Hard and soft interacting dimensions: differential effects of dual context on classification.

In this article, we extend Garner's speeded classification procedure to investigate processes underlying the interaction of the auditory dimensions pitch, loudness, and timbre. In the experiments reported here, subjects classified attributes on these three auditory dimensions. Our extended procedure, called multiclass, is based conceptually on our model of how such dimensions interact; the model explains the perception of attributes from an attended dimension through the action of contextual constraints created by variation along an unattended dimension. Two forms of context are present simultaneously in each multiclass task: intraclass context, variation along the unattended dimension that interferes with the classification of attributes, and redundant context, variation along the unattended dimension that enhances classification. We find that such dual-context situations reliably distinguish two kinds of interacting dimensions. Subjects classifying hard dimensions, here pitch and timbre, resist the ill effects of intraclass context and reap gains from redundant context. Subjects classifying soft dimensions, here loudness, show interference because the attributes are veiled perceptually in dual context. These findings, we argue, demonstrate the power of the multiclass procedure and fit well our view that dimensional interaction entails processing both at the level of the stimulus whole and at the level of stimulus attributes.