A number of studies have recently demonstrated the importance of organizational
properties of object components to picture recognition in avian species
(e.g., Brown & Dooling, 1993; Kirkpatrick-Steger, Wasserman, & Biederman,
1996, 1998; Wasserman et al., 1993; Watanabe & Ito, 1991). The primary approach
in these studies has been to train birds to recognize particular intact objects and then
test with scrambled versions of those objects. For example, pigeons might be trained to discriminate
among line drawings of four objects such as a watering can, an iron, a desk lamp,
and a sailboat. Following, training, the pigeons would then receive tests in which the
object components would be spatially rearranged, such as in the example below.
The scrambled versions to the right resemble the intact objects because they contain the same parts.
However, to the human eye, they are also discriminably different from the
original object
because the organization of the components is different.
The following set of studies examined 
whether pigeons, too, would be able
to discriminate the scrambled verions of the objects from the intact verions.
The pigeons were tested with several different
scrambled versions of each object.
According to Particulate feature theory
(Cerella, 1986), pigeons should
not be able to recognize a scrambled version as different from an intact
version of an object because the scrambled and intact versions contain
the same features (see Charlie Brown example).
On the other hand, Recognition-by-components (Biederman, 1987) postulates
that scrambled versions should be discriminated from the original objects
because the geon interrelations are altered by the operation of scrambling.
Three different experiments using different pigeons
(Wasserman et al., 1993; Kirkpatrick-Steger, Wasserman, Biederman, 1996, 1998) involved
tests
with scrambled versions of the watering can, the iron, the desk lamp, and
the sailboat. In all three studies, the
original drawings were discriminated
above 80% correct at the end of training. Performance to the scrambled
versions was significantly poorer than the performance to the original
versions in all three studies. However, performance to the scrambled versions
consistently exceeded the chance level of 25%. The level of performance
to the scrambled versions is consistent with the notion that the pigeons
were sensitive to the change in the spatial organization of the components,
but they must have still recognized some features of the original objects
because of the above-chance performance to the scrambled versions.
One interpretation of the detrimental effect of scrambling on recognition
accuracy is that the scrambled versions contained different points of contact
between the geons. An adept particulate perceiver might be able to discriminate
the change in contact points between the intact and scrambled objects.
Kirkpatrick-Steger, Wasserman, and Biederman (1998) conducted tests to
assess the contribution of the geon intersections to object recognition.
Following training on the
four-key
choice procedure to discriminate among the intact versions (Connected-Original,
CO) of the watering can, the iron, the desk lamp, and the sailboat, pigeons
were tested with three different types of stimuli
in addition to the original training objects. One type of test drawing,
the Disconnected-Original (DO
) drawings, contained the four geons in their
original spatial organization, but the geons were moved apart slightly,
so as to remove their intersections. A second type of test stimulus, the
Connected-Scrambled (CS) drawings, were scrambled images shown above with
novel spatial organizations and altered geon intersections. The third type
of test stimulus, the Disconnected-Scrambled (DS) drawings, were the same
scrambled images, but with the geons moved apart slightly to remove any
information about the change in geon intersections due to the operation
of scrambling. If the alterations in the geon intersections were responsible
for the scrambling effect, then one would expect similar levels of performance
on the three test stimuli.
Disconnection of the geons in the original spatial
organization (DO) resulted in accuracy scores that did not differ from
the original objects (CO). The connected-scrambled (CS) and
disconnected-scrambled
(DS) drawings were discriminated at a similar level of accuracy, which
was significantly poorer than the original drawings. The test results indicate
that the geon intersections were not a major contributor to object recognition.
These results are consistent with a study by Van Hamme, Wasserman, and
Biederman (1992). They trained pigeons to discriminate four objects in
which half of the contours and vertices were deleted. Then pigeons were
tested with complimentary contours which were in an intact or scrambled
arrangement. The complementary images were discriminated at a high level
of accuracy, but the scrambled contours were recognized much more poorly.
Their results indicated that the contours and geon intersections alone
were insufficient to account for successful object recognition.
Because scrambling had a significant effect on recognition accuracy
that
could not be accounted for by the changes in the geon intersections,
it appears that pigeons are sensitive to the spatial organization of object
components. This sensitivity should then allow pigeons to discriminate
between objects that are composed of the same components, but with different
organizations. (see the cup vs. pail example).
In order to test this proposition, pigeons were
trained to discriminate
four different scrambled versions of an object
(Wasserman et al., 1993). Bird 1 was trained with the four-key choice procedure
to discriminate among scrambled versions of the watering can; bird 2 was
trained with scrambled versions of the iron; bird 3 was trained with
scrambled versions of the desk lamp; and, bird 4 was
trained with scrambled
versions of the sailboat. All four pigeons learned to discriminate among
the four scrambled versions of an object. The degree of accuracy at the
end of training (mean of four pigeons = 75.9% correct) was similar to accuracy
levels obtained with pigeons that were trained to discriminate among the
intact training objects (mean of four pigeons = 80.5% correct). The results
provide further evidence that pigeons are sensitive to the spatial organization
of object components.
All of the above results indicate that pigeons
are sensitive to the spatial organization of object components. This sensitivity
is inconsistent with Particulate feature theory (Cerella, 1986). Because
Recognition-by-components (Biederman, 1987) proposes that both
the local features (geons) and their spatial organization are important
for recognition, an additional demonstration that geons also contribute
to object recognition in pigeons would provide substantial support for
the application of RBC to object recognition in pigeons as well as humans.
Evidence from studies where geons were deleted or moved (Kirkpatrick-Steger,
Wasserman, and Beiderman (1998)) indicate that pigeons may be sensitive
to an object's geons as well as their spatial organization.
