Biomedical subjects

Stephen Dopkins

Publications and source records attributed to Stephen Dopkins.

5 recordsLinked to original sources

PubMed2006

Spatial memory following temporal lobe resection.

The present study sought a clearer understanding of spatial memory function consequent to temporal lobe resection, and, in particular, of spatial memory function with respect to two- as well as three-dimensional frames of reference. Relative to a group of 15 control participants, a group of 15 epilepsy patients with right temporal resections demonstrated deficits of memory for locations in a two-dimensional display. A group of 13 epilepsy patients with left temporal resections did not demonstrate such deficits. The right and the left resection groups both demonstrated deficits of memory for item-location relationships in a two-dimensional display. The right but not the left resection group demonstrated deficits of memory for item-location relationships in a three-dimensional display. The differing results that were observed for item-location relationships in two- and three-dimensional displays were attributed to differences in the way item information is bound with location information concerning two- and three-dimensional domains.

Adult↗

PubMed2006

Exploring a recognition-induced recognition decrement.

Four experiments were performed to explore a recognition decrement that is associated with the recognition of a word from a short list. The stimulus material for demonstrating the phenomenon was a list of words of different syntactic types. A word from the list was recognized less well following a decision that a word of the same type had occurred in the list than following a decision that such a word had not occurred in the list. A recognition decrement did not occur for a word of a given type following a positive recognition decision to a word of a different type. A recognition decrement did not occur when the list consisted exclusively of nouns. It was concluded that the phenomenon may reflect a criterion shift but, probably, does not reflect a list strength effect, suppression, or familiarity attribution consequent to a perceived discrepancy between actual and expected fluency.

Humans↗

PubMed2005

Access to dimensional values can be unselective during early perceptual processing.

On each trial of the primary task for the study, a pair of small circles appeared on a computer screen. Across trials, the circles appeared in an array of positions on the screen. The participant was required on each trial to indicate whether or not the test circles were two or fewer position units apart in terms of the horizontal dimension of this array. The discrimination that the task required was easier to the extent that the vertical distance between the circles was ignored. When the task was performed under a high degree of speed stress, vertical distance and horizontal distance exerted equivalent effects on measures of performance. When the task was performed under a lesser degree of speed stress, horizontal distance exerted a larger effect than vertical distance did. The results supported the early holistic hypothesis over the dimensional similarity hypothesis as an account of the way information from different dimensions is accessed in perceptual processing.

Cognition↗

PubMed2004

Loss of distinctive features and a broader pattern of priming in Alzheimer's disease.

The results of 2 experiments support the contention that patients with Alzheimer's disease (AD) show a relative loss of the semantic features that distinguish concepts from one another and that the representations of pairs of concepts consequently share a larger proportion of their associated features in AD than in normal aging. In Experiment 1, AD patients listed fewer features for a set of concepts than did healthy older adults and were more deficient at listing features if the features were distinctive to particular concepts than if they were shared by multiple concepts. In Experiment 2, AD patients showed online priming at levels of relatedness at which healthy older adults did not.

Adult↗

PubMed2002

What do Alzheimer's disease patients know about animals? It depends on task structure and presentation format.

Deficits on tasks requiring semantic memory in Alzheimer's disease (AD) may be due to storage loss, a retrieval deficit, or both. To address this question, we administered multiple tasks involving 9 exemplars of the category "animals," presented as both words and pictures, to 12 AD patients and 12 nondemented individuals. Participants made semantic judgments by class (sorting task), similarity (triadic comparison task), and dimensional attributes (ordering task). Relative to control participants, AD patients were impaired on an unstructured sorting task, but did not differ on a constrained sorting task. On the triadic comparison task, the patients were as likely to make judgments based on size as domesticity attributes, whereas control participants made judgments based primarily on domesticity. The patients' judgments were also less consistent across tasks than those of control participants. On the ordering tasks, performance was generally comparable between groups with pictures but not words, suggesting that pictures enable AD patients to access information from semantic memory that is less accessible with lexical stimuli. These results suggest that AD patients' semantic judgments are impaired when the retrieval context is unstructured, but perform normally under supportive retrieval conditions.

Aged↗