In previous work, we have shown that sudden image
displacements well outside the classical receptive field
modulate the visual sensitivity of LGN relay cells. Here
we report the effect of image displacements on the response
versus contrast function. The stimuli consisted
of a central spot of optimal size and polarity (contrast
range: 3–98%), flashed alone or in the presence of
a peripheral annulus (radii: 5–15 deg) containing
a low spatial-frequency grating displaced at saccade-like
velocities (shift). The most consistent effect
of the shift on the response to a central spot was to reduce
the responsiveness of Y relay cells and, to a lesser extent,
of X relay cells. The reduction in responsiveness was primarily
a divisive rather than a subtractive effect and could be
modelled by assuming that a greater contrast was required
to produce a given excitatory response. In the absence
of a central spot, remote motion had inhibitory effects
on the firing rates of the majority of relay cells, but
its effect on retinal ganglion cells was mainly excitatory.
When the shifting grating covered the classical receptive
field and its periphery, facilitatory effects
or suppressive effects, depending on the spatial phase
of the pattern, were observed in both retinal and geniculate
cells. Remote motion strongly suppresses the responsiveness
of relay cells to stimuli within the classical receptive
field. This suppressive effect involves intrageniculate
processing and is primarily associated with a reduction
in contrast gain. It is likely that shift suppression contributes
to the loss of visual sensitivity observed in saccadic
suppression.