UNCONSCIOUS ACTION
VERSUS CONSCIOUS
PERCEPTION?
Milner and Goodale (1995; Goodale and Mil-
ner, 2013) suggest a functional dissociation
between two vision systems and map this
onto the two neural streams in the visual
system: the dorsal and ventral streams (Chap-
ter 6). These two streams had often been
described as being concerned with spatial
vision and object vision respectively, or with
the ‘where’ and ‘what’ of vision (Ungerleider
and Mishkin, 1982). Instead, Milner and
Goodale argue for a distinction based on
two fundamentally different tasks that the brain has to carry out. One is fast
visuomotor control, which needs egocentric models, relating the self to objects
in the world; the other is the less urgent visual perception, which needs more
allocentric processing – relating objects in the envi-
ronment to each other. They call these the vision-
for-action and the vision-for-perception systems
(Goodale, 2007).
Much of Milner and Goodale’s evidence comes
from patients with brain damage. One patient, D.F.,
was taking a shower and was nearly asphyxiated
by carbon monoxide poisoning from a faulty water
heater. Her partner found her before she died, and
when she emerged from her coma, it became clear
that her brain had been badly damaged from lack of
oxygen. In particular, she was left with visual form
agnosia. This means she is unable to recognise the
shapes of objects by sight, even though her low-level
vision of basic visual features including pattern and
colour appears to be intact. She cannot name simple
line drawings or recognise letters and digits, nor can
she copy them, even though she can produce letters
correctly from dictation and can recognise objects by
touch. She can, however, reach out and grasp every-
day objects (objects that she cannot recognise) with
remarkable accuracy.
One experiment with D.F. reveals this extraordinary
split between motor performance and awareness.
She was shown a vertically mounted disc in which
a slot was randomly cut at 0, 45, 90, or 135 degrees.
When asked to draw the orientation of the slot, or
adjust a comparison slot to the same angle, she
was quite unable to do so. However, when given
FIGURE 8.8 • The layout in the experiment by
Castiello et al. (1991), showing
the arm trajectories both when the
lit dowel stays the same and when
it changes.PRoFILe 8.1
Melvyn Goodale (b. 1943)
Having emigrated with his parents
from England to Canada as a child,
Mel Goodale studied psychology
before setting off to ‘find himself’
travelling around Europe. Getting
sick of casual jobs and damp apart-
ments and with still no idea what he wanted to do, he
headed for graduate school in Calgary, ended up in a lab
studying visual neuroscience, and was instantly captivat-
ed. He is now Director of the Brain and Mind Institute
at the University of Western Ontario, and Co-Director of
the Azrieli Program on Brain, Mind, and Consciousness at
the Canadian Institute for Advanced Research. He is best
known for his work with David Milner on the functional
organisation of the visual pathways in the cerebral cor-
tex. Their studies of visuomotor control in neurological
patients led to their characterising the two streams of the
primate visual system as ‘vision for perception’ and ‘vi-
sion for action’. He has since also begun to explore how
the blind use echolocation to navigate.