1. Measuring bias in movement perception Our measure of visual perception (that could be adapted by movement practice) is the bias to see ambiguous apparent movement toward the observer or away from the observer. The staircase procedure used to measure the bias was developed by Lewis & McBeath (2004). Participants view on a computer monitor a screen tiled with stimuli that appear to recede into the distance (Figure 2). Figure 2. The tiling for one stimulus, the bean hand A second screen frame is presented one second later with shape tiles slightly shifted, which induces an illusion of motion that can be in either depth direction. A shift of 50% of the inter-tile distance is completely ambiguous, whereas a shift of 20% in either direction is perceived as movement in the smaller direction of shift. We start with a shift of 20% and then small increments in shift are added until the observer perceives movement in the opposite direction (a turn point). The increment is then reduced and the turn point measured in the opposite direction. Two sets of eight turn points are collected, and the averages of the last seven (in each set) are used as the measure of the threshold, or bias, to perceive movement in one direction or another. A behavioral method for studying mirror neurons: Repetitive action affects visual perception Arthur M. Glenberg 1,2, Gabriel Lopez-Mobilia 1, Michael McBeath 1, Michael Toma 1, Marc Sato 3, and Luigi Cattaneo 4 1 Arizona State University, 2 University of Wisconsin - Madison, 3 University of Grenoble, 4 University of Trento Abstract Mirror neurons may underlie the ability to make sensorimotor predictions when observing action, and thus contribute to “reading” intentions of other animals and facilitating social interaction. Neurophysiological and brain imaging studies have shown that observation of both biological and non- biological movements activates a fronto-parietal network of motor regions which forms the core of the human mirror-neuron system (MNS). However, many past findings are intrinsically correlational. We developed a behavioral method to study mirror neurons, based on use-induced plasticity. Participants engage in a repetitive motor task of moving beans from one location to another, thereby adapting the neural systems used in control of the action. Participants then engage in a second task, which measures if performance is affected by the motor adaptation. In the current study, the second task measures perceptual bias of ambiguous apparent motion in one direction or another. We found that the direction of bean movement (toward or away from the participant) systematically increases the bias to experience ambiguous movement in the opposite direction (consistent with habituation). The results corroborate previous findings in which the second tasks were language-based The findings support the claim that a MNS is being tapped, and confirm functionality of our method for studying the causal contribution of MNS to cognitive processes. Why not fMRI? 1.Because the fMRI voxel is sensitive to activity from many neurons, simply showing that an area is active both during action and perception does not guarantee that the same neurons are responding to both action and perception (e.g., Dinstein et al, 2007). 2.In most fMRI experiments, the signal only indicates a correlation, not a causal or functional relation. 3.fMRI is difficult to use with children. 4.It’s expensive. Use-induced plasticity Repetitive practice of a movement can produce a temporary re-organization of the brain. For example, Classen et al. (1998) used a TMS pulse over motor cortex controlling the thumb and elicited a movement in a particular direction. Then participants practiced moving the thumb in a different direction for about 20 minutes. Finally, TMS over the same area of motor cortex now tended to elicit movement in the practiced direction. Use-induced plasticity and mirror neurons: The logic Mirror neurons play a role in both producing action and perceiving action. Thus, if practice adapts part of a mirror neuron system, then the effects of that practice should be revealed in a perceptual task that uses the same mirror neuron system. In our experiments, we rule out non-specific effects of practice by adapting the motor system using two opposing practice directions. Showing different effects of the direction of practice on visual perception rules out non-specific (e.g., fatigue) effects. The bi-directional action task Participants move beans, one at a time, from a wide-mouth container to a narrow-mouth container an arms-length away (Figure 1.) Half of the participants move the beans in a direction Away from the self, and half move the beans in a direction Toward the self. Note that very similar muscles are used in the two conditions. Thus the actions are defined in terms of target location and specifics of the movement (e.g., a power grip is used in the Away movement but not the return toward the body, and vice versa in the Toward movement). Figure 1. Bean containers illustrating the Away condition. Experiment 1 Procedure 1.Bias in motion perception was measured for the three stimulus shapes: a hand holding a bean, an open hand with palm up, and a plain diamond (see Figure 3a). The three stimuli were used to determine if we are tapping “strictly-congruent” (only the hand stimulus should show evidence of change in bias) or “broadly-congruent” mirror neurons (all directional stimuli may show a change in bias). The type of stimulus was manipulated within-subjects, and the tests of bias for each of the three stimuli were interleaved so that a participant might see a diamond shift, a hand holding a bean shift, and then an open hand shift. 2.Next, 48 participants moved 600 beans in one direction or another. The movement direction was manipulated between-subjects. 3.Last, bias in motion perception was measured again for the three stimuli. Results Figure 3 (right) shows the change in measured bias as a function of bean movement direction on the second, post-movement, measure of bias. The interaction of bean movement direction and pre-movement or post- movement measure of bias was significant, F(1, 46) = 5.16, p=.03. Figure 3. Stimuli (left) & Results (right) for Exp. 1. Conclusions 1.Direction of action (bean movement) systematically affects visual perception of ambiguous apparent motion in aligned directions. Findings support the claim that we tapped into a mirror neuron system. 2.The mirror neuron response is “broadly-congruent” with the same effect found for all three stimuli (all exhibited a similar habituation bias). Experiment 2 We made several changes in the methodology to rule out alternative explanations. Most importantly, participants were blindfolded during the bean movement task. Thus, any affect of movement on the bias measure can be more securely attributed to adapting an action system rather than visual stimulation. Second, to eliminate any sensitization to toward and away movement due to the initial bias measure, the 24 participants first moved 300 beans in one direction, and then we measured bias. Participants then moved an additional 300 beans in the same direction, and the bias was measured again. The data for the first, post-movement bias measure are in Figure 4. The effect of bean movement direction was significant, F(1,22) = 5.89, p =.02. The effects were not significant when measured after the second set of bean movements. Figure 4. Experiment 2: Results for the first, post-movement bias measure. Error bars are one standard error. A = bean movement away from the body; T = bean movement toward the body. Plasticity and language comprehension Glenberg, Sato, and Cattaneo (2008) used the same bean task as in Experiment 1. Participants then read and responded to sentences describing action Toward the participant (e.g., “Art gives the pen to you”) or Away from the participant (e. g., “You give the pen to Art”). The response was whether the sentence was sensible or nonsense (e.g., “You give Art to the pen”). Participants indicated sensible by depressing a key with the right index finger, and they indicated nonsense by depressing a key with the left index finger. Neither response required arm movements. The findings indicated an interaction such that the time to respond sensible to Toward sentences was faster when the beans were moved in the away direction and the time respond sensible to the Away sentences was faster when the beans were moved in the toward direction. Interestingly, the same effects were found for sentences describing the transfer of concrete objects and sentences describing the transfer of abstractions (e.g., “Anna delegates the responsibilities to you”). Apparently, neural systems used in action control were also used for comprehending sentences describing actions of the same general sort. Plasticity and speech perception Sato, Brisebois, Grabski, Basirat, Menard, Glenberg, & Cattaneo (2008) had participants purse their lips 150 times to induce changes in corticomotor control of the orofacial musculature. Subsequently, they performed a speeded two-choice identification task of acoustically presented /pa/ and /ta/ CV syllables either embedded in acoustic noise or not. A control task was identical but without the lip pursing. They observed a decrease in “pa” responses in the control session and overall faster RTs in the motor session. References Casile A., Giese, M.A. (2006) Nonvisual motor training influences biological motion perception. Current Biology, 16, 69–74. Classen, J., Liepert, J., Wise, S.P., Hallett, M., Cohen, L.G. (1998). Rapid plasticity of human cortical movement representation induced by practice. J. Neurophysiol. 79, 1117-1123. Dinstein, I., Thomas, C., Behrmann, M. and Heeger, D. (2008) A mirror up to nature. Current Biology, 18, 1, R13-18. Di Pellegrino G., Fadiga L., Fogassi L., Gallese V., Rizzolatti G. (1992). Understanding motor events: a neurophysiological study. Exp. Brain Res. 91, 176–80. Gallese V., Fadiga L., Fogassi L., Rizzolatti G. (1996). Action recognition in the premotor cortex. Brain, 119, 593–609. Glenberg, A.M., Sato, M., Cattaneo, L. (2008). Use-induced motor plasticity affects the processing of abstract and concrete language. Current Biology, 18, R1-R2. Lewis C.F., McBeath M.K. (2004). Bias to experience approaching motion in a three-dimensional virtual environment. Perception, 33, 259-276. Rizzolatti, G., Craighero, L. (2004). The Mirror-Neuron System. Annual Review of Neuroscience, 27, 169-192. Rizzolatti G., Fadiga L., Fogassi L., Gallese V. (1996). Premotor cortex and the recognition of motor actions. Cogn. Brain Res. 3, 131-41. Sato, M., Brisebois, A., Grabski, K., Basirat, A, Ménard, L, Glenberg, A. M., & Cattaneo, L. (October, 2008). Paper presented at the Speech and Face to Face Communication Workshop, Grenoble, France. Author Note: This research was support in part by NSF grant BCS 0744105. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. Direct correspondence to Arthur Glenberg, glenberg@asu.edu Conclusions Our technique appears to have adapted a neural system tuned to multiple modalities including motor, visual, and language processes. Although more research is needed, so far these results are consistent with claims that a human mirror neuron system exists and that it contributes to action perception, speech perception, and language comprehension. Furthermore, this simple method provides researchers with a promising instrument to study the role of mirror neuron systems in these and other cognitive processes without the expense and inconvenience of fMRI. Ago, ergo Cogito Two-frame apparent motion tasks show promise as a hit with some observers!