Biomedical subjects

Nancy A Dennis

Publications and source records attributed to Nancy A Dennis.

6 recordsLinked to original sources

PubMed2006

Effects of aging on transient and sustained successful memory encoding activity.

Event-related fMRI studies have investigated age-related changes in encoding by identifying greater activity for items that are later remembered than for those that are forgotten (difference in memory, or Dm). The present study used hybrid blocked/event-related analyses to distinguish between transient Dm versus sustained Dm. Dm was identified as parametric increases in encoding activity as a function of a combined subsequent memory/confidence scale. Dm was measured in each trial (transient activity) and in blocks of eight trials (sustained activity). Transient Dm analyses showed age-related reductions in the left hippocampus but increases in left prefrontal cortex (PFC). Sustained Dm analyses showed age-related reductions in right PFC, but no region showing increased activity in older adults. These findings suggests that during semantic classification older adults show less spontaneous hippocampal-mediated encoding processes, but greater PFC-mediated semantic processes. Additionally, the decline in sustained Dm in PFC may involve age-related deficits in sustained attention that impact encoding processes. The results underscore the importance of investigating aging effects on both transient and sustained neural activity.

Adaptation, Physiological↗

PubMed2006

Implicit sequence learning without motor sequencing in young and old adults.

The ability to detect patterns and organize individual events into complex sequences is a fundamental cognitive skill that is often learned implicitly. The serial response time (SRT) task has been widely used to investigate implicit sequence learning, but it remains unclear whether people learn a perceptual or motor sequence in this task. This study reports three experiments that build on previous research by Goschke and colleagues using an auditory SRT task in which the stimulus-to-response mapping changes on every trial to eliminate spatio-motor sequencing. The current study extends earlier work in three ways. First, healthy young and older adults were tested rather than the neuropsychological patients used in previous research. Second, sequences of different structural complexity were investigated including first- and second-order repeating sequences as well as higher-order probabilistic sequences. Third, the potential role of explicit knowledge was examined using three separate tests of declarative knowledge. Results indicate that young and old adults are able to learn purely perceptual auditory sequences, but that explicit knowledge contributes to learning of repeating sequences by young adults.

Acoustic Stimulation↗

PubMed2004

Implicit spatial contextual learning in healthy aging.

Three experiments investigated the aging of implicit spatial and spatiotemporal context learning in 2 tasks. In contextual cuing, people learn to use repeated spatial configurations to facilitate search for a target, whereas in higher order serial learning, they learn to use subtle sequence regularities to respond more quickly and accurately to a series of events. Results reveal a dissociation; overall contextual cuing is spared in healthy aging, whereas higher order sequence learning is impaired in the same individuals. This finding suggests that these 2 forms of implicit learning rely on different neural substrates that age differently; the results are also consistent with recent evidence that fronto-striatal circuits are particularly susceptible to decline in health aging.

Adolescent↗

PubMed2003

Age deficits in learning sequences of spoken words.

Previous research has demonstrated age-related deficits in implicit learning of visual sequences characterized by subtle predictive relationships among the sequence elements. This study investigates whether this reflects modality-specific, or more general, sequence learning deficits by using an auditory sequence-learning task. Young and old adults responded with a key press to each of a series of unrelated spoken words. Unknown to the participants, every other word was presented in a fixed, repeating order with alternate words chosen at random. Both groups responded more quickly and accurately to the predictable than to unpredictable words, revealing sequence learning. However, elderly participants showed less learning than young participants on several measures. This suggests that age-related deficits in implicit sequence learning reflect a general impairment in learning subtle environmental covariations rather than a modality-specific visual impairment.

Adolescent↗

PubMed2002

Guided visual search in individuals with mental retardation.

The ability of individuals with mental retardation to focus on task-relevant elements of complex visual arrays and increase visual-search efficiency was investigated. Initial assessments of visual-search efficiency were conducted to identify pairs of features for the form and size dimensions for which each participant demonstrated serial search. Subsequently, color was added as a defining feature that could guide search to a subset of the elements in the array. Results indicated that all of the individuals with mental retardation were able to limit attention to the task-relevant items on the guided search task, thus greatly reducing overall target identification times. Results show that individuals with mental retardation can demonstrate sophisticated visual selective attention skills when visual arrays are structured appropriately.

Adolescent↗

PubMed2002

Guiding visual attention during acquisition of matching-to-sample.

Matching-to-sample skills are involved in language acquisition and the development of basic reading and counting abilities. The rapid, even errorless, induction of matching performances in young children and individuals with mental retardation was demonstrated here through the structuring of a visual array so as to promote detection of the relevant stimulus. Implications for theory and application are discussed.

Adolescent↗