Statement of Purpose
Timmer's Statement of Purpose - October 1994
A critical behavior in all creatures is the
orientation response to novel or ``interesting'' stimuli. In the
struggle to find food and to avoid predators, this behavior must be
fast and reliable. In most animals the neural pathway from sensor to
muscle is short and typically initiates an orienting response to
improve sensory conditions. This orientation behavior is usually
quick (e.g. saccades) and often requires specialized neural
controllers which do not use proprioceptive or visual feedback during
the movement. Such systems use past performance to calibrate the
movement to maintain accuracy throughout the lifetime of the organism.
In vertebrates, visual information from the retina is known to project
directly to a brainstem structure called the superior colliculus (or
optic tectum) which is involved in orientation movements. Activation
of the superior colliculus by indirect visual stimulus or direct
electrical stimulation generates head movements in owls, head and eye
movements in cats, and eye movements in primates. In addition to
visual input, acoustic localization information and somatosensory
information also converge in the superior colliculus. The superior
colliculus is an important convergence point for multimodal spatial
information involved in orientation behaviors. In all these
behaviors, learning is incorporated to achieve rapid, accurate, and
stable eye movements and to keep the various sensory modalities
aligned to each other. While it is not known specifically where the
sites of learning are, models which incorporate data from both
adaptation experiments and neuroanatomical studies are being
investigated.
My research interest lies in understanding the neurobiological
mechanisms of orientation responses and how these systems learn to
improve their performance over time. I am building a saccadic eye
movement system with analog VLSI implementations of
neural models proposed for this sensorimotor system. In particular, I
am developing a hardware model of the superior colliculus and
brainstem burst generator system which will participate in the
generation of saccades and will be capable of continually improving
its own performance.
The investigation of neural information processing architectures in
analog VLSI can provide insight into the issues that real biological
nervous systems face. Analog VLSI architectures share many of the
advantageous properties with neural systems such as speed, space
efficiency, and low power consumption. In addition, analog VLSI must
face similar constraints such as real-world noise, component
variability or failure, and interconnection limits. Not only can
adaptive neural systems which self-calibrate overcome many of these
drawbacks, they will be useful in the exploration of
architectures which control non-linear devices.