Understanding how organisms learn perceptual categories on the basis of
experience has been an important goal for researchers in a number of subdisciplines of
psychology, including behavior analysis, experimental psychology, and comparative
cognition. The primary aim of this thesis is to investigate how nonhumans (pigeons) and
humans learn to make visual category judgments when stimuli vary quantitatively along
two dimensions, particularly when accurate responding requires integration of
information from both dimensions. The thesis consists of four chapters and a technical
appendix. Chapter 1 is a literature review which provides a broad overview of studies on
categorization by nonhumans and humans, as well as specific background for the current
research. Chapters 2 and 3 constitute the empirical portion of this thesis. Four
experiments are described, using a category task based on the ‘randomization’ procedure
developed originally by Ashby and Gott (1988) with human participants and employed in
subsequent research by Ashby, Maddox and their colleagues (see Ashby & Maddox,
2005; Maddox & Ashby, 2004, for review). Stimuli were Gabor patches that varied in
frequency and orientation. Our primary goals were to determine whether pigeons could
respond accurately in an information integration task with dimensionally-separable
stimuli, and to compare performances of pigeons and humans.
Chapter 2 reports two experiments with pigeons. Experiment 1 compared
performance in two conditions which varied in terms of whether accurate performance
required control by both dimensions (“information integration; II) or by a single
dimension (“rule based”; RB). Results showed that pigeons learned both category tasks,with an average percentage of correct responses of 85.5% and 82% in the II and RB
conditions, respectively. Although perfect performance was possible, responding for all
pigeons fell short of optimality. Model comparison analyses showed that the General
Linear Classifier (GLC; Ashby, 1992), which has been proposed to account for category
learning in similar tasks with humans, provided a better account of responding in the II
conditions, but a unidimensional model that assumed control only by frequency provided
a better account of results from the RB condition. Thus results show that pigeons can
respond accurately in an information integration task based on dimensionally-separable
stimuli. However, analysis of residuals showed that systematic deviations of GLC
predictions from the obtained data were present in both II and RB conditions.
Specifically, accuracy for one category (A) was an inverted-U shaped function of
orientation, whereas accuracy for the other category (B) did not vary systematically with
orientation. Results from the RB condition showed evidence of an interaction between
frequency and orientation, such that accuracy was higher for orientation values that were
relatively low (i.e. close to horizontal) than high (i.e., close to vertical). Experiment 2
compared responding in two RB conditions which differed in terms of whether frequency
or orientation was the relevant dimension. Pigeons again responded accurately in the
task. Results from the frequency-relevant condition replicated the interaction obtained in
Experiment 1, whereas results from the orientation-relevant condition gave no evidence
of an interaction.
Chapter 3 reports two experiments which compare performances of pigeons
(Experiment 1) and humans (Experiment 2) in category tasks using identical stimuli. In
each experiment there were two conditions, both based on the information-integration task in which the range of orientation values was wide or narrow. There were two
primary goals. First, we wanted to test whether the inverted-U shaped pattern for
Category A accuracy as a function of orientation would be replicated with different
pigeons and stimulus values. Second, we wanted to compare responding of pigeons and
humans. A secondary aim was to test whether restriction of range would affect control
by orientation. Results from the condition with a wide orientation range were similar to
those from Chapter 2, and showed that the inverted-U shaped pattern was replicated for
both pigeons and humans. When the range of orientation values was narrow, responding
for both pigeons and humans was exclusively controlled by orientation. Overall, results
for pigeons and humans were similar and suggest that a common process may underlie
information-integration category learning in both species.
Chapter 4 provides a summary of the empirical results from Chapters 2 and 3, and
shows that the inverted-U shaped pattern of accuracy for Category A as a function of
orientation is unanticipated by current models for category learning, such as the GLC,
prototype theory, and exemplar theory. A new ‘fuzzy prototype’ model is described
which provides a good account of the results and predicts the inverted-U shaped pattern.
According to the new model, subjects associate a linear segment in the stimulus space
(‘fuzzy prototype’) with one of the category responses. When a stimulus is presented on
a trial, subjects are assumed to use an ‘A/Not-A’ decision rule, with the probability of a
Category A response determined as a function of the minimum distance of the stimulus
from the fuzzy prototype. Possible directions for future research are considered.
The thesis concludes with a technical appendix which describes the experimental
chambers, interface hardware, and computer software developed to conduct the research,and a detailed user’s manual for the software. The system allows the same control
procedure for both human and pigeon experiments, and should be useful for future
research on categorization
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/3820 |
| Date | January 2010 |
| Creators | Berg, Mark |
| Publisher | University of Canterbury. Psychology |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Mark Berg, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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