As we grow older our cognitive and physical abilities decline, but do we adjust our behaviour accordingly? If one’s perception of their declined physical ability is not adjusted to the new situation, unsafe behaviour could occur. A disparity between one’s perceived and actual ability, also known as misjudgment, may lead to risk-taking or inefficiency. As a consequence, this disparity might explain why some older adults fall while their peers with similar cognitive and physical ability do not. Fall prediction algorithms might benefit from a misjudgment term if it is a trait variable that is consistent between tasks. On the contrary, a lack of consistency between tasks would indicate that the degree of misjudgment on one task cannot be predicted by evaluation of prior tasks and suggests that a misjudgment term may have limited benefit for fall prediction. To this end, we investigated whether the degree of misjudgment of stepping ability is consistent between several stepping tasks in young and older adults.

We introduced four tasks (see figure) in which the participant’s perceived ability and actual stepping ability were determined. The tasks consisted of: A) stepping over a raised bar, B) stepping over a twelve-meter-long converging piece of paper at a self-selected width, while starting at the broad end of 2-meter width, C) making a recovery step after release from an inclined position, and D) crossing a declining cord at a self-selected height, while starting at the highest end of 1.2 meter. For each task, a linear model was used to determine the relationship between the perceived and actual ability, where the distance between the perceived ability and the corresponding predicted actual ability served as the degree to which a participant misjudged their physical ability. Moreover, the validity of the tasks were examined using the following criteria: “1) the perceived and actual physical ability measure of one task should relate highly to the same measures of another task, 2) the relation between perceived and actual physical ability should be linear,” 3) the linear regression model should be parallel to the identity line.

Figure. A) stepping over a raised bar, B) stepping over a converging piece of paper at a self-selected width, C) making a recovery step after release from an inclined position, D) crossing a declining cord at a self-selected height.

We showed that the actual ability measures and perceived ability measures were consistent across tasks. However, the degree of misjudgment was not consistent between different stepping tasks, but rather task-specific and could not be generalised to other stepping tasks. Furthermore, only one of the tasks satisfied our validity criteria of, which hampers comparison of the degree of misjudgment over tasks. Future research should implement novel and valid tasks to investigate the added value of a misjudgment term in fall prediction models.

Publication

Kluft N, Bruijn SM, Weijer RHA, van Dieën JH, Pijnappels M (2017). On the validity and consistency of misjudgment of stepping ability in young and older adults. PLOS ONE 12(12): e0190088. https://doi.org/10.1371/journal.pone.0190088

About the Author

Concussion results in a wide variety of impairments such as cognitive deficits in memory, reaction time and processing speed. Moreover, post-concussion dizziness and balance impairments are found to be common and predictive of worse recovery times.  Therefore, an increasing number of patients with concussion are referred for vestibular physical therapy.
Although it is likely that cognitive and vestibular impairments after concussion are related, they have only been examined in isolation. This study examined the relationship between cognitive performance and various gait and balance measures in patients referred for vestibular physical therapy after concussion.

Our study investigated the relationship between gait and balance performance with cognitive performance in a group of 60 adolescents referred for vestibular therapy after concussion. We tested our participants on a range of functional gait and balance measures, such as the Functional Gait Assessment, Timed “UP & GO”, and Five Times Sit to Stand. Our results suggest that, after concussion, both memory deficits and impaired gait and balance can occur in individuals. Our results further show that they are associated with each other. First, we demonstrated that functional balance and gait measures were associated with worse verbal and visual memory on the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT). For example, in the figure below, we observed that better performance in visual memory (i.e. higher scores) and verbal memory was related to better performance in the Five Times Sit to Stand (i.e. less time). We also found that higher scores on the Post-Concussion Symptom Scale were associated with lower scores on the Activities-specific Balance Confidence scale and higher scores on the Dizziness Handicap Inventory.

Spatial navigation is frequently affected after concussion and is important for both gait and balance tasks as well as memory tasks. Clinicians working with patients after concussion should check whether any observed cognitive impairments might be partially attributed to declines in spatial navigation rather than an isolated memory decline. Vestibular therapists should consider giving dual-task exercises, combining balance and cognition, during the rehabilitation process to reduce the impact of cognitive performance on gait and balance function. It will be interesting to see in future studies whether the associations between cognitive and balance affect recovery trajectories after concussion.

Figure: Association between Five Times Sit to Stand Performance and Visual and Verbal Memory performance in 60 adolescents with a concussion who were referred for vestibular physical therapy. Higher visual and verbal memory scores were related to better performance on the Five Times Sit to Stand.

Publication
Alsalaheen BA, Whitney SL, Marchetti GF, Furman GM, Kontos AP, Collins MW, Sparto PJ:  Relationship between cognitive assessment and balance measures in adolescents treated with vestibular physical therapy after concussion. Clin J Sport Med. 2016. 26(1):46-52. PMCID:  PMC4856020

http://journals.lww.com/cjsportsmed/Citation/2016/01000/Relationship_Between_Cognitive_Assessment_and.7.aspx

About the Author

During daily life, locomotion tasks are often accompanied by a concurrent task such as talking, texting or recalling a shopping list. There is a wide body of empirical evidence on the profound negative effects of concurrent cognitive challenges on gait, the cognitive task itself, and other clinical outcomes such as falls. Such reductions in performance are commonly interpreted as competition for attentional resources between the postural and cognitive task. Various cognitive tasks have been utilized in dual-task research, such as backwards counting, reaction time, memory recall, Stroop and verbal fluency tasks. Performance for these tasks is traditionally measured through the rate of error or the response time. However, such descriptive measures lack the temporal resolution to track the dynamics of attention allocation during postural control. Hence, we aimed to evaluate the timing of postural prioritization during stepping using a continuous finger-tapping task.

Ten healthy young adults with a mean age of 21 years participated in this study. Participants were asked to perform a rapid voluntary step with either their left or right foot after hearing an auditory tone (simple/choice reaction paradigm), while also tapping their right index finger continuously on a handhold numeric keypad (Figure A). Three variants of concurrent attentional tasks were used: (1) single task: holding keypad only, no finger-tapping; (2) low attention-demanding: one-button tapping task; (3) high attention-demanding: four-button tapping task. We performed wavelet analysis on the stimulus-locked finger-tapping data to determine the temporal change of tapping frequency related to reactive stepping (Figure B). Results showed that the postural performance was negatively affected only by the high attention-demanding task. Significant reduction of post-stimulus tapping speed was observed across all test conditions, indicating attention shift during the execution of a step. In addition, the high attention-demanding task induced early postural prioritization during the choice reaction stepping condition when different motor programs needed to be prepared and executed.

Our study shows that a continuous finger-tapping task can be used to track attention allocation during step initiation, by detecting the reduction of tapping speed in response to the stimulus presentation. The results suggest that the postural task is prioritized during step planning and execution, especially when the motor program cannot be pre-selected in case of the choice reaction condition. Our novel method can be used to probe when and how attention shifts during other locomotion tasks, as well as track attention allocation in various aging and pathological populations.

Publication

Sun, R, & Shea, J. B. (2016). Probing attention prioritization during dual-task step initiation: a novel method. Experimental brain research, 234(4), 1047-1056. https://link.springer.com/article/10.1007/s00221-015-4534-z

About the Author

Humans have the ability to mentally visualize all sorts of objects, events or scenes. This is known as mental imagery. For example, I can generate a vivid experience of swimming in a pool: I ‘feel’ the water flow, I ‘sense’ the temperature, and I ‘move’ my arms and legs. Research has shown that mental imagery (especially of motor acts) is accompanied by changes in bodily states, such as heart rate, muscle tension, and respiration, often in a highly specific manner. Mental imagery also affects postural control, as evidenced by analysis of the center-of-pressure (COP) trajectory as a function of mental content. We performed an experiment inspired by a study by Miles et al. (2010). They found that mental imagery of the (own) future and past induced COP changes. Thinking of the past caused backward displacement of the  COP, whereas thinking of the future caused forward displacement. The authors concluded that the direction of subjective time is represented along a spatial dimension, which in turn led to directional changes in body posture (unintentional ‘leaning’). We performed a conceptual replication and extension of this study, in order to test how general and robust the effect of ‘mental time travel’ is.

Thirty-two participants stood upright and imagined various scenarios that were read aloud. Scenarios described a typical day in the past or in the future; 4 days or 4 years. In addition, some scenarios were pleasant (e.g., receiving a diploma) or unpleasant (being at a funeral). We analyzed postural displacements in the anterior-posterior direction, as a function of the mental content. An important finding was that there was no statistically significant difference between past and future imagery (see Figure). Also, no postural effects of emotion were found. This apparent null finding (all F’s < 1) received support from Bayesian statistics, which quantifies the relative predictive success of the null hypothesis relative to the alternative hypothesis. This Bayesian analysis revealed that the null hypothesis (i.e., no difference between past and future imagery) was 4.8 more likely than the alternative, which is typically considered ‘substantial’ evidence.

Figure 1. Grand averaged wave forms of the COP trace (bold line), plus straight line fit (red line) for past (left panel) and future (right panel) mental imagery. There was no statistical difference between these two conditions.

We have no explanation for why our results diverged from Miles et al. (2010). It could be due to subtle unidentified methodological differences. Alternatively, it could be that the effect is not robust and that posture is insensitive to abstract thought, such as mental time travel.

Publication

Stins JF, Habets L, Jongeling W, Cañal-Bruland R. (2016). Being (un)moved by mental time travel. Consciousness and Cognition; 42: 374–81. http://www.sciencedirect.com/science/article/pii/S1053810016300666

About the Author

Stroke survivors often suffer from motor paralysis on one side of the body. It can be challenging for them to walk through narrow openings, such as doorways or space created by pedestrians. This is because, while body rotation with a pivot-like turn is necessary to fit through apertures without contact, performing such a turn using the paretic limb is difficult. Therefore, we investigated how they could successfully avoid obstacles and fit through apertures in spite of their motor paralysis.

Participants included 10 stroke fallers, 13 stroke non-fallers, and 23 controls. A door-like aperture was created as a space between two projector screens (Fig. 1a). Participants were asked to approach and cross the aperture without contacting the screen. In some trials, the aperture was so narrow that body rotation was necessary to avoid contacting the screen. Our results showed that stroke fallers contacted the screens more frequently than any of the other participants. This suggests that the inability to safely cross an aperture is related to the risk of falling. As expected, stroke fallers contacted the screen mainly on their paretic side. Interestingly, enough, these contacts were less frequent when they tried to navigate the opening starting with their paretic side (Fig. 1b). Three-dimensional motion analyses showed that stroke participants rotated their bodies in multiple steps (rather than with pivot-like turns), possibly to deal with their motor paralysis.

Our results suggest that, although stroke fallers have difficulty avoiding contact with obstacles on their paretic side, adopting a strategy to fit through an opening from their paretic side can help them avoid contacts. We have two explanations as to why such a strategy helped improve their behavior; it could be that vision of the paretic side helped guiding the movement or that spatial attention was directed to the location of the paretic side of the body. We are now investigating whether such a strategy would be a helpful intervention to help stroke patients pass narrow openings safely.

Figure 1(a) Participants were asked to walk through a narrow opening created by two projector screens. Our focus was on how successfully they avoided contacts with the screen and how they approached and crossed a narrow opening while dealing with their motor paralysis. (b) Contact frequency classified according to the body side where contact occurred.

Publication
Muroi D, Hiroi Y, Koshiba T, Suzuki Y, Kawaki M, Higuchi T. (2017) Walking through apertures in individuals with stroke. PLOS ONE 12: e0170119.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0170119

About the Author

During walking, we rely on visual information to identify tripping hazards and navigate safely through the environment. The way we shift our gaze and scan the environment (our visual-search behaviour) is affected by ageing and fall risk. Older adults at high-risk of falling will transfer their gaze away from a stepping target before the step has been completed (i.e., prior to heel contact); a behaviour which is causally linked to reduced stepping accuracy. Moreover, when navigating a series of stepping constraints, high-risk older adults will adopt a less-variable pattern of visual-search, whereby their gaze is fixated predominately on the initial stepping target, at the expense of upcoming obstacles or targets. We hypothesised that this maladaptive and less-variable pattern of visual-search behaviour may be caused by inefficiencies in attentional processing, with high-risk older adults possessing insufficient cognitive resources to generate and store a ‘spatial map’ of their environment. Insufficient cognitive resources for attentional processing during walking may be due to psychological factors. When anxious or following injury or accident (e.g., falls), individuals may attempt to consciously monitor and control movements, which are usually considered largely ‘automatic’. This phenomenon is frequently described as ‘reinvestment’. It is believed that cognitive resources are required to consciously attend to the process of walking, which would limit the resources available for other processes, such as proactively scanning one’s environment. Yet, little is known about how either cognitive load or reinvestment influence visual-search behaviour during walking.

Younger adults traversed a non-linear path (containing two precision stepping targets) while performing a secondary serial-subtraction task and wearing a gaze-tracker unit. Outcome measures included gaze behaviour, stepping accuracy, and time to complete the walking task. When walking while simultaneously carrying out the serial-subtraction task, participants visually fixated on task-irrelevant areas ‘outside’ the walking path more often and for longer durations, and fixated on task-relevant areas ‘inside’ the walkway for shorter durations. These changes were most pronounced in high-trait-reinvesters. The increased task-irrelevant ‘outside’ fixations were accompanied by slower walking times and greater gross stepping errors. Interestingly, these ‘outside’ fixations were temporally related to the performance of the dual-task, with participants more likely to look away from the walkway (or, ‘gaze into thin air’) in the 330ms directly preceding the verbalisation of the dual-task calculation.

Our findings suggest that attention is important for the maintenance of effective gaze behaviours, supporting previous claims that maladaptive changes in visual-search observed in high-risk older adults may be a consequence of inefficiencies within attentional processing. As these changes were most pronounced in high-trait-reinvesters, we speculate that reinvestment-related processes placed additional cognitive demands upon working memory.

Figure. A: An example of a task-relevant ‘inside’ fixation, whereby the participant fixates on an area within their walking path. B: An example of a task-irrelevant ‘outside’ fixation, whereby the participant fixates on an area outside of their walking path. C: Duration (as a percentage of overall fixation durations) of task-relevant ‘inside’ and task-irrelevant ‘outside’ fixations under conditions of Cognitive Load, ** p <.01. D: Number of task-irrelevant ‘outside’ fixations (per second) under conditions of Cognitive Load, * p <.05.

Publication

Ellmers TJ, Cocks AJ, Doumas M, Williams AM, Young WR (2016) Gazing into Thin Air: The Dual-Task Costs of Movement Planning and Execution during Adaptive Gait. PLoS ONE 11(11): e0166063.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0166063

About the Author

The young woman trips on an uneven sidewalk, recovers smoothly and resumes texting. The older woman encounters the same perturbation and crashes.

My colleagues and I have been trying to identify the key neuromuscular attributes responsible for successful response to perturbation in our clinical practice for quite some time. We have been particularly interested in older people with diabetic neuropathy since this population is advised to walk for exercise, and yet commonly falls. Traditionally, we looked at hip muscle strength generation and ankle proprioceptive precision to explain unipedal stance time and gait speed. However, against our expectations these neuromuscular attributes did not predict lateral gait variability or the few major injuries sustained by our study participants.

Since the neuromuscular variables were unrevealing, I looked for relationships between step width variability and Simple Reaction Time and Complex Reaction Accuracy using our ReacStick device (see Figure). The ReacStick is a rigid, lightweight rod with a rectangular box at one end. To determine SRT the participant sits with an open hand around the box, and as quickly as possible catches the suspended device, which is dropped at random intervals by the examiner. When determining Complex Reaction Accuracy, the participant catches the device solely when the LED lights illuminate on the housing when dropped during 50% of the trials. If the LED lights do not illuminate then the participant is asked to let the device fall to the floor, requiring a Jedi-quick decision as the ReacStick hits the floor in about 400 msec (an interval similar to the swing phase of gait).

Our results showed that the ratio of Complex Reaction Accuracy to Simple Reaction Time, which rewards accuracy and/or quick reaction, was strongly and inversely associated with uneven surface gait variability in participants suffering from neuropathy (R² = .61). Further, the participants with major fall-related injuries appeared less accurate and slower than those without. The effects were less prominent in the older participants without neuropathy.

The results suggest that people with lower limb neuromuscular impairment rely on neurocognitive speed, as determined by the ability to perceive a stimulus and quickly inhibit a motor response, to maintain postural control when navigating an uneven surface and, possibly, to prevent severe injury in the event of a fall.

The texting young woman likely has a quicker brain… which may be clinically detectable.

Publication

Richardson JK, Eckner JT, Allet LA, Kim H, Ashton-Miller JA. Complex and simple clinical reaction times are associated with gait, balance, and major fall injury in older subjects with diabetic peripheral neuropathy. Am J Phys Med Rehabil 2017;96:8-16.

http://journals.lww.com/ajpmr/Citation/2017/01000/Complex_and_Simple_Clinical_Reaction_Times_Are.2.aspx

About the Author