Is retrieval-induced forgetting an inhibitory process?

Three experiments investigated memory performance in the retrieval practice paradigm (Anderson, Bjork, & Bjork, 1994; Anderson & Spellman, 1995). This paradigm produces a retrieval-induced forgetting effect, wherein practicing some members of a studied category decreases the recall of other members of that category relative to a baseline. Our findings indicate that the retrieval-induced forgetting effect is replicable but that previous findings supporting an inhibitory account of this phenomenon may not be.

A limit on retrieval-induced forgetting.

Retrieving some members of a memory set impairs later recall of semantically related but not unrelated members (M. C. Anderson, R. A. Bjork, & E. L. Bjork, 1994; M. C. Anderson & B. A. Spellman, 1995). The authors investigated whether this retrieval-induced forgetting effect would generalize to testing procedures other than category-cued recall. Although the authors demonstrated a retrieval-induced forgetting effect using a category-cued recall task, they failed to show retrieval-induced forgetting on several different memory tests that used item-specific cues, including a category-plus-stem-cued recall test, a category-plus-fragment-cued recall test, a fragment-cued recall test, and a fragment completion task.

Timing, instructions, and inhibitory control: some missing factors in the age and memory debate.

In response to Luszcz and Bryan, we point to three omitted factors that have been found to influence the presence and size of age differences in memory tasks and that, as such, have important implications for resolving theoretical questions about aging and memory. These include: (1) age differences in circadian rhythms and testing time effects that are associated with such differences; (2) instructions that may have a particularly disruptive effect on older adults, and (3) inhibitory control differences that have an age-related impact on both estimates of working memory span and on performance in multitask studies.

Suppression of reflexive saccades in younger and older adults: age comparisons on an antisaccade task.

Inhibitory control of prepotent responses has been examined by using the antisaccade task, during which a reflexive saccade toward a peripheral onset must be suppressed before an eye movement in the opposite direction from the onset can be executed. In the present experiments, we sought to determine whether older and younger adults would perform similarly on this task. Older adults had a harder time suppressing their reflexive responses, as measured by an increase in the proportion of saccade direction errors. Despite an age-related decline in saccade direction accuracy, the increase in saccade latency associated with the antisaccade condition was the same for both younger and older adults. These results support the view that the effectiveness of inhibitory control declines with age (Hasher & Zacks, 1988; Hasher, Zacks, & May, 1999).

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.

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. Zacks's (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.

On the time course of negative priming: Another look.

In two experiments, the pattern of persistence of negative priming effects across delay intervals of 500 and 2,500 msec was assessed using a within-subjects, random sequencing of delays. Neill and Valdes (1992; Neill, Valdes, Terry, & Gorfein, 1992) have argued that a within-subject experimental design is required for decay of negative priming to be seen, in contrast to results reported elsewhere (e.g., Tipper, Weaver, Cameron, Brehaut, & Bastedo, 1991) showing stable negative priming effects across delays. In neither experiment was substantial evidence of decay detected, raising questions for the notion that suppression necessarily declines across brief temporal intervals and for the assertion that episodic retrieval is the sole source of negative priming.

Aging, distraction, and the benefits of predictable location.

Three experiments examined the impact on reading time for younger and older adults in the absence vs. presence of distraction (marked by font type) in either fixed predictable locations (Experiments 1 and 2) or unpredictable locations (Experiment 3). Consistent with earlier work (S. L. Connelly, L. Hasher, & R. T. Zacks, 1991), older adults were markedly disrupted, relative to young adults, when distraction was present in unpredictable locations. When the location of distraction was fixed, however, the very large disadvantage that older adults otherwise experienced (slowed by as much as 46 s) diminished substantially (to as little as 2 s). Fixed location also eliminated the relatedness effect, by which older adults are especially susceptible to distraction from meaningfully related material.

Inhibitory attentional mechanisms and aging.

Two experiments sought to elicit distractor suppression in older adults. Experiment 1 used a procedure that increased suppression in younger adults, thus creating a more sensitive measure of suppression in older adults. To compensate for older adults' slowed processing, Experiment 2 used a longer stimulus exposure duration. Neither experiment produced suppression in older adults; both experiments, however, included trial types that elicited parallel facilitatory effects for both age groups. Older adults thus seemed to process distractors but failed to engage inhibitory mechanisms in their rejection of distracting stimuli. Finally, both experiments tested the relationships among suppression, interference, and everyday cognitive failure. Neither experiment suggested relationships between reaction time effects and self-reported cognitive lapses. Results are discussed within L. Hasher and R. T. Zacks's (1988) attentional framework.

Visual search times assessed without reaction times: a new method and an application to aging.

We consider several ways in which the interpretation of reaction time (RT) data might confound differences in visual search rates with non-search-related factors. To determine whether estimates of search rates for groups differing in age suffered this problem, we compared estimates provided by the RT method with those obtained using a forced-choice method with limited-duration stimuli. The forced-choice method provided faster estimates of search rates. The effects of age, the variable in which we were interested, were comparable, but the difference between results obtained using the two methods suggests the need for caution in using the RT method. We discuss how the forced-choice method can be used, under appropriate circumstances, to provide an independent test of whether subjects are carrying out serial searches and, if they are, to provide search rate estimates even from data obtained using only a single array size.

Investigations of inhibition and interference in younger and older adults.

Previous work (Hasher, Stoltzfus, Zacks, & Rypma, 1991) suggested the existence of adult age-related differences in the ability to suppress or inhibit irrelevant information. This investigation explored age differences in the time course of suppression. Experiments 1 and 2 showed that younger adults demonstrate the same level of suppression at 300 as they do at 1,700 ms after a selection response. Older adults consistently show no suppression. Experiments 2 and 3 also examined the relationship between suppression and the degree to which distractors interfere with concurrent selection. The absence of a reliable relationship--both within and across age groups--together with other findings in the literature, raise questions about the function of suppression as a mechanism of concurrent selection. Another function, one that aids in the establishment of a coherent thought stream, is proposed.

Mental model organization.

Previous research (Radvansky & Zacks, 1991) has shown that the fan effect is mediated not by the number of nominal associations paired with a concept but by the number of mental models into which related concepts are organized. Specifically, newly learned "facts" about different objects in one location are integrated into a single mental model and no fan effect is produced, whereas facts about one object in different locations are not integrated and a fan effect is produced. In 6 experiments we investigated several factors' influence on location-based organization preferences. We found no impact of either article type (definite or indefinite) or object transportability. However, animate sentence subjects (people) reduced preference for location-based organizations. A clear person-based organization emerged by using locations that typically contain only a single person (e.g., phone booth) to make location-based situations less plausible.

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.

Mental models and the fan effect.

Explanations of data from fan effect experiments have been based on propositional network models. This article presents findings not readily predicted by such models. In particular, in three experiments we found that, during a speeded-recognition test, subjects retrieved facts about several objects associated with a single location faster than facts about several locations associated with a single object. Indeed, there was no fan effect in the former case despite the fact that there were an equivalent number of associations among concepts in both conditions. We suggest that such data are consistent with a mental model representational account.

Age deficits in retrieval: the fan effect.

The fan effect paradigm was used to investigate age-related changes in the effects of different levels of interference on retrieval. Younger and older adults learned a list of person-activity "facts" in which each person and each activity occurred in 1, 2, or 3 different facts (fan level). A subsequent speeded recognition test required the participants to distinguish the learned facts from foils constructed by recombining the same concepts. On this recognition test, both groups showed an increase in response time and errors as the fan level of the probe increased. For older adults these effects were larger, however, indicating an age-related increase in interference effects in retrieval. These results are consistent with a theoretical framework (Hasher & Zacks, 1988) which proposes an age-related decline in the ability to screen irrelevant information out of working memory. The findings also have implications for age differences in discourse processing and other cognitive tasks that crucially depend on the timely and accurate retrieval of stored information.

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.

Younger and older adults' use of mental models as representations for text materials.

Recent work suggests that formation and use of mental model (representations of situations described) is an integral part of discourse comprehension. In an experiment comparing younger and older adults on this aspect of text comprehension, subjects heard readings of a list of sentences and took a forced-choice recognition test. The test contained 2 types of distractors with an equal degree of verbatim similarity to the target sentences. One type described the same situation as the corresponding target sentence; the other did not. If mental models are an integral part of text representation formed at encoding, then a large number of confusions of the first, but not the second, type of distractor with the target sentence would be obtained. Younger and older adults showed this pattern to equal degrees. These data are consistent with those indicating that linguistic competence remains stable over the adult years (cf. Light, 1988).

Encoding and memory of explicit and implicit information.

The usefulness of a general capacity model for predicting age differences in memory for critical information in text was assessed. Passages that either explicitly stated or implied, in either a predictable or unpredictable manner, a fact central to understanding were read to study participants. No age differences were obtained in the recall of explicit central facts, but the younger adults outperformed the older adults when these facts had to be inferred. A revised capacity model, which implicates encoding processes in the breakdown of inference formation, is outlined to account for these and other data.

Truly incidental encoding of frequency information.

Four experiments demonstrated that adults can reliably remember frequency of occurrence information about items they have been exposed to under truly incidental memory conditions. Subjects neither knew that the ultimate test task would concern item frequency nor that they had any reason to remember the items. This was accomplished by presenting items under the guise of one of three cover tasks: anagram solving, sentence completion, and picture naming in a Stroop-like task. In addition, one experiment found that subjects who were prewarned for either a nonspecific memory test or a frequency test were no better able to judge frequency than were subjects operating under truly incidental conditions.