Effects of aging on whole body and segmental control while obstacle crossing under impaired sensory conditions

The ability to safely negotiate obstacles is an important component of independent mobility, requiring adaptive locomotor responses to maintain dynamic balance. This study examined the effects of aging and visual–vestibular interactions on whole-body and segmental control during obstacle crossing. Twelve young and 15 older adults walked along a straight pathway and stepped over one obstacle placed in their path. The task was completed under 4 conditions which included intact or blurred vision, and intact or perturbed vestibular information using galvanic vestibular stimulation (GVS). Global task performance significantly increased under suboptimal vision conditions. Vision also significantly influenced medial–lateral center of mass displacement, irrespective of age and GVS. Older adults demonstrated significantly greater trunk pitch and head roll angles under suboptimal vision conditions. Similar to whole-body control, no GVS effect was found for any measures of segmental control. The results indicate a significant reliance on visual but not vestibular information for locomotor control during obstacle crossing. The lack of differences in GVS effects suggests that vestibular information is not up-regulated for obstacle avoidance. This is not differentially affected by aging. In older adults, insufficient visual input appears to affect ability to minimize anterior–posterior trunk movement despite a slower obstacle crossing time and walking speed. Combined with larger medial–lateral deviation of the body COM with insufficient visual information, the older adults may be at a greater risk for imbalance or inability to recover from a possible trip when stepping over an obstacle.     

Age effects on the control of dynamic balance during step adjustments under temporal constraints

This study investigated the age effects on the control of dynamic balance during step adjustments under temporal constraints. Fifteen young adults and 14 older adults avoided a virtual white planar obstacle by lengthening or shortening their steps under free or constrained conditions. In the anterior–posterior direction, older adults demonstrated significantly decreased center of mass velocity at the swing foot contact under temporal constraints. Additionally, the distances between the ‘extrapolated center of mass’ position and base of support at the swing foot contact were greater in older adults than young adults. In the mediolateral direction, center of mass displacement was significantly increased in older adults compared with young adults. Consequently, older adults showed a significantly increased step width at the swing foot contact in the constraint condition. Overall, these data suggest that older adults demonstrate a conservative strategy to maintain anterior–posterior stability. By contrast, although older adults are able to modulate their step width to maintain mediolateral dynamic balance, age-related changes in mediolateral balance control under temporal constraints may increase the risk of falls in the lateral direction during obstacle negotiation.     

The contribution of the dorsolateral prefrontal cortex in full and divided encoding: a paired-pulse transcranial magnetic stimulation study

This research investigated the contribution of the dorsolateral prefrontal cortex (DLPFC) in the attentional resources in episodic encoding for both verbal and non-verbal material. Paired-pulse transcranial magnetic stimulations (TMS) were used to interfere transiently with either the left or right DLPFC during encoding under full attention (FA) or under divided attention (DA) in a recognition paradigm using words and random shapes. Participants recognized fewer items after TMS over the left DLPFC than over the right DLPFC during FA encoding. However, TMS over the left DLPFC did not impair performance when compared to sham condition. Conversely, participants produced fewer items after TMS over the right DLPFC in DA encoding compared to sham condition, but not compared to TMS over the left DLPFC. These effects were found for both words and random shapes. These results suggest that the right DLPFC play an important role in successful encoding with a concomitant task regardless of the type of material.     

Face recognition memory: The effects of exposure duration and encoding instruction

Two experiments test the effects of exposure duration and encoding instruction on the relative memory for five facial features. Participants viewed slides of Identi-kit faces and were later given a recognition test with same or changed versions of each face. Each changed test face involved a change in one facial feature: hair, eyes, chin, nose or mouth. In both experiments the upper-face features of hair and eyes were better recognized than the lower-face features of nose, mouth, and chin, as measured by false alarm rates. In Experiment 1, participants in the 20-second exposure duration condition remembered faces significantly better than participants in the 3-second exposure duration condition; however, memory for all five facial features improved at a similar rate with the increased duration. In Experiment 2, participants directed to use feature scanning encoding instructions remembered faces significantly better than participants following age judgement instructions; however, the size of the memory advantage for upper facial features was less with feature scanning instructions than with age judgement instructions. The results are discussed in terms of a quantitative difference in processing faces with longer exposure duration, versus a qualitative difference in processing faces with various encoding instructions. These results are related to conditions that affect the accuracy of eyewitness identification.     

Eye Remember What Happened: Eye‐Closure Improves Recall of Events but not Face Recognition

Eye‐closure improves event recall. We investigated whether eye‐closure can also facilitate subsequent performance on lineup identification (Experiment 1) and face recognition tasks (Experiment 2). In Experiment 1, participants viewed a theft, recalled the event with eyes open or closed, mentally rehearsed the perpetrator's face with eyes open or closed, and viewed a target‐present or target‐absent lineup. Eye‐closure improved event recall, but did not significantly affect lineup identification accuracy. Experiment 2 employed a face recognition paradigm with high statistical power to permit detection of potentially small effects. Participants viewed 20 faces and were later asked to recognize the faces. Thirty seconds before the recognition task, participants either completed an unrelated distracter task (control condition), or were instructed to think about the face with their eyes open (rehearsal condition) or closed (eye‐closure condition). We found no differences between conditions in discrimination accuracy or response criterion. Potential explanations and practical implications are discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Evaluating the Acute Contributions of Dopaminergic Replacement to Gait With Obstacles in Parkinson's Disease

The influence of dopaminergic replacement (DR) on gait in people with Parkinson's disease (PD) is well documented. However, little is known about the acute effects of dopamine on more complex locomotor tasks that require visual guidance to avoid obstacles during gait. The authors investigated the influence of DR on locomotor behavior in a task where movement planning and control might be challenged by the height of the obstacle. The PD group included patients diagnosed with idiopathic PD (n = 12), as well as healthy controls (n = 12). Patients walked and stepped over obstacles of different heights before (OFF) and after (ON) levodopa intake. Spatial adjustments were not modulated by DR, but the step time to perform these anticipatory gait adjustments was longer only in PD-OFF (compared with healthy controls) when approaching the highest obstacle, but not PD-ON. During the crossing phase, trail limb toe clearance of PD patients was shorter than healthy controls only during the OFF state. ON-OFF comparisons were significantly different only for the time to reach the lead foot clearance over the highest obstacle. In summary, DR partially improved movement slowness but did not directly affect movement amplitude of lower limb regulation in this gait task.     

Saccade-stepping interactions revise the motor plan for obstacle avoidance

The authors used a stimulus-response compatibility paradigm to assess the effect of changing the estimated time to obstacle contact. A limb-selection cue was presented in different phases of gait to young (n = 5) and to older (n = 4) adults while they were moving toward a foam obstacle in the walking path. A downward saccade was initiated after the cue; the saccade typically occurred during the stance phase of the target limb (the foot cued to lead the step over the obstacle). The mean saccade-step latency after the cue was on the order of -500 ms in both young and elderly participants. On reaching the obstacle, both groups generated an upward saccade approximately -300 ms before target footlift in both groups. Saccades following the limb-selection cue appeared to direct the gaze toward footfall targets just beyond the obstacle, whereas saccades generated just before obstacle footlift moved the gaze to the forward-looking direction. The elderly had significantly longer saccade-trailing-footlift latencies and prolonged gaze-fixation times than did the younger adults. Transient disruptions in optical flow appeared to be necessary for successful obstacle-avoidance behavior when there was an unexpected change in the estimated time to obstacle contact.     

Eye remember you: the effects of gaze direction on face recognition in children and adults

Children and adults were tested on a forced‐choice face recognition task in which the direction of eye gaze was manipulated over the course of the initial presentation and subsequent test phase of the experiment. To establish the effects of gaze direction on the encoding process, participants were presented with to‐be‐studied faces displaying either direct or deviated gaze (i.e. encoding manipulation). At test, all the faces depicted persons with their eyes closed. To investigate the effects of gaze direction on the efficiency of the retrieval process, a second condition (i.e. retrieval manipulation) was run in which target faces were presented initially with eyes closed and tested with either direct or deviated gaze. The results revealed the encoding advantages enjoyed by faces with direct gaze was present for both children and adults. Faces with direct gaze were also recognized better than faces with deviated gaze at retrieval, although this effect was most pronounced for adults. Finally, the advantage for direct gaze over deviated gaze at encoding was greater than the advantage for direct gaze over deviated gaze at retrieval. We consider the theoretical implications of these findings.     

Effects of explicit sway-minimization on postural--suprapostural dual-task performance

Participants performed a visual search task under immersive visualization conditions while standing in open or closed stance. In the combined instruction condition, participants were asked to minimize their sway while they performed the search task, and in the search-only condition, they were advised that sway was not of interest, and they were asked to focus their efforts on performing the search task. Regardless of instructions, participants swayed more and made more errors as search load increased. Participants also succeeded in reducing their sway when asked to do so. While search in closed stance tended to be faster than in open stance under search-only instructions, this pattern reversed significantly under combined instructions. We suggest that neither the facilitatory control hypothesis nor any resource-competition model of postural--suprapostural dual-tasking can fully account for the observed interplay of task-facilitation and task-interference effects. We offer adaptive resource-sharing as an alternative to these theories.     

The effect of moving and static trans-scleral illumination of visual afterimages

The inside of the eye was illuminated by shining a small light through the upper eyelid and the sclera. After viewing a bright light flash, Ss closed their eyes and reported the duration of the afterimage under the following conditions: the light on and moving across the S’s eyelid (moving trans-scleral illumination), the light on but stationary (static trans-scleral illumination), and two corresponding control conditions in which the light was turned off (darkness). Results indicate that when the trans-scleral light is moving, afterimages are seen clearly for periods of approximately the same duration as those seen in complete darkness. However, when the trans-scleral illumination is stationary, the duration of the afterimages is significantly reduced. These results are compatible with other afterimage data that suggest that changes within the field after initial stimulation are needed to prolong afterimages.     

I Spy With My Dominant Eye

The authors investigated how visual information from the nondominant and dominant eyes are utilized to control ongoing dominant hand movements. Across 2 experiments, participants performed upper-limb pointing movements to a stationary target or an imperceptibly shifted target under monocular-dominant, monocular-nondominant, and binocular viewing conditions. Under monocular-dominant viewing conditions, participants exhibited better endpoint precision and accuracy. On target jump trials, participants spent more time after peak limb velocity and significantly altered their trajectories toward the new target location only when visual information from the dominant eye was available. Overall, the results suggest that the online visuomotor control processes that typically take place under binocular viewing conditions are significantly influenced by input from the dominant eye.     

Saccade-Stepping Interactions Revise the Motor Plan for Obstacle Avoidance

The authors used a stimulus-response compatibility paradigm to assess the effect of changing the estimated time to obstacle contact. A limb-selection cue was presented in different phases of gait to young (n = 5) and to older (n = 4) adults while they were moving toward a foam obstacle in the walking path. A downward saccade was initiated after the cue; the saccade typically occurred during the stance phase of the target limb (the foot cued to lead the step over the obstacle). The mean saccade-step latency after the cue was on the order of ?500 ms in both young and elderly participants. On reaching the obstacle, both groups generated an upward saccade approximately ?300 ms before target footlift in both groups. Saccades following the limb-selection cue appeared to direct the gaze toward footfall targets just beyond the obstacle, whereas saccades generated just before obstacle footlift moved the gaze to the forward-looking direction. The elderly had significantly longer saccade-trailing-footlift latencies and prolonged gaze-fixation times than did the younger adults. Transient disruptions in optical flow appeared to be necessary for successful obstacle-avoidance behavior when there was an unexpected change in the estimated time to obstacle contact.     

Eye remember you two: gaze direction modulates face recognition in a developmental study

The effects of gaze direction on memory for faces were studied in children from three different age groups (6-7, 8-9, and 10-11 years old) using a computerized version of a task devised by Hood, Macrae, Cole-Davies and Dias (2003). Participants were presented with a sequence of faces in an encoding phase, and were then required to judge which faces they had previously encountered in a surprise two-alternative forced-choice recognition test. In one condition, stimulus eye gaze was either direct or deviated at the viewing phase, and eyes were closed at the test phase. In another condition, stimulus eyes were closed at the viewing phase, with either direct or deviated gaze at the test phase. Modulation of gaze direction affected hit rates, with participants demonstrating greater accuracy for direct gaze targets compared to deviated gaze targets in both conditions. Reaction times (RT) to correctly recognized stimuli were faster for direct gaze stimuli at the viewing phase, but not at the test phase. The age group of participants differentially affected these measures: there was a greater hit rate advantage for direct gaze stimuli in older children, although RTs were less affected by age. These findings suggest that while the facilitation of face recognition by gaze direction is robust across encoding and recognition stages, the efficiency of the process is affected by the stage at which gaze is modulated.     

Effect of narrowing the base of support on the gait,gaze and quiet eye of elite ballet dancers and controls

We determined the gaze and stepping behaviours of elite ballet dancers and controls as they walked normally and along progressively narrower 3-m lines (l0.0, 2.5 cm). The ballet dancers delayed the first step and then stepped more quickly through the approach area and onto the lines, which they exited more slowly than the controls, which stepped immediately but then slowed their gait to navigate the line, which they exited faster. Contrary to predictions, the ballet group did not step more precisely, perhaps due to the unique anatomical requirements of ballet dance and/or due to releasing the degrees of freedom under their feet as they fixated ahead more than the controls. The ballet group used significantly fewer fixations of longer duration, and their final quiet eye (QE) duration prior to stepping on the line was significantly longer (2,353.39 ms) than the controls (1,327.64 ms). The control group favoured a proximal gaze strategy allocating 73.33% of their QE fixations to the line/off the line and 26.66% to the exit/visual straight ahead (VSA), while the ballet group favoured a ‘look-ahead’ strategy allocating 55.49% of their QE fixations to the exit/VSA and 44.51% on the line/off the line. The results are discussed in the light of the development of expertise and the enhanced role of fixations and visual attention when more tasks become more constrained.     

Just a minute meditation: Rapid voluntary conscious state shifts in long term meditators

Meditation induces a modified state of consciousness that remains under voluntary control. Can meditators rapidly and reversibly bring about mental state changes on demand? To check, we carried out 128 channel EEG recordings on Brahma Kumaris Rajayoga meditators (36 long term: median 14240 h meditation; 25 short term: 1095 h) and controls (25) while they tried to switch every minute between rest and meditation states in different conditions (eyes open and closed; before and after an engaging task). Long term meditators robustly shifted states with enhanced theta power (4–8 Hz) during meditation. Short term meditators had limited ability to shift between states and showed increased lower alpha power (8–10 Hz) during eyes closed meditation only when pre and post task data were combined. Controls could not shift states. Thus trained beginners can reliably meditate but it takes long term practice to exercise more refined control over meditative states.     

Changes of Gait Kinematics in Different Simulators of Reduced Gravity

Gravity reduction affects the energetics and natural speed of walking and running. But, it is less clear how segmental coordination is altered. Various devices have been developed in the past to study locomotion in simulated reduced gravity. However, most of these devices unload only the body center of mass. The authors reduced the effective gravity acting on the stance or swing leg to 0.16g using different simulators. Locomotion under these conditions was associated with a reduction in the foot velocity and significant changes in angular motion. Moreover, when simulated reduced gravity directly affected the swing limb, it resulted in significantly slower swing and longer foot excursions, suggesting an important role of the swing phase dynamics in shaping locomotor patterns.     

Sustained attention can create an (illusory) experience of seeing dynamic change

Recent studies speculated that two types of change detection exist, one involving the experience of seeing dynamic change (change over brief interval), the other involving detecting a completed change (change over long interval), with only the former requiring sustained attention. To examine this supposition, a flicker change detection task was conducted in which the spatial location of objects was manipulated (shift, no-shift). In shift conditions, changed image display appeared in different locations than they did in the original display. The time interval separating images was manipulated (200 or 1000 ms). Results showed that a shift led to poor change detection only in the short interval condition. The performance decline by the image shift was not attenuated even when participants knew beforehand whether or not a shift would occur. Results indicate that sustained attention, which is sustained for a brief time, is related to the experience of seeing dynamic change.     

Prospective dynamic balance control during the swing phase of walking: Stability boundaries and time-to-contact analysis

This study examined the prospective control of the swing phase in young healthy adults while walking at preferred speed over unobstructed ground and during obstacle clearance. Three aspects of swing were examined: (1) the relation of the body Center of Mass (CoM) to the stability boundaries at the base of support; (2) a dynamic time-to-contact analysis of the CoM and swing foot to these boundaries; and (3) the role of head movements in the prospective control of gait and field of view assessment. The time-to-contact analysis of CoM and swing foot showed less stable swing dynamics in the trail foot compared to the lead foot in the approach to the unstable equilibrium, with the CoM leading the swing foot and crossing the anterior stability boundary before the swing foot. Compensations in temporal coupling occurred in the trail limb during the late swing phase. Time-to-contact analysis of head movement showed stronger prospective control of the lead foot, while fixation of the field of view occurred earlier in swing and was closer to the body in the obstacle condition compared to unobstructed walking. The dynamic time-to-contact analysis offers a new approach to assessing the unstable swing phase of walking in different populations.     

产品空间位置、价格音节长度对消费者价格感知的影响

本研究采用实验法考察了视听单通道及双通道下产品空间位置与价格音节长度对消费者价格感知的潜在影响。结果发现,呈现在空间右侧以及以较长音节播放的产品使得被试的价格感知升高;短音节条件下,个体对空间右侧产品的价格感知显著高于空间左侧,长音节条件下两侧则无显著差异;相对于单通道刺激呈现,视听通道呈现信息一致时出现信息冗余效应,个体判断的速度更快,验证了共激活模型假设,视听不一致条件下的速度降低则支持了预测编码模型。     

Look away! Eyes and arrows engage oculomotor responses automatically

The present study investigates how people’s voluntary saccades are influenced by where another person is looking, even when this is counterpredictive of the intended saccade direction. The color of a fixation point instructed participants to make saccades either to the left or right. These saccade directions were either congruent or incongruent with the eye gaze of a centrally presented schematic face. Participants were asked to ignore the eyes, which were congruent only 20% of the time. At short gaze—fixation-cue stimulus onset asynchronies (SOAs; 0 and 100 msec), participants made more directional errors on incongruent than on congruent trials. At a longer SOA (900 msec), the pattern tended to reverse. We demonstrate that a perceived eye gaze results in an automatic saccade following the gaze and that the gaze cue cannot be ignored, even when attending to it is detrimental to the task. Similar results were found for centrally presented arrow cues, suggesting that this interference is not unique to gazes.