Barrie Frost: Neural selectivity for different classes of complex visual motion
Many tectal neurons are selective for local relative motion such as
that produced by moving objects or animals, and this selectivity is
produced by a double opponent process, centre-surround directionally
specific mechanism. This motion system is subsequently differentiated so
that higher order cells can perform figure/ground discrimination, or are
sensitive to moving occluding edges, or are specifically responsive to
'time to collision' with moving objects. We are currently investigating
other higher order cells in the tectofugal pathway, to determine if they
selectively respond to "Biological Motion" patterns produced by
conspecific behaviour, particularly those involved in the dynamics of
courtship displays. In contrast, the Accessory Optic System (AOS)
contains neurons responsive to large areas of optic flow, that are
implicated in the optokinetic control of eyes, head and posture, and
maybe are even involved in navigation.
Recent experiments on both the Tectofugal animate motion pathway
and the AOS self-motion pathway will be described.
Nucleus rotundus neurons that respond very selectively to looming objects
will be shown to fall neatly into three classes, one group computes rho
or rate of image expansion, another computes tau or relative rate of
expansion, and a third group computes eta, an early warning device for
approaching objects. In the AOS our recent research has shown that
translation specific neurons prefer simulated panoramic translation
flow-fields and are maximally responsive to translation along three
orthogonal axes (vestibular frame of reference) oriented 45 degrees on
either side of the midline, and vertical. The different functions these
different classes of motion neurons are performing will be discussed.