Context dependent responses to moving objects.

The courses of N responses to a respective stimulus sequence are visualized for selected neurons by normalized instantaneous interspike intervals (norm. ISI), averaged across trials when N > 1. For a TB1 neuron, raster plots were preferred. Values of 0 or 1 indicate highest consistency in response course across trials. A-A'''. Each subplot represents N responses to a specific stimulus sequence, obtained from cells identified by capital letters within each cell type (compare to subfigure B). A-A'': Horizontal trajectories; forward (f) or backward (b) motion at high (H) or low (L) elevation. In A'', the third and fourth stimulus consist of two objects that move in the same direction but at different elevations. A''', Responses to upward (u) and downward (d) motion along vertical trajectories at different azimuths (-38°, 7.5° and 54°). Here, the transitions from d to u' and d' to u'' correspond to switches in the azimuth of the trajectory, whereas the particular sequence of azimuths was randomized in each trial. As a consequence, the lower subplot shows data pooled across 3 different chronological orders of azimuths. For both vertical and horizontal trajectories, it is the switch in trajectory that triggers responses, not the particular position of the trajectory or changes of the direction of motion. Bars, 1 s. B. Responses of the same types of neuron are also suited to detect a distinct object that changes its direction of motion (pop out) against a moving background of identical and very similar objects. For detailed description of the stimulus sequence, see Fig 2.