Who Needs Emotions? The Brain Meets the Robot

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Specific methods, partly based on introspection but also relying on
changes of physiological variables, have been designed to experimentally
access these mental states characterized by absence or paucity of overt behavior.
One of the most extensively studied of these representational aspects
of action is mental motor imagery. Behavioral studies of motor imagery have
revealed that motor images retain the same temporal characteristics as the
corresponding real action when it comes to execution. For example, it takes
the same time to mentally “walk” to a prespecified target as it takes to actually
walk to the same place (Decety, Jeannerod, & Prablanc, 1989). Similarly,
temporal regularities which are observed in executed actions, such as
the classical speed–accuracy tradeoff, are retained in their covert counterparts
(Sirigu et al., 1996). Along the same line, other situations have been
described where the subject uses a motor imagery strategy in spite of the
fact that no conscious image is formed. Those are situations where the subject
is requested to make a perceptually based “motor” decision. Consider,
for example, the situation where a subject is simply requested to make an
estimate about the feasibility of an action, like determining the feasibility
of grasping an object placed at different orientations: the time to give the
response will be a function of the object’s orientation, suggesting that the
arm has to be mentally moved to an appropriate position before the response
can be given. Indeed, the time to make this estimate is closely similar
to the time it takes to actually reach and grasp an object placed at the same
orientation (Frak, Paulignan, & Jeannerod, 2001; see also Parsons, 1994).
One may speculate whether the same isochrony would also exist for performing
an action with a disembodied artifact (e.g., a car) and mentally
estimating its consequences. The question would be whether one can simulate
an action performed, not by a human body, but with a mechanical
device. A tentative answer will be given below.
This indication of a similar temporal structure for executed and nonexecuted
actions by a biological system is reinforced by a similarity at the
level of physiological indicators. Examining autonomic activity in subjects
imagining an action at different effort rates reveals changes in heart rate and
respiration frequency proportional to the imagined effort in the absence of
any metabolic need. These results (Decety, Jeannerod, Durozard, & Baverel,
1993, see review in Jeannerod, 1995) reveal the existence of a central patterning
of vegetative commands during covert actions, which would parallel
the preparation of muscular commands. Autonomic changes occurring
during motor imagery are closely related to those observed during central
preparation of an effortful action (Krogh & Lindhard, 1913). Those are
mechanisms that anticipate forthcoming metabolic needs, with the function
of shortening the intrinsic delay required for heart and respiration to adapt
to effort (e.g., Adams, Guz, Innes, & Murphy, 1987).