Saccade-Stepping Interactions Revise the Motor Plan for Obstacle Avoidance

Fabio, Richard P. Di; Greany, John; Zampieri, Cris

doi:10.1080/00222890309603158

Cited by 49 publications

(36 citation statements)

References 36 publications

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“…Re-direction of visual Wxation was made to the landing area in compensatory stepping reactions following platform translation as well (Zettel et al 2005), albeit infrequent, and Patla and Vickers (1997) have shown when the ART is long information regarding the obstacle is acquired in the steps before crossing but peripheral vision of the obstacle and crossing limb is suYcient to perform the task: Wxations are directed to the landing area during the cross-over step. This has been supported more recently by Di Fabio et al (2003a). Interestingly, in a later study with older adults Di Fabio et al (2005) reported a reduction in the frequency of down saccades in high-risk cognitively challenged older adults initiating obstacle step-over.…”

Section: Bfisupporting

confidence: 52%

“…Di Fabio et al (2003b) argue stepping movements use this visual anchoring behavior, proposed by Johansson et al (2001) for object manipulation, and hence saccadic eye movements are linked to stepping. Studies on obstacle avoidance suggest that visual input is utilized during the approach phase, which is evident from visual Wxations directed to the obstacle (Patla and Vickers 1997) or downward saccades made to an area behind the obstacle following a cue as to which limb to initiate the step over the obstacle (Di Fabio et al 2003a). However, peripheral vision is suYcient while stepping over the obstacle as Wxation is directed to the landing area (Patla and Vickers 1997) or upward saccades are made to adjust gaze to a forward looking direction (Di Fabio et al 2003a) and not the obstacle during the cross-over phase.…”

Section: Introductionmentioning

confidence: 99%

“…Studies on obstacle avoidance suggest that visual input is utilized during the approach phase, which is evident from visual Wxations directed to the obstacle (Patla and Vickers 1997) or downward saccades made to an area behind the obstacle following a cue as to which limb to initiate the step over the obstacle (Di Fabio et al 2003a). However, peripheral vision is suYcient while stepping over the obstacle as Wxation is directed to the landing area (Patla and Vickers 1997) or upward saccades are made to adjust gaze to a forward looking direction (Di Fabio et al 2003a) and not the obstacle during the cross-over phase. Patla and Vickers (2003) have also shown that individuals Wxate two steps ahead when walking on speciWc targets in the travel path, whereas Hollands et al (1995) showed that just prior to every step onto a target horizontal saccadic eye movements directed to the stepping area occurred.…”

Section: Introductionmentioning

confidence: 99%

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Keep looking ahead? Re-direction of visual fixation does not always occur during an unpredictable obstacle avoidance task

et al. 2006

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Visual information about the environment, especially Wxation of key objects such as obstacles, is critical for safe locomotion. However, in unpredictable situations where an obstacle suddenly appears it is not known whether central vision of the obstacle and/or landing area is required or if peripheral vision is suYcient. We examined whether there is a re-direction of visual Wxation from an object Wxated ahead to a suddenly appearing obstacle during treadmill walking. Furthermore, we investigated the temporal relationship between the onset of muscle activity to avoid the obstacle and saccadic eye and head movements to shift Wxation. Eight females (mean § SD; age = 24.8 § 2.3 years) participated in this experiment. There were two visual conditions: a central vision condition where participants Wxated on two obstacles attached to a bridge on the treadmill and a peripheral vision condition where participants Wxated an object two steps ahead. There were two obstacle release conditions: only an obstacle in front of the left foot was released or an obstacle in front of either foot could be released. Only trials when the obstacle was released in front of the left foot were analyzed such that the diVerence in the two obstacle conditions was whether there was a choice of which foot to step over the obstacle. Obstacles were released randomly in one of three phases during the step cycle corresponding to available response times between 219 and 462 ms. We monitored eye and head movements along with muscle activity and spatial foot parameters. Performance on the task was not diVerent between vision conditions. The results indicated that saccades are rarely made (< 18% of trials) and, when present, are initiated » 350 ms after muscle activity for limb elevation, often accompanied by a downward head movement, and always directed to the landing area. Therefore, peripheral vision of a suddenly appearing obstacle in the travel path is suYcient for successful obstacle avoidance during locomotion: visual Wxation is generally not re-directed to either the obstacle or landing area.

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Section: Bfisupporting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Keep looking ahead? Re-direction of visual fixation does not always occur during an unpredictable obstacle avoidance task

et al. 2006

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“…He et al [34] showed that the resolution of attention was better in the lower versus upper visual field (measured by a greater percentage of correct responses). Their findings could not be due to a neuroanatomical infrastructure since functional magnetic resonance imaging shows roughly equal representations of the upper and lower visual fields in the primary motor cortex [34].…”

Section: Discussionmentioning

confidence: 99%

“…The requirement to step over an obstacle once the visual stimulus location was detected facilitated a down-saccade prior to initiating the step. The 'saccade-stepping' sequence has been observed previously in both young and elderly people and is a component of a feedforward motor program that controls stepping behaviors [34,48]. It is important to note that the down-saccade after the stimulus had been extinguished was acceptable and was used as a 'limb-independent' measure of RT that signaled the onset of a stepping motor program (see the statistical analysis).…”

Section: Experiments Nomentioning

confidence: 99%

Influence of Elderly Executive Cognitive Function on Attention in the Lower Visual Field during Step Initiation

Fabio¹,

Zampieri²,

Henke³

et al. 2005

Gerontology

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Background: There is a well-established relationship between poor executive cognitive abilities and elderly fall risk, but the precise mechanism underlying this relationship is unknown. Older persons frequently fall or trip on objects below eye level, and it was hypothesized that the pathological mechanism linking low executive function and fall risk is a selective impairment in the resolution of visual attention in the lower visual fields. Objective: To determine ifnormally sighted older persons living in the community with deficits in executive cognitive abilities have a reduced resolution of visual attention in the lower visual fields compared to elderly and younger subjects with high executive abilities. Methods: Eye and head angulations were monitored as subjects fixated on a point rear-projected at eye level at the end of a 3- meter walkway. Visual stimuli were briefly presented (<300 ms) in the peripheral visual field (with and without distractors) to directly cue the selection of the right or left foot to lead a step over a foam obstacle resting at the subject’s feet. No saccades were allowed until the stimulus was extinguished, at which time a down-saccade-step sequence moved the foot over the obstacle. The resolution of visual attention (tested with gratings) and the influence of target eccentricity in the upper and lower visual fields were evaluated. The primary outcome measures were step error and obstacle contact rate, saccade occurrence after extinguished stimulus and the log of cue-saccade latency (limb-independent reaction time). Results: All groups experienced greater stepping errors than expected by chance when stimuli were presented in the lower versus upper visual field and with increasing eccentricity. However, the obstacle contact rate was greater, cue-saccade latency was prolonged, and fewer down-saccades were generated in the elderly group with poor executive abilities compared to those with high executive function and younger subjects. Conclusions: Loss of visual attention in the lower visual fields was not unique to elderly subjects with poor executive function. However, slowed processing time and reduction in the frequency of down-saccades associated with a low level of executive function potentially account for the mechanism linking executive abilities and fall risk.

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