Understanding intentions from actions: Direct perception, inference, and the roles of mirror and mentalizing systems
Introduction
The overarching question of this special issue is how humans acquire information about other people’s mental states. In this review I focus on one particular type of mental state: that of having an intention, i.e. a motive to perform an action in order to produce an effect; and I discuss the processes by which humans can acquire information about others’ intentions, i.e. identify why an action was performed, from the observation of their actions.
The link between action observation and intention understanding has garnered particular interest over the last two decades due to the discovery of ‘mirror’ neurons in the macaque (Di Pellegrino, Fadiga, Fogassi, Gallese, & Rizzolatti, 1992) and subsequently the human (Mukamel, Ekstrom, Kaplan, Iacoboni, & Fried, 2010) brain. These neurons have been found primarily in motor areas of the macaque brain (although the human data suggest that they may be considerably more widespread) including premotor, primary motor, and parietal cortex (Di Pellegrino et al., 1992, Fogassi et al., 2005, Kraskov et al., 2009). The defining characteristic of a mirror neuron is that it fires both when performing an action, and when passively perceiving the same, or a related, action performed either by a conspecific or an experimenter (the perceived action can be presented in either the auditory or visual modality: Cook, 2012, Kohler et al., 2002; but for conciseness, this review will focus on vision as the modality in which the majority of research has been performed). Thus, mirror neurons appear to match the observation of another’s action with the motor program that would be required for the observer to produce that action themselves. This characteristic has led to speculation that mirror neurons underlie the ability to understand others’ intentions by observing their actions. For example, it has been claimed that mirror neurons allow us to “… understand the actions of others by means of our own ‘motor knowledge’: this knowledge enables us immediately to attribute an intentional meaning to the movements of others” (Rizzolatti & Sinigaglia, 2007, p. 205). The term ‘intention’ has been used in the mirror neuron literature to refer both to the immediate outcome of an action, and to the higher-level motivation that produced the action. This review focuses on the latter definition because it is more clearly related to the mental state of having an intention. In addition, this definition has excited the most interest precisely because it suggests that mirror neurons provide a mechanism for identifying an actor’s underlying intention. However, the evidence either for or against this claim is relatively sparse (Cook, Bird, Catmur, Press, & Heyes, 2014). It is therefore important to establish: whether we can indeed acquire information about others’ intentions from observation of their actions; whether this process is performed by mirror neurons, and if not, what are the alternative candidate processes for acquiring information about intentions; and which of these processes is best supported by the existing data.
In Section 2 I review evidence for whether it is possible to acquire information about intentions from the observation of others’ actions: is information about intentions indeed present in performed actions, and if so, do observers make use of this information? The third section asks how observers can acquire this information, and sets out the competing possibilities, with reference to the distinction between direct perception and inferential processes described by Michael and de Bruin (2015). I discuss what would constitute evidence for one of these processes over another, and review the current research in this area. I conclude that there is insufficient evidence to support the involvement of mirror neurons in understanding others’ intentions, and that the existing data are better explained by the involvement of inferential processes.
Section snippets
Can we acquire intentions from actions?
In order to acquire information about an actor’s intentions from the observation of their actions, two conditions need to be fulfilled (see Ansuini, Cavallo, Bertone, & Becchio, 2014, for a more detailed discussion of this literature). First, there need to exist reliable perceptual differences between actions performed with different intentions; and second, observers must be able to detect and utilise these differences to make judgements about the actor’s intentions.
How do we acquire intentions from actions?
In cases where observers are able to acquire intention information from action kinematics, how does this process occur? Michael and de Bruin (2015) set out two competing possibilities: intention information may be acquired from action kinematics via ‘direct’ perception, or via inferential processes. Direct perception accounts suggest that perception of others (in this case of their action kinematics) results in ‘direct’ awareness of their mental states (in this case of their intentions). The
Summary and conclusions
Actions performed with different intentions produce different kinematic profiles, meaning that it is in principle possible to use perceptual information as a starting point for decoding another’s intentions; and in most cases observers seem to be able to achieve this, raising the question of whether they do so using direct perceptual or inferential processes. I proposed that four conditions should be fulfilled in order to conclude that others’ intentions can be understood using direct
Funding source
The preparation of this article was supported by the Economic and Social Research Council (ES/K00140X/1 to C.C.). The funder had no involvement in the writing of the article or in the decision to submit the article for publication.
Acknowledgments
I would like to thank Punit Shah, Geoff Bird, and John Michael for comments on an earlier version of this manuscript.
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