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.     

Reflexive orienting in response to short- and long-duration gaze cues in young,young-old,and old-old adults

Shifting visual focus on the basis of the perceived gaze direction of another person is one form of joint attention. In the present study, we investigated whether this socially relevant form of orienting is reflexive and whether it is influenced by age. Green and Woldorff (Cognition 122:96–101, 2012) argued that rapid cueing effects (i.e., faster responses to validly than to invalidly cued targets) were limited to conditions in which a cue overlapped in time with a target. They attributed slower responses following invalid cues to the time needed to resolve the incongruent spatial information provided by the concurrently presented cue and target. In the present study, we examined the orienting responses of young (18–31 years), young-old (60–74 years), and old-old (75–91 years) adults following uninformative central gaze cues that overlapped in time with the target (Exp. 1) or that were removed prior to target presentation (Exp. 2). When the cue and target overlapped, all three groups localized validly cued targets more quickly than invalidly cued targets, and validity effects emerged earlier for the two younger groups (at 100 ms post-cue-onset) than for the old-old group (at 300 ms post-cue-onset). With a short-duration cue (Exp. 2), validity effects developed rapidly (by 100 ms) for all three groups, suggesting that validity effects resulted from reflexive orienting based on the gaze cue information rather than from cue–target conflict. Thus, although old-old adults may be slow to disengage from persistent gaze cues, attention continues to be reflexively guided by gaze cues late in life.     

Human Eye Movements During Visually Guided Stepping

Visually guided locomotion was studied in an experiment in which human subjects (N = 8) had to accurately negotiate a series of irregularly spaced stepping-stones while infrared reflectometry and electrooculography were used to continuously record their eye movements. On average, 68% of saccades made toward the next target of footfall had been completed (visual target capture had occurred) while the foot to be positioned was still on the ground; the remainder were completed in the first 300 ms of the swing phase. The subjects' gaze remained fixed on a target, on average, until 51 ms after making contact with it, with little variation. A greater amount of variation was seen in the timing of trailing footlift relative to visual target capture. Assuming that subjects sampled the visual cues as and when they were required, visual information appeared most useful when the foot to be positioned was still on the ground.     

Inhibitory tagging at subsequently fixated locations: Generation of “inhibition of return” without saccade inhibition

In two experiments, an inhibitory tag was activated by a peripheral cue after which a saccade was made to either the cued or, with equal probability, the uncued location. Key press RTs were measured for detecting a target that then appeared, with equal probability, either at fixation or at an eccentric location. In Experiment 1, the peripheral cue onset 400 ms before the saccade instruction, and participants therefore were obliged to inhibit a saccade towards the cue. Detection was slower at the cued location whether it appeared at, or eccentric from, fixation. In Experiment 2, the peripheral cue onset after the instruction to make the saccade but before the eyes had moved. Inhibitory tagging was again observed for targets at fixation, but the effect was smaller than for eccentric targets. These findings confirm that withdrawal of attention from a cued location is not required to generate an inhibitory tag, and that the cued locus remains inhibited even if it is subsequently attended and a saccade made to fixate it. Moreover, saccade inhibition is not sufficient to account for inhibitory tagging, although it may also engender an independent inhibitory effect.     

Developmental changes in the control of saccadic eye movements in response to directional eye gaze and arrows

We investigated developmental differences in oculomotor control between 10-year-old children and adults using a central interference task. In this task, the colour of a fixation point instructed participants to saccade either to the left or to the right. These saccade directions were either congruent or incongruent with two types of distractor cue: either the direction of eye gaze of a centrally presented schematic face, or the direction of arrows. Children had greater difficulties inhibiting the distractor cues than did adults, which revealed itself in longer saccade latencies for saccades that were incongruent with the distractor cues as well as more errors on these incongruent trials than on congruent trials. Counter to our prediction, in terms of saccade latencies, both children and adults had greater difficulties inhibiting the arrow than the eye gaze distractors.     

Developmental changes in the control of saccadic eye movements in response to directional eye gaze and arrows

We investigated developmental differences in oculomotor control between 10-year-old children and adults using a central interference task. In this task, the colour of a fixation point instructed participants to saccade either to the left or to the right. These saccade directions were either congruent or incongruent with two types of distractor cue: either the direction of eye gaze of a centrally presented schematic face, or the direction of arrows. Children had greater difficulties inhibiting the distractor cues than did adults, which revealed itself in longer saccade latencies for saccades that were incongruent with the distractor cues as well as more errors on these incongruent trials than on congruent trials. Counter to our prediction, in terms of saccade latencies, both children and adults had greater difficulties inhibiting the arrow than the eye gaze distractors.     

Automatic attentional orienting to other people’s gaze in schizophrenia

Explicit tests of social cognition have revealed pervasive deficits in schizophrenia. Less is known of automatic social cognition in schizophrenia. We used a spatial orienting task to investigate automatic shifts of attention cued by another person’s eye gaze in 29 patients and 28 controls. Central photographic images of a face with eyes shifted left or right, or looking straight ahead, preceded targets that appeared left or right of the cue. To examine automatic effects, cue direction was non-predictive of target location. Cue–target intervals were 100, 300, and 800?ms. In non-social control trials, arrows replaced eye-gaze cues. Both groups showed automatic attentional orienting indexed by faster reaction times (RTs) when arrows were congruent with target location across all cue–target intervals. Similar congruency effects were seen for eye-shift cues at 300 and 800?ms intervals, but patients showed significantly larger congruency effects at 800?ms, which were driven by delayed responses to incongruent target locations. At short 100-ms cue–target intervals, neither group showed faster RTs for congruent than for incongruent eye-shift cues, but patients were significantly slower to detect targets after direct-gaze cues. These findings conflict with previous studies using schematic line drawings of eye-shifts that have found automatic attentional orienting to be reduced in schizophrenia. Instead, our data indicate that patients display abnormalities in responding to gaze direction at various stages of gaze processing—reflected by a stronger preferential capture of attention by another person’s direct eye contact at initial stages of gaze processing and difficulties disengaging from a gazed-at location once shared attention is established.     

Eye movements and visual memory: detecting changes to saccade targets in scenes

Saccade-contingent change detection provides a powerful tool for investigating scene representation and scene memory. In the present study, critical objects presented within color images of naturalistic scenes were changed during a saccade toward or away from the target. During the saccade,the critical object was changed to another object type, to a visually different token of the same object type, or was deleted from the scene. There were three main results. First, the deletion of a saccade target was special: Detection performance for saccade target deletions was very good, and this level of performance did not decline with the amplitude of the saccade. In contrast, detection of type and token changes at the saccade target, and of all changes including deletions at a location that had just been fixated but was not the saccade target, decreased as the amplitude of the saccade increased. Second, detection performance for type and token changes, both when the changing object was the target of the saccade and when the object had just been fixated but was not the saccade target, was well above chance. Third, mean gaze durations were reliably elevated for those trials in which the change was not overtly detected. The results suggest that the presence of the saccade target plays a special role in trassaccadic integration, and together with other recent findings, suggest more generally that a relatively rich scene representation is retained across saccades and stored in visual memory.     

The owl and the pussycat: Gaze cues and visuospatial orienting

Recent research has shown that nonpredictive gaze cues trigger reflexive shifts in attention toward the looked-at location. But just how generalizable is this spatial cuing effect? In particular, are people especially tuned to gaze cues provided by conspecifics, or can comparable shifts in visual attention be triggered by other cue providers and directional cues? To investigate these issues, we used a standard cuing paradigm to compare the attentional orienting produced by different cue providers (i.e., animate vs. inanimate) and directional cues (i.e., eyes vs. arrows). The results of three experiments revealed that attentional orienting was insensitive to both the identity of the cue provider and the nature of the triggering cue. However, compared with arrows, gaze cues prompted a general enhancement in the efficiency of processing operations. We consider the implications of these findings for accounts of reflexive visual orienting.     

认知老化中有意控制对自动抑制的调节作用

结合比例控制范式与基于空间位置的返回抑制范式, 探讨了认知老化过程中自上而下的有意认知控制对自动抑制的调节作用。结果表明, 当线索有效率由50%提升至80%时, 两组被试的返回抑制量均下降, 老年组表现为返回抑制消失, 但年轻组出现返回抑制的反转, 表明有意认知控制对自动抑制的调节作用受认知老化的影响而发生衰减。同时文章还就认知老化机制的新兴理论—— 执行衰退假说进行了讨论。     

Social Beliefs and Visual Attention: How the Social Relevance of a Cue Influences Spatial Orienting

We are highly tuned to each other's visual attention. Perceiving the eye or hand movements of another person can influence the timing of a saccade or the reach of our own. However, the explanation for such spatial orienting in interpersonal contexts remains disputed. Is it due to the social appearance of the cue—a hand or an eye—or due to its social relevance—a cue that is connected to another person with attentional and intentional states? We developed an interpersonal version of the Posner spatial cueing paradigm. Participants saw a cue and detected a target at the same or a different location, while interacting with an unseen partner. Participants were led to believe that the cue was either connected to the gaze location of their partner or was generated randomly by a computer (Experiment 1), and that their partner had higher or lower social rank while engaged in the same or a different task (Experiment 2). We found that spatial cue‐target compatibility effects were greater when the cue related to a partner's gaze. This effect was amplified by the partner's social rank, but only when participants believed their partner was engaged in the same task. Taken together, this is strong evidence in support of the idea that spatial orienting is interpersonally attuned to the social relevance of the cue—whether the cue is connected to another person, who this person is, and what this person is doing—and does not exclusively rely on the social appearance of the cue. Visual attention is not only guided by the physical salience of one's environment but also by the mental representation of its social relevance.     

Coordination of Eye and Leg Movements During Visually Guided Stepping

In the present study, 2 related hypotheses were tested: first, that vision is used in a feedforward control mode during precision stepping onto visual targets and, second, that the oculomotor and locomotor control centers interact to produce coordinated eye and leg movements during that task. Participants' (N = 4) eye movements and step cycle transition events were monitored while they performed a task requiring precise foot placement at every step onto irregularly placed stepping stones under conditions in which the availability of visual information was either restricted or intermittently removed altogether. Accurate saccades, followed by accurate steps, to the next footfall target were almost always made even when the information had been invisible for as long as 500 ms. Despite delays in footlift caused by the temporary removal (and subsequent reinstatement) of visual information, the mean interval between the start of the eye movement and the start of the swing toward a target did not vary significantly (p > .05). In contrast, the mean interval between saccade onset away from a target and a foot landing on that target (stance onset) did vary significantly (p < .05) under the different experimental conditions. Those results support the stated hypotheses.     

Advancing age progressively affects obstacle avoidance skills in the elderly

The ability to adequately avoid obstacles while walking is an important skill that allows safe locomotion over uneven terrain. The high proportion of falls in the elderly that is associated to tripping over obstacles potentially illustrates an age-related deterioration of this locomotor skill. Some studies have compared young and old adults, but very little is known about the changes occurring within different age groups of elderly. In the present study, obstacle avoidance performance was studied in 25 young (20-37 years) and 99 older adults (65-88 years). The participants walked on a treadmill at a speed of 3 km/h. An obstacle was dropped 30 times in front of the left foot at various phases in the step cycle. Success rates (successful avoidance) were calculated and related to the time available between obstacle appearance and the estimated instant of foot contact with the obstacle (available response times or ARTs ranging from 200 to more than 350 ms). In addition, latencies of avoidance reactions, the choice of avoidance strategies (long or short step strategy, LSS or SSS), and three spatial parameters related to obstacle avoidance (toe distance, foot clearance, and heel distance) were determined for each participant. Compared to the young, the older adults had lower success rates, especially at short ARTs. Furthermore, they had longer reaction times, more LSS reactions, smaller toe and heel distances, and larger foot clearances. Within the group of elderly, only the 65-69 year olds were not different from young adults with respect to success rate, despite marked changes in the other parameters measured. In particular, even this younger group of elderly showed a dramatic reduction in the amount of SSS trials compared to young adults. Overall, age was a significant predictor of success rates, reaction times, and toe distances. These parameters deteriorated with advancing age. Finally, avoidance success rates at short ARTs were considerably worse in elderly participants who sustained recurrent falls in the six-month period prior to the assessment compared to those who sustained no or only one fall. An exercise program has been shown to improve avoidance success rates, especially at short ARTs, but the training effects on the determinants of success still need to be assessed.     

Opening the cuebox: The information children and young adults generate and rely on when making inferences from memory

We used a cue‐generation and a cue‐selection paradigm to investigate the cues children (9‐ to 12‐year‐olds) and young adults (17‐year‐olds) generate and select for a range of inferences from memory. We found that children generated more cues than young adults, who, when asked why they did not generate some particular cues, responded that they did not consider them relevant for the task at hand. On average, the cues generated by children were more perceptual but as informative as the cues generated by young adults. When asked to select the most informative of two cues, both children and young adults tended to choose a hidden (i.e., not perceptual) cue. Our results suggest a developmental change in the cuebox (i.e., the set of cues used to make inferences from memory): New cues are added to the cuebox as more cues are learned, and some old, perceptual cues, although informative, are replaced with hidden cues, which, by both children and young adults, are generally assumed to be more informative than perceptual cues.     

Modulation of distraction in ageing

A cueing paradigm was employed to examine modulation of distraction due to a visual singleton. Subjects were required to make a saccade to a shape‐singleton target. A predictive location cue indicated the hemifield where a target would appear. Older adults made more anticipatory saccades than younger adults, and were less accurate for making an eye movement in the vicinity of a target. However, younger and older adults likewise benefited from the cue; distraction was reduced when the distractor singleton appeared in an uncued hemisphere. The ability to compensate for problems with distraction in older and younger adults through use of the precue suggests that attention to a general region of space, rather than a specific location, may be enough to modulate distraction.     

The control of saccade trajectories: direction of curvature depends on prior knowledge of target location and saccade latency

Recent reports have shown that saccades can deviate either toward or away from distractors. However, the specific conditions responsible for the change in initial saccade direction are not known. One possibility, examined here, is that the direction of curvature (toward or away from distractors) reflects preparatory tuning of the oculomotor system when the location of the target and distractor are known in advance. This was investigated by examining saccade trajectories under predictable and unpredictable target conditions. In Experiment 1, the targets and the distractors appeared unpredictably, whereas in Experiment 2 an arrow cue presented at fixation indicated the location of the forthcoming target prior to stimulus onset. Saccades were made to targets on the horizontal, vertical, and principal oblique axis, and distractors appeared simultaneously at an adjacent location (a separation of +/- 45 degrees of visual angle). On average, saccade trajectories curved toward distractors when target locations were unpredictable and curved away from distractors when target locations were known in advance. There was no overall difference in mean saccade latencies between the two experiments. The magnitude of the distractor modulation of saccade trajectory (either toward or away from) was comparable across the different saccade directions (horizontal, vertical, and oblique). These results are interpreted in terms of the time course of competitive interactions operating in the neural structures involved in the suppression of distractors and the selection of a saccade target. A relatively slow mechanism that inhibits movements to distractors produces curvature away from the distractor. This mechanism has more time to operate when target location is predictable, increasing the likelihood that the saccade trajectory will deviate away from the distractor.     

Emotional attention: effects of emotion and gaze direction on overt orienting of visual attention

In the present study we considered the two factors that have been advocated for playing a role in emotional attention: perception of gaze direction and facial expression of emotions. Participants performed an oculomotor task in which they had to make a saccade towards one of the two lateral targets, depending on the colour of the fixation dot which appeared at the centre of the computer screen. At different time intervals (stimulus onset asynchronies, SOAs: 50,100,150 ms) following the onset of the dot, a picture of a human face (gazing either to the right or to the left) was presented at the centre of the screen. The gaze direction of the face could be congruent or incongruent with respect to the location of the target, and the expression could be neutral or angry. In Experiment 1 the facial expressions were presented randomly in a single block, whereas in Experiment 2 they were shown in separate blocks. Latencies for correct saccades and percentage of errors (saccade direction errors) were considered in the analyses. Results showed that incongruent trials determined a significantly higher percentage of saccade direction errors with respect to congruent trials, thus confirming that gaze direction, even when task-irrelevant, interferes with the accuracy of the observer’s oculomotor behaviour. The angry expression was found to hold attention for a longer time with respect to the neutral one, producing delayed saccade latencies. This was particularly evident at 100 ms SOA and for incongruent trials. Emotional faces may then exert a modulatory effect on overt attention mechanisms.     

One-year-olds comprehend the communicative intentions behind gestures in a hiding game

This study explored infants' ability to infer communicative intent as expressed in non-linguistic gestures. Sixty children aged 14, 18 and 24 months participated. In the context of a hiding game, an adult indicated for the child the location of a hidden toy by giving a communicative cue: either pointing or ostensive gazing toward the container containing the toy. To succeed in this task children had to do more than just follow the point or gaze to the target container. They also had to infer that the adult's behaviour was relevant to the situation at hand - she wanted to inform them that the toy was inside the container toward which she gestured. Children at all three ages successfully used both types of cues. We conclude that infants as young as 14 months of age can, in some situations, interpret an adult behaviour as a relevant communicative act done for them.     

Inhibition of return generated by voluntary saccades is independent of attentional momentum

Summoning attention to a peripheral location, either by a peripheral cue with the eyes fixed or when a voluntary saccade is made to it and gaze is then returned to the centre, delays detection of subsequent targets at that location compared to a location in the opposite visual field. It has been proposed that oculomotor activation generates this inhibition of return (IOR). This account presupposes that the asymmetry in detection results from inhibition at the cued location rather than facilitation at the uncued location. This has been confirmed for exogenously generated IOR. However, it has not, heretofore, been confirmed for “IOR” generated by voluntary saccades. The current study investigated whether the asymmetry in target detection, elicited either by a peripheral flash or by an eye movement generated in response to a central arrowhead, reflects facilitation at the opposite location due to the path of attentional momentum. Reaction times at the cued location were slower than reaction times at the opposite or perpendicular locations, which did not differ. Opposite facilitation due to attentional momentum requires that opposite be faster than perpendicular, which was not obtained. The results were the same whether IOR was generated by an exogenous cue or by a saccade executed endogenously to a central arrow.     

Timing of reflexive visuospatial orienting in young, young-old, and old-old adults

This study examined adult age differences in reflexive orienting to two types of uninformative spatial cues: central arrows and peripheral onsets. In two experiments using a Posner cuing task, young adults (ages 18–28 years), young-old adults (60–74 years), and old-old adults (75–92 years) responded to targets that were preceded 100–1,000 ms earlier by a central arrow or a peripheral abrupt onset. In Experiment 1, the cue remained present upon target onset. Facilitation effects at short cue–target stimulus onset asynchronies (SOAs) were prolonged in duration for the two older groups relative to the young adults. At longer cue–target SOAs, inhibition of return (IOR) that was initiated by peripheral onset cues was observed in the performance of young adults but not in that of the two older groups. In Experiment 2, the cue was presented briefly and removed prior to target onset. The change in cue duration minimized age differences (particularly for young-old adults) in facilitation effects and led to IOR for all three age groups. The findings are consistent with the idea that attentional control settings change with age, with higher settings for older adults leading to delayed disengagement from spatial cues.