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Department of Psychology : Uppsala University
Leo Poom, Ph.D.
Research:
VISUAL PERCEPTION AND WORKING MEMORY
My research interest is focused on visual
perception and concerns questions about information integration, gestalt
formation, three-dimensional shape perception, motion perception, and
visual working memory.
Information
integration
The aim of one of the current research
projects, supported by grants from the Swedish research council
(Vetenskapsrådet, VR), is, among other things, to use psychophysical
methods to test visual information integration models. Link to brief
description, in Swedish on VR’s homepage, can be found here.
Information about visually specified shapes
can be mediated by several surface media. For instance, contrasts in
brightness, colour, texture, motion and stereoscopic depth can be used to
distinguish shapes against the background (figure-ground segregation and
gestalt formation). Are these features promoting activity in independent
channels (race models) or are they combined to activate a common channel
(co-activation models)? These models can be distinguished empirically by
comparing results from conditions where two features are combined with
corresponding conditions where the features are used in isolation. In laboratory
settings, where images are generated by a computer and displayed on a
screen, different information media can be used in isolation or combined in
controlled conditions. In typical experiments the task may be to localise
or identify some target embedded in noise elements. The target may be an
individual element or multiple elements forming a specific pattern which
forms the target. The first target condition is used to examine information
integration in element detection and the second target condition is used to
examine information integration in gestalt formation. These two processes
are believed to occur sequentially in the visual system. The variables
under investigation are the information media, used either in isolation or
combined, to display the target and the results may be the measured
response times or the percent correct responses.
Visual
working memory
In collaboration with Henrik Olsson (Center
for Adaptive Behavior and Cognition
Max Planck Institute for Human Development, Berlin)
and supported by grants from the Riksbankens Jubileumsfond (RJ) we are
currently investigating human visual working memory.
What we today call working memory is closely
related to executive processes, attention, consciousness, and intelligence.
In order to understand human thinking it is of fundamental importance to
understand the nature of working memory representations. In the literature
on working memory, a prominent theme is its limited capacity. There are,
however, several problems associated with the measurement of working memory
capacity which may contribute to inflated capacity estimates. In regard to
visual working memory, earlier methods sometimes made it possible for
people to enhance their performance with the help of verbal strategies,
categorization, and use of long term memory. We have started the
development of a new method for measuring visual working memory capacity in
which people’s use of strategies is minimized. When the influence of
other processes and representations besides the visual ones, our
preliminary results indicate that the capacity of visual working memory is
only one object. This is in contrast to recent capacity estimates of around
four easily categorized objects such as, for example, squares and
triangles. With our new method we are going to investigate how limited our
visual working memory capacity really is and the contributing factors to
this limitation. In short: What and how much can we really represent in
visual working memory?
Teaching:
Part of an undergraduate perception course, chapters about visual
neuroscience. Powerpoint presentation (in Swedish) can be found here.
Part of an undergraduate perception course. Introduction, object
perception, attention and colour. Powerpoint presentation (in Swedish) can
be found here. Sound and chemical senses
here. Lecture by Hans Richter
here.
Selected recent publications:
Olsson, H., & Poom, L.
(2005). Visual
memory needs categories. Proceedings
of the National Academy of Sciences, 102, 8776-8780. [Press Release in
Swedish]
Poom, L., & Börjesson, E. (2005). Color, polarity,
disparity, and texture contributions to the detection of global motion. Perception, 34, 1193-1203.
Poom, L.,
& Börjesson, E. (2004). Good
continuation with kinetic edges. Vision
Research, 44 (18),
2101-2108.
Dissertation thesis:
Poom, L. (2003). Binding
three kinds of vision. Comprehensive Summaries
of Uppsala Dissertations from the Faculty of Social Sciences 121. [Press Release in
Swedish]
A complete list of
publications can be found here.
Links:
Optical
illusions
Lightness
perception and illusions
VisionScience
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