Cynthia P. May

DETERMINANTS OF NEGATIVE PRIMING

The negative priming task is widely used to investigate attentional inhibition. A critical review of the negative priming literature considers various parameters of the task (e.g., time course, relation to interference, level of occurence, and susceptibility to changes in task context). It takes into account life span data and the performance of patients diagnosed with schizophrenia. On these bases, the review suggests that negative priming can be produced by 2 mechanisms: memorial and inhibitory. With respect to inhibition, the review suggests that (a) there are 2 systems, one responsible for identity and the other for location information; and (b) inhibition is a flexible, postselection process operating to prevent recently rejected information from quickly regaining access to effectors, thus helping to establish coherence among selected thought and action streams.

Working memory span and the role of proactive interference.

The authors investigated the possibility that working memory span tasks are influenced by interference and that interference contributes to the correlation between span and other measures. Younger and older adults received the span task either in the standard format or one designed to reduce the impact of interference with no impact on capacity demands. Participants then read and recalled a short prose passage. Reducing the amount of interference in the span task raised span scores, replicating previous results (C. P. May, L. Hasher, & M. J. Kane, 1999). The same interference-reducing manipulations that raised span substantially altered the relation between span and prose recall. These results suggest that span is influenced by interference, that age differences in span may be due to differences in the ability to overcome interference rather than to differences in capacity, and that interference plays an important role in the relation between span and other tasks.

The role of interference in memory span

In two experiments, we investigated the possibility that susceptibility to proactive interference (PI) affects performance on memory span measures. We tested both younger and older adults (older adults were tested because of the suggestion that they are differentially susceptible to PI). We used two different span measures and manipulated testing procedures to reduce PI for these tasks. For older adults, span estimates increased with each PI-reducing manipulation; for younger adults, scores increased when multiple PI manipulations were combined or when PI-reducing manipulations were used in paradigms in which within-task PI was especially high. The findings suggest that PI critically influences span performance. We consider the possibility that interference-proneness may influence cognitive behaviors previously thought to be governed by capacity.

Synchrony effects in inhibitory control over thought and action.

Two experiments explore whether synchrony between peak circadian arousal periods and time of testing influences inhibitory efficiency for younger and older adults. Experiment 1 assesses inhibitory control over no-longer-relevant thoughts, and Experiment 2 assesses control over unwanted but strong responses, as well as performance on neuropsychological tasks that index frontal function. Inhibitory control is greatest at optimal times for both age groups and is generally greater for younger than for older adults. Performance on 2 neuropsychological measures (Stroop and Trails) also changes over the day, at least for older adults, and is correlated with inhibitory indexes, suggesting that for older adults changes in inhibition may be mediated by circadian variations in frontal functioning. By contrast, access to well-learned responses is not vulnerable to synchrony or age effects.

Optimal Time of Day and the Magnitude of Age Differences in Memory

Across two studies comparing younger and older adults, age differences in optimal performance periods were identified (Study 1), and then shown to be an important determinant of memory differences (Study 2). A norming study showed that while most younger adults were Evening or Neutral types, as determined by a standard questionnaire, the vast majority of older adults were Morning types. A second study compared the recognition performance of younger and older adults tested in the morning or in the late afternoon. Substantial age differences were found in the late afternoon, when younger but not older adults were at their optimal times. However, no age differences in memory performance were found in the morning, when older but not younger adults were at their peak period. Thus, synchrony between optimal performance periods and the time at which testing is conducted may well be a critical variable in determining group differences in intellectual performance, particularly between older and younger adults.

Synchrony effects in cognition: The costs and a benefit

The present study investigated whether younger and older adults’ ability to inhibit distractors in a problem-solving task is affected by synchrony, or the match between circadian arousal periods and time of testing. Consistent with an inhibitory-deficit explanation of synchrony effects, both age groups showed heightened susceptibility to distraction at off-peak relative to peak times. In most instances, increased sensitivity to distraction disrupted problem-solving performance; however, when distracting material was related to task goals, individuals actually benefited from reduced inhibitory efficiency. The present data are also consistent with other research in showing that access to and production of well-learned or familiar responses are not vulnerable to synchrony effects.

Implicit Memory, Age, and Time of Day

Memory retrieval can occur by at least two routes: a deliberate one, as when one attempts to retrieve an event or fact, and an unintentional one, as when ones behavior is triggered by the past without ones knowledge or awareness. We assessed the efficacy of these retrieval systems as a function of circadian arousal and time of day. Evening-type younger adults and morning-type older adults were tested at either peak (morning for old; evening for young) or off-peak times on implicit and explicit stem completion (Experiment 1) or on implicit category generation (Experiment 2). Results for explicit stem-cued recall replicated better performance for each age group at its peak time. In stark contrast, implicit performance was better at off-peak than at peak times of day, raising the possibility that the processes that serve explicit and implicit retrieval are on different circadian schedules, and highlighting the need to consider individual differences in circadian arousal when assessing either memory system.

Inhibitory control over no-longer-relevant information: Adult age differences

Hartman and Hasher (1991) used a garden-path task in which younger and older adults generated the final word for each of a series of high-cloze sentences. Under instructions to remember the final word, the experiment included critical sentences for which the generated word was replaced by a new, to-be-remembered target. Using an implicit priming task, the first experiment replicated a basic finding: Younger adults showed priming only for the target words, whereas older adults showed priming for both the generated and target words. Two experiments explored boundary conditions. One showed that an additional sentence that interpreted the new target word enabled older adults to narrow access to only the target word. The provision of additional time following the introduction of the new target word did not. Specific information, not more time, is required for inefficient inhibitory mechanisms to clear the recent past from memory.

Inhibition in the processing of garden-path sentences.

The Hartman and Hasher (1991) garden-path sentence completion task has been used in several studies to assess the efficiency of the deletion function of inhibition (e.g., L. Hasher, R. Zacks, & C. P. May, 1999 ), with results suggesting that younger adults are efficient at suppressing once relevant but no longer appropriate information, whereas older adults generally are not (e.g., M. Hartman & L. Hasher, 1991: L. Hasher. M. B. Quig, & C. P. May, 1997; C. P. May & L. Hasher, 1998). An alternative interpretation of patterns of access to relevant and no-longer-relevant sentence endings focuses on the difficulty of selecting final words for sentence frames and on integration effects in implicit memory (M. Hartman, 1995). This alternative is considered and found wanting on the basis of both new and old empirical data. On the basis of present data and related findings, it is concluded that the task does measure inhibitory efficiency.

Distractibility, circadian arousal, and aging: A boundary condition?

Two studies assessed the presence of a synchrony effect between peak circadian arousal and time of testing for both older and younger adults. Participants performed a reading aloud task that included distracting words that were either present or absent and, if present, were either thematically related or unrelated to the target text. As well, the distracting material was presented in either spatially predictable or unpredictable locations. In each experiment, older and younger adults were tested at optimal versus nonoptimal times. Both experiments showed age differences in susceptibility to distraction, replicating earlier findings (e.g., M. C. Carlson, L. Hasher, R. T. Zacks, & S. L. Connelly, 1995). Neither showed differences due to time of testing, suggesting a boundary condition for cognitive disruptions associated with circadian arousal patterns.