- Email: [email protected]
Subliminal priming and effects of hand dominance
Acta Psychologica 141 (2012) 73–77
Contents lists available at SciVerse ScienceDirect
Acta Psychologica journal homepage: www.elsevier.com/ locate/actpsy
Subliminal priming and effects of hand dominance Deborah J. Serrien ⁎, Michiel M. Sovijärvi-Spapé, Gita Rana School of Psychology, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
a r t i c l e
i n f o
Article history: Received 12 March 2012 Received in revised form 30 June 2012 Accepted 7 July 2012 Available online 2 August 2012 PsycINFO classification: 2330 Keywords: Motor behavior, Handedness Bimanual coordination
a b s t r a c t In the masked priming paradigm, motor responses to targets are influenced by previously presented subliminal primes, and are guided by facilitatory and inhibitory mechanisms that depend on prime-target compatibility/duration. In this study, we evaluate subliminal-driven priming in right- and left-handers during unimanual as well as bimanual tasks. The data from the unimanual tasks confirmed that prime-target compatibility affects performance as a function of prime-target duration. In a bimanual setting, the preferred hand benefitted from facilitation in both handedness groups whereas the non-preferred hand showed a positive priming effect only in left-handers. This denotes that left-handers are more susceptible to response activation of either hand. In addition, inhibitory priming had a stronger effect on the non-preferred than preferred hand, independent of handedness group. Overall, the findings suggest that subliminal-driven mechanisms that assist adaptive motor behavior are sensitive not only to extrinsic (task-related) factors such as prime-target compatibility but also to intrinsic (performer-related) factors such as hand dominance. The data further provide support for handedness-specific effects in motor functions and underline a significant role of hand dominance in the control of bimanual actions. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Although most of our behavior is considered voluntary, some responses can be triggered by stimuli that are inaccessible to conscious awareness. These stimuli influence behavioral performance; subliminal priming effects that can be examined by means of masked prime designs. In these paradigms, a target is preceded by a masked prime that is associated with the same or different response as the target (Eimer & Schlaghecken, 1998; Klapp & Haas, 2005; Neumann & Klotz, 1994; Vorberg, Mattler, Heinecke, Schmidt, & Schwarzbach, 2003). Masked primes speed-up responses to target stimuli if prime and target are compatible and slow down responses if they are incompatible. This performance benefit reflects a positive compatibility effect (PCE), and occurs when the prime-target interval is short (0–60 ms). However, the priming pattern reverses when the prime-target interval is longer (100–200 ms); a so-called negative compatibility effect (NCE), (Eimer & Schlaghecken, 1998; Jaśkowski, 2008; Lingnau & Vorberg, 2005). One explanation is that the NCE represents motor inhibition during which a self-inhibition process suppresses the initial response tendency triggered by the prime when it is no longer supported by sensory evidence (Eimer & Schlaghecken, 2003; Klapp & Hinkley, 2002). However, alternative interpretations suggest that NCE is driven by perceptual characteristics of the stimuli (Lleras & Enns, 2004; Verleger, Jaśkowski, Aydemir, van der Lubbe, & ⁎ Corresponding author at: School of Psychology, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. Tel.: +44 115 951 5285; fax: +44 115 951 5324. E-mail address: [email protected] (D.J. Serrien). 0001-6918/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.actpsy.2012.07.008
Groen, 2004). At present, it is generally believed that NCE reflects motor inhibition, either as self-inhibition (Schlaghecken & Eimer, 2002), or as mask-triggered inhibition (Jaśkowski, 2007; Lleras & Enns, 2004). Low-level inhibition differs from high-level inhibition that occurs during voluntary response withholding as there is no intentional effort to suppress a response to the prime (Eimer & Schlaghecken, 2003; Sumner et al., 2007). Most behavioral studies have examined the influence of subliminal priming on individual right and left hand performances. Less is known about the role of priming in a bimanual context. That is, when both hands are required to perform simultaneously. The evaluation of bimanual actions is relevant since the constraints that underlie coordinated behavior do not necessarily follow the rules that regulate unimanual movements (Serrien, 2009; Swinnen, 2002). In particular, bimanual control structures impose interdependence of movement parameters (Franz, Zelaznik, & McCabe, 1991; Kelso, Southard, & Goodman, 1979; Serrien & Swinnen, 1997; Steglich, Heuer, Spijkers, & Kleinsorge, 1999), although the coordination constraints are considered flexible (Serrien & Wiesendanger, 2001). Distinct processing demands due to bimanual constraints are further highlighted from simple reaction time tasks, which show longer response times in bimanual than unimanual conditions; also labelled as the bimanual deficit/cost (Hughes & Franz, 2007; Taniguchi, Burle, Vidal, & Bonnet, 2001). In view of motor priming, Schlaghecken, Klapp, and Maylor (2009) observed that primes that linked with a response hand produced NCEs during unimanual tasks, but not during bimanual tasks. The latter observation suggested that NCEs operate at an abstract (non-effector) response level.
74
D.J. Serrien et al. / Acta Psychologica 141 (2012) 73–77
However, it is unclear how control processes as determined by hand dominance would interact with subliminal-driven motor priming. Overall, most research on motor control has been conducted in right-handers whereas less is known from left-handers. Although left-handers demonstrate structural asymmetries of the motor system that are opposite to those of right-handers, these are less prominent and defined (Amunts et al., 1996). Furthermore, functional imaging data have revealed that left-handers show less hemispheric lateralization than right-handers during intricate unimanual patterns (Solodkin, Hlustik, Noll, & Small, 2001) and bimanual actions (Kloppel et al., 2007; Vingerhoets et al., 2012). These observations suggest that left- and right-handers have distinct control mechanisms of motor behavior (Kloppel et al., 2007; Reid & Serrien, 2012). Subsequently, the aim of this study was to examine the PCE and NCE processes in left- vs. right-handers during unimanual and bimanual assignments. Although these processes are considered low-level and automatic as they occur outside conscious awareness, they are in line with intentions (Klapp & Haas, 2005). Accordingly, it was hypothesized that primed responses would display different profiles in left- and right-handers due to differences in lateralization of motor functions. Effects were expected to become most apparent during bimanual responses due to the increased task complexity as compared to unimanual responses. 2. Method 2.1. Participants Participants in the experiment were 26 left-handers (21.8± 3.4 years) and 23 right-handers (20.5±1.8 years). Their laterality index was −88.2±13.2 and 84.4±13.1 for the left- and right-handers, respectively (Oldfield, 1971). The participants gave informed consent prior to participation in accordance with the declaration of Helsinki, and the study was approved by the local ethics committee. 2.2. Task and procedure A standard masked prime design was used during which double arrows were used as prime and target stimuli. The participants were asked to respond to the target stimuli with the left index by pressing the C-key (arrows pointing to the left, bb), the right index by pressing the M-key (arrows pointing to the right, >>) or both index fingers by pressing the C- and M-keys (bilateral arrows, b>) on a keyboard. Before the target stimuli appeared, a prime was displayed that pointed to the left (bb) or to the right (>>). As illustrated in Fig. 1, each trial started with a centrally presented fixation cross. After 250 ms, the fixation cross disappeared and was followed by a blank screen for 300 ms, a prime for 17 ms and a feature-mask (overlapping horizontal, vertical and oblique lines) for 100 ms. In the short inter-stimulus-onset (ISO) condition, the target appeared simultaneously with the mask whereas it appeared 100 ms after the mask and was shown for 100 ms in the long ISO condition. Thereafter, a blank screen was present for an inter-trial interval (ITI) of 800 ms. Trials were compatible when prime and target arrows pointed in the same direction and incompatible when they pointed in different directions. Primes and targets were randomized within blocks of 180 trials. The short and long ISO trials were presented in separate blocks, which were counterbalanced between participants. Short breaks were offered every 60 trials. Familiarization trials were provided prior to the experimental blocks. Participants were instructed to maintain central eye fixation throughout the experiment and to respond as quickly and accurately as possible to the direction of the target arrows. After completion of the main experiment, the participants were queried about the primes. No one had noticed the primes. Subsequently, information was provided to the participants about the primes, and masking efficiency was evaluated in a forced-choice control experiment,
Fig. 1. Schematic presentation of the trial structure.
which assessed prime identification. In these prime identification trials, prime and mask were presented, but there were no targets. Participants were asked to identify the prime and to respond with corresponding finger(s) across 45 trials. In order to have all the responses from the main experiment, the prime stimuli were pointing to the left (bb), right (>>) or bidirectional (b>). Trials were randomized. Participants were told to guess on trials in which they could not identify the primes. There was no emphasis on reaction time. 2.3. Measurements and data analysis The reaction time (RT) to targets (filtered to exclude erroneous responses) and number of errors were used as behavioral measurements in the main experiment. The unimanual data were analyzed by means of 2 × 2 × 2 ANOVAs (Group: right- vs. left-handers; Response Hand: preferred vs. non-preferred; Compatibility: compatible vs. incompatible priming) whereas the bimanual data were analyzed by means of 2 × 2 × 2 ANOVAs (Group: right- vs. left-handers; Response Hand: preferred vs. non-preferred; Primed Hand: preferred vs. non-preferred), separately for the short and long ISO conditions. Additional 2 × 2 ANOVAs (Group: right- vs. left-handers; Condition: Unimanual vs. Bimanual) were conducted on the RT in order to establish the processing demands for bimanual as compared to unimanual responses. Post-hoc t-tests were conducted and Bonferroni correction was made where appropriate. In the prime identification task, the observed (correct response) frequency was calculated for the primes and contrasted with the expected (chance level) frequency by means of a non-parametric χ 2 test. The statistical threshold was set at p b .05. Means ± SE are reported. 3. Results 3.1. Short ISO: unimanual conditions For the unimanual responses, the RT revealed a significant main effect of Response Hand, F(1, 47) = 9.15, p b .01, η 2 = .129, with the preferred hand (400.2 ± 4.6 ms) responding quicker than the non-preferred hand (408.1 ± 4.3 ms). The main effect of Compatibility was also significant, F(1, 47)= 120.21, p b .01, η2 = .167, with faster compatible responses (391.0 ± 4.7 ms) than incompatible responses (417.5± 4.8 ms). Fig. 2 (upper panel) illustrates the unimanual RTs for the short ISO. The error scores showed a significant main effect of
D.J. Serrien et al. / Acta Psychologica 141 (2012) 73–77
435
η 2 = .186. The RTs of the primed and unprimed responses were 422.4 ±3.9 ms and 434.1± 4.2 ms (preferred hand), 428.3 ± 4.6 ms and 425.4± 3.7 ms (non-preferred hand), indicating positive priming for the preferred but not for the non-preferred hand. The error scores revealed no significant effects, p >.05. Accordingly, the outcome of this additional experiment supports our initial results.
Preferred hand - Compatible Preferred hand - Incompatible Non-preferred hand - Compatible Non-preferred hand - Incompatible
420
RT (ms)
75
3.3. Short ISO: unimanual vs. bimanual conditions
405
A main effect of Condition was observed for the preferred hand, F(1, 47) = 79.59, p b .01, η 2 = .582, and for the non-preferred hand, F(1, 47) = 31.94, p b .01, η 2 = .327. The RTs of the preferred and non-preferred hand were faster during unimanual trials (400.2 ± 4.4 ms and 407.3 ± 4.2 ms) than during bimanual trials (426.7 ± 5.1 ms and 428.1 ± 5.3 ms).
390
375 Left-handers
Right-handers
3.4. Long ISO: unimanual conditions
Handedness group 450
For the unimanual responses, the RT demonstrated a significant main effect of Compatibility, F(1, 47) = 16.23, p b .01, η 2 = .134, with faster incompatible responses (406.7 ± 5.2 ms) than compatible responses (414.9 ± 4.7 ms). The Group × Response Hand was also significant, F(1, 47) = 10.83, p b .01, η 2 = .196. There was a slower RT for the non-preferred as compared to preferred hand in the left-handers whereas a reversed pattern was observed in the right-handers. The RTs of the preferred and non-preferred hand were 417.7 ± 5.8 ms and 407.0 ± 5.0 ms (right-handers), 412.1 ± 5.5 ms and 405.7 ± 4.7 ms (left-handers). Fig. 3 (upper panel) demonstrates the unimanual RTs for the long ISO. The error scores showed a significant main effect of Compatibility, F(1, 47) = 4.88, p b .05, η 2 = .145, with fewer errors during incompatible trials (5.5 ± 1.3%) than during compatible trials (8.3 ± 1.2%).
Preferred hand - Primed Preferred hand - Unprimed Non-preferred hand - Primed Non-preferred hand - Unprimed
RT (ms)
440
430
420
410
3.5. Long ISO: bimanual conditions Left-handers
Right-handers
Handedness group Fig. 2. RTs in the unimanual tasks (upper panel) and bimanual tasks (lower panel) with short ISO.
Compatibility, F(1, 47) = 36.37, p b .01, η 2 = .182, and a significant Group× Compatibility interaction, F(1, 47) = 11.01, p b .01, η2 = .175. The error scores for the compatible and incompatible responses were 4.7 ± 1.0% and 8.3± 1.3% (right-handers), 6.4 ±1.2% and 14.2± 2.0% (left-handers), 3.2. Short ISO: bimanual conditions For the bimanual responses, the RT showed a significant Response Hand × Primed Hand interaction, F(1, 47) = 11.88, p b .01, η 2 = .113, and a Group × Response Hand × Primed Hand interaction, F(1, 47) = 4.50, p b .04, η 2 = .201. The preferred hand responded faster when it was primed. However, the non-preferred hand benefitted from positive priming in left-handers, but not in right-handers. Fig. 2 (lower panel) shows the bimanual RTs for the short ISO. The error (a response with one hand) scores demonstrated no significant main effects or interactions, p > .05. As these results from the bimanual conditions are a novel finding, we conducted an additional experiment in order to replicate the observation. In particular, we repeated the experiment for the bimanual trials in 10 right-handed participants (24.6 ± 2.8 years, laterality index = 90.2 ±8.5). These data were analyzed by means of 2 × 2 ANOVAs (Response Hand: preferred vs. non-preferred; Primed Hand: preferred vs. non-preferred). The RT analysis showed a significant Response Hand × Primed Hand interaction, F(1, 9) = 6.67, p = .02,
For the bimanual responses, the RT revealed a significant Group× Response Hand interaction, F(1, 47) = 4.93, p b .05, η 2 = .203. There was a delayed RT for the non-preferred as compared to preferred hand in the left-handers whereas the RTs of both hands were similar in the right-handers. The RTs of the preferred and non-preferred hand were 434.1±5.0 ms and 432.8±5.1 ms (right-handers), 425.2± 5.5 ms and 431.3±4.6 ms (left-handers). Also, the Response Hand× Primed Hand interaction was significant, F(1, 47)=16.58, pb .05, η2 = .165. Inhibitory priming occurred for both hands (i.e., a slower RT when primed as compared to unprimed) with the strongest effect for the non-preferred hand. The RTs of the primed and unprimed responses were 431.9±5.6 ms and 427.2±4.4 ms (preferred hand), 437.0± 5.5 ms and 428.3±4.2 ms (non-preferred hand). Fig. 3 (lower panel) illustrates the bimanual RTs for the long ISO. The error scores showed no significant main effects or interactions, p>.05. 3.6. Long ISO: unimanual vs. bimanual conditions A main effect of Condition was observed for the preferred hand, F(1, 47) = 37.27, p b .01, η 2 = .479, and for the non-preferred hand, F(1, 47) = 41.32, p b .01, η 2 = .492. The RTs for the preferred and non-preferred hand were faster during unimanual trials (410.5 ± 4.9 ms and 409.9 ± 4.8 ms) than during bimanual trials (428.6 ± 5.3 ms and 431.8 ± 5.7 ms). 3.7. Prime identification The analysis of the observed (correct response) vs. expected (chance level) frequency of the primes revealed no significant effect, χ 2(48) = 1.42, p > .05. The scores were 35.2% and 33.3% for the observed and expected frequencies, respectively. The data of the participants who
76
D.J. Serrien et al. / Acta Psychologica 141 (2012) 73–77
435
Preferred hand - Compatible Preferred hand - Incompatible Non-preferred hand - Compatible Non-preferred hand - Incompatible
RT (ms)
420
405
390
375 Left-handers
Right-handers
Handedness group 450
Preferred hand - Primed Preferred hand - Unprimed Non-preferred hand - Primed Non-preferred hand - Unprimed
RT (ms)
440
430
420
410
Left-handers
Right-handers
Handedness group Fig. 3. RTs in the unimanual tasks (upper panel) and bimanual tasks (lower panel) with long ISO.
performed the additional bimanual experiment with short ISO showed no significant effect, χ 2(9) = 1.03, p > .05. The observed frequency was 37.0%. That participants failed to perform with better-than-chance accuracy on this control task supports the verbal reports from the participants and suggests the subliminal nature of the primes. 4. Discussion A widely used method for studying the influence of subliminal processing on response planning is the masked priming paradigm. Factors that influence the priming effects are the prime-target compatibility and interval. In particular, at short prime-target intervals, subliminal primes trigger a partial activation of the response, resulting in a performance benefit when the prime is identical to the target (Eimer & Schlaghecken, 1998). In line with previous unimanual data, the present results revealed that compatible responses were faster and more accurate than incompatible responses. Furthermore, the data indicated that the preferred hand reacted faster than the non-preferred hand, which suggests an increased response readiness due to hand preference. A behavioral benefit of the preferred hand was further observed when it was primed during bimanual actions. However, the non-preferred hand showed a positive priming effect in left-handers, but not in right-handers. This proposes that left-handers are more receptive to response activation of either hand whereas the
non-preferred hand is less easily primed in right-handers. Accordingly, it is hypothesized that subliminal-driven responses support distinct processes in left- vs. right-handers: A control mechanism that favors response facilitation of the preferred hand in right-handers in contrast to a control mechanism that assists more equally activation of both hands in left-handers. These data are in line with previous work that has found handedness-specific effects in bimanual behavior (Buckingham, Main, & Carey, 2009; Kloppel et al., 2007). A potential account is that these effects result from biases in response organization. In particular, bimanual actions require extra activation of motor areas in right- as compared to left-handers, suggesting differences in neural effort for task performance. In this respect, it is possible that bimanual activities generate increased processing in right-handers or that left-handers have an enhanced efficiency due to their experience in using both hands as a result of environmental constraints (e.g., tool use), (Kloppel et al., 2007). Alternatively, between-group differences in bimanual assignments may arise due to distinct attentional regulation as right-handers tend to have attention biased toward their preferred hand whereas no consistent pattern of asymmetry exists in left-handers (Buckingham et al., 2009; Peters, 1981). At longer prime-target intervals, the initial effect of facilitation observed in masked priming turns into inhibition when the prime is identical to the target. In particular, the inhibitory process suppresses the initially activated response whenever it is relatively strong and has the potential to affect behavior. Accordingly, the mechanism contributes to the control of incorrect response tendencies (Eimer & Schlaghecken, 2003). In agreement with previous observations on unimanual responses, the current data showed that incompatible trials were faster and more accurate than compatible trials. In addition, the results demonstrated that the responses of the non-preferred as compared to preferred hand were slower in the left-handers whereas a reversed pattern was observed in the right-handers. In a bimanual context, the response latencies followed the same trend as in the unimanual trials for the left-handers, but not for the right-handers. This resulted in similar RTs for both hands in the right-handers, suggesting synchronized responses. Conversely, the non-preferred as compared to preferred hand was delayed in the left-handers, indicating uncoupled responses. The bimanual data further revealed that inhibitory priming had the strongest effect on the non-preferred hand, independent of handedness group. This suggests that low-level inhibition in bimanual tasks is influenced by dominant hand use. That a response hand could be primed during bimanual actions shows that coding occurred, at least partially, at the effector-specific level. That priming effects during bimanual conditions also operate at an abstract response level (Schlaghecken et al., 2009), suggests that these are driven by task-specific factors such as prime-target similarity and type of mask as relevant masks such as used in the present study are known to be sensitive to perceptual features (Sumner, 2008). However, it is unlikely that mask-induced inhibition would be fully responsible for the observed effects as the NCE was distinct for both handedness groups and was twice as large for the non-preferred as compared to preferred hand. Accordingly, it is suggested that the response codes that represent the actions are influenced by perceptual information, resulting in defined perceptuo-motor associations. The effector coding observed in this experiment is also in line with data that have shown that unilateral stimuli can influence both hands individually (Diedrichsen, Nambisan, Kennerley, & Ivry, 2004; Miller & Franz, 2005). In conclusion, the findings from this study illustrate that subliminal-driven mechanisms that assist adaptive motor behavior are sensitive not only to extrinsic (task-related) factors such as prime-target compatibility but also to intrinsic (performer-related) factors such as hand dominance, which accordingly guide performance. The data further provide support for handedness-specific effects in motor functions and underline a significant role of hand dominance in the control of bimanual actions.
D.J. Serrien et al. / Acta Psychologica 141 (2012) 73–77
Acknowledgments This research was supported by the Biotechnology and Biological Sciences Research Council (Grant BB/F012454/1 to DJS). References Amunts, K., Schlaug, G., Schleicher, A., Steinmetz, H., Dabringhaus, A., Roland, P. E., et al. (1996). Asymmetry in the human motor cortex and handedness. Neuroimage, 4, 16–22. Buckingham, G., Main, J. C., & Carey, D. P. (2009). Asymmetries in motor attention during a cued bimanual reaching task: Left and right handers compared. Cortex, 47, 432–440. Diedrichsen, J., Nambisan, R., Kennerley, S. W., & Ivry, R. B. (2004). Independent on-line control of the two hands during bimanual reaching. European Journal of Neuroscience, 19, 1643–1652. Eimer, M., & Schlaghecken, F. (1998). Effects of masked stimuli on motor activation: Behavioral and electrophysiological evidence. Journal of Experimental Psychology Human Perception and Performance, 24, 1737–1747. Eimer, M., & Schlaghecken, F. (2003). Response facilitation and inhibition in subliminal priming. Biological Psycholology, 64, 7–26. Franz, E. A., Zelaznik, H. N., & McCabe, G. (1991). Spatial topological constraints in a bimanual task. Acta Psychologica, 77, 137–151. Hughes, C. M., & Franz, E. A. (2007). Experience-dependent effects in unimanual and bimanual reaction time tasks in musicians. Journal of Motor Behavior, 39, 3–8. Jaśkowski, P. (2007). The effect of nonmasking distractors on the priming of motor responses. Journal of Experimental Psychology Human Perception and Performance, 33, 456–468. Jaśkowski, P. (2008). The negative compatibility effect with nonmasking flankers: A case for mask-triggered inhibition hypothesis. Conscious Cognition, 17, 765–777. Kelso, J. A. S., Southard, D. L., & Goodman, D. (1979). On the nature of human interlimb coordination. Science, 203, 1029–1031. Klapp, S. T., & Haas, B. W. (2005). Nonconscious influence of masked stimuli on response selection is limited to concrete stimulus–response associations. Journal of Experimental Psychology, 31, 193–209. Klapp, S. T., & Hinkley, L. B. (2002). The negative compatibility effect: unconscious inhibition influences reaction time and response selection. Journal of Experimental Psychology General, 131, 255–269. Kloppel, S., van Eimeren, T., Glauche, V., Vongerichten, A., Munchau, A., Frackowiak, R. S., et al. (2007). The effect of handedness on cortical motor activation during simple bilateral movements. NeuroImage, 34, 274–280. Lingnau, A., & Vorberg, D. (2005). The time course of response inhibition in masked priming. Perception and Psychophysics, 67, 545–557. Lleras, A., & Enns, J. T. (2004). Negative compatibility or object updating? A cautionary tale of mask-dependent priming. Journal of Experimental Psychology General, 133, 475–493. Miller, J. O., & Franz, E. A. (2005). Dissociation of bimanual responses with the Simon effect: On the nonunitization of bimanual responses. Journal of Motor Behavior, 37, 146–156.
77
Neumann, O., & Klotz, W. (1994). Motor responses to nonreportable, masked stimuli: Where is the limit of direct parameter specification? In C. Umilta, & M. Moskovitch (Eds.), Attention and Performance XV (pp. 123–150). Cambridge, MA: MIT Press. Oldfield, R. C. (1971). The assessment and analysis of handedness: The Edinburgh Inventory. Neuropsychologia, 9, 97–113. Peters, M. (1981). Attentional asymmetries during concurrent bimanual performance. Quarterly Journal of Experimental Psycholology, 33A, 95–103. Reid, C. S., & Serrien, D. J. (2012). Handedness and asymmetries in cortical inhibitory circuits. Behavioural Brain Research, 230, 144–148. Schlaghecken, F., & Eimer, M. (2002). Motor activation with and without inhibition: Evidence for a threshold mechanism in motor control. Perception and Psychophysics, 64, 148–162. Schlaghecken, F., Klapp, S. T., & Maylor, E. A. (2009). Either or neither, but not both: Locating the effects of masked primes. Proceedings of the Royal Society Biological Sciences, 276, 515–521. Serrien, D. J. (2009). Functional connectivity patterns during motor behaviour: The impact of past on present activity. Human Brain Mapping, 30, 523–531. Serrien, D. J., & Swinnen, S. P. (1997). Coordination constraints induced by effector combination under isofrequency and multifrequency conditions. Journal of Experimental Psychology: Human Perception and Performance, 23, 1493–1510. Serrien, D. J., & Wiesendanger, M. (2001). A higher-order mechanism overrules the automatic grip-load force constraint during bimanual asymmetrical movements. Behavioural Brain Research, 118, 153–160. Solodkin, A., Hlustik, P., Noll, D. C., & Small, S. (2001). Lateralization of motor circuits and handedness during finger movements. European Journal of Neurology, 8, 425–434. Steglich, C., Heuer, H., Spijkers, W., & Kleinsorge, T. (1999). Bimanual coupling during the specification of isometric forces. Experimental Brain Research, 129, 302–316. Sumner, P. (2008). Mask-induced priming and the negative compatibility effect. Experimental Psycholology, 55, 133–141. Sumner, P., Nachev, P., Morris, P., Peters, A. M., Jackson, S. R., Kennard, C., et al. (2007). Human medial frontal cortex mediates unconscious inhibition of voluntary action. Neuron, 54, 697–711. Swinnen, S. P. (2002). Intermanual coordination: From behavioural principles to neural-network interactions. Nature Reviews Neuroscience, 3, 348–359. Taniguchi, Y., Burle, B., Vidal, F., & Bonnet, M. (2001). Deficit in motor cortical activity for simultaneous bimanual responses. Experimental Brain Research, 137, 259–268. Verleger, R., Jaśkowski, P., Aydemir, A., van der Lubbe, R. H., & Groen, M. (2004). Qualitative differences between conscious and nonconscious processing? On inverse priming induced by masked arrows. Journal of Experimental Psychology General, 133, 494–515. Vingerhoets, G., Acke, F., Alderweireldt, A. -S., Nys, J., Vandemaele, P., & Achten, E. (2012). Cerebral Lateralization of praxis in right- and left-handedness: Same pattern, different strength. Human Brain Mapping, 33, 763–777. Vorberg, D., Mattler, U., Heinecke, A., Schmidt, T., & Schwarzbach, J. (2003). Different time courses for visual perception and action priming. Proceedings of the National Academy of Sciences of the United States of America, 100, 6275–6280.
Contents lists available at SciVerse ScienceDirect
Acta Psychologica journal homepage: www.elsevier.com/ locate/actpsy
Subliminal priming and effects of hand dominance Deborah J. Serrien ⁎, Michiel M. Sovijärvi-Spapé, Gita Rana School of Psychology, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
a r t i c l e
i n f o
Article history: Received 12 March 2012 Received in revised form 30 June 2012 Accepted 7 July 2012 Available online 2 August 2012 PsycINFO classification: 2330 Keywords: Motor behavior, Handedness Bimanual coordination
a b s t r a c t In the masked priming paradigm, motor responses to targets are influenced by previously presented subliminal primes, and are guided by facilitatory and inhibitory mechanisms that depend on prime-target compatibility/duration. In this study, we evaluate subliminal-driven priming in right- and left-handers during unimanual as well as bimanual tasks. The data from the unimanual tasks confirmed that prime-target compatibility affects performance as a function of prime-target duration. In a bimanual setting, the preferred hand benefitted from facilitation in both handedness groups whereas the non-preferred hand showed a positive priming effect only in left-handers. This denotes that left-handers are more susceptible to response activation of either hand. In addition, inhibitory priming had a stronger effect on the non-preferred than preferred hand, independent of handedness group. Overall, the findings suggest that subliminal-driven mechanisms that assist adaptive motor behavior are sensitive not only to extrinsic (task-related) factors such as prime-target compatibility but also to intrinsic (performer-related) factors such as hand dominance. The data further provide support for handedness-specific effects in motor functions and underline a significant role of hand dominance in the control of bimanual actions. © 2012 Elsevier B.V. All rights reserved.
1. Introduction Although most of our behavior is considered voluntary, some responses can be triggered by stimuli that are inaccessible to conscious awareness. These stimuli influence behavioral performance; subliminal priming effects that can be examined by means of masked prime designs. In these paradigms, a target is preceded by a masked prime that is associated with the same or different response as the target (Eimer & Schlaghecken, 1998; Klapp & Haas, 2005; Neumann & Klotz, 1994; Vorberg, Mattler, Heinecke, Schmidt, & Schwarzbach, 2003). Masked primes speed-up responses to target stimuli if prime and target are compatible and slow down responses if they are incompatible. This performance benefit reflects a positive compatibility effect (PCE), and occurs when the prime-target interval is short (0–60 ms). However, the priming pattern reverses when the prime-target interval is longer (100–200 ms); a so-called negative compatibility effect (NCE), (Eimer & Schlaghecken, 1998; Jaśkowski, 2008; Lingnau & Vorberg, 2005). One explanation is that the NCE represents motor inhibition during which a self-inhibition process suppresses the initial response tendency triggered by the prime when it is no longer supported by sensory evidence (Eimer & Schlaghecken, 2003; Klapp & Hinkley, 2002). However, alternative interpretations suggest that NCE is driven by perceptual characteristics of the stimuli (Lleras & Enns, 2004; Verleger, Jaśkowski, Aydemir, van der Lubbe, & ⁎ Corresponding author at: School of Psychology, University of Nottingham, University Park, Nottingham, NG7 2RD, UK. Tel.: +44 115 951 5285; fax: +44 115 951 5324. E-mail address: [email protected] (D.J. Serrien). 0001-6918/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.actpsy.2012.07.008
Groen, 2004). At present, it is generally believed that NCE reflects motor inhibition, either as self-inhibition (Schlaghecken & Eimer, 2002), or as mask-triggered inhibition (Jaśkowski, 2007; Lleras & Enns, 2004). Low-level inhibition differs from high-level inhibition that occurs during voluntary response withholding as there is no intentional effort to suppress a response to the prime (Eimer & Schlaghecken, 2003; Sumner et al., 2007). Most behavioral studies have examined the influence of subliminal priming on individual right and left hand performances. Less is known about the role of priming in a bimanual context. That is, when both hands are required to perform simultaneously. The evaluation of bimanual actions is relevant since the constraints that underlie coordinated behavior do not necessarily follow the rules that regulate unimanual movements (Serrien, 2009; Swinnen, 2002). In particular, bimanual control structures impose interdependence of movement parameters (Franz, Zelaznik, & McCabe, 1991; Kelso, Southard, & Goodman, 1979; Serrien & Swinnen, 1997; Steglich, Heuer, Spijkers, & Kleinsorge, 1999), although the coordination constraints are considered flexible (Serrien & Wiesendanger, 2001). Distinct processing demands due to bimanual constraints are further highlighted from simple reaction time tasks, which show longer response times in bimanual than unimanual conditions; also labelled as the bimanual deficit/cost (Hughes & Franz, 2007; Taniguchi, Burle, Vidal, & Bonnet, 2001). In view of motor priming, Schlaghecken, Klapp, and Maylor (2009) observed that primes that linked with a response hand produced NCEs during unimanual tasks, but not during bimanual tasks. The latter observation suggested that NCEs operate at an abstract (non-effector) response level.
74
D.J. Serrien et al. / Acta Psychologica 141 (2012) 73–77
However, it is unclear how control processes as determined by hand dominance would interact with subliminal-driven motor priming. Overall, most research on motor control has been conducted in right-handers whereas less is known from left-handers. Although left-handers demonstrate structural asymmetries of the motor system that are opposite to those of right-handers, these are less prominent and defined (Amunts et al., 1996). Furthermore, functional imaging data have revealed that left-handers show less hemispheric lateralization than right-handers during intricate unimanual patterns (Solodkin, Hlustik, Noll, & Small, 2001) and bimanual actions (Kloppel et al., 2007; Vingerhoets et al., 2012). These observations suggest that left- and right-handers have distinct control mechanisms of motor behavior (Kloppel et al., 2007; Reid & Serrien, 2012). Subsequently, the aim of this study was to examine the PCE and NCE processes in left- vs. right-handers during unimanual and bimanual assignments. Although these processes are considered low-level and automatic as they occur outside conscious awareness, they are in line with intentions (Klapp & Haas, 2005). Accordingly, it was hypothesized that primed responses would display different profiles in left- and right-handers due to differences in lateralization of motor functions. Effects were expected to become most apparent during bimanual responses due to the increased task complexity as compared to unimanual responses. 2. Method 2.1. Participants Participants in the experiment were 26 left-handers (21.8± 3.4 years) and 23 right-handers (20.5±1.8 years). Their laterality index was −88.2±13.2 and 84.4±13.1 for the left- and right-handers, respectively (Oldfield, 1971). The participants gave informed consent prior to participation in accordance with the declaration of Helsinki, and the study was approved by the local ethics committee. 2.2. Task and procedure A standard masked prime design was used during which double arrows were used as prime and target stimuli. The participants were asked to respond to the target stimuli with the left index by pressing the C-key (arrows pointing to the left, bb), the right index by pressing the M-key (arrows pointing to the right, >>) or both index fingers by pressing the C- and M-keys (bilateral arrows, b>) on a keyboard. Before the target stimuli appeared, a prime was displayed that pointed to the left (bb) or to the right (>>). As illustrated in Fig. 1, each trial started with a centrally presented fixation cross. After 250 ms, the fixation cross disappeared and was followed by a blank screen for 300 ms, a prime for 17 ms and a feature-mask (overlapping horizontal, vertical and oblique lines) for 100 ms. In the short inter-stimulus-onset (ISO) condition, the target appeared simultaneously with the mask whereas it appeared 100 ms after the mask and was shown for 100 ms in the long ISO condition. Thereafter, a blank screen was present for an inter-trial interval (ITI) of 800 ms. Trials were compatible when prime and target arrows pointed in the same direction and incompatible when they pointed in different directions. Primes and targets were randomized within blocks of 180 trials. The short and long ISO trials were presented in separate blocks, which were counterbalanced between participants. Short breaks were offered every 60 trials. Familiarization trials were provided prior to the experimental blocks. Participants were instructed to maintain central eye fixation throughout the experiment and to respond as quickly and accurately as possible to the direction of the target arrows. After completion of the main experiment, the participants were queried about the primes. No one had noticed the primes. Subsequently, information was provided to the participants about the primes, and masking efficiency was evaluated in a forced-choice control experiment,
Fig. 1. Schematic presentation of the trial structure.
which assessed prime identification. In these prime identification trials, prime and mask were presented, but there were no targets. Participants were asked to identify the prime and to respond with corresponding finger(s) across 45 trials. In order to have all the responses from the main experiment, the prime stimuli were pointing to the left (bb), right (>>) or bidirectional (b>). Trials were randomized. Participants were told to guess on trials in which they could not identify the primes. There was no emphasis on reaction time. 2.3. Measurements and data analysis The reaction time (RT) to targets (filtered to exclude erroneous responses) and number of errors were used as behavioral measurements in the main experiment. The unimanual data were analyzed by means of 2 × 2 × 2 ANOVAs (Group: right- vs. left-handers; Response Hand: preferred vs. non-preferred; Compatibility: compatible vs. incompatible priming) whereas the bimanual data were analyzed by means of 2 × 2 × 2 ANOVAs (Group: right- vs. left-handers; Response Hand: preferred vs. non-preferred; Primed Hand: preferred vs. non-preferred), separately for the short and long ISO conditions. Additional 2 × 2 ANOVAs (Group: right- vs. left-handers; Condition: Unimanual vs. Bimanual) were conducted on the RT in order to establish the processing demands for bimanual as compared to unimanual responses. Post-hoc t-tests were conducted and Bonferroni correction was made where appropriate. In the prime identification task, the observed (correct response) frequency was calculated for the primes and contrasted with the expected (chance level) frequency by means of a non-parametric χ 2 test. The statistical threshold was set at p b .05. Means ± SE are reported. 3. Results 3.1. Short ISO: unimanual conditions For the unimanual responses, the RT revealed a significant main effect of Response Hand, F(1, 47) = 9.15, p b .01, η 2 = .129, with the preferred hand (400.2 ± 4.6 ms) responding quicker than the non-preferred hand (408.1 ± 4.3 ms). The main effect of Compatibility was also significant, F(1, 47)= 120.21, p b .01, η2 = .167, with faster compatible responses (391.0 ± 4.7 ms) than incompatible responses (417.5± 4.8 ms). Fig. 2 (upper panel) illustrates the unimanual RTs for the short ISO. The error scores showed a significant main effect of
D.J. Serrien et al. / Acta Psychologica 141 (2012) 73–77
435
η 2 = .186. The RTs of the primed and unprimed responses were 422.4 ±3.9 ms and 434.1± 4.2 ms (preferred hand), 428.3 ± 4.6 ms and 425.4± 3.7 ms (non-preferred hand), indicating positive priming for the preferred but not for the non-preferred hand. The error scores revealed no significant effects, p >.05. Accordingly, the outcome of this additional experiment supports our initial results.
Preferred hand - Compatible Preferred hand - Incompatible Non-preferred hand - Compatible Non-preferred hand - Incompatible
420
RT (ms)
75
3.3. Short ISO: unimanual vs. bimanual conditions
405
A main effect of Condition was observed for the preferred hand, F(1, 47) = 79.59, p b .01, η 2 = .582, and for the non-preferred hand, F(1, 47) = 31.94, p b .01, η 2 = .327. The RTs of the preferred and non-preferred hand were faster during unimanual trials (400.2 ± 4.4 ms and 407.3 ± 4.2 ms) than during bimanual trials (426.7 ± 5.1 ms and 428.1 ± 5.3 ms).
390
375 Left-handers
Right-handers
3.4. Long ISO: unimanual conditions
Handedness group 450
For the unimanual responses, the RT demonstrated a significant main effect of Compatibility, F(1, 47) = 16.23, p b .01, η 2 = .134, with faster incompatible responses (406.7 ± 5.2 ms) than compatible responses (414.9 ± 4.7 ms). The Group × Response Hand was also significant, F(1, 47) = 10.83, p b .01, η 2 = .196. There was a slower RT for the non-preferred as compared to preferred hand in the left-handers whereas a reversed pattern was observed in the right-handers. The RTs of the preferred and non-preferred hand were 417.7 ± 5.8 ms and 407.0 ± 5.0 ms (right-handers), 412.1 ± 5.5 ms and 405.7 ± 4.7 ms (left-handers). Fig. 3 (upper panel) demonstrates the unimanual RTs for the long ISO. The error scores showed a significant main effect of Compatibility, F(1, 47) = 4.88, p b .05, η 2 = .145, with fewer errors during incompatible trials (5.5 ± 1.3%) than during compatible trials (8.3 ± 1.2%).
Preferred hand - Primed Preferred hand - Unprimed Non-preferred hand - Primed Non-preferred hand - Unprimed
RT (ms)
440
430
420
410
3.5. Long ISO: bimanual conditions Left-handers
Right-handers
Handedness group Fig. 2. RTs in the unimanual tasks (upper panel) and bimanual tasks (lower panel) with short ISO.
Compatibility, F(1, 47) = 36.37, p b .01, η 2 = .182, and a significant Group× Compatibility interaction, F(1, 47) = 11.01, p b .01, η2 = .175. The error scores for the compatible and incompatible responses were 4.7 ± 1.0% and 8.3± 1.3% (right-handers), 6.4 ±1.2% and 14.2± 2.0% (left-handers), 3.2. Short ISO: bimanual conditions For the bimanual responses, the RT showed a significant Response Hand × Primed Hand interaction, F(1, 47) = 11.88, p b .01, η 2 = .113, and a Group × Response Hand × Primed Hand interaction, F(1, 47) = 4.50, p b .04, η 2 = .201. The preferred hand responded faster when it was primed. However, the non-preferred hand benefitted from positive priming in left-handers, but not in right-handers. Fig. 2 (lower panel) shows the bimanual RTs for the short ISO. The error (a response with one hand) scores demonstrated no significant main effects or interactions, p > .05. As these results from the bimanual conditions are a novel finding, we conducted an additional experiment in order to replicate the observation. In particular, we repeated the experiment for the bimanual trials in 10 right-handed participants (24.6 ± 2.8 years, laterality index = 90.2 ±8.5). These data were analyzed by means of 2 × 2 ANOVAs (Response Hand: preferred vs. non-preferred; Primed Hand: preferred vs. non-preferred). The RT analysis showed a significant Response Hand × Primed Hand interaction, F(1, 9) = 6.67, p = .02,
For the bimanual responses, the RT revealed a significant Group× Response Hand interaction, F(1, 47) = 4.93, p b .05, η 2 = .203. There was a delayed RT for the non-preferred as compared to preferred hand in the left-handers whereas the RTs of both hands were similar in the right-handers. The RTs of the preferred and non-preferred hand were 434.1±5.0 ms and 432.8±5.1 ms (right-handers), 425.2± 5.5 ms and 431.3±4.6 ms (left-handers). Also, the Response Hand× Primed Hand interaction was significant, F(1, 47)=16.58, pb .05, η2 = .165. Inhibitory priming occurred for both hands (i.e., a slower RT when primed as compared to unprimed) with the strongest effect for the non-preferred hand. The RTs of the primed and unprimed responses were 431.9±5.6 ms and 427.2±4.4 ms (preferred hand), 437.0± 5.5 ms and 428.3±4.2 ms (non-preferred hand). Fig. 3 (lower panel) illustrates the bimanual RTs for the long ISO. The error scores showed no significant main effects or interactions, p>.05. 3.6. Long ISO: unimanual vs. bimanual conditions A main effect of Condition was observed for the preferred hand, F(1, 47) = 37.27, p b .01, η 2 = .479, and for the non-preferred hand, F(1, 47) = 41.32, p b .01, η 2 = .492. The RTs for the preferred and non-preferred hand were faster during unimanual trials (410.5 ± 4.9 ms and 409.9 ± 4.8 ms) than during bimanual trials (428.6 ± 5.3 ms and 431.8 ± 5.7 ms). 3.7. Prime identification The analysis of the observed (correct response) vs. expected (chance level) frequency of the primes revealed no significant effect, χ 2(48) = 1.42, p > .05. The scores were 35.2% and 33.3% for the observed and expected frequencies, respectively. The data of the participants who
76
D.J. Serrien et al. / Acta Psychologica 141 (2012) 73–77
435
Preferred hand - Compatible Preferred hand - Incompatible Non-preferred hand - Compatible Non-preferred hand - Incompatible
RT (ms)
420
405
390
375 Left-handers
Right-handers
Handedness group 450
Preferred hand - Primed Preferred hand - Unprimed Non-preferred hand - Primed Non-preferred hand - Unprimed
RT (ms)
440
430
420
410
Left-handers
Right-handers
Handedness group Fig. 3. RTs in the unimanual tasks (upper panel) and bimanual tasks (lower panel) with long ISO.
performed the additional bimanual experiment with short ISO showed no significant effect, χ 2(9) = 1.03, p > .05. The observed frequency was 37.0%. That participants failed to perform with better-than-chance accuracy on this control task supports the verbal reports from the participants and suggests the subliminal nature of the primes. 4. Discussion A widely used method for studying the influence of subliminal processing on response planning is the masked priming paradigm. Factors that influence the priming effects are the prime-target compatibility and interval. In particular, at short prime-target intervals, subliminal primes trigger a partial activation of the response, resulting in a performance benefit when the prime is identical to the target (Eimer & Schlaghecken, 1998). In line with previous unimanual data, the present results revealed that compatible responses were faster and more accurate than incompatible responses. Furthermore, the data indicated that the preferred hand reacted faster than the non-preferred hand, which suggests an increased response readiness due to hand preference. A behavioral benefit of the preferred hand was further observed when it was primed during bimanual actions. However, the non-preferred hand showed a positive priming effect in left-handers, but not in right-handers. This proposes that left-handers are more receptive to response activation of either hand whereas the
non-preferred hand is less easily primed in right-handers. Accordingly, it is hypothesized that subliminal-driven responses support distinct processes in left- vs. right-handers: A control mechanism that favors response facilitation of the preferred hand in right-handers in contrast to a control mechanism that assists more equally activation of both hands in left-handers. These data are in line with previous work that has found handedness-specific effects in bimanual behavior (Buckingham, Main, & Carey, 2009; Kloppel et al., 2007). A potential account is that these effects result from biases in response organization. In particular, bimanual actions require extra activation of motor areas in right- as compared to left-handers, suggesting differences in neural effort for task performance. In this respect, it is possible that bimanual activities generate increased processing in right-handers or that left-handers have an enhanced efficiency due to their experience in using both hands as a result of environmental constraints (e.g., tool use), (Kloppel et al., 2007). Alternatively, between-group differences in bimanual assignments may arise due to distinct attentional regulation as right-handers tend to have attention biased toward their preferred hand whereas no consistent pattern of asymmetry exists in left-handers (Buckingham et al., 2009; Peters, 1981). At longer prime-target intervals, the initial effect of facilitation observed in masked priming turns into inhibition when the prime is identical to the target. In particular, the inhibitory process suppresses the initially activated response whenever it is relatively strong and has the potential to affect behavior. Accordingly, the mechanism contributes to the control of incorrect response tendencies (Eimer & Schlaghecken, 2003). In agreement with previous observations on unimanual responses, the current data showed that incompatible trials were faster and more accurate than compatible trials. In addition, the results demonstrated that the responses of the non-preferred as compared to preferred hand were slower in the left-handers whereas a reversed pattern was observed in the right-handers. In a bimanual context, the response latencies followed the same trend as in the unimanual trials for the left-handers, but not for the right-handers. This resulted in similar RTs for both hands in the right-handers, suggesting synchronized responses. Conversely, the non-preferred as compared to preferred hand was delayed in the left-handers, indicating uncoupled responses. The bimanual data further revealed that inhibitory priming had the strongest effect on the non-preferred hand, independent of handedness group. This suggests that low-level inhibition in bimanual tasks is influenced by dominant hand use. That a response hand could be primed during bimanual actions shows that coding occurred, at least partially, at the effector-specific level. That priming effects during bimanual conditions also operate at an abstract response level (Schlaghecken et al., 2009), suggests that these are driven by task-specific factors such as prime-target similarity and type of mask as relevant masks such as used in the present study are known to be sensitive to perceptual features (Sumner, 2008). However, it is unlikely that mask-induced inhibition would be fully responsible for the observed effects as the NCE was distinct for both handedness groups and was twice as large for the non-preferred as compared to preferred hand. Accordingly, it is suggested that the response codes that represent the actions are influenced by perceptual information, resulting in defined perceptuo-motor associations. The effector coding observed in this experiment is also in line with data that have shown that unilateral stimuli can influence both hands individually (Diedrichsen, Nambisan, Kennerley, & Ivry, 2004; Miller & Franz, 2005). In conclusion, the findings from this study illustrate that subliminal-driven mechanisms that assist adaptive motor behavior are sensitive not only to extrinsic (task-related) factors such as prime-target compatibility but also to intrinsic (performer-related) factors such as hand dominance, which accordingly guide performance. The data further provide support for handedness-specific effects in motor functions and underline a significant role of hand dominance in the control of bimanual actions.
D.J. Serrien et al. / Acta Psychologica 141 (2012) 73–77
Acknowledgments This research was supported by the Biotechnology and Biological Sciences Research Council (Grant BB/F012454/1 to DJS). References Amunts, K., Schlaug, G., Schleicher, A., Steinmetz, H., Dabringhaus, A., Roland, P. E., et al. (1996). Asymmetry in the human motor cortex and handedness. Neuroimage, 4, 16–22. Buckingham, G., Main, J. C., & Carey, D. P. (2009). Asymmetries in motor attention during a cued bimanual reaching task: Left and right handers compared. Cortex, 47, 432–440. Diedrichsen, J., Nambisan, R., Kennerley, S. W., & Ivry, R. B. (2004). Independent on-line control of the two hands during bimanual reaching. European Journal of Neuroscience, 19, 1643–1652. Eimer, M., & Schlaghecken, F. (1998). Effects of masked stimuli on motor activation: Behavioral and electrophysiological evidence. Journal of Experimental Psychology Human Perception and Performance, 24, 1737–1747. Eimer, M., & Schlaghecken, F. (2003). Response facilitation and inhibition in subliminal priming. Biological Psycholology, 64, 7–26. Franz, E. A., Zelaznik, H. N., & McCabe, G. (1991). Spatial topological constraints in a bimanual task. Acta Psychologica, 77, 137–151. Hughes, C. M., & Franz, E. A. (2007). Experience-dependent effects in unimanual and bimanual reaction time tasks in musicians. Journal of Motor Behavior, 39, 3–8. Jaśkowski, P. (2007). The effect of nonmasking distractors on the priming of motor responses. Journal of Experimental Psychology Human Perception and Performance, 33, 456–468. Jaśkowski, P. (2008). The negative compatibility effect with nonmasking flankers: A case for mask-triggered inhibition hypothesis. Conscious Cognition, 17, 765–777. Kelso, J. A. S., Southard, D. L., & Goodman, D. (1979). On the nature of human interlimb coordination. Science, 203, 1029–1031. Klapp, S. T., & Haas, B. W. (2005). Nonconscious influence of masked stimuli on response selection is limited to concrete stimulus–response associations. Journal of Experimental Psychology, 31, 193–209. Klapp, S. T., & Hinkley, L. B. (2002). The negative compatibility effect: unconscious inhibition influences reaction time and response selection. Journal of Experimental Psychology General, 131, 255–269. Kloppel, S., van Eimeren, T., Glauche, V., Vongerichten, A., Munchau, A., Frackowiak, R. S., et al. (2007). The effect of handedness on cortical motor activation during simple bilateral movements. NeuroImage, 34, 274–280. Lingnau, A., & Vorberg, D. (2005). The time course of response inhibition in masked priming. Perception and Psychophysics, 67, 545–557. Lleras, A., & Enns, J. T. (2004). Negative compatibility or object updating? A cautionary tale of mask-dependent priming. Journal of Experimental Psychology General, 133, 475–493. Miller, J. O., & Franz, E. A. (2005). Dissociation of bimanual responses with the Simon effect: On the nonunitization of bimanual responses. Journal of Motor Behavior, 37, 146–156.
77
Neumann, O., & Klotz, W. (1994). Motor responses to nonreportable, masked stimuli: Where is the limit of direct parameter specification? In C. Umilta, & M. Moskovitch (Eds.), Attention and Performance XV (pp. 123–150). Cambridge, MA: MIT Press. Oldfield, R. C. (1971). The assessment and analysis of handedness: The Edinburgh Inventory. Neuropsychologia, 9, 97–113. Peters, M. (1981). Attentional asymmetries during concurrent bimanual performance. Quarterly Journal of Experimental Psycholology, 33A, 95–103. Reid, C. S., & Serrien, D. J. (2012). Handedness and asymmetries in cortical inhibitory circuits. Behavioural Brain Research, 230, 144–148. Schlaghecken, F., & Eimer, M. (2002). Motor activation with and without inhibition: Evidence for a threshold mechanism in motor control. Perception and Psychophysics, 64, 148–162. Schlaghecken, F., Klapp, S. T., & Maylor, E. A. (2009). Either or neither, but not both: Locating the effects of masked primes. Proceedings of the Royal Society Biological Sciences, 276, 515–521. Serrien, D. J. (2009). Functional connectivity patterns during motor behaviour: The impact of past on present activity. Human Brain Mapping, 30, 523–531. Serrien, D. J., & Swinnen, S. P. (1997). Coordination constraints induced by effector combination under isofrequency and multifrequency conditions. Journal of Experimental Psychology: Human Perception and Performance, 23, 1493–1510. Serrien, D. J., & Wiesendanger, M. (2001). A higher-order mechanism overrules the automatic grip-load force constraint during bimanual asymmetrical movements. Behavioural Brain Research, 118, 153–160. Solodkin, A., Hlustik, P., Noll, D. C., & Small, S. (2001). Lateralization of motor circuits and handedness during finger movements. European Journal of Neurology, 8, 425–434. Steglich, C., Heuer, H., Spijkers, W., & Kleinsorge, T. (1999). Bimanual coupling during the specification of isometric forces. Experimental Brain Research, 129, 302–316. Sumner, P. (2008). Mask-induced priming and the negative compatibility effect. Experimental Psycholology, 55, 133–141. Sumner, P., Nachev, P., Morris, P., Peters, A. M., Jackson, S. R., Kennard, C., et al. (2007). Human medial frontal cortex mediates unconscious inhibition of voluntary action. Neuron, 54, 697–711. Swinnen, S. P. (2002). Intermanual coordination: From behavioural principles to neural-network interactions. Nature Reviews Neuroscience, 3, 348–359. Taniguchi, Y., Burle, B., Vidal, F., & Bonnet, M. (2001). Deficit in motor cortical activity for simultaneous bimanual responses. Experimental Brain Research, 137, 259–268. Verleger, R., Jaśkowski, P., Aydemir, A., van der Lubbe, R. H., & Groen, M. (2004). Qualitative differences between conscious and nonconscious processing? On inverse priming induced by masked arrows. Journal of Experimental Psychology General, 133, 494–515. Vingerhoets, G., Acke, F., Alderweireldt, A. -S., Nys, J., Vandemaele, P., & Achten, E. (2012). Cerebral Lateralization of praxis in right- and left-handedness: Same pattern, different strength. Human Brain Mapping, 33, 763–777. Vorberg, D., Mattler, U., Heinecke, A., Schmidt, T., & Schwarzbach, J. (2003). Different time courses for visual perception and action priming. Proceedings of the National Academy of Sciences of the United States of America, 100, 6275–6280.