Lesion or inactivation of the superior colliculus (SC) of the cat
results in an animal that fails to orient toward peripheral visual
stimuli which normally evoke a brisk, reflexive orienting response. A
failure to orient toward a visual stimulus could be the result of a
sensory impairment (a failure to detect the visual stimulus) or a motor
impairment (an inability to generate the orienting response). Either
mechanism could explain the deficit observed during SC inactivation
since neurons in the SC can carry visual sensory signals as well as
motor commands involved in the generation of head and eye movements. We
investigated the effects of SC inactivation in the cat in two ways.
First, we tested cats in a visual detection task that required the
animals to press a central, stationary foot pedal to indicate detection
of a peripheral visual stimulus. Such a motor response does not involve
any components of the orienting response and is unlikely to depend on
SC motor commands. A deficit in this task would indicate that the SC
plays an important role in the detection of visual targets even in a
task that does not require visual orienting. Second, to further
investigate the visual orienting deficit observed during SC
inactivation and to make direct comparisons between detection and
orienting performance, we tested cats in a standard perimetry paradigm.
Performance in both tasks was tested following focal inactivation of
the SC with microinjections of muscimol at various depths and
rostral/caudal locations throughout the SC. Our results reveal a
dramatic deficit in both the visual detection task and the visual
orienting task following inactivation of the SC with muscimol.