Facilitation of length discrimination using real and imaged context frames.

In the first experiment we showed that difficult length discriminations can be facilitated by imagining a visual context frame that serves to emphasize small length differences between pairs of horizontal and vertical lines. This facilitative effect of imagery cannot be attributed to response-bias or expectancy effects because we have separated the object to be imagined from the objects to be discriminated. In the second experiment we showed that real context facilitates the line-length discrimination in much the same way as imagined context does. The results from these experiments suggest that (a) functional interactions can occur between imagery and perception at feature-processing levels of the visual system, and (b) there is a functional equivalence between the imagination and perception of helpful context. Results of a third experiment suggest that although imagery and perception may be functionally equivalent at the levels of visual processing where parts of patterns are combined, they are not functionally equivalent at the lower levels of simple detection.