A central problem agents face is determining which events they have caused, and which they have not. When a room goes dark, it could be because one flipped the light switch, but it could also be because someone else in the room clapped, or because somewhere else a butterfly flapped its wings (straight into a power line, perhaps). It has been proposed that to solve this problem of authorship, the mind must weigh a variety of authorship indicators and arrive at an appropriate causal inference (Wegner & Sparrow, 2004
; Wegner, 2002
). An important authorship indicator is the temporal contiguity between one’s action and a subsequent event (Shanks, Pearson, & Dickinson, 1989
), which is a special case of the more general principle that causality is perceived when one event is followed closely by another (Hume, 1739/1888
; Michotte, 1963
). When one’s flip of the switch is followed immediately by the room’s going dark, one can be more certain of having authored the darkness.
It is hardly controversial to say that perceived contiguity enhances perceived authorship, but there is now reason to believe that its less familiar converse is also true: perceived authorship enhances perceived contiguity. Evidence for this hypothesis comes from research on intentional binding
, a perceptual illusion in which actions and their effects seem to occur especially close in time (Haggard, Clark, & Kalogeras, 2002
). In an experiment based on Libet’s time judgment paradigm (Libet, Gleason, Wright, & Pearl, 1983
), participants were asked to press a key when they felt the urge to do so, and an auditory tone was played shortly after they acted. Participants were supposed to judge, in separate blocks, the time of either their keypress or the subsequent tone, by referring to a hand that rotated around a clock face. The main results showed that participants’ judgments of when their action occurred were shifted forward in time (toward the tone), whereas judgments of when the tone occurred were shifted backward (toward the action), relative to judgments made in baseline blocks in which action and tone occurred alone. Critically, these perceptual shifts did not occur when transcranial magnetic stimulation (TMS) induced the participant to make an involuntary keypress, suggesting that voluntary action is needed. Haggard et al. (2002)
concluded that the perceived shifts in time result from the mind’s attempt to construct a coherent conscious experience of our own agency, by binding our intentional actions to their effects.
Several experiments have provided additional support for the hypothesis that binding arises when personal authorship for an event is inferred. Some have focused on the “personal” aspect of this hypothesis, showing that binding occurs for one’s own, voluntary actions, but not for involuntary movements (Engbert, Wohlschläger, & Haggard, 2008
; Haggard & Clark, 2003
) or the actions of others (Engbert et al., 2008
; Engbert, Wohlschläger, Thomas, & Haggard, 2007
). Others have focused on the “authorship” aspect, showing that the presence of authorship indicators (Moore, Wegner, & Haggard, in press
) or the provision of control over events (Cravo, Claessens, & Baldo, 2009
; Moore, Lagnado, Deal, & Haggard, 2008
) enhances binding (see also Stetson, Cui, Montague, & Eagleman, 2006
Still, many questions remain about the link between authorship and binding. Previous investigations into binding have not included a corroborating self-report measure of authorship, and without such a measure it is not possible to know for sure whether binding occurs alongside the experience of authorship, increasing and decreasing in response to the same indicators. The lack of a self-report measure has also precluded research into dissociations between what might be considered relatively implicit (binding) and explicit (self-report) measures of authorship (see Synofzik, Vosgerau, & Newen, 2008
). One possible dissociation is that people readily report authorship for events that occur several seconds after their actions (Shanks et al., 1989
) – and indeed can claim responsibility for an event taking place years after their action – yet binding has been found only for action-event delays lasting a fraction of a second (Haggard et al., 2002
; Stetson et al., 2006
). Another open question is whether binding occurs for the kinds of actions performed, and events encountered, in everyday life, such as kicking a ball and watching it fly away. Nearly all previous investigations have based their methods on the Libet paradigm, asking participants to press a key and judge either the time of their keypress or a subsequent tone, which raises concerns about the external validity of the phenomenon.
We conducted two experiments to address validity concerns and explore the relationship between binding and self-reported authorship. Both experiments employed a novel “push/pull” paradigm that was designed to be relatively naturalistic. Rather than press a key, participants pushed or pulled on a joystick in response to images of everyday objects; rather than hear a tone, participants saw these objects move away or come closer. Unlike a keypress, the acts of pushing and pulling are imbued with bodily significance, implying both an orientation toward whatever is acted upon and an expected outcome of that action. Specifically, pushing corresponds to an avoidance orientation and is undertaken with the expectation that an object will go away, whereas pulling corresponds to an approach orientation and is undertaken with the expectation that an object will come closer (Cacioppo, Priester, & Berntson, 1993
; Chen & Bargh, 1999
). In both experiments, we manipulated whether an event was consistent with the participant’s prior action (i.e., whether the object moved in the same direction as the action), both because action-event consistency is an important authorship indicator (Wegner & Sparrow, 2004
), and because previous research had not directly examined its effect on binding. In addition to measuring binding, we asked participants to report their feelings of authorship. Our main hypothesis was that action-event consistency would enhance both self-reported authorship and intentional binding – but we were also interested in any differences the two measures might reveal.