Figure 1.

Apparatus used in expectancy-violation experiments. Not drawn to scale. Side Walls, Front Wall, Ceiling and Pan not shown. Beginning of trial: test spider (Portia africana) walks out of Pit and on to top of Starting Tower. Test spiders complete successful trials by proceeding from Starting Tower along Pathway to top of Viewing Tower. Thin arrows indicate path test spider takes to reach lures; dotted arrow indicates path test spider takes to opt out of completing detour. Inset: example of a Scene with four lures visible to test spider from Starting or Viewing Tower. Cable-release device moves Scene up and down once every 30 s while the test spider is on top of Starting Tower and while test spider is on top of Viewing Tower. When test spider arrives at Island, Scene is removed and then replaced by a different Scene or else the previous Scene is returned.