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Abstract

Males generally achieve higher levels of performance than females on mental rotation
tasks (Linn & Petersen, 1985, Voyer, Voyer, & Bryden, 1995); though the factors which
contribute to this sex difference are poorly understood. The present research aimed to
investigate the cognitive mechanisms that underlie sex differences in mental rotation
task performance using event-related potentials (ERPs). Specifically, the effects of
image type, task repetition and image familiarity on the cognitive processes used by
males and females in mental rotation were explored. This research also investigated
similarities and differences in the way that males and females performed specific
cognitive operations within the task (e.g., forming a mental representation of the
stimulus, accessing an existing representation from memory and mental rotation per se). In Experiment 1, 18 males and 18 females completed three mental rotation tasks.
The three tasks were the same, except that stimulus category was manipulated between
tasks (letters, familiar symbols or unfamiliar abstract figures). Males and females were
found to achieve similar performance levels. For both sexes, performance was highest
for the letters condition and lowest for the unfamiliar abstract figures condition. ERP
analysis revealed sex differences in the P2 and P3 components and for mental-rotation
related negativity (e.g., P2 was left-lateralised in females and symmetrical in males).
This indicates that males' strategic approach to the task was different to females', but
the ultimate performance outcome did not differ between the sexes.
In Experiment 2, the effects of image familiarity on sex differences in mental
rotation were further explored. Participants were trained to reach a determined level of
familiarity with initially unknown polygons which ensured that familiarity with the
images was reasonably similar for all participants. Nineteen males and 20 females
completed three mental rotation tasks, which were largely the same, except that image
familiarity was manipulated between tasks (trained, or initially unfamiliar/repeated
during the task, or unfamiliar/never repeated). Again, males and females demonstrated similar overall performance levels, except during the unfamiliar condition. In this
condition, there was a trend for males' accuracy to be higher than females'. ERP results
revealed the P2 component to be larger for females than for males. Females showed
differentiation in P2 amplitude between mirrored and normal images when presented
upright rotated by 45°, while males did not demonstrate any parity differentiation in this
component. P2 indexes early stimulus processing, including feature detection processes
(Crowley & Colrain, 2004; Luck & Hillyard, 1994). The P2 sex difference indicates that
early stimulus processing was undertaken differently by males and females. It was also
found that mean amplitude (300-600ms) was symmetrical for males and rightlateralised
for females. Interpreted within a resource allocation framework (Isreal,
Wickens, Chesney, & Donchin, 1980; Kok, 1997; 2001), this result indicates that
females probably allocated a high proportion of visuospatial resources to character
classification and the formation of an elaborate mental image while males did not
demonstrate this same visuospatial resource recruitment strategy. In both experiments, ERP rotation-related negativity was demonstrated
differently by males compared to females. Give that this negativity is regarded as a
direct index of mental rotation (Heil, 2002), this indicates that males and females used
different mental rotation strategies. Females showed strong left hemisphere rotationrelated
negativity and weak negativity in the right hemisphere. Males showed
symmetrical rotation-related negativity. These lateralisation patterns indicate that
females adopted a piecemeal strategy and males used a holistic strategy.
For females, performance generally improved as each mental rotation task
progressed (i.e., performance was higher in the second half than in the first half of most
tasks). Males' performance remained consistent within each mental rotation task. (These
effects were observed when data for each task was split into two equal halves and
compared.) Within-task performance enhancements were present for females when the
mental rotation task contained a set of four stimuli which were repeated throughout but not when the task contained a large set of stimuli which were never repeated. Thus
females' performance improved when stimuli became familiar, but did not improve
when there was no opportunity for stimuli to become familiar. Although females
showed marked performance changes, there were no similar, consistent ERP changes
over time. This indicates that performance changes were probably not caused by a
strategy shift in the way that repeated images were processed. It appears that both sexes
adopted relatively consistent strategies throughout the task which, for females, were
more successful when the images were repeated and became familiar.
In summary, males' and females' strategic approach to the mental rotation task
differed during early stimulus processing and mental rotation. Because sex differences
were not limited merely to mental rotation, it is recommended that future investigation
of the root(s) of sex differences on the task explores each stage of processing independently. Additionally, image familiarity was found to be an important influence
on females' processing, particularly when they were familiar with rotated and upright
versions of the stimuli. Females showed clear performance benefits when they had
mental representations of images at multiple orientations but these effects were not
present for males. These benefits for females were interpreted with reference to sex
difference frameworks which emphasise the underlying processes recruited to perform
cognitive tasks (Colom, Escorio, & Rebollo, 2004; Halpern, 1992; Halpern & Wright,
1996; Vecchi & Girelli, 1998). Females were thought to have excelled at mental
rotation of familiar images because of their high skill in retrieving previously stored
mental representations from memory. The present research provides a basis for
understanding, at least in part, why the magnitude of performance sex differences has
varied so widely between studies (Voyer & Hou, 2006; Voyer & Saunders, 2004; Voyer
et al., 1995): image familiarity has differed markedly between studies. Image familiarity
differences between studies subsequently alter the underlying cognitive requirements of
the mental rotation task and, ultimately, the likelihood that sex differences will occur.

Item Type:	Thesis - PhD
Authors/Creators:	Coleman, Sarah Amy
Copyright Holders:	The Author
Copyright Information:	Copyright 2009 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (PhD)--University of Tasmania, 2009. Includes bibliographical references
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