and was reduced once they were informed. For young adults there was no significant difference between these conditions. Both Age Groups could significantly reduce overflow when so requested, independent of visual feedback. Thus motor overflow can be modulated by higher order cognitive control with directed attention.     

Fitts’ law holds for pointing movements under conditions of restricted visual feedback

Fitts’ law robustly predicts the time required to move rapidly to a target. However, it is unclear whether Fitts’ law holds for visually guided actions under visually restricted conditions. We tested whether Fitts’ law applies under various conditions of visual restriction and compared pointing movements in each condition. Ten healthy participants performed four pointing movement tasks under different visual feedback conditions, including full-vision (FV), no-hand-movement (NM), no-target-location (NT), and no-vision (NV) feedback conditions. The movement times (MTs) for each task exhibited highly linear relationships with the index of difficulty (r² > .96). These findings suggest that pointing movements follow Fitts’ law even when visual feedback is restricted or absent. However, the MTs and accuracy of pointing movements decreased for difficult tasks involving visual restriction.     

Hand dominance influences the processing of observed bodies

In motor tasks, subgroups of lefthanders have been shown to differ in the distribution of attention about their own bodies. The present experiment examined whether similar attentional biases also apply when processing observed bodies. Sixteen right handers (RHs), 22 consistent left handers (CLHs) and 11 relatively ambidextrous inconsistent left handers (ILHs) performed an own body transformation task in which they were instructed to make speeded left–right judgements about a schematic human figure. Attentional biases associated with handedness were found to extend to observed bodies: CLHs’ judgements were faster to the figure’s left side, while ILHs, like RHs, showed facilitated performance to the figure’s right side. These results demonstrate a novel embodiment effect whereby the processing of a static schematic human figure is modulated by an individual’s personal motor capabilities. This finding suggests that motor simulation may contribute to whole body perception in the absence of actual or implied actions.     

Perceptual-attentional and motor-intentional bias in near and far space

Spatial bias demonstrated in tasks such as line-bisection may stem from perceptual-attentional (PA) "where" and motor-intentional (MI) "aiming" influences. We tested normal participants' line bisection performance in the presence of an asymmetric visual distracter with a video apparatus designed to dissociate PA from MI bias. An experimenter stood as a distractor to the left or right of a video monitor positioned in either near or far space, where participants viewed lines and a laser point they directed under (1) natural and (2) mirror-reversed conditions. Each trial started with the pointer positioned at either the top left or top right corner of the screen, and alternated thereafter. Data analysis indicated that participants made primarily PA leftward errors in near space, but not in far space. Furthermore, PA, but not MI, bias increased bilaterally in the direction of distraction. In contrast, MI, but not PA, bias was shifted bilaterally in the direction of startside. Results support the conclusion that a primarily PA left sided bias in near space is consistent with right hemisphere spatial attentional dominance. A bottom-up visual distractor specifically affected PA "where" spatial bias while top-down motor cuing influenced MI "aiming" bias.     

Motor programming in apraxia of speech

Apraxia of Speech (AOS) is an impairment of motor programming. However, the exact nature of this deficit remains unclear. The present study examined motor programming in AOS in the context of a recent two-stage model [Klapp, S. T. (1995). Motor response programming during simple and choice reaction time: The role of practice. Journal of Experimental Psychology: Human Perception and Performance, 21, 1015–1027; Klapp, S. T. (2003). Reaction time analysis of two types of motor preparation for speech articulation: Action as a sequence of chunks. Journal of Motor Behavior, 35, 135–150] that proposes a preprogramming stage (INT) and a process that assigns serial order to multiple programs in a sequence (SEQ). The main hypothesis was that AOS involves a process-specific deficit in the INT (preprogramming) stage of processing, rather than in the on-line serial ordering (SEQ) and initiation of movement. In addition, we tested the hypothesis that AOS involves a central (i.e., modality-general) motor programming deficit. We used a reaction time paradigm that provides two dependent measures: study time (the amount of time for participants to ready a motor response; INT), and reaction time (time to initiate movement; SEQ). Two experiments were conducted to examine INT and SEQ in AOS: Experiment 1 involved finger movements, Experiment 2 involved speech movements analogous to the finger movements. Results showed longer preprogramming time for patients with AOS but normal sequencing and initiation times, relative to controls. Together, the findings are consistent with the hypothesis of a process-specific, but central (modality-independent) deficit in AOS; alternative explanations are also discussed.     

Investigating speech motor practice and learning in people who stutter

In this exploratory study, we investigated whether or not people who stutter (PWS) show motor practice and learning changes similar to those of people who do not stutter (PNS). To this end, five PWS and five PNS repeated a set of non-words at two different rates (normal and fast) across three test sessions (T1, T2 on the same day and T3 on a separate day, at least 1 week apart). The results indicated that PWS and PNS may resemble each other on a number of performance variables (such as movement amplitude and duration), but they differ in terms of practice and learning on variables that relate to movement stability and strength of coordination patterns. These findings are interpreted in support of recent claims about speech motor skill limitations in PWS.

Educational objectives: The reader will be able to: (1) define oral articulatory changes associated with motor practice and learning and their measurement; (2) summarize findings from previous studies examining motor practice and learning in PWS; and (3) discuss hypotheses that could account for the present findings that suggest PWS and PNS differ in their speech motor learning abilities.     

Flexible and inflexible response components: a Stroop study with typewritten output

Two experiments were directed at investigating the relationship between response selection and execution in typewriting, and specifically the extent to which concurrent processing takes place. In a Stroop paradigm adapted from [Logan, G. D., & Zbrodoff, N. J. (1998). Stroop-type interference: Congruity effects in colour naming with typewritten responses. Journal of Experimental Psychology: Human Perception and Performance, 24, 978–992], participants typed the names of colour patches with incongruent, congruent, or neutral distractors presented at various stimulus-onset asynchronies. Experiment 1 showed Stroop interference and facilitation for initial keystroke latencies and errors, contrasting with response durations (a measure of response execution) being unaffected by Stroop manipulation. Experiment 2 showed that all three measures were responsive to time pressure; again, Stroop effects were confined to latencies and errors only. The observation that response duration is both flexible under time pressure and protected from response competition, may imply either that response execution is structurally segregated from earlier processing stages, or that encapsulation develops during the acquisition of typing skills.     

Change detection evokes a Simon-like effect

The present experiment studied choice response context effects on the programming of response sequences using behavioural and electrophysiological methods. Participants were asked to produce responses differing in sequence length (1-key vs. 3-key responses) with either their left or right hand in a choice reaction time (RT) task. The choice response context was manipulated by a blocked or mixed execution of 1-key and 3-key responses. A sequence length effect on RT was observed in the blocked but not in the mixed condition. The time course of the lateralized readiness potential indicates a motoric locus of the sequence length effect, suggesting that the response hand is activated before the entire motor program is established.