  NIR velocity variations are compared with simultaneous visual light curves
for a sample of late-type semiregular variables (SRV). Precise radial velocity
measurements are also presented for the SRV V450 Aql. Our aim is to investigate
the nature of the irregular light changes found in these variables.
  Light and velocity variations are correlated in all stars of our sample.
Based on these results we discuss several possibilities to explain the observed
behavior. We find that pulsation is responsible for large amplitude variations.
In a recent paper Lebzelter (1999) invoked large convective cells to understand
observed velocity variations. This possibility is discussed with respect to the
observed correlation between light and velocity changes. In the light of these
results we investigate the origin of the semiregular variations.
