In the past two decades, cognitive science has begun to consider social influences on cognitive processes, especially when people jointly perform the same task [for a review, see, Sebanz et al. (2006); Dolk et al. (2011, 2014a)]. Using a joint (or social) Simon task (Knoblich and Sebanz, 2006; Sebanz et al., 2006; Dolk et al., 2011, 2014a), two participants, sitting next to each other, displayed a joint Simon effect (JSE) in similar way to a classical Simon effect (SE; Simon, 1969, 1990). Taking into account that the SE reflects a stimulus-response congruency effect (i.e., when there is a spatial correspondence between the spatial position of the target and the spatial position of the response key, the responses are faster than those when there is a spatial incongruency between target and response key; Kornblum et al., 1990), the JSE indicates that both actors represent their own and another person’s action, as well as the representation of the spatial dimension of the responses, introducing a stimulus-response congruency effect (Sebanz et al., 2003). In other words, for the actor, sitting on the left side, all his/her own targets presented on the left space are represented as compatible trials (i.e., spatial congruency between target and response key), while all targets presented on the right space (which is the space of the co-author) are represented as incompatible trials (i.e., spatial incongruency between target and response key). Although the joint Simon task is essentially a go/no-go task (i.e., each participant with a single response has to decide whether to respond to his/her assigned target or to withhold any response), the JSE could be evidence of a dedicate social perception-action mechanism: with a co-representation of another’s task rule/instruction, participants take the active response of their co-actor into consideration when selecting their own responses, and thus in incompatible trials a response selection conflict arises (Sebanz et al., 2003, 2006; Knoblich and Sebanz, 2006; Tsai et al., 2006). This action (or task) co-representation view suggests that each participant has a competition between their own and the other’s response [Sebanz et al., 2003, 2006; Knoblich and Sebanz, 2006; Tsai et al., 2006; Yamaguchi et al., 2017; for a review see Sebanz and Knoblich (2009)].

Intriguingly, the JSE has been also reported in the presence of various dynamic non-human co-actors, such as a Japanese waving cat, suggesting that the joint effect can be induced by any dynamic event (Dolk et al., 2013). These findings indicate that the JSE can be induced by any attention-grabbing event, which facilitates the discrimination between its cognitive representation and the representation of the participant’s own action [Dolk et al., 2013; see also, Liepelt et al. (2011), Pfister et al. (2014), Sellaro et al. (2015), Klempova and Liepelt (2016)]. Even if the spatial response coding account can explain the JSE as matching (or mismatching) between spatial stimulus location and spatial response location (Guagnano et al., 2010; Dittrich et al., 2012, 2013; but see Welsh et al. (2013) for different results) in these conditions, a possible explanation of the JSE is the referential coding account (Dolk et al., 2011, 2013), based on the general assumptions of ideomotor theory [for a review see Stock and Stock (2004)] and Theory of Event Coding (TEC; Hommel et al., 2001; Hommel, 2009, 2011) in particular. TEC assumes that action and perception are tightly linked together, and individuals represent self-produced actions and other perceived events through codes of the effects their actions usually produce. Accordingly, the perception of alternative action or object events representing the same or similar feature codes produces an action selection conflict between actions trigged externally (by another actor) and activated internally. This conflict can be resolved by emphasizing (i.e., intentional weighting principle; Memelink and Hommel, 2013) an action feature, thus better discriminating between self-own and other-own actions [i.e., referential coding; Hommel et al., 2001; Dolk et al., 2013; for a review see, Dolk et al. (2014a)]. Thus, it is possible to expect changes of the JSE related to the perceived similarity between actor and co-actor (Müller et al., 2011; McClung et al., 2013). For example, when group membership (i.e., in-group vs. out-group members) was considered, Müller et al. (2011) found a social Simon effect when white students performed the task with a white left hand displayed on the screen while this effect disappeared when they interacted with a black out-group member, suggesting an action co-representation only when both actor and co-actor belonged to the same group. According to this assumption, gender composition of pairs in joint tasks should affect the joint effect, given that gender is one of the most salient types of social categorization since it is one of the most basic and immediately available social factors that is activated automatically for the construction of social identity and group membership (e.g., Tajfel and Turner, 1979; Stangor et al., 1992; Powlishta, 1995). Mussi et al. (2015) were the first to reveal this gender composition effect with a larger JSE for the same-gender (i.e., female-female or male-male) pair than mixed-gender (i.e., female-male or male-female) pairs showed. These findings indicated that gender, which is automatically accessible, increased the conflict discrimination between self-own and other-own actions in a same-gender pair [for similar results see also, van der Weiden et al. (2016)]. Thus, gender information could influence the joint selective attention. However, van der Weiden et al. (2016) reported a general gender effect on RTs, with faster responses to congruent trials for men independently from co-actor’s sex. This finding limits the influence of gender composition of pairs on joint selective attention, given that gender effect on SE can mask the influence. In addition, van der Weiden et al. (2016) suggested that their results should be replicated in future research because their investigation was the only study, which replicated and extended previous findings provided by Mussi et al. (2015), and the interpretations about the sex of participants in influencing the joint action effect should be taken with caution. However, both Mussi et al. (2015) and van der Weiden et al. (2016) suggested that the gender composition of pairs in joint action paradigms is relevant to better understand the underlying mechanisms of and implications for social interaction. Finally, alternative interpretation (e.g., spatial response coding account; Dittrich et al., 2012, 2013, 2017) for the JSE has been challenged the social nature of the joint Simon task, while different paradigms (e.g., joint Flanker or Navon tasks; Böckler et al., 2012; Dittrich et al., 2017, see below) have been proposed to better understand the social mechanism of joint action.

Interestingly for the purpose of the present study, a growing body of literature shows gender differences for the ability to prioritize the processing of task-relevant information and to filter out distracting task-irrelevant information that might trigger wrong decision [for a review see for e.g., Lee and Choo (2013)]. Using a flanker paradigm, in which participants are generally instructed to attend and respond to centrally presented stimuli (e.g., H) while ignoring nearby flanking stimuli (e.g., S; Eriksen and Eriksen, 1974), it has been observed that females had slower response times (RTs) for incompatible trials (i.e., the central target H is associated with a specific key while the surrounding flankers S are associated with another key) and made more errors, suggesting a higher susceptibility to irrelevant stimuli more than males (Bayliss et al., 2005; Stoet, 2010), demonstrating differential conflict monitoring (Clayson et al., 2011). At the same time, gender differences have been observed when the focus of the attention is shifted from global to local processing of the visual stimuli [for a review see, Herrera et al. (2019)]. In the Navon task (Navon, 1977, 2003) with hierarchically-organized objects, such as large letters (global level; e.g., H) composed of small letters (local level; e.g., h), an advantage or precedence in detecting a target at the global level has been reported, and this advantage is larger for males than females (Navon, 1981; Razumnikova and Volf, 2011). In addition, it has been also reported a congruency effect at local level (Navon, 1977; Kimchi, 1992), that is faster RTs when there is a congruency at global and local levels (e.g., a big H composed of small Hs) respect to there is an incongruency (e.g., a big H composed by small Ss). In this case, the attending to local level processing is easier for women than for men (Müller-Oehring et al., 2007). It is worth noting that both tasks are used in the joint paradigm, suggesting that these cognitive tasks are eligible for examining joint action (Atmaca et al., 2011; Böckler and Sebanz, 2012; Böckler et al., 2012; Dolk et al., 2014b; Dittrich et al., 2017; Fabbri et al., 2017, 2018a,b; Peterburs et al., 2017).

The aim of the present study was to assess how gender information of co-actors influenced the joint selective attention measured in a joint flanker (Experiment 1) and joint Navon (Experiment 2) tasks. We expected to find joint flanker and Navon effects in same-gender pairs, while these effects should disappear in mixed-gender pairs, given that in this latter situation the (diverse) gender information should be sufficient to resolve the action selection conflict between self-own and other-own action turn. In addition, in the Experiment 1, we expected a larger joint flanker effect in female-female pairs than that in male-male pairs, because of females are more prone to process task-irrelevant information than males in a flanker task (Stoet, 2010, 2017). In a similar way, in the Experiment 2, we also expected a larger global advantage in male-male pairs than female-female pairs, whereas the opposite was expected for local processing, because of gender differences in global and local processing (Roalf et al., 2006; Pletzer, 2014).

Atmaca et al. (2011) found a joint flanker effect in a go/no-go version of the Eriksen task. Specifically, the joint flanker effect revealed that participants were slower in detecting their own targets surrounded by flankers which were potential targets for their co-actors, compared to stimuli with flankers being part of identical, compatible, and neutral trials. This joint effect was found with a non-human co-actor (a Japanese waving cat), supporting the notion that the joint condition increased the impact of that rule on performance probably because the actor drew attention to it (Dolk et al., 2014b). A person or an inanimate object represented an attention-grabbing event which required participants to discriminate between self-own and other events.

Adopting a procedure used in previous studies (van der Weiden et al., 2016), in this Experiment, in which a joint Eriksen flanker task was used (Atmaca et al., 2011), we tested how the gender of actor and co-actor influenced the joint flanker effect (JFE). Specifically, we expected a JFE in same gender (actor-co-actor gender: female-female and male-male) compared to mixed gender (actor-co-actor gender: female-male and male-female). This finding was expected because in female-female or male-male pairs, the (same) gender of a co-actor increased the perceived similarity to the actor (such as in-group membership; Müller et al., 2011), and therefore representations should become more similar and more difficult to distinguish in the turn-taking response setting. Considering that females are more prone to interference than males in a flanker task (e.g., Stoet, 2010, 2017), it could be possible to find a larger joint flanker effect in female-female pairs than in other types of pairs. To assess this gender difference in selective attention, a sample composed of males and females also undertook a standard two-choice flanker task in which each participant performed lateralized key presses in response to the four target stimuli. This condition also allowed us to ensure that the materials used in the joint/solo conditions yielded a standard flanker effect (following the procedure of Atmaca et al., 2011) and to compare the standard flanker effect with joint and solo flanker effects for both genders.

Böckler et al. (2012); see also Böckler and Sebanz (2012); Fabbri et al. (2017, 2018a) required two participants, sitting next to each other, to perform a two-choice task on the identity of Navon letters (i.e., S and F for an actor and H and O for the co-actor). The letters assigned to the two participants were never intermixed and participants performed a go/no-go task. The Navon letters could either be congruent (linked to the same response: a large S composed of small Ss) or incongruent (linked to different responses: a large S composed by small Fs). In different experimental blocks, the authors required participants to focus either on the global or local features of letters. Crucially, the participants’ task required them to adopt the same focus of attention (e.g., both participants attending to global stimulus features) or a different focus of attention (one attending to the global features and the other attending to local features). The main finding was a slowing of RTs when participants attended to different stimulus features, indicating that actors hold a representation not only of their own but also of the co-actor’s attentional focus (i.e., JNE). This increase in RTs for different foci of attention was found for both congruent and incongruent stimuli as well as when participants attended to global or local stimulus aspects (Böckler and Sebanz, 2012; Böckler et al., 2012), supporting the selection-conflict hypothesis (i.e., the representation of the other’s different task generally increases the difficulty of selecting and maintaining one’s own focus of attention). Although Fabbri et al. (2017, 2018a) confirmed the JNE in different populations and with specific experimental protocol, their results more supported the biased-focus hypothesis (i.e., co-actors are biased toward the focus of the other, shifting, for example, their own local focus toward the other’s global focus). As noted by Böckler et al. (2012), neither of these hypotheses necessarily excludes the other, because they suggested that participants experience a conflict as to which focus to select and shift toward the focus of the other with a slowing-down of responses when attentional foci differ and an increased difference in RTs between congruent and incongruent stimuli.

The aim of this Experiment 2 was to find a larger JNE for same-gender pairs and no (or even reversed) JNE for mixed-gender pairs. Indeed, in the joint condition, a response discrimination problem existed when a different instruction was provided because the decision as to which response to make needed to await the resolution of the slowest completion (among a number of different competing items in event representations) and Navon letters exerted their effect on response competition, with an increase in RTs for incongruent stimuli, suggesting a greater response discrimination. Thus, the gender information provided by the co-actor should induce faster responses in mixed-gender pairs when participants attend to different foci because if the co-actor is of a different gender this should resolve the conflict involved in selecting the adequate focus. Indeed, when a different task instruction (to attend to global features for one and to attend to local features for the other) was provided, it was more probable that the information of (different) gender of participants was used to discriminate between self-own and other events than when both actors attended to same foci. Given that it has been reported a male’s superiority for global processing and a female’s advantage for local processing (Roalf et al., 2006; Pletzer, 2014), a larger JNE for same-gender pairs than mixed-gender pairs should represent a proof of how gender information played a role in social cognition.

The aim of the present research was to assess how gender composition (same-gender vs. mixed-gender) of pairs influences JFE (Experiment 1) and JNE (Experiment 2), using two previously used joint action tasks (Atmaca et al., 2011; Böckler et al., 2012). The results clearly demonstrate that the gender of both actors influenced the joint action effects, given that JFE and JNE appeared in same-gender pairs while they disappeared (or were reversed) in mixed-gender pairs. The presence of another attention-grabbing event induced the tendency to discriminate its cognitive representation from the representation of the participant’s own action. A different gender between participants in a joint task could be considered a distinctive feature to resolve the response discrimination problem, that is, to discriminate between self-generated and other-generated actions. In line with previous results regarding the joint Simon effect (Mussi et al., 2015; van der Weiden et al., 2016), gender may instigate in-group/out-group categorization processes (Tajfel and Turner, 1979; Stangor et al., 1992; Powlishta, 1995; Ito and Urland, 2003; Müller et al., 2011; McClung et al., 2013). Indeed, gender is spontaneously used to categories social partners as in-group or out-group as compared to themselves. This information is used when participants represent their own action and the actions of another person, or, in other words, it is used to discriminate between one’s own turn and the other’s turn in joint tasks (Dolk et al., 2013). This explanation was further confirmed by two additional facts. First, the results of our first experiment resembled those reported by Dolk et al. (2014b) using a non-human co-actor (a Japanese waving cat), thus supporting this data interpretation. Second, the RT pattern of Experiment 2 resembled the RT patterns displayed by Böckler et al. (2012) in Figure 2, 3 of their study (pages 1,407 and 1,409). This similarity could, again, be discussed considering the role of gender composition in interacting pairs as a distinctive feature dimension to resolve the response discrimination problem. Future studies should address in depth the role of gender in modulating other joint action effects.

Even though it was not a direct goal of the present study, in both experiments we found some results related to gender differences in selective attention, measured by flanker and Navon tasks. On one hand, we confirmed that the difficulty reported by women in inhibition function using a go/no-go version of the Eriksen flanker task (Bayliss et al., 2005; Stoet, 2010, 2017), probably reflects gender differences in the general conflict monitoring process (Botvinick et al., 2001). This finding could also be discussed in terms of the sensibility of women in processing the social context in joint paradigm (Eagly and Wood, 1999; Witt and Wood, 2010). On the other hand, we found that males were faster at responding to stimuli than females, suggesting general differences in spatial and verbal abilities (Roalf et al., 2006; Halpern, 2012; Pletzer, 2014), most probably due to the visuospatial nature of the task (Lee et al., 2012), even if we did not confirm the preference of men for global processing (Roalf et al., 2006; Pletzer, 2014). Although the gender difference in the joint flanker task could limit the influence of gender composition of pairs in the joint selective attention, this possibility was excluded in the joint Navon task, which appeared to be more reliable to capture the role of gender composition of pairs in social contexts. Future studies should address gender differences in selective attention using standard and joint versions of flanker (Eriksen and Eriksen, 1974) and Navon (Navon, 1977, 1981, 2003) tasks to deeply understand these effects.

Although our study, through two experiments, had the merit to shed some light on joint action, the present research is not without limitations. Indeed, it has been found that the joint action effect is high when the two co-acting participants are engaged in a positive (Hommel et al., 2009), a cooperative relationship (Ruys and Aarts, 2010; Iani et al., 2011), and/or in interpersonal relationship (Mussi et al., 2015; van der Weiden et al., 2016). These types of information were not controlled for in the present study, despite of large sample in both experiments. At the same time, a cognitive state which induces information integration, such as good mood, should counteract discrimination between actors and co-actors, which in turn should increase the JFE and JNE (e.g., Colzato et al., 2013). Future studies should address these possibilities, using the social paradigms of the present study. Another limit regards the possibility that our participants in the same- and mixed-gender pairs used alternative strategies, such as specific stimulus-response rule or association, in order to perform correctly the task, limiting the impact of the processing of gender similarity or difference as discrimination rule for self-own and other turn to respond (Dolk et al., 2011). Additional studies investigating the social nature of the joint Flanker and Navon effects when two participants interact in the same task are needed.

To sum up, the present findings suggest that it is important to consider the gender composition of interacting pairs when the underlying mechanisms of, and implications for, social interaction are studied, considering the automatic in-group/out-group categorization processes provided by gender. The referential coding and co-representation account seem to be both comprehensive and valid approaches to explain the social nature of joint action paradigm and attentional joint effects. Indeed, our data could be discussed by co-representation account given that this account could predict that same gender (i.e., in-group member) is more likely to be co-represented than other gender co-actor (i.e., an out-group member; Sebanz et al., 2003, 2006; Sebanz and Knoblich, 2009; Atmaca et al., 2011; Böckler et al., 2012). At the same time, our data could be discussed by the referential coding account because it is possible to speculate that women and men represent the different (from themselves) gender of their co-actor and use this information for the representation of self-generated events (Dolk et al., 2013, 2014a,b; Fabbri et al., 2017, 2018a). Thus, the JFE and JNE might be taken as indicators of the similarity between self- and other-generated events, and measures of the degree of self-other integration, particularly in social contexts, with emphasis on more basic features of participants, such as their gender. Future studies should address in deep way which account in a better way explains the joint action effects. Finally, the go/no-go joint paradigms are a valuable educational or rehabilitative tool (Fabbri et al., 2018b).

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by Ethics Committee of the Department of Psychology, University of Campania Luigi Vanvitelli. The patients/participants provided their written informed consent to participate in this study.

MF, MM, and VN designed the study. MF and AB collected and analysed the data. MM and LT supervised the study. MF wrote the original draft. MM, LT, AB, and VN revised the draft. All authors contributed to the article and approved the submitted version.