Why do picture naming latencies increase with age: general slowing, greater sensitivity to interference, or task-specific deficits?

To test different hypotheses about age-related slowing of word and picture naming, response latencies of young and older adults were compared in 2 experiments using the same 4 tasks: picture naming, written word pronunciation, and picture and word categorization. In each case, the target word or picture was presented with a distractor word that had to be ignored. Analyses showed the expected main effects of age, modality, and interference conditions but no consistent interaction between age and other factors. More particularly, age-related slowing was similar in word and picture processing and interference was proportional to overall speed of responding. Thus, no support was found for the hypotheses assuming either declining inhibitory mechanisms or task-specific deficits in older adults. These results were discussed in relation to characteristics of the experimental tasks