Phenomenal permanence and the development of predictive tracking in infancy

The perceived spatiotemporal continuity of objects depends on the way they appear and disappear as they move in the spatial layout. This study investigated whether infants' predictive tracking of a briefly occluded object is sensitive to the manner by which the object disappears and reappears. Five-, 7-, and 9-month-old infants were shown a ball rolling across a visual scene and briefly disappearing via kinetic occlusion, instantaneous disappearance, implosion, or virtual occlusion. Three different measures converged to show that predictive tracking increased with age and that infants were most likely to anticipate the reappearance of the ball following kinetic occlusion. These results suggest that infants' knowledge of the permanence and nonpermanence of objects is embodied in their predictive tracking.     

The development of infant sensitivity to biomechanical motions

3 experiments were conducted to examine infant sensitivity at 20, 30, and 36 weeks of age to the 3-dimensional structure of a human form specified through biomechanical motions. All 3 experiments manipulated occlusion information in computer-generated arrays of point-lights moving as if attached to the major joints and head of a person walking. These displays are readily recognized as persons by adults when occlusion information is present, but not when it is absent or inconsistent with the implicit structure of the human body. Converging findings from Experiments 1 and 2 suggested that 36-week-old infants were sensitive to the presence of occlusion information in point-light walker displays; neither 20- nor 30-week-old infants showed any sensitivity to this information. The results of Experiment 3 revealed further that 36-week-old infants were sensitive to whether or not the pattern of occlusion was consistent with the implicit form of the human body, but only when the displays were presented in an upright orientation. These findings are interpreted as suggesting that infants, by 36 weeks of age, are extracting fundamental properties necessary for interpreting a point-light display as a person.     

Orientation Effects in the Development of Linear Object Tracking in Early Infancy

Infants' oculomotor tracking develops rapidly but is poorer when there are horizontal and vertical movement components. Additionally, persistence of objects moving through occlusion emerges at 4 months but initially is absent for objects moving obliquely. In two experiments, we recorded eye movements of thirty-two 4-month-old and thirty-two 6-month-old infants (mainly Caucasian-White) tracking horizontal, vertical, and oblique trajectories. Infants tracked oblique trajectories less accurately, but 6-month olds tracked more accurately such that they tracked oblique trajectories as accurately as 4-month olds tracked horizontal and vertical trajectories. Similar results emerged when the object was temporarily occluded. Thus, 4-month olds’ tracking of oblique trajectories may be insufficient to support object persistence, whereas 6-month olds may track sufficiently accurately to perceive object persistence for all trajectory orientations.     

The development of visual short-term memory capacity in infants

Four experiments assessed visual short-term memory capacity in 4- to 13-month-old infants by comparing their looking to changing and nonchanging stimulus streams presented side by side. In each stream, 1 to 6 colored squares repeatedly appeared and disappeared. In changing streams, the color of a different randomly chosen square changed each time the display reappeared; the colors remained the same in nonchanging streams. Infants should look longer at changing streams, but only if they can remember the colors of the squares. The youngest infants preferred changing streams only when the displays contained one object, whereas older infants preferred changing streams when the displays contained up to 4 objects. Thus, visual short-term memory capacity increases significantly across the first year of life.     

A longitudinal study of visual expectation and reaction time in the first year of life

Developmental change and stability of visual expectation and reaction times (RT) were examined at 5, 7, and 12 months in a longitudinal sample of term and preterm infants (birthweight <1,750 g). Using the traditional 200-ms cut-point to separate anticipatory from reactive saccades, RTs (and their standard deviations) declined markedly over age, whereas anticipations increased. Those infants who had faster RTs were more likely to anticipate upcoming events and were more attentive (fewer trials off-task and less response variability). Crossage stability was modest for most measures from 5 to 7 and 7 to 12 months, but rarely significant from 5 to 12 months. When the cut-point was lowered to 150 ms (to accommodate recent concerns that the higher cut-point may misclassify some true RTs as anticipations), the age-related increase in anticipations disappeared. Thus, although the results indicate marked increases in processing speed with age, evidence for increasing anticipations is equivocal. Findings were similar for preterm and term infants.     

Effects of a backward conditioning procedure following acquisition on extinction of conditioned suppression

A one-trial-a-day procedure was used to investigate the effects of US-CS pairings on extinction of conditioned suppression of licking by rats. Following acquisition trials, response suppression was immediately eliminated when US preceded CS, but it reappeared during subsequent CS-alone presentations. Ss that received backward pairings reached a significant level of extinction one trial before Ss that received conventional extinction trials.     

Conditions for young infants' perception of object trajectories

When an object moves behind an occluder and re-emerges, 4-month-old infants perceive trajectory continuity only when the occluder is narrow, raising the question of whether time or distance out of sight is the important constraining variable. One hundred and forty 4-month-olds were tested in five experiments aimed to disambiguate time and distance out of sight. Manipulating the object's visible speed had no effect on infants' responses, but reducing occlusion time by increasing object speed while occluded induced perception of trajectory continuity. In contrast, slowing the ball while it was behind a narrow or intermediate screen did not modify performance. It is concluded that 4-month-olds perceive trajectory continuity when time or distance out of sight is short.     

Recognition of Moving and Static Faces by Young Infants

This study compared 3- to 4-month-olds' recognition of previously unfamiliar faces learned in a moving or a static condition. Infants in the moving condition showed successful recognition with only 30 s familiarization, even when different images of a face were used in the familiarization and test phase (Experiment 1). In contrast, infants in the static condition showed successful recognition only when the familiarization duration was lengthened to 90 s and when the same image was used between the familiarization and test phase (Experiments 2 and 3). Furthermore, presentation of multiple static images of a face did not yield the same level of performance as the moving condition (Experiment 4). These results suggest that facial motion promotes young infants' recognition of unfamiliar faces.     

基于KPKM算法的动目标检测与跟踪

针对均值偏移算法在跟踪目标发生形变和遮挡时丢失问题,提出了一种自适应目标检测、核函数带宽可变、Kalman滤波预测和重心轨迹跟踪的改进均值偏移算法（KPKM）。该算法利用目标检测中得到的外接矩形和重心作为均值偏移算法的初值,用改进的Kalman滤波器预测目标运动趋势,使本算法能沿着梯度方向快速收敛到目标中心。实验和仿真结果表明,该方法实现了在复杂场景下,对运动目标的精确检测和准确跟踪。     

Infants' perception of object trajectories

Filling in the gaps in what humans see is a fundamental perceptual skill, but little is known about the developmental origins of occlusion perception. Three experiments were conducted with infants between 2 and 6 months of age to investigate perception of the continuity of an object trajectory that was briefly occluded. The pattern of results across experiments provided little evidence of veridical responses to trajectory occlusion in the youngest infants, but by 6 months, perceptual completion was more robust. Four-month-olds' responses indicated that they perceived continuity under a short duration of occlusion, but when the object was out of sight for a longer interval, they appeared to perceive the trajectory as discontinuous. These results suggest that perceptual completion of a simple object trajectory (and, by logical necessity, veridical object perception) is not functional at birth but emerges across the first several months after onset of visual experience.     

Individual and Developmental Differences in Disengagement of Fixation in Early Infancy

The current study investigated whether individual and developmental differences in look duration are correlated with the latency for infants to disengage fixation from a visual stimulus. Ninety-four infants (52 3-month-olds, 42 4-month-olds) were tested in a procedure that measured ocular reaction time to shift fixation from a central target to a peripheral target under conditions in which the central-target either remained present ("competition" condition) or was removed from the display ("noncompetition" condition). Look duration was correlated with disengagement latency; longer-looking infants were slower than shorter-looking infants to shift fixation to the peripheral target on competition trials, but not noncompetition trials. Results were similar for 3- and 4-month-olds, although 3-month-olds showed slower latencies on all trials. Furthermore, long-looking infants were not consistently slower, but rather showed greater variability in their response latencies under conditions that required disengagement of fixation. The results support the position that developmental and individual differences in look duration are linked to the development of the neural attentional systems that control the ability to disengage, or inhibit, visual fixation.     

In Defense of Core Competencies,Quantitative Change,and Continuity

J. Kagan (2008) urges contemporary developmentalists to (a) be cautious when attributing conceptual knowledge to infants based on looking‐time performance, (b) constrain their interpretation of infant performance with multiple methodologies, and (c) reconsider the possibility that qualitative development may be the path by which perceptual infants become conceptual adults. This commentary outlines an account of conceptual development that adheres to two of the three Kagan provisos. It is (a) circumspect in the core competencies attributed to infants and (b) grounded in convergent measures including looking time, event‐related potentials, computational modeling, and eye tracking, but (c) maintains that the transition from the perceptually based category representations of infants to the knowledge‐rich concepts of adult is a continuous developmental process marked by quantitative change.     

The difficulties of representing continuous extent in infancy: using number is just easier

This study investigates the ability of 6-month-old infants to attend to the continuous properties of a set of discrete entities. Infants were habituated to dot arrays that were constant in cumulative surface area yet varied in number for small (< 4) or large (> 3) sets. Results revealed that infants detected a 4-fold (but not 3-fold) change in area, regardless of set size. These results are in marked contrast to demonstrations that infants of the same age successfully discriminate a 2- or 3-fold change in number, providing strong counterevidence to the claim that infants use solely nonnumerical, continuous extent variables when discriminating sets. These findings also shed light on the processes involved in tracking continuous variables in infants.     

Smooth-pursuit eye movements in the newborn infant.

The capacity of newborn infants to smooth-pursuit eye movements in single-target tracking and in optokinetic nystagmus to a moving striped field was examined utilizing DC electrooculography. Smooth-pursuit movements were observed in all infants who were alert during testing, but they occupied less than 15% of viewing time during single-target tracking. The velocity of smooth-pursuit segments in single-target tracking increased linearly to a target velocity of 19 degrees/sec and deteriorated rapidly at faster speeds. No smooth pursuit occurred above 32 degrees/sec in single-target tracking. By contrast, optokinetic nystagmus was observed at all field velocities to 40 degrees/sec, but the speed of the mean slow component increased linearly to 25 degrees/sec and diminished above that field velocity. Infant optokinetic nystagmus differed strikingly from that of adults in that tonic ocular deviation was in the direction of field movement rather than away from it. This feature of neonatal optokinetic nystagmus is consistent with deficient foveal function and suggests that the relatively poor smooth-pursuit performance of newborns may be related to foveal immaturity.     

Sequence Learning in 4‐Month‐Old Infants: Do Infants Represent Ordinal Information?

This study investigated how 4‐month‐old infants represent sequences: Do they track the statistical relations among specific sequence elements (e.g., AB, BC) or do they encode abstract ordinal positions (i.e., B is second)? Infants were habituated to sequences of 4 moving and sounding elements—3 of the elements varied in their ordinal position while the position of 1 target element remained invariant (e.g., A B CD, C B DA)—and then were tested for the detection of changes in the target’s position. Infants detected an ordinal change only when it disrupted the statistical co‐occurrence of elements but not when statistical information was controlled. It is concluded that 4‐month‐olds learn the order of sequence elements by tracking their statistical associations but not their invariant ordinal position.     

Inability of five-month-old infants to retrieve a contiguous object: a failure of conceptual understanding or of control of action?

Infants of 5 to 6 months of age can retrieve a free-standing object, but fail to retrieve the same object from atop a slightly larger object. The accepted explanation has been that the infants do not understand that an object continues to exist independently when placed upon another. Predictions based on that explanation were tested against the hypothesis that infants' problem consists of lack of precision in visually guided reaching and lack of ability to inhibit reflexive reactions to touch. Twelve infants each at 5 and 7 months of age were tested on 16 trials. More 5-month-olds succeeded, in less time, and with fewer touches to an edge of the base, on trials more forgiving of an imprecise reach than on less forgiving trials. Success in retrieving objects close in size and fully contiguous with their bases was seen even at 5 months when the demands on skill in reaching were reduced. It is proposed that when 5-month-old infants fail to retrieve one object placed upon another, it is not because of a lack of conceptual understanding, but because they lack the skill to reach to the top object without accidentally touching an edge of the base en route.     

基于行为和部分观测的多目标跟踪

针对复杂环境下的多目标跟踪问题提出了一种新的跟踪方法．在检测部分,采用第三级离散小波变换和背景差分进行了目标分割．在跟踪部分,首先利用卡尔曼滤波器和缩放因子估计目标在下一帧中的中心位置和矩形框尺寸,然后在中心关联和区域关联的基础上提出了投射率和遮挡率的概念,并结合投射率和遮挡率推断目标行为．最后针对具体目标行为,自适应地调整跟踪方案和卡尔曼参数实现了多目标跟踪．在遮挡情况下利用部分观测调整估计框以获得目标测量值和最优框尺寸．提出的方法对处于遮挡、新出现以及稳定等情况下的运动目标均具有鲁棒的跟踪性能．实验结果表明提出的方法是有效的．     

Development of feedforward control in a dynamic manual tracking task

To examine the development of feedforward control during manual tracking, 117 participants in 5 age groups (6 to 7, 8 to 9, 10 to 11, 12 to 14, and 15 to 17 years) tracked an accelerating dot presented on a monitor by moving an electronic pen on a digitizer. To remain successful at higher target velocities, they had to create a predictive model of the target's motion. The ability to track the target at higher velocities increased, and the application of a feedback-based step-and-hold strategy decreased with age, as shown by increases in maximum target velocity and decreases in number of stops between ages 6–7 and 8–9 and between ages 8–9 and 10–11. The ability to exploit feedforward control in a dynamic tracking task improves significantly with age.     

Infants' Selective Attention to Reliable Visual Cues in the Presence of Salient Distractors

With many features competing for attention in their visual environment, infants must learn to deploy attention toward informative cues while ignoring distractions. Three eye tracking experiments were conducted to investigate whether 6‐ and 8‐month‐olds (total N = 102) would shift attention away from a distractor stimulus to learn a cue–reward relation. While 8‐month‐olds showed evidence of increasingly selective attention toward the predictive cues, even when the distractors were highly salient, 6‐month‐olds shifted attention toward the predictive cues only when the distractors were equally (not more) engaging. These experiments suggest that attention in infancy is highly dependent on the relative weightings of predictiveness and visual salience, which may differ across development and context.