  While extracting the temporal dynamical features based on the time-frequency
analyses, like the reassignment and synchrosqueezing transform, attracts more
and more interest in bio-medical data analysis, we should be careful about
artifacts generated by interpolation schemes, in particular when the sampling
rate is not significantly higher than the frequency of the oscillatory
component we are interested in. In this study, we formulate the problem called
the reflection effect and provide a theoretical justification of the statement.
We also show examples in the anesthetic depth analysis with clear but
undesirable artifacts. The results show that the artifact associated with the
reflection effect exists not only theoretically but practically. Its influence
is pronounced when we apply the time-frequency analyses to extract the
time-varying dynamics hidden inside the signal. In conclusion, we have to
carefully deal with the artifact associated with the reflection effect by
choosing a proper interpolation scheme.
