Proceedings of the Annual Meeting of the Cognitive Science Society

The role of midbrain visual centers for orienting attention was studied in chronometric experiments measuring the effect of pre-cues on simple reaction time to detect a peripheral luminance change. Two types of cues were tested: Exogenous cues—a peripheral luminance change which did not predict target location; and Endogenous cues—a central arrow vrfiich predicted the likely target location. Patients with peri-tectal midbrain degeneration from progressive supranuclear palsy showed deficits in orienting to both types of cues. In normal human subjects tested monocularly, we compared orienting into the tenporal hemifield which has more direct access to the midbrain superior colliculus) with orienting into the nasal hemifield. Exogenous cues produced equivalent speeding of detection at cued locations in both hemifields; but nasal cues produced more slowing of detection at uncued locations. Endogenous nasal cues produced earlier speeding of detection at cued locations than temporal cues; and at later intervals, they produced more slowing of detection at uncued locations. Both cortical and subcortical visual systems appear to be integrated in orienting to both exogenous and endogenous information. Whereas the subcortical pathway receives input mainly from the temporal hemifield, the cortical system is biased in orienting to the nasal hemifield; and its committment produces moreslowing of detection at unattended locations.