Phonologically-derived environment effects (henceforth, PDEEs) describe patterns where a phonological process P applies only if accompanied by another phonological process P’. This paper proposed that PDEEs follow from the hypothesis that the input-output distance is perceived logarithmically: this predicts that a feature change may be less salient perceptually and therefore represent a smaller violation of faithfulness if accompanied by another feature change. This theory has two desirable consequences: (i) it reconciles the analysis of PDEEs with the hypothesis of a preference for minimal input-output changes in phonological grammar and (ii) it derives a number of constraints on the features that can interact in PDEEs, therefore providing a restrictive account of the typology.