Several studies have demonstrated disturbances of visual perception in pati
ents suffering from cerebellar disease. In an attempt to determine the caus
e of these visual disturbances and thereby the cerebellar contribution to v
ision, we designed two sets of experiments in which we tested (i) the possi
bility of a general magnocellular deficit in cerebellar disease and (ii) th
e alternative possibility of impaired spatial attention underlying visual d
isturbances in cerebellar patients. The first set of experiments consisted
of a test of position discrimination, a parvocellular function and tests ta
pping different aspects of motion perception including speed discrimination
, direction discrimination and the ability to extract a coherent motion sig
nal embedded in noise. The second set of experiments compared the performan
ce on two different classes of texture discrimination. The first one requir
ed fast and precise shifts of focal spatial attention ('serial search'), th
e second one, testing preattentive texture discrimination ('pop-out') did n
ot. In the first set of experiments cerebellar patients were impaired on th
e position discrimination task as well as several, albeit not all, tests of
motion perception. The pattern of disturbances obtained was neither compat
ible with the notion of a selective magnocellular deficit nor the idea, ori
ginally put forward by Ivry and Diener (J Cogn Neurosci 1991; 3: 355-56) th
at visual deficits are secondary to an impaired measurement of time. In the
second set of experiments, cerebellar patients showed normal performance o
n pop-out tasks and normal performance on all variants of the serial search
task except for the one requiring comparison of a single element presented
with a sample of the target in short-term memory. In summary, our results
support the existence of visual disturbances in cerebellar disease, but pro
vide evidence against a common, simple denominator such as a timing deficit
, deficient cerebellar modulation of magnocellular circuitry, deficits of s
patial attention or visual working memory.