To: CVNetList@skivs.ski.org
Subject: Inquiry on OSPs
From: Ted Bullock tbullock@ucsd.edu
I wonder if someone has observed something like the following, or can send
me to relevant literature.
It concerns a kind of OFF response, what we call the Omitted Stimulus
Potential (OSP).
A considerable literature on human scalp-recorded ERPs to attended missing
stimuli (clicks or flashes) in series of regular stimuli with ISI
(interstimulus intervals) of 0.6 - 3 s led us to look in nonmammalian taxa
and lower brain levels. We found robust OSPs to omitted flashes, first in
the optic tectum, then in the retina and forebrain in elasmobranchs (rays)
and reptiles (turtles), without controlled attention, at ISIs of anything
less than ca. 500 ms. Since the OSPs have components out to >1000 ms, we
usually omit several stimuli or simply terminate a train.
A feature of special interest is that OSPs have a nearly fixed latency, if
measured after the due-time of the missing stimulus - suggesting a kind of
temporally specific expectation. This is already conspicuous in recordings
from the opened eye cup or optic nerve head, after cutting the optic nerve.
The fixed latency (ca.90 ms) applies to the early, fast peak; thereafter
slower waves and a ca.20 Hz oscillation last for most of a second or more.
(See Bullock et al., J.Neurophysiol., 64:903-914, 1990; ibid.,
J.Comp.Physiol., A172:501-510, 1993; Karamuersel & Bullock, EEG
Clin.Neurophysiol. 90:461-471, 1994; Prechtl & Bullock, loc.cit., 91:54-66,
1994; Hofmann & Bullock, Soc. Ns. Abstr 21:653, 1995). We proposed a very
simple qualitative model.
Is this kind of "apparent expectation" predicted by any of
the retinal models? Have others noticed OFF effects at the end of trains
that might have these properties - whether retinal or higher; whether visual
or in other modalities?
Ted Bullock, U.C.S.D., La Jolla, CA 92093-0201; fax: 619-534-3919