Visual cues two-steps ahead are adequate to grasp an object while walking without compromising stability

In our prior studies, participants walked and grasped a dowel using an anticipatory mode of control. However, it is unknown how this combined task would change in a less predictable environment. We investigated the online control aspects involved in the combined task of walking and grasping under different coordination patterns between upper- and lower-limbs in young adults. Fifteen young adults walked and grasped a dowel under several experimental conditions combining the instant of visual cue appearance and coordination pattern of upper and lower limbs used to grasp the dowel. Visual cues provided two steps ahead or earlier were enough for executing the combined task of walking and prehension appropriately. Visual cues provided within this window impacted both walking stability and the execution of the prehension movement. Although an ipsilateral arm-leg coordination pattern increased mediolateral stability, a contralateral pattern significantly decreased mediolateral center of mass stability when the visual cue appeared one-step before grasping the object. These results imply that acquiring information to plan the combined task of walking and reaching for an object two steps ahead allows the maintenance of the general movement characteristics present when the decision to reach out for the object is defined two or more steps ahead. These results indicate that the prehension movement is initiated well before heel contact on that side when given sufficient planning time, but that a disruption of the natural arm-leg coordination dynamics emerges to accomplish the task when the cue is provided one step before the object.     

Reaching while walking: Reaching distance costs more than walking distance

Surprisingly little is known about how people plan and control everyday physical actions, such as walking along and picking up objects. In order to explore this topic, we conducted an experiment in which university students were asked to pick up a common object (a child’s beach bucket) that stood on a table several meters from the participant’s start position. The bucket stood either on the left side, in the middle, or on the right side of the table and, depending on instructions, was to be carried to a farther target whose horizontal position was also varied. The questions were which side of the table the participant would walk along when picking up the bucket and which hand the participant would use to pick up and carry the bucket. Participants, most of whom were righthanded, preferred to walk along the left side of the table and to pick up the bucket with the right hand, although they departed from that preference when the reaching distance across the table was uncomfortable or if the target was too far to the right. The data were well fit with a mathematical model that included a right-hand bias and an estimate of functional distance that expressed the cost of reaching over some distance as approximately twice the cost of walking over the same distance.     

Memorizing while walking: increase in dual-task costs from young adulthood to old age

The dual task of memorizing word lists while walking was predicted to become more difficult with age because balance and gait are in greater need of "attentional resources." Forty-seven young (ages 20-30 years), 45 middle-aged (40-50), and 48 old (60-70) adults were trained to criterion in a mnemonic technique and instructed to walk quickly and accurately on 2 narrow tracks of different path complexity. Then. participants encoded the word lists while sitting, standing, or walking on either track; likewise, speed and accuracy of walking performance were assessed with and without concurrent memory encoding. Dual-task costs increased with age in both domains; relative to young adults, the effect size of the overall increase was 0.98 standard deviation units for middle-aged and 1.47 standard deviation units for old adults. It is argued that sensory and motor aspects of behavior are increasingly in need of cognitive control with advancing age.     

Cost of transport at preferred walking speeds are minimized while walking on moderately steep incline surfaces

Research has shown that preferred walking speed results in a minimization of the cost of transport on flat surfaces. However, it has also been shown that over non-smooth surfaces other variables, such as stability, are necessary for task completion increasing the cost of transport. The purpose of this research was to investigate the effect of incline walking on the cost of transport, assessing the effect of raising the center of mass as a potential variable affecting preferred walking speed, such that the cost of transport is no longer minimized. 12 healthy, college-aged male participants completed walking trials on a treadmill at inclines of 0%, 5%, 10%, 15%, and 20% at three different continuous speeds (1mph, 2mph and 3mph) and a preferred walking speed for 4–5 min. Cost of transport was calculated using the oxygen consumption collected during the last minute of each stage. Up to 20% incline, the cost of transport was lowest on each incline for the preferred walking speed trials. On inclines greater than 20%, many participants were unable to complete the task with respiratory exchange ratios less than 1.0. We conclude that inclines up to 20% do not induce an alternative challenge affecting the established relationship that humans prefer to walk at speeds that minimize the cost of transport despite the increased need to raise the center of mass.     

Sensitivity of early human vision to 3-D orientation in line-drawings.

The modern "textbook" view of visual perception contains an inherent paradox. On the one hand, it claims that relatively simple edge-extraction processes requires a stimulus exposure of approximately 50 ms. On the other hand, it says that the identification of objects in photographs and line-drawings can be highly accurate with exposure durations as short as 100 ms. It is tempting to conclude that all the difficult work of perception occurs in the 50 ms that elapse between when these two tasks are accomplished. This article argues against this view, suggesting instead that much more than edge-extraction is accomplished by the early visual processes. To illustrate this view, a computational model is described that is capable of recovering the 3-D orientation of objects from some line-drawings, rapidly and in parallel. Data from recent visual search experiments with human observers are presented in support of this model and the implications of this view for the "textbook" view are discussed.     

Crossing without vision of path gaps

Two experiments considered the behavior of subjects who cross gaps in a pathway without benefit of vision. The first experiment contrasted visually and nonvisually guided locomotion, finding a significantly greater number of refusals under nonvisual guidance but no loss of appropriate modulation of step components to the salient dimensions of the actor and layout. Different components of crossing were modified under guidance of different sensory systems; the lengths of the crossing and support spans were primarily altered under nonvisual guidance, and the distance of the support foot to the near edge of the gap was the component of preference under visual guidance. In the second experiment, subjects crossed nonvisually, using probes that varied in length and moment of inertia. The adaptability of the step components to actor and layout dimensions was unchanged, but there was no effect of these mechanical manipulations on the components of crossing identified in Experiment 1.     

Sensitivity to grammatical structure in so-called agrammatic aphasics

Comprehension failures in agrammatic aphasics, as well as their difficulties in sentence construction, have been attributed to an underlying deficit involving the retrieval of syntactic structure. In this study we show that four agrammatic patients display a remarkable sensitivity to structural information, as indicated by their performance on a grammaticality judgment task. These results indicate significant sparing of syntactic knowledge in agrammatism, and suggest that the sentence comprehension disturbances in these patients do not reflect loss of the capacity to recover syntactic structure. In particular, accounts of the comprehension deficit in agrammatism that implicate a failure to exploit information carried by the closed class (function word) vocabulary are called seriously into question. Alternative explanations of the comprehension problem in agrammatism are explored.     

Sensitivity to pictorial shape perspective in 5-year-old children and adults

Five-year-old children’s and adults’ sensitivity to shape perspective was tested with relative length judgments of two crossed lines on the surface of a tilted “box.” The stimuli were presented in both slides and three-dimensional viewing conditions. Judgments in the three-dimensional condition corresponded closely to the actual three-dimensional lengths. Responses in the slide-viewing condition were similar for both age groups, and showed about a one-third regression toward picture-plane length judgments. The lack of age effects was considered with respect to theories of the development of sensitivity to shape perspective.     

Sensitivity to inflectional morphology in aphasia: A real-time processing perspective

The present study investigates Broca's aphasics' sensitivity to morphological information in an on-line task. German is used as the test language because it is highly inflected. Results from two word monitoring experiments show first that Broca's patients like normal controls are sensitive to the presence of a contextually incorrect inflection. Contrary to normals, they are, however, not sensitive to the absence of an obligatory inflection even when its presence is syntactically highly constrained. Second, they reveal that Broca's aphasics are only sensitive to the presence of an incorrect inflection when it functions as a marker of lexical category (noun vs. verb) and not when it functions as a diacritical marker (second person singular vs. third person singular). The results are taken as evidence for the claim that Broca's aphasics are impaired in the ability to process the full syntactic information encoded in closed class elements in a fast, automatic, and obligatory way.     

The effect of instruction to synchronize over step frequency while walking with auditory cues on a treadmill

Walking to a pacing stimulus has proven useful in motor rehabilitation, and it has been suggested that spontaneous synchronization could be preferable to intentional synchronization. But it is still unclear if the paced walking effect can occur spontaneously, or if intentionality plays a role. The aim of this work is to analyze the effect of sound pacing on gait with and without instruction to synchronize, and with different rhythmic auditory cues, while walking on a treadmill.Firstly, the baseline step frequency while walking on a treadmill was determined for all participants, followed by experimental sessions with both music and footstep sound cues. Participants were split into two groups, with one being instructed to synchronize their gait to the auditory stimuli, and the other being simply told to walk. Individual auditory cues were generated for each participant: for each trial, cues were provided at the participant’s baseline walking frequency, at 5% and 10% above baseline, and at 5% and 10% below baseline.This study’s major finding was the role of intention on synchronization, given that only the instructed group synchronized their gait with the auditory cues. No differences were found between the effects of step or music stimuli on step frequency.In conclusion, without intention or cues that direct the individual’s attention, spontaneous gait synchronization does not occur during treadmill walking.     

Enhanced optic flow speed discrimination while walking: contextual tuning of visual coding

We tested the hypothesis that long-term adaptation to the normal contingencies between walking and its multisensory consequences (including optic flow) leads to enhanced discrimination of appropriate visual speeds during self-motion. In experiments 1 (task 1) and 2 a two-interval forced-choice procedure was used to compare the perceived speed of a simulated visual flow field viewed while walking with the perceived speed of a flow field viewed while standing. Both experiments demonstrated subtractive reductions in apparent speed. In experiments 1 and 3 discrimination thresholds were measured for optic flow speed while walking and while standing. Consistent with the optimal-coding hypothesis, speed discrimination for visual speeds near walking speed was enhanced during walking. Reduced sensitivity was found for slower visual speeds. The multisensory context of walking alters the coding of optic flow in a way that enhances speed discrimination in the expected range of flow speeds.     

Sensitivity to prosodic structure in left- and right-hemisphere-damaged individuals

An experiment was conducted in order to determine whether left- (LHD) and right-hemisphere-damaged (RHD) patients exhibit sensitivity to prosodic information that is used in syntactic disambiguation. Following the work of, a cross-modal lexical decision task was performed by LHD and RHD subjects, as well as by adults without brain pathology (NC). Subjects listened to sentences with attachment ambiguities with either congruent or incongruent prosody, while performing a visual lexical decision task. Results showed that each of the unilaterally damaged populations differed from each other, as well as from the NCs in terms of sensitivity regarding prosodic cues. Specifically, the RHD group was insensitive to sentence prosody as a whole. This was in contrast to the LHD patients, who responded to the prosodic manipulation, but in the unexpected direction. Results are discussed in terms of current hypotheses regarding the hemispheric lateralization of prosodic cues.     

The role of central and peripheral vision in postural control during walking

Three hypotheses have been proposed for the roles of central and peripheral vision in the perception and control of self-motion: (1) peripheral dominance, (2) retinal invariance, and (3) differential sensitivity to radial flow. We investigated postural responses to optic flow patterns presented at different retinal eccentricities during walking in two experiments. Oscillating displays of radial flow (0 degree driver direction), lamellar flow (90 degrees), and intermediate flow (30 degrees, 45 degrees) patterns were presented at retinal eccentricities of 0 degree, 30 degrees, 45 degrees, 60 degrees, or 90 degrees to participants walking on a treadmill, while compensatory body sway was measured. In general, postural responses were directionally specific, of comparable amplitude, and strongly coupled to the display for all flow patterns at all retinal eccentricities. One intermediate flow pattern (45 degrees) yielded a bias in sway direction that was consistent with triangulation errors in locating the focus of expansion from visible flow vectors. The results demonstrate functionally specific postural responses of both central and peripheral vision, contrary to the peripheral dominance and differential sensitivity hypotheses, but consistent with retinal invariance. This finding emphasizes the importance of optic flow structure for postural control regardless of the retinal locus of stimulation.     

Visual perception and the guidance of locomotion without vision to previously seen targets

Two experiments were performed to assess the accuracy and precision with which adults perceive absolute egocentric distances to visible targets and coordinate their actions with them when walking without vision. In experiment 1 subjects stood in a large open field and attempted to judge the midpoint of self-to-target distances of between 4 and 24 m. In experiment 2 both highly practiced and unpracticed subjects stood in the same open field, viewed the same targets, and attempted to walk to them without vision or other environmental feedback under three conditions designed to assess the effects on accuracy of time-based memory decay and of walking at an unusually rapid pace. In experiment 1 the visual judgments were quite accurate and showed no systematic constant error. The small variable errors were linearly related to target distance. In experiment 2 the briskly paced walks were accurate, showing no systematic constant error, and the small, variable errors were a linear function of target distance and averaged about 8% of the target distance. Unlike Thomson's (1983) findings, there was not an abrupt increase in variable error at around 9 m, and no significant time-based effects were observed. The results demonstrate the accuracy of people's visual perception of absolute egocentric distances out to 24 m under open field conditions. The accuracy of people's walking without vision to previously seen targets shows that efferent and proprioceptive information about locomotion is closely calibrated to visually perceived distance. Sensitivity to the correlation of optical flow with efferent/proprioceptive information while walking with vision may provide the basis for this calibration when walking without vision.     

Reliability of forward head posture evaluation while sitting,standing, walking and running

Forward head posture has been evaluated mostly by visual observation or simple non-invasive measurements without a standardized evaluation method or protocol. In this experimental study, the reliability of existing forward head-posture measurement methods was evaluated by computing the intra-class correlation coefficients of three different head-position variables (two horizontal gap variables and one head-orientation variable) in seven different posture conditions from 20 asymptomatic participants. The position variables of the head were measured three times using a three-dimensional motion capture system while sitting comfortably, sitting with the back straight, standing comfortably, standing with the back straight, walking at 4 and 6 km/h on a treadmill, and running at 8 km/h on a treadmill. Intra-class correlation coefficients between repetitive measures ranged from 0.81 to 0.96, and high correlation coefficient values (>0.9) were produced when the head-position variables were measured during straight sitting, straight standing, and walking at 6 km/h. Among the three head-position variables, a horizontal gap between the tragus and the 7th cervical vertebra was recorded more consistently than other variables. Results of this study highlight the importance of a standardized evaluation protocol for more reliable assessment of the forward head posture.     

Rapid serial visual presentation display on a small screen: reading Chinese while walking

This study examined the effects of presentation unit (word-by-word or single line) and presentation duration [171, 213, 240, and 308 msec. per character (msec./C)] on the comprehension of Chinese rapid serial visual presentation (RSVP) displays read from the small screen of a mobile phone in three different contexts (seated, walking on a treadmill, and walking through an outdoor course). 30 native Chinese readers ages 19 to 26 were recruited as participants. Scores on reading comprehension showed that presentation unit and presentation duration significantly affected reading comprehension, and interactions between factors were also significant. When the presentation unit was word-by-word, no significant difference in reading comprehension was observed under different presentation durations. However, when the presentation unit was a single line, reading comprehension deteriorated with the shortest presentation duration of 171 msec./C. With regard to context, participants had a higher mean reading comprehension score in the seated context than in walking contexts, but the difference was not significant.     

Adaptations to walking on an uneven terrain for individuals with and without Developmental Coordination Disorder

Given the importance of walking in everyday life, understanding why this is challenging for some populations is particularly important. Studies focusing on gait patterns of individuals with Developmental Coordination Disorder (DCD) have shown that whilst increased variability is characteristic of walking patterns for this group, differences in spatio-temporal gait variables seem only to arise when task demands increase. However, these differences occur under rather artificial conditions, for example using a treadmill. The aim of this study, therefore was to examine the step characteristics of individuals with and without DCD whilst walking along an irregular terrain. Thirty-five individuals with DCD aged 8–32 years and 35 age and gender-matched controls participated in this study. Participants were divided into 3 age groups; 8–12 years (n = 12), 13–17 years (n = 12) and 18–32 years (n = 11). Participants walked up and down a 6 m walkway for two minutes on two terrains: level and irregular. VICON 3D motion analysis was used to extract measures of foot placement, velocity and angle of the head and trunk. Results showed that both groups adapted their gait to negotiate the irregular terrain, but the DCD group was more affected than their TD peers; walking significantly slower with shorter, wider steps and inclining their head more towards the ground. This suggests an adaptive approach used by individuals with DCD to preserve stability and increase visual sampling whilst negotiating an irregular terrain.