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Abstract

It was previously shown that saccadic latency in humans can be increased by sudden changes
in luminance or orientation of a structured background. This result was led back to the limited
capacity of channels in the visuomotor pathway. We expand this finding in a series of studies
from a rather qualitative to a more quantitative result : The intervall in which a distraction
is possible is refined to lie below 14 ms SOA. Next we seek to incorporate a measure of the
strength of a distracting stimulus the increase in saccadic latency is functionally dependant
on the amount of change in background luminance. The findings from the experiments will
also be examined from the viewpoint of the LATER-model which allows a distinction between
different possible cases of latency changes based on latency distributions. In our case it points
to a difference in available visual information due to different background changes. As eye and
hand movement commands partly share a common pathway, i.e. the superior colliculus, we also
repeat the amentioned experiment with combined eye and hand movements. The result that the
latency of hand movements underlies the same functional dependance on sudden background
changes further strengthens the relation between goal-oriented behaviour by these two kinds of
actions. These results indicate that information from luminance-changes is an important factor
for the building of saliency maps, since it cannot be deliberately suppressed at critical times which demand fast and top-down modulated responses.