The sudden displacement of the retinal image during
a saccade raises the visual threshold of human observers
to foveal stimuli. The fall in visual sensitivity observed
during this phenomenon, known as saccadic suppression,
seems to occur very early in the visual processing chain.
The lateral geniculate nucleus (LGN) is a likely locus
for the multiple retinal and extraretinal interactions
occurring during saccadic eye movements, therefore we used
the responses of relay cells of adult cats to simulate
a pychophysical experiment. We first measured the responses
of X and Y relay cells (27 X and 13 Y) to central spots
of optimal size and different contrasts. The spots were
presented either alone or time locked with the rapid movement
of a large, high-contrast peripheral pattern, referred
to as shift. We measured the percentage of trials
on which the relay cell fired more spikes when the spot
(contrast: 0.03–1.0) was present than when it was
absent. In experiments with human observers the task was
to indicate, by a keypress, which of two otherwise identical
temporal intervals contained the spot. The shift reduces
the sensitivity (raises the contrast threshold) of neurones
in the cat relay cells to brief, stationary targets presented
to the receptive-field center. The suppression of visual
sensitivity is significantly greater in Y cells than in
X cells (average sensitivity ratios 5.6 ± 5.4 in
Y cells, 1.59 ± 0.9 in X cells: P <
0.001, U test). The shift also reduces the sensitivity
of human observers to the same target. This suggests that
the LGN is a potential locus for the modulation of visual
responses that leads to saccadic suppression.