Examining the role of context variability in memory for items and associations.

What properties of a word make it easy or difficult to remember? Word frequency and context variability are separate, closely related word properties that have disparate influences on memorability. The influence of word frequency changes depending on the memory task, with high-frequency words tending to be recalled better and low-frequency words to be recognized better. Conversely, low-context-variability words tend to be remembered better across tasks. One proposed explanation for the low-variability advantage is that low-variability words are easier to associate with the experimental context, given that they are associated with fewer extra-experimental contexts. On the basis of this explanation, it has been suggested that the formation of interitem associations during encoding should interfere with the formation of item-to-context associations, attenuating the low-variability advantage. Across experiments, we tested whether focusing on interitem associations disrupted the low-variability advantage, by manipulating encoding tasks, test expectancy, final test condition, word frequency, and context variability. Focusing on interitem associations did not harm performance for low-variability words. Words low in both frequency and variability were recognized better, but word pairs composed of high-frequency, low-variability words were recognized better in associative recognition. On the basis of the data, we suggest that focusing on interitem associations does not come at the expense of item-to-context associations. Moreover, the data further support the idea that frequency and variability are distinct properties.

Information and processes underlying semantic and episodic memory across tasks, items, and individuals.

The development of memory theory has been constrained by a focus on isolated tasks rather than the processes and information that are common to situations in which memory is engaged. We present results from a study in which 453 participants took part in five different memory tasks: single-item recognition, associative recognition, cued recall, free recall, and lexical decision. Using hierarchical Bayesian techniques, we jointly analyzed the correlations between tasks within individuals-reflecting the degree to which tasks rely on shared cognitive processes-and within items-reflecting the degree to which tasks rely on the same information conveyed by the item. Among other things, we find that (a) the processes involved in lexical access and episodic memory are largely separate and rely on different kinds of information, (b) access to lexical memory is driven primarily by perceptual aspects of a word, (c) all episodic memory tasks rely to an extent on a set of shared processes which make use of semantic features to encode both single words and associations between words, and (d) recall involves additional processes likely related to contextual cuing and response production. These results provide a large-scale picture of memory across different tasks which can serve to drive the development of comprehensive theories of memory. (PsycINFO Database Record

Dynamic memory searches: Selective output interference for the memory of facts.

The benefits of testing on later memory performance are well documented; however, the manner in which testing harms memory performance is less well understood. This research is concerned with the finding that accuracy decreases over the course of testing, a phenomena termed "output interference" (OI). OI has primarily been investigated with episodic memory, but there is limited research investigating OI in measures of semantic memory (i.e., knowledge). In the current study, participants were twice tested for their knowledge of factual questions; they received corrective feedback during the first test. No OI was observed during the first test, when participants presumably searched semantic memory to answer the general-knowledge questions. During the second test, OI was observed. Conditional analyses of Test 2 performance revealed that OI was largely isolated to questions answered incorrectly during Test 1. These were questions for which participants needed to rely on recent experience (i.e., the feedback in episodic memory) to respond correctly. One possible explanation is that episodic memory is more susceptible to the sort of interference generated during testing (e.g., gradual changes in context, encoding/updating of items) relative to semantic memory. Alternative explanations are considered.

A distributed representation of internal time.

This article pursues the hypothesis that a scale-invariant representation of history could support performance in a variety of learning and memory tasks. This representation maintains a conjunctive representation of what happened when that grows continuously less accurate for events further and further in the past. Simple behavioral models using a few operations, including scanning, matching and a "jump back in time" that recovers previous states of the history, describe a range of behavioral phenomena. These behavioral applications include canonical results from the judgment of recency task over short and long scales, the recency and contiguity effect across scales in episodic recall, and temporal mapping phenomena in conditioning. A growing body of neural data suggests that neural representations in several brain regions have qualitative properties predicted by the representation of temporal history. Taken together, these results suggest that a scale-invariant representation of temporal history may serve as a cornerstone of a physical model of cognition in learning and memory.

Cyclic variations in sustained human performance.

Biological rhythms play a prominent role in the modulation of human physiology and behavior. [Smith, K., Valentino, D., & Arruda, J. (2003). Rhythmic oscillations in the performance of a sustained attention task. Journal of Clinical and Experimental Neuropsychology, 25, 561-570] suggested that sustained human performance may systematically fluctuate in a cyclic manner with periods of 1.5 min and 5.2 min. The current series of investigations sought to manipulate those periodicities by altering task difficulty, administering caffeine, and testing on a more ecologically valid task. Strong evidence of a 1.5 min periodicity was found across studies. Most participants did not demonstrate the 5.2 min periodicity. Moreover, the 1.5 min periodicity was resistant to task manipulations and appeared in similar levels across conditions in all three experiments. These rhythms may be indicative of an endogenous system that modulates sustained attention in humans. Evidence supporting this idea and implications of the research are discussed.

Rhythmic oscillations in quantitative EEG measured during a continuous performance task.

The objective of the present investigation was to determine if cyclic variations in human performance recorded during a 30 min continuous performance task would parallel cyclic variations in right-hemisphere beta-wave activity. A fast fourier transformation was performed on the quantitative electroencephalogram (qEEG) and the performance record of each participant (N = 62), producing an individual periodogram for each outcome measure. An average periodogram was then produced for both qEEG and performance by combining (averaging) the amplitudes associated with each periodicity in the 62 original periodograms. Periodicities ranging from 1.00 to 2.00 min and from 4.70 to 5.70 min with amplitudes greater than would be expected due to chance were retained (Smith et al. 2003). The results of the present investigation validate the existence of cyclic variations in human performance that have been identified previously (Smith et al. 2003) and extend those findings by implicating right-hemisphere mediated arousal in the process (Arruda et al. 1996, 1999, 2007). Significant cyclic variations in left-hemisphere beta-wave activity were not observed. Taken together, the findings of the present investigation support a model of sustained attention that predicts cyclic changes in human performance that are the result of cyclic changes in right-hemisphere arousal.