Same-Different Texture Discrimination in Pigeons: Testing Competing Models of Discrimination and Stimulus Integration
Landmark Geometry and Identity Controls Spatial Navigation in Rats
Three experiments using a new reference memory procedure examined
how male rats search for consistently located food in a cue-controlled
spatial environment. The animals searched the tops of 24 poles for six
hidden baits in an enclosed circular arena containing a fixed configuration
of six object landmarks. In Experiment 1, acquisition was faster and overall
performance superior for the Consistent group (10 rats), in which
the six baited poles were fixed relative to the landmarks for each session,
than for the Random group (4 rats), in which baited poles were randomly
configured. Cue-control tests and computer simulations suggested that the
Consistent group relied on the landmarks to directly go to the baited poles,
while the Random group used them to employ a response strategy for searching
the arena. Experiments 2 and 3 revealed that the number, identity, and
geometric configuration of the landmarks were important to the Consistent
group's search performance. Overall, these results are most consistent
with the use of a geometric representation by male rats which includes
information about both the identity and relative geometry of discrete landmarks
in the surrounding spatial environment.
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Same/different texture discrimination and concept learning in pigeons.
The acquisition and transfer of a "same/different" conditional
discrimination using multidimensional visual texture stimuli was investigated
in pigeons. Using a choice task, four pigeons were reinforced for discriminating
different displays,
created from aggregated differences in element color or shape, from uniform
displays, in which all elements were identical. Discrimination of these
two display types was readily acquired by the birds when required to locate
and peck the contrasting target region of the different displays. The birds
showed high levels of discrimination transfer to novel texture stimuli
both during acquisition and in two subsequent transfer tests. The results
suggest pigeons may be able to learn a generalized "same/different"
concept when promoted by the use of large numbers of multi-element stimuli
during training.
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Mechanisms of multidimensional grouping, fusion, and search in avian texture discrimination.
Three experiments examined the influence of dimensional organization on pigeon texture perception in a simultaneous conditional discrimination procedure. Six experienced pigeons were reinforced for pecking at a small block of target elements randomly located within a larger array of distractor elements in each texture stimulus. Target/distractor differences in color, size, orientation, and combinations of these dimensions were examined. Experiment 1 investigated how target/distractor similarity influenced performance with different forms of unidimensional and conjunctively-organized texture stimuli made of two and three dimensions. Targets in feature displays, in which the two regions consistently differed along a single dimension, were located more accurately than in conjunctive displays, where a combination of values from all dimensions defined each region. Experiment 2 found a trade-off between response speed and accuracy in the pigeons' processing of conjunctive displays. Experiment 3 found that the number of distractors differentially influenced the localization of feature and conjunctive targets. Overall, the pigeons' reactions to these feature and conjunctive stimuli paralleled those of humans, suggesting that functionally equivalent mechanisms may mediate the perceptual grouping, search, and discrimination of textured multidimensional stimuli in both species.