Superior colliculus and visual neglect in rat and hamster. III. Functional implications.

In comparison with the geniculostriate pathway, the retinotectal projection in rat and hamsters appears to emphasize information concerning localized transient stimuli, particularly in the periphery of the visual field. An important question is whether the superior colliculus merely relays this information elsewhere, or instead takes part in its analysis. This question is broken down into two parts. First, what decisions do rats and hamsters have to take concerning localized transient visual stimuli in the periphery? It is suggested that the following decisions are taken: (a) does the stimulus require any response? If the transient is self-produced, or is known on the basis of past experience to predict no important consequence, then it may be ignored; and (b) does the stimulus convey enough information to determine a response, either unlearnt (e.g. attack, flee, freeze) or learnt? If the stimulus appears to warrant some response, but it is not clear which, then it requires investigation. Second, what evidence is there that the superior colliculus participates in any of these decisions? It is argued on general grounds that the involvement of the superior colliculus in investigative orienting necessitates its knowing about the other decisions, since a useful orienting device cannot respond promiscuously to uninteresting or dangerous stimuli. This argument is supported by evidence from stimulation and recording studies, which in addition suggest that the superior colliculus is directly involved in producing a number of responses appropriate to peripheral transients, besides orienting. Thus, one function of the superior colliculus may be to help analyze and take decisions about localized transients in the periphery of the field.(ABSTRACT TRUNCATED AT 250 WORDS)