Fig 7.

Log initial-link response ratios (standard/variable) across successive 12ths of the session for individual pigeons, shown separately for sessions in which the variable terminal-link schedule was 16 s (circles) and 4 s (triangles). Data from control sessions are shown by open symbols, and data from sessions following administration of 1.7 mg/kg (or 1.0 mg/kg for Pigeons 107 and 228) d-amphetamine are shown by filled symbols. Data points are means; error bars around the points for control show ± 1 SD. Missing points for Pigeons 225 and 228 at 12 on the x axis are from conditions in which these birds did not finish one or more of the sessions at this dose.