Who Needs Emotions? The Brain Meets the Robot

348 conclusions
at the much higher level of visual cortex? Different animals live in different
environments, have different behaviors, and have different capabilities for
motor behavior. As a result, the information that they need about their world
varies greatly. On this basis, we may hope to better understand the problem
of vision if we can come to see which aspects of visual system design converge
and which differences are correlated with the differing behavioral needs
of different species. The frog will snap at, or orient toward, an object moving
in prey-like fashion and will avoid a large moving object. It responds to
localized features of the environment—information from a large region of
its visual field only affects its action when determining a barrier it must avoid
when seeking prey or escaping an enemy, and this is mediated elsewhere in
the brain. Thus, preprocessing at the ganglion cell level in the frog is already
action-oriented. In the cat (and monkeys and humans), processing in the
primary visual cortex is “action-neutral,” providing efficient encoding of
natural stimuli and serving as a precursor to processes as diverse as face recognition
and manual dexterity. Specializations appropriate to certain crucial
tasks do occur but only further along the visual pathway.
The Where, What, and How of Vision
Until the late 1960s, the study of the visual system of mammals emphasized
the contributions of the visual cortex, with little attention paid to midbrain
mechanisms. An important move toward a more subtle understanding came
with the symposium contributed to by Ingle, Schneider, Trevarthen, and Held
(1967), who suggested that we should think of vision not in terms of a single
pathway running through the lateral geniculate nucleus to the visual cortex
(the geniculostriate pathway) but rather in terms of the interaction of two
pathways: the geniculostriate system for identifying and a midbrain system,
the superior colliculus or tectum, for locating (see Schneider, 1969, for relevant
data on the hamster). It thus became fashionable to talk about the “two
visual systems” in mammals, one for what and one for where.
However, analysis of the frog (e.g., Arbib, 1987, for a review) showed
that there could be more than two visual systems even subcortically, with
different parts of the brain serving different visual mechanisms. For example,
prey catching by the frog seems to rely on the tectum for processing of visual
cues. The pretectum seems necessary for the tectum to play its role in
the avoidance of visual threat, as well as in mediating the recognition of
barriers. The role of the tectum in directing whole-body movements in the
frog is analogous to the role of the superior colliculus in directing eye movements
in the cat and monkey. When humans without primary visual cortex
are asked “Am I moving my left or right hand?” they say “I can’t see” but,