Testing Independence in 2 × 2 Contingency Tables

Three of the potential models for the 2 × 2 contingency table are discussed: the hyper geometric Independence Trial, the double-binomial Comparative Trial, and the multinomial Double Dichotomy Trial. Then the critical regions of seven statistical tests are evaluated within each of these models. The uncorrected Pearson’s Chi-Square test and Upton’s correction are found to be overly liberal in all three models, particularly for the hypergeometric. A continuity correction, when properly applied, is shown to be an extremely good approximation to Fisher’s Exact test, which employs the hypergeometric distribution to evaluate outcome probabilities—but is an extremely conservative approximation to the double binomial and multinomial models. Haber’s test is recommended for these two cases, but the amount of work required may be prohibitive for many investigators.

Distinctiveness and the recognition mirror effect: evidence for an item-based criterion placement heuristic

Superior detection and rejection of 1 versus another class of items during recognition is called the mirror effect. Some mirror effects may involve strategic criterion adjustments based on item distinctiveness and its relation to memorability. Three experiments demonstrated mirror effects for known versus unknown scenes and 1 suggested a similar pattern for faces. In opposition to preexperimental familiarity, lures from known and frequently encountered locations were confidently rejected more often than unknown lures. Forgetting and speeding recognition reversed this lure response pattern, suggesting abandonment of strategic adjustment in favor of a single fixed criterion. With sufficient response time and recent encoding, observers demand more evidence for conceptually distinctive items, perhaps because such items typically foster vivid recollection during retrieval.

Lag-sensitive repetition suppression effects in the anterior parahippocampal gyrus

Single-unit recording studies of monkeys have shown that neurons in perirhinal and entorhinal cortex exhibit activity reductions following stimulus repetition, and some have suggested that these "repetition suppression" effects may represent neural signals that support recognition memory. Critically, repetition suppression effects are most pronounced at short intervals between stimulus repetitions. Here, we used event-related functional magnetic resonance imaging (fMRI) to identify repetition suppression effects in the human medial temporal lobe and determine whether these effects are sensitive to the length of the interval between repetitions. Twenty-one participants were scanned while performing a continuous recognition memory task in which the interval between item repetitions was parametrically varied from 2 to 32 intervening items. We found evidence of repetition suppression in the anterior parahippocampal gyrus, but only when the repetition interval was relatively short. Moreover, bilateral hippocampal regions showed lag-sensitive repetition effects. Our results demonstrate that activity in the human medial temporal cortex, like that of monkeys, exhibits repetition suppression effects that are sensitive to the length of the interval between repetitions.

Oscillatory EEG correlates of episodic trace decay

Recent studies suggest that human theta oscillations appear to be functionally associated with memory processes. It is less clear, however, to what type of memory sub-processes theta is related. Using a continuous word recognition task with different repetition lags, we investigate whether theta reflects the strength of an episodic memory trace or general processing demands, such as task difficulty. The results favor the episodic trace decay hypothesis and show that during the access of an episodic trace in a time window of approximately 200-400 ms, theta power decreases with increasing lag (between the first and second presentation of an item). LORETA source localization of this early theta lag effect indicates that parietal regions are involved in episodic trace processing, whereas right frontal regions may guide the process of retrieval. We conclude that episodic encoding can be characterized by two different stages: traces are first processed at parietal sites at approximately 300 ms, then further processing takes place in regions of the medial temporal lobe at approximately 500 ms. Only the first stage is related to theta, whereas the second is reflected by a slow wave with a frequency of approximately 2.5 Hz.

Bilateral Thalamic Lesions Affect Recollection-and Familiarity-Based Recognition Memory Judgments

The contribution of the thalamus to different forms of explicit memory is poorly understood. In the current study, explicit memory performance was examined in a 40-year-old male (RG) with bilateral anterior and medial thalamic lesions. Standardized tests indicated that the patient exhibited more severe recall than recognition deficits and his performance was generally worse for verbal compared to nonverbal memory. Recognition memory tests using the remember-know (R/K) procedure and the confidence-based receiver operating characteristic (ROC) procedure were used to examine recollection- and familiarity-based recognition. These tests revealed that RG had deficits in recollection and smaller, but consistent deficits in familiarity. The results are in agreement with models indicating that the anteromedial thalamus is important for both recollection- and familiarity-based recognition memory.

Mild hypoxia disrupts recollection, not familiarity

Yonelinas et al. (2002) found that hypoxic patients exhibited deficits in recollection that left familiarity relatively unaffected. In contrast, Manns, Hopkins, Reed, Kitchener, and Squire (2003) studied a group of hypoxic patients who suffered severe and equivalent deficits in recollection and familiarity. We reexamine those studies and argue that the discrepancy in results is likely due to differences in the hypoxic groups that were tested (i.e., differences in amnestic severity, subject sampling methods, and patient etiology). Yonelinas et al. examined memory in 56 cardiac arrest patients who suffered a brief hypoxic event, whereas Manns et al. examined a group of severely amnesic patients that consisted of 2 cardiac arrest patients, 2 heroin overdose patients, 1 carbon monoxide poisoning patient, and 2 patients with unknown etiologies. We also consider an alternative explanation proposed by Wixted and Squire (2004), who argued that the two patient groups suffered similar deficits, but that statistical or methodological artifacts distorted the results of each of Yonelinas et al.'s experiments. A consideration of those results, however, indicates that such an explanation does not account for the existing data. All of the existing evidence indicates that recollection, but not familiarity, is disrupted in mild hypoxic patients. In more severe cases of hypoxia, or those with more complex etiologies such as heroin overdose, more profound deficits may be observed.

Dissociating familiarity from recollection using rote rehearsal

Recollection-based recognition memory judgments benefit greatly from effortful elaborative encoding, whereas familiarity-based judgments are much less sensitive to such manipulations. In this study, we have examined whether rote rehearsal under divided attention might produce the opposite dissociation, benefiting familiarity more than recollection. Subjects rehearsed word pairs during the "distractor" phase of a working memory span task, and were then given a surprise memory test for the distractor items at the end of the experiment. Experiment 1 demonstrated that increasing rehearsal elevated the recognition rate for intact and rearranged pairs, but neither associative recognition accuracy nor implicit fragment completion benefited from rehearsal. The results suggest that rote rehearsal leads to a greater increase in familiarity than in recollection, and that the increase in observed familiarity cannot be attributed to effects of repetition priming. In Experiment 2, we tested item recognition with the remember/know procedure, and the results supported the conclusions of Experiment 1. Moreover, a signal detection model of remember/know performance systematically overpredicted rehearsal increases in remember rates, and this worsened when high-rehearsal items were assumed to be more variable in strength. The results suggest that rote rehearsal can dissociate familiarity from recollection at the time of encoding and that item recognition cannot be fully accommodated within a one-dimensional signal detection model.

Recall and recognition in mild hypoxia: using covariance structural modeling to test competing theories of explicit memory

To test theories of explicit memory in amnesia, we examined the effect of hypoxia on memory performance in a group of 56 survivors of sudden cardiac arrest. Structural equation modeling revealed that a single-factor explanation of recall and recognition was insufficient to account for performance, thus contradicting single-process models of explicit memory. A dual-process model of recall in which two processes (e.g., declarative memory and controlled search) contribute to recall performance, whereas only one process (e.g., declarative memory) underlies recognition performance, also failed to explain the results adequately. In contrast, a dual-process model of recognition provided an acceptable account of the data. In this model, two processes--recollection and familiarity--underlie recognition memory, whereas only the recollection process contributes to free recall. The best-fitting model was one in which hypoxia and aging led to deficits in recollection, but left familiarity unaffected. Moreover, a controlled search process was correlated with recollection, but was not associated with familiarity or the severity of hypoxia. The results support models of explicit memory in which recollection depends on the hippocampus and frontal lobes, whereas familiarity-based recognition relies on other brain regions.

The neural substrates of visual implicit memory: do the two hemispheres play different roles?

Identification of visually presented words is facilitated by implicit memory, or visual priming, for past visual experiences with those words. There is disagreement over the neuro-anatomical substrates of this form of implicit memory. Several studies have suggested that this form of priming relies on a visual word-form system localized in the right occipital lobe, whereas other studies have indicated that both hemispheres are equally involved. The discrepancies may be related to the types of priming tasks that have been used because the former studies have relied primarily on word-stem completion tasks and the latter on tasks like word-fragment completion. The present experiments compared word-fragment and word-stem measurements of visual implicit memory in patients with right occipital lobe lesions and patients with complete callosotomies. The patients showed normal visual implicit memory on fragment completion tests, but essentially no visual priming on standard stem completion tests. However, when we used a set of word stems that had only one correct solution for each test item, as was true of the items in the fragment completion tests, the patients showed normal priming effects. The results indicate that visual implicit memory for words is not solely dependent upon the right hemisphere, rather it reflects changes in processing efficiency in bilateral visual regions involved in the initial processing of the items. However, under conditions of high lexical competition (i.e., multiple completion word stems), the lexical processes, which are dominant in the left hemisphere, overshadow the visual priming supported by the left hemisphere.

Effects of extensive temporal lobe damage or mild hypoxia on recollection and familiarity

Memory for past events can be based on recollection or on assessments of familiarity. These two forms of human memory have been studied extensively by philosophers and psychologists, but their neuroanatomical substrates are largely unknown. Here we examined the brain regions that are involved in these two forms of memory by studying patients with damage to different temporal lobe regions. Our results come from (i) structural covariance modeling of recall and recognition, (ii) introspective reports during recognition and (iii) analysis of receiver operating characteristics. In sum, we found that the regions disrupted in mild hypoxia, such as the hippocampus, are centrally involved in conscious recollection, whereas the surrounding temporal lobe supports familiarity-based memory discrimination.

Recognition memory for source and occurrence: the importance of recollection

Previous recognition memory studies indicate that when both recollection and familiarity are expected to contribute to recognition performance (e.g., discriminating studied items from nonstudied items) the dual-process and the unequal-variance signal detection models provide comparable accounts of performance. When familiarity is not expected to be useful (e.g., when items from two equally familiar sources are discriminated between), the dual-process model provides a significantly better account of performance. In the present study, source recognition was tested under conditions in which familiarity could have been used to perform a list-discrimination task; participants were required to discriminate between strong studied items, weak studied items, and new items. The dual-process model provided a better account of performance than did the unequal-variance model. Moreover, the results indicated that the unequal-variance assumption in a single-process signal detection model was not a valid substitution for recollection and that recollection was used to make recognition judgments even when assessments of familiarity were useful.

Separating sensitivity from response bias: implications of comparisons of yes-no and forced-choice tests for models and measures of recognition memory

A fundamental challenge to psychological research is the measurement of cognitive processes uncontaminated by response strategies resulting from different testing procedures. Test-free estimates of ability are vital when comparing the performance of different groups or different conditions. The current study applied several sets of measurement models to both forced-choice and yes-no recognition memory tests and concluded that the traditional signal-detection model resulted in distorted estimates of accuracy. Two-factor models were necessary to separate memory sensitivity from response bias. These models indicated that (a) memory accuracy did not differ across the tests and (b) the tests relied on the same underlying memory processes. The results illustrate the pitfalls of using a single-component model to measure accuracy in tasks that reflect 2 or more underlying processes.

Memory Encoding Following Complete Callosotomy

Three patients with complete resection of the corpus callosum were tested in a series of memory tasks to determine the effects of callosotomy on the encoding and retrieval of information in memory. Verbal and pictorial conjunction tests were administered to measure patients' ability to consolidate the elements of a stimulus into an accurate composite memory. Patients were also tested in a paired-associate learning task to determine the consequences of callosotomy on the encoding and retrieval of associations between stimuli. Although callosotomy patients were unimpaired in the verbal conjunction task, results from both the pictorial conjunction task and the paired-associate learning task suggest that the absence of callosal cross-talk impairs encoding in these patients. In addition, the pattern of results in the paired-associate learning task suggests that callosotomy impairs retrieval processes. The role of the callosum in the formation of memory traces for nonverbal material and associations between verbal stimuli is discussed.

Variations in Death Rates in the Proximity of Christmas: An Opponent Process Interpretation

Previous attempts to show that death is sometimes postponed until after an important social occasion have focused on the relationship between birthdates and deathdates. The present research uses Christmas as the focal social event. Study I, which involved the number of obituaries published in a major metropolitan newspaper during the eight weeks centering on Christmas, showed a significant death dip immediately prior to Christmas and a significant death surge immediately thereafter. Study II, which was based on the actual death dates of eminent Americans, yielded the same general pattern of results and also revealed that the post-Christmas upswing was significant only in the case of people who had surpassed the sample's median age. Study II, which involved a day-by-day analysis, showed that the post-holiday increase was very abrupt. All of these findings are fully consistent with Solomon and Corbit's opponent process theory of motivation.

Birth Dates and Death Dates: An Examination of two Baseline Procedures and Age at Time of Death

The present study continues analyses of variations in the frequencies of death in the near temporal proximity of decedents' birthdays. Observed frequencies were compared with expected frequencies as ascertained from two baseline distributions. One distribution was the usual rectangular distribution, based on summing the number of deaths across all frequency categories and then dividing by the number of categories. The other distribution was constructed by pairing one person's birth date with another person's death date. This latter distribution was intended to provide a true baseline, and provide a better gauge for assessing the likelihood that any obtained relationship reflected coincidence or chance. Two weeks before and two weeks after the birthday there were more deaths, and one week after the birthday there were fewer deaths, than would be expected on the basis of either baseline distribution. Day-by-day analyses within the birthweek confirmed earlier reports of high followed by low frequencies of death. Compared to relatively old men, relatively young men were more likely to die on the eve of their birthdays or on their birthdays themselves. Compared to relatively young men, relatively old men's death dip begins at an earlier point in time. Methodological and theoretical implications are discussed.