A dotted line assimilates in visibility to a solid line.

This study tested the theory that a context-produced increase in visibility of a target is due to its assimilation in visibility to the context. A context + target and a context are discriminated better than are a target and background. This occurs for two different context + targets in which the context is a solid line and the target is a dotted line. But it does not occur when solid lines replace these dotted lines. The dotted lines are much less visible than the solid lines. Therefore, the dotted lines increase in similarity in visibility to the solid lines, which is assimilation, but for visibility, rather than for a typical part. Assimilation does not occur between perceptually equal parts. Consequently, the reason why the two context + targets with only solid lines do not result in increases in visibility may be that these lines are sufficiently equal in visibility that assimilation in visibility is precluded. So, the theory is supported. This theory is consistent with evidence that one group (phenomenal whole) is associated with both assimilation and an increase in visibility. Accordingly, a stimulus with a relatively large distance between its solid and dotted lines is apprehended as a relatively weak group, and does not result in an increase in visibility.