Tracking the time course of multidimensional stimulus discrimination: Analyses of viewing patterns and processing times during "same" - different decisions

We investigated the time course of conjunctive "same''-"different'' judgements for visually presented object pairs by means of combined reaction time and on-line eye movement measurements. The analyses of viewing patterns, viewing times, and reaction times showed that participants engaged in a parallel self-terminating search for differences. In addition, the results obtained for objects differing in only one dimension suggest that processing times may depend on the relative codability of the stimulus dimensions. The results are reviewed in a broader framework in view of higher-order processes. We propose that overspecifications of colour, often found in object descriptions, may have an "early'' visual rather than a "late'' linguistic origin. In a parallel assessment of the detection materials, participants overspecified the objects' colour substantially more often than their size. We argue that referential overspecifications of colour are largely attributable to mechanisms of visual discrimination.