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Shared learning shapes human performance: Transfer effects in task sharing
Cognition 116 (2010) 15–22
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Shared learning shapes human performance: Transfer effects in task sharing Nadia Milanese, Cristina Iani *, Sandro Rubichi Università di Modena e Reggio Emilia, Italy
a r t i c l e
i n f o
Article history: Received 2 September 2009 Revised 1 March 2010 Accepted 10 March 2010
Keywords: Spatial compatibility Simon effect Social cognition Learning Incidental learning
a b s t r a c t We investigated whether performing a task with a co-actor shapes the way a subsequent task is performed. In four experiments participants were administered a Simon task after practicing a spatial compatibility task with an incompatible S-R mapping. In Experiment 1 they performed both tasks alongside another person; in Experiment 2 they performed the spatial compatibility task alone, responding to only one stimulus position, and the Simon task with another person; in Experiment 3, they performed the spatial compatibility task with another person and the Simon task alone; finally, in Experiment 4, they performed the spatial compatibility task alone and the Simon task with another person. The incompatible practice eliminated the Simon effect in Experiments 1 and 4. These results indicate that when a task is distributed between two participants with each one performing a different part of it, they tend to represent the whole task rather than their own part of it. This experience can influence the way a subsequent task is performed, as long as this latter occurs in a social context. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction Many everyday activities require interaction with other people. While some of these interactions involve little or no interpersonal coordination, others clearly put to the test our coordination abilities. If we think of a situation like moving together with another person a heavy piece of furniture up a curvy staircase, it is clear that efficient performance requires an understanding of what the other is doing in order to predict his or her future actions and to behave accordingly. As recent studies suggest, our ability to understand others and to coordinate with them depends on the creation of shared task representations, that is representations integrating current and predicted self and other’s actions (cf. Sebanz, Bekkering, & Knoblich, 2006; see also Tomasello, Carpenter, Call, Behne, & Moll, 2005).
* Corresponding author at: Dipartimento di Scienze Sociali, Cognitive e Quantitative, Università di Modena e Reggio Emilia, Via Allegri, 9, 42121 Reggio Emilia, Italy. E-mail address: [email protected] (C. Iani). 0010-0277/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cognition.2010.03.010
These shared representations emerge in a variety of situations involving jointly acting individuals even when considering the other’s actions is not necessary, thus suggesting that human cognition is biased toward joint action (e.g., Atmaca, Sebanz, Prinz, & Knoblich, 2008; Hommel, Colzato, & van den Wildenber, 2009; Sebanz, Knoblich, & Prinz, 2003, 2005; Sebanz, Knoblich, Prinz, & Wascher, 2006; Sebanz, Rebbechi, Knoblich, Prinz, & Frith, 2007; Tsai, Kuo, Hung, & Tzeng, 2008; Welsh, Higgins, Ray, & Weeks, 2007). Social interactions play an important role in learning too. Indeed, our ability to perform novel tasks depends on the application of knowledge previously acquired through learning, which often occurs through social interaction (e.g., Vygotsky, 1978). Given these considerations, we believe it is of particular interest to investigate the relationship between learning and performance in individual and social contexts. This requires an investigation into whether learning derived from social interactions may be transferred to distinct but similar tasks performed either in social or individual contexts and whether individual
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learning may transfer to performance in social contexts as well. As regards individual performance, there are clear indications of transfer of learning in tasks investigating spatial correspondence effects. Spatial correspondence effects are evident in choice-reaction tasks in which the stimulus appears in a right or left location and the response is produced manually (for a review see Proctor and Vu (2006)). In the spatial stimulus–response compatibility task, the response is selected on the basis of stimulus location. In compatible mappings participants are instructed to respond with the key that is located on the same side of the stimulus, whereas in incompatible mappings the instructions are reversed. In the Simon task, the task-relevant stimulus feature is non-spatial (e.g., shape or color), and subjects respond with assigned right and left keys (Simon & Rudell, 1967). Thus, there are trials in which stimulus and response locations correspond (i.e., corresponding S-R pairings) and trials in which they do not (i.e., non-corresponding pairings). In both tasks, performance is usually faster and more accurate when there is spatial correspondence between stimulus and response (i.e., when the mapping is compatible for the spatial SRC task and when stimulus and response locations correspond for the Simon task) than when there is not (i.e., when the mapping is incompatible for the spatial SRC task and when stimulus and response locations do not correspond for the Simon task). By using the transfer paradigm developed by Proctor and Lu (1999), it has been shown that when participants perform a spatial compatibility task in which they are required to respond to stimulus location by emitting a spatially incompatible response (i.e., responding to the left stimulus with the right key and vice versa) and then transfer to a Simon task, the Simon effect is reduced, absent of even reversed, that is, reaction times for non-corresponding responses are faster than those for corresponding responses (Iani, Rubichi, Gherri, & Nicoletti, 2009; Proctor & Lu, 1999; Tagliabue, Zorzi, Umiltà, & Bassignani, 2000). This is thought to occur because responding for a certain amount of trials with a spatially incompatible mapping strengthen the non-corresponding association between a stimulus and a response to the extent that this association continues to affect performance even when the task is changed and the response should no longer be emitted on the basis of a spatial stimulus feature (cf. Tagliabue et al., 2000). Notably, the Simon task has proven to be a good candidate task to investigate the emergence of shared representations. In a pioneer study by Sebanz et al. (2003), participants were shown photographs of a centrally presented right hand pointing to the right, to the left, or straight, with the instruction to press one of two lateralized keys according to the color of a ring appearing on the index finger. They were required to perform the task either alone or paired with another participant. When they performed the task individually, responses were faster when the pointing direction of the hand spatially corresponded to the required response. Hence, the direction conveyed by the stimulus influenced the response even if task irrelevant. Interestingly, the advantage for corresponding trials (i.e., Simon effect) was absent when each participant performed the task alone with the instruction
to respond to only one color, but was present when participants performed the task alongside another participant, each responding to only one color. The occurrence of the Simon effect in the latter condition was taken as evidence that each participant represented the other’s action and integrated this representation in action planning. In the present study the transfer paradigm described above was used to assess whether performing a task with a co-actor shapes the way a subsequent task is performed. To this aim, we ran four experiments in which participants were administered a Simon task after practicing a spatial compatibility task with an incompatible S-R mapping (see Fig. 1). In Experiment 1 they performed both tasks alongside another person; in Experiment 2, they performed the spatial compatibility task alone, responding to only one stimulus position and the Simon task with another person; in Experiment 3, they performed the spatial compatibility task with another person and the Simon task alone; finally, in Experiment 4, they performed the spatial compatibility task alone and the Simon task with another person. The use of the transfer paradigm will allow us to test whether shared practice shapes performance in a subsequent task. Specifically, if joint prior practice modulates subsequent
Baseline
Practice
Transfer
Exp. 1
Exp. 2
Exp. 3
Exp. 4
Fig. 1. Schematic representation of the experimental conditions used in the four experiments. The participant responding to the red stimulus is depicted in dark grey, while the participant responding to the green stimulus is depicted in light grey. (For interpretation of the references to colours in this figure legend, the reader is referred to the web version of this paper.)
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performance, we should find a reduction or an elimination of the Simon effect, similarly to what occurs in individual settings. Furthermore, this paradigm will allow us to test if joint practice can influence individual performance and if individual practice can influence joint performance. 2. Experiment 1 The aim of the present experiment was to assess whether a practice performed alongside another person can modulate performance in a subsequent Simon task. To this end, participants were required to perform a joint Simon task before and after performing a joint practice with a spatially incompatible mapping between stimulus and response. 2.1. Methods 2.1.1. Participants Sixteen students (seven males; four left-handed; age range: 19–25 years) of the University of Modena and Reggio Emilia took part in Experiment 1 for either a financial reward (8 Euros) or partial fulfillment of course credit. They had normal or corrected-to normal vision and were naïve as to the purpose of the experiment. Once recruited, they were randomly paired. 2.1.2. Apparatus and stimuli Stimuli in the spatial compatibility task were white solid squares, whereas stimuli in the Simon task were red or green solid squares (4.5 4.5 cm). They were presented on a color screen controlled by an IBM computer, 9.5 cm to the left or to the right of a central fixation cross (1 1 cm). In both tasks, responses were executed by pressing the ‘‘z”
Baseline
or ‘‘-” key of a standard Italian keyboard with the left or right index finger, respectively. Viewing distance was about 60 cm. 2.1.3. Design and procedure The experiment consisted of three consecutive sessions separated by a 5-min interval: a baseline session, a practice session and a transfer session. In the baseline and transfer sessions participants were administered a Simon task, whereas in the practice session they were administered a spatial compatibility task with an incompatible S-R mapping. Both Simon and spatial compatibility tasks were performed jointly with participants sitting side-by-side in front of the same computer screen. In the spatial compatibility task, each participant was instructed to respond to only one stimulus location by pressing the contralateral key. Hence the participant sitting on the right chair responded to left stimuli with the right key, whereas the participant sitting on the left chair responded to right stimuli with the left key. In the Simon task, each participant was instructed to respond to only one stimulus color. For half of the pairs, the participant sitting on the right chair was instructed to press the right key to the red stimulus whereas the participant sitting on the left chair was instructed to respond with the left key to the green stimulus. The other half experienced the opposite mapping. In both tasks, a trial began with the presentation of the fixation cross at the center of a black background. After 1 s the stimulus appeared to the right or to the left of fixation. In the Simon task, the stimulus remained visible for 800 ms and maximum time allowed for a response was 1 s. In the spatial compatibility task the stimulus remained visible for 600 ms and maximum time allowed for a response was
Practice
Transfer
450 C
RT (ms)
425
NC
*
400 375 350
Baseline
Session
Transf er
Fig. 2. Mean reaction times (ms) for the baseline and transfer sessions of Experiment 1 as a function of stimulus–response correspondence. Bars indicate standard errors of the means. Asterisks denote significant differences. C = corresponding; NC = non-corresponding.
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1200 ms. In both task, a response terminated the trial and the inter-trial-interval was 1 s. Both baseline and transfer sessions consisted of 12 practice trials and 160 experimental trials that were divided into two blocks of 80 trials each. The practice session consisted of 12 practice trials and 300 experimental trials that were divided into three blocks of 100 trials each.
During the practice session participants performed a go-nogo spatial compatibility task by themselves, with the instruction to respond to only one stimulus position with the contralateral key. Half of the participants responded to left stimuli with the right key, whereas the other half responded to right stimuli with the left key. During both baseline and transfer sessions participants performed a Simon task jointly.
2.2. Results and discussion 3.3. Results Here and in the following experiments we report only the data for the Simon task (baseline and transfer sessions). Correct RTs and arcsin-transformed error rates were submitted to repeated-measures ANOVAs with session (baseline vs. transfer) and correspondence (corresponding vs. non-corresponding) as within-subject factors. The RTs analysis revealed main effects of session, F(1, 15) = 11.33, p < .01, g2p = .43, and correspondence, F(1, 15) = 6.37, p < .03, g2p = .30. Participants were faster in the transfer (373 ms) than in the baseline (390 ms) session, and in corresponding (379 ms) than in non-corresponding (385 ms) trials. Most important, there was a significant interaction between the two factors indicating that the Simon effect differed in the two sessions, F(1, 15) = 13.36, p < .01, g2p = .47 (see Fig. 2). Post-hoc analyses confirmed that the 14-ms Simon effect observed in the baseline session was significant, while a null effect ( 0.6 ms) was evident in the transfer session. The error rate was 1% in the baseline session and 1.6% in the transfer session. The analysis revealed no main effects or interactions. Hence, a spatially incompatible practice performed jointly influences subsequent performance on the joint Simon task.
Responses were comparable in the baseline and transfer sessions, F < 1. Responses were faster in corresponding (374 ms) than in non-corresponding (383 ms) trials, F(1, 15) = 19.69, p < .01, g2p = .57. The 10-ms Simon effect evident in the baseline session did not differ from the 9ms effect evident in the transfer session, as indicated by the non-significant interaction between session and correspondence, F < 1 (see Fig. 3). Errors were comparable in the baseline (1.2%) and transfer (1.3%) sessions, F < 1. Errors tended to be fewer in corresponding (0.6%) than in non-corresponding (1.9%) trials, F(1, 15) = 3.91, p = .07. The same pattern was evident in both sessions, as indicated by the lack of an interaction between correspondence and session, F < 1. These results allow us to conclude that when the participants practice a specific stimulus–response link by themselves and then transfer to a joint Simon task, no transfer of learning occurs. The following experiments are aimed at assessing whether a joint practice can influence subsequent individual performance (Experiment 3) and whether individual practice can influence subsequent joint performance (Experiment 4).
3. Experiment 2
4. Experiment 3
The aim of the present experiment was to assess whether the joint Simon effect can be modulated by an individually- performed go-nogo practice with an incompatible mapping. In other words, we evaluated whether the practice task used in Experiment 1 modulates joint Simon task performance even when practice is performed by a single individual. To this end, participants were required to perform a joint Simon task before and after performing a spatially incompatible practice in which they responded to only one stimulus position. The finding of a modulation would mean that practice of a specific incompatible stimulus–response link per se is responsible for the modulation observed in Experiment 1.
The aim of the present experiment was to assess whether shared prior practice modulates the way a single individual performs a subsequent Simon task. To this end, participants were required to perform alone a Simon task before and after performing a joint practice with a spatially incompatible mapping between stimulus and response. 4.1. Participants Sixteen new right-handed students (seven males; age range = 19–23 years) took part in Experiment 3. They were selected as in Experiment 1. 4.2. Apparatus, stimuli and procedure
3.1. Participants Sixteen new students (eight males; four left-handers; age range = 19–27 years) took part in Experiment 2. They were selected as in Experiment 1. 3.2. Apparatus, stimuli and procedure Apparatus, stimuli and procedure were the same as Experiment 1 except for the followings.
Apparatus, stimuli and procedure were the same as Experiment 1 except for the followings. During the baseline and transfer sessions participants performed a standard Simon task by their own, whereas during the practice session they performed a spatial compatibility task jointly. During both baseline and transfer sessions participants sat back-to-back in front of two different computers and were instructed to respond to both stimulus colors with a left or right response.
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Baseline
Practice
Transfer
450 C NC
RT (ms)
425 400
*
*
375 350
Baseline
Transf er
Session Fig. 3. Mean reaction times (ms) for the baseline and transfer sessions of Experiment 2 as a function of stimulus–response correspondence. Bars indicate standard errors of the means. Asterisks denote significant differences. C = corresponding; NC = non-corresponding.
4.3. Results Responses were faster in the transfer session (439 ms) compared to the baseline session (469 ms), F(1, 15) = 15.55, p < .01, g2p = .51, and in corresponding (442 ms) than in non-corresponding (467 ms) trials, F(1, 15) = 17.61, p < .01, g2p = .54. The 29-ms Simon effect evident in the baseline session did not differ from the 21-ms effect evident in the transfer session, as indicated by the non-significant interaction between session and correspondence, F(1, 15) = 1.29, p = .27, g2p = .08 (see Fig. 4). To assess whether only the specific S-R link practiced by each participant during the practice session was transferred to the Simon task, RTs in the transfer session were analyzed as a function of stimulus position, response position and practiced S-R link. No interaction involving S-R link reached significance, Fs < 1. Errors were comparable in the baseline (3.5%) and transfer (4.3%) sessions, F(1, 15) = 2.80, p = .11. The analysis revealed a main effect of correspondence, F(1, 15) = 4.29, p = .05, with fewer errors in corresponding (2.9%) than in non-corresponding (5%) trials. The same pattern was evident in both sessions, as indicated by the lack of an interaction between correspondence and session, F < 1. Hence, a spatially incompatible practice performed jointly with another person seems to have no influence on individual performance on a subsequent Simon task. 5. Experiment 4 The aim of the present experiment was to assess whether an individually-performed prior practice can modulate the way a subsequent joint Simon task is per-
formed. To this end, participants were required to perform a joint Simon task before and after performing alone a practice with a spatially incompatible mapping between stimulus and response. 5.1. Participants Sixteen new students (five males; one left-hander; age range = 22–29 years), selected as in the previous experiments, took part in Experiment 4. 5.2. Apparatus, stimuli and procedure Apparatus, stimuli and procedure were the same as Experiment 3 except that during the baseline and transfer sessions participants performed a joint Simon task, whereas during the practice session they performed a spatial compatibility task alone, sitting back-to-back in front of two different computers. 5.3. Results Responses were faster in corresponding (383 ms) than in non-corresponding (390 ms) trials, F(1, 15) = 4.29, p = .05, g2p = .22. Session did not reach statistical significance, F < 1, but interacted with correspondence, F(1, 15) = 6.99, p < .02, g2p = .32 (see Fig. 5), indicating that the Simon effect differed in the two sessions. Post-hoc analyses confirmed that the 10-ms Simon effect observed in the baseline session was significant, while a null effect (3 ms, n.s.) was evident in the transfer session. Errors were comparable in the baseline (0.2%) and transfer (0.5%) sessions, F(1, 15) = 1.19, p = .29. The
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Baseline
Practice
Transfer
500
RT (ms)
475
*
*
C NC
450 425 400 Baseline
Transf er
Session Fig. 4. Mean reaction times (ms) for the baseline and transfer sessions of Experiment 3 as a function of stimulus–response correspondence. Bars indicate standard errors of the means. Asterisks denote significant differences. C = corresponding; NC = non-corresponding.
Baseline
Practice
Transfer
450 C NC
RT (ms)
425 400
*
375 350 Baseline
Transf er
Session Fig. 5. Mean reaction times (ms) for the baseline and transfer sessions of Experiment 4 as a function of stimulus–response correspondence. Bars indicate standard errors of the means. Asterisks denote significant differences. C = corresponding; NC = non-corresponding.
analysis revealed a main effect of correspondence, F(1, 15) = 5.99, p = .03, with fewer errors in corresponding (0.6%) than in non-corresponding (0.1%) trials. The same pattern was evident in both sessions, as indicated by the
lack of an interaction between correspondence and session, F < 1. These results indicated that a spatially incompatible practice performed by a single individual influences the
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subsequent performance on the joint Simon task, eliminating the Simon effect in RTs. 5.4. Meta-analysis To note, even though in Experiment 3 the session correspondence interaction did not reach statistical significance, there was a 8-ms reduction in the size of the Simon effect from baseline to transfer. This absolute reduction was smaller than the reduction observed in Experiment 1 but comparable to that observed in Experiment 4. To further assess whether the session correspondence interaction changed across the three experiments, we computed the difference between mean baseline and transfer Simon effects divided by the baseline Simon effect for each subject. Then we performed a repeated-measures ANOVA on these values with experiment as between-subjects factor1. The main effect of experiment approached significance, F(2, 45) = 2.75, p = .07, g2p = .11. Planned comparisons showed that the reduction of the Simon effect from practice to transfer was comparable in Experiments 1 and 4 (104% vs. 70%). These reductions significantly differed (ps 6 .05) from the (non-significant) reduction observed in Experiment 3 (28%). Hence, these results clearly show that the modulation of the Simon effect by prior practice occurred only in Experiments 1 and 4. 6. General discussion The main aim of the present study was to assess whether transfer-of-learning effects observed when individuals perform a task in isolation are evident under task sharing situations. Previous studies have shown that when a task is distributed between two agents, each one tends to integrate the other’s task and actions into his/her action plan. This is thought to occur because, as suggested by the ideomotor theory (e.g., Greenwald, 1970), the observation or even the imagination of an action activates a representation in the observer similar to the representation activated when the same action is actually performed (e.g., Brass, Bekkering, & Prinz, 2001; Sebanz et al., 2003; Tsai et al., 2008). Although the effects of acting jointly with another individual on immediate performance are well documented, there are no studies assessing the influence exerted by shared practice on subsequent performance. This is a relevant issue because we often learn to perform novel tasks interacting with other people and then have to transfer the acquired skills and knowledge to similar tasks we may perform either alone or together with another person. Similarly, we may learn to perform a task alone and then transfer this learning to activities performed with a co-actor. Knowing whether learning transfers from social to indi1 Since the individual Simon effect is numerically larger than the joint Simon effect, to compare the different conditions, we adjusted the difference between the Simon effects evident in the baseline and transfer sessions taking the baseline value as a reference. The obtained values represent the relative reduction in the size of the effect from baseline to transfer.
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vidual contexts and vice versa may have important practical implications in several domains and may also help us to shed light on some open issues regarding the nature and the boundary conditions of shared representations. To address this issue, we conducted four experiments in which participants were required to practice on a spatial compatibility task with an incompatible S-R mapping and then transfer to a Simon task. We manipulated the presence of a co-actor in the practice and/or in the transfer sessions. Our results showed that an incompatible practice performed with a co-actor eliminated the Simon effect only when also the Simon task was distributed between two participants (Experiment 1). No reduction was evident when a single individual performed a go-nogo incompatible practice before performing a joint Simon task (Experiment 2). While an individually-performed practice modulated the way the joint Simon task was performed, eliminating the joint Simon effect (Experiment 4), a shared practice did not reduce the Simon effect when the Simon task was performed by a single participant (Experiment 3). The results of the present study may provide some important information on the nature of shared representations and may help us understand the similarities and differences between the representations activated by action execution and those activated by action observation. It has been shown that in humans action execution and action observation activate partially overlapping areas (e.g., Grèzes & Decety, 2001). However, even though there is growing evidence of the functional similarity between representations of self and other’s action, it is still unclear whether they are completely equivalent. The smaller magnitude of the joint Simon effect compared to the standard effect seems to suggest that they are somehow different. The observation that the Simon effect is modulated by a joint incompatible practice would suggest that a specific SR link that a participant is not actually practicing but is practiced by his/her co-actor is able to exert an influence on his/her own future behavior in the same way as a link that has been actually practiced. Hence, it would be plausible to conclude that shared representations are completely equivalent to the representations elicited when an agent performs alone the whole task. Our results showed that this occurs only under some circumstances. On the one hand, the finding of a modulation of the Simon effect under joint action conditions in Experiment 1 supports the view that shared practice may have the same effects of an individually-performed practice. Specifically, similarly to what occurs with individuals acting in isolation (Iani et al., 2009; Proctor & Lu, 1999; Tagliabue et al., 2000), a spatially incompatible practice performed in a social context strengthens the non-corresponding association between a stimulus position and its incompatible response and influences subsequent performance even when stimulus location is no longer task relevant. On the other hand, the results of Experiment 3 demonstrate that these transferof-learning effects are maximal only when both practice and transfer take place in a social setting. Hence, learning taking place in either individual or social settings can influence shared performance in a subsequent task. On the contrary, a shared practice has no effect on individual performance.
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The lack of transfer-of-learning effects from social to individual contexts may be explained by the mechanisms involved in task sharing. When a task is distributed between two agents, each one tends to represent the other’s part of the task. However, to emit the correct response at the right time, they also need to keep their own and the other’s part of the task separated. Consistent with this idea, results of Sebanz et al. (2007) showed that acting with another person led to increased brain activity in ventral mediofrontal cortex, which is thought to be involved in the distinction between self and other (e.g., Amodio & Frith, 2006). Hence, performing the whole task does not completely correspond, at least at a neural level, to performing only part of the task. At a more general level, we showed the influence of joint task performance on incidental learning and the transfer of this learning to subsequent performance. These results may allow us to better define the relationship between social learning and performance. According to Vygotsky’s idea, what makes human beings different from other species is their ability to learn by interacting with other people (cf. Tomasello & Carpenter, 2007; Tomasello, Kruger, & Ratner, 1993). Children learn by observing what the adult is doing, internalize what is learned and then transfer the acquired knowledge to individual performance. Our results underline the importance of social learning but allow us to identify some of its boundary conditions and to better define what is learned. Specifically, they show that under task sharing conditions, the knowledge acquired during the performance of a task is internalized and transferred to a similar task. The finding that a joint practice influences performance only when also the transfer task occurs in a social context suggests that what is transferred is not only what is specifically practiced but also aspects of the interactive context in which learning took place. Acknowledgements We would like to thank two anonymous Reviewers for useful comments on an earlier version of the manuscript. We also wish to thank Luca Ferraro for helping with data collection for Experiment 2. References Amodio, D. M., & Frith, C. D. (2006). Meeting of minds: The medial frontal cortex and social cognition. Nature Reviews Neuroscience, 7, 268–277.
Atmaca, S., Sebanz, N., Prinz, W., & Knoblich, G. (2008). Action corepresentation: The joint SNARC effect. Social Neuroscience, 3, 410–420. Brass, M., Bekkering, H., & Prinz, W. (2001). Movement observation affects movement execution in a simple response task. Acta Psychologica, 106, 3–22. Greenwald, A. G. (1970). Sensory feedback mechanisms in performance control: Which special reference to the ideo-motor mechanism. Psychological Review, 77, 73–99. Grèzes, J., & Decety, J. (2001). Functional anatomy of execution, mental simulation, observation, and verb generation of actions: A metaanalysis. Human Brain Mapping, 12, 1–19. Hommel, B., Colzato, L., & van den Wildenber, W. P. M. (2009). How social are task representations? Psychological Science, 20, 794–798. Iani, C., Rubichi, S., Gherri, E., & Nicoletti, R. (2009). Co-occurrence of sequential and practice effects in the Simon task: Evidence for two independent mechanisms affecting response selection. Memory & Cognition, 37, 358–367. Proctor, R. W., & Lu, C.-H. (1999). Processing irrelevant information: Practice and transfer effects in choice-reaction tasks. Memory & Cognition, 27, 63–77. Proctor, R. W., & Vu, K.-P. L. (2006). Stimulus-response compatibility principle: Data, theory, and application. Boca Raton, FL: Taylor & Francis. Sebanz, N., Bekkering, H., & Knoblich, G. (2006). Joint action: Bodies and minds moving together. Trends in Cognitive Sciences, 10, 70–76. Sebanz, N., Knoblich, G., & Prinz, W. (2003). Representing other’s actions: Just like one’s own? Cognition, 88, B11–B21. Sebanz, N., Knoblich, G., & Prinz, W. (2005). How two share a task: Corepresenting stimulus-response mappings. Journal of Experimental Psychology: Human Perception and Performance, 31, 1234–1246. Sebanz, N., Knoblich, G., Prinz, W., & Wascher, E. (2006). Twin peaks: An ERP study of action planning and control in coacting individuals. Journal of Cognitive Neuroscience, 18, 859–870. Sebanz, N., Rebbechi, D., Knoblich, G., Prinz, W., & Frith, C. D. (2007). Is it really my turn? An event-related fMRI study of task sharing. Social Neuroscience, 2, 81–95. Simon, J. R., & Rudell, A. P. (1967). Auditory S-R compatibility: The effect of an irrelevant cue on information processing. Journal of Applied Psychology, 51, 300–304. Tagliabue, M., Zorzi, M., Umiltà, C., & Bassignani, F. (2000). The role of long-term-memory and short-term-memory links in the Simon effect. Journal of Experimental Psychology: Human Perception and Performance, 26, 648–670. Tomasello, M., & Carpenter, M. (2007). Shared intentionality. Developmental Science, 10, 121–125. Tomasello, M., Carpenter, M., Call, J., Behne, T., & Moll, H. (2005). Understanding and sharing intentions: The origins of cultural cognition. Behavioral and Brain Sciences, 28, 675–735. Tomasello, M., Kruger, A., & Ratner, H. (1993). Cultural learning. Behavioral and Brain Sciences, 16, 495–552. Tsai, C.-C., Kuo, W.-J., Hung, D. L., & Tzeng, O. J. L. (2008). Action corepresentation is tuned to other humans. Journal of Cognitive Neuroscience, 20, 2015–2024. Vygotsky, L. S. (1978). Mind and society: The development of higher mental processes. Cambridge, MA: Harvard University Press. Welsh, T. N., Higgins, L., Ray, M., & Weeks, D. J. (2007). Seeing vs. believing: Is believing sufficient to activate the process of response co-representation? Human Movement Science, 26, 853–866.
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Cognition journal homepage: www.elsevier.com/locate/COGNIT
Shared learning shapes human performance: Transfer effects in task sharing Nadia Milanese, Cristina Iani *, Sandro Rubichi Università di Modena e Reggio Emilia, Italy
a r t i c l e
i n f o
Article history: Received 2 September 2009 Revised 1 March 2010 Accepted 10 March 2010
Keywords: Spatial compatibility Simon effect Social cognition Learning Incidental learning
a b s t r a c t We investigated whether performing a task with a co-actor shapes the way a subsequent task is performed. In four experiments participants were administered a Simon task after practicing a spatial compatibility task with an incompatible S-R mapping. In Experiment 1 they performed both tasks alongside another person; in Experiment 2 they performed the spatial compatibility task alone, responding to only one stimulus position, and the Simon task with another person; in Experiment 3, they performed the spatial compatibility task with another person and the Simon task alone; finally, in Experiment 4, they performed the spatial compatibility task alone and the Simon task with another person. The incompatible practice eliminated the Simon effect in Experiments 1 and 4. These results indicate that when a task is distributed between two participants with each one performing a different part of it, they tend to represent the whole task rather than their own part of it. This experience can influence the way a subsequent task is performed, as long as this latter occurs in a social context. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction Many everyday activities require interaction with other people. While some of these interactions involve little or no interpersonal coordination, others clearly put to the test our coordination abilities. If we think of a situation like moving together with another person a heavy piece of furniture up a curvy staircase, it is clear that efficient performance requires an understanding of what the other is doing in order to predict his or her future actions and to behave accordingly. As recent studies suggest, our ability to understand others and to coordinate with them depends on the creation of shared task representations, that is representations integrating current and predicted self and other’s actions (cf. Sebanz, Bekkering, & Knoblich, 2006; see also Tomasello, Carpenter, Call, Behne, & Moll, 2005).
* Corresponding author at: Dipartimento di Scienze Sociali, Cognitive e Quantitative, Università di Modena e Reggio Emilia, Via Allegri, 9, 42121 Reggio Emilia, Italy. E-mail address: [email protected] (C. Iani). 0010-0277/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cognition.2010.03.010
These shared representations emerge in a variety of situations involving jointly acting individuals even when considering the other’s actions is not necessary, thus suggesting that human cognition is biased toward joint action (e.g., Atmaca, Sebanz, Prinz, & Knoblich, 2008; Hommel, Colzato, & van den Wildenber, 2009; Sebanz, Knoblich, & Prinz, 2003, 2005; Sebanz, Knoblich, Prinz, & Wascher, 2006; Sebanz, Rebbechi, Knoblich, Prinz, & Frith, 2007; Tsai, Kuo, Hung, & Tzeng, 2008; Welsh, Higgins, Ray, & Weeks, 2007). Social interactions play an important role in learning too. Indeed, our ability to perform novel tasks depends on the application of knowledge previously acquired through learning, which often occurs through social interaction (e.g., Vygotsky, 1978). Given these considerations, we believe it is of particular interest to investigate the relationship between learning and performance in individual and social contexts. This requires an investigation into whether learning derived from social interactions may be transferred to distinct but similar tasks performed either in social or individual contexts and whether individual
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learning may transfer to performance in social contexts as well. As regards individual performance, there are clear indications of transfer of learning in tasks investigating spatial correspondence effects. Spatial correspondence effects are evident in choice-reaction tasks in which the stimulus appears in a right or left location and the response is produced manually (for a review see Proctor and Vu (2006)). In the spatial stimulus–response compatibility task, the response is selected on the basis of stimulus location. In compatible mappings participants are instructed to respond with the key that is located on the same side of the stimulus, whereas in incompatible mappings the instructions are reversed. In the Simon task, the task-relevant stimulus feature is non-spatial (e.g., shape or color), and subjects respond with assigned right and left keys (Simon & Rudell, 1967). Thus, there are trials in which stimulus and response locations correspond (i.e., corresponding S-R pairings) and trials in which they do not (i.e., non-corresponding pairings). In both tasks, performance is usually faster and more accurate when there is spatial correspondence between stimulus and response (i.e., when the mapping is compatible for the spatial SRC task and when stimulus and response locations correspond for the Simon task) than when there is not (i.e., when the mapping is incompatible for the spatial SRC task and when stimulus and response locations do not correspond for the Simon task). By using the transfer paradigm developed by Proctor and Lu (1999), it has been shown that when participants perform a spatial compatibility task in which they are required to respond to stimulus location by emitting a spatially incompatible response (i.e., responding to the left stimulus with the right key and vice versa) and then transfer to a Simon task, the Simon effect is reduced, absent of even reversed, that is, reaction times for non-corresponding responses are faster than those for corresponding responses (Iani, Rubichi, Gherri, & Nicoletti, 2009; Proctor & Lu, 1999; Tagliabue, Zorzi, Umiltà, & Bassignani, 2000). This is thought to occur because responding for a certain amount of trials with a spatially incompatible mapping strengthen the non-corresponding association between a stimulus and a response to the extent that this association continues to affect performance even when the task is changed and the response should no longer be emitted on the basis of a spatial stimulus feature (cf. Tagliabue et al., 2000). Notably, the Simon task has proven to be a good candidate task to investigate the emergence of shared representations. In a pioneer study by Sebanz et al. (2003), participants were shown photographs of a centrally presented right hand pointing to the right, to the left, or straight, with the instruction to press one of two lateralized keys according to the color of a ring appearing on the index finger. They were required to perform the task either alone or paired with another participant. When they performed the task individually, responses were faster when the pointing direction of the hand spatially corresponded to the required response. Hence, the direction conveyed by the stimulus influenced the response even if task irrelevant. Interestingly, the advantage for corresponding trials (i.e., Simon effect) was absent when each participant performed the task alone with the instruction
to respond to only one color, but was present when participants performed the task alongside another participant, each responding to only one color. The occurrence of the Simon effect in the latter condition was taken as evidence that each participant represented the other’s action and integrated this representation in action planning. In the present study the transfer paradigm described above was used to assess whether performing a task with a co-actor shapes the way a subsequent task is performed. To this aim, we ran four experiments in which participants were administered a Simon task after practicing a spatial compatibility task with an incompatible S-R mapping (see Fig. 1). In Experiment 1 they performed both tasks alongside another person; in Experiment 2, they performed the spatial compatibility task alone, responding to only one stimulus position and the Simon task with another person; in Experiment 3, they performed the spatial compatibility task with another person and the Simon task alone; finally, in Experiment 4, they performed the spatial compatibility task alone and the Simon task with another person. The use of the transfer paradigm will allow us to test whether shared practice shapes performance in a subsequent task. Specifically, if joint prior practice modulates subsequent
Baseline
Practice
Transfer
Exp. 1
Exp. 2
Exp. 3
Exp. 4
Fig. 1. Schematic representation of the experimental conditions used in the four experiments. The participant responding to the red stimulus is depicted in dark grey, while the participant responding to the green stimulus is depicted in light grey. (For interpretation of the references to colours in this figure legend, the reader is referred to the web version of this paper.)
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performance, we should find a reduction or an elimination of the Simon effect, similarly to what occurs in individual settings. Furthermore, this paradigm will allow us to test if joint practice can influence individual performance and if individual practice can influence joint performance. 2. Experiment 1 The aim of the present experiment was to assess whether a practice performed alongside another person can modulate performance in a subsequent Simon task. To this end, participants were required to perform a joint Simon task before and after performing a joint practice with a spatially incompatible mapping between stimulus and response. 2.1. Methods 2.1.1. Participants Sixteen students (seven males; four left-handed; age range: 19–25 years) of the University of Modena and Reggio Emilia took part in Experiment 1 for either a financial reward (8 Euros) or partial fulfillment of course credit. They had normal or corrected-to normal vision and were naïve as to the purpose of the experiment. Once recruited, they were randomly paired. 2.1.2. Apparatus and stimuli Stimuli in the spatial compatibility task were white solid squares, whereas stimuli in the Simon task were red or green solid squares (4.5 4.5 cm). They were presented on a color screen controlled by an IBM computer, 9.5 cm to the left or to the right of a central fixation cross (1 1 cm). In both tasks, responses were executed by pressing the ‘‘z”
Baseline
or ‘‘-” key of a standard Italian keyboard with the left or right index finger, respectively. Viewing distance was about 60 cm. 2.1.3. Design and procedure The experiment consisted of three consecutive sessions separated by a 5-min interval: a baseline session, a practice session and a transfer session. In the baseline and transfer sessions participants were administered a Simon task, whereas in the practice session they were administered a spatial compatibility task with an incompatible S-R mapping. Both Simon and spatial compatibility tasks were performed jointly with participants sitting side-by-side in front of the same computer screen. In the spatial compatibility task, each participant was instructed to respond to only one stimulus location by pressing the contralateral key. Hence the participant sitting on the right chair responded to left stimuli with the right key, whereas the participant sitting on the left chair responded to right stimuli with the left key. In the Simon task, each participant was instructed to respond to only one stimulus color. For half of the pairs, the participant sitting on the right chair was instructed to press the right key to the red stimulus whereas the participant sitting on the left chair was instructed to respond with the left key to the green stimulus. The other half experienced the opposite mapping. In both tasks, a trial began with the presentation of the fixation cross at the center of a black background. After 1 s the stimulus appeared to the right or to the left of fixation. In the Simon task, the stimulus remained visible for 800 ms and maximum time allowed for a response was 1 s. In the spatial compatibility task the stimulus remained visible for 600 ms and maximum time allowed for a response was
Practice
Transfer
450 C
RT (ms)
425
NC
*
400 375 350
Baseline
Session
Transf er
Fig. 2. Mean reaction times (ms) for the baseline and transfer sessions of Experiment 1 as a function of stimulus–response correspondence. Bars indicate standard errors of the means. Asterisks denote significant differences. C = corresponding; NC = non-corresponding.
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1200 ms. In both task, a response terminated the trial and the inter-trial-interval was 1 s. Both baseline and transfer sessions consisted of 12 practice trials and 160 experimental trials that were divided into two blocks of 80 trials each. The practice session consisted of 12 practice trials and 300 experimental trials that were divided into three blocks of 100 trials each.
During the practice session participants performed a go-nogo spatial compatibility task by themselves, with the instruction to respond to only one stimulus position with the contralateral key. Half of the participants responded to left stimuli with the right key, whereas the other half responded to right stimuli with the left key. During both baseline and transfer sessions participants performed a Simon task jointly.
2.2. Results and discussion 3.3. Results Here and in the following experiments we report only the data for the Simon task (baseline and transfer sessions). Correct RTs and arcsin-transformed error rates were submitted to repeated-measures ANOVAs with session (baseline vs. transfer) and correspondence (corresponding vs. non-corresponding) as within-subject factors. The RTs analysis revealed main effects of session, F(1, 15) = 11.33, p < .01, g2p = .43, and correspondence, F(1, 15) = 6.37, p < .03, g2p = .30. Participants were faster in the transfer (373 ms) than in the baseline (390 ms) session, and in corresponding (379 ms) than in non-corresponding (385 ms) trials. Most important, there was a significant interaction between the two factors indicating that the Simon effect differed in the two sessions, F(1, 15) = 13.36, p < .01, g2p = .47 (see Fig. 2). Post-hoc analyses confirmed that the 14-ms Simon effect observed in the baseline session was significant, while a null effect ( 0.6 ms) was evident in the transfer session. The error rate was 1% in the baseline session and 1.6% in the transfer session. The analysis revealed no main effects or interactions. Hence, a spatially incompatible practice performed jointly influences subsequent performance on the joint Simon task.
Responses were comparable in the baseline and transfer sessions, F < 1. Responses were faster in corresponding (374 ms) than in non-corresponding (383 ms) trials, F(1, 15) = 19.69, p < .01, g2p = .57. The 10-ms Simon effect evident in the baseline session did not differ from the 9ms effect evident in the transfer session, as indicated by the non-significant interaction between session and correspondence, F < 1 (see Fig. 3). Errors were comparable in the baseline (1.2%) and transfer (1.3%) sessions, F < 1. Errors tended to be fewer in corresponding (0.6%) than in non-corresponding (1.9%) trials, F(1, 15) = 3.91, p = .07. The same pattern was evident in both sessions, as indicated by the lack of an interaction between correspondence and session, F < 1. These results allow us to conclude that when the participants practice a specific stimulus–response link by themselves and then transfer to a joint Simon task, no transfer of learning occurs. The following experiments are aimed at assessing whether a joint practice can influence subsequent individual performance (Experiment 3) and whether individual practice can influence subsequent joint performance (Experiment 4).
3. Experiment 2
4. Experiment 3
The aim of the present experiment was to assess whether the joint Simon effect can be modulated by an individually- performed go-nogo practice with an incompatible mapping. In other words, we evaluated whether the practice task used in Experiment 1 modulates joint Simon task performance even when practice is performed by a single individual. To this end, participants were required to perform a joint Simon task before and after performing a spatially incompatible practice in which they responded to only one stimulus position. The finding of a modulation would mean that practice of a specific incompatible stimulus–response link per se is responsible for the modulation observed in Experiment 1.
The aim of the present experiment was to assess whether shared prior practice modulates the way a single individual performs a subsequent Simon task. To this end, participants were required to perform alone a Simon task before and after performing a joint practice with a spatially incompatible mapping between stimulus and response. 4.1. Participants Sixteen new right-handed students (seven males; age range = 19–23 years) took part in Experiment 3. They were selected as in Experiment 1. 4.2. Apparatus, stimuli and procedure
3.1. Participants Sixteen new students (eight males; four left-handers; age range = 19–27 years) took part in Experiment 2. They were selected as in Experiment 1. 3.2. Apparatus, stimuli and procedure Apparatus, stimuli and procedure were the same as Experiment 1 except for the followings.
Apparatus, stimuli and procedure were the same as Experiment 1 except for the followings. During the baseline and transfer sessions participants performed a standard Simon task by their own, whereas during the practice session they performed a spatial compatibility task jointly. During both baseline and transfer sessions participants sat back-to-back in front of two different computers and were instructed to respond to both stimulus colors with a left or right response.
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Baseline
Practice
Transfer
450 C NC
RT (ms)
425 400
*
*
375 350
Baseline
Transf er
Session Fig. 3. Mean reaction times (ms) for the baseline and transfer sessions of Experiment 2 as a function of stimulus–response correspondence. Bars indicate standard errors of the means. Asterisks denote significant differences. C = corresponding; NC = non-corresponding.
4.3. Results Responses were faster in the transfer session (439 ms) compared to the baseline session (469 ms), F(1, 15) = 15.55, p < .01, g2p = .51, and in corresponding (442 ms) than in non-corresponding (467 ms) trials, F(1, 15) = 17.61, p < .01, g2p = .54. The 29-ms Simon effect evident in the baseline session did not differ from the 21-ms effect evident in the transfer session, as indicated by the non-significant interaction between session and correspondence, F(1, 15) = 1.29, p = .27, g2p = .08 (see Fig. 4). To assess whether only the specific S-R link practiced by each participant during the practice session was transferred to the Simon task, RTs in the transfer session were analyzed as a function of stimulus position, response position and practiced S-R link. No interaction involving S-R link reached significance, Fs < 1. Errors were comparable in the baseline (3.5%) and transfer (4.3%) sessions, F(1, 15) = 2.80, p = .11. The analysis revealed a main effect of correspondence, F(1, 15) = 4.29, p = .05, with fewer errors in corresponding (2.9%) than in non-corresponding (5%) trials. The same pattern was evident in both sessions, as indicated by the lack of an interaction between correspondence and session, F < 1. Hence, a spatially incompatible practice performed jointly with another person seems to have no influence on individual performance on a subsequent Simon task. 5. Experiment 4 The aim of the present experiment was to assess whether an individually-performed prior practice can modulate the way a subsequent joint Simon task is per-
formed. To this end, participants were required to perform a joint Simon task before and after performing alone a practice with a spatially incompatible mapping between stimulus and response. 5.1. Participants Sixteen new students (five males; one left-hander; age range = 22–29 years), selected as in the previous experiments, took part in Experiment 4. 5.2. Apparatus, stimuli and procedure Apparatus, stimuli and procedure were the same as Experiment 3 except that during the baseline and transfer sessions participants performed a joint Simon task, whereas during the practice session they performed a spatial compatibility task alone, sitting back-to-back in front of two different computers. 5.3. Results Responses were faster in corresponding (383 ms) than in non-corresponding (390 ms) trials, F(1, 15) = 4.29, p = .05, g2p = .22. Session did not reach statistical significance, F < 1, but interacted with correspondence, F(1, 15) = 6.99, p < .02, g2p = .32 (see Fig. 5), indicating that the Simon effect differed in the two sessions. Post-hoc analyses confirmed that the 10-ms Simon effect observed in the baseline session was significant, while a null effect (3 ms, n.s.) was evident in the transfer session. Errors were comparable in the baseline (0.2%) and transfer (0.5%) sessions, F(1, 15) = 1.19, p = .29. The
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Baseline
Practice
Transfer
500
RT (ms)
475
*
*
C NC
450 425 400 Baseline
Transf er
Session Fig. 4. Mean reaction times (ms) for the baseline and transfer sessions of Experiment 3 as a function of stimulus–response correspondence. Bars indicate standard errors of the means. Asterisks denote significant differences. C = corresponding; NC = non-corresponding.
Baseline
Practice
Transfer
450 C NC
RT (ms)
425 400
*
375 350 Baseline
Transf er
Session Fig. 5. Mean reaction times (ms) for the baseline and transfer sessions of Experiment 4 as a function of stimulus–response correspondence. Bars indicate standard errors of the means. Asterisks denote significant differences. C = corresponding; NC = non-corresponding.
analysis revealed a main effect of correspondence, F(1, 15) = 5.99, p = .03, with fewer errors in corresponding (0.6%) than in non-corresponding (0.1%) trials. The same pattern was evident in both sessions, as indicated by the
lack of an interaction between correspondence and session, F < 1. These results indicated that a spatially incompatible practice performed by a single individual influences the
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subsequent performance on the joint Simon task, eliminating the Simon effect in RTs. 5.4. Meta-analysis To note, even though in Experiment 3 the session correspondence interaction did not reach statistical significance, there was a 8-ms reduction in the size of the Simon effect from baseline to transfer. This absolute reduction was smaller than the reduction observed in Experiment 1 but comparable to that observed in Experiment 4. To further assess whether the session correspondence interaction changed across the three experiments, we computed the difference between mean baseline and transfer Simon effects divided by the baseline Simon effect for each subject. Then we performed a repeated-measures ANOVA on these values with experiment as between-subjects factor1. The main effect of experiment approached significance, F(2, 45) = 2.75, p = .07, g2p = .11. Planned comparisons showed that the reduction of the Simon effect from practice to transfer was comparable in Experiments 1 and 4 (104% vs. 70%). These reductions significantly differed (ps 6 .05) from the (non-significant) reduction observed in Experiment 3 (28%). Hence, these results clearly show that the modulation of the Simon effect by prior practice occurred only in Experiments 1 and 4. 6. General discussion The main aim of the present study was to assess whether transfer-of-learning effects observed when individuals perform a task in isolation are evident under task sharing situations. Previous studies have shown that when a task is distributed between two agents, each one tends to integrate the other’s task and actions into his/her action plan. This is thought to occur because, as suggested by the ideomotor theory (e.g., Greenwald, 1970), the observation or even the imagination of an action activates a representation in the observer similar to the representation activated when the same action is actually performed (e.g., Brass, Bekkering, & Prinz, 2001; Sebanz et al., 2003; Tsai et al., 2008). Although the effects of acting jointly with another individual on immediate performance are well documented, there are no studies assessing the influence exerted by shared practice on subsequent performance. This is a relevant issue because we often learn to perform novel tasks interacting with other people and then have to transfer the acquired skills and knowledge to similar tasks we may perform either alone or together with another person. Similarly, we may learn to perform a task alone and then transfer this learning to activities performed with a co-actor. Knowing whether learning transfers from social to indi1 Since the individual Simon effect is numerically larger than the joint Simon effect, to compare the different conditions, we adjusted the difference between the Simon effects evident in the baseline and transfer sessions taking the baseline value as a reference. The obtained values represent the relative reduction in the size of the effect from baseline to transfer.
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vidual contexts and vice versa may have important practical implications in several domains and may also help us to shed light on some open issues regarding the nature and the boundary conditions of shared representations. To address this issue, we conducted four experiments in which participants were required to practice on a spatial compatibility task with an incompatible S-R mapping and then transfer to a Simon task. We manipulated the presence of a co-actor in the practice and/or in the transfer sessions. Our results showed that an incompatible practice performed with a co-actor eliminated the Simon effect only when also the Simon task was distributed between two participants (Experiment 1). No reduction was evident when a single individual performed a go-nogo incompatible practice before performing a joint Simon task (Experiment 2). While an individually-performed practice modulated the way the joint Simon task was performed, eliminating the joint Simon effect (Experiment 4), a shared practice did not reduce the Simon effect when the Simon task was performed by a single participant (Experiment 3). The results of the present study may provide some important information on the nature of shared representations and may help us understand the similarities and differences between the representations activated by action execution and those activated by action observation. It has been shown that in humans action execution and action observation activate partially overlapping areas (e.g., Grèzes & Decety, 2001). However, even though there is growing evidence of the functional similarity between representations of self and other’s action, it is still unclear whether they are completely equivalent. The smaller magnitude of the joint Simon effect compared to the standard effect seems to suggest that they are somehow different. The observation that the Simon effect is modulated by a joint incompatible practice would suggest that a specific SR link that a participant is not actually practicing but is practiced by his/her co-actor is able to exert an influence on his/her own future behavior in the same way as a link that has been actually practiced. Hence, it would be plausible to conclude that shared representations are completely equivalent to the representations elicited when an agent performs alone the whole task. Our results showed that this occurs only under some circumstances. On the one hand, the finding of a modulation of the Simon effect under joint action conditions in Experiment 1 supports the view that shared practice may have the same effects of an individually-performed practice. Specifically, similarly to what occurs with individuals acting in isolation (Iani et al., 2009; Proctor & Lu, 1999; Tagliabue et al., 2000), a spatially incompatible practice performed in a social context strengthens the non-corresponding association between a stimulus position and its incompatible response and influences subsequent performance even when stimulus location is no longer task relevant. On the other hand, the results of Experiment 3 demonstrate that these transferof-learning effects are maximal only when both practice and transfer take place in a social setting. Hence, learning taking place in either individual or social settings can influence shared performance in a subsequent task. On the contrary, a shared practice has no effect on individual performance.
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The lack of transfer-of-learning effects from social to individual contexts may be explained by the mechanisms involved in task sharing. When a task is distributed between two agents, each one tends to represent the other’s part of the task. However, to emit the correct response at the right time, they also need to keep their own and the other’s part of the task separated. Consistent with this idea, results of Sebanz et al. (2007) showed that acting with another person led to increased brain activity in ventral mediofrontal cortex, which is thought to be involved in the distinction between self and other (e.g., Amodio & Frith, 2006). Hence, performing the whole task does not completely correspond, at least at a neural level, to performing only part of the task. At a more general level, we showed the influence of joint task performance on incidental learning and the transfer of this learning to subsequent performance. These results may allow us to better define the relationship between social learning and performance. According to Vygotsky’s idea, what makes human beings different from other species is their ability to learn by interacting with other people (cf. Tomasello & Carpenter, 2007; Tomasello, Kruger, & Ratner, 1993). Children learn by observing what the adult is doing, internalize what is learned and then transfer the acquired knowledge to individual performance. Our results underline the importance of social learning but allow us to identify some of its boundary conditions and to better define what is learned. Specifically, they show that under task sharing conditions, the knowledge acquired during the performance of a task is internalized and transferred to a similar task. The finding that a joint practice influences performance only when also the transfer task occurs in a social context suggests that what is transferred is not only what is specifically practiced but also aspects of the interactive context in which learning took place. Acknowledgements We would like to thank two anonymous Reviewers for useful comments on an earlier version of the manuscript. We also wish to thank Luca Ferraro for helping with data collection for Experiment 2. References Amodio, D. M., & Frith, C. D. (2006). Meeting of minds: The medial frontal cortex and social cognition. Nature Reviews Neuroscience, 7, 268–277.
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