Mean percentage of correct choices made by individual pigeons during each control series.

<p>a) Coils on-off series consisting of standard sessions as well as control sessions for which half of the trials had normal current input to the magnetic coil system (solid symbols with solid lines) and the other half had no current input based on a pseudorandom schedule (solid symbols with dashes lines). b) Parallel-anti-parallel series for which sessions with current running parallel through a double-wound coil system were alternated with sessions with current running anti-parallel.