Principal Investigator: R.M. Klein
On the Relationships Between Overt Orienting and Covert Shifts of Visual Attention
It is a well-known fact that we can move our attention around in visual space without moving our eyes (covert orienting). Yet, when the eyes do move (overt orienting), there appears to be an obligatory shift of attention. Together with early neuroscientific evidence, this finding strongly implicates oculomotor programming in the generation of attentional shifts. Is attention shifted covertly by preparing an overt oculomotor response? Does the answer depend on whether orienting is controlled by endogenous (voluntary) or exogenous (reflexive) mechanisms? Existing data from behavioral, neuroscientific and neuroimaging studies are either conflicting or ambiguous in their implications. The three applicants have joined together in this multidisciplinary collaboration to delineate how the brain controls both endogenous and exogenous shifts of attention, and how these mechanisms are related to the control of eye movements.
Each member of the collaborative team contributes unique and important
knowledge and experience. Klein, who trained with Posner, is an expert
on covert and overt orienting as well as behavioral paradigms for eliciting
them exogenously and endogenously. He developed and tested the original
oculomotor readiness proposal for covert orienting; and his laboratory
has produced important data showing that endogenous vs exogenous control
over attention has profoundly different consequences for subsequent processing.
Munoz, who trained with Guitton and Wurtz, is an expert on the oculomotor
system and neuroscientific approaches for exploring it (including single
unit recording, chemical modulation of neural excitability, training monkeys
to do complex tasks). He has precisely characterized the activity of single
neurons in the SC subserving overt orienting (including express saccades)
and oculomotor preparation. This work has led to the distinction between
buildup, burst and fixation neurons. Sweeney is an expert on the oculomotor
system and on techniques for neuroimaging it. He is particularly interested
in voluntary (endogenous) versus reflexive (exogenous) control of eye
movements. Through the use of neuroimaging he has not only demonstrated
that the FEF is much more posterior in man than in monkey, but he has
located, with exquisite precision, distinct regions in the FEF that are
activated by saccades versus pursuit. Klein & Munoz have a track record
of collaboration (that was funded by a Canadian program that has since
been canceled) combining human performance and monkey neurophysiology.
This led to a neural network model (Trappenberg, et al, 1997) which incorporates
both endogenous and exogenous inputs and can account for a wide range
of behavioral data (timecourse of the gap effect, IOR, antisaccade, distractors,
target probability) as well as single unit activity. Although Klein and
Munoz had previously, and independently, discussed the possibility of
doing collaborative work with Sweeney, it was our discovery of the McDonnell-Pew
Program in Cognitive Neuroscience that breathed life into this idea (because
we do not otherwise have the resources to implement this specific interdisciplinary
project). We believe that interdisciplinary work in cognitive neuroscience
along the lines we propose is not only rewarding and highly synergistic,
but is essential for delineating the fundamental brain mechanisms of higher
cognitive processes.
