48 Informational environments
These two cases, being quite distinct affairs themselves, are rather different, but
not clearly distinguished by Gibson, from two other kinds of cases:
(pi 3) Naturally occurring perceptual illusions, such as illusions of length, colour or brightness.
(pi 4) Instances of misperceiving an object for another object that would have
afforded different activities to the perceiver.
The primary issue here is not the naturalness vs. artificiality of the illusions and
misperceptions in question – although, quite obviously, (pi 1 and pi 2) are based
on artefacts, whereas illusions of kind (pi 3) occur naturally (while typically being
investigated in laboratory settings), and misperceptions of kind (pi 4) might do so
as well. More fundamental than this distinction, and not fully coextensive with
it, is the one between perceptual illusions and misperception and their normative
status.
In distinguishing illusion from misperception, I am following a fairly straightforward and presumably commonsensical distinction discussed by David Armstrong (1960, 4) in his interpretation of George Berkeley’s theory of vision in
Berkeley (1709): if I see something as red, round and having all the visual qualities of a tomato, and it turns out not to be a tomato but a plastic replica, I am likely
to have misperceived it, for having mistaken it for another thing on the grounds
of some similarity in perceivable surface properties. Still, I have not fallen for a
visual illusion – that is unless I was mistaken about the replica’s redness, roundness and so forth to begin with. If, in turn, conditions in the environment or my
sense organs are such that I see something as square, purple and perhaps lacking
other visual qualities of a tomato, and it turns out to be a very normally shaped and
coloured fruit of that kind, I have been subject to visual illusion or hallucination
respectively, in not getting the surface properties of the object right.
In either case, I might be at a disadvantage, and it seems natural to assume
that this is the standard, the statistically normal result of instances of misperception, hallucination and illusion. If, on Gibson’s theory, information for perception
is supposed to specify an environment for a perceiving organism, it seems selfsuggesting to characterise any divergence between what is perceived and how the
environment stands as a failure, and to look either for deficiencies and dysfunctions in the organism’s perceptual system or for inconducive or even treacherous conditions in the environment as the causes of that failure. And this is what
Gibson does in his earlier The Senses Considered as Perceptual Systems (1966),
and in his discussion of the difference between natural perception and hallucination (1970).
However, not every divergence between instances of perception and how the
world stands needs to be a failure. The case is clear for hallucination but not for
perceptual illusions. Perceptual illusions do not automatically result in misperception, and they may not be maladaptive per se – as Gibson’s discussion of pictures as illusions that nonetheless preserve some of the information pertaining to
their subject matter should have demonstrated. In naturally occurring perceptual
These two cases, being quite distinct affairs themselves, are rather different, but
not clearly distinguished by Gibson, from two other kinds of cases:
(pi 3) Naturally occurring perceptual illusions, such as illusions of length, colour or brightness.
(pi 4) Instances of misperceiving an object for another object that would have
afforded different activities to the perceiver.
The primary issue here is not the naturalness vs. artificiality of the illusions and
misperceptions in question – although, quite obviously, (pi 1 and pi 2) are based
on artefacts, whereas illusions of kind (pi 3) occur naturally (while typically being
investigated in laboratory settings), and misperceptions of kind (pi 4) might do so
as well. More fundamental than this distinction, and not fully coextensive with
it, is the one between perceptual illusions and misperception and their normative
status.
In distinguishing illusion from misperception, I am following a fairly straightforward and presumably commonsensical distinction discussed by David Armstrong (1960, 4) in his interpretation of George Berkeley’s theory of vision in
Berkeley (1709): if I see something as red, round and having all the visual qualities of a tomato, and it turns out not to be a tomato but a plastic replica, I am likely
to have misperceived it, for having mistaken it for another thing on the grounds
of some similarity in perceivable surface properties. Still, I have not fallen for a
visual illusion – that is unless I was mistaken about the replica’s redness, roundness and so forth to begin with. If, in turn, conditions in the environment or my
sense organs are such that I see something as square, purple and perhaps lacking
other visual qualities of a tomato, and it turns out to be a very normally shaped and
coloured fruit of that kind, I have been subject to visual illusion or hallucination
respectively, in not getting the surface properties of the object right.
In either case, I might be at a disadvantage, and it seems natural to assume
that this is the standard, the statistically normal result of instances of misperception, hallucination and illusion. If, on Gibson’s theory, information for perception
is supposed to specify an environment for a perceiving organism, it seems selfsuggesting to characterise any divergence between what is perceived and how the
environment stands as a failure, and to look either for deficiencies and dysfunctions in the organism’s perceptual system or for inconducive or even treacherous conditions in the environment as the causes of that failure. And this is what
Gibson does in his earlier The Senses Considered as Perceptual Systems (1966),
and in his discussion of the difference between natural perception and hallucination (1970).
However, not every divergence between instances of perception and how the
world stands needs to be a failure. The case is clear for hallucination but not for
perceptual illusions. Perceptual illusions do not automatically result in misperception, and they may not be maladaptive per se – as Gibson’s discussion of pictures as illusions that nonetheless preserve some of the information pertaining to
their subject matter should have demonstrated. In naturally occurring perceptual