Biomedical subjects

L R Gottlob

Publications and source records attributed to L R Gottlob.

9 recordsLinked to original sources

PubMed1999

Adult age differences in the functional neuroanatomy of verbal recognition memory.

Adult age differences are frequently observed in the performance of memory tasks, but the changes in neural function mediating these differences are largely unknown. We used (H2)15O positron emission tomography (PET) to measure changes in regional cerebral blood flow (rCBF) during Encoding, Baseline, and Retrieval conditions of a recognition memory task. Twelve young adults (20-29 years) and 12 older adults (62-79 years) participated. During each task condition, participants made a two-choice manual response to each of 64 words. Analyses of the performance data yielded evidence of age-related slowing of encoding and retrieval processes, and an age-related decline in the accuracy of yes/no recognition (d'). The rCBF activation associated with both encoding and retrieval was greater for older adults than for young adults, but this pattern was more clearly evident for memory retrieval. For young adults, rCBF activation during retrieval occurred primarily in right prefrontal cortex, whereas older adults exhibited a more bilateral pattern of prefrontal activation. Regression analyses predicting reaction time in the memory task from regional PET counts confirmed that the neural system mediating memory retrieval is more widely distributed for older adults than for young adults. Both age groups exhibited some decrease in rCBF activation in the second half of the test session, relative to the first half. The practice-related decrease in rCBF activation was more prominent for young adults, suggesting that the older adults' recruitment of additional neural systems reflects a more continual allocation of attention to support task performance.

Adult↗

PubMed1999

Reading homographs: orthographic, phonologic, and semantic dynamics.

Reading processes were compared across 3 word types: homographs (separate pronunciations and meanings, such as lead), homonyms (singular pronunciations but separate meanings, such as spring), and control words (e.g., clock). In Experiment 1, naming reaction times were significantly slower to homographs than to all other words. Experiments 2 and 3 used an association judgment task, with referent words related to the dominant or subordinate meanings of homonyms and homographs. In Experiment 2, homonyms and homographs were presented 1st, followed by disambiguating associates. In Experiment 3, presentation order was reversed. For homographs, performance costs always occurred for subordinate meanings. For homonyms, these costs vanished when context was provided by the preceding associates. The data underscore the priority of phonologic information in word meaning access and suggest that low- and high-level constraints combine to shape word perception.

Humans↗

PubMed1999

Adult age differences in visual search accuracy: attentional guidance and target detectability.

Previous research, relying primarily on reaction time measures of highly accurate performance, suggests that both younger and older adults can increase the efficiency of visual search by guiding attention to a candidate subset of items. The authors investigated attentional guidance when accuracy was well below ceiling to focus more specifically on the role of perceptual processes. In the most difficult condition (conjunction search), the likelihood of missing a target was greater for older adults than for younger adults, and this effect was not attributable entirely to generalized slowing. Both age groups were able to improve search efficiency by attending to a distinct subset of display items, indicating that attentional guidance to perceptual features does not exhibit age-related decline. A signal-detection model of the conjunction search data demonstrated that the age difference represented an age-related decline in target detectability.

Adult↗

PubMed1999

Age differences in the strategic allocation of visual attention.

The allocation of visual spatial attention was investigated in two groups of adults, younger (n = 24; M = 19 yrs) and older (n = 24; M = 68 yrs). Two sequential target displays were presented on a computer screen. If a target letter appeared in Display 1, then observers were to identify a target letter in Display 2. Based on accuracy of Display 1 target detection, the older adults had a more restricted range of visual processing than the younger adults. Based on reaction times for Display 2 target identification, older adults appeared to use a spotlight (serial) scanning mechanism, whereas younger adults appeared to use an activity-distribution (parallel) mechanism. Results are consistent with age-related cognitive slowing, but also suggest a difference in strategy according to the availability of visual information.

Adolescent↗

PubMed1999

Aging and recognition memory: changes in regional cerebral blood flow associated with components of reaction time distributions.

We used H(2)15O positron emission tomography (PET) to measure age-related changes in regional cerebral blood flow (rCBF) during a verbal recognition memory task. Twelve young adults (20 to 29 years) and 12 older adults (62 to 79 years) participated. Separate PET scans were conducted during Encoding, Baseline, and Retrieval conditions. Each of the conditions involved viewing a series of 64 words and making a two-choice response manually. The complete reaction time (RT) distributions in each task condition were characterized in terms of an ex-Gaussian model (convolution of exponential and Gaussian functions). Parameter estimates were obtained for the mean of the exponential component (tau), representing a task-specific decision process and the mean of the Gaussian component (mu) representing residual sensory coding and response processes. Independently of age group, both tau and mu were higher in the Encoding and Retrieval conditions than in the Baseline condition, and tau was higher during Retrieval than during Encoding. Age-related slowing in task performance was evident primarily in mu. For young adults, rCBF activation in the right prefrontal cortex, in the Retrieval condition, was correlated positively with mu but not with tau. For older adults, rCBF changes (both increases and decreases) in several cortical regions were correlated with both mu and tau. The data suggest that the attentional demands of this task are relatively greater for older adults and consequently lead to the recruitment of additional neural systems during task performance.

Adult↗

PubMed1999

Age similarities in the inertial properties of attention.

Adult age differences in the mode of allocation of visual attention were investigated, using a visual search task with a circular display containing one target letter and seven distractor letters. In two experiments, a total of 56 younger adults (M = 20 years) and 56 older adults (M = 66 years) searched for a target appearing with equal probability at one of two cued locations. The first cue appeared 115 msec before display onset, and the second cue appeared with display onset; distance between the two cued locations was varied. Target identification performance indicated that attention was inertial, in that reaction time for second-cued targets was related either to the area of the portion of the visual field containing possible target locations or to the mean path length of a serial self-terminating search. There were no age-related decrements in the allocation of visual attention.

Adolescent↗

PubMed1998

Time course of allocation of visual attention after equating for sensory differences: an age-related perspective.

Adult age differences in the time course of the allocation of visual attention were investigated, in 2 experiments that both included the same 10 younger adults (M = 22 years) and 10 older adults (M = 68 years). In Experiment 1, older adults accumulated information about target identity at a slower rate than younger adults, as represented by the rise in accuracy as a function of target duration. To equate performance in a baseline condition in a spatial-cuing paradigm (Experiment 2), target duration was set for each observer on the basis of the data in Experiment 1. Performance for the 2 age groups was comparable, both in the baseline condition and in the time course of attention, as indexed by the function relating accuracy to cue-target onset asynchrony. The authors conclude that, in this spatial-cuing paradigm, an age-related change is evident in sensory processing but not in attentional allocation.

Adult↗

PubMed1998

Response time distributions in multidimensional perceptual categorization.

Three speeded categorization experiments were conducted using separable dimension stimuli. The form of the category boundary was manipulated across experiments, and the distance from category exemplars to the category boundary was manipulated within each experiment. Observers completed several sessions in each experiment, yielding 300-400 repetitions of each stimulus. The large sample sizes permitted accurate estimates of the response time (RT) distributions and RT hazard functions. Analyses of these data indicated: (1) RT was faster for stimuli farther from the category boundary, and this stochastic dominance held at the level of the RT distributions; (2) RT was invariant for all stimuli the same distance from the category boundary; (3) when task difficulty was high, errors were slower than correct responses, whereas this difference disappeared when difficulty was low; (4) small, consistent response biases appeared to have a large effect on the relation between correct and error RT; (5) the shape of the RT hazard function was qualitatively affected by distance to the category boundary. These data establish a rich set of empirical constraints for testing developing models of categorization RT.

Humans↗

PubMed1996

Bayesian analysis of foraging by pigeons (Columba livia).

In this article, the authors combine models of timing and Bayesian revision of information concerning patch quality to predict foraging behavior. Pigeons earned food by pecking on 2 keys (patches) in an experimental chamber. Food was primed for only 1 of the patches on each trial. There was a constant probability of finding food in a primed patch, but it accumulated only while the animals searched there. The optimal strategy was to choose the better patch first and remain for a fixed duration, thereafter alternating evenly between the patches. Pigeons were nonoptimal in 3 ways: (a) they departed too early, (b) their departure times were variable, and (c) they were biased in their choices after initial departure. The authors review various explanations of these data.

Animals↗