This chapter is based on Damen, T. G. E., Dijksterhuis, A., & van Baaren, R. B. (2014). On the other hand: Non-dominant hand use increases sense of agency. Social Psychological and
In two studies we investigated the influence of hand dominance on the sense of self- causation, or agency. Participants alternately used their dominant or non-dominant hand to cause the occurrence of an effect (a tone) in a task in which agency was made ambiguous. Participants were subsequently asked to indicate the degree to which they felt they had caused that tone to occur. Results showed that the sense of agency was increased when individuals used their non-dominant hand prior to the onset of the tone, compared to when they used their dominant hand. Furthermore, the degree of experienced agency was moderated by perceived effort. The difference in agency levels occurred independently of experimentally induced or naturally occurring differences in response latencies, and even occurred in the absence of (major) arm movement.
Our hands play a vital role in shaping our everyday experience. They reach out to inform our bodies about the world and to relay back into the world our physical response. The precise origins of handedness remain unknown (Vuoksimaa, Koskenvuo, Rose, & Kaprio, 2009), but ultrasound studies suggest that the formation of handedness already takes place prenatally (Hepper, Mccartney, & Shannon, 1998). Over time the dominant hand becomes both stronger and more precise than the non-dominant hand (Petersen, Petrick, Connor, & Conklin, 1989). While one can learn to do simple tasks with the non-dominant hand, the non-dominant hand will seldom reach or exceed the level of skill of the dominant hand (Annett, 2002; Peters, 1981). In general, whereas people experience relative ease when using their dominant hand, performing actions with their non-dominant hand often requires considerable effort, even when it concerns relatively simple tasks.
The sensations of effort that may accompany our actions have consequences for our conscious experience of those actions: They are able to contribute to the experience of performing an action or causing an effect, an experience also known as the sense of agency (Jeannerod, 1997; Pacherie, 2008). For example, research has shown that squeezing a handgrip (Preston & Wegner, 2007), or pulling stretch bands during action performance (Demanet, Muhle-Karbe, Lynn, Blotenberg, & Brass, 2013) can increase this sense of agency for concurrent actions and events.
Conversely, a degree of effortlessness in action is more characteristic of automaticity, and thus a low sense of agency, as the easiest actions require little control or conscious supervision (Bargh, 1994; Wegner & Sparrow, 2004). Actions that become more efficient over time, due to practice, can operate effortless and without conscious guidance (Bargh & Chartrand, 1999; Schooler, 2002). Effortlessness can thereby give the impression of events happening to a person instead of being authored by that person (Csikszentmihalyi, Abuhamdeh, & Nakamura, 2005). The question is whether the degree of effort or effortlessness that we experience in our everyday hand use can also influence these perceptions of agency. Does use of the non-dominant hand, because it is relied upon less often (Hollis & Watson, 1993) also influence the sense of agency, and in a different way than dominant hand use?
In two studies we investigated the sense of agency as a function of hand dominance. Participants alternated between using their dominant and non-dominant hand in a task in which agency was ambiguous. We expected that use of the non-dominant hand would be experienced as less automatic and more effortful, and would therefore lead to higher experienced agency compared to dominant hand use.
Thirty-two undergraduate students (29 females; 28 right-handed; Mage = 21.75) at the Radboud University Nijmegen participated in exchange for 4 Euro‘s or course credit.
Materials & Procedure
Participants performed a mouse-click agency task. Participants had to respond to targets by clicking on them with the mouse cursor, and clicks were followed by tones presented through a headset. Participants were told that the tones could be generated by their mouse- clicks, but could also be produced by the computer; participants had to indicate the degree to which they felt that they - not the computer - had caused the tone to occur. In fact, participants always produced the tones.
The mouse cursor was always positioned center screen at trial start. Targets were black squares (1 cm2) that were presented in the center of the monitor at trial start. As the mouse cursor was also positioned in the center of the monitor at the beginning of each trial, participants were only required to click to give their response; no arm movement was necessary. Clicks on the squares were followed by 1000 Hz tones for 500 ms. To increase agency ambiguity, the time interval between clicks and the subsequent tones was manipulated (100 ms vs. 400 ms vs. 700 ms evenly divided over trials). For sake of interpretation, we collapsed the temporal delay conditions over the other factors in the design1. While an increased delay between action performance and its subsequent outcome is well known to reduce the sense of agency (Sato & Yasuda, 2005), we thought it was also possible that a delay in action initiation could influence agency (e.g., Chambon & Haggard, 2012). We were interested in the possible effects of a delay in action initiation as our non- dominant hand may similarly be slower to act than our dominant hand. In the present study we therefore experimentally manipulated the moment participants were able to successfully click on the squares, which was after a presented timer reached 0 (timer duration: 4s vs. 3s vs. 2s). At the end of each trial, participants used the keyboard to enter a number between 1-100 to indicate the degree to which they felt that they had caused the tone to occur (1=
absolutely no self-causation; 100 = certainty of self-causation).
The task consisted of 144 trials divided over 8 blocks. At the start of each block, participants were instructed to use the left or right hand; block-order was counterbalanced between subjects.
1 Temporal delay between action and effect has been shown to influence the sense of agency (Sato & Yasuda, 2005). In the present study, we indeed found that shorter intervals led to higher agency ratings than longer intervals (Sato & Yasuda, 2005). Study 5.1: F(2, 62) = 63.36, p < .001. Study 5.2: F(2, 58) = 28.00, p < .001. There were no interactions between intervals and experimental conditions.