Protocol and average tuning curves for adaptation-induced plasticity of orientation tuning. (A) Schematic representation of the adaptation protocol. Responses to a sine-wave drifting grating presented to multi-unit receptive fields were measured for 25 trials of 4.1 s. Nine oriented stimuli presented in random order were tested, covering 180° (22.5° interval). The manually determined preferred orientation was used as the middle value of the test orientation range. Orientation tuning curves were measured before and after adaptation (12 min) to a non-preferred stimulus 22.5° to 67.5° off the control preferred orientation. Following a recovery period of 60-90 min, orientation tuning curves were measured once again. (B) Average orientation-tuning curves for cells displaying attractive and repulsive shifts. All parameters (shift amplitude, response rate and bandwidth) were averaged from the population of the present investigation (n = 105). Color code - gray: control, blue: post-adaptation for attractive shifts, red: post-adaptation for repulsive shifts. Downward triangles indicate the adapting orientation. For attractive shifts, there is response facilitation at the adapted flank, which includes the adapting orientation, and response depression at the opposite flank. For repulsive shifts, there is solely response depression at the adapted flank.