Using a combination of intracellular recording and computer modelling, this thesis explores the mechanisms underlying motion adaptation in identified wide-field neurons of the lobula plate of the dronefly, <I>Eristalis tenax</I>. The responses of the wide-field cells are consistent with them taking input from an array of correlation-based elementary motion detections (EMDs). The prevailing theory of fly motion adaptation proposes that adaptation shortens the delay in the EMDs, tuning the detectors to higher image velocities. Experimental evidence is presented that challenges this hypothesis. In particular, a key prediction of the theory is that the temporal frequency optimum of the wide-field cells should increase following adaptation. However, direct measurement shows little chant in the temporal or spatial frequency optima following adaptation. This demonstrates that motion adaptation does not alter the inherent velocity tuning of the elementary motion detectors. Measurements of contrast-response functions before and after adaptation provide clear evidence for at least two separate adapting mechanisms in the fly motion pathway: an antagonistic after-potential and a reduction in contrast gain. Further experiments demonstrate that these two mechanisms are recruited by different properties of the visual stimulus. The antagonist after-potential is induced by any adapting stimulus that exists the wide-field cell. The contrast gain reduction is only weakly recruited by flicker, but is strongly recruited by motion presented in <I>any</I> direction, even if that stimulus does not excite the wide-field cell.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:603754 |
| Date | January 2000 |
| Creators | Harris, R. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.002 seconds