Volume 17, Number 24,
Issue of December 15, 1997
pp. 9706-9725
A Neural Model of Multimodal Adaptive Saccadic Eye Movement
Control by Superior Colliculus
Received May 27, 1997; revised Sept. 23, 1997; accepted Sept. 25, 1997.
Stephen Grossberg,
Karen Roberts,
Mario Aguilar, and
Daniel Bullock
Department of Cognitive and Neural Systems and Center for Adaptive
Systems, Boston University, Boston, Massachusetts 02215
How does the saccadic movement system select a target when visual,
auditory, and planned movement commands differ? How do retinal,
head-centered, and motor error coordinates interact during the
selection process? Recent data on superior colliculus (SC) reveal a
spreading wave of activation across buildup cells the peak activity of
which covaries with the current gaze error. In contrast, the locus of
peak activity remains constant at burst cells, whereas their activity
level decays with residual gaze error. A neural model answers these
questions and simulates burst and buildup responses in visual, overlap,
memory, and gap tasks. The model also simulates data on multimodal
enhancement and suppression of activity in the deeper SC layers and
suggests a functional role for NMDA receptors in this region. In
particular, the model suggests how auditory and planned saccadic target
positions become aligned and compete with visually reactive target
positions to select a movement command. For this to occur, a
transformation between auditory and planned head-centered
representations and a retinotopic target representation is learned.
Burst cells in the model generate teaching signals to the spreading
wave layer. Spreading waves are produced by corollary discharges that
render planned and visually reactive targets dimensionally consistent and enable them to compete for attention to generate a movement command
in motor error coordinates. The attentional selection process also
helps to stabilize the map-learning process. The model functionally
interprets cells in the superior colliculus, frontal eye field,
parietal cortex, mesencephalic reticular formation, paramedian pontine
reticular formation, and substantia nigra pars reticulata.
Key words:
saccades;
eye movements;
superior colliculus;
attention;
learning;
burst neurons;
buildup neurons;
parietal cortex;
frontal eye
fields;
reticular formation;
substantia nigra