The localization and orientation to various novel or interesting events in
the environment is a critical sensorimotor ability in all animals, predator
or prey. In mammals, the superior colliculus (SC) plays a major role in this
behavior, the deeper layers exhibiting responses to visual, auditory, and
somatosensory stimuli. While the different sensory modalities are naturally
in different coordinates, the representation in the SC is found to be
retinotopic. Auditory cues, in particular, are thought to be computed in
head-based coordinates which must be transformed to retinal coordinates.
In this paper, an analog VLSI implementation for auditory localization is
described which extends the barn owl architecture to primates where further
transformation is required due to moveable eyes. This transformation is
intended to model the projection in primates from auditory cortical areas to
the deeper layers of the primate superior colliculus. This system was
developed to interface with an analog VLSI-based saccadic eye movement
system also being constructed in our laboratory.
The system is a mixed system combining discrete analog components and analog VLSI techniques. The amplification and filtering has been performed in discrete electronics and is therefore not a particularly compact system (yet). Note that for these reasons, the current system uses only one frequency band and thus does not deal with the problems of phase ambiguity. Please note that this system builds off of the thesis work done by John Lazzaro while here at Caltech. His work included two cochleas and compared information across many frequencies.
We have connected this system to the saccadic eye movement system which now orients to both auditory and visual targets.
An Auditory Localization and Coordinate Tranform Chip (220K Postscript)
(Special thanks goes to Brooks Bishofberger for building the current version of the auditory chip interface and the demo box.)