How shared are age-related influences on cognitive and noncognitive variables?

Several theories have suggested that age-related declines in cognitive processing are due to a pervasive unitary mechanism, such as a decline in processing speed. Structural equation model tests have shown some support for such common factor explanations. These results, however, may not be as conclusive as previously claimed. A further analysis of 4 cross-sectional data sets described in Salthouse, Hambrick, and McGuthry (1998) and Salthouse and Czaja (2000) found that although the best fitting model included a common factor in 3 of the data sets, additional direct age paths were significant, indicating the presence of specific age effects. For the remaining data set, a factor-specific model fit at least as well as the best fitting common factor model. Three simulated data sets with known structure were then tested with a sequence of structural equation models. Common factor models could not always be falsified--even when they were false. In contrast, factor-specific models were more easily falsified when the true model included a unitary common factor. These results suggest that it is premature to conclude that all age-related cognitive declines are due to a single mechanism. Common factor models may be particularly difficult to falsify with current analytic procedures.

Misguided multiplication: creating false memories with numbers rather than words.

We built Deese (1959)/Roediger and McDermott (1995) (DRM) false memory lists composed of multiplication problems rather than words. Half these lists contained table-related, near neighbors (e.g., 3 x 7 = ??, 3 x 9 = ??) of a missing multiplication answer lure (e.g., 24). The other half contained problems unrelated to the lure (e.g., 5 x 5 = ??, 11 x 3 = ??). Participants solved each problem in a single list and then took immediate recognition (Experiment 1) or recall and then recognition tests (Experiment 2) for the answers. Many people misremembered that the lure was an answer to a study-phase problem, but only when solving the study list that contained the lure's neighbors. False memory was also greater for some list-lure combinations than others, as seen previously with words. We have thus demonstrated that numbers can also produce false memory, and we use the mental math and DRM task literatures to explain these results.

Diagnosing fictional diseases: age and variability of training content in concept formation.

This experiment had two purposes: investigation of the effect of variability in the content used during training on concept learning, retention, and transfer and the extent to which this training manipulation interacts with age. Participants were 27 older adults (M = 68.2 yr., SD = 7.4) and 54 younger adults (M = 20.6 yr., SD = 4.0) who were asked to learn an imaginary disease by reviewing the symptoms of fictional patients. Participants were assigned to one of two variability groups in training, which were defined by how much patient cases resembled each other. Dependent measures were classification accuracy over eight blocks of training, followed by retention and transfer ("diagnosing new patients") two days later. Analysis of variance yielded only one significant interaction of age and training variability (on retention), but none of the paired comparisons were significantly different. There were no main effects of training group on any dependent variable.

Are emotionally charged lures immune to false memory?

Using the Deese-Roediger-McDermott task and E. Tulving's (1985) remember-know judgments for recognition memory, the authors explored whether emotional words can show the false memory effect. Participants studied lists containing nonemotional, orthographic associates (e.g., cape, tape, ripe; part, perk, dark) of either emotional (e.g., rape) or nonemotional (e.g., park) critical lures. This setup produced significant false "remembering" of emotional lures, even though initially no emotional words appeared at study. When 3 emotional nonlure words appeared at study, emotional-lure false recognition more than doubled. However, when these 3 study words also appeared on the recognition test, false memory for the emotional lures was reduced. Across experiments, participants misremembered nonemotional lures more often than they did emotional lures, but they were more likely to rate emotional lures as "remembered," once they had been recognized as "old." The authors discuss findings in light of J. J. Freyd and D. H. Gleave's (1996) criticisms of this task.

Aging and negative priming: is ignored information inhibited or remembered?

We had younger and older adults complete two tasks that tested the attentional- and memory-based inhibition models of negative priming. One task violated May, Kane, & Hasher (1995, Psychological Bulletin, 118, 35-54) criteria for measuring just attentional inhibition, by including a repeated-target condition. The other task complied with these criteria and included a depth of processing manipulation, where participants selected prime targets based either on their letter-length (nonsemantic processing) or weight (semantic processing). On balance, results supported the memory model, because depth of processing clearly moderated younger adult negative priming, and older adults displayed negative priming only in the task satisfying the attentional-inhibition criteria (i.e., the depth of processing task). We conclude that memory factors moderate negative priming, and that May et al.'s criteria fail to predict when older adults will show the effect.

A beautiful day in the neighborhood: what factors determine the generation effect for simple multiplication problems?

In four experiments, we examined the generation effect for the free recall of simple multiplication answers. Large-product-size problems showed a consistent generation-effect advantage over small-product-size problems, except when each answer was generated twice, via two different sets of operands (Experiment 2). Also, measures of problem-solution time and strategy use accounted for the large-product-size advantage. Across experiments, however, small-product-size problems (but not large-product-size problems) showed considerable variation in the size of their generation effect. We discovered that solving small-product-size problems via direct memory retrieval increased the episodic recall probability of other problems that were near neighbors to the generated answer, and we attribute this result to a spreading activation mechanism in semantic memory. A measure of neighbor activations, combined with RT to solve each problem, accounted for 51% of the observed generation-effect variance.

Older adults' strategic superiority with mental multiplication: a generation effect assessment.

Recent studies suggest that older adults' simple arithmetic fact knowledge may be superior to that of college students, as evidenced by the older adults' more frequent use of direct memory retrieval (versus computation) as an answer generation mechanism. Whereas previous studies assessed strategy selection via self-report and/or reaction time, we have adopted the "generation effect" paradigm-better memory for items that are subject-generated versus those that are simply read. The memorial advantage of generation depends in part on the degree of effort involved in generating versus reading an item. Because direct retrieval is less effortful than computation, we expected qualitative age differences in answer generation strategies to manifest themselves as age differences in the magnitude of the generation effect, especially for problems with larger answers. With simple multiplication problem materials, the expected Age x Problem Size interaction was found. In a verbal materials comparison condition, the size of the generation effect did not differ across adult age.

Adult age comparisons in the processing of event frequency information.

The usual superiority in frequency-of-occurrence judgments of younger vs. older subjects was hypothesized to result from greater strategic encoding of the materials conveying frequency information. A subject-paced, visual search task was designed to control nontarget word encoding. Relative frequency judgments for the nontarget word pairs were equally accurate for younger and older subjects, and performance of both groups was above chance. Results suggest that strategic cover-task encoding can induce age differences in incidental frequency processing. Consistent with a nonoptimal as opposed to an optimal view, automatic processes require only minimal capacity for above-chance performance, but additional strategic resources can increase performance. When such additional resources are used more by younger than by older subjects, the former are better in frequency performance.

Metamemory in older adults: the role of monitoring in serial recall.

Older and younger adults were asked to think aloud while studying sets of pictures matched in difficulty for immediate serial recall. When instructed only to remember, young adults tended to study longer, rehearse more, and recall better than did older adults on the most difficult lists. Young adults were also much more likely to spontaneously test themselves during study in the most difficult condition. Older adult groups instructed either to study longer or to self-test, both showed improved recall. Only the older adults who had been instructed to self-monitor, however, recalled better on tests of short-term maintenance and generalization; overt rehearsal data showed that these older adults continued to test themselves. Metamemory deficits may be present with older adults when a strategy, like self-testing, is needed to generate metamemorial knowledge. Strategies such as self-testing can be easily taught, however, and they hold promise of being useful across situations.

Training older adult free recall rehearsal strategies.

Three groups of older adults (mean age 72.1 years) were compared on a free recall task with categorizable lists. The nine females and two males in each group were instructed to rehearse overtly while studying. A group instructed to rehearse by category showed higher levels of free recall and category organization than either a control group instructed only to remember or a group instructed to rehearse actively at study. Strategy instructed subjects' rehearsal was organized serially early in a list and then categorically organized for the remainder of a list. Activity instructed subjects showed a high number of same-item repetitions but adopted no clear pattern of strategic category rehearsal. Control subjects' rehearsal was essentially inactive and nonstrategic, mainly consisting of single mentions of each list item and an associate. These data show that older adults' memory performance is modifiable and that efficient performance is obtained when instructional training is aimed at the processes that are crucial to task performance. Direct strategy measures, such as those used as here, yield important information about the processes underlying age differences in memory and can aid greatly in the design of training aimed at exploring older adult potential.

Metamemory in the aged.

College age (mean age 20 years) and older adults (mean age 69 years) were asked to predict their memory spans and to indicate readiness to recall sets of line drawings in Experiment 1. Although no age differences were found in span prediction accuracy, clear differences were obtained in recall readiness. When given unlimited study time with sets of items matched in difficulty, young adults chose to study longer and then recalled more accurately than did older adults. In Experiment 2 the recall of a chunking and rehearsal trained group of older adults was better than that of a control group given standard instructions. However, the best recall was obtained in a group required to take extra study time but given no strategy training. The older adult recall readiness deficit may thus not have been due to lack of available memory strategies. Instead, we hypothesize that older adults may have failed to monitor their readiness to recall so that they did not know how long to study.

Age differences in free recall rehearsal strategies.

Younger (mean age = 23.9 years) and older (mean age = 73.9 years) adults were compared on a free recall task with lists of categorizable words. One-half of the subjects were given instructions to rehearse overtly during list study, and the remainder received standard (covert) instructions. Relative to covert rehearsal, overt rehearsal did not appear to affect the type of study strategy used by subjects. Age differences in free recall and category clustering were found, paralleled by clear age differences in rehearsal strategies. Young adults' rehearsal was active, serially organized early in a list, and then categorically organized for the rest of a list. Older adults' rehearsal was inactive and essentially nonstrategic, consisting mostly of single mentions of each list item. These results also show that direct strategy measures provide more information about the processes underlying age differences in memory than do outcome measures alone.

Host-Symbiont Interactions: III. Purification and Partial Characterization of Rhizobium Lipopolysaccharides.

The lipopolysaccharides of three strains each of Rhizobium leguminosarum, R. phaseoli, and trifolii have been purified and partially characterized. The last step in the purification procedure is gel filtration column chromatography using Sepharose 4B with an elution buffer consisting of ethylenediaminetetraacetic acid and triethylamine. Each of the lipopolysaccharides reported in this paper elutes as a symmetrical peak in the partially included volume of this Sepharose 4B column. The ratio of 2-keto-3-deoxyoctonate acid (a sugar which is characteristic of lipopolysaccharides) to hexose is constant throughout the carbohydrate-containing peaks as they elute from the Sepharose 4B. The compositions and immunodominant structures of the purified lipopolysaccharides vary as much among strains of a single Rhizobium species as among the different species of Rhizobium. There is no obvious correlation between the nodulation group to which a Rhizobium belongs and the chemical composition or immunochemistry of the Rhizobium's lipopolysaccharide. There is extensive crosslysis by phage of strains of R. trifolii, R. phaseoli, and R. leguminosarum. This suggests that the receptors for these cross-lysing phage reside either in nonlipopolysaccharide structures or in common structures within the lipopolysaccharide which are not detected by compositional or immunochemical analysis.

Long-term durability and transfer of enhanced conceptual performance in the elderly.

To evaluate the durability and transfer of enhanced cognitive functioning in the elderly, subjects (ages 64 to 84) who had previously participated in a unidimensional concept identification study were tested on a bidimensional conjunctive concept identification problem. The conjunctive problem was administered approximately 12 mo after completion of the unidimensional study. In the earlier unidimensional study, substantial and equivalent improvement had been found with both a training group and a reinforced training group. In this study, efficient conjunctive problem solving was found with the (unidimensional) training group, showing that enhanced cognitive performance can be durable and transfer to a similar task. Durability and trasnfer were not observed with the (unidimensional) reinforced training group, however, a finding that appears to have resulted from the extrinsic reinforcement token system employed in the unidimensional training with that group.

Detection of a deficit in visual discrimination of pattern following lesions of anterior cortex: role of type of motivation.

6 albino rats were trained under appetitive motivation to perform diametrically opposed visual discriminations of pattern via opposite eyes. Small lesions were subsequently placed unilaterally in anterior neocortex. Following a period of post-surgical recovery, subjects were re-trained on the diammetrically opposed discriminations in alternating 10-trial blocks. Every subject made more post-surgical errors on the discrimination mediated by the eye contralateral to the lesion. Since albino rats have virtually complete decussation of the visual system, this indicates selective impairment in mediation of performance of pattern discrimination in the part of the lesioned hemispheres. Thus, findings previously obtained in studies involving aversive motivation are general to appetitively motivated tasks.

Further evaluation of a sensitive method for detecting experimental brain lesions.

Small, unilateral cortical lesions were placed in either medial-anterior, lateral-anterior, or posterior cortex of 20 male, Sprague-Dawley, albino rats. In addition, unilateral sham operations were performed on 8 rats from the same stock. All subjects had been trained prior to surgery with diametrically opposed visual habits mediated by opposite cerebral hemispheres. The opposing habits were, insofar as possible, evenly matched prior to surgery. After surgery, lesioned hemispheres, regardless of locus of lesion, were slower in acquiring the habit they mediated, than were unlesioned hemispheres. Further, unlesioned hemispheres dominated in test trials in which subjects chose one of the two cue doors with both eyes open. These findings confirm that the "interocularly conflicting discrimination" baseline detects a role of extrastriate cortex in mediation of pattern discrimination habits. They further indicated that losses occur without regard to the various locations of lesion employed.

Observing behavior in the albino rat: a within-subjects' comparison of increasing levels of visual complexity.

54 male CD strain Charles River albino rats were tested for complexity preference using a non-locomotor response. Each subject was presented an array of photographic slides containing an incremental series of complexity elements, i.e., 1, 2, 5 and 25 elements. All photographic slides were randomized both within and across subjects. Each photographic slide of each level of complexity was repeated three times. Results of an analysis of covariance, with luminance as the covariate, showed that cummulative viewing time increased with an increase in stimulus complexity. The relationship between looking and level of complexity was shown to be different when covariance procedures were used than without them.