Lynn Hasher

Working Memory, Comprehension, and Aging: A Review and a New View

Publisher Summary This chapter discusses the theoretical and empirical literature that addresses aging and discourse comprehension. A series of five studies guided by a particular working memory viewpoint regarding the formation of inferences during discourse processing is described in the chapter. Compensatory strategies may be used with different degrees of likelihood across the life span largely as a function of efficiency with which inhibitory mechanisms function because these largely determine the facility with which memory can be searched. The consequences for discourse comprehension in particular may be profound because the establishment of a coherent representation of a message hinges on the timely retrieval of information necessary to establish coreference among certain critical ideas. Discourse comprehension is an ideal domain for assessing limited capacity frameworks because most models of discourse processing assume that multiple components, demanding substantially different levels of cognitive resources, are involved. For example, access to a lexical representation from either a visual array or an auditory message is virtually capacity free.

Automatic Processing of Fundamental Information The Case of Frequency of Occurrence

One view of memory supposes that several fundamental aspects of experience are stored in memory by an implicit or automatic encoding process. In this article we review the evidence that suggests that information about frequency of occur- rence is encoded in such a manner. This evidence shows that frequency information is stored for a wide variety of naturally occurring events. Laboratory research shows that usually powerful task variables (for example, instructions, practice) and subject vari- ables (for example, age, ability) do not influence the encoding process. Evidence is also reviewed that either directly or indirectly implicates the use of frequency information across issues in psychology ranging from the acquisition and representation of knowledge domains to decision making to sex role development.

Age and Inhibition

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 when 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.

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.

Age and Reading: The Impact of Distraction

Older and younger adults read aloud and answered questions about texts that did or did not have distracting material interspersed amid target text. When present, distracting material occurred in a different type font from that of target material. Across 2 experiments, distracting material was meaningless, meaningful but unrelated to the text, or meaningful and text related. Subjects were instructed to attend only to the target text. Reading time measures indicated that compared with younger adults, older adults have a more difficult time ignoring the distracting information, particularly information meaningfully related to target text. Verbal ability differences among older, but not younger, adults moderated distraction effects. Age differences in inhibitory attentional mechanisms were considered as processes influencing distraction effects.

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.

Frequency and the conference of referential validity.

Subjects rated how certain they were that each of 60 statements was true or false. The statements were sampled from areas of knowledge including politics, sports, and the arts, and were plausible but unlikely to be specifically known by most college students. Subjects gave ratings on three successive occasions at 2-week intervals. Embedded in the list were a critical set of statements that were either repeated across the sessions or were not repeated. For both true and false statements, there was a significant increase in the validity judgments for the repeated statements and no change in the validity judgments for the non-repeated statements. Frequency of occurrence is apparently a criterion used to establish the referential validity of plausible statements.

STUDIES OF DIRECTED FORGETTING IN OLDER ADULTS

Younger and older adults were compared in 4 directed forgetting experiments. These varied in the use of categorized versus unrelated word lists and in the use of item by item versus blocked remember-forget cueing procedures. Consistent with L. Hasher and R. T. Zackss (1988) hypothesis of impaired inhibitory mechanisms in older adults, a variety of findings indicated that this age group is less able than younger adults to suppress the processing and retrieval of items designated as to be forgotten (TBF). Specifically, in comparison with younger adults, older adults produced more TBF word intrusions on an immediate recall test (Experiments 1A and 1B), took longer to reject TBF items (relative to a neutral baseline) on an immediate recognition test (Experiment 3), and recalled (Experiments 1A, 1B, and 2) and recognized (Experiment 1B and 2) relatively more TBF items on delayed retention tests in which all studied items were designated as targets.

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.