Gregory K. Shenaut

Semantic priming of word pronunciation and lexical decision in schizophrenia

Experimental assessments of semantic memory structure and function in schizophrenic subjects can be a useful approach for delineating some of the information processing deficits in schizophrenia. In this study, a pronunciation and a lexical decision semantic priming experiment were conducted with 19 schizophrenic subjects and 20 normal controls. A short stimulus-onset asynchrony (250 msec) and a relatively low proportion of related prime-target pairs were used in order to examine automatic priming and in order to avoid the contribution of attentional, controlled processes. On the pronunciation task, schizophrenic subjects showed a significant priming effect, equal to the priming shown by normal controls. However, on the lexical decision task, schizophrenics, unlike normal controls, did not show a priming effect which is significantly greater than zero, even though the group difference in priming effect (interaction of priming effect by group) was nonsignificant. The lack of priming on the lexical decision task is consistent with the hypothesis that schizophrenic subjects may show abnormalities in the realm of post-lexical, controlled information processing. The equal-to-normal priming for schizophrenic subjects indicates that the basic structure of the semantic network, including associations among related concepts, is intact in schizophrenia, and that spreading activation also occurs normally.

Automatic semantic priming with various category relations in Alzheimer's disease and normal aging.

The 6 experiments reported here tested the effects of various category relations on automatic semantic priming in 20 Alzheimers disease (AD), 20 older control, and 22 younger control subjects. The tasks were either word pronunciation or lexical decision; the prime-target stimulus-onset asynchrony (SOA) was always 250 ms. A variety of category relationships between prime and target were examined: highly associated category comembers, subordinate-superordinate or superordinate-subordinate pairs, and pairs selected on the basis of category typically to form typical-typical, atypical-typical, typical-atypical, and atypical-atypical pairings. Both for AD versus older control subjects and for older versus younger control subjects, no significant group differences were found in the magnitude of overall semantic priming or in the effects on priming of factors pertaining to the prime-target relationship.

Naturally occurring and experimentally induced tip-of-the-tongue experiences in three adult age groups.

Tip-of-the-tongue (TOT) experiences were examined in 30 young (ages 18-24 years), 30 young-old (ages 60-74), and 30 old-old (ages 80-92) adults. In Study 1, TOT experiences were experimentally induced with definitions of to-be-retrieved targets. If the target was not retrieved, orthographic or semantic cues were provided. Age-related increases in the occurrence of TOT experiences and in the time needed to resolve TOT experiences were found for young versus young-old and young-old versus old-old groups; all comparisons were significant except for young versus young-old TOT occurrence, which approached significance. In Study 2, the same participants recorded naturally occurring TOT experiences in structured diaries during a 4-week interval. Both the number of TOT experiences and the resolution time for TOT experiences increased with age. However, the percentage of TOT experiences resolved was equal across age groups; given enough time, even the oldest participants resolved virtually all TOT experiences.

Automatic versus controlled semantic priming in schizophrenia.

Schizophrenic individuals (n = 31), including paranoid and nonparanoid diagnostic subgroups, and normal controls (n = 20) participated in a semantic priming experiment involving a single-choice lexical decision task. For the automatic priming blocks, a 260-ms stimulus onset asynchrony (SOA) was used; for the controlled priming blocks, 1,000-ms SOA was used. The paranoid subgroup showed significantly less priming than did the control group. The nonparanoid subgroup showed a decrease in priming compared with the control group that approached significance. There was an increased priming effect for the controlled compared with the automatic priming condition; this difference was not modulated by participant group. Nonsignificant semantic priming (equal to 0) occurred only for schizophrenic subgroups and only in automatic priming conditions.

Slower and more variable reaction times in schizophrenia: what do they signify?

Extensive research has demonstrated that schizophrenic subjects are slower than normal comparison subjects on a range of reaction-time tasks. Some investigators have also observed that schizophrenic patients exhibit larger intraindividual variability in reaction times when performing these tasks than do normal comparison subjects. This study, using a lexical decision choice reaction time (CRT) task, explored the relation of mean CRT and it intra-individual variability (CRT-SD) to psychiatric symptoms and to performance on executive-motor tasks in 26 medication-free schizophrenic out-patients and 17 normal comparison subjects. Schizophrenic subjects had both significantly slower and more variable CRTs which were unrelated to general intellectual abilities (IQ). Among schizophrenic subjects, both CRT and CRT-SD were significantly related to severity of psychotic symptoms, failure to maintain cognitive set, and poorer motor coordination and global functioning. After controlling for mean CRT, CRT-SD showed unique covariation with clinical symptoms (positive, disorganized and tension/hostility). Conversely, mean CRT showed unique covariation with the failure to maintain cognitive set and with stereotypic mannerisms, independent of CRT-SD. These results suggest that slower CRT and increased intra-individual variability in CRT, while not fully independent of one another, may reflect separate aspects of symptomatic and cognitive dysfunction in schizophrenia.

Semantic priming in Alzheimer's disease: Meta-analysis and theoretical evaluation

Publisher Summary The chapter discusses semantic priming in Alzheimers disease (AD). The lexical priming paradigm has frequently been used as a tool for assessing the intactness of semantic memory in AD. In this paradigm, the effect of the related context on reaction time (RT) to pronounce a word or recognize a word (in a mixed list of word and nonword targets) is measured. The reduction in target RT produced by a preceding related context word (related prime) compared to an unrelated context word (unrelated prime) is known as the “semantic priming effect.” The chapter presents a critical review of the theory and methods relevant to research on lexical, semantic priming in AD compared to elderly normal (EN) subjects. It also presents several types of meta-analyses on the data from all available AD–EN semantic priming experiments. AD hyperpriming is attentionally based, coinciding with the disproportionate slowing in RT that occurs in controlled but not automatic priming paradigms.

Well-organized conceptual domains in Alzheimer's disease

We used a novel apparatus called the flags board to elicit similarity judgments from 32 Alzheimers disease (AD) patients and 32 elderly normal (EN) controls for two 12-member conceptual domains, ANIMALS and (musical) INSTRUMENTS. Based on Pathfinder and multidimensional scaling (MDS) analyses, performance by AD patients was nearly identical to that of EN controls for ANIMALS. Performance differed for INSTRUMENTS, but the AD groups Pathfinder network was found to agree with the intuitions of a panel of 18 raters as well as the EN groups. MDS analysis showed no deficit on abstract dimensions for the AD group, for either domain. The results are discussed in the context of degradation versus preservation of semantic memory in AD.

Both processing speed and semantic memory organization predict verbal fluency in schizophrenia

We systematically examined the relationship of both lexical retrieval and semantic memory organization to categorical verbal fluency performance in 40 outpatient schizophrenic subjects and 16 healthy controls. Mean choice reaction time (RT) on a lexical decision task was used as a measure of lexical retrieval efficiency. The complexity of semantic memory organization was measured using a Pathfinder semantic network analysis (calculated as the number of inter-node links obtained from a similarity rating task). In the schizophrenia group only, RT and semantic network links were each significantly negatively correlated with fluency and, together, accounted for 23% of the variance in fluency. RT and links were not significantly correlated with one another. Findings were unrelated to age, sex, education, or medication dose. Controlling for IQ reduced but did not abolish the relationship between fluency and network links. We conclude that the restricted verbal output of schizophrenic subjects is related both to impaired lexical retrieval and to variation in semantic memory organization, which partly reflects general intelligence. The statistical independence of the retrieval speed and organizational factors suggests that individuals with schizophrenia differ in the underlying processes that contribute to their reduced verbal fluency.

Methodological control of semantic priming in Alzheimer's disease

We conducted a lexical-decision, semantic priming experiment that included 250- and 1000-ms stimulus onset asynchronies (SOAs) with 32 probable Alzheimers disease (AD) and 40 older normal persons. Attention-based, controlled processes are assumed to occur only at the longer of the 2 SOAs. The AD group showed greater than normal priming in the long-SOA but not the short-SOA condition. We conclude that greater than normal AD priming is a function of controlled processing rather than semantic network degradation.

Assessment of associative relations in alzheimer's disease: Evidence for preservation of semantic memory

Abstract Semantic priming was assessed in Alzheimers disease (AD), elderly control, and young control subjects with three lexical decision, continuous priming experiments. the stimuli were intracategory, associated pairs in Experiments 1 and 2 and varied types of associated pairs in Experiment 3. AD priming effects were equal to those of elderly control subjects; elderly and young control priming effects were also equal. We interpret this as evidence for the relative preservation of the semantic memory network in early AD, as in normal aging, at least to the extent necessary for normal access of concept nodes and normal automatic spreading activation between concept nodes. In a final study (Experiment 4) knowledge of the associations between the targets and related primes used in Experiments 1 and 2 was explicitly assessed; 20 out of 22 AD subjects showed perfect or close to perfect performance.