Uncrossed Condition Research Articles

Multiple Spatial Coordinates Influence the Prediction of Tactile Events Facilitated by Approaching Visual Stimuli.

Interaction with other sensory information is important for prediction of tactile events. Recent studies have reported that the approach of visual information toward the body facilitates prediction of subsequent tactile events. However, the processing of tactile events is influenced by multiple spatial coordinates, and it remains unclear how this approach effect influences tactile events in different spatial coordinates, i.e., spatial reference frames. We investigated the relationship between the prediction of a tactile stimulus via this approach effect and spatial coordinates by comparing ERPs. Participants were asked to place their arms on a desk and required to respond tactile stimuli which were presented to the left (or right) index finger with a high probability (80%) or to the opposite index finger with a low probability (20%). Before the presentation of each tactile stimulus, visual stimuli approached sequentially toward the hand to which the high-probability tactile stimulus was presented. In the uncrossed condition, each hand was placed on the corresponding side. In the crossed condition, each hand was crossed and placed on the opposite side, i.e., left (right) hand placed on the right (left) side. Thus, the spatial location of the tactile stimulus and hand was consistent in the uncrossed condition and inconsistent in the crossed condition. The results showed that N1 amplitudes elicited by high-probability tactile stimuli only decreased in the uncrossed condition. These results suggest that the prediction of a tactile stimulus facilitated by approaching visual information is influenced by multiple spatial coordinates.

Age-related decline in interhemispheric transfer of tactile information: The fingertip cross-localization task

According to the disconnection hypothesis of cognitive aging, cognitive deficits associated with brain aging could be a result of damage to connective fibres. It has been suggested that the age-related decline in cognitive abilities is accompanied by age-related changes in interhemispheric communication ensured by commissural fibres. This study aimed to contribute to this topic by investigating the effects of aging on the efficiency of interhemispheric transfer of tactile information. A total of 168 right-handed subjects, aged 20–90 years, have been tested using the fingertip cross-localization task: the subject must respond to a tactile stimulus presented to one hand using the ipsilateral (uncrossed condition) or contralateral hand (crossed condition). Because the crossed task requires interhemispheric transfer of information, the value of the difference between the uncrossed and crossed conditions (CUD) can be deemed to be a reliable measure of the efficiency of the interhemispheric interactions. The uncrossed condition was more accurate than the crossed condition for all ages. However, the degree of the CUD was significantly age-dependent. The effectiveness of the interhemispheric transfer of tactile information decreased significantly with age and may indicate the occurrence of age-related changes of the corpus callosum. Considerably, performance appears to decline around the seventh decade of life with the fastest decline in the subsequent decades. The results suggest a relationship between brain aging and the efficiency of the interhemispheric transfer of tactile information. The findings are discussed in relation to the strategic role of white matter integrity in preserving behavioural performances.

Testing the exteroceptive function of nociception: The role of visual experience in shaping the spatial representations of nociceptive inputs

Adequately localizing pain is crucial to protect the body against physical damage and react to the stimulus in external space having caused such damage. Accordingly, it is hypothesized that nociceptive inputs are remapped from a somatotopic reference frame, representing the skin surface, towards a spatiotopic frame, representing the body parts in external space. This ability is thought to be developed and shaped by early visual experience. To test this hypothesis, normally sighted and early blind participants performed temporal order judgment tasks during which they judged which of two nociceptive stimuli applied on each hand's dorsum was perceived as first delivered. Crucially, tasks were performed with the hands either in an uncrossed posture or crossed over body midline. While early blinds were not affected by the posture, performances of the normally sighted participants decreased in the crossed condition relative to the uncrossed condition. This indicates that nociceptive stimuli were automatically remapped into a spatiotopic representation that interfered with somatotopy in normally sighted individuals, whereas early blinds seemed to mostly rely on a somatotopic representation to localize nociceptive inputs. Accordingly, the plasticity of the nociceptive system would not purely depend on bodily experiences but also on crossmodal interactions between nociception and vision during early sensory experience.

Revisiting Strephosymbolie: The Connection between Interhemispheric Transfer and Developmental Dyslexia.

The hypothesis that an atypical hemispheric specialization is associated to developmental dyslexia (DD) is receiving renewed interest, lending some support to Orton’s theory. In this article, we investigated whether interhemispheric transfer processes (IHT) are likely to be involved in developmental dyslexia. In this study, we tested 13 children with developmental dyslexia and 13 matched controls (aged 8 to 13 years) in four different tasks. In a tactile transfer task, the dyslexic children’s performance was less accurate. In a standard Poffenberger paradigm, dyslexic children performed slower than the controls in all conditions and did not show any difference between crossed and uncrossed conditions. Furthermore, they showed an increased asymmetry of performance according to the responding hand, while controls gave more coherent responses. In a visual task of object orientation discrimination, dyslexic children had slower Response Times (RTs) than controls, especially for mirror-reversed objects in the right visual field. Finally, a higher number of dyslexic children showed mirror-drawing or mirror-writing with respect to controls. Our results as a whole show that children with DD are impaired in interhemispheric transfer, although the differences in performance among dyslexic individuals suggest the impairment of different psychophysiological mechanisms. As such, a common origin in terms of connectivity problems is proposed.

Long-Term Musical Training Alters Tactile Temporal-Order Judgment.

Long-term musical training is an enriched multisensory training environment that can alter uni- and multisensory substrates and abilities. Amongst these altered abilities are faster reaction times for simple and complex sensory tasks. The crossed arm temporal-order judgement (TOJ) task is a complex tactile task in which TOJ error rate increases when arms are crossed. Reaction times (RTs) for this task are typically proportionate to the difficulty of the stimulus onset asynchrony (SOA) and increase more when the arms are crossed than when uncrossed. The objective of this study was to study the impact of musical training on RTs and accuracy for the crossed arm TOJ task. Seventeen musicians and 20 controls were tested. Musicians had significantly faster RTs for all crossed arm conditions and half of the uncrossed conditions. However, musicians had significantly more TOJ errors for the crossed posture. We speculate that faster musician TOJ RTs leave little time to consolidate conflicting internal and external task-related information when crossing the arms, leading to increased incorrect responses. These results provide novel insights on the potential mechanisms underlying the increased TOJ error rates when arms are crossed. Moreover, they add to the growing literature of altered sensory ability in musicians and propose an unexpected consequence of faster reaction times.

Arm crossing updates brain functional connectivity of the left posterior parietal cortex.

The unusual configuration of body parts can cause illusions. For example, when tactile stimuli are delivered to crossed arms a reversal of subjective temporal ordering occurs. Our group has previously demonstrated that arm crossing without sensory stimuli causes activity changes in the left posterior parietal cortex (PPC) and an assessment of tactile temporal order judgments (TOJs) revealed a positive association between activity in this area, especially the left intraparietal sulcus (IPS), and the degree of the crossed-hand illusion. Thus, the present study investigated how the IPS actively relates to other cortical areas under arms-crossed and -uncrossed conditions by analyzing the functional connectivity of the IPS. Regions showing connectivity with the IPS overlapped with regions within the default mode network (DMN) but the IPS also showed connectivity with other brain areas, including the frontoparietal control network (FPCN). The right middle/inferior frontal gyrus (MFG/IFG), which is included in the FPCN, showed greater connectivity in the arms-crossed condition than in the arms-uncrossed condition. These findings suggest that there is state-dependent connectivity during arm crossing, and that the left IPS may play an important role during the spatio-temporal updating of arm positions.

Connectivity measures in the Poffenberger paradigm indicate hemispheric asymmetries.

The Poffenberger paradigm is a well-known measure of interhemispheric transfer delays, calculated on the basis of the crossed vs uncrossed reaction time difference (CUD). However, the proper interpretation of CUD is extensively debated in the literature. In this study we used connectivity measures in an attempt to interpret CUD from the perspective of functional connectivity. Accordingly, we tried to define functional couplings in the Poffenberger paradigm; we used a simple choice version of the paradigm, and included a stimulation only (SO) condition for comparison. As an index of functional coupling we employed partial directed coherence, exploiting bilateral grouping of the electrodes to compute intra-and interhemispheric connection weight ratios (CWRs). Our findings indicated modulations in functional weights in relation to the SO condition, rather than the crossed and uncrossed conditions, such that the response executed by the right hemisphere yielded a decrease in intra-, yet an increase in interhemispheric CWRs, whereas the left hemisphere interactions showed connectivity patterns similar to the SO condition irrespective of the side of movement. Overall, our results suggest modulation of connectivity in the same/similar system, which was found to be optimized, in terms of hemispheric asymmetries, to different tasks.

Crossed and uncrossed acoustic reflex growth functions in normal-hearing adults, typically developing children, and children with suspected auditory processing disorder

Objective: Previous data suggested that children with suspected auditory processing disorders (APD) often show elevated or absent acoustic reflex thresholds, especially in crossed conditions (e.g. Allen & Allan, 2014). This study further explored these effects by measuring acoustic reflex growth functions (ARGF). Design: Crossed and uncrossed ARGF slopes were obtained by linear fits between reflex amplitudes and increases in activator level from threshold to 15 dB above it. Study sample: Normal-hearing adults, typically developing children and children with reported listening difficulties and suspected of having an APD, participated. Results: The ARGF slopes were shallower in crossed than in uncrossed conditions for all groups but the magnitude of the effect was significantly greater in the children with suspected APD. There were no differences between the typically developing children and the adults. Conclusions: The results suggest shallower ARGFs in children with suspected APD. Given the role of the acoustic reflex in facilitating hearing speech in noise these findings may begin to shed light on physiologic explanations for some of the difficulties that are reported by children with suspected APD.

Flexibly weighted integration of tactile reference frames

To estimate the location of a tactile stimulus, the brain seems to integrate different types of spatial information such as skin-based, anatomical coordinates and external, spatiotopic coordinates. The aim of the present study was to test whether the use of these coordinates is fixed, or whether they are weighted according to the task context. Participants made judgments about two tactile stimuli with different vibration characteristics, one applied to each hand. First, they always performed temporal order judgments (TOJ) of the tactile stimuli with respect to the stimulated hands that were either crossed or uncrossed. The resulting crossing effect, that is, impaired performance in crossed compared to uncrossed conditions, was used as a measure of reference frame weighting and was compared across conditions. Second, in dual judgment conditions participants subsequently made judgments about the stimulus vibration characteristics, either with respect to spatial location or with respect to temporal order. Responses in the spatial secondary task either accented anatomical (Experiment 1) or external (Experiment 2) coding. A TOJ crossing effect emerged in all conditions, and secondary tasks did not affect primary task performance in the uncrossed posture. Yet, the spatial secondary task resulted in improved crossed hands performance in the primary task, but only if the secondary judgment stressed the anatomical reference frame (Experiment 1), rather than the external reference frames (Experiment 2). Like the anatomically coded spatial secondary task, the temporal secondary task improved crossed hand performance of the primary task. The differential influence of the varying secondary tasks implies that integration weights assigned to the anatomical and external reference frames are not fixed. Rather, they are flexibly adjusted to the context, presumably through top-down modulation.

Crossed hands strengthen and diversify proprioceptive drift in the self-touch illusion.

In the self-touch illusion (STI), some can feel that both hands are touching each other even when they are separated actually. This is achieved by giving synchronized touches to both hands. Because the STI involves both hands (an administrating hand and a receptive hand) of a single person, two types of proprioceptive drifts (PDs) simultaneously occur in such a way that both hands are attracted to each other. It is known that the PD distance is generally larger for the administrating hand than for the receptive hand when the two hands are uncrossed. However, it remains unclear why such an asymmetrical relationship is observed universally. In this study, we conducted two types of experiment to induce the STI. The first experiment involved four conditions combining a factor of “whether the hands are uncrossed or crossed” and a factor of “whether the administrating hand is resting or active on the surface,” with the receptive (left) hand located at the body's midline. The result demonstrated that crossing hands and resting on surface (ROS) induced the STI. Specifically, crossing hands enhanced the amount of PD distance by more than two or three times. Moreover, it is interesting that strong PD with dominance of the receptive hand, which did not appear in the uncrossed condition, was observed frequently. The second experiment collected seven “illusion-sensitive” participants from the first experiment, all of whom had a strong tendency to feel the self-touch, and examined the effect of the location of the body midline on the PD when hands are crossed with the administrating hand ROS. The result demonstrated that the dominant hand on the PD completely differed among participants, but was relatively stable over the midline position and time in the same person. We also found that a small number of participants exhibited quite a different pattern of the PD in the identical posture. On the basis of the results, we analyze in detail how the dominant hand on the PD is determined in the STI.

Examining tactile spatial remapping using transcranial magnetic stimulation

Previous research has provided evidence for two stages of tactile processing (e.g., Azañon and Soto-Faraco, 2008; Groh and Sparks, 1996). First, tactile stimuli are represented in a somatotopic representation that does not take into account body position in space, followed by a representation of body position in external space (body posture representation, see Medina and Coslett, 2010). In order to explore potential functional and neural dissociations between these two stages of processing, we presented eight participants with TMS before and after a tactile temporal order judgment (TOJ) task (see Yamamoto and Kitazawa, 2001). Participants were tested with their hands crossed and uncrossed before and after 20 min of 1 Hz repetitive TMS (rTMS). Stimulation occurred at the left anterior intraparietal sulcus (aIPS, somatotopic representation) or left Brodmann Area 5 (BA5, body posture) during two separate sessions. We predicted that left aIPS TMS would affect a somatotopic representation of the body, and would disrupt performance in both the uncrossed and crossed conditions. However, we predicted that TMS of body posture areas (BA5) would disrupt mechanisms for updating limb position with the hands crossed, resulting in a paradoxical improvement in performance after TMS. Using thresholds derived from adaptive staircase procedures, we found that left aIPS TMS disrupted performance in the uncrossed condition. However, left BA5 TMS resulted in a significant improvement in performance with the hands crossed. We discuss these results with reference to potential dissociations of the traditional body schema.

The effect of vision on tactile TOJ during arm crossing

When people cross their arms, subjective rank ordering of successive unseen tactile stimuli delivered to both arms is affected (often being reversed) (Shore et al., 2002; Yamamoto and Kitazawa, 2001). It is also known that vision plays a significant role in modulating perceived limb position (Graziano et al., 2000). In this study, we examined the effect of vision; i.e., eyes opening and closing on tactile temporal order judgment (TOJ) with their arms crossed or uncrossed. In a psychophysical experiment, participants (, 13 males, 27.3 ± 1.8 y.o.) were required to judge temporal order of two tactile stimuli that were delivered to their both ring fingers with four conditions: uncrossed arms with eyes closed, crossed arms with eyes closed, uncrossed arms with eyes open and crossed arms with eyes open. To evaluate judgment probabilities of the participants, degree of reversals of their judgment was calculated as the sum of differences between correct response rates of the arms crossed condition and those of the arms uncrossed condition. In arms uncrossed conditions, judgment probabilities of the participants were not significantly different between eyes closed and open conditions. In contrast, reversal of the judgment with eyes closed was significantly larger than that with eyes open in arms crossed conditions (). The results suggest that vision play a significant role in tactile order judgment when the subject arms crossed.

What decision-making models can tell us about tactile remapping

To locate an object by touch, for example when fumbling around in the dark, or to react to a tactile event on the skin, somatosensory information must be quickly combined with the current position of the hand relative to the rest of the body. Not much is know yet about the time course of this integration between touch and body posture (e.g., proprioception), called tactile remapping. A tactile localization task in which there is a spatial conflict between the somatotopic and the external spatial representations can provide some constraints on the timing of the proprioceptive signal (necessary for the remapping) relative to the tactile input. Here, we construe this localization task as a perceptual discrimination problem. By making use of established models of decision-making, we aim to shed light on the internal processes during tactile remapping. In the experiment, participants had to make a speeded saccade towards a brief somatosensory stimulus applied to the finger of one hand, while their arms were either crossed or uncrossed about the body midline. The eye movement trajectories were recorded and revealed that especially in the crossed condition fast saccades occasionally started toward the incorrect (anatomically congruent) side and were corrected in-flight, resulting in a turn-around saccade (about 250 ms after tactile onset, which might reflect the completion of tactile remapping). Similar curved traces have been observed recently in a random-dot motion (RDM) discrimination task were subjects had to report their decision by moving a handle to a left or right target [1]. While in the RDM task the curved traces were interpreted as a change of mind, direction-reversal here is thought to be induced by the (delayed) proprioceptive signal. With crossed hands, the current body posture needs to be taken into account and the representation of touch changes through time due to the remapping [2]. In the uncrossed posture remapping is trivial as the anatomical and external reference frames are aligned. In the framework of decision-making and in line with [1], we treat the initial direction of a saccade as a first choice, caused by crossing a decision-threshold. Accordingly, we apply two computational models able to account for changes of mind, a simple drift-diffusion model [1] and a biophysically-realistic nonlinear attractor model [3], to fit experimental reaction-time distributions and performance. In the models, turn-around saccades originate from a second threshold crossing if the accumulated evidence of the initially losing alternative overtakes the first choice. Remapping only the outcome of the decision to a different motor response in the crossed-hand condition proved insufficient to explain the differences in reaction times and performance to the uncrossed case. This suggests that internal differences between the two conditions are already present prior to the decision-making stage. From the modeling perspective the proprioceptive signal thus changes the input (evidence) for deciding on a saccade to the left or right. Allowing only the model inputs to vary between crossed and uncrossed conditions, we gain predictions on the relative size and timing of the internal proprioceptive signal for tactile remapping.

Interhemispheric transmission time in persons with Down syndrome

The study of cerebral specialization in persons with Down syndrome (DS) has revealed an anomalous pattern of organization. Specifically, persons with DS elicit a right cerebral hemisphere lateralization for receptive language and a left cerebral hemisphere lateralization for the production of simple and complex movements: a pattern quite different from the left hemisphere lateralization typically characterizing the aforementioned processes in the non-DS population. It is thought that the putative separation between speech perception and movement planning systems as well as the cost of interhemispheric integration impedes verbal-motor behaviours in persons with DS. Moreover, morphological anomalies of callosal structure may further amplify between-hemisphere communication difficulties in the DS population. In the present investigation, we employed a behavioural technique (i.e. the Poffenberger paradigm; Poffenberger) to determine whether global anomalies of callosal structure further amplify deficits in interhemispheric communication. Fourteen individuals with DS and 25 chronological age-matched and gender-equated participants without intellectual disability performed a visuomotor reaction time (RT) test with their left or right hand to visual stimuli appearing left or right of visual fixation. Typically it is reported that responses to visual stimuli appearing ipsilateral to the responding hand (i.e. the uncrossed condition) are faster than responses wherein visual stimuli and responding hand are contralaterally mapped (i.e. the crossed condition). The increased RT associated with the crossed condition is reported on the order of 4 ms and has been interpreted to reflect the physiological result of interhemispheric transmission. Not surprisingly persons with DS exhibited slower and more variable RTs relative to control counterparts. In addition, a reliable RT advantage favouring the uncrossed conditions was observed among control participants but not persons with DS. In keeping with the extant literature, RT performance of the DS group was slower and more variable than control counterparts. This finding has been interpreted to reflect an 'adaptive reaction' wherein the perceptual-motor abilities of persons with DS are not optimized to respond to externally paced stimuli. In terms of evaluating interhemispheric transmission via the Poffenberger paradigm, our results show the finite measures of explicit brain-behaviour relations characterizing so-called healthy controls are not always tenable in the DS population. Indeed, we believe such a finding underpins the aforementioned 'adaptive reaction' exemplifying preferred movement control in persons with DS.

Handedness effects on interhemispheric transfer time: A TMS study

The crossed–uncrossed difference (CUD) estimates the interhemispheric transfer time (ITT) through the corpus callosum. Previous research has shown that transcranial magnetic stimulation (TMS) to the occipital cortex determines an increased CUD during cognitive tasks. The aim of the present study was to investigate whether TMS stimulation applied at a motor stage can interfere with the ITT, comparing the performance of left- and right-handed people. Results showed a significant TMS effect, i.e. increasing reaction times were reported when stimulation was delivered on the left primary motor area. Effects were more evident when information was primarily perceived through the dominant hemisphere. Both left and right stimulations increased CUD times in right-handed subjects; however, left-handed subjects showed significant effects associated with left stimulation only. Furthermore, in both groups, TMS produced larger effects in the crossed than in the uncrossed condition. TMS stimulation increased reaction times, thus supporting the idea that the interhemispheric transfer of visuo-motor information occurs at a motor processing stage. The dominant hemisphere seems to play a major role within this process: our data indicates that left- and right-handed people have different ITT latencies associated with the transfer of information to the contralateral hemisphere.

Exploratory data analysis reveals visuovisual interhemispheric transfer in functional magnetic resonance imaging

We used an exploratory data analysis approach to detect interhemispheric processing of complex visual stimuli in functional magnetic resonance imaging (fMRI). A crossed-uncrossed visual field paradigm was used to elicit interhemispheric transfer of picture/word information. Under the uncrossed (control) condition, the stimuli were presented to the preferential hemispheres (pictures to the left visual field/right hemisphere and words to the right visual field/left hemisphere). Under the crossed condition, the visual field presentation was switched in order to elicit increased interhemispheric processing. Fuzzy cluster analysis revealed significantly more crossed activity in cortical areas near the splenium of the corpus callosum. As expected, examination of the activation revealed smaller responses in perisplenial regions (relative to visual responses in the medial extrastriate regions). The exploratory results were compared with those obtained from parametric and masked analyses. The findings confirm that fMRI can be used to detect interhemispheric transfer of picture/word information. The activation was optimally characterized using exploratory data analysis.

Visual spatial integrity in the absence of splenium

Several lines of evidence have confirmed that visual integrity among the two hemifields is severely impaired following transection of posterior part of the corpus callosum (splenium). But the extent of this impairment differs for various visual functions. Here, in a posterior callosectomized patient (MD), interhemispheric visual spatial integrity is investigated in three experiments. In the first experiment, MD was asked to make decision about horizontal alignment of two balls presented simultaneously in one of three conditions: both in right or left hemifield, or each in one hemifield. We have previously shown that she is not able to perform a shape-matching task for stimuli presented to different hemifields. But in this task, MD was able to compare location of the two bilaterally presented stimuli significantly above chance level.Then we investigated whether attentive visual object tracking across vertical meridian of the visual field is possible in the absence of splenium. MD had to attentively track one bouncing ball among three identical balls, while it crossed the vertical midline in half of trials. Her performance in crossed conditions was significantly above chance level, but it was lower than uncrossed conditions. Finally, we investigated the contribution of simple interhemispheric temporal signals in performing the attentive tracking task. Results suggest that the patient was not using such temporal signals. Our results suggest that interhemispheric connections other than splenium can contribute in making an integral visual map across hemifields. Such an integrated map can be used for bilateral visual spatial comparisons and visual spatial attention.

Early Visual Evoked Potentials in Callosal Agenesis.

Three participants with callosal agenesis and 12 neurologically normal participants were tested on a simple reaction time task, with visual evoked potentials collected using a high-density 128-channel system. Independent-components analyses were performed on the averaged visual evoked potentials to isolate the components of interest. Contrary to previous research with acallosals, evidence of ipsilateral activation was present in all 3 participants. Although ipsilateral visual components were present in all 4 unilateral conditions in the 2 related acallosal participants, in the 3rd, these were present only in the crossed visual field-hand conditions and not in the uncrossed conditions. Suggestions are made as to why these results differ from earlier findings and as to the neural mechanisms facilitating this ipsilateral activation.

What drives children's limb selection for reaching in hemispace?

Arguably, the act of reaching constitutes one of the most devoted lines of contemporary developmental research. In addition to the underlying dynamical characteristics of motor coordination, a key element in programming is limb selection, a phenomenon (handedness) that has so far resisted any reasonable unified explanation. From a more contemporary view, two factors appear to have the most influence on hand selection for a given task: motor dominance and attentional information related to task demands. This study was designed to determine what factor(s) influence choice of limb for reaching in hemispace in reference to motor dominance, object proximity, and a hemispheric bias favoring use of the hand on the same side as the stimulus. Strong right-handed children were asked to reach and retrieve a small object across right and left hemispace locations beginning with the arms uncrossed and arms-crossed. With the arms-crossed condition, an imagined and actual movement execution was administered. Results from the uncrossed condition supported previous reported findings for adults and children. That is, participants responded ipsilaterally using the hand on the same side as the stimulus, thus supporting the case for object proximity and hemispheric bias. However, in the arms-crossed condition the vast majority of participants preferred keeping the limbs crossed in response to right and left hemispace stimuli, which leads to the suggestion that object proximity rather than hemispheric bias was the driving factor in this context. The behavioral pattern for imagined and actual movement was not significantly different. Overall, the findings add to the growing acceptance that limb selection is task and context dependent, rather than a biologically based invariant feature of motor behavior.

Effects of handedness on tactile temporal order judgment

We examined effects of handedness on the judgment of temporal order of successive taps delivered to both hands. When the subjects’ arms were uncrossed, the temporal resolution (84% correct responses) of right-handed subjects (52 ± 4 ms, n = 16) was significantly better than that of left-handed subjects (83 ± 9 ms, n = 16). When their arms were crossed, both groups tended to invert their judgment to a similar extent at intervals as long as 200–300 ms. In the arms crossed condition, right handed subjects inverted their judgment more often in response to left-hand-first stimuli than to right-hand-first stimuli, whereas left-handed subjects did not show the same asymmetry. We infer that hemispheric lateralization, which is generally stronger in right- than in left-handed subjects, contributes to the relatively better temporal resolution of right-handed subjects in the uncrossed condition, as well as to the asymmetric effect of stimulation order in the crossed condition.