Temporal integration differences between crossed and uncrossed stereoscopic mechanisms

In this study, we investigated temporal integration of disparity information for crossed and uncrossed stereopsis. Across three experiments, exposure duration thresholds were measured for stereoscopic stimuli created from dynamic random-dot stereograms. In Experiment 1, an investigation of disparity detection showed that detection thresholds were equal for the crossed and uncrossed directions. In Experiment 2, an examination of duration limits for depth perception showed that critical durations were lower, and depth more veridical, for crossed depth than for uncrossed depth. In Experiment 3, an investigation of depth discrimination revealed that discrimination thresholds were lower for crossed depth than for uncrossed depth. These results suggest that crossed and uncrossed mechanisms differ in terms of their temporal integration properties at processing levels involving the computation and discrimination of depth.     

The crossed-hands deficit in tactile temporal-order judgments: the effect of training

Several recent studies have shown that judgments of temporal order for tactile stimuli presented to the two hands are greatly affected by crossing the hands. The size of the threshold for judging temporal order may be up to four times larger with the hands crossed as compared to the hands uncrossed. The results from these recent studies suggest that with crossed hands, contrary to many situations involving the integration of tactile and proprioceptive information, subjects have difficulty in adjusting their perception of tactile inputs to correspond with the spatial positions of the hands. In the present study we examined the effect of training in judging temporal order on the size of this crossed-hands deficit--the difference in the thresholds for temporal-order judgments when the hands are crossed and uncrossed. All training procedures produced significant declines in the size of the deficit. With training, the difference between crossed-hands and uncrossed-hands temporal-order thresholds dropped from several hundred milliseconds to as little as 19 ms. A group of percussionists with experience in playing with crossed hands showed the same crossed-hands effects as non-musicians. The results were consistent in showing that the crossed-hands deficit was never completely eliminated but was greatly reduced with training. The implication is that subjects are able to adjust to the crossed-hands posture with modest amounts of training. The results are discussed in terms of the explanations that have been offered for the crossed-hands deficit.     

Tactile stimulation and interhemispheric communication by learning disabled children: an exploratory study

33 right-handed, learning disabled children aged 8-10 yr., 11-13 yr., and 14-16 yr. were presented a tactile discrimination task. Pairs of fabrics of different or the same texture were presented to the same hand (uncrossed condition) or alternating hands (crossed condition). Analysis indicated that the total number of crossed errors was significantly greater for the youngest children. There were no significant differences between the groups for the uncrossed condition. These results suggest that younger learning disabled children may experience greater difficulty on a task which required interhemispheric transfer.     

Processing load impairs coordinate integration for the localization of touch

To perform an action toward a touch, the tactile spatial representation must be transformed from a skin-based, anatomical reference frame into an external reference frame. Evidence suggests that, after transformation, both anatomical and external coordinates are integrated for the location estimate. The present study investigated whether the calculation and integration of external coordinates are automatic processes. Participants made temporal order judgments (TOJs) of two tactile stimuli, one applied to each hand, in crossed and uncrossed postures. The influence of the external coordinates of touch was indicated by the performance difference between crossed and uncrossed postures, referred to as the crossing effect. To assess automaticity, the TOJ task was combined with a working memory task that varied in difficulty (size of the working memory set) and quality (verbal vs. spatial). In two studies, the crossing effect was consistently reduced under processing load. When the load level was adaptively adjusted to individual performance (Study 2), the crossing effect additionally varied as a function of the difficulty of the secondary task. These modulatory effects of processing load on the crossing effect were independent of the type of working memory. The sensitivity of the crossing effect to processing load suggests that coordinate integration for touch localization is not fully automatic. To reconcile the present results with previous findings, we suggest that the genuine remapping process—that is, the transformation of anatomical into external coordinates—proceeds automatically, whereas their integration in service of a combined location estimate is subject to top-down control.     

Task-irrelevant sounds influence both temporal order and apparent-motion judgments about tactile stimuli applied to crossed and uncrossed hands

It has been suggested that judgments about the temporal–spatial order of successive tactile stimuli depend on the perceived direction of apparent motion between them. Here we manipulated tactile apparent-motion percepts by presenting a brief, task-irrelevant auditory stimulus temporally in-between pairs of tactile stimuli. The tactile stimuli were applied one to each hand, with varying stimulus onset asynchronies (SOAs). Participants reported the location of the first stimulus (temporal order judgments: TOJs) while adopting both crossed and uncrossed hand postures, so we could scrutinize skin-based, anatomical, and external reference frames. With crossed hands, the sound improved TOJ performance at short (≤300 ms) and at long (>300 ms) SOAs. When the hands were uncrossed, the sound induced a decrease in TOJ performance, but only at short SOAs. A second experiment confirmed that the auditory stimulus indeed modulated tactile apparent motion perception under these conditions. Perceived apparent motion directions were more ambiguous with crossed than with uncrossed hands, probably indicating competing spatial codes in the crossed posture. However, irrespective of posture, the additional sound tended to impair potentially anatomically coded motion direction discrimination at a short SOA of 80 ms, but it significantly enhanced externally coded apparent motion perception at a long SOA of 500 ms. Anatomically coded motion signals imply incorrect TOJ responses with crossed hands, but correct responses when the hands are uncrossed; externally coded motion signals always point toward the correct TOJ response. Thus, taken together, these results suggest that apparent-motion signals are likely taken into account when tactile temporal–spatial information is reconstructed.

     

Integration of anatomical and external response mappings explains crossing effects in tactile localization: A probabilistic modeling approach

To act upon a tactile stimulus its original skin-based, anatomical spatial code has to be transformed into an external, posture-dependent reference frame, a process known as tactile remapping. When the limbs are crossed, anatomical and external location codes are in conflict, leading to a decline in tactile localization accuracy. It is unknown whether this impairment originates from the integration of the resulting external localization response with the original, anatomical one or from a failure of tactile remapping in crossed postures. We fitted probabilistic models based on these diverging accounts to the data from three tactile localization experiments. Hand crossing disturbed tactile left–right location choices in all experiments. Furthermore, the size of these crossing effects was modulated by stimulus configuration and task instructions. The best model accounted for these results by integration of the external response mapping with the original, anatomical one, while applying identical integration weights for uncrossed and crossed postures. Thus, the model explained the data without assuming failures of remapping. Moreover, performance differences across tasks were accounted for by non-individual parameter adjustments, indicating that individual participants’ task adaptation results from one common functional mechanism. These results suggest that remapping is an automatic and accurate process, and that the observed localization impairments in touch result from a cognitively controlled integration process that combines anatomically and externally coded responses.     

Crossing the arms confuses the clocks: Sensory feedback and the bimanual advantage

The bimanual advantage refers to the finding that tapping with two fingers on opposite hands exhibits reduced timing variability, as compared with tapping with only one finger. Two leading theories propose that the bimanual advantage results from the addition of either sensory (i.e., enhanced feedback) or cognitive (i.e., multiple timekeeper) processes involved in timing. Given that crossing the arms impairs perception of tactile stimuli and modulates cortical activation following tactile stimulation, we investigated the role of crossing the arms in the bimanual advantage. Participants tapped unimanually or bimanually with their arms crossed or uncrossed on a tabletop or in the air. With arms crossed, we expected increased interval timing variance. Similarly, for air tapping, we expected reduced bimanual advantage, due to reduced sensory feedback. A significant bimanual advantage was observed for the uncrossed, but not the crossed posture in tabletop tapping. Furthermore, removing tactile feedback from taps eliminated the bimanual advantage for both postures. Together, these findings suggest that crossing the arms likely impairs integration of internal (i.e., effector-specific) and external (i.e., environment-specific) information and that this multisensory integration is crucial to reducing timing variability during repetitive coordinated bimanual tasks.     

部件类型还是交错关系信息的习得促进问题解决？

本研究旨在探讨知觉组块中部件类型和空间交错关系信息的学习是否促进问题解决。研究采用学习-测试范式,71名有效被试（女性25名,平均年龄=20.51±2.35岁）先学习解答组块破解问题然后进行测试。研究分别在学习和测试阶段基于组块破解任务操纵了部件类型（汉字水平vs.笔画水平）和空间交错关系（交错vs.非交错）。学习阶段,被试分别在四组中完成组块破解练习;在测试阶段完成所有四组问题。研究发现,对交错关系信息的学习与利用相对于部件类型信息促进了问题解决：在涉及交错信息的测试任务上,涉及交错信息比非交错信息的学习条件解答率更高,反应时更短;反之则不是。然而部件类型则没有发现类似的促进效应。与此同时,交错关系信息的习得需要对任务的重复操作学习：涉及交错关系信息的组块破解学习成绩在不同任务间并不随时间推移而提高,但会随重复学习次数而提高。     

Interhemispheric transmission time in an auditory two-choice reaction task

An unimanual auditory choice reaction task was performed by 16 right-handed male subjects. Upon release of a central ready button subjects pressed a target button on their right or left side depending on the ear in which they heard a tone. A significant 'Ear' x 'Hand' interaction effect appeared on both reaction time (RT) and the first component of movement (MT₁), showing that uncrossed conditions give rise to faster responses than crossed conditions. Interhemispheric transmission time (IHTT) was estimated from the difference of response latency in the two types of conditions. No asymmetry in the speed of information transfer between the hemispheres was found. IHTT was 16 ms in the case of RT, which supported previous research with visual reaction tasks, and IHTT for MT₁ was 13 ms, which has not been reported before.     

Influences of motion and depth on brightness induction: an illusory transparency effect?

To experiments were performed to investigate whether motion and binocular disparity influence brightness induction, and whether the effects of motion and binocular disparity, if any, interact with each other. In order to introduce motion, textured backgrounds were used as the inducing field. The results showed that motion and/or crossed disparity reduce brightness induction, whereas uncrossed disparity increases it. The effect of motion and the effect of disparity are independent of each other and additive, which suggests that, to the extent that brightness induction reflects segmentation of objects, motion and binocular disparity serve independently to segment objects from their background. The difference between the effects of crossed and uncrossed disparity can be explained by what we call 'illusory transparency'.     

组块紧密性导致组块破解困难：部件类型还是交错关系？

本研究的目的是澄清“组块紧密性为何导致组块破解困难”。研究基于汉字减法任务,也即让被试从一个源汉字中移动一个目标部件从而得到一个新汉字,在三个实验中检验了部件类型和交错关系的作用。结果显示,交错条件比非交错条件解答率更低反应时更长;而部件类型效应则主要体现在非交错条件的反应时指标上。结果提示,组块紧密性导致了组块破解困难,这主要取决于空间交错关系;相对的,部件类型作用较小。     

Task effects on tactile temporal order judgments: when space does and does not matter

The ability to report the temporal order of 2 tactile stimuli (1 applied to each hand) has been shown to decline when the arms are crossed over compared with when they are uncrossed. However, these effects have only been measured when temporal order was reported by stimulus location. It is unknown whether this spatial manipulation of the body affects all tactile temporal order judgments (TOJs) or only those judgments that are spatially defined. The authors examined the effect of crossing the arms on tactile TOJs when stimuli were identified by either spatial (location) or nonspatial (frequency or duration) attributes. Spatial TOJs were significantly impaired when the arms were in crossed compared with uncrossed postures, but there was no effect of posture when order was judged by nonspatial attributes. Task-dependent modulation of the effects of posture was also evident when response complexity was reduced to go/no-go responses. These results suggest that crossing the arms impairs tactile localization and thus spatial TOJs. However, the data also suggest that localization is not a necessary precursor when temporal order can be computed by nonspatial means.     

Infants’ discrimination of crossed and uncrossed horizontal disparity

In a series of preferential-looking experiments, infants 5 to 6 months of age were tested for their responsiveness to crossed and uncrossed horizontal disparity. In Experiments 1 and 2, infants were presented with dynamic random dot stereograms displaying a square target defined by either a 0.5° crossed or a 0.5° uncrossed horizontal disparity and a square control target defined by a 0.5° vertical disparity. In Experiment 3, infants were presented with the crossed and the uncrossed horizontal disparity targets used in Experiments 1 and 2. According to the results, the participants looked more often at the crossed (Experiment 1), as well as the uncrossed (Experiment 2), horizontal disparity targets than at the vertical disparity target. These results suggest that the infants were sensitive to both crossed and uncrossed horizontal disparity information. Moreover, the participants exhibited a natural visual preference for the crossed over the uncrossed horizontal disparity (Experiment 3). Since prior research established natural looking and reaching preferences for the (apparently) nearer of two objects, this finding is consistent with the hypothesis that the infants were able to extract the depth relations specified by crossed (near) and uncrossed (far) horizontal disparity.     

RT to tactile stimuli presented ipsi- and contralaterally to the responding hand

Subjects had to react with the hand which received a tactile stimulus (uncrossed condition) or with the hand opposite to the hand which received the stimulus (crossed condition). Four experiments were conducted. In the first three, subjects knew which hand would receive the stimulus and which hand would have to respond. In the first two experiments, subjects reacted to a simple tactile stimulus while in the third subjects had to perform a tactile discrimination before responding. No significant differences in RT under the crossed and uncrossed conditions were observed in the first three experiments. In the fourth experiment, subjects did not know which hand would receive the stimulus, and they also did not know which hand would have to respond. Under these conditions, large significant differences in RT between the crossed and uncrossed condition emerged.

The study includes a criticism of a simple structural interpretation of interhemispheric transmission time (IHTT) as proposed by Bashore (1981). Support is provided for the view that in paradigms of the kind used here, allocation of attention to a psychologically defined hemispace is a more important factor in observed RT than structural links between stimulus and response mechanisms.     

Tactile localization performance in children with developmental coordination disorder (DCD) corresponds to their motor skill and not their cognitive ability

When localizing touches to the hands, typically developing children and adults show a “crossed hands effect” whereby identifying which hand received a tactile stimulus is less accurate when the hands are crossed than uncrossed. This demonstrates the use of an external frame of reference for locating touches to one’s own body. Given that studies indicate that developmental vision plays a role in the emergence of external representations of touch, and reliance on vision for representing the body during action is atypical in developmental coordination disorder (DCD), we investigated external spatial representations of touch in children with DCD using the “crossed hands effect”. Nineteen children with DCD aged 7–11 years completed a tactile localization task in which posture (uncrossed, crossed) and view (hands seen, unseen) were varied systematically. Their performance was compared to that of 35 typically developing controls (19 of a similar age and cognitive ability, and 16 of a younger age but similar fine motor ability). Like controls, the DCD group exhibited a crossed hands effect, whilst their overall tactile localization performance was weaker than their peers of similar age and cognitive ability, but in line with younger controls of similar motor ability. For children with movement difficulties, these findings indicate tactile localization impairments in relation to age expectations, but apparently typical use of an external reference frame for localizing touch.     

Visual reaction time and high-speed ball games

Laboratory measures of visual reaction time suggest that some aspects of high-speed ball games such as cricket are 'impossible' because there is insufficient time for the player to respond to unpredictable movements of the ball. Given the success with which some people perform these supposedly impossible acts, it has been assumed by some commentators that laboratory measures of reaction time are not applicable to skilled performers. An analysis of high-speed film of international cricketers batting on a specially prepared pitch which produced unpredictable movement of the ball is reported, and it is shown that, when batting, highly skilled professional cricketers show reaction times of around 200 ms, times similar to those found in traditional laboratory studies. Furthermore, professional cricketers take roughly as long as casual players to pick up ball flight information from film of bowlers. These two sets of results suggest that the dramatic contrast between the ability of skilled and unskilled sportsmen to act on the basis of visual information does not lie in differences in the speed of operation of the perceptual system. It lies in the organisation of the motor system that uses the output of the perceptual system.     

Handedness and footedness in Korean college students

This study was conducted to obtain normative data on foot preference and to compare footedness and handedness in a large sample (N = 866) of college students in Korea, where left-hand use for writing and other public acts is severely restricted (Kang & Harris, 1993). Based on scores from Korean-language versions of the Edinburgh Handedness Inventory (EHI; Oldfield, 1971) and the Waterloo Footedness Questionnaire Revised (WFQ-R; Elias, Bryden, & Bulman-Fleming, 1988), 11% of the subjects were left-footed but only 4.2% as left-handed. A significantly higher percentage of left-handers than right-handers showed crossed lateral preference, that is, for preference of the opposite-side foot. Of the left-handers with crossed preference, the majority were inconsistent left-handers (ILH; Peters & Servos, 1989), whereas most of those with uncrossed preference were consistent left-handers (CLH). Factor analysis of the EHI and WFQ-R revealed 2 handedness factors and 2 footedness factors. The footedness factors for skilled unipedal actions and for balancing-stabilizing varied in direction, strength, and relation to handedness in mixed-footers and left-handers, consistent with the possibility that the division of footedness into these categories might be neuropsychologically meaningful.     

The effect of limb crossing and limb congruency on multisensory integration in peripersonal space for the upper and lower extremities

The present study investigated how multisensory integration in peripersonal space is modulated by limb posture (i.e. whether the limbs are crossed or uncrossed) and limb congruency (i.e. whether the observed body part matches the actual position of one’s limb). This was done separately for the upper limbs (Experiment 1) and the lower limbs (Experiment 2). The crossmodal congruency task was used to measure peripersonal space integration for the hands and the feet. It was found that the peripersonal space representation for the hands but not for the feet is dynamically updated based on both limb posture and limb congruency. Together these findings show how dynamic cues from vision, proprioception, and touch are integrated in peripersonal limb space and highlight fundamental differences in the way in which peripersonal space is represented for the upper and lower extremity.     

Suprathreshold stereo-depth matches as a function of contrast and spatial frequency

Thresholds for stereoscopic-depth perception increase with decreasing spatial frequency below 2.5 cycles deg-1. Despite this variation of stereo threshold, suprathreshold stereoscopic-depth perception is independent of spatial frequency down to 0.5 cycle deg-1. Below this frequency the perceived depth of crossed disparities is less than that stimulated by higher spatial frequencies which subtend the same disparities. We have investigated the effects of contrast fading upon this breakdown of stereo-depth invariance at low spatial frequencies. Suprathreshold stereopsis was investigated with spatially filtered vertical bars (difference of Gaussian luminance distribution, or DOG functions) tuned narrowly over a broad range of spatial frequencies (0.15-9.6 cycles deg-1). Disparity subtended by variable width DOGs whose physical contrast ranged from 10-100% was adjusted to match the perceived depth of a standard suprathreshold disparity (5 min visual angle) subtended by a thin black line. Greater amounts of crossed disparity were required to match broad than narrow DOGs to the apparent depth of the standard black line. The matched disparity was greater at low than at high contrast levels. When perceived contrast of all the DOGs was matched to standard contrasts ranging from 5-72%, disparity for depth matches became similar for narrow and broad DOGs. 200 ms pulsed presentations of DOGs with equal perceived contrast further reduced the disparity of low-contrast broad DOGs needed to match the standard depth. A perceived-depth bias in the uncrossed direction at low spatial frequencies was noted in these experiments. This was most pronounced for low-contrast low-spatial-frequency targets, which actually needed crossed disparities to make a depth match to an uncrossed standard. This bias was investigated further by making depth matches to a zero-disparity standard (ie the apparent fronto-parallel plane). Broad DOGs, which are composed of low spatial frequencies, were perceived behind the fixation plane when they actually subtended zero disparity. The magnitude of this low-frequency depth bias increased as contrast was reduced. The distal depth bias was also perceived monocularly, however, it was always greater when viewed binocularly. This investigation indicates that contrast fading of low-spatial-frequency stimuli changes their perceived depth and enhances a depth bias in the uncrossed direction. The depth bias has both a monocular and a binocular component.     

Effects of posture on tactile localization by 4 years of age are modulated by sight of the hands: evidence for an early acquired external spatial frame of reference for touch

Adults show a deficit in their ability to localize tactile stimuli to their hands when their arms are in the less familiar, crossed posture. It is thought that this ‘crossed‐hands deficit’ arises due to a conflict between the anatomical and external spatial frames of reference within which touches can be encoded. The ability to localize a single tactile stimulus applied to one of the two hands across uncrossed‐hands and crossed‐hands postures was investigated in typically developing children (aged 4 to 6 years). The effect of posture was also compared across conditions in which children did, or did not, have visual information about current hand posture. All children, including the 4‐year‐olds, demonstrated the crossed‐hands deficit when they did not have sight of hand posture, suggesting that touch is located in an external reference frame by this age. In this youngest age group, when visual information about current hand posture was available, tactile localization performance was impaired specifically when the children's hands were uncrossed. We propose that this may be due to an early difficulty with integrating visual representations of the hand within the body schema.