Mind, Body, World- Foundations of Cognitive Science, 2013a

Double dissociation evidence from cognitive neuroscience has been used to
support the duplex theory. The study of one brain-injured subject (Goodale et al.,
1991) revealed normal basic sensation. However, the patient could not describe
the orientation or shape of any visual contour, no matter what visual information
was used to create it. While this information could not be consciously reported, it
was available, and could control actions. The patient could grasp objects, or insert
objects through oriented slots, in a fashion indistinguishable from control subjects,
even to the fine details that are observed when such actions are initiated and then
carried out. This pattern of evidence suggests that the patient’s ventral stream was
damaged, but that the dorsal stream was unaffected and controlled visual actions.
“At some level in normal brains the visual processing underlying ‘conscious’ perceptual
judgments must operate separately from that underlying the ‘automatic’
visuomotor guidance of skilled actions of the hand and limb” (p. 155).
Other kinds of brain injuries produce a very different pattern of abnormalities,
establishing the double dissociation that supports the duplex theory. For instance,
damage to the posterior parietal cortex—part of the dorsal stream—can cause optic
ataxia, in which visual information cannot be used to control actions towards objects
presented in the part of the visual field affected by the brain injury (Jakobson et al.,
1991). Optic ataxia, however, does not impair the ability to perceive the orientation
and shapes of visual contours.
Healthy subjects can also provide support for the duplex theory. For instance, in
one study subjects reached toward an object whose position changed during a saccadic
eye movement (Pelisson et al., 1986). As a result, subjects were not conscious
of the target’s change in location. Nevertheless, they compensated to the object’s
new position when they reached towards it. “No perceptual change occurred,
while the hand pointing response was shifted systematically, showing that different
mechanisms were involved in visual perception and in the control of the motor
response” (p. 309). This supports the existence of “horizontal” sense-act modules in
the human brain.
5.7 Mind in Action
Shakey was a 1960s robot that used a variety of sensors and motors to navigate
through a controlled indoor environment (Nilsson, 1984). It did so by uploading
its sensor readings to a central computer that stored, updated, and manipulated a
model of Shakey’s world. This representation was used to develop plans of action
to be put into effect, providing the important filling for Shakey’s classical sandwich.
Shakey impressed in its ability to navigate around obstacles and move objects
to desired locations. However, it also demonstrated some key limitations of the classical
sandwich. In particular, Shakey was extremely slow. Shakey typically required
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