Learned perceptual associations influence visuomotor programming under limited conditions: cues as surface patterns.

The present set of three experiments was designed to extend the findings that visuomotor programming can make use of learned size information under some, but not all, conditions. An association was established between the size of square wooden blocks and a perceptual cue in all experiments. In Experiment 1 the perceptual cue to size was a small two-dimensional drawing of a shape affixed to the top of the blocks (e.g. triangle = large; circle = small, or vice versa). In Experiment 2 size and shape were again associated but this time a pattern of two-dimensional shapes covered the visible surface of the blocks. In Experiment 3 block size was associated with the colour of a small circle affixed to the top of the blocks (e.g. red = large; yellow = small, or vice versa). All of the subjects grasped the blocks, and on other trials estimated the size of the blocks by opening their thumb and finger a matching amount. Consistent with previous reports, in all experiments, the learned associations changed the perceived size of two test blocks halfway in size between the large and small blocks: estimations of the test block matched by shape or colour to the group of large objects were smaller than estimations of the test block matched to the group of small objects. The effect appears to result from relative-size comparisons being made between the medium-sized test blocks and the size category (large or small) associated with the matching shape or colour cue. Despite the significant effect of the learned perceptual associations on manual estimations, no effect on grip scaling was seen when the cues associated with size were single small elements centred on the top of the block (Experiment 1 and Experiment 3). Changes in grip scaling corresponded to the change in perceived size only when the cue to size covered the entire block (Experiment 2), forming a surface pattern. These findings suggest that visuomotor programming is more likely to use learned size information when the cue providing the size association covers the visible surface of the target objects, perhaps by acting as a texture that provides reliable information about the target's material and identity.