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Three experiments examined whether negative priming is a dually determined effect produced by inhibitory mechanisms and by a memorial process. Younger adults (Experiment 1) and older adults (Experiments 1-3) were tested in procedures that varied the likelihood of inducing retrieval of the prior trial. This was done by making test-trial target decoding difficult (Experiments 1 & 2) or by making prior information useful on some nonnegative priming trials (Experiment 3). Younger adults demonstrated negative priming under retrieval and nonretrieval conditions, with patterns of performance indicating different sources of negative priming effects. Older adults showed negative priming only under retrieval-inducing conditions, consistent with the view of deficient inhibitory mechanisms for older adults. The data suggest that contextual variables critically determine whether negative priming is largely due to inhibition or to episodic retrieval.

Two experiments to extract distractor suppression in elderly people by increasing suppression in young adults and using a longer stimulus exposure failed to produce suppression. The experiments analyzed the relationship between suppression, interference and daily cognitive failure. Older adults' inability to process distractor information does not explain the absence of suppression in them.

Two investigations established age differences in optimal performance periods when comparing younger and older adults, and proved that they significantly influence memory differences. A morning investigation revealed that most older adults were morning types, but a majority of younger adults were evening or neutral types. Another investigation compared the recognition performance of older and younger adults in the late afternoon, or in the morning. Investigations of group differences in intellectual performance, especially between younger and older adults, should match the time at which the investigation is conducted and the optimal performance periods.

Three experiments measured age differences in the increase or decrease of letter-naming suppression effects, and tested the theory that inhibition plays a crucial role in concurrent selection. Clear age differences were found in suppression, with adults exhibiting no suppression and young adults showing a consistent level of suppression over the time period measured. No reliable connection was found between suppression and interference with concurrent selection. Suppression may serve to promote coherent thought in the face of distraction, rather than to assist selection.

Two experiments assess adult age differences in the extent of inhibition or negative priming generated in a selective-attention task. Younger adults consistently demonstrated negative priming effects; they were slower to name a letter on a current trial that had served as a distractor on the previous trial relative to one that had not occurred on the previous trial. Whether or not inhibition dissipated whn the response to stimulus interval was lengthened from 500 ms in Experiment 1 to 1,200 ms in Experiment 2 depended upon whether young subjects were aware of the patterns across trial types. Older adults did not show inhibition at either interval. The age effects are interpreted within the Hasher-Zacks (1988) framework, which proposes inhibition as a central mechanism determining the contents of working memory and consequently influencing a wide array of cognitive functions.