On-Line Updating of Spatial Information Druing Locomotion Without Vision

Two experiments are reported in which the control of locomotion without vision was investigated. In Experiment 1, subjects (N = 10) made similar, although less functional, locomotor adjustments when walking without vision to a target than they did when walking with vision. That result suggests that while walking without vision, the subjects updated their positions on-line with respect to a representation of the target rather than operating from a preformulated action plan. In Experiment 2, there was a significant weakening and loss of functionality of the locomotor adjustments when subjects (N = 10) had to walk without vision the correct distance to the target but in a direction opposite to its true location, as compared with when they walked without vision directly to the target. That finding suggests that the subjects were nonvisually updating their positions not with respect to an abstract representation of the target's distance but with respect to a representation of its relative location within the task environment.     

A comparison of visual and nonvisual sensory inputs to walked distance in a blind-walking task

Two experiments were conducted in order to assess the contribution of locomotor information to estimates of egocentric distance in a walking task. In the first experiment, participants were either shown, or led blind to, a target located at a distance ranging from 4 to 10 m and were then asked to indicate the distance to the target by walking to the location previously occupied by the target. Participants in both the visual and locomotor conditions were very accurate in this task and there was no significant difference between conditions. In the second experiment, a cue-conflict paradigm was used in which, without the knowledge of the participants, the visual and locomotor targets (the targets they were asked to walk to) were at two different distances. Most participants did not notice the conflict, but despite this their responses showed evidence that they had averaged the visual and locomotor inputs to arrive at a walked estimate of distance. Together, these experiments demonstrate that, although they showed poor awareness of their position in space without vision, in some conditions participants were able to use such nonvisual information to arrive at distance estimates as accurate as those given by vision.     

The effect of perceived locomotor constraints on distance estimation

Two experiments were conducted to examine the ways in which the visual estimation of distance to a target is affected by constraints perceived to be placed on the subsequent locomotion to the target without vision. We hypothesized that an appraisal of impending effort would play a role in ascertaining the distance to be walked. In Experiment 1, the amount of resistance to walking was variable and unpredictable. One group of subjects performed against relatively low resistance, whereas another group performed against substantially greater resistance. In the low-resistance condition, no significant differences in CE, VE, time to target, or number of steps to target were found between any of the eight combinations of predictable or unpredictable resistances during walking. In the high-resistance condition, however, significant differences were found for CE and number of strides to target when resistance varied unpredictably during walking. Experiment 2 was similar in design but required subjects to walk with combinations of normal or short steps after they had viewed the target knowing only the gait type that would be used to begin locomotion. No differences in CE, VE, or time to target were found between four different combinations of gait type and predictability, under subjectively controlled conditions. When the step constraints were externally imposed, however, differences were found for CE. None of the results from either experiment, in which the number of strides needed to reach the target or the predictability of gait did not change from normal, supported the hypothesis that motor output requirements are necessary in forming a mental representation of the target position that can be used to walk to the target with eyes closed. Whichever locomotor technique was used to walk the estimated distance in these cases, the representation was able to be used independently. When walking mechanics were altered by externally imposed constraints, however, the success at reaching the estimated target position was reduced. These latter results are consistent with those obtained using up, down, and level walking and support the premise that mental representations used in blind walking are linked to the locomotor mechanics afforded by environmental conditions.     

The Effect of Perceived Locomotor Constraints on Distance Estimation

Two experiments were conducted to examine the ways in which the visual estimation of distance to a target is affected by constraints perceived to be placed on the subsequent locomotion to the target without vision. We hypothesized that an appraisal of impending effort would play a role in ascertaining the distance to be walked. In Experiment 1, the amount of resistance to walking was variable and unpredictable. One group of subjects performed against relatively low resistance, whereas another group performed against substantially greater resistance. In the low-resistance condition, no significant differences in CE, VE, time to target, or number of steps to target were found between any of the eight combinations of predictable or unpredictable resistances during walking. In the high-resistance condition, however, significant differences were found for CE and number of strides to target when resistance varied unpredictably during walking. Experiment 2 was similar in design but required subjects to walk with combinations of normal or short steps after they had viewed the target knowing only the gait type that would be used to begin locomotion. No differences in CE, VE, or time to target were found between four different combinations of gait type and predictability, under subjectively controlled conditions. When the step constraints were externally imposed, however, differences were found for CE. None of the results from either experiment, in which the number of strides needed to reach the target or the predictability of gait did not change from normal, supported the hypothesis that motor output requirements are necessary in forming a mental representation of the target position that can be used to walk to the target with eyes closed. Whichever locomotor technique was used to walk the estimated distance in these cases, the representation was able to be used independently. When walking mechanics were altered by externally imposed constraints, however, the success at reaching the estimated target position was reduced. These latter results are consistent with those obtained using up, down, and level walking and support the premise that mental representations used in blind walking are linked to the locomotor mechanics afforded by environmental conditions.     

Intact spatial updating with severely degraded vision

Critical to low-vision navigation are the abilities to recover scale and update a 3-D representation of space. In order to investigate whether these abilities are present under low-vision conditions, we employed the triangulation task of eyes-closed indirect walking to previously viewed targets on the ground. This task requires that the observer continually update the location of the target without any further visual feedback of his/her movement or the target’s location. Normally sighted participants were tested monocularly in a degraded vision condition and a normal vision condition on both indirect and direct walking to previously viewed targets. Surprisingly, we found no difference in walked distances between the degraded and normal vision conditions. Our results provide evidence for intact spatial updating even under severely degraded vision conditions, indicating that participants can recover scale and update a 3-D representation of space under simulated low vision.     

Response competition: a major source of interference in a tactile identification task.

Two experiments investigated the ability of subjects to identify a moving, tactile stimulus. In both experiments, the subjects were presented with a target to their left index fingerpad and a nontarget (also moving) to their left middle fingerpad. Subjects were instructed to attend only to the target location and to respond "1" if the stimulus moved either to the left or up the finger, and to respond "2" if the stimulus moved either right or down the finger. The results showed that accuracy was better and reaction times were faster when the target and nontarget moved in the same direction than when they moved in different directions. When the target and nontarget moved in different directions, accuracy was significantly better and reaction times were significantly faster when the two stimuli had the same assigned response than when they had different responses. The results provide support for the conclusion that movement information is processed across adjacent fingers to the level of incipient response activation, even when subjects attempt to focus their attention on one location on the skin.     

Response competition: A major source of interference in a tactile identification task

Two experiments investigated the ability of subjects to identify a moving, tactile stimulus. In both experiments, the subjects were presented with a target to their left index fingerpad and a nontarget (also moving) to their left middle fingerpad. Subjects were instructed to attend only to the target location and to respond “1” if the stimulus moved either to the left or up the finger, and to respond “2” if the stimulus moved either right or down the finger. The results showed that accuracy was better and reaction times were faster when the target and nontarget moved in the same direction than when they moved in different directions. When the target and nontarget moved in different directions, accuracy was significantly better and reaction times were significantly faster when the two stimuli had the same assigned response than when they had different responses. The results provide support for the conclusion that movement information is processed across adjacent fingers to the level of incipient response activation, even when subjects attempt to focus their attention on one location on the skin.     

Perceptual localization of visual stimuli flashed during saccades

Subjects were asked to make a saccade to a visual target flashed in the dark during a prior primary saccade, and to report its apparent position by moving an adjustable light spot to that position. When targets were presented at the beginning of the primary saccade, subjects perceptually mislocated them in the direction of the saccade, whereas when targets were presented immediately before the end of the primary saccade, the flashed targets were mislocated in the opposite direction. The perceptually localized position of the target was primarily determined by its retinal position. However, at all actual and retinal positions of the target, the localized position shifted from the position that would be predicted if the location of the target was determined only by its retinal position to the prior primary saccade direction. The results were discussed in relation to extraretinal eye position signals. Subjects moved their eyes not to the actual position of the target, but to its apparent position. In some trials, there was a discrepancy between perceptual and oculomotor localization, which was interpreted as having been caused by the imprecise localization ability of the oculomotor system.     

Differential use of distance and location information for spatial localization

Five experiments are reported in which subjects judged the movement or spatial location of a visible object that underwent a combination of real and induced (illusory) motion. When subjects attempted to reproduce the distance that the object moved by moving their unseen hands, they were more affected by the illusion than when they pointed to the object's perceived final location. Furthermore, pointing to the final location was more affected by the illusion when the hand movement began from the same position as that at which the object initially appeared, as compared with responses that began from other positions. The results suggest that people may separately encode two distinct types of spatial information: (1) information about the distance moved by an object and (2) information about the absolute spatial location of the object. Information about distance is more susceptible to the influence of an induced motion illusion, and people appear to rely differentially on the different types of spatial information, depending on features of the pointing response. The results have important implications for the mechanisms that underlie spatially oriented behavior in general.     

Is continuous visual monitoring necessary in visually guided locomotion?

Subjects were asked to walk to targets that were up to 21 m away, either with vision excluded during walking or under normal visual control. Over the entire range, subjects were accurate whether or not vision was available as long as no more than approximately 8 sec elapsed between closing the eyes and reaching the target. If more than 8 sec elapsed, (a) this had no influence on distances up to 5 m, but (b) distances between 6-21 m were severely impaired. The results are interpreted to mean that two mechanisms are involved in guidance. Up to 5 m, motor programs of relatively long duration can be formulated and used to control activity. Over greater distances, subjects internalized information about the environment in a more general form, independently of any particular set of motor instructions, and used this to control activity and formulate new motor programs. Experiments in support of this interpretation are presented.     

Visual stimulation affects the perception of voluntary leg movements during walking

When a limb is used for locomotion, patterns of afferent and efferent activity related to its own motion are present as well as visual, vestibular, and other proprioceptive information about motion of the whole body. A study is reported in which it was asked whether visual stimulation present during whole-body motion can influence the perception of the leg movements propelling the body. Subjects were tested in conditions in which the stepping movements they made were identical but the amount of body displacement relative to inertial space and to the visual surround varied. These test conditions were created by getting the subjects to walk on a rotatable platform centered inside a large, independently rotatable, optokinetic drum. In each test condition, subjects, without looking at their legs, compared, against a standard condition in which the floor and drum were both stationary, their speed of body motion, their stride length and stepping rate, the direction of their steps, and the perceived force they exerted during stepping. When visual surround motion was incompatible with the motion normally associated with the stepping movements being made, changes in apparent body motion and in the awareness of the frequency, extent, and direction of the voluntary stepping movements resulted.     

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.     

词边界信息对读者阅读歧义短语时眼跳策略的影响

采用Eye Link 2000眼动仪,选取60个歧义短语,要求大学生被试阅读包含有歧义短语的句子。句子的呈现设置了四种条件:正常无阴影、词间阴影、歧义阴影和字间阴影,以探讨词边界信息是否影响读者阅读歧义短语时的注视位置效应。结果发现:读者对歧义短语的首次注视位置在四种条件下基本一致;词边界信息影响读者对歧义短语的再注视概率。结果表明,词边界信息对歧义短语的影响主要体现在眼跳行动(即"where")的晚期阶段。     

Distance underestimation in virtual space is sensitive to gender but not activity-passivity or mode of interaction.

Four groups of undergraduates (half of each gender) experienced a movement along a corridor containing three distinctive objects, in a virtual environment (VE) with wide-screen projection. One group simulated walking along the virtual corridor using a proprietary step-exercise device. A second group moved along the corridor in conventional flying mode, depressing a keyboard key to initiate continuous forward motion. Two further groups observed the walking and flying participants, by viewing their progress on the screen. Participants then had to walk along a real equivalent but empty corridor, and indicate the positions of the three objects. All groups underestimated distances in the real corridor, the greatest underestimates occurring for the middle distance object. Males' underestimations were significantly lower than females' at all distances. However, there was no difference between the active participants and passive observers, nor between walking and flying conditions.     

Sex Differences in Object Location Memory

The ability to remember where objects were is thought to require multiple separate processes. One has to encode the precise positions occupied, assign the various objects to the correct (relative) locations, and achieve an integration of both types of spatial information. This study examined whether sex differences exist for these selective components of object location memory. Twenty males and 20 females participated in the following task. On a PC screen, they were shown a square with 10 different objects for 30 s. Subsequently, the objects disappeared from the screen, reappeared in a row above the square, and subjects were asked to relocate them in three different conditions. In the object-to-position-assignment condition, the original positions were premarked in the square, so subjects needed only to assign the correct object to the correct position. In the positions-only condition, all objects assumed the same identity. Therefore, subjects had only to reproduce the precise positions. Finally, in the combined condition, subjects were required to replace all the different objects in the square without any of object positions premarked. The absolute displacements between an object's original and its relocated position reflect the integration mechanism. Females did as well as males in the object-to-position-assignment condition and on the absolute displacements in the combined condition, but they were less efficient than males in positional reconstruction per se. Thus, it seems that the male advantage in spatial memory is not a general effect but applies only to certain specific processing components. Moreover, the employment of a dual task during encoding, concurrent articulatory suppression, yielded no significant interactions with sex. This suggests that females' weaker positional encoding does not derive from the use of an inefficient verbal strategy.     

Simultaneous spatial updating in nested environments

When one moves, the spatial relationship between oneself and the entire world changes. Spatial updating refers to the cognitive process that computes these relationships as one moves. In two experiments, we tested whether spatial updating occurs automatically for multiple environments simultaneously. Participants turned relative to either a room or the surrounding campus buildings and then pointed to targets in both the environment in which they turned (updated environment) and the other environment (nonupdated environment). The participants automatically updated the room targets when they moved relative to the campus, but they did not update the campus targets when they moved relative to the room. Thus, automatic spatial updating depends on the nature of the environment. Implications for theories of spatial learning and the structure of human spatial representations are discussed.     

Evidence for a Multiple-process Account of the Generation Effect

In a naturalistic study, we aimed to uncover the relationship between thinking about and remembering intentions. Electronic badges allowed us to track the activities of subjects within their work environment. Over two weeks, subjects were asked to respond using a button on their badges (1) every two hours (Time task); (2) whenever they were in a particular room (Place task). In addition, whenever they thought about the task, they were asked to indicate this with their badges. Although subjects thought about the Time task more, they forgot to respond more often than in the Place task. In the Time task, there was a marked absence of thoughts about the task following successful remembering. When subjects remembered the Place task, thoughts increased with proximity to the target location. In both tasks, thoughts about intentions occurred more in places such as stairwells than in locations where people tended to settle. On the basis of these findings, possible mechanisms for prospective memory are discussed.     

Spatial updating of multiple targets: Comparison of younger and older adults

When walking without vision, people mentally keep track of the directions and distances of previously viewed objects, a process called spatial updating. The current experiment indicates that while people across a large age range are able to update multiple targets in memory without perceptual support, aging negatively affects accuracy, precision, and decision time. Participants (20 to 80 years of age) viewed one, three, or six targets (colored lights) on the floor of a dimly lit room. Then, without vision, they walked to a target designated by color, either directly or indirectly (via a forward turning point). The younger adults’ final stopping points were both accurate (near target) and precise (narrowly dispersed), but updating performance did degrade slightly with the number of targets. Older adults’ performance was consistently worse than the younger group, but the lack of interaction between age and memory load indicates that the effect of age on performance was not further exacerbated by a greater number of targets. The number of targets also significantly increased the latency required to turn toward the designated target for both age groups. Taken together, results extend previous work showing impressive updating performance by younger adults, with novel findings showing that older adults manifest small but consistent degradation of updating performance of multitarget arrays.     

Afferent Information for Motor Control: The Role of Visual Information in Different Portions of the Movement

The question addressed in the present study was whether subjects (N = 24) can use visual information about their hand, in the first half of an aiming movement, to ensure optimal directional accuracy of their aiming movements. Four groups of subjects practiced an aiming task in either a complete vision condition, a no-vision condition, or in a condition in which their hand was visible for the first half [initial vision condition (IV)] or the second half of the movement [final vision condition (FV)]. Following 240 trials of acquisition, all subjects were submitted to a transfer test that consisted of 40 trials performed in a no-vision condition. The results indicated that seeing the hand early in movement did not help subjects to optimize either directional or amplitude accuracy. On the other hand, when subjects viewed their hand closer to the target, movements resulted that were as accurate as those performed under a complete vision condition. In transfer, withdrawing vision did not cause any increase in aiming error for the IV or the no-vision conditions. These results replicated those of Carlton (1981) and extended those of Bard and colleagues (Bard, Hay, & Fleury, 1985) in that they indicated that the kinetic visual channel hypothesized by Paillard (1980; Paillard & Amblard, 1985) appeared to be inoperative beyond 40deg of visual angle.