The importance of a mirror neuron system (MNS) as a mecha-nism for understanding the actions of others has been estab-lished (e.g., Rizzolatti, Fadiga, Gallese,  &amp; Fogassi, 1996). Neurons in the primate premotor cortex fire both when a monkey performs an action (e.g., grasping) and when the monkey ob-serves someone else performing the same action. It has also been proposed that theMNS is the starting point for understanding the intentions and goal-directed behavior of others (Fogassi et al., 2005; Gallese &amp; Goldman, 1998). Consistent with this view, Falck-Ytter, Gredebäck, and von Hofsten (2006) argued that the MNS is implicated in proactive goal-directed (predictive) eye movements. In a series of eye-tracking studies, participants observed a toy object moving along a trajectory toward a con-tainer. Adults and 1-year-old infants looked ahead of the toy and toward the goal container only when a hand was observe

Coventry, Kenny

Eshuis, Rik

Vulchanova, Mila

English

Coventry, Kenny R.

University of East Anglia digital repository

Predictive eye movements are driven by goals, not by the mirror neuron system

Northumbria University Research Portal

Predictive Eye Movements Are Driven byGoals, Not by the Mirror Neuron SystemRik Eshuis, 1 Kenny R. Coventry, 2, 3 and Mila Vulchanova11. Norwegian University of Science and Technology,2. Northumbria University, and3. Hanse Institute for Advanced Studies, Delmenhorst, GermanyThe importance of a mirror neuron system (MNS) as a mechanism for understanding theactions of others has been established (e.g., Rizzolatti, Fadiga, Gallese, & Fogassi,1996). Neurons in the primate premotor cortex fire both when a monkey performs anaction (e.g., grasping) and when the monkey observes someone else performing thesame action. It has also been proposed that the MNS is the starting point forunderstanding the intentions and goal-directed behavior of others (Fogassi et al., 2005;Gallese & Goldman, 1998). Consistent with this view, Falck-Ytter, Gredeba¨ck, and vonofsten (2006) argued that the MNS is implicated in proactive goal-directed (predictive)eye movements. In a series of eye-tracking studies, participants observed a toy objectmoving along a trajectory toward a container. Adults and 1-year-old infants lookedahead of the toy and toward the goal container only when a hand was observed movingthe toy (the human-agent condition). Proactive goaldirected eye movements were notfound in two further conditions: a self-propelled condition, in which a toy withrudimentary facial features moved along the trajectory by itself, or a mechanical motioncondition, in which a ball with no distinctive features moved along the trajectory. Falck-Ytter et al. interpreted these data as evidence that the MNS is necessary for proactivegoal-directed eye movements. Moreover, the absence of proactive goal-directed eyemovements in 6-month-old infants (who are too young to perform the actionsthemselves) is taken as further support for the MNS account.These claims are premature. The conditions run by Falck- Ytter et al. (2006) do notdiscriminate between predicted human motion tied to intention and predicted agentgoals tied to intention consistent with the mirror neuron hypothesis, movement of thehand may necessarily involve the simulation of motion via the MNS, and proactive goal-directed eye movements may therefore only occur when a hand is shown to move theobject. Alternatively, a hand moving an object involves the intention of an agent to placethe object in the goal container, and the expectation that the agent intends for theobject to end up in a goal location may cause the proactive eye movements (consistentwith teleological stance theory; Gergely & Csibra, 2003). To arbitrate between theseaccounts, it is necessary to run a human-agent condition without human movement.Therefore, we set out to test the claims of Falck-Ytter, et al. (2006), but with theaddition of a new critical condition missing in the original study. We ran three movementconditions: the human-agent condition, in which a human agent was shown moving atoy frog toward a goal container (i.e., [1human agent, 1human motion]); the self-propelled condition, in which no human agent was shown moving the frog (i.e., [_humanagent, _human motion]); and the new condition, in which a human agent was shownwith hand behind the starting point of the frog, flicking it so as to propel it along atrajectory (as in the game ‘‘Tiddlywinks’’; i.e., [1human agent, _human motion]; seeFig. 1a). In the latter condition, the human-agent intention is matched to that of thehuman-agent condition, but human motion is not shown along the trajectory. This allowsa clean test of the MNS versus goal-intention explanations for the proactive eye-movement data.abFig. 1. Example of the video used in the new (Tiddlywinks) condition and experimentalresults. In the illustration (a), the trajectories traversed by the frogs have been drawn in,but they were not visible during the experiment. The graph (b) shows mean gaze-arrivaltime relative to the frog’s arrival time (time 0; positive values indicate that gaze arrivedbefore the frog) for the human-agent, new (Tiddlywinks), and self-propelled conditionswith and without end effects. Error bars indicate _1 SEM.We also ran each condition in two ways. In the original humanagent condition run byFalck-Ytter et al. (2006), when the toy object reached the bucket, a sound was playedand a smiley face on the bucket was animated. This could serve to heighten thedesirability of the goal state, encouraging proactive eye movements in a mannerconsistent with teleological stance theory. Therefore, we ran each of the three conditionswith and without end effects. For the conditions with end effects, when the toy enteredthe bucket, water ripples were shown and the sound of a frog croaking was played. InMeanGaze-ArrivalTime(ms)[+End Effects][–End Effects]3002001000-100Human-Agent[+Human Agent,+Human Motion]Tiddlywinks[+Human Agent,-Human Motion]Self-Propelled[-Human Agent,-Human Motion]Conditionthe conditions without end effects, no animated ripples were seen or sounds were heardwhen the frog entered the bucket.The procedures and analyses mirrored those of the original study as closely as possible.Seventy-two adult participants were randomly allocated to one of six conditions: humanagent with (i.e., [1human agent, 1human motion, 1end effects]) or without (i.e.,[1human agent, 1human motion, _end effects]) end effects, self-propelled with (i.e.,[_human agent, _human motion, 1end effects]) or without (i.e., [_human agent,_human motion, _end effects]) end effects, and the new condition with (i.e., [1humanagent, _human motion, 1end effects]) or without (i.e., [1human agent, _human motion,_end effects]) end effects. Participants sat in front of the monitor of a Tobii 1750 eyetracker; after the tracker was calibrated, participants were instructed simply to watchthe video that followed. The video comprised 27 trials (the same number used by Falck-Ytter et al., 2006).A 3 (movement) _ 2 (end effects) analysis of variance examining the average gaze-arrival time relative to the arrival time of the frog (Fig. 1b) produced only a significantmain effect of end effects on gaze-arrival time, F(1, 66) 5 7.153, prep 5 .97, Zp 2 ¼:098). Gaze-arrival time at goal was earlier for conditions with end effects (M 5 122 ms)than those without end effects (M 5 33 ms).For each condition, we also compared gaze arrival times to the arrival times of the frog.Significant proactive goal-directed eye movements occurred for the human-agentcondition with end effects (i.e., [1human agent, 1human motion, 1end effects]), t(11) 54.34, prep 5 .99, d 5 1.25, and the new (Tiddlywinks) condition with end effects (i.e.,[1human agent, _human motion, 1end effects]), t(11) 5 2.38, prep 5 .93, d 5 0.69, butnot for any of the other four conditions, all t(11)s _ 1.99, all preps _ .90, all ds _0.57. Most notably, predictive eye movements do not occur for the human-agentcondition without end effects (i.e., [1human agent, 1human motion, _end effects]),t(11) 5 0.35, prep 5 .59, d 5 0.10.These results allow us to tease apart the relative merits of the MNS explanation ofproactive goal-directed eye movements compared to an alternative account based onunderstanding of goals. Proactive eye movements occur as a function of the combinationof the intention of an agent to achieve a goal and the desirability of a goal state, and notas a consequence of whether a human agent is seen moving an object. Thus, our resultssupport teleological stance theory, as well as recent accounts claiming that the MNS is areflection of action understanding rather than the origins of it (Csibra, 2007).REFERENCESCsibra, G. (2007). Action mirroring and action understanding: An alternative account. In P. Haggard, Y.Rosetti, & M. Kawato (Eds.), Attention and performance: Vol. 22. Sensorimotor foundations of higher cognition(pp. 435–459). Oxford, England: Oxford University Press.Falck-Ytter, T., Gredeba¨ck, G., & von Hofsten, C. (2006). Infants predict other people’s action goals. NatureNeuroscience, 9, 878– 879.Fogassi, L., Ferrari, P.F., Gesierich, B., Rozzi, S., Chersi, F., & Rizzolatti, G. (2005). Parietal lobe: From actionorganization to intention understanding. Science, 308, 662–667.Gallese, V., & Goldman, A. (1998). Mirror neurons and the simulation theory of mind-reading. Trends inCognitive Sciences, 3, 493–501.Gergely, G., & Csibra, G. (2003). Teleological reasoning in infancy: The naive theory of rational action. Trendsin Cognitive Sciences, 7, 287–292.Rizzolatti, G., Fadiga, L., Gallese, V., & Fogassi, L. (1996). Premotor cortex and the recognition of motoractions. Cognitive Brain Research, 3, 131–141.

Predictive eye movements are driven by goals, not by the mirror neuron system

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