Breanna Erin Studenka

Noise and complexity in human postural control: Interpreting the different estimations of entropy

Background Over the last two decades, various measures of entropy have been used to examine the complexity of human postural control. In general, entropy measures provide information regarding the health, stability and adaptability of the postural system that is not captured when using more traditional analytical techniques. The purpose of this study was to examine how noise, sampling frequency and time series length influence various measures of entropy when applied to human center of pressure (CoP) data, as well as in synthetic signals with known properties. Such a comparison is necessary to interpret data between and within studies that use different entropy measures, equipment, sampling frequencies or data collection durations. Methods and Findings The complexity of synthetic signals with known properties and standing CoP data was calculated using Approximate Entropy (ApEn), Sample Entropy (SampEn) and Recurrence Quantification Analysis Entropy (RQAEn). All signals were examined at varying sampling frequencies and with varying amounts of added noise. Additionally, an increment time series of the original CoP data was examined to remove long-range correlations. Of the three measures examined, ApEn was the least robust to sampling frequency and noise manipulations. Additionally, increased noise led to an increase in SampEn, but a decrease in RQAEn. Thus, noise can yield inconsistent results between the various entropy measures. Finally, the differences between the entropy measures were minimized in the increment CoP data, suggesting that long-range correlations should be removed from CoP data prior to calculating entropy. Conclusions The various algorithms typically used to quantify the complexity (entropy) of CoP may yield very different results, particularly when sampling frequency and noise are different. The results of this study are discussed within the context of the neural noise and loss of complexity hypotheses.

The distinction between tapping and circle drawing with and without tactile feedback: An examination of the sources of timing variance

An internal clock-like process has been implicated in the control of rhythmic movements performed for short (250–2,000 ms) time scales. However, in the past decade, it has been claimed that a clock-like central timing mechanism is not required for smooth cyclical movements. The distinguishing characteristic delineating clock-like (event) from non-clock-like (emergent) timing is thought to be the kinematic differences between tapping (discrete-like) and circle drawing (smooth). In the archetypal event-timed task (tapping), presence of perceptual events is confounded with the discrete kinematics of movement (table contact). Recently, it has been suggested that discrete perceptual events help participants synchronize with a metronome. However, whether discrete tactile events directly elicit event timing has yet to be determined. In the present study, we examined whether a tactile event inserted into the circle drawing timing task could elicit event timing in a self-paced (continuation) timing task. For a majority of participants, inserting an event into the circle drawing task elicited timing behaviour consistent with the idea that an internal timekeeper was employed (a correlation of circle drawing with tapping). Additionally, some participants exhibited characteristics of event timing in the typically emergently timed circle drawing task. We conclude that the use of event timing can be influenced by the insertion of perceptual events, and it also exhibits persistence over time and over tasks within certain individuals.

Narrative Intervention for Children With Autism Spectrum Disorder (ASD)

PURPOSE This study was conducted to determine whether a narrative intervention program that targeted the use of mental state and causal language resulted in positive gains in narrative production for children with autism spectrum disorder (ASD). METHOD Five children (2 girls and 3 boys) who had been diagnosed with ASD participated in the study. Children ranged in age from 8 to 12 years and were recruited through an autism clinic. Intervention was provided for two 50-min individual sessions per week for a total of 21-33 sessions (depending on the student). Childrens spontaneous stories, collected weekly, were analyzed for overall story complexity, story structure, and the use of mental state and causal language. Following a multiple-baseline across-participants design, data were collected for lagged baseline and intervention phases over a 6-month period. RESULTS All of the children made gains on all 3 measures of narration after participating in the instruction, with clear changes in level for all 5 children and changes in trend for 4 of the 5 children. The gains were maintained after intervention was discontinued. CONCLUSION The results demonstrate the efficacy of the 3-phase narrative instruction program for improving the fictional narration abilities of children with ASD.

End-state comfort trumps handedness in object manipulation.

A goal of research on human perception and performance is to explore the relative importance of constraints shaping action selection. The present study concerned the relative importance of two constraints that have not been directly contrasted: (1) the tendency to grasp objects in ways that afford comfortable or easy-to-control final postures; and (2) the tendency to grasp objects with the dominant rather than the nondominant hand. We asked participants to reach out and grasp a horizontal rod whose left or right end was to be placed into a target after a 90° rotation. In one condition, we told participants which hand to use and let them choose an overhand or underhand initial grasp. In another condition, we told participants which grasp to use and let them choose either hand. Participants sacrificed hand preference to perform the task in a way that ensured a comfortable or easy to control thumb-up posture at the time of object placement, indicating that comfort trumped handedness. A second experiment confirmed that comfort was indeed higher for thumb-down postures than thumb-up postures. A third experiment confirmed that the choice data could be linked to objective performance differences. The results point to the importance of identifying constraint weightings for action selection and support an account of hand selection that ascribes hand preference to sensitivity to performance differences. The results do not support the hypothesis that hand preference simply reflects a bias to use the dominant hand.

Circle Drawing Does Not Exhibit Auditory–Motor Synchronization

ABSTRACT Differences in timing control processes between tapping and circle drawing have been extensively documented during continuation timing. Differences between event and emergent control processes have also been documented for synchronization timing using emergent tasks that have minimal event-related information. However, it is not known whether the original circle-drawing task also behaves differently than tapping during synchronization. In this experiment, 10 participants performed a table-tapping and a continuous circle-drawing task to an auditory metronome. Synchronization performance was assessed via the value and variability of asynchronies. Synchronization was substantially more difficult in circle drawing than in tapping. Participants drawing timed circles exhibited drift in synchronization error and did not maintain a consistent phase relationship with the metronome. An analysis of temporal anchoring revealed that timing to the timing target was not more accurate than timing to other locations on the circle trajectory. The authors conclude that participants were not able to synchronize movement with metronome tones in the circle-drawing task despite other findings that cyclical tasks do exhibit auditory motor synchronization, because the circle-drawing task is unique and absent of event and cycle position information.

Motor interactions with another person: do individuals with Autism Spectrum Disorder plan ahead?

Interpersonal motor interactions (joint-actions) occur on a daily basis. In joint-action situations, typically developing (TD) individuals consider the end-goal of their partner and adjust their own movements to accommodate the other person. The movement planning processes required for joint-action may, however, be difficult for individuals with an Autism Spectrum Disorder (ASD) given documented difficulties in performance on theory of mind (ToM) and motor tasks. The goal of this experiment was to determine if individuals with ASD exhibit end-state comfort behaviors similar to their TD peers in joint-action situations. Participants were asked to either pass, place, or use three common tools: a wooden toy hammer, a stick, or a calculator. These tools were selected because the degree of affordance they offer (i.e., the physical characteristics they posses to prompt proper use) ranges from direct (hammer) to indirect (calculator). Participants were asked to pass the tool to a confederate who intended to place the tool down, or use the tool. Variables of interest included beginning and end-state grip orientations of the participant and confederate (comfortable or uncomfortable) as a function of task goal, and the side to which the tool was placed or passed. Similar to Gonzalez et al. (2011), some individuals with ASD maximized their partners beginning-state comfort by adopting personally uncomfortable postures. That said, their performance was more variable than their TD peers who consistently passed tools in a manner that facilitated comfortable use by the confederate. Therefore, the movement planning processes used to prepare to pass a tool are not stereotypical across all individuals with ASD. We propose that the novel joint-action task described herein provides the basis for testing an important link between motor performance and more complex social and communication behaviors.

Visual information for prospective control of tracking irregular target paths with isometric force production

The prospective control of isometric force tracking was investigated as a function of the duration of visual information about past and future properties of target paths that varied in regularity. Longer duration of information specifying future behavior significantly enhanced performance when past information was not available. Furthermore, target path regularity differentially influenced local and global performance properties as the duration of prospective information increased. For more regular target paths, longer duration of prospective visual information improved local properties (e.g., decreased error), whereas, for less regular target paths, longer duration of prospective visual information enhanced global properties of force production (e.g., spectral slope). The strategies of prospective control depend on the interaction of the regularity of motor output and the available informational support.

Crossing the arms confuses the clocks: Sensory feedback and the bimanual advantage

The bimanual advantage refers to the finding that tapping with two fingers on opposite hands exhibits reduced timing variability, as compared with tapping with only one finger. Two leading theories propose that the bimanual advantage results from the addition of either sensory (i.e., enhanced feedback) or cognitive (i.e., multiple timekeeper) processes involved in timing. Given that crossing the arms impairs perception of tactile stimuli and modulates cortical activation following tactile stimulation, we investigated the role of crossing the arms in the bimanual advantage. Participants tapped unimanually or bimanually with their arms crossed or uncrossed on a tabletop or in the air. With arms crossed, we expected increased interval timing variance. Similarly, for air tapping, we expected reduced bimanual advantage, due to reduced sensory feedback. A significant bimanual advantage was observed for the uncrossed, but not the crossed posture in tabletop tapping. Furthermore, removing tactile feedback from taps eliminated the bimanual advantage for both postures. Together, these findings suggest that crossing the arms likely impairs integration of internal (i.e., effector-specific) and external (i.e., environment-specific) information and that this multisensory integration is crucial to reducing timing variability during repetitive coordinated bimanual tasks.

Differential time scales of change to learning frequency structures of isometric force tracking.

Multiple processes support the persistent (learning) and transient (adaptive) change in behavior over time. We investigated whether practice and rest influence similarly the learning and adaptation of slow and fast frequency structures in isometric force tracking of pathways that varied in their regularity. Participants practiced 25 trials on each of 5 days in either a constant force target or 1 with the 1/f distributional properties of brown or pink noise. There was a reduction in root mean squared error (RMSE) as well as an increasing positive correlation between force output and the target pathway for all noise conditions over days. The spectral frequency analysis of force output and RMSE revealed task dependent outcomes of learning and adaptation as a function of the relatively slow (0-4 Hz) and fast (8-12 Hz) oscillatory time scales. These contrasting findings show that the persistent and transient properties of learning occur across different timescales and dimensions of behavior (force output and outcome-RMSE).

Response to period shifts in tapping and circle drawing: A window into event and emergent components of continuous movement

Synchronization of movement to a metronome is a well-studied task for both discretely and smoothly produced rhythmic movement. In particular, behavioral responses to unexpected changes in a regular metronome can reveal both the strength and the completeness of error correction mechanisms and temporal control. Clock-like control is exhibited by discretely produced movement and movement with discrete perceptual information, whereas smoothly produced movement does not rely on internal clock mechanisms. Documented differences in error correction between discretely and smoothly produced movements have been attributed to this different underlying control. In this study, error correction mechanisms were examined by inducing changes in the pace of rhythmic movement. An overshoot response following the pace change for both tapping and circle drawing is documented, and suggests the presence of phase and period correction in both tasks. The presence of phase correction in circle drawing also suggests that clock and non-clock timing may co-exist within the same movement. Furthermore, a sub-group of participants emerged who appropriately changed pace, but were not able to correct the phasing of their movement while performing the circle drawing task, supporting that phase and period maintenance in timing are independently controlled processes.