Priming performance in Alzheimer's disease: the role of task sensitivity.

Studies examining implicit memory performance in Alzheimer's disease (AD) have yielded inconsistent findings, with these patients demonstrating impaired performance within some priming studies and intact performance within others. The present study examined the role of task sensitivity in detecting impaired priming in memory-impaired patients. Twelve healthy older adults and 12 AD patients were administered a picture fragment identification test. Task sensitivity was increased by employing stimulus cues expected to produce larger and more variable priming effects than obtained in previous studies. A simple comparison of priming scores revealed that the AD patients demonstrated significantly impaired priming relative to normal control participants. However, further analysis of priming in relation to certain stimulus characteristics revealed that AD patients often demonstrated impaired priming when overall priming effects were large but relatively intact priming when priming effects were small. These findings suggest that the prevention of ceiling effects in control participants may aid in the detection of impaired priming in patient populations.

Mesial temporal, diencephalic, and striatal contributions to deficits in single word reading, word priming, and recognition memory.

Fifty-three volunteer participants were studied with the fade-in task (Ostergaard, 1998) to measure naming latency, word priming, and recognition-memory performance. and with morphometric magnetic resonance imaging (MRI) techniques to measure volumes of mesial temporal lobe, diencephalic, striatal, and neocortical structures. The relationship between measures of cerebral volume loss and performance deficits was modeled using simultaneous regression analyses in which the behavioral measures were dependent variables. The results suggested that damage in both hippocampal and amygdala/entorhinal areas as well as damage in the diencephalon and the nucleus accumbens all contributed independently to the severity of recognition-memory deficits. Both caudate nucleus damage and hippocampal damage contributed independently to increased naming latency (slowed single-word reading). Finally, only damage in the hippocampus appeared to result in decreased word priming. These results provide further evidence against the assertion that word priming represents a form of memory unaffected by damage to the mesial temporal lobes.

Priming deficits in amnesia: now you see them, now you don't.

The rate with which perceptual information becomes available was manipulated in 2 word naming experiments. Word priming effects, in terms of reduced naming latencies for repeated items, and recognition memory measures were obtained with matched groups of amnesic patients and control participants. In both experiments, the amnesic patients evidenced significantly reduced priming effects compared to control participants under difficult task conditions. Under easy task conditions the baseline naming latencies of the amnesics were significantly longer than those of controls, but the difference in priming effects failed to reach significance. The findings are consistent with the Information Availability model of priming positing that both priming and explicit memory are mediated by episodic information from a study or information processing episode. It is argued that word priming does not represent a memory function that is spared in amnesia.

Brain activation during word identification and word recognition.

Previous memory research has suggested that the effects of prior study observed in priming tasks are functionally, and neurobiologically, distinct phenomena from the kind of memory expressed in conventional (explicit) memory tests. Evidence for this position comes from observed dissociations between memory scores obtained with the two kinds of tasks. However, there is continuing controversy about the meaning of these dissociations. In recent studies, Ostergaard (1998a, Memory Cognit, 26:40-60; 1998b, J. Int. Neuropsychol. Soc., in press) showed that simply degrading visual word stimuli can dramatically alter the degree to which word priming shows a dissociation from word recognition; i.e., effects of a number of factors on priming paralleled their effects on recognition memory tests when the words were degraded at test. In the present study, cerebral blood flow changes were measured while subjects performed the word identification (reading) and recognition memory tasks used previously by Ostergaard. The results are the direct comparisons of the two tasks and the effects of stimulus degradation on blood flow patterns during the tasks. Clear differences between word identification and word recognition were observed: the latter task evoked considerably more prefrontal activity and stronger cerebellar activation. Stimulus degradation was associated with focal increases in bilateral fusiform regions within the occipital lobe. No task, degradation, or item repetition effects were demonstrated in mesial temporal regions, no repetition effects were observed in any region, and there was no evidence for different effects of stimulus degradation in the priming and recognition memory conditions. Power limitations may have contributed to the null effects.

The effects on priming of word frequency, number of repetitions, and delay depend on the magnitude of priming.

Conflicting findings with respect to the effects of experimental manipulations on priming have been reported in previous studies. It is argued that, in many priming tasks, large amounts of task-relevant information are available from various sources, and that, therefore, the information available from a specific study episode will have only a small impact on overall performance level. Under such circumstances, high levels of baseline performance and small priming effects will be observed. The experiments reported here investigated the hypothesis that a high baseline performance in information-processing tasks that are used to measure priming may constrain priming effects. In a series of word-naming experiments, perceptual difficulty and, therefore, baseline performance was manipulated. Under easy conditions, priming effects were relatively small and were not affected by word frequency, spaced repetition, or delay. Under more difficult conditions, priming effects were larger, and significant effects of all of the above-mentioned experimental manipulations were observed. Under conditions that produced the largest priming effects, a significant relationship between priming and explicit-memory performance could be observed. In the last experiment, it was shown that the characteristics of the retrieval task can substantially affect the magnitude of priming. It is argued that priming effects should be considered to reflect interactions between memory traces and the information-processing components of the priming task.

The biasing effect of verbal labels on memory for ambiguous figures in patients with progressive dementia.

This experiment investigated the effects of verbal labels on recognition memory for ambiguous visual figures in patients with Alzheimer's disease (AD), patients with Huntington's disease (HD), and matched normal control subjects. The study employed ambiguous figures that could be interpreted in two different ways. During the study phase each figure was presented together with a verbal label that corresponded to one interpretation of the figure. After a 30-min retention interval a recognition memory test was given during which the study figures and distractor figures were presented one at a time without verbal labels. For each study figure two distractor figures were employed, each corresponding to a different interpretation of the study figure. The patients' overall recognition memory performance was severely impaired compared to control subjects. However, all subject groups tended to produce responses and response latencies to distractor items that were consistent with the verbal labels presented during the study phase. This bias effect occurred in the AD patients despite the fact that their recognition memory performance was at chance level. Indeed, there was no significant difference in the bias evidenced by the AD and HD patients and their respective matched control subjects. The bias effects were obtained in an explicit memory task, and the findings are discussed in terms of unconscious influences on explicit memory processes.

Dissociations between word priming effects in normal subjects and patients with memory disorders: multiple memory systems or retrieval?

Repetition priming was measured in two different tasks within a single experiment--one in which subjects named briefly (tachistoscopically) presented words, and one requiring naming of visually fragmented/degraded words. Thirteen amnesic patients, 12 patients with Alzheimer's disease (AD), and 15 normal control subjects were tested under 4 experimental conditions involving the factorial combination of two variables: delay of test (10 minutes and 24 hours), and number of prior occurrences of the primed items (1 and 4). The two tasks produced very different patterns of priming effects, despite the fact that common study phases were employed. In one task the priming effect showed no decay and virtually no effect of the number of prior occurrences of the primed items, whereas both these variables affected priming in the other task. The AD patients evidenced impaired priming in both tasks. However, in the degraded-word-naming task the deficit was only apparent under some experimental conditions. The amnesics produced priming effects that in absolute terms were similar to those produced by control subjects. However, when group differences in overall performance level were taken into account in the tachistoscopic task, these patients also showed clear evidence of impaired priming. It is argued that the complex pattern of priming effects obtained is best explained by the characteristics of the retrieval cues provided in the tasks, and, generally, that such characteristics may determine whether or not experimental variables will affect measured priming.

A method for judging measures of stochastic dependence: further comments on the current controversy.

A large number of reports have been published on stochastic independence between implicit and explicit measures of memory. This is often taken to imply that different memory systems mediate implicit and explicit memory performance. In these cases, stochastic independence is inferred from contingency analysis of overall success rates in two memory tasks when performance in one or both of the tasks is, to a large extent, mediated by factors other than memory. Typically, the difference between performance with studied and nonstudied items is not large in implicit memory tasks. It is argued that this must be taken into account when evaluating the contingency analysis. A method is presented for estimating the relevant joint and conditional probabilities, assuming that the aspects of performance in the two tasks that are related to memory are dependent to the maximum possible extent. The method is applied to a number of published studies, and it is shown that the difference between these estimated probabilities and those given by stochastic independence is too small to allow any conclusion to be drawn about memory systems from contingency analysis of data reported in these studies.

Episodic, semantic and procedural memory in a case of amnesia at an early age.

The patient C.C. developed an amnesic syndrome at the age of 10 yr. Like adult amnesics, C.C. demonstrated impaired episodic memory for both verbal and visual materials although immediate memory span was spared. However, striking deficits were also observed on a wide variety of semantic memory tasks, including reading vocabulary and verbal fluency tests, semantic classification and lexical decision tasks and tests of verbal intelligence. On the other hand, C.C. showed normal learning and retention of two procedural tasks. It was argued that this evidence is inconsistent with the view that the amnesic syndrome represents a selective defect of episodic memory that leaves semantic memory relatively unaffected.

Some effects of color on naming and recognition of objects.

In this article, we investigated the role of color in the recognition and naming of everyday objects. In the first experiment we found that color pictures were named faster than black-and-white and that shape information did not facilitate color naming. Experiment 2 was carried out to determine at which stage of object processing the color facilitation occurred. We found that color had no effect on object recognition but did facilitate object naming, even when color was redundant for discrimination. This did not apply to naming abstract shapes. Experiment 3 replicated the findings of Experiment 2 using different objects and colors. The results showed that color could facilitate but not inhibit object naming and did not affect object recognition.

The effect of sentence boundaries upon aphasic patients' immediate memory for connected speech.

Memory for the terminal portion of connected speech was investigated in Broca's, Wernicke's and Conduction aphasic patients. A multiple choice probe recognition paradigm was employed so that the results would not be contaminated by expressive speech errors. The effects on retention performance of sentence boundaries and the number of words intervening between target word presentation and test were studied. The different aphasic groups showed similar patterns of performance. Sentence boundaries had no effect on retention but more errors were produced with seven than with four words intervening between presentation and test. Errors were classified as semantic, phonemic or unrelated and in all conditions of the experiment semantic confusion errors predominated. It was argued that there was no evidence that the aphasic patients retained the last heard sentence in a superficial form in short-term memory.

Colour anomia resulting from weakened short-term colour memory. A case study.

A patient exhibited marked colour anomia without object anomia, but was able to point to named colours. Five experiments were conducted to investigate his immediate colour memory. It was concluded that his colour anomia was the result of an impaired short-term memory deficit specific to colour. Temporary activation of specific entries in the colour lexicon enabled pointing and even naming to take place. A general model incorporating all forms of colour anomia is presented.

Immediate memory span, recognition memory for subspan series of words, and serial position effects in recognition memory for supraspan series of verbal and nonverbal items in Broca's and Wernicke's aphasia.

Four Broca's aphasics, four Wernicke's aphasics, and four matched controls were investigated on three verbal and one visual short-term memory tasks. Experiment 1 considered memory span and subspan recognition memory for verbal items and Experiment 2 assessed serial position effects in supraspan verbal recognition memory. The Broca's aphasics demonstrated verbal memory deficits, which could not be attributed to linguistic disturbances, while the verbal memory deficiencies seen with the Wernicke's aphasics could be regarded as secondary to linguistic defects. In Experiment 3, where visual recognition memory was investigated, only the Broca's aphasics showed deficient performance. The wider context of deficient mnemonic performance in aphasia is discussed.