Arrays with horizontal or vertical texture boundaries formed by element orientation and length cues were displayed, and the texture boundary formed by one cue was specified as the target. The boundaries formed by the two cues were coincident on some trials and orthogonal on others. Observers' accuracy in reporting the orientation of the target boundary was improved by a coincident nontarget boundary and was worsened by an orthogonal one. Conditional mutual information measures are used to show how effects due to contextual modulation can be distinguished from effects due to additive combination of the cues. The results of five experiments are interpreted as evidence that the transmission of information about specific texture boundary cues is modulated by task context but not by a coincident or orthogonal boundary in another cue. We therefore distinguish between the effects of "context," as shown by the effects of any variable not called the target, and "modulatory contextual effects," as shown by the effects of one variable on the transmission of information specifically about another.