Effects of Progressive Removal of Distance Cues on Prey Capture Behavior in the Frog

Abstract

Frogs prey capture behavior was assessed under three conditions: preliminary, post-bilateral oculomotor nerve lesion (oculomotor-carried distance cues absent), and post-bilateral oculomotor and unilateral optic nerve lesion (binocular parallax and oculomotor-carried distance cues absent). Significant correlations were found between the response amplitudes of the pre-surgery and postbilateral oculomotor and unilateral optic nerve lesion conditions, as was the preservation of a snap/hop border across conditions, supporting the hypothesized existence of a third distance cue in anurans. Response amplitudes were significantly attenuated and snap/hop border was increased from the pre-surgery to postbilateral oculomotor and unilateral optic nerve lesion condition, supporting the theory that, under this condition, corollary discharge signals indicate that the stimulus' distance is closer than it actually is. The post-bilateral oculomotor and unilateral optic nerve lesion condition response amplitudes were unaffected by surgery for stimuli at close distances, possibly also due to the mechanism of corollary discharge signals. Snap/hop border was increased from the pre-surgery to post-bilateral oculomotor nerve lesion condition, possibly due to an interaction between the corollary discharge and binocular parallax information. It is suggested that because response amplitude continues to vary with stimulus distance, there is a separation between the mechanisms underlying response amplitude and movement character.