Re: The Mind's Eye

Damien Broderick (
Sat, 28 Sep 1996 12:14:35 +1000

At 12:29 PM 9/27/96 +0200, Anders wrote:
>On Thu, 26 Sep 1996 wrote:
>> When one imagines a visual stimuli, does it also register (measurably) as a
>> change in the visual part of the brain?
>I don't think we can image it well yet, but in PET or FMRI scans it is
>visible as an activity increase in the visual cortices. Yes, there are
>several high-level cortices dealing with vision, and presumably the
>purple walrus will exist as activity in some of them. V1 (the "classic"
>visual cortex) deals mostly with what we really see (plus what our brain
>extrapolates from it), while V2-V5 seem to deal with various aspects of
>it (color, movement, edges etc).

A recent report in New Scientist describes a `blindsighted' subject whose V1
is inoperative but who can still detect fast (but not slow) motion within
the visual field. This is processed directly by V5. I'm not sure if this
subject *experiences* the motion `visually', since many blindsighters insist
that they're blind as bats yet when asked to `guess' manage to be right way
too often. So this is presumably a neurologically different process from
the optional hallucination/transduction process induced by `aura reading'.

Damien Broderick