The visual-response properties of single cells in the cat's superior colliculus and parabigeminal nucleus were compared. In the colliculus, 151 cells (restricted to the upper layer) were studied, and in the parabigeminal nucleus, 134 cells. 2. Response characteristics in the two structures were similar in many respects: among these were receptive-field size, ocular dominance, and lack of specificity for stimulus shape and contrast (light versus dark). 3. Quantitatively, there were some significant differences between the two populations of cells. Parabigeminal neurons tended to respond more brisky and reliably, while being less selective for those stimulus parameters tested (size, velocity, and direction of movement). Spontaneous activity was much higher in the parabigeminal nucleus than in the colliculus. Finally, parabigeminal cell responses to stationary stimuli were somewhat brisker than those of tectal cells. 4. These data suggest that a physiologically distinct population of tectal cells sends input to the parabigeminal nucleus, probably with some convergence on individual cells.
