Who Needs Emotions? The Brain Meets the Robot

eware the passionate robot 349
asked to make a guess, will point in the direction of the moving hand. They
can catch a ball even though they believe they cannot see it. This phenomenon
is referred to as blindsight (Weiskrantz, Warrington, Sanders, & Marshall,
1974; see Stoerig, 2001, for a review and Humphrey, 1970, for a study linking
frog and monkey). The midbrain visual system is thus quite powerful
but not connected to consciousness. Indeed, when a normal person catches
a ball, he or she is usually aware of seeing the ball and of reaching out to
catch it but certainly not of the processes which translate retinal stimulation
into muscle contraction, so most neural net activity is clearly unconscious.
The lesson is that even schemas that we think of as normally under
conscious control can in fact proceed without our being conscious of their
activity.
Recent research has extended the what and where dichotomy to a variety
of cortical systems. Studies of the visual system of monkeys led Ungerleider
and Mishkin (1982) to distinguish inferotemporal mechanisms for object recognition
(what) from parietal mechanisms for localizing objects (where). Goodale,
Milner, Jakobson, and Carey (1991) studied a human patient (D. F.) who had
developed a profound visual form of agnosia following a bilateral lesion of the
occipito-temporal cortex. The pathways from the occipital lobe toward the
parietal lobe appeared to be intact. When the patient was asked to indicate
the width of any one of a set of blocks either verbally or by means of her index
finger and thumb, her finger separation bore no relationship to the dimensions
of the object and showed considerable trial-to-trial variability. Yet, when
she was asked simply to reach out and pick up the block, the peak aperture
between her index finger and thumb (prior to contact with the object) changed
systematically with the width of the object, as in normal controls. A similar
dissociation was seen in her responses to the orientation of stimuli. In other
words, D. F. could preshape her hand accurately, even though she appeared
to have no conscious appreciation (either verbal or by pantomime) of the visual
parameters that guided the preshape. With Goodale and Milner (1992),
then, we may rename the where pathway as the how pathway, stressing that it
extracts a variety of affordances relevant to action (recall that affordances are
parameters for motor interactions extracted from sensory cues), not just object
location.
The Many Systems of Vision
This brief tour of the neural mechanisms of vertebrate vision, and a great
body of related modeling and empirical data, supports the enunciation of a
general property of vertebrate neural control: a multiplicity of different representations
must be linked into an integrated whole. However, this may be