Research
Philosophy
Each time we engage in a moderately complex task,
we likely enlist the help of an untold number of simpler visuo-motor
operations that exist largely outside of our conscious awareness.
Consider for instance the steps involved in preparing a cup of
coffee. For the sake of simplicity, assume that the coffee has
already been brewed and is waiting in the pot, and that all of the
essential accessories, an empty cup, a spoon, a carton of cream, and
a tin of sugar, are sitting on a countertop in front of you. What is
your first step toward accomplishing this goal? The very first thing
that you might do is to move your eyes to the handle of the coffee
pot, followed shortly thereafter by the much slower movement of your
preferred hand to the same target. Because the coffee pot is hot and
the handle is relatively small, this change in fixation is needed to
guide your hand to a safe and useful place in which to grasp the
object. After lifting the pot, your eye may then dart over to the
cup. This action is needed, not only to again guide the pot to a
very specific point in space directly over the cup, but also to
provide feedback to the pouring operation so as to avoid a spill.
After sitting the pot back on the counter (an act that may or may
not require another eye movement), your gaze will likely shift to
the spoon. Lagging shortly behind this behavior may be simultaneous
movements of your hands, with your dominant hand moving toward the
sugar tin and your non-preferred hand moving to the spoon. The spoon
is a relatively small and slender object that again requires
assistance from foveal vision for grasping; the tin is a rather
bulky and indelicate object that does not require precise Visual
information to inform the grasping operation. Once the spoon is in
hand and the lid to the tin is lifted, gaze can then be directed to
the tin in order to help scoop out the correct measure of sugar. To
ensure that the spoon is kept level, a tracking operation may be
used to keep your gaze on the loaded spoon as it moves slowly to the
cup. After receiving the sugar, and following a few quick turns of
the spoon, your coffee would finally be ready to drink (see Land et
al., 1998, for a similarly framed example).
Projects
Using
eye movements to reveal memory for objects in scenes
see all projects
A long-term research focus of the lab is to better
understand people's ability to remember real-world objects in
scenes. Previous research had shown that many of the Visual
details
of an object seem to vanish from memory once gaze shifts away from
that object (Irwin, 1996). This phenomenon, however, had only been
documented using relatively simple stimuli (e.g., letters) and only
over a very limited range of eye movements (e.g., one or two). With
David Irwin, a gaze contingent display change methodology (meaning
that online changes were made to the display depending on the
observer's gaze behavior while viewing the scene) was developed that
allowed observers to view a complex real-world scene for either 3,
9, or 15 fixations. Following the criterion number of allowed
fixations, the scene was replaced by a spatial probe at one of the
previously viewed object locations and the observer was asked to
report the identity of that object. Perhaps counterintuitively, we
found that memory was better after viewing the scene for only 3
fixations compared to 9 or 15 fixations—consistent with previous
work on transsaccadic memory. We also found that accuracy was
extremely high (approaching 100%) for objects that were about to be
fixated when the display was terminated, suggesting that attention
precedes gaze to a location in space (Irwin & Zelinsky, 2002).
Using a similar gaze-contingent memory paradigm, another project
extended the Irwin and Zelinsky (2002) logic to the question of
memory serial order effects for objects presented simultaneously in
scenes. When trying to recall a list of items, such as the digits of
a telephone number, people usually find it easier to remember the
last few items relative to those presented earlier in the list. This
"recency" effect has been the topic of innumerable memory studies
and a cornerstone of memory theory since the dawn of modern
experimental psychology. All of these studies, however, have in
common a similar methodology. List items are presented singularly
one after the other, and this serial order is later used to derive
the Accuracy x Order function defining the recency effect.
Unfortunately, many everyday memory tasks require us to remember
objects appearing simultaneously as part of complex scenes rather
than singularly over time. We introduced a method to remove this
serial presentation constraint by using a person's eye movements
during scene viewing to serialize the order in which objects are
encoded. Specifically, we systematically varied the number of
objects that an observer was allowed to fixate following the initial
fixation of a target object. Using this technique, we found that
memory for a target object declined precipitously after fixating 1-3
intervening objects, but then plateaued at a level well above chance
performance (Zelinsky, 1999b, 1999c, Zelinsky & Loschky, submitted).
Together with the Irwin and Zelinsky (2002) study, these findings
suggest a dual-representation model for spatial memory in
multi-object scenes, with one representation being veridical but
easily disrupted and a second representation being less detailed but
far more enduring. In a related ongoing project, we analyzed how
often observers look back or "refixate" a previously viewed object
in a scene memory task to determine if these eye movements are being
used as part of an active strategy to rehearse, and hopefully
retain, object information in memory. This work is currently under
revision (Zelinsky & Loschky, in revision).