Performance of unimanual and bimanual multiphased prehensile movements

By manipulating task action demands in 2 experiments, the author investigated whether the context-dependent effects seen in unimanual multiphase movements are also present in bimanual movements. Participants (N = 14) in Experiment 1 either placed or tossed objects into targets. The results indicated that the intention to perform a subsequent action with an object could influence the performance of an earlier movement in a sequence in both unimanual and bimanual tasks. Furthermore, assimilation effects were found when the subsequent tasks being performed by the 2 hands were incongruent. In Experiment 2, the author investigated in 12 participants whether planning in a multiphase movement includes some representation of the accuracy demands of the subsequent task. The accuracy demands of a subsequent task did not appear to influence initial movement planning. Instead, the present results support the notion that it is the action requirements of the subsequent movement that lead to context-dependent effects.     

Experience-dependent effects in unimanual and bimanual reaction time tasks in musicians

Engaging in musical training has been shown to result in long-term cognitive benefits. The authors examined whether basic cognitive-motor processes differ in people with extensive musical training and in nonmusicians. Musicians (n = 20) and nonmusicians (n = 20) performed a simple reaction time (RT) task under unimanual and bimanual conditions. Musicians' RTs were faster overall than were those of nonmusicians, and those who began their musical training at an earlier age (around age 7-8 years, on average) exhibited a larger bimanual cost than did those who began later (around 12 years, on average). The authors conclude that experience-dependent changes associated with musical training can result in greater efficacy of interhemispheric connections if those changes occur during certain critical periods of brain development.     

Development of unimanual versus bimanual task performance in an isometric task

Sixty-three children between 5 and 12 years of age and 15 adults performed a unimanual and a bimanual isometric force task. The performance of the preferred hand in the unimanual task was compared to the performance of the preferred hand in the bimanual task. It was hypothesized that in the bimanual task the absolute error will be higher, there will be more irregularity and the participants will need more time due to the additional effort from the central nervous system, especially with respect to the communication between the hemispheres. Furthermore, in younger children bimanual force variability was expected to be higher due to developmental aspects concerning callosal maturation and attention. It was found that with respect to force generation the preferred hand was not affected by bilateral isometric force generation, but with respect to force regulation it was. The coefficient of variation (CV) of the force was 34% larger in the bimanual task as compared to the unimanual task. For the time to target force, the increase was 28%. With repetition of the trials the CV decreased in the bimanual task, but only in the youngest age group. During development there was no change in absolute error, yet there was a major reduction in force variability in the bimanual task. It is suggested that improvement in interhemispheric communication and in the ability to focus attention plays a role in the decrease in variability with age.     

Intermovement interval and spatial assimilation effects in sequential bimanual and unimanual movements

This study extended earlier work by showing spatial assimilations in sequential bimanual and unimanual movements separated by 1.5-3.5 s. In Experiments 1 and 2, 30 right-handed participants (18-22 years of age) made rapid single and bimanual lever reversals of 20 degrees and 60 degrees assigned to 1.5, 2.5, or 3.5 s intermovement interval groups. Participants self-timed the intermovement interval in the first experiment, but it was provided in the second experiment using separate auditory stimuli. In the third experiment, participants performed both the 20 degree and 60 degree movement with the same hand. In all experiments, the shorter-distance limb overshot and the longer-distance limb undershot the targets in both bimanual and unimanual sequential movements relative to single movements in all three intermovement interval groups, particularly in the non-dominant left limb. The results suggest that assimilation effects in sequential movements are caused by command interactions at the planning level, but the effects are reduced by practice.     

Auditory instructional cues benefit unimanual and bimanual drawing in Parkinson's disease patients

The present study investigated performance of unimanual and bimanual anti-phase and in-phase upper limb line drawing using three different types of cues. Fifteen Parkinson’s disease (PD) patients, 15 elderly, and 15 young adults drew lines away from and towards their body on a tabletop every 1000 ms for 30 s under three different cueing conditions: (1) verbal (‘up’, ‘down’); (2) auditory (high tone, low tone); (3) visual (target line switched from top to bottom). PD patients had larger and more variable amplitudes which may be related to the finding that they also produced more curvilinear movements than young and elderly adults. Consistent with previous research, when compared to the elderly and young adult group PD patients produced a mean relative phase which deviated more from the instructed coordination modes and they showed larger variability of relative phase in bimanual coordination, especially in anti-phase conditions. For all groups, auditory and verbal cues resulted in lower coefficient of variance of cycle time, lower variability of amplitude and lower variability of relative phase than visual cues. The benefit of auditory cues may be related to the timing nature of the task or factors related to the auditory cues (e.g., reduced attentional demands, more kinesthetic focus).     

Dissociation of bimanual responses with the Simon effect: on the nonunitization of bimanual responses

The authors examined whether responses of the 2 hands were completely unitized when participants (N=36) produced bimanual responses to lateralized targets in a Simon-type paradigm. Their primary aim was to investigate whether lateralized stimuli differentially influence the response dynamics of the 2 hands. Simon effects were obtained in reaction time and force components of the bimanual response by the hand on the same side as the lateralized stimulus were more forceful than were those of the other hand. Also, Simon effects were larger when the lateralized target appeared alone than when it was accompanied by a distractor on the other side of the display. Finally, responses of the 2 hands were correlated most strongly when stimulus displays were symmetrical. The authors conclude that bimanual responses are strongly coupled, but not perfectly so.     

Signal detectability in the presence of monotic or dichotic noise bands of equal or unequal levels

The application of the power-spectrum model of masking to the detectability of a signal masked by dichotic noise was investigated in three experiments. In each experiment, the signal was a 2-kHz sinusoid of 400-msec duration, masked by either one or two 800-Hz wide bands of noise presented singly or in pairs. In Experiment 1, we compared the detectability of a diotic signal masked by dichotic noise with the detectability of a monaural signal masked by each of the noises separately. The spectrum level of the noise was 35 dB SPL. For dichotic presentations, the signal was sent to both ears while pairs of noise bands, one below and one above the signal frequency, were presented together, one band to each ear. Threshold levels with the dichotic stimuli were lower than or equal to the thresholds with either ear's stimulus on its own. Similar dichotic stimuli were used in Experiment 2, except that the signal frequency was nearer to one or the other of the bands of masking noise, and the noise had a spectrum level of 50 dB SPL. In Experiment 3, thresholds were obtained with two sets of symmetrically and asymmetrically placed notched-noise maskers. For one of these sets, the spectrum level of both noise bands was 35 dB SPL; for the other set, interaural intensity differences were introduced in the form of an inequality in the levels of the noise bands on either side of the signal. In one ear, the spectrum level of the lower frequency noise band was 35 dB SPL and the spectrum level of the higher frequency noise band was 25 dB SPL, whereas in the other ear, the allocation of noise level to noise band was reversed. The dichotic thresholds obtained with the unequal noise maskers could be predicted from the shapes of the auditory filters derived with equal noise maskers. The data from all three experiments suggest that threshold signal levels in the presence of interaural differences in masker intensity depend principally on the ear with the higher signal-to-masker ratio at the output of its auditory filter, a finding consistent with the power-spectrum model of masking.     

Hand preferences in unimanual and bimanual feeding by wild vervet monkeys (Cercopithecus aethiops)

Lateral preference was examined in spontaneous feeding actions in 2 troops of wild vervet monkeys (Cercopithecus aethiops). Processing of 4 foods (termites, leaf shoots, sugarcane, and fruit) was studied. Actions included unimanual reaching to moving objects, operating from an unstable posture, and coordinated bimanual processing. Between 19 and 31 subjects were available, according to the task. In 2 tasks, laterality of 2 independent stages was measured separately, giving 6 measures in all. On 4 of these measures, most monkeys were ambipreferent, and only a few showed significant hand preferences. Only for termite feeding and detaching material from fruits did the majority show significant lateralization; no tasks elicited exclusive use of 1 hand. Preference appeared labile, because in 2 tasks, population trends reversed with increasing age. No population trends to left or right were found; instead, these monkeys showed ambilaterality, with lateralization associated with task complexity.     

Hand preference and performance on unimanual and bimanual tasks in capuchin monkeys (Cebus apella)

Patterns of manual preference and the extent to which preference provided a benefit in performance (movement time) were evaluated in 7 young adult capuchin monkeys (Cebus apella). Directions of preference were inconsistent within individual animals across home-cage activities, unimanual, and bimanual experimental tasks. Preferences were more strongly expressed in the experimental tasks than in the home cage. A left bias in the population for prehension, predicted by recent theories, was not evident in any setting. Movement time was moderately negatively correlated with degree of preference within experimental tasks. The benefit to performance conferred by lateral preference was not dependent on whether the right or left hand was preferred. Lateralization of prehension appears to be a flexible process in these monkeys, which can result in quickly realized benefits in some conditions.     

Vertical versus horizontal spatial compatibility: Right-left prevalence with bimanual responses

For two-choice tasks in which stimulus and response locations vary along horizontal and vertical dimensions, the spatial compatibility effect is often stronger on the horizontal than vertical dimension. Umiltà and Nicoletti [(1990) Spatial stimulus-response compatibility (pp. 89–116). Amsterdam: North-Holland] attributed this right-left prevalence effect to an inability to code vertical location when horizontal codes are present simultaneously. Hommel [(1996) Perception & Psychophysics, 43, 102–110] suggested instead that it reflects a voluntary strategy. This study reports four experiments that examine this issue. Experiment 1 was a conceptual replication of Hommel's Experiment 1, with responses made on a numeric keypad and subjects instructed in terms of the vertical or horizontal dimension. The results replicated Hommel's findings that showed a right-left advantage with horizontal instructions; however, with vertical instructions, we found a benefit of vertical compatibility alone that he did not. This benefit for vertical compatibility alone was eliminated in Experiment 2 using a varied practice schedule similar to that used by Hommel. Experiment 3 showed right-left prevalence and a benefit of vertical compatibility alone, even with varied practice and vertical instructions, when subjects responded on perpendicularly arranged handgrips. These benefits were eliminated in Experiment 4 using Hommel's method of urging subjects to respond only in terms of the instructed dimension. With bimanual responses, right-left prevalence is a robust phenomenon that is evident when comparing across vertical and horizontal instructions and, when the right-left distinction is relatively salient, within the vertical instructions condition alone. Received: 4 February 2000 / Accepted: 5 May 2000     

Electrodermal responses to attended and nonattended significant stimuli during dichotic listening

Some investigators have found that words previously associated with shock elicit electrodermal responses (EDRs) when presented in the nonattended channel of a dichotic listening task. The present experiment tested for this phenomenon while closely monitoring for shifts in attention to the nonattended channel. College student volunteers verbally shadowed a series of unrelated words presented to the attended channel while words made significant by previous association with shock (and semantically related words) were occasionally presented to the nonattended channel. Three principal findings were obtained. Fist, when EDRs were averaged across all trials and across all subjects, it was found that EDRs were elicited by the significant words presented in the nonattended channel. Second, for the subgroup of subjects that had the significant words presented to the right ear (activating the left cerebral hemisphere), it was found that EDRs were elicited by the significant words presented to the left ear (activating the right cerebral hemisphere), it was found that EDRs were elicited by the significant word seven on trials on which there were no apparent shifts in attention. The results of this study indicate the importance of closely controlling and monitoring for shifts in attention and suggest the potential importance of cerebral laterality in mediating EDRs to stimuli presented in a nonatttended channel.     

Use of the dichotic listening technique with learning disabilities

Dichotic listening (DL) techniques have been used extensively as a non-invasive procedure to assess language lateralization among children with and without learning disabilities (LD), and with individuals who have other auditory system related brain disorders. Results of studies using DL have indicated that language is lateralized in children with LD and that the lateralized language asymmetries do not develop after age 6 nor are they affected by gender. Observed differences in lateralized language processes between control children and those with LD were found not due to delayed cerebral dominance, but rather to deficits in selective attention. In addition, attention factors have a greater influence on auditory processing of verbal than nonverbal stimuli for children with LD, and children with LD exhibit a general processing bias to the same hemisphere unlike control children. Furthermore, employing directed attention conditions in DL experiments has played an important role in explaining learning disabled children's performance on DL tasks. We conclude that auditory perceptual asymmetries as assessed by DL with children who experience LD are the result of the interaction of hemispheric capability and attention factors.     

Outcomes of hemisphericity questionnaires correlate with unilateral dichotic deafness

Using the Dichotic Deafness Test, 145 university workers were separated into dichotic deafness and hearing groups based on minor ear responses to dichotic consonant-vowel stimuli. They were also separated into putative right and left brain-oriented groups by Zenhausern's Preference Questionnaire. Interestingly, members of the dichotically hearing group chose mainly right brain-oriented answers and vice versa. A correlation coefficient twice that obtained for Zenhausern's Preference Questionnaire resulted when subject groups separated by the novel Polarity Questionnaire were compared to Dichotic Deafness Test groups. Only 30% of Preference Questionnaire items, versus 90% of Polarity Questionnaire items, were significantly correlated with Dichotic Deafness Test groups. This is the first report of hemisphericity-type questionnaires showing significant correlations with a biophysical measure of brain laterality.     

Simultaneous and staggered dichotic word and digit tests with stutterers and nonstutterers

The present study compared the performance of stuttering adults and matched controls on the Staggered Spondaic Word (SSW) test and three experimental digit tests—Two Pair Digit—TPD, Staggered Digits Simultaneous—SDS, and Staggered Digits Offset—SDO. Results indicated differences between stuttering and nonstuttering group mean values on the left ear scores of the TPD test, and on the numbers of reversals on both the SDS and SDO tests. The SSW, SDS, and SDO tests were all found to produce similar results in both stutteres and nonstutterers. However, the numbers of reversals on the SDS and SDO tests were significantly greater than those observed on the SSW test for both groups. Finally, the TPD test was found to be significantly more difficult for both groups than either of the other two experimental tests (i.e., SDS and SDO). These results are discussed in terms of similarity and differences with other dichotic listening studies. Limitations of the study and implications for further research are also presented.     

The perception of clicks in linguistic and nonlinguistic messages

Three experiments were run analyzing Ss’ abilities to locate clicks in auditory messages. In Expenment 1 it was found that the intonation pattern of the linguistic message largely determined the types of errors Ss made in click placement; syntactic factors were only marginally effective and semantic factors were effectively irrelevant. In addition to these linguistic factors, there was evidence that such nonlinguistic factors as attention, memory, and response biases were contributing to the data. Experiment 2 supplied additional evidence favoring these nonlinguistic factors. Experiment 3 was a mock-up of Experiment 2 except that broad-band white noise was used as the primary message instead of English sentences. The patterns of placement errors Ss made in these several experiments (especially Experiments 2 and 3) were sufficiently similar to one another to force the conclusion that nonlinguistic factors are primarily responsible for the errors Ss make in trying to locate clicks in messages. A neo-Titchenerian attention hypothesis based upon the law of prior entry was proposed to account for the data.     

Reliability and magnitude of laterality effects in dichotic listening with exogenous cueing

The purpose of the present study was to replicate and extend to word recognition previous findings of reduced magnitude and reliability of laterality effects when exogenous cueing was used in a dichotic listening task with syllable pairs. Twenty right-handed undergraduate students with normal hearing (10 females, 10 males) completed a dichotic listening task in which the words bower, dower, power, and tower were presented in a sad, angry, happy, or neutral tone. Each stimulus pair (one to each ear) was preceded by a lateralized tone cue. Participants were required to identify the word presented to the ear where the cue was heard. When correct responses were analyzed, results replicated the pattern of reduced magnitude and reliability of laterality effects observed in previous studies. However, the percentage of intrusions (identification of the stimulus presented to the uncued ear) increased with the time between the onset of the cue and the target, suggesting that the cue was not fully effective. These results are discussed in terms of their implications for the use of exogenous cueing to control attention. It seems that, in the present task, an effective means of attention control has yet to be identified.     

Timing and co-ordination of repetitive bimanual movements

Similar timing of movements of the two hands has been observed when they are moved to separate targets (Kelso et al., 1979). This was taken as evidence for a low-level, co-ordinative structure that constrains the muscles of the arms to function as a single unit.

An experiment to investigate the relation between voluntary timing control and timing in bimanual movement is described. The task required subjects to make repetitive movements of unequal difficulty for the two hands with the hands arriving synchronously at their respective targets. Estimates of the covariance of successive intervals defined by pairs of left-right responses (arrivals at the targets) were not negative. It is shown that this indicates that the motor delay between the timer regulating repetition rate and the overt responses has no component common to left- and right-responses. Although the co-ordinative structure is described as low-level, in terms of the time sequence of operations associated with each response pair, the data indicate its place is before, not after, the timer.